Ebook Averys diseases of the newborn (10th edition): Part 2

Chia sẻ: _ _ | Ngày: | Loại File: PDF | Số trang:688

Thêm vào BST

Báo xấu

5
lượt xem 1
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Part 2 book "Averys diseases of the newborn" includes content: Palliative care, immunology of the fetus and newborn, viral infections of the fetus and newborn, newborn sepsis and meningitis, health care associated infections, fungal infections in the neonatal intensive care unit, lung development,... and other contents.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Ebook Averys diseases of the newborn (10th edition): Part 2

35 Palliative Care DONNAMARIA E. CORTEZZO AND BRIAN S. CARTER KEY POINTS treatments in an attempt to cure a patient or prolong his or her life independently of when the transition to EOL care occurs. • Palliative care is the total care of a patient with a life-limiting illness Hospice care is a small but important part of palliative care. Once regardless of the disease trajectory or treatment options chosen. it has been determined that there is no chance of meaningful • There is a special focus on pain/symptom management, survival, the focus of the care shifts to pain and symptom manage- communication, quality of life, family support, and grief support. ment, grief support, preparing for the dying process, and bereave- • Roughly one-third of deaths in children’s hospitals in the United States occur in neonatal intensive care units (NICUs). Many babies and ment support (Davis et al., 2015). families in the NICU would benefit from palliative care. In recent years, the American Academy of Pediatrics has • While palliative care is essential to individuals in the NICU, it is often acknowledged the importance of this growing field and recognizes overlooked, and there are still many barriers to its being considered or that all large healthcare organizations providing care to children implemented in suitable cases. with life-limiting illnesses should have a dedicated pediatric palliative • Palliative care can readily be integrated into the management of care team. The American Academy of Pediatrics has discussed in neonates with life-limiting illnesses and can be provided concurrently detail the principles for palliative care as well as the importance with cure-oriented or life-extending care. of educating trainees (American Academy of Pediatrics, Committee on Bioethics and Committee on Hospital Care, 2000; Section on Hospice and Palliative Medicine and Committee on Hospital Care, 2013). Governing academies and families alike have come to see the importance of the provision of palliative care in pediatrics and What Is Palliative Care? more specifically in taking care of the sickest babies. The US News and World Reports Best Children’s Hospitals Rankings in Neonatol- The concept of palliative care has been acknowledged in medicine ogy now include a section for neonatal intensive care unit (NICU)- for centuries. The name is derived from the Latin word palliare, specific palliative care programs. meaning to cloak, and has been more broadly interpreted to mean Despite the recent increasing focus on neonatal palliative care, “to alleviate without the intent of curing.” Over the years the the idea has been around for decades. In the 1970s the difficulties definition and scope of palliative care have evolved (Lutz, 2011). of withholding therapies in a special care nursery were described The field gained great momentum in the adult world during the for the first time (Duff and Campbell, 1973). In this landmark 1960s with the hospice movement and the realization that modern article, the authors describe a collaborative process in which parents medicine alone does not address all of the issues patients with and physicians through joint decision making determined the serious and life-limiting illnesses experience. More recently, the likelihood of a meaningful life as an outcome from the special incorporation of palliative care into the pediatric world has become care nursery was very low for 43 babies and opted to redirect care critical (Feudtner et al., 2003; Knapp et al., 2009; Wolff et al., for them. They also acknowledge the difficulty of these decisions 2010; Bona et al., 2011; Jones, 2011; Rendón-Macías et al., 2011; for parents and physicians, something that is still faced today. Wolfe, 2011; Wolfe et al., 2011; Feudtner et al., 2013; Catlin Several years later, the notion of adapting concepts from an adult et al., 2015). The World Health Organization defines pediatric hospice model to address the issues of caring for a neonate dying palliative care as the total care of a child with a life-limiting illness. in various settings was described (Silverman, 1982; Whitfield et al., It involves caring for the mind, body, and spirit of the child and 1982; Butler, 1986; Landon-Malone et al., 1987). supporting the family through the process. It begins with diagnoses and continues regardless of the disease trajectory or treatment Paradigms of Palliative Care options chosen. There is a special focus on pain and symptom management and alleviating distress through a multidisciplinary There are multiple paradigms in which palliative care can be provided approach (World Health Organization, 2015). Palliative care is (Fig. 35.1). In Fig. 35.1 the first model represents the serial not limited to EOL care. It can occur concurrently with other approach. This is the earliest view of palliative care. Once a terminal 446
CHAPTER 35 Palliative Care 447 Series can be challenging to shift goals of care in the face of a life-limiting D illness (Carter et al., 2006; Kain, 2006; Wright et al., 2011; Cortezzo e et al., 2013). Curing Palliation a Bereavement t h Scope of the Problem While neonatal–perinatal palliative care provides unique challenges Parallel for families and healthcare providers alike, it is something that D most individuals who provide care for neonates will be faced with. Curing e Despite the many advances in medical therapies and improvements a Bereavement Palliation t in neonatal survival and outcomes, newborns will still die. Often h these babies will die regardless of the treatment options chosen by the family and medical care team. In 2013 in the United States, there were more than 1 million fetal deaths, with more than 20,000 Integrative* occurring after 20 weeks’ gestational age. In addition, there were more than 15,000 neonatal deaths, accounting for nearly 70% of t t en en D Curing al deaths within the first year of life (MacDorman and Gregory, vem e vem tinu a 2015). Most of those who died within the first year experienced rea rea Healing t Con (including palliation) h severe and chronic illnesses stemming from the time of birth. Be Be Roughly one-third of deaths in children’s hospitals in the United States occur in the NICU setting (Brandon et al., 2007). As a *Mindset of “Being with” and “Doing to” result, most medical care providers who care for neonates will be faced with the death of a patient and navigating the goals of care Diagnosis with a family. t0 Time Given the likelihood that neonatologists will be faced throughout their careers with patients having life-limiting illnesses, it is pertinent • Fig. 35.1 Various models for providing palliative care. (Modified from that they incorporate palliative care into daily practices to best Milstein J. A paradigm of integrative care: healing with curing throughout care for patients and families. The uncertainty of prognosis, physical life, “being with” and “doing to.” J Perinatol. 2005;25:563–568.) constraints of the NICU, time constraints, moral distress, and lack of education are known barriers to providing palliative care in the NICU (Lantos et al., 1994; McHaffie et al., 1999; Romesberg, 2007; Davies et al., 2008; Wright et al., 2011; Cortezzo et al., condition has been diagnosed, curative therapies continue until 2013). In an intensive care setting it can be challenging to shift they are seen as futile. Then palliation and comfort measures are from cure-directed aggressive and invasive interventions to palliation offered until the point of death. After death, bereavement support and comfort care. However, early initiation of palliative care has is offered. As the field of palliative care has evolved, the adult been associated with improved memory making, decreased pain, world has adapted the parallel model in which palliative care is decreased rates of invasive procedures that will likely not change introduced early in combination with curative therapies, and as the outcome, and increased parental satisfaction (Eden and Callister the disease trajectory changes with time, the care model changes 2010; Wolff et al., 2010; Cortezzo et al., 2015; Kenner et al., with it. Again, once death occurs, bereavement support is offered. 2015). Consequently, it is imperative that healthcare providers The final model, the integrated model, is one that has been adopted view success for the unique subset of patients with life-limiting most often by the growing field of pediatric palliative care and is illnesses who will die despite intensive medical interventions as most conducive to the unique environment of the NICU. When eliminating unnecessary suffering, supporting families through the a life-limiting diagnosis is made, the concepts of palliation are dying process, and helping them find meaning in their baby’s life introduced along with curative therapies and change with the (Milstein, 2005; Carter et al., 2011). Failure in these situations is disease trajectory. With recognition that the family is experiencing not the inability to sustain life but rather unnecessary pain and loss on multiple levels at the time of diagnosis, bereavement and suffering and an undignified death. grief support are offered in a multidisciplinary fashion from the time of diagnosis, through the entire illness course, and after death (Milstein, 2005). Which Patients Benefit From Palliative Care Because the perinatal/neonatal period is so unique, it requires in the Neonatal Intensive Care Unit? an approach to palliative care different from that in most other fields. The perinatal/neonatal period is usually a time of joy, Many neonates will respond to intensive care therapies, graduate anticipation of life, and hope for many memories to be made by from the NICU, and lead meaningful lives. Knowing this, which growing as a family. When there is a diagnosis of a life-limiting patients and families would benefit from palliative care in the condition that results in a fetal or neonatal death, every milestone NICU setting? There is a role for palliative care in caring for and stage of the pregnancy, birth, life, and death are very different neonates with serious but possibly treatable conditions. Arguably, from what was hoped for and anticipated (Carter, 2004; Carter many aspects of palliative care should be incorporated into the et al., 2006; Breeze et al., 2007; Munson and Leuthner, 2007; multidisciplinary approach to the care of any baby in the NICU. Romesberg, 2007; Balaguer et al., 2012; Catlin et al., 2015). Any family member of a newborn requiring resuscitation or intensive Similarly, in the NICU environment, providers are trained to offer interventions, regardless of the ultimate outcome, experiences grief intensive and invasive therapies with the goal of saving lives. It and loss. The family has to alter its expectations for a healthy and
448 PART V I I I High-Risk Newborn Care uneventful pregnancy leading to a healthy baby. The family often care clinicians can facilitate it being readily integrated into the requires spiritual, emotional, and psychosocial support to deal management of neonates with life-limiting illnesses (Kang et al., with this trauma both in the immediate period and moving forward 2014). (Sydor-Greenberg and Dokken, 2000). However, there is a special and more pronounced role for palliative care when the likelihood of long-term survival is minimal. Components of Palliative Care in the Often, when death is almost certain, continuing life-sustaining Neonatal Intensive Care Unit treatments may only prolong the suffering of the neonate and give the family false hope of meaningful survival. The care initiated The major components of palliative care incorporated into the and the treatments that follow may be aggressive and at the expense care of neonatal patients with a life-limiting illness are a focus on of the comfort of the baby. Palliative care focuses on the prevention communication, quality of life, family support, and grief support and relief of physical pain and suffering of the periviable extremely (Catlin and Carter, 2002; Madden et al., 2015). Ideally, care premature infant, actively dying infants, or those severely com- providers who have become familiar with the family (including promised and possibly technology dependent, as well as on sup- neonatologists, nurses, social workers, and chaplains) and have porting the needs of the family (Lorenz, 2004). Everyone involved developed a rapport with them should initiate and be present for in the care of these neonates, as well as the neonates themselves, difficult conversations. These conversations with family members can strongly benefit from this type of care. Regardless of whether should be clear, direct, and honest (Janvier et al., 2014). They or not a neonate dies, lives with a permanent impairment, or goes should happen in a quiet environment where the family has the on to live a normal life, there is a necessary role for palliative care. care provider’s undivided attention. Parents wish that difficult news Beyond addressing symptoms such as pain, this approach offers be delivered in an honest and compassionate manner that lets support to families and addresses short-term and long-term measures them know their child matters (Widger and Picot, 2008; Kavanaugh to ensure that the infant has the best quality of life for as long as et al., 2009; Armentrout and Cates, 2011; Janvier et al., 2014). he or she may live (Carter and Levetown, 2004; Carter et al., After the diagnosis and the relative certainty of the prognosis have 2011). been discussed, the focus of these conversations should shift to While every patient and family dynamic is different and goals exploring the values of the family, wherein the care team can better need to be explored for each patient, there are several categories understand the family, how the family members make decisions, where it is appropriate to discuss transitioning from life-extending and what is important to them. therapies to comfort measures (Carter and Bhatia, 2001; Carter, Key among goals in these conversations is helping to identify— 2004; Carter and Levetown, 2004; Carter et al., 2006; Romesberg, and often redefine or redirect—their hopes. By being open and 2007; Carter et al., 2011): compassionate, providers can give family members a sense of realistic 1. Any periviable, extremely premature newborns based on ges- hope during this difficult time without misleading them toward tational age or birth weight, especially when they have significant a false sense of the likely survival (Widger and Picot, 2008; Eden complications and Callister, 2010; Armentrout and Cates, 2011). It is often 2. Neonates with multiple congenital anomalies incompatible helpful to focus the conversation on what is meaningful to the with long-term survival. Under these circumstances, intensive family members in the context of a poor prognosis (Carter et al., care therapies may alter the time course and the baby’s/family’s 2011). Their idea, or object, of hope may change over the course life experience but will not, unfortunately, change the long-term of the baby’s life. With a better understanding of the family’s outcome. These conditions may involve any single-organ or values, the care team can participate with the family in shared multiple-organ system and at times are the result of genetic decision making and ultimately define or redefine the goals of abnormalities. care. These conversations and the decisions made are unique to 3. Newborns who have received intensive interventions and despite each family regardless of the diagnosis. It is not uncommon for efforts are not responding to therapy, continue to decline, or parents and the care team to have different agendas and priorities have continued life-threatening events (severe hypoxic–ischemic during this time (Midson and Carter, 2010). It is critical to attend encephalopathy, multiple-organ system failure, overwhelming to the parent’s priorities and ensure that they feel valued, listened sepsis, necrotizing enterocolitis totalis). to, and a member of the care team. It is the care provider’s job to When these unfortunate situations arise, it is important to have understand the family’s values and goals and to make medical a multidisciplinary approach to caring for the patient and family. recommendations based on those goals. There are times when the The NICU provides a unique environment in which intensive choices of the family may be in opposition to the views of the life-sustaining therapies are provided that focus on comfort of the care team (Kopelman, 2006; Back, 2009). It is the care team’s patient and involvement of the family in the care process (Carter, obligation to continue conversations with the intent of better 2004). It is one of the few places in hospitals where a multidisci- understanding the reasoning behind the family member’s decisions/ plinary team (physicians, nurses, social workers, chaplains, etc.) goals and supporting them through the process. The goal should is focusing on multiple aspects of the total care of the baby–family not be to try to convince the family that an alternative approach unit. This lends itself nicely to the provision of palliative care is most appropriate. In partnership with the NICU team, palliative because much of the framework already exists. Yet, while many care clinicians may be instrumental in facilitating such ongoing care providers in NICU settings feel they are comfortable and conversations, especially as primary neonatal clinicians may change competent in providing EOL care for neonates, there is a wide every week or every 2 weeks. variety in the care patients receive and in the discussions of care When the end of life (EOL) is approaching, it may also be with families (Leuthner, 2001; Carter, 2004; Cortezzo et al., 2015). important to have open conversations about organ or tissue dona- Similarly, there may be attitudinal barriers to consulting palliative tion, autopsy, and funeral, memorial, or burial services. Many care clinicians. Evidence suggests, however, that once the need for NICUs have a team of social workers, chaplains, and psychologists and importance of palliative care in the NICU are realized, palliative to help attend to these needs. The addition of palliative care
CHAPTER 35 Palliative Care 449 clinicians can bring expertise in providing additional support during throughout the pregnancy. They also have time to navigate the these very unique and difficult times. When there is an anticipated goals of care and develop a care plan that includes a birth plan compassionate withdrawal of life-sustaining medical treatment, it and advance care planning known by all providers at the time of may be beneficial to contact a liaison with a regional organ procure- delivery. Box 35.1 highlights important components of a perinatal ment organization to engage families in discussions about organ/ palliative care birth plan. A delivery room resuscitation plan should tissue donation. be discussed ahead of time with the family (Catlin and Carter, Regardless of the family’s care goals or treatment options, the 2002; Widger and Picot, 2008; Balaguer et al., 2012; Engelder baby’s quality of life should remain paramount. Care should be et al., 2012; Kenner et al., 2015). But the staff still needs to remain taken to ensure that painful procedures are minimized, unnecessary ready to adapt such plans to the reality of the newborn’s condition tests stopped, the physical environment is made comfortable and at birth. Families may change their minds, the newborn’s condition conducive to family bonding, and that pain and symptoms are may be better or worse than anticipated, and decision making addressed with nonpharmacologic and pharmacologic management remains rather fluid. Ethics and palliative care support may aid when necessary. parents and facilitate their navigation through difficult decisions and how they choose to spend whatever amount of time they have Grief and Bereavement Support with their baby. Grief support should be initiated shortly after a life-limiting diagnosis. Initially such support may focus on grieving the loss of Late Prenatal Diagnosis the healthy newborn and the life the family members anticipated If the news of a life-limiting illness is discovered late in the pregnancy in the context of still celebrating and enjoying their baby. Attention or just before delivery, it often results in a more chaotic and less should be given to ensure the parents, siblings, grandparents, and formulated approach. Teams are working rapidly to provide extended family members are able to make memories with the immediate care to the mother and fetus/neonate. There is often baby. During this stressful time, especially if it is their first child, not time to have lengthy discussions or learn the parent’s values. parents are often unable to think about what memories would be In the chaos, communication can be rushed and fragmented. It important for them to make. Some families wish to take pictures, remains imperative to provide accurate information and support have handprints/footprints or molds made, record heartbeats, bathe to the parents while making the environment as calm and private the child, sing/read to the child, take the child outside, have the as possible, allowing the family members to express their emotions. child meet a family pet, taste foods, sleep in a bed, or participate In the time that follows, discussions can be continued. in spiritual/religious ceremonies. Every effort should be made to help these families maximize the experiences they have with their baby during what may be a brief life span. Bereavement support Postnatal Diagnosis for parents, siblings, and family members should start before the If the news of a life-limited illness is not discovered until after death of the baby and continue for a period afterward (Kenner delivery, parents are often shocked. Most assume that if a delivery et al., 2015). Parents appreciate bereavement support and follow-up phone calls from or meetings with physicians who provided care for their child and other forms of acknowledgment such as con- dolence cards (Kenner et al., 2015). It is also imperative to recognize • BOX 35.1 Components of a Perinatal Palliative that staff members benefit greatly from grief support (Cavaliere Birth Plan et al., 2010; Cortezzo et al., 2015). Often the NICU staff has Clarify Maternal Goals been involved in the care of the baby for much of his or her life • Site of delivery and has spent time becoming familiar with the family. News of a • Community or tertiary poor prognosis can be emotionally trying for such staff as well. • Fetal monitoring Because the staff are attending to the immediate care needs of the • E-FHR, auscultation, none baby, family, and other babies in the unit, they may be unable to • Mode of delivery process such difficult news. It is important that we support them • Burdens, benefits, values as well. • Who will be in attendance? • Who matters? • Maternal and neonatal medications Timing of the News • Anesthesia and otherwise Clarify Neonatal Goals Early Prenatal Diagnosis • Specified components of resuscitation and care • Intubate, CPAP, O2? Families may learn of a life-limiting condition in the early prenatal • Medications and lines? period, late prenatal period, or early neonatal period (Wolfe et al., • Site of care of the baby 2011). While the job of the healthcare team remains the same in • L & D, nursery, ICN, home supporting the family members and helping them find meaning • Feeding plan in their baby’s life, the timing can slightly alter the approach to • Breast, tube(s), cup, finger, no? care. If the news is given in the early prenatal period, parents often • Special events and spiritual care have time to begin grieving the loss of a healthy pregnancy and • Memories, mementoes, rituals • Contingency postdischarge plan reframe their idea of hope. If palliative care is initiated early on, the family members may benefit from the involvement of palliative CPAP, Continuous positive airway pressure; E-FHR, external fetal heart rate; ICN, Intensive Care care providers who learn about the family and support them through Neonatal; L & D, labor and delivery. the process. They can facilitate bonding and memory making
450 PART V I I I High-Risk Newborn Care goes well, their baby will be healthy. For them it is an abrupt loss present and if they would like to hold their baby or perform any of the healthy baby they were holding moments before they received rituals. Care should be taken to respect any cultural or spiritual the news. It is vital to continue to promote bonding with the baby desires of the family. If parents desire to take their baby home for and ease suffering. The care team should use the medical information EOL care, care providers should coordinate with local home hospice along with the knowledge of the family’s values to shape the goals programs or home-health services to ensure that the family will of care and aid in decision making. Extra time is often necessary have access to the care, support, equipment, and medication that in this situation, with care to provide support for the family and will be needed during this time. Parents should be reassured that staff in redefining and redirecting hope and the goals for the regardless of location, they will not be abandoned and that care newborn’s care. will be taken to attend to pain and symptom management. The Parents note that the delivery of the news and the discussions focus should be on what the team can do for the baby and family that follow shape their experience with the care team, their memories as opposed to what the team can no longer do (Catlin and Carter, of time with their child, and their subsequent bereavement. Some 2002; Leuthner, 2004; Gale and Brooks, 2006). Symptom manage- parents report that the news about a diagnosis, prognosis, or ment is available with an array of medications (Carter and Jones, treatment options were given in an insensitive manner. They wish 2013), and dyspnea, pain, and agitation should be anticipated and to be included in the decision-making process and know that their appropriately assessed. Neonates feel pain and other symptoms of input as parents is what matters the most. They also desire privacy, distress, and they should be addressed accordingly (Anand and support, and time to come to terms with their loss (Contro et al., International Evidence-Based Group for Neonatal Pain, 2001; 2002; Davies and Connaughty, 2002; Berg, 2006; Dokken, 2006; American Academy of Pediatrics et al., 2007). Symptoms that may Brosig et al., 2007; Henley and Schott, 2008; Eden and Callister, need to be treated at the EOL include pain, agitation, dyspnea, 2010; Armentrout and Cates, 2011). and secretions (Komatz and Carter, 2015). Nonpharmacologic interventions to address these issues are equally important, such End-of-Life Care as decreasing stimulation, a soothing environment, massage, elevat- ing the head, fluid restriction, and gentle suctioning. At times, Palliative care is extremely important during EOL care, when a especially during the EOL, nonpharmacologic interventions will neonate is imminently dying. Every effort is made to ensure the not be enough. It is important to anticipate this and alleviate the family members can shape the experience of the death in a way stress of the family. It is both clinically and ethically appropriate that is most meaningful to them and that they are as prepared as to provide pharmacologic symptom relief. While there may be a they can be for the dying process. For some families, it is important concern of hastening death with certain medications (e.g., opioids), that they understand the physiologic changes that they will likely at appropriate doses this generally does not happen. The intent to see ahead of time. If family members wish to stay in the hospital provide relief of pain and suffering, it can be argued, outweighs for the death of their baby, every effort should be made to bring the small chance of respiratory depression. Tables 35.1–35.2 provide them to a private room within the NICU or to a different location a guide to common pharmacologic symptom management at the within the hospital. The environment should be as peaceful and EOL. It is important to note that these doses and the medication homelike as possible. Monitors and unnecessary equipment should choices may need to be altered on the basis of the patient’s previous be removed. Families should determine who they wish to have exposure. TABLE 35.1 Symptom Management for End-of-Life Care: Pharmacologic Starting Dose Symptom Medication Category (per Kilogram) Route and Interval Pain Acetaminophen Antipyretic 15 mg PO/PR q6 hour Analgesic 6–8 mg IV q8 hour Fentanyl Opioid 0.5–2 µg IN/IV q2 Methadone Opioid 0.05–0.2 mg IV/PO q12–24 Morphine Opioid 0.05–0.2 mg IV/IM q2 0.2–0.5 mg PO/sublingual q4 Agitation Lorazepam Benzodiazepine 0.05–0.1 mg IV q4–6 Midazolam Benzodiazepine 0.05–0.1 mg IV q2–4 0.2–0.3 mg Sublingual 0.25 mg IN Dyspnea Morphine Opioid 0.15 mg PO/sublingual q2 0.05–0.1 mg IV q2 Lorazepam Benzodiazepine 0.05–0.1 mg PO/IV q4 Secretions Atropine Anticholinergic 0.01–0.02 mg PO q2 Glycopyrrolate Anticholinergic 0.01–0.02 mg IV q4 0.04–0.1 mg PO q4 IN, Intranasal; IM, intramuscular; IV, intravenous; PO, per os; PR, per rectum; q2, every 2 hours; q2–4, every 2–4 hours; q4–6, every 4–6 hour; q6, every 6 hours; q8, every 8 hours; q12–24, every 12–24 hours.
CHAPTER 35 Palliative Care 451 TABLE Symptom Management for End-of-Life Care: the treatment course (Lantos, Tyson et al., 1994; McHaffie, Cuttini 35.2 Nonpharmacologic et al., 1999). Withdrawing/withholding LSMT, while a relatively infrequent Symptom Action Provider phenomenon in a given NICU, is the most frequent mode of Pain or Reduce ambient noise Clinician dying in both neonatal and pediatric ICUs (Walther, 2005; Fontana, agitation Reduce procedural touching Clinician Farrell et al., 2013; Meert, Keele et al., 2015). It is understandable (handling, suctioning, laboratory that parents want to be sure that there is essentially no chance of tests, and imaging) survival before such decisions are made and it warrants open Reduce temperature swings Clinician communication, transparency in prognostication, and attention Swaddle; facilitated tuck Clinician or parent to empathy (Singh 2004, Meyer, Brodsky et al., 2011). Nonnutritive suckling Clinician or parent Skin-to-skin contact Parent Dyspnea Postural positioning (may be lateral, Clinician or parent Barriers to Palliative Care in the Neonatal upright, or prone; may include Intensive Care Unit neck, chest, or shoulder roll) Consider fan or humidified air Clinician While palliative care is essential to individuals in the NICU, it is Secretions Oral and nasal suctioning Clinician or parent often overlooked and there are many barriers. The NICU environ- ment is often noisy and crowded, with little room for privacy (Carter and Bhatia, 2001). Also, with current advances in technol- ogy, death may be viewed as a failure as the technologic imperative Ethical Concerns is so operant that if a therapy is available, it must be used without full consideration of how burdensome it is or if it will ultimately With advances in equipment and medicine, and more rigorously benefit the neonate (Carter and Bhatia, 2001; Carter and Miller- studied and implemented practices, increasingly neonates are Smith, 2016). Often families are overwhelmed by the technology benefiting from their stays in the NICU. The age of viability has and feel an incredible burden that the decisions are solely on their dropped with continuously improving clinical capabilities (Rennie, shoulders. If the outcome is certain and the treatment is a standard 1996; MacDonald, 2002). As we become better at saving one of care, then this is often not an issue. However, there is rarely group, the limits are pushed for another group of neonates (Singh, such certainty. 2004). Yet with these advances, have come a variety of uncertainties and outcomes. Difficulty remains around the borderlines of viability with resuscitation, and when to forego life-sustaining therapies, Training in Neonatal–Perinatal or whether to redirect care. At 22 weeks of gestation some centers Palliative Care universally offer a treatment trial of intensive care whereas others do not, or do so on only an individual basis (Patel, Kandefer, Clinicians’ discomfort to address the limits of medicine and technol- et al., 2015; Rysavy, Li et al., 2015). ogy and redirect the prevailing care paradigm from one that is It is often difficult to predict a neonate’s course or future disease based and cure oriented to one that is palliative and comfort complications. This uncertainty brings many questions and discus- oriented is likely contributed to by a relative lack of palliative care sions among professionals and families about the neonate’s response training in neonatal and perinatal training programs. A study was to intensive care, complications encountered, and what actions published regarding training of neonatal fellows in discussions with are in neonate’s best interests (Whitelaw, 1986; Rhoden, 1989; families and helping them make decisions regarding critically ill Silverman, 1992; Sanders, Donohue et al., 1995; Rennie, 1996; neonates (Boss et al., 2009). Fellows from 83% of the accredited MacDonald, 2002; Lorenz, 2004; Silverman, 2004). Families are programs participated. For the most part, all of the fellows felt often faced with decisions that are not seen elsewhere in medicine, confident in their medical training. However, more than 40% and these decisions are complicated by both the urgency of need stated that they had not had any formal communication training for action and the uncertainty of prognosis (Wolfe, Hinds et al., or clinical communication skills training. More than 90% felt that 2011). Many times both families and care teams feel that once training in this area—specifically palliative care, spiritual needs, care is initiated, everything possible must be done to save the and managing conflicts of opinion—was lacking or nonexistent in neonate. However, there may come a point in time when certain their training program. It is imperative that neonatologists learn life-sustaining interventions are considered acceptable by some these skills because families who have lost a child often cite how families whereas others believe such continued intervention or important it is that the physician communicates with them in a technology dependence render a quality of life for their baby that way they can understand/handle and address all of their palliative they do not find acceptable. care and spiritual needs so that collaboratively they can come up Both ethically and legally withholding an intervention or with a clear plan (Baker et al., 2007; Boss et al., 2009; Michelson withdrawing one already started are considered equivalent (Bell et al., 2009; Orgel et al., 2010; Cortezzo et al., 2013, 2015). and Newborn, 2007). In other fields of medicine this seems to be more readily accepted. The thought of withdrawing LSMT from Research Opportunities/Future Directions a neonate leads many parents to believe they are actively aiding in their baby’s death. When based on notions or descriptions of While there have been many advances in the field of neonatal futility or a perceived quality of life, a contest of whose perception palliative care in recent years, there are still many exciting opportuni- of these terms matters most (clinicians or families) often results. ties for research. Studies have yet to determine which interventions Consequently, physicians may have difficulties addressing these offer optimal pain and symptom management at the EOL. There issues, discussions may be limited, and if they occur it is late in are also many opportunities for research addressing communication
452 PART V I I I High-Risk Newborn Care training and quality improvement investigations looking at the Catlin A, Carter B. Creation of a neonatal end-of-life palliative care timing and delivery of palliative care, which paradigm of delivery protocol. J Perinatol. 2002;22(3):184-195. is most effective, and how it will alter the course of living with Henley A, Schott J. The death of a baby before, during or shortly after neonatal loss for these families. birth: good practice from the parents’ perspective. Semin Fetal Neonatal Med. 2008;13(5):325-328. Leuthner SR. Fetal palliative care. Clin Perinatol. 2004;31(3):649-665. Suggested Readings MacDorman MF, Gregory EC. Fetal and perinatal mortality: United States, 2013. Natl Vital Stat Rep. 2015;64(8):1-24. American Academy of Pediatrics. Committee on Bioethics and Committee Romesberg TL. Building a case for neonatal palliative care. Neonatal Netw. on Hospital Care. Palliative care for children. Pediatrics. 2000;106 2007;26(2):111-115. (2 Pt 1):351-357. Section on Hospice and Palliative Medicine and Committee on Hospital American Academy of Pediatrics Committee on Fetus and Newborn, Bell Care. Pediatric palliative care and hospice care commitments, guidelines, EF. Noninitiation or withdrawal of intensive care for high-risk newborns. and recommendations. Pediatrics. 2013;132(5):966-972. Pediatrics. 2007;119(2):401-403. Toce SS, Leuthner SR, Dokken DL, Catlin AJ, Brown J, Carter BS. Back A. Mastering Communication with Seriously Ill Patients. New York, Palliative care in the neonatal-perinatal period. In: Carter BS, Levetown NY: Cambridge University Press; 2009. M, Friebert SE, eds. Palliative Care for the Infants, Children, and Boss RD, Hutton N, Donohue PK, Arnold RM. Neonatologist training Adolescents: A Practical Handbook. 2nd ed. Baltimore, MD: Johns to guide family decision making for critically ill infants. Arch Pediatr Hopkins University Press; 2011:345-386. Adolesc Med. 2009;163(9):783-788. Wolfe J, Hinds P, Sourkes B. Textbook of Interdisciplinary Pediatric Palliative Carter BS, Jones PM. Evidence-based comfort care for neonates towards Care. Philadelphia, PA: Elsevier; 2011. the end of life. Semin Fetal Neonatal Med. 2013;18(2):88-92. Carter B, Miller-Smith L. The lure of technology. In: Verhagen E, Janvier A, eds. Ethical Dilemmas for Critically Ill Babies. Dordrecht, Netherlands: Complete references used in this text can be found online at www Springer; 2016:81-91. .expertconsult.com
CHAPTER 35 Palliative Care 452.e1 References Cavaliere TA, Daly B, Dowling D, Montgomery K. Moral distress in neonatal intensive care unit RNs. Adv Neonatal Care. 2010;10(3): American Academy of Pediatrics. Committee on Bioethics and Committee 145-156. on Hospital Care. Palliative care for children. Pediatrics. 2000;106(2 Contro N, Larson J, Scofield S, Sourkes B, Cohen H. Family perspectives Pt 1):351-357. on the quality of pediatric palliative care. Arch Pediatr Adolesc Med. American Academy of Pediatrics, Committee on Fetus and Newborn, 2002;156(1):14-19. Canadian Paediatric Society, Fetus and Newborn Committee. Prevention Cortezzo DE, Sanders MR, Brownell E, Moss K. Neonatologists’ perspec- and management of pain in the neonate. An update. Adv Neonatal tives of palliative and end-of-life care in neonatal intensive care units. Care. 2007;7(3):151-160. J Perinatol. 2013;33(9):731-735. American Academy of Pediatrics Committee on Fetus and Newborn, Bell Cortezzo DE, Sanders MR, Brownell EA, Moss K. End-of-life care in EF. Noninitiation or withdrawal of intensive care for high-risk newborns. the neonatal intensive care unit: experiences of staff and parents. Am Pediatrics. 2007;119(2):401-403. J Perinatol. 2015;32(8):713-724. Anand KJ, International Evidence-Based Group for Neonatal Pain. Davies B, Connaughty S. Pediatric end-of-life care: lessons learned from Consensus statement for the prevention and management of pain in parents. J Nurs Adm. 2002;32(1):5-6. the newborn. Arch Pediatr Adolesc Med. 2001;155(2):173-180. Davies B, Sehring SA, Partridge JC, et al. Barriers to palliative care for Armentrout D, Cates LA. Informing parents about the actual or impending children: perceptions of pediatric health care providers. Pediatrics. death of their infant in a newborn intensive care unit. J Perinat Neonatal 2008;121(2):282-288. Nurs. 2011;25(3):261-267. Davis MP, Gutgsell T, Gamier P. What is the difference between palliative Back A. Mastering Communication with Seriously Ill Patients. New York, care and hospice care? Cleve Clin J Med. 2015;82(9):569-571. NY: Cambridge University Press; 2009. Dokken DL. In their own voices: families discuss end-of-life decision Baker JN, Torkildson C, Baillargeon JG, Olney CA, Kane JR. National making—part 1. Interview by Elizabeth Ahmann. Pediatr Nurs. survey of pediatric residency program directors and residents regarding 2006;32(2):173-175. education in palliative medicine and end-of-life care. J Palliat Med. Duff RS, Campbell AG. Moral and ethical dilemmas in the special-care 2007;10(2):420-429. nursery. N Engl J Med. 1973;289(17):890-894. Balaguer A, Martín-Ancel A, Ortigoza-Escobar D, Escribano J, Argemi Eden LM, Callister LC. Parent involvement in end-of-life care and decision J. The model of palliative care in the perinatal setting: a review of the making in the newborn intensive care unit: an integrative review. J literature. BMC Pediatr. 2012;12:25. Perinat Educ. 2010;19(1):29-39. Berg S. In their own voices: families discuss end-of-life decision making— Engelder S, Davies K, Zeilinger T, Rutledge D. A model program part 2. Pediatr Nurs. 2006;32(3):238-242, 237. for perinatal palliative services. Adv Neonatal Care. 2012;12(1): Bona K, Bates J, Wolfe J. Massachusetts’ Pediatric Palliative Care Network: 28-36. successful implementation of a novel state-funded pediatric palliative Feudtner C, DiGiuseppe DL, Neff JM. Hospital care for children and care program. J Palliat Med. 2011;14(11):1217-1223. young adults in the last year of life: a population-based study. BMC Boss RD, Hutton N, Donohue PK, Arnold RM. Neonatologist training Med. 2003;1:3. to guide family decision making for critically ill infants. Arch Pediatr Feudtner C, Womer J, Augustin R, et al. Pediatric palliative care programs Adolesc Med. 2009;163(9):783-788. in children’s hospitals: a cross-sectional national survey. Pediatrics. Brandon D, Docherty SL, Thorpe J. Infant and child deaths in acute care 2013;132(6):1063-1070. settings: implications for palliative care. J Palliat Med. 2007;10(4):910-918. Fontana MS, Farrell C, Gauvin F, Lacroix J, Janvier A. Modes of death Breeze AC, Lees CC, Kumar A, Missfelder-Lobos HH, Murdoch EM. in pediatrics: differences in the ethical approach in neonatal and pediatric Palliative care for prenatally diagnosed lethal fetal abnormality. Arch patients. J Pediatr. 2013;162(6):1107-1111. Dis Child Fetal Neonatal Ed. 2007;92(1):F56-F58. Gale G, Brooks A. Implementing a palliative care program in a newborn Brosig CL, Pierucci RL, Kupst MJ, Leuthner SR. Infant end-of-life care: intensive care unit. Adv Neonatal Care. 2006;6(1):37-53. the parents’ perspective. J Perinatol. 2007;27(8):510-516. Henley A, Schott J. The death of a baby before, during or shortly after Butler NC. The NICU culture versus the hospice culture: can they mix? birth: good practice from the parents’ perspective. Semin Fetal Neonatal Neonatal Netw. 1986;5(2):35-42. Med. 2008;13(5):325-328. Carter BS. Providing palliative care for newborns. Pediatr Ann. Janvier A, Barrington K, Farlow B. Communication with parents concerning 2004;33(11):770-777. withholding or withdrawing of life-sustaining interventions in neonatol- Carter B, Bhatia J. Comfort/palliative care guidelines for neonatal practice: ogy. Semin Perinatol. 2014;38(1):38-46. development and implementation in an academic medical center. J Jones BW. The need for increased access to pediatric hospice and palliative Perinatol. 2001;21:279-283. care. Dimens Crit Care Nurs. 2011;30(5):231-235. Carter BS, Hubble C, Weise KL. Palliative medicine in neonatal and Kain VJ. Palliative care delivery in the NICU: what barriers do neonatal pediatric intensive care. Child Adolesc Psychiatr Clin N Am. nurses face? Neonatal Netw. 2006;25(6):387-392. 2006;15(3):759-777. Kang TI, Munson D, Hwang J, Feudtner C. Integration of palliative care Carter BS, Jones PM. Evidence-based comfort care for neonates towards into the care of children with serious illness. Pediatr Rev. 2014;35(8):318- the end of life. Semin Fetal Neonatal Med. 2013;18(2):88-92. 325, quiz 326. Carter B, Levetown M. Palliative Care for the Infants, Children, and Kavanaugh K, Moro TT, Savage TA, Reyes M, Wydra M. Supporting Adolescents: A Practical Handbook. Baltimore, MD: Johns Hopkins parents’ decision making surrounding the anticipated birth of an University Press; 2004:247-272. extremely premature infant. J Perinat Neonatal Nurs. 2009;23(2): Carter B, Levetown M, Friebert S. Palliative Care for the Infants, Children, 159-170. and Adolescents: A Practical Handbook. Baltimore, MD: Johns Hopkins Kenner C, Press J, Ryan D. Recommendations for palliative and bereave- University Press; 2011. ment care in the NICU: a family-centered integrative approach. J Carter B, Miller-Smith L. In: Verhagen E, Janvier A, eds. Ethical Dilemmas Perinatol. 2015;35(suppl 1):S19-S23. for Critically Ill Babies. Dordrecht, Netherlands: Springer; Knapp C, Thompson L, Madden V, Shenkman E. Paediatricians’ perceptions 2016:81-91. on referrals to paediatric palliative care. Palliat Med. 2009;23(5): Catlin A, Brandon D, Wool C, Mendes J. Palliative and end-of-life care 418-424. for newborns and infants: from the National Association of Neonatal Komatz K, Carter B. Pain and symptom management in pediatric palliative Nurses. Adv Neonatal Care. 2015;15(4):239-240. care. Pediatr Rev. 2015;36(12):527-534. Catlin A, Carter B. Creation of a neonatal end-of-life palliative care Kopelman AE. Understanding, avoiding, and resolving end-of-life conflicts protocol. J Perinatol. 2002;22(3):184-195. in the NICU. Mt Sinai J Med. 2006;73(3):580-586.
452.e2 PART V I I I High-Risk Newborn Care Landon-Malone KA, Kirkpatrick JM, Stull SP. Incorporating hospice care Rennie J. Perinatal management at the lower limits of viability. Arch Dis in a community hospital NICU. Neonatal Netw. 1987;6(1):13-19. Child. 1996;74:F214-F218. Lantos JD, Tyson JE, Allen A, et al. Withholding and withdrawing life Rhoden N. Treating Baby Doe: the ethics of uncertainty. Hastings Center sustaining treatment in neonatal intensive care: issues for the 1990s. Rep. 1989;16:34-42. Arch Dis Child Fetal Neonatal Ed. 1994;71:F218-F223. Romesberg TL. Building a case for neonatal palliative care. Neonatal Netw. Leuthner SR. Decisions regarding resuscitation of the extremely premature 2007;26(2):111-115. infant and models of best interest. J Perinatol. 2001;21(3):193-198. Rysavy MA, Li L, Bell EF, et al. Between-hospital variation in treatment Leuthner SR. Fetal palliative care. Clin Perinatol. 2004;31(3):649-665. and outcomes in extremely preterm infants. N Engl J Med. Lorenz J. Compassion and perplexity. Pediatrics. 2004;113:403-404. 2015;372(19):1801-1811. Lutz S. The history of hospice and palliative care. Curr Probl Cancer. Sanders M, Donohue P, Oberdoff M, Rosenkrantz T, Allen M. Perceptions 2011;35(6):304-309. of the limit of viability. J Perinatol. 1995;15:494-502. MacDonald H, American Academy of Pediatrics, Committee on Fetus Section on Hospice and Palliative Medicine and Committee on Hospital and Newborn. Perinatal care and the threshold of viability. Pediatrics. Care. Pediatric palliative care and hospice care commitments, guidelines, 2002;110:1024-1027. and recommendations. Pediatrics. 2013;132(5):966-972. MacDorman MF, Gregory EC. Fetal and perinatal mortality: United Silverman WA. A hospice setting for humane neonatal death. Pediatrics. States, 2013. Natl Vital Stat Rep. 2015;64(8):1-24. 1982;69(2):239. Madden K, Wolfe J, Collura C. Pediatric palliative care in the intensive Silverman W. Overtreatment of neonates? a personal retrospective. Pediatrics. care unit. Crit Care Nurs Clin North Am. 2015;27(3):341-354. 1992;90:971-976. McHaffie HE, Cuttini M, Brölz-Voit G, et al. Withholding/withdrawing Silverman W. Compassion or opportunism. Pediatrics. 2004; treatment from neonates. J Med Ethics. 1999;25:440-446. 113:402-403. Meyer EC, Brodsky D, Hansen AR, Lamiani G, Sellers DE, Browning Singh J, Lantos J, Meadow W. End-of-life after birth: death and dying DM. An interdisciplinary, family-focused approach to relational learning in the NICU. Pediatrics. 2004;114:1620-1626. in neonatal intensive care. J Perinatol. 2011;31(3):212-219. Sydor-Greenberg N, Dokken D. Coping and caring in different ways: Meert KL, Keele L, Morrison W, et al. End-of-life practices among tertiary understanding meaningful involvement. Pediatr Nurs. 2000;26: care picus in the United States: a multicenter study. Pediatr Crit Care 185-190. Med. 2015;16(7):e231-e238. Walther FJ. Withholding treatment, withdrawing treatment, and palliative Michelson KN, Ryan AD, Jovanovic B, Frader J. Pediatric residents’ and care in the neonatal intensive care unit. Early Hum Dev. 2005; fellows’ perspectives on palliative care education. J Palliat Med. 81(12):965-972. 2009;12(5):451-457. Whitelaw A. Death as an option in neonatal intensive care. Lancet. Midson R, Carter B. Addressing end of life care issues in a tertiary treatment 1986;2:328-331. centre: lessons learned from surveying parents’ experiences. J Child Whitfield JM, Siegel RE, Glicken AD, Harmon RJ, Powers LK, Goldson Health Care. 2010;14(1):52-66. EJ. The application of hospice concepts to neonatal care. Am J Dis Milstein J. A paradigm of integrative care: healing with curing throughout Child. 1982;136(5):421-424. life, “being with” and “doing to.” J Perinatol. 2005;25(9):563-568. Widger K, Picot C. Parents’ perceptions of the quality of pediatric and Munson D, Leuthner SR. Palliative care for the family carrying a fetus perinatal end-of-life care. Pediatr Nurs. 2008;34(1):53-58. with a life-limiting diagnosis. Pediatr Clin North Am. 2007;54(5): Wolfe J. Recognizing a global need for high quality pediatric palliative 787-798. care. Pediatr Blood Cancer. 2011;57(2):187-188. Orgel E, McCarter R, Jacobs S. A failing medical educational model: a Wolfe J, Hinds P, Sourkes B. Textbook of Interdiscipinary Pediatric Palliative self-assessment by physicians at all levels of training of ability and Care. Philadelphia, PA: Elsevier; 2011:388. comfort to deliver bad news. J Palliat Med. 2010;13(6):677-683. Wolff J, Robert R, Sommerer A, Volz-Fleckenstein M. Impact of a pediatric Patel RM, Kandefer S, Walsh MC, et al. Causes and timing of death in palliative care program. Pediatr Blood Cancer. 2010;54(2):279-283. extremely premature infants from 2000 through 2011. N Engl J Med. World Health Organization (2015). “WHO definition of palliative care.” 2015;372(4):331-340. http://www.who.int/cancer/palliative/definition/en/. Rendón-Macías ME, Olvera-González H, Villasís-Keever MA. [The pediatric Wright V, Prasun MA, Hilgenberg C. Why is end-of-life care delivery patient at the end-of-life. A challenge for its identification and treatment. sporadic?: A quantitative look at the barriers to and facilitators of A survey in pediatricians and medical residents]. Rev Invest Clin. providing end-of-life care in the neonatal intensive care unit. Adv 2011;63(2):135-147. Neonatal Care. 2011;11(1):29-36.
PA RT IX Immunology and Infections 36 Immunology of the Fetus and Newborn JOERN-HENDRIK WEITKAMP, DAVID B. LEWIS, AND OFER LEVY KEY POINTS variability in the pace at which developmentally and genetically programmed human fetal and newborn immunity changes from • The fetus and newborn express a distinct and evolving immune system graft preservation to identification and destruction of invading that mediates transition from intrauterine life to the microbe- and pathogens. antigen-rich world. • Multiple mechanisms including regulatory T cells help ensure maternofetal immune compatibility. Maternal and Placental Immunology • Newborns are highly reliant on soluble and cellular innate immune mechanisms whose ontogeny depends on gestational and Immunologic tolerance to the growing fetus is a prerequisite for postnatal age. a successful pregnancy. The maternal–fetal interface is a dynamic • Adaptive immunity in newborns features distinct ontogeny and site that encompasses multiple cellular interactions in an environ- functionality of T and B cells. ment rich in cytokines and hormones. While immune mechanisms • Primary immunodeficiencies that present in early life include genetic need to be in place to defend against microbial invasion (von defects in innate and adaptive immunity. Rango, 2008; Aagaard et al., 2014), the placenta is typically • Maternal and early-life immunization are the most effective biomedical programmed to protect the fetus from rejection by the maternal interventions to prevent infection in the newborn and young infant. immune system (Aluvihare et al., 2004; von Rango, 2008). • Some live vaccines such as bacille Calmette–Guérin, which is given to newborns in tuberculosis-endemic regions, may afford broad protection Several distinct but complementary innate and adaptive immune against infections with antigenically unrelated pathogens. mechanisms contribute to the commensal immunologic relationship between the mother and the fetus throughout pregnancy (Fig. 36.1 and Table 36.1). Local (placental) and systemic (circulatory) factors mediate maternal tolerance to the fetus (Aluvihare et al., 2004). For example, human trophoblasts do not express conventional O f any age group, newborns and young infants are at the major histocompatibility complex (MHC) class I human leukocyte highest risk of infection-induced morbidity and death. antigen (HLA)-A or HLA-B molecules, likely contributing to Understanding the contribution of the newborn’s dis- reduced alloantigenic recognition at the fetal–maternal interface. tinct immune response to age-dependent susceptibility to infec- Human trophoblasts express HLA-C, principally during the first tious diseases has important implications for efforts to protect trimester of pregnancy (King et al., 1996a), and two nonclassical newborns from infection and entails review of the immunologic HLA molecules, HLA-E and HLA-G. HLA-G class Ib is expressed environment of pregnancy and the ontogeny of fetal and neonatal on extravillous cytotrophoblast and endothelial cells of fetal vessels immunity (Kollmann et al., 2017). The unique functions of fetal, in the chorionic villi as well as in amnion cells and amniotic fluid neonatal, and maternal immunity reflect adaptation to develop- (Le Bouteiller et al., 1999; Rebmann et al., 2014). Unlike classical mental challenges such as preservation of fetal well-being as an MHC molecules, HLA-G does not have a significant role in allogeneic graft versus adequate immunologic protection in the stimulating CD8+ T cells via the T-cell receptor (TCR) complex. extrauterine environment. These immunologic transitions are Rather, the principal function of HLA-G molecules expressed by regulated by a number of incompletely understood developmental the trophoblast appears to be modulation of the activity of natural and genetic mechanisms. The diversity and importance of these killer (NK) cells. HLA-G has additional immunomodulatory mechanisms are suggested by the heterogeneity and frequency of properties, including inhibition of activity of cytotoxic T cells, neonatal infections. Differences in immunologic responsiveness inhibition of alloproliferative responses by CD4+ T cells, and between newborns and adults are not defects or abnormalities but modulation of dendritic cell (DC) maturation and function rather highly regulated ontogenic differences that facilitate transi- (Carosella et al., 2008). These data reveal that the unique MHC tions between distinct age-specific challenges. Just as the ductus class I molecule expression pattern on fetal trophoblast constitutes arteriosus, a cardiopulmonary necessity in the intrauterine envi- an intricate mechanism for orchestrating the activity of immune ronment, closes at different rates in different infants, there is cells. 453
454 PART I X Immunology and Infections Lymphatic vessel TABLE Selected Local and Systemic Factors Mediating 36.1 Maternal Tolerance to the Fetus 6 7 Myometrium Blood vessel 5 Factor Function 8 5 4 Decidua Expression of nonclassical Inhibition of NK cells, CD4+ T cells, and 9 Fetal membrane HLA molecules (e.g., cytotoxic T cells, and modulation of HLA-G) dendritic cell maturation and function Indoleamine Depletes tryptophan and prevents T-cell 9 2,3-dioxygenase proliferation 2 1 Fas ligand Apoptosis of activated fetal and maternal T cells Programmed death 1 and Negative regulator of T-cell responses 3 its ligand Galectins Apoptosis of activated fetal and maternal T cells Decay-accelerating factor Control of complement activation Cytokines Th2 bias prevents immune activation Decidual macrophages Suppressing immune activation 1: Amniotic cavity 6: NK cell 2: Chorionic cavity 7: Macrophage Decidual NK cells Suppressing immune activation 3: Uterine cavity 8: Placental antigen + 4: Dendritic cell 9: Microbial Antigens FoxP3 regulatory T cells Suppressing immune effector cells 5: Treg cell (e.g., in response to paternal antigens) • Fig. 36.1 Immunology of the Fetomaternal Interphase. While compe- tent immune cells and bacteria can enter the fetomaternal interphase, Microbiome Balanced immune response multiple complex immune interactions are in place during healthy preg- FoxP3, Forkhead box P3; HLA, human leukocyte antigen, NK, natural killer. nancy to balance immune defense with immune tolerance between the mother and the allogeneic fetus. Several distinct but complementary innate and adaptive immune mechanisms contribute to the commensal immunologic relationship that exists between the mother and the fetus throughout pregnancy. In humans the decidua represents the uterine with many resorption sites and small litters (Hunt et al., 1997). implantation site, where maternal blood flows into the intervillous space, Progesterone-induced blocking factor is an immunomodulatory “bathing” fetus-derived villous trees composed primarily of cytotropho- molecule released in response to progesterone by trophoblasts blasts. The surface of these villi consists of multinucleate syncytiotropho- (Anderle et al., 2008). Its properties include indirect suppression blasts mediating nutrient and gas exchange between maternal and fetal of NK-cell function and inducement of bias of CD4+ T cells tissues. The villi are directly exposed to circulating maternal immune cells. However, these cells do not recognize fetal tissue as “foreign” mainly toward Th2-type cytokine secretion (Szekeres-Bartho and Wegmann, because human trophoblasts lack classical class I and class II antigens 1996). and instead express human leukocyte antigen G (HLA-G). HLA-G and Galectins are expressed in human placenta primarily by the pregnancy hormones suppress natural killer (NK) cell and macrophage syntrophoblast early in pregnancy (Than et al., 2009). On cell function and induce a bias of CD4+ T cells toward Th2-type cytokine secre- surface contact, galectins downregulate the cellular immune response, tion. Dendritic cells are present in small numbers during pregnancy in in part by inducing programmed cell death (apoptosis) of T decidual tissue but show impaired migration to draining uterine lymph lymphocytes (Liu and Rabinovich, 2010). nodes (entrapment). Regulatory T (Treg) cells specific to the fetus increase On a cellular level, DCs, an important type of antigen-presenting in number in the mother during gestation, and cells maintaining tolerance cell (APC) critical for cellular and humoral immune responses, to fetal antigen can rapidly expand during a subsequent pregnancy. The play a prominent role in organ transplant rejection. The potential role of exposure to microbial antigens in fetal immune priming seems important, but the exact mechanism is still being explored. deleterious actions of DCs against the fetus may be curtailed by at least two factors: the progressive decline of decidual DC tissue densities shortly after implantation and impaired migration from Other local factors contributing to maternal–fetal tolerance decidual tissue to draining uterine lymph nodes. This entrapment include selective degradation of tryptophan by the inducible enzyme of DCs during pregnancy may be a combined result of disappearing indoleamine 2,3-dioxygenase inhibiting T-cell proliferation (Munn lymphatic vessels during decidualization (Volchek et al., 2010) et al., 1998) and engagement of the proapoptotic molecule Fas and stromal cell–based processes limiting chemokine-directed cell on maternal lymphocytes by its ligand (FasL) on interstitial tro- migration (Collins et al., 2009). Other important cellular factors phoblast cells (Hammer et al., 1999). FasL is expressed in both that may limit a potential immune reaction toward the fetus include maternal and fetal components of the uteroplacental unit throughout the immunosuppressive phenotype of decidual macrophages gestation. Activated T cells express the Fas receptor, which delivers (Gustafsson et al., 2008) and decidual NK cells. an apoptotic (death) signal when bound by FasL. Therefore expres- Complement inhibition is essential for normal pregnancy in a sion of FasL limits the reciprocal migration of activated fetal and murine model of antiphospholipid syndrome, an autoimmune maternal T cells. Mice with a nonfunctional FasL demonstrate condition characterized by thrombosis, thrombocytopenia, and leukocyte infiltration and necrosis at the decidual–placental border, recurrent fetal loss. In this model, fetal injury results from placental
CHAPTER 36 Immunology of the Fetus and Newborn 455 inflammation initiated by local dysregulation of complement immunity and rejection and are characterized by production of proteins. Both complement activation and fetal loss can be prevented interleukin (IL)-2, interferon gamma (IFN-γ), and tumor necrosis by administration of anticoagulants with complement-inhibitory factor alpha (TNF-α). In contrast, Th2 cells are mediators of properties such as heparin but not by anticoagulants lacking humoral immunity and produce IL-4, IL-5, and IL-13. Traditional complement-binding properties (Girardi et al., 2003, 2004). Some dogma holds that a bias in T-cell cytokine secretion toward Th2-type but not all human clinical interventional studies using anticoagulants cytokines and away from Th1-type cytokines is an immunologic with complement-binding properties to prevent fetal loss in condition necessary for maintaining healthy pregnancy (Dealtry antiphospholipid syndrome have suggested benefit (Di Nisio et al., et al., 2000). For example, IL-10 is a pregnancy-compatible cytokine 2005). Control of complement activation during human pregnancy that plays a vital role in maintaining immune tolerance (Cheng is achieved by expression of decay-accelerating factor, membrane and Sharma, 2015). Significant shifts in the Th1/Th2 balance have cofactor protein, and CD59 (protectin) on the trophoblast mem- been associated with various immune-mediated pregnancy complica- brane (Denny et al., 2013), as well as high reproductive tract and tions. However, the emerging role of NK cells and emerging systemic prostaglandin E2 levels contributing to maternal immune cytokines such as IL-12, IL-15, IL-18, IL-19, and IL-20 question tolerance to the fetus (Parhar et al., 1988). the Th1/Th2 paradigm as oversimplified (Chaouat et al., 2004; In addition to local components, systemic elements are in place Menon et al., 2006). For example, a subset of CD4 T cells that to maintain immune tolerance at the maternal–fetal interface. produce IL-17A and IL-17F, called Th17 cells, may be involved in Abatement of certain autoimmune diseases during pregnancy (de rejection of the fetus (Wang et al., 2010). Man et al., 2008) and an increased risk of infections (Jamieson et al., 2006) provide evidence for a more generalized immunosup- Role of Regulatory T Cells in Pregnancy pressive state during pregnancy (Poole and Claman, 2004). Although the precise mechanisms underlying this phenomenon are incom- The discovery of a distinct lineage of T lymphocytes with dominant pletely characterized, several reproductive hormones may play immunosuppressive properties (Brunkow et al., 2001) enabled critical roles. For example, a relatively large study demonstrated major breakthroughs in understanding the mechanisms, whereby that 48% of patients with at least moderate disease activity of adaptive allogeneic responses against paternal antigens are actively rheumatoid arthritis showed signs of remission in the first trimester suppressed during pregnancy. This type of Treg cell is characterized of pregnancy, while approximately 40% had a disease flare-up in by expression of a lineage-specific transcription factor, FoxP3 (Fig. the postpartum period (de Man et al., 2008). The rate of relapse 36.2). On activation via their antigen-specific TCR, Treg cells in multiple sclerosis declines during pregnancy (Confavreux et al., are capable of suppressing immune effector cells, including DCs 1998), and treatment with pregnancy levels of estriol significantly and effector T cells through a variety of mechanisms (Tang and reduced enhancing lesions on brain imaging (Camras et al., 1992). Bluestone, 2008), thereby preventing a fatal form of autoimmune In addition, estrogen (17β-estradiol) in concentrations typically disease throughout life (Kim et al., 2007). Treg cells and Th17 cells expressed during normal pregnancy augments forkhead box P3 are two distinct lymphocyte subsets with opposing actions and (FoxP3) expression and expansion of T regulatory (Treg) cells in share a complex relationship. Treg cells have a role in suppressing vitro and in vivo (Polanczyk et al., 2004; Tai et al., 2008). autoimmune responses and preventing the rejection of the fetus, T cells and T-cell–derived cytokines play a central role in immune and a decrease in Treg cell number is associated with miscarriage. In regulation and inflammation. Th1 cells are involved in cellular contrast, Th17 cells promote inflammation, transplant rejection, and Bone marrow Thymus Periphery T-cell progenitor cell CD4+ CD25high FOXP3high CD4+ CD25high FOXP3high “nTreg” 1 T-cell progenitor cell Naive CD4+ T cell CD4+ CD25high FOXP3high + TGFβ “iTreg” 2 Intestine T-cell progenitor cell Naive CD4+ T cell CD4+ CD25high FOXP3high CD103+ DC “iTreg” 3 + TGFβ + Retinoic acid • Fig. 36.2 Forkhead Box P3–Positive Regulatory T-Cell Subpopulations and Their Development. Most human regulatory T (Treg) cells in peripheral blood originate from the thymus and are typically called natural Treg (nTreg) or thymus-derived Treg cells (1). Treg cells can originate from naive T cells in the periphery and are induced to express the identifying transcription factor forkhead box P3 (FOXP3) under the influence of transforming growth factor beta (TGFβ), at least in vitro (2). The Treg cells are often called induced Treg (iTreg) cells. Most Treg cells in the intestinal mucosa are thought to be iTreg cells originating from naive T cells in the mucosal immune system under the influence of specific antiinflammatory dendritic cells (CD103+ dendritic cells), TGFβ, and retinoic acid (3). The iTreg cells play an important role in preg- nancy maintenance. DC, Dendritic cell.
456 PART I X Immunology and Infections autoimmunity, and increases in Th17 cell numbers and decreases in The exact mechanism of prenatal immune priming is unknown, Treg cell numbers are associated with recurrent miscarriage (Wang but in an experimental asthma model, microbial exposure to et al., 2010a, 2010b; La Rocca et al., 2014). The numbers of Treg pregnant mice resulted in epigenetic changes in promoter regions cells specific to the fetus increase in the mother during gesta- of cytokines associated with an allergic phenotype-increased expres- tion, and cells maintaining tolerance to fetal antigen can rapidly sion of IFN-γ and reduced expression of IL-4, IL-5, and IL-13 expand during subsequent pregnancy (Rowe et al., 2012). Paternal (Furuya et al., 1990). This concept has been confirmed in human antigens may induce expansion of Treg cells, likely contributing studies where exposure to farms during pregnancy has been associ- to maternal tolerance to the allogeneic fetus (Zenclussen et al., ated with increased DNA demethylation of the FoxP3 locus and 2005). Maternal and fetal Treg cells are essential in promoting increased number and function of Treg cells in UCB cells (Schaub fetal survival by avoiding the recognition of paternal semiallogeneic et al., 2009). tissues by the maternal immune system (Mold et al., 2008; La Rocca While exposure to commensal bacteria during pregnancy seems et al., 2014). beneficial for a healthy developing immune system, inflammatory The interaction between the costimulatory molecule programmed states during pregnancy can have long-lasting adverse effects on death 1 (PD1) and its ligand (PDL1) plays important roles in the offspring. For example, in murine models, maternal immune maintaining tolerance at the fetomaternal interface. PDL1 is activation can trigger autism-like behavior and neuropathology in expressed on the trophoblasts of the placenta, and PD1 is expressed the offspring (Hsiao et al., 2013). Despite the importance of on the maternal effector T cells and Treg cells. PDL1 expression immune regulation for a healthy pregnancy and recent scientific maintains Treg cell/effector T-cell ratios and suppresses increases advances, much remains to be learned regarding the molecular in the number of Th17 cells (D’Addio et al., 2011). Blockade of mechanisms used by the fetal immune system to promote tolerance PDL1 signaling in animal models results in fetal rejection (Guleria or suppression. et al., 2005). The role and ontogeny of fetal Treg cells is discussed more fully in the section entitled Adaptive Immunity. Effect of Pregnancy Complications on the Developing Fetal Immune System Role of the Microbiome To enable initiation and maintenance of pregnancy, the intrauterine The paradigm of a sterile uterus postulates that the fetus develops environment significantly shapes the developing immune system free of bacteria and antigenic agents (Mackie et al., 1999). However, as is evident from the antiinflammatory cytokine profile and bacteria can be cultured from amniotic fluid and fetal tissues in protection from atopic sensitization in offspring after maternal pregnancies complicated by preterm labor even without rupture exposure to farming activities and farm dairy products during of membranes (Goldenberg et al., 2000). Bacterial DNA can be pregnancy (Ege et al., 2008; Pfefferle et al., 2010). This effect is detected in meconium and umbilical cord blood (UCB) of healthy at least in part mediated through an increase in the number of neonates as well as amniotic fluid obtained by cesarean section fetal Treg cells (Schaub et al., 2009). and placentas following undisturbed, healthy pregnancies without In contrast, fetal exposure to inflammation during critical histologic evidence for chorioamnionitis. The exact mechanisms developmental windows can influence immune programming to by which bacteria pass from the mother to the fetus are being augment inflammatory neonatal responses. Histologic chorioam- investigated. Increased bacterial translocation from the intestine nionitis (HCA) is a common complication of pregnancy, typically to other organs can be found during pregnancy, and bacterial caused by intrauterine bacterial infection and defined by inflam- DNA signatures can be detected in the peripheral blood of pregnant mation of the fetal membranes. Fetal exposure to HCA induces women (Perez et al., 2007). Placental bacteria resemble most closely immune activation, resulting in fetal inflammatory response the human oral microbiome (Aagaard et al., 2014), suggesting syndrome (FIRS), and shapes the neonatal transcriptomic immune hematogenous bacterial transfer. While not yet widely accepted response (Weitkamp et al., 2016). The clinical characteristics of in humans, maternal microbial transmission to the fetus is a universal FIRS consist of systemic inflammation and elevation of fetal plasma phenomenon in animals, likely constituting an essential evolutionary IL-6 and other proinflammatory cytokine levels (Gomez et al., act of symbiosis (Funkhouser and Bordenstein, 2013). 1998). Long-term sequelae of the sustained systemic inflammation Globally, these studies imply a possibly critical role of maternal precipitated by fetal exposure to HCA include blindness (Chen bacteria to inform normal immune development of the developing et al., 2011), cerebral palsy (Wu et al., 2000), impaired cardiac fetus. While the importance of fetal programming has been well function (Romero et al., 2004), lung disease (Kramer et al., 2009), described for cardiovascular and metabolic diseases, it is now also and disruption of normal fetal immune development (Leviton discussed in the context of environmentally influenced immune- et al., 2011; O’Shea et al., 2012; Savasan et al., 2012; Bastek et al., mediated diseases. A possible reason for the initial exposure of 2014; Kallapur et al., 2014). In humans, placental infection, bacterial molecular patterns to the fetus in utero is to prime the chorioamnionitis, or villitis together with a fetal inflammatory immune system and/or the epithelium to respond appropriately response appear to increase the risk of surgical necrotizing entero- to pathogens and commensals after birth (Abrahamsson et al., colitis (NEC) (Moore et al., 2013). 2015). For example, maternal exposure to farm animals during Studies of fetal sheep and human UCB have demonstrated pregnancy was associated with greater Toll-like receptor (TLR) activation of the adaptive immune system following exposure to gene expression and lower risk of atopic sensitization in children HCA. In a model of chorioamnionitis and FIRS caused by (Ege et al., 2006). Similar protective effects against atopic sensitiza- administration of intra-amniotic lipopolysaccharide (LPS) in rhesus tion were observed after dietary interventions during pregnancy, monkeys at approximately 80% of gestation, fetal Treg cell genera- such as maternal supplementation with fish oil (Dunstan et al., tion in the thymus was inhibited, while the concentration of 2003) or probiotics (Elazab et al., 2013). In contrast, antibiotic proinflammatory cells in the spleen increased (Rueda et al., 2016). use in pregnancy was associated with asthma during the fifth year The immunologic changes associated with endotoxin-induced of life (Benn et al., 2002). systemic and organ-specific immune priming in the fetus can be
CHAPTER 36 Immunology of the Fetus and Newborn 457 mimicked by administration of IL-1α or IL-1β, suggesting a possibly Activation of the complement cascade occurs via three important role of IL-1 receptor signaling in FIRS. In a similar pathways—classical, lectin, or alternative (Thiel, 2007; Zipfel and model using intra-amniotic injection of LPS 7 or 14 days before Skerka, 2009). Several characteristics of the complement cascade preterm delivery in fetal sheep, involution and activation of the are important for fetal–neonatal immunity. First, the complement fetal thymus with structural organ changes was observed (Kuypers system features both antibody-dependent specificity via the classical et al., 2012). Furthermore, UCB derived from human neonates pathway activation triggered by interaction of antigens with antibod- with clinical evidence of perinatal infection exhibited a higher ies, and antibody-independent activation of the alternative and proportion of Th1 cells than UCB from uninfected neonates lectin pathways initiated by pathogen-associated structures such (Matsuoka et al., 2001). as endotoxin and polysaccharides. Thus for the fetus or infant who Overall, epidemiologic and experimental data point to the central has not received from the mother or has not yet produced antigen- role of maternal immune activation and/or FIRS in the pathogenesis specific immunoglobulin (Ig) G for immunologic recognition, the of many immune-mediated complications of prematurity such as alternative and lectin pathways may be critical for triggering the chronic lung disease, brain damage, retinopathy of prematurity, effector functions of the complement cascade (Kielgast et al., 2003; gut injury, and behavior abnormalities. On the other hand, prenatal Simister, 2003). Second, the enzymatic activation of the complement immune activation may improve vaccine responses and render the cascade enables rapid functional amplification: deposition of a newborn more resistant to infectious challenges later in life (Strunk single Ig molecule or C3b fragment can generate enzymatic cleavage et al., 2012). of thousands of later-acting components and thus multiple comple- ment activities (Carroll, 2004; Zipfel and Skerka, 2009). In addition, Developmental Fetal–Neonatal Immunology the alternative pathway can be amplified via a positive feedback activation mechanism, because C3b, an activation product of the Newborn and young infants, especially those born preterm, alternative pathway C3 convertase, is a component of this convertase are at increased risk of developing a range of bacterial and viral (Janssen et al., 2006). As the fetus and newborn are particularly opportunistic infections. This age-dependent susceptibility is in dependent on antibody-independent pathogen recognition for part based on immune ontogeny (Dowling and Levy, 2014). In immunologic responsiveness, the positive amplification loop of the past few decades research has focused on the molecular, cel- the alternative pathway may be particularly critical for rapid genera- lular, and functional bases for immunologic differences between tion of complement effector functions in early life in the absence newborns and older individuals, which we discuss as they relate to of antibody-based recognition. Third, the continuous activation innate and adaptive immunity. of the alternative pathway requires rigorous regulation in the fetus to avoid tissue damage during organ remodeling (Zipfel et al., 2007). Finally, the contributions of the lectin pathway to fetal– Innate Immunity neonatal complement activation and fetal well-being are still under During fetal/newborn adaptation from the intrauterine environment investigation. to the colonization of skin and mucosal surfaces following birth, Studies of fetal and neonatal complement have focused on the innate immune system shields the newborn from infection quantification of serum concentrations of individual components, while orchestrating the acquisition of protective adaptive immune examining maternal–fetal transport of these proteins, assessing responses (Levy, 2007). These innate mechanisms evolve across specific effector functions of the classical and alternative pathways, gestation and postnatal age (Fig. 36.3) and include protective and investigating contributions of complement activation to barriers such as the vernix caseosa, which contains antimicrobial common neonatal diseases. Detectable concentrations of C3 (1% proteins and peptides (APPs) and microbicidal fatty acids (Tollin of adult levels) and C1 inhibitor (20% of adult levels) can be et al., 2005), developmentally controlled functional regulation of measured as early as 5 to 6 weeks’ gestation (Gitlin and Biasucci, TLR signaling (Kollmann et al., 2012), expression of acute-phase 1969). By 26 to 28 weeks’ gestation, both C3 and C1 inhibitor reactants (Levy, 2007; Fig. 36.4) and complement proteins, and concentrations increased to 66% of adult levels. Functionally and alterations in neutrophil and monocyte function (Forster-Waldl immunochemically measured classical and alternative pathway et al., 2005; Levy et al., 2006). Importantly, functional matura- protein concentrations in UCB increase with advancing gestational tion of innate immunity enables colonization with commensal age, such that impairment in CH50 is particularly evident in the organisms while limiting potentially dangerous inflammatory preterm (Grumach et al., 2014), and at full-term gestation the responses (Kollmann et al., 2017). Herein we discuss key fea- concentrations are only approximately 50%–75% of adult concentra- tures of innate immunity in early life beginning with soluble- tions (Wolach et al., 1997; Sonntag et al., 1998). Although neonatal based defense systems that progress to leukocyte-based defense UCB lectin pathway component concentrations are lower than systems. those in older children and adults, the correlation between mannose- binding lectin (MBL) and gestational age has not been consistently Complement observed (Hilgendorff et al., 2005; Swierzko et al., 2009). Of note, Central to the innate immune response is the complement system on the basis of studies of genetically determined, structurally distinct that consists of more than 40 plasma, cell surface, and regulatory complement variants in maternal and umbilical cord serum, no proteins that interact to regulate multiple physiologic functions, transplacental passage from the mother to the fetus of C3, C4, including resistance to pyogenic infections, interaction between factor B, or C6 has been observed (Colten et al., 1981). innate and adaptive immunity, and elimination of immune Much remains to be learned regarding regulation of complement complexes, products of inflammatory injury, and apoptotic self effector functions in the fetus and newborn. Activation of the cells (Zipfel and Skerka, 2009). Components of the complement alternative pathway or the lectin pathway enables opsonization of system recognize and lyse bacteria, opsonize microorganisms, release invading microorganisms without specific Ig recognition. Accord- anaphylatoxins, solubilize immune complexes, and induce B-cell ingly, for preterm infants or those without organism-specific proliferation and differentiation. maternal IgG, alternative or lectin pathway activation provides a
458 PART I X Immunology and Infections Fetal/Preterm Newborn/Full Term Infant Adult Developmental Tolerance to noninherited Shield vs. infection Commensal tolerance/ challenge: maternal alloantigens Controlled inflammation Pathogen protection Vernix caseosa SKIN Epidermis MUCOUS MEMBRANES Paneth cells Maternal Innate antibodies lymphocytes Th1 polarizing cytokines Adenosine BLOOD MDSCs Treg cells APPs Complement Endothelial cells proteins Antimicrobial proteins Adenosine Adult-like cells and peptides (APPs) (bone marrow derived): Complement proteins Colonizing bacteria Effector cytokines Monocytes Maternal secretory IgA Innate lymphocytes Maternal IgG Th1 polarizing cytokines Myeloid-derived Endogenous IgG CD71+ Nucleated RBC suppressor cells (MDSCs) TLRs Fetal cells (liver derived) Treg cells • Fig. 36.3 Ontogeny of Skin, Soluble, and Cellular Innate Defense Systems. Host-protective barrier functions include physical, chemical, and func- tional components of the skin and mucous membrane epithelia of the fetus, neonate (birth to 28 days of age), and infant (1 month to 1 year of age). Skin: while physical and chemical barriers are impaired in early in life, especially in the preterm newborn, the vernix caseosa and skin epithelia of full-term newborns robustly express antimicrobial proteins and peptides (APPs). Mucous membranes: in parallel with and induced by an increasingly complex microbiota, the newborn intestinal mucosal epithelium rapidly changes structurally, with an increase in the population of crypts and crypt-based Paneth cells, as well as functionally with increasing APP expression. Blood: the composition of neonatal blood is distinct, with relatively low concentrations of complement components and APPs and high concentrations of the immunosuppressive purine metabolite adenosine. Plasma also contains maternal antibodies that are transferred beginning midgestation and supplemented by postnatal factors derived from breast milk. Innate immunity is detectable from the end of the first month of gestation, with changes driven largely by the increasing exposure to environmental microbes. Neonatal antigen- presenting cells such as blood monocytes express pattern recognition receptors (e.g., Toll-like receptors, TLRs) with distinct functional responses, including limited Th1-polarizing cytokine production, to most stimuli. Adaptive immunity develops from 4 weeks of gestation onward, with changes driven by an evolving chimerism reflecting fetal (liver-derived, shaded cells) regulatory T (Treg)-cell–rich lymphocytes, and more adultlike (bone marrow derived, unshaded cells) lymphocytes with distinct epigenetically encoded functional programs. Ig, Immunoglobulin; RBC, red blood cell. (Modified from Kollmann TR, Kampmann B, Mazmanian SK, Marchant A, Levy O. Protecting the newborn and young infant from infectious diseases: lessons from immune ontogeny. Immunity. 2007;46:350–363.)
CHAPTER 36 Immunology of the Fetus and Newborn 459 Acute phase Defensins NEUTROPHIL products LIVER C/EBP-α BPI IL-1 IL-6 02- HEPATOCYTE NADPH Oxidase SCD14 Receptors e- CRP Hepatic vein MBL LBP BACTERIUM LPS IL-1β LPS IL-6 High LBP Lipoprotein Adenosine TNF CLR CD14 TLR cAMP RIG-1 NF-κB Kinase NOD2 NF-κB Inflammatory gene transcription TLR7 RelA TLR8 TLR9 DNA MONOCYTE • Fig. 36.4 Innate Detection, Signaling, and Effector Functions of Blood Phagocytic Leukocytes and Hepatocytes. Innate immune signals are detected via signaling loops. Monocytes express pattern rec- ognition receptors, including C-type lectin receptors (CLRs), CD14, and Toll-like receptors (TLRs). TLR- mediated monocyte activation engages signaling pathways resulting in kinase and nuclear factor κB (NF-κB) pathway activation, culminating in inflammatory gene transcription, including generation of cyto- kines that amplify an antiinfective response. For example, interleukin (IL)-1β and IL-6 engage cognate cytokine receptors on hepatocytes, inducing acute-phase response, including production and secretion of lipopolysaccharide (LPS)-binding protein (LBP), mannose-binding lectin (MBL), the pentraxin C–reactive protein (CRP), and soluble CD14 (SCD14). These molecules recognize and modulate inflammatory activity of microbial products. For example, LBP at low concentrations delivers LPS to TLR4, thereby enhancing signaling but at higher LBP concentrations detoxifies LPS by delivering it to plasma lipoproteins. Monocyte production of tumor necrosis factor (TNF) activates neutrophils that deploy antimicrobial systems that are oxygen dependent, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, as well as those that are oxygen independent, such as membrane-active antimicrobial proteins and peptides, includ- ing defensins and bactericidal/permeability-increasing protein (BPI), an LBP homologue that binds to and neutralizes endotoxin. Soluble mediators, such as the antiinflammatory purine metabolite adenosine, can limit proinflammatory responses. cAMP, Cyclic adenosine monophosphate; C/EBP-α, CCAAT/enhancer binding protein; NOD2, nucleotide-binding oligomerization domain-containing protein 2; RelA, NF-κB subfamily protein; RIG-1, retinoic acid-inducible gene 1. critical mechanism for engaging complement effector functions the absence of specific antibodies and thus enables characterization (Super et al., 1989; Maruvada et al., 2008; Swierzko et al., 2009). of classical pathway function. In 8 of 20 neonatal serum samples The functional contribution of the classical pathway to effector examined, decreased bactericidal activity was detected and correlated functions has been assessed through the use of blood-mediated with significantly lower functional activity of C1q and C4. These opsonophagocytosis by polymorphonuclear leukocytes of group studies did not determine whether this decrease was mediated by B streptococci (GBS) type Ia (Edwards et al., 1983). This GBS an inhibitor of function or by an intrinsic change in functional serotype may be opsonized by classical pathway components in activity of these components in neonatal sera. Studies of MBL
460 PART I X Immunology and Infections concentrations and pathway activity suggest a contribution of the APPs vary with gestational age such that preterm plasma is relatively lectin pathway to neonatal susceptibility to infection (Super et al., deficient in multiple APPs, likely contributing to reduced micro- 1989; Sumiya et al., 1991; Thiel et al., 1995; Kilpatrick et al., bicidal capacity (see Fig. 36.3; Battersby et al., 2016). Examples 1996; Kielgast et al., 2003; Swierzko et al., 2009). Complement of APPs include (1) lactoferrin, an 80-kDa protein with iron-binding regulatory proteins (e.g., C4b-binding protein and factor H) also and direct membrane perturbing properties found in tear fluid, contribute to neonatal susceptibility as suggested by the failure of saliva, and neutrophil secondary granules, (2) the 5-kDa bactericidal/ neonatal serum to reduce invasion by GBS and Escherichia coli permeability-increasing protein, expressed on certain mucosal into human brain microvascular endothelial cells (Maruvada et al., epithelia as well as neutrophil primary granules, with high affinity 2008). In vitro experiments in which killing of E. coli by neonatal for LPS that enables it to neutralize the inflammatory activity of serum samples was limited by C9, but not by other classical pathway endotoxin and targets its microbicidal activity toward gram-negative components, suggest that this terminal complement component bacteria, (3) 14-kDa phospholipase A2, an acute-phase reactant is apparently important for cytolysis of this pathogen (Lassiter expressed in liver with ability to enzymatically kill a range of et al., 1992, 1994). Although relatively lower concentrations of gram-positive pathogens, and (4) 4-kDa disulfide-rich defensin complement components likely contribute to poor control of peptides of neutrophil primary (azurophilic) granules with broad bacterial replication, these complement concentrations are neverthe- microbicidal activity (Levy, 2004). Ongoing efforts are aimed at less sufficient, via C3- and factor B–dependent activity in the developing congeners of APPs as novel antiinfective agents for alternative pathway, to enhance GBS-induced production of TNF-α individuals who are relatively APP deficient, including preterm by monocytes in human newborn UCB tested in vitro (Levy et al., infants and those undergoing chemoradiotherapy (Palmer et al., 2003). 2011). For example, oral administration of lactoferrin to human In addition to relatively low serum concentrations of classical, preterm newborns has shown promise in reducing the incidence alternative, and lectin pathway complement proteins, additional of sepsis and NEC (Pammi and Abrams, 2015). complement functions important for fetal and neonatal well-being can contribute to reduced capacity to activate the classical and Innate Lymphoid Cells, Including Natural Killer Cells alternative pathways. For example, fetal and neonatal serum Innate lymphoid cells (ILCs) are derived from a common lymphoid demonstrates reduced concentration of C4b-binding protein, a progenitor, are defined by the absence of antigen-specific B-cell critical regulator of classical pathway C3 convertase activity (Malm receptors (BCRs) or TCRs, and do not express myeloid or DC et al., 1988; Melissari et al., 1988; Moalic et al., 1988; Fernandez markers (Klose and Artis, 2016). ILCs are divided into subgroups et al., 1989). Lower C4b-binding protein concentration increases based in part on the cytokine profile they produce: (1) group 1 the functional anticoagulant activity of protein S, with which it ILCs produce IFN-γ and are functionally dependent on the complexes and thereby contributes to decreased coagulation function transcription factor T-bet; (2) group 2 ILCs produce type 2 cytokines of the fetus and newborn. Consideration of complement components (e.g., IL-4, IL-5, IL-9, and IL-13) in response to helminth infection that also express nonimmunologic functions will likely be important and are dependent on RORα and GATA3; and (3) group 3 ILCs in characterizing developmental regulation of complement com- produce IL-17A and/or IL-22 and are dependent on the transcrip- ponent production. tion factor RORγt. Complement activation contributes to tissue injury in several NK cells are the most studied of the ILCs. These group 1 ILCs common neonatal diseases, including neonatal hypoxic–ischemic constitute approximately 10%–15% of all peripheral blood lym- encephalopathy, NEC, meconium aspiration syndrome, and phocytes. They are present in the spleen, lungs, and liver and are intrauterine growth restriction and fetal loss (Girardi and Salmon, also rarely found in lymph nodes and thoracic duct lymph 2003; Lassiter, 2004; Schultz et al., 2005; Girardi et al., 2006; (Cerwenka and Lanier, 2001). NK cells represent up to 70% of Mollnes et al., 2008; Schlapbach et al., 2008). Unregulated comple- all lymphocytes in the maternal decidual tissue (King et al., 1996b). ment activation may occur in selected infants undergoing extra- They demonstrate distinct morphology, function, and surface corporeal membrane oxygenation therapy, raising concern for molecule expression, including expression of CD16 (Fc gamma inflammatory injury on that basis (Johnson, 1994; Kozik and receptor [FγR]III) and CD56 (nerve cell adhesion molecule 1). Tweddell, 2006). C5a is present in the cerebrospinal fluid of human Mature NK cells appear larger and more granular than T or B newborns, at especially high concentrations in those born preterm cells (Cooper et al., 2001) and express both activating and inhibitory (Pataky et al., 2016), raising the possibility that complement receptors that are used to selectively identify and kill virally infected activation in the neonatal brain may contribute to preterm brain cells and tumors (Biassoni et al., 2001). The presence of MHC injury. class I molecules on potential target cells induces signals that suppress Overall, study of the complement system in early life, including NK-cell function. MHC class I–deficient target cells activate NK-cell characterization of the developmental and genetic regulation of function, triggering release of lysosomal granules containing serine this important group of plasma and cell surface proteins, promises proteases, perforin, and transforming growth factor beta (TGF-β), to shed further light on immune ontogeny in relation to health thereby disrupting the target cell membrane and inducing an and disease. inflammatory response. Fetuses and neonates demonstrate reduced NK-cell activity compared with adults (Georgeson et al., 2001; Antimicrobial Proteins and Peptides Kadowaki et al., 2001). The human body expresses natural antibiotics, including APPs NK cells are derived from a common hematopoietic progenitor that act alone and in combination with endogenous (e.g., comple- that retains T-cell and B-cell developmental potential (Boos et al., ment) and exogenous (e.g., conventional antibiotic) systems to 2008). NK cells first make their appearance in fetal liver as early prevent infection and/or eliminate invading microorganisms (Levy, as 6 weeks’ gestation. Committed CD34+CD56– NK cell progenitors 2004). APPs are expressed by a range of cells, including epithelial have been identified in the fetal thymus, bone marrow, and liver. cells and leukocytes, especially neutrophils (see Fig. 36.4), and are In the human neonate, the NK-cell population is immature: only found associated both with cells and in plasma. Plasma levels of half of all NK cells express CD56, and the NK-cell cytolytic activity
CHAPTER 36 Immunology of the Fetus and Newborn 461 is lower (Dominguez et al., 1998). This functional reduction in evidenced in humans with X-linked lymphoproliferative disease, NK-cell activity may contribute to the severity of neonatal herpes caused by loss-of-function mutations in the SAP linker. In the simplex virus (HSV) infections. Profound defects in NK-cell activity absence of SAP, interactions with EAT-2 may be inhibitory result in familial hemophagocytic lymphohistiocytosis (HLH), a (Lanier, 2008). disease characterized by fever, hepatosplenomegaly, cytopenia, Recent studies have explored the potential contribution of ILCs hyperferritinemia, and hemophagocytosis. Familial HLH arises beyond NK cells. A role for lung group 2 ILCs in mediating from mutations in genes that encode proteins involved in the respiratory syncytial virus (RSV)-induced IL-33–driven Th2-biased granule-exocytosis pathway and can be fatal without bone marrow immunopathology has been demonstrated in neonatal mice (Saravia transplant (Orange, 2006; Jordan and Filipovich, 2008). et al., 2015). IL-23–responsive group 3 ILCs played a role in the NK-cell receptors are fundamentally different from TCRs and pathogenesis of neonatal intestinal inflammation in a murine model BCRs. NK-cell receptor gene expression does not require gene (Chen et al., 2015). Much remains to be learned regarding the segment rearrangement, and the receptors are not clonally distrib- ontogeny of ILC function with respect to both the quantity and uted. Instead, NK cells use an array of stimulatory and inhibitory the quality of these cells in the very young. receptors to regulate their cytolytic functions (Lanier, 2008). A cluster of 10 or more genes encoding killer-cell Ig-like receptors Polymorphonuclear Neutrophils (KIRs) is located on human chromosome band 19q13.4 (Biassoni Neonatal polymorphonuclear neutrophils (PMNs) are present at et al., 2001). Each of these type I glycoproteins recognizes a different early stages of gestation, but their functional capacities are different allelic group of HLA-A–, HLA-B–, HLA-C–, or HLA-G–encoded from those of adult PMNs. Progenitor cells that are committed proteins, and each KIR is expressed by only a subset of NK cells. to maturation along granulocyte or macrophage cell lineages Another family of Ig-like receptor genes termed ILT is present (granulocyte–macrophage colony-forming units) are detectable in near the KIR locus at 19q13.3. These receptors are not as restricted the human fetal liver between 6 and 12 weeks’ gestation in similar as the KIRs and bind multiple HLA class I molecules. A third proportions as in adult bone marrow (Christensen, 1989). Human inhibitory receptor gene locus is on chromosome band 12p12-p13, fetal blood has detectable granulocyte–macrophage colony-forming encoding a C-type lectin inhibitory heterodimeric receptor called units from 12 weeks’ gestation to term (Christensen, 1989). CD94/NKG2 that binds HLA-E. Those KIRs, ILT receptors, and Although these progenitor cells are detectable in the fetus and CD94/NGK2 molecules with long cytoplasmic tails and two newborn, developmental differences between adult and mature immunoreceptor tyrosine-based inhibitory motifs (ITIMs) function neonatal PMNs have been demonstrated—in signal transduction, as inhibitory receptors. On phosphorylation, the two ITIMs recruit cell surface protein expression, cytoskeletal rigidity, rolling adhesion, and activate the Src homology domain 2 (SH2)-containing microfilament contraction, transmigration oxygen metabolism, phosphatases, which turn off the kinase-driven activation cascade intracellular antioxidant mechanisms, and neutrophil extracellular (Ravetch and Lanier, 2000). The KIR family member KIR2DL4 trap formation (Hill, 1987; Carr, 2000; Henneke and Berner, is distinct from other KIRs in structure and distribution. KIR2DL4 2006; Levy, 2007; Yost et al., 2009). The magnitude of PMN binds HLA-G and has a single ITIM in the cytoplasmic tail and functional differences correlates with the maturity of the infant a lysine in the transmembrane region, enabling association with and begins to decrease within the first few weeks after birth (Carr, adaptor proteins. This inhibitory receptor was found on all decidual 2000). NK cells in the placenta at term but not on circulating maternal In addition to intrinsic age-dependent differences in PMN NK cells, suggesting that expression of KIR2DL4 is induced during function, age-dependent cell extrinsic soluble factors may devel- pregnancy (Rajagopalan and Long, 1999). opmentally regulate induction of specific functions and maturation Other KIRs or members of the C-type lectin receptor superfamily of these cells (Christensen, 1989; Pettengill et al., 2014). For are activating receptors (Moretta et al., 2001). These receptors lack example, low concentrations of the chemoattractant complement the long cytoplasmic tail of the inhibitory receptors and therefore component C5a in neonatal sera might impair establishment of do not contain ITIMs. Instead, they have a charged amino acid chemoattractant gradients at sites of inflammation. In addition, in the transmembrane region that enables receptor association elevated concentrations in human neonatal blood plasma of with the adaptor molecule DAP12 (Lanier et al., 1998). This adaptor adenosine (Pettengill et al., 2013), an endogenous purine metabolite contains an immunoreceptor tyrosine-based activation motif (ITAM) that acts via seven-transmembrane adenosine receptors to inhibit that allows these receptors to activate NK cells. The physiologic inflammatory leukocyte responses, could contribute to inhibition role of these HLA class I–specific activating receptors remains of newborn neutrophil function. unknown. NK cell–activating receptors also include natural cytotoxic- Systemic bacterial infection in newborns is frequently accompanied ity receptors (NKp46, NKp30, NKp44), proteins that are Ig by profound neutropenia, prompting investigation of neutrophil superfamily members with little similarity to one another or to kinetics in infected infants (Santos et al., 1980; Christensen et al., other NK-cell receptors (Moretta et al., 2001). These receptors are 1982). These studies have suggested diverse, developmentally specific highly specific for NK cells and apparently interact with non-HLA regulatory mechanisms required for mobilization of the neutrophil molecules. response to infection. The absence of detectable neutrophil precursors CD244 (2B4) is a member of the signaling lymphocyte in bone marrow aspirates of infected infants and systemic neutropenia activation molecule (SLAM) family of receptors expressed on motivated studies of neutrophil replacement therapy in neutropenic, all human NK cells (Ma et al., 2007). On interaction with the infected infants (Christensen et al., 1980). Although this approach ligand CD48 on target cells, NK-cell signaling proceeds via has been successful in some cases, the results have not been uniformly interactions between the immunoreceptor tyrosine-based switch beneficial, and a Cochrane review suggests a need for adequately motif (ITSM) (switch motif ) in the cytoplasmic tail of CD244 powered multicenter trials of granulocyte transfusions in neutropenic and one of two SH2 domain–containing adaptor proteins, septic neonates (Pammi and Brocklehurst, 2011). Metaanalysis SLAM-associated protein (SAP) and Ewing sarcoma–associated suggesting that granulocyte colony-stimulating factor or granulocyte– transcript 2 (EAT-2). SAP interactions trigger activation, as macrophage colony-stimulating factor may reduce mortality in
462 PART I X Immunology and Infections newborns when systemic infection is accompanied by severe neu- function and act early in immune responses, such as marginal zone tropenia requires confirmation in adequately powered trials (Carr B cells; and those with regulatory-like suppressive function et al., 2003). Heterogeneity in the impact of neutrophil modulation (“Breg cells”). may reflect the importance of individualizing immunologic interven- All major lymphocyte lineages, which include T cells, B cells, tions for the genetic background, developmental stage, and pathogenic and ILCs, which lack antigen-specific receptors and include NK microorganism being treated. cells (Hazenberg and Spits, 2014), develop from CD34+CD38dim pluripotent hematopoietic stem cells (HSCs) found in the fetal Monocytes, Macrophages, and Dendritic Cells liver and bone marrow in a perivascular niche (Chen et al., 2016; Cells committed to phagocyte maturation, including granulocyte Fig. 36.5). The process of lymphocyte differentiation and hema- or monocyte–macrophages, are detectable in the human fetal liver topoiesis in general has been traditionally viewed as a linear progres- by 6 weeks’ gestation and in peripheral fetal blood by 15 weeks’ sive narrowing of differentiation potential based on the sequential gestation. Unlike granulocytes, whose tissue half-life is hours to expression of specific transcriptional regulators. However, recent days, macrophages migrate into tissues and reside for weeks to work indicates that the pathways of development of the human months. In a tissue-specific fashion, these cells regulate availability myeloid, erythroid, and megakaryocyte lineages may undergo major of multiple factors, including proteases, antiproteases, prostaglandins, shifts during ontogeny. For example, in fetal liver, the HSCs and growth factors, reactive oxygen intermediates, and a range of their CD34+CD38+ progenitor cell derivatives have a similar ratio cytokines and chemokines. Importantly, monocytes can migrate of cells with multipotent versus unilineage potential, whereas in from the bloodstream to tissue sites, becoming tissue-based DCs. bone marrow, which is the definitive site of hematopoiesis starting Monocytes, macrophages, and DCs share the ability to present in the second trimester of gestation, CD34+CD38+ progenitor antigens to T lymphocytes, thereby triggering the classic adaptive cells predominantly have unilineage potential (Notta et al., 2016). immune responses. Another example is that the HSCs of UCB have a greater potential Compared with their adult counterparts, newborn monocytes, to differentiate into the T lineage than HSCs of adult bone marrow macrophages, and DCs demonstrate reduced chemotaxis and (De Smedt et al., 2011). phagocytosis as well as distinct TLR signaling that is polarized toward Th2 and antiinflammatory cytokine production (Kollmann T Lymphocytes et al., 2012). The distinct function of newborn APCs reflects both Thymocyte Development intrinsic characteristics, including reduced nucleosome remodeling Most T cells develop in the thymus, which includes cell types for IL-12 p70 production (Goriely et al., 2004) as well as the of nonhematopoietic origin, such as epithelial cells, as well modulatory effects of age-specific extrinsic factors such as the as multiple cell types of hematopoietic origin, including the antiinflammatory purine metabolite adenosine, the level of which developing immature T cells or thymocytes, DCs, mononuclear is relatively elevated in human newborn UCB plasma (Pettengill phagocytes, and small numbers of B cells. The thymic epithelial et al., 2013, 2014). cells are derived from the third branchial cleft and the third A growing literature documents that stimulation of monocytes or fourth branchial pouch, a process that is perturbed in results in a change in innate “setpoint” such that responses to DiGeorge syndrome, resulting in thymic epithelial hypoplasia. subsequent stimuli are altered (Saeed et al., 2014). This phenom- Thymic lobes can be divided into four regions, which, going enon, reflecting adaptive features of the innate immune system from outward to inward, are the subcapsular region, cortex, that are mediated by epigenetic changes, has been termed trained corticomedullary junction, and medulla. Prothymocytes, which immunity (Netea and van der Meer, 2017) and may contribute to are bone marrow–derived CD34+CD38+CD62L+ lymphoid cells, the heterologous beneficial (“nonspecific”) effects of live attenuated have the capacity to commit to the T-cell or other lymphocyte vaccines (Goodridge et al., 2016). Much remains to be learned lineages depending on their receipt of instructive signals (Spits, regarding the scope, ontogeny, and mechanisms underlying innate 2002). Circulating prothymocytes enter the thymus via vessels training/innate memory. at the cortical–medullary junction. The prothymocyte becomes committed to the T-cell lineage by the engagement of its surface notch 1 receptor by ligands displayed on the thymic epithelium, Adaptive Immunity such as delta-like ligand 4. This engagement leads to the surface Antigen-specific T and B lymphocytes bearing TCRs and BCRs, expression of CD1 and its differentiation into a pro–T cell that respectively, play multiple critical roles in adaptive immunity. T migrates to the subcapsular region just below the outer capsule. cells responding to a specific antigen secrete cytokines and kill The subcapsular pro–T cell expresses all of the internal proteins infected target cells and tumor cells by cell-mediated cytotoxicity. required for V(D)J recombination, including the recombinase These functions of CD4 and CD8 T cells depend on their TCRs activating gene (RAG) 1 and RAG2 endonucleases that make specifically recognizing antigenic peptides bound to MHC molecules. double-stranded breaks in DNA; the proteins involved in nonho- Several T-cell populations have a more restricted expression of mologous end joining repair (e.g., Artemis, XLF [Cernunnos], and TCRs that recognize ligands other than peptide/MHC ligands DNA ligase IV); and those that are essential for generating junctional and have an innate-like role early in the immune response; these diversity at complementarity determining region (CDR) 3 (e.g., include NK T (NKT) cells, mucosal-associated invariant T (MAIT) terminal deoxynucleotidyl transferase [TdT]). CDR3, which is the cells, and T cells expressing γδ TCRs (γδ T cells). As already most variable in amino acid sequence, is located at the center of the discussed in the section entitled Role of Regulatory T Cells in antigen-specific binding site of both TCRs and BCRs. The pro–T Pregnancy, CD4+ Treg cells serve as negative regulators of effector cell lacks most cell surface proteins characteristic of mature peripheral responses. Analogously, antigen-specific B cells can be divided into T cells, including CD3, CD4, and CD8, and is therefore also referred populations that are involved in the conventional immune response to as a triple-negative thymocyte (Fig. 36.6). The pro–T cell is the and that depend on CD4 T-cell help for their differentiation into first stage in which there is VDJ rearrangement of TCR gene loci, antibody-secreting cells; those that have an innate immunity–like with the TCRγ gene rearrangement occurring most frequently
CHAPTER 36 Immunology of the Fetus and Newborn 463 Self-renewing stem cell Pluripotent stem cell Myeloerythroid progenitor LMPP CMP THYMUS BONE MARROW GFU-GM Prothymocyte Myeloblasts Monoblast Pro-B cell NK progenitor Thymocyte Basophilic Eosinophilic Neutrophilic Promonocyte CDP Pre-B cell myelocyte myelocyte myelocyte BLOOD Basophil Eosinophil Neutrophil Monocyte Dendritic cell B cell NK cell T cell TISSUES Mast cell Macrophage Plasma cell • Fig. 36.5 Myeloid and Lymphoid Differentiation in the Bone Marrow, Blood, and Tissues. CDP, Committed dendritic cell progenitor; CFU-GM, colony-forming unit granulocyte–macrophage; CMP, common myeloid progenitor; LMPP, lymphoid primed multipotent progenitor; NK, natural killer. (Sherwood et al., 2011). If this rearrangement is productive (i.e., as molecular targets for tyrosine phosphorylation and binding by capable of expressing a full-length TCRγ chain protein) and the tyrosine kinases, such as Lck and zeta chain–associated protein of thymocyte subsequently undergoes a productive TCRδ gene arrange- 70 kDa (ZAP-70), which generate intracellular signals leading to ment, a γδ TCR heterodimer is expressed on the cell surface, allowing the induction of target genes (Lopez-Rodriguez et al., 2015). These the thymocyte to differentiate into a mature γδ T cell that emigrates signals direct the pre–T cell to (1) proliferate, (2) upregulate expression from the thymus into the periphery. More frequently (>95% of the of CD4 and CD8 and become a double-positive (CD4+CD8+) time) these TCRγ and/or TCRδ gene rearrangements are nonproduc- thymocyte, (3) migrate from the subcapsular area to the thymic tive, and the pro-T cell attempts TCRβ chain gene rearrangement. cortex, and (4) start rearrangement of the TCRα chain gene locus If this arrangement is productive, the TCRβ chain is expressed on (see Fig. 36.6). the cell surface in association with an invariant pre-T alpha chain Rearrangement of the TCRα chain gene by CD4+CD8+ thy- forming the pre-TCR complex, which defines the pre–T-cell stage mocytes is a two-step process in which there first is an internal of development. Like the mature TCR, the pre-TCR is associated deletion of a ψδ rec segment that brings the unrearranged Vα with the CD3 complex of proteins, which includes CD3γ, CD3δ, segments in close proximity with Jα segments and the Cα constant CD3ε, and CD3ζ chains, all of which have cytoplasmic tails contain- region (Hazenberg et al., 2001). The intervening DNA, which is ing specific amino acid sequences called ITAMs. These ITAMs serve excised as a circular product with fused signal joint sequences,