Immunology and Immunodeficienciesin Children

Saima Aslam, Fiona O’Hare, Hassan Eliwan, andEleanor J. Molloy

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Monocytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Neutrophils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Toll-Like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Mucosal Immunity, Human Milk, and Necrotizing Enterocolitis (NEC) . . . . . . . . . . . 5

Neonatal Innate Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Pediatric Adaptive Immune Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Lymphocyte Phenotype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

B-Cell Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Immunoglobulins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Cytokines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

The Inflammatory Response Syndromes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Clinical Outcomes in Neonatal Sepsis and Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Pediatric Sepsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Primary Immunodeficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12B-Cell Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12T-Cell Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Combined B- and T-Cell Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Complement Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Phagocytic Cell Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

S. Aslam (*) · F. O’Hare · H. Eliwan · E. J. MolloyDiscipline of Paediatrics, Trinity College, The Universityof Dublin, Dublin, Ireland

Tallaght Hospital & Coombe Women’s and InfantsUniversity Hospital, Dublin, Irelande-mail: saimaaslam@ymail.com; oharemarie@yahoo.co.uk;aliwandr@gmail.com; elesean@hotmail.com

# Springer-Verlag GmbH Germany, part of Springer Nature 2019P. Puri (ed.), Pediatric Surgery,https://doi.org/10.1007/978-3-642-38482-0_29-2

1

Acquired Immunodeficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Immunomodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Conclusion and Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

AbstractThe immune system in neonates is different tothat of adults and evolves in the first few yearsof life to achieve adult-like responses. Thischapter highlights the response of the immunesystem to sepsis both in pediatric and neonatalage groups and the intricate balance betweenpro-inflammatory and anti-inflammatoryresponses to limit the damage secondary toinfections. Immunodeficiencies primary oracquired are described in detail includingtheir common presentations, common patho-gens involved, the cell type involved, mecha-nism of deficiency, treatment, and prognosisincluding specific considerations for thesepatients prior to surgery. Immunomodulationof immune system either by alteration in ligandreceptor binding or intracellular signal can helpto modulate the disease process and may alterthe prognosis for children with sepsis in thefuture.

KeywordsInnate immune system · Neutrophils ·Lymphocytes · Toll-like receptors · Systemicinflammatory response syndrome · Naturalkiller cell · Dendritic cells ·Immunomodulation · Primaryimmunodeficiencies · Acquiredimmunodeficiencies

Introduction

Sepsis remains a prominent cause of neonatalmortality especially among preterm neonates.The first line of defense against infection is theinnate immune system, and activation occurswhen a pathogen breaches the host’s natural

barriers. The innate immune system developedbefore the separation of vertebrates from inverte-brates and is the primary immune response formost multicellular organisms (Janeway andMedzhitov 2002).

It responds instantaneously to microbes and iscomposed of both soluble (the alternative andmannan-binding lectin pathways of the comple-ment system, acute-phase proteins, and cytokines)and cellular elements (monocytes, macrophages,neutrophils, dendritic cells, and natural killercells). Careful modulation of the innate immunesystem is vital to prevent either uncontrolledmicrobial growth or devastating inflammatoryresponses with tissue injury, vascular collapse,and multi-organ failure.

Detection of invading microorganisms is medi-ated firstly by recognition, then activation andresponse of immune system leading to destructionof invading microorganisms. The process of rec-ognition is complex and depends upon structurescommon to many microbial pathogens calledpathogen-associated molecular patterns (PAMPs),antigen or epitopes such as endotoxins (lipopoly-saccharide: LPS), peptidoglycan, lipoteichoicacid, lipopeptides, flagellin, mannan, and viralRNA, which are essential for survival of themicroorganisms and therefore do not undergomajor mutations. Pattern recognition receptorshave been evolutionarily conserved not to recog-nize any self-structure. Autoimmunity is pre-vented when the only available recognitionsystem is the innate immune system.

Recognition in cell-mediated immunity dependsupon interaction between major histocompatibil-ity molecules, macrophages, and helper and cyto-toxic antibody-mediated immunity; the process ofrecognition depends on macrophages, helper Tcells, and B cells (Fig. 1). Several intracellular

2 S. Aslam et al.

signaling pathways are activated when a PAMPbinds to a pattern recognition receptor, resulting inactivation of transcription factors (NF-kB, AP-1,Fos, Jun). These transcription factors control theexpression of immune response genes and therelease of numerous effector molecules, such ascytokines. Cytokines are chemical mediators withan essential role in orchestrating the innate andacquired immune responses to an invading path-ogen (Calandra 2001).

The acquired immune system has evolved rel-atively recently and is built upon the phylogenet-ically older innate immune system, by which it iscontrolled and assisted. The principal mediatorsof acquired immunity are the highly evolved lym-phocytes, which express an enormous array of

recombinant receptors, immunoglobulin, andT-cell receptors. They can recognize any potentialpathogen with which the host may come in con-tact. This response takes from days to weeks todevelop optimally.

Newborns acquire passive immunity from theirmothers by maternally derived IgG crossing theplacenta. Transferable maternal immunologicmemory is essential for the survival of the fetus,newborn, and infant. Moreover, the attenuation ofinfection by transferable maternal immunity per-mits microbial agents to immunize the child underoptimal conditions. This provides protection forup to the first 6 months of life at which timeneonatal acquired immunity has developed.

HUMORAL IMMUNITY CELLULAR IMMUNITY

B

B

Extracellular microbes(e.g., bacteria)

B Lymphocytes

Secretedantibody

Neutralization

Lysis(complement)

Phagocytosis(PMN, macrophage)

T

Intracellular microbes(e.g., viruses)

Antigen-presentingcell

HelperT cell

T cell receptor

Cytokines

Cytokinereceptor

Proliferationand activationof effector cells

(cytotoxic T cells,natural killer cells,

macrophages)

Lysis of Infected cells

Fig. 1 Immune function: humoral and cellular immunity.Humoral immunity is mediated by B lymphocytes whichproduce soluble antibody proteins. These antibodies caneither (a) directly neutralize extracellular microbes or (b)activate complement, neutrophils, and macrophages to kill

microorganisms. Cellular immunity is mediated by T lym-phocytes. Cytotoxic T cells directly lyse pathogens. HelperT cells produce cytokines which stimulate other immunecells to remove microorganisms

Immunology and Immunodeficiencies in Children 3

Monocytes

The crucial role of monocytes/macrophages in theimmune response resides in immunoregulatoryfunctions of both humoral and cellular immunity.They are important for phagocytosis, antigen pre-sentation, and cytokine production. Humanumbilical cord blood contains almost three timesas many monocytes as adult blood does, andmajor changes occur in the levels of monocytesduring the first few weeks of life. Newborn mac-rophages show poor resistance against facultativeintracellular organisms. Newborn monocytesexhibit marked heterogeneity with respect to den-sity and function. Neonatal blood monocytes arealso characterized as having a much lower fre-quency of class II molecular expression thanadult monocytes, which may be related to theselective incapacity of neonates to secrete signif-icant levels of interferon-γ (IFN-γ). The preciserole of the monocyte in the newborn’s uniquesusceptibility to infections with various agentsremains a challenging area for future study. Den-dritic cells are the primary antigen-presentingcells for optimum sensitization of naive T cellsto antigen. Newborn dendritic cells have beenshown to be deficient in IL-12 (p35) expression,a key regulator of Th1-type T-cell responses.

Neutrophils

The critical role of the neutrophil in host defensesagainst microbial infection has long suggestedthat defects in this particular cell type might bethe cause of the increased susceptibility of thenewborn to serious bacterial infections. Impairedneonatal neutrophil function at birth has also beenimplicated in neonatal inflammatory disorders(Cairo 1989). Recent advances in the understand-ing of the molecular basis of cell adherence andphagocytosis have provided greater insight intothe role of the neutrophil in the newborn’s defensesystem. Numerous in vitro abnormalities includedecreased chemotaxis, leukocyte adherence, bac-terial killing, and depressed oxidative metabolism(Carr 2000). However, most of these neonatalneutrophil functions have been found in the cord

blood, which contains immature forms of thecells, and therefore care must be taken ininterpreting some of the data. Oxidative metabolicfunction of cord blood monocytes, measured bychemiluminescence, has been shown to bedepressed 12–36 h after birth. Cytoskeletal actinpolymerization is also altered in neonates.

Neonatal neutrophils exhibit normal phagocy-tosis of opsonized particles as well as particles thatrequired no opsonization. The major opsonic roleof neutrophils for the uptake of antibody orcomplement-coated microorganisms is reflectedin their expression of a number of receptors bothfor antibody (Fc receptors) and complement(CR receptors). In newborn cord blood, the levelsof these receptors are similar to those in adultneutrophils. The level of expression of Fc recep-tors is significantly more upregulated in responseto in vitro stimuli such as f-met-leu-phe (FMLP)on adult neutrophils compared to newbornneutrophils.

Neonatal neutrophils have diminished function(Koenig et al. 2005) and delayed apoptosis (pro-grammed cell death) compared with adults. Inaddition, neonatal neutrophil lipopolysaccharide(LPS) responses are altered (Bonner et al. 2001;Henneke et al. 2003) which may further increasesusceptibility to sepsis in this population. Theeffects of granulocyte colony-stimulating factor(GCSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) on neonatal neutro-phils are altered compared with adults showingthat GCCF may improve neutrophil survivalwhereas GM-CSF augments function (Molloyet al. 2005).

NETs are lattices of extracellular DNA, chro-matin, and antibacterial proteins that mediateextracellular killing of microorganisms and arethought to form via a unique death pathway sig-naled by nicotinamide adenine dinucleotide phos-phate (NADPH) oxidase-generated reactiveoxygen species (ROS). Neutrophils from termand preterm infants fail to form NETs when acti-vated by inflammatory agonists in contrast to leu-kocytes from healthy adults reflecting a deficit inextracellular bacterial killing (Yost et al. 2009).

Recently, Raymond et al. (Raymond et al.2017) investigated neutrophil chemotaxis and

4 S. Aslam et al.

transcriptomics of both term and preterm neonatesusing whole blood samples obtained in the firstfew days of life. They demonstrated that preterminfants have significant differences in neutrophils,compared to term neonates and adults includingreduced percent neutrophil migration and velocityin response to a microbial product, as well astranscriptomic evidence of impaired pathogenrecognition, cytokine production and antimicro-bial activity.

Toll-Like Receptors

The toll-like receptors (TLR) are vital transmem-brane receptors that provide the critical linkbetween microbial immune stimulants and initia-tion of host defense. TLR-4 is the transmembraneLPS receptor that initiates the innate immuneresponse to common Gram-negative bacteria.Neonates have an equivalent if not enhancedcapacity compared with adult white-blood cellTLR-mediated response to support Th17- andTh2-type immunity, which promotes defenseagainst extracellular pathogens. However neo-nates have reduced Th1-type responses, whichpromote defense against intracellular pathogens(O’Hare et al. 2013). TLR4, TLR2, and CD14(cluster differentiation 14) are increased on neo-natal immune cells, and cytokine release isdecreased to a greater extent than adults withTLR-4 antagonists. During infections, pathogensbind to TLR-4 and CD14 receptors and inducecytokine release, leading to inflammation. Neona-tal IL-10 and TNF-α release depends on LPSbinding not only to CD14/TLR-4 but also toCD14 associated with another TLR. There is adifferential expression of TLR-2 but not TLR-4in the course of neonatal sepsis (Viemann et al.2005). Decreased levels of MyD88 have beendescribed in neonatal monocytes in response toLPS (Yan et al. 2004). There have been few stud-ies on neonatal neutrophils. Wynn et al. haverecently demonstrated improved survival follow-ing polymicrobial sepsis induced by TLR4 ago-nist pretreatment which enhanced peritonealneutrophil recruitment with increased oxidativeburst production. Similarly TLR-7/TLR-

8 agonism also enhanced peritoneal neutrophilrecruitment with increased phagocytic ability.However, these outcomes were independent ofthe adaptive immune system and type I interferonsignaling. Labor upregulates TLR-2 and TLR-4on cord blood monocytes at the protein level,suggesting that labor may be immunologicallybeneficial to normal newborns (DiGiulio et al.2008). Augmenting innate immune functionusing TLR signaling may be a potential futureadjunctive therapy in neonatal sepsis.

Mucosal Immunity, Human Milk,and Necrotizing Enterocolitis (NEC)

Although the intestinal tract of the fetus is consid-ered to be sterile, recent studies suggest that manypreterm infants are exposed to microbes found inthe amniotic fluid, even without a history of rup-ture of membranes or culture-positive chorioam-nionitis (Wolfs et al. 2009). Infants are colonizedduring vaginal delivery and subsequentbreastfeeding with maternal vaginal and fecalflora. The fecal microbial profile of infants deliv-ered vaginally versus caesarean section showedno colonization with Bacteroides sp. before2 months of age in infants in the latter group andBacteroides colonization that was half that ofvaginally delivered infants by 6 months of age.The common use of antibiotics, type of feeding(human milk versus formula), mode of delivery(vaginal versus caesarean section), decreasedmaternal-infant direct skin contact, and variousmanipulations in the neonatal intensive care unit(nursing in an incubator versus under radiantwarmers) have the potential to alter the intestinalmicrobiota. In response to pathogenic intestinalmicrobiota, pro-inflammatory cytokines canincrease barrier permeability, facilitating bacterialtranslocation with elaboration of the systemicinflammatory response syndrome (SIRS) andmultiple organ failure.

Necrotizing enterocolitis is one of the mostdevastating diseases in newborns. It is associatedwith loss of gut integrity and immune dysfunc-tion. NEC is thought to develop following com-bination of prematurity, formula feeding, and

Immunology and Immunodeficiencies in Children 5

adverse microbial colonization. Many studies inrecent years support an important role of a height-ened mucosal immune response initiating a pro-inflammatory signaling cascade which can lead tothe destruction of the intestinal epithelium andtranslocation of pathogenic species (Mara et al.2018). One of the major cornerstone in under-standing the development of NEC is the role thatTLR-4 signaling plays in the pathogenesis(Hodzic et al. 2017). Activation of TLR-4 withinthe intestinal epithelium in the setting of prema-turity results in decreased enterocyte proliferation,increased enterocyte apoptosis, disruption ofintestinal barrier integrity and bacterial transloca-tion, resulting in a systemic inflammatoryresponse (Hodzic et al. 2017). As a result of bac-terial translocation, TLR-4 is activated on theendothelium of the premature gut, leading toimpaired blood flow and subsequent ischemiavia reduction of endothelial nitric oxide synthase(Yazji et al. 2013). Increased intestinal expressionof TLRs (especially TLR-2 and TLR-4) and cyto-kines precedes histological injury in theexperimental NEC.

There is a dose-related association of humanmilk feeding with a reduction of risk of NEC ordeath after the first 2 weeks of life amongextremely low birth weight infants. Human milkinfluences neonatal microbial recognition bymodulating TLR-mediated responses specificallyand differentially. Fresh human milk containsmany immunoprotective factors, such as immu-noglobulins (Igs), lactoferrin, neutrophils, lym-phocytes, lysozyme, and PAF acetylhydrolase(which inhibits PAF). Human milk also isbelieved to promote intestinal colonization withLactobacillus. The efficacy of banked humanmilk is less clear because freezing and pasteuriza-tion reduce the cellular components andimmunoglobulins.

Neonatal Innate Immunity

Newborns rely on their innate immune systeminitially following birth as there are deficienciesin the adaptive response due to lack of previousexposure to antigens in utero (Levy 2007). The

intrauterine environment is usually sterile, andtransition postnatally to the foreign antigen-richexternal world starts with colonization of skin andgut with microorganisms. The fetus is consideredto be immunologically naive and exists in a stateof immune privilege in utero, to prevent rejectionby the maternal immune cells. The in uterodefense system is largely unknown althoughrecent evidence hints at a powerful fetal systemof innate immunity. The antibacterial properties ofvernix caseosa, the creamy white substance cov-ering the skin of term babies, have also beenrecognized and in particular the presence of anti-microbial peptides including alpha defensins andinflammatory mediators. Antimicrobial peptidesmay be an adjunctive compensatory mechanismin the neonate as adaptive immunity evolves(Dorschner et al. 2003). Neonates are immunecompetent but with a predominant Th2 profilebeing geared toward immune tolerance insteadof toward defense from microbial infections(Th1 skewed). Th1 responses are suppressed byplacental products such as progesterone, prosta-glandin E2, and cytokines such as IL-4 and IL-10.

Pediatric Adaptive Immune Response

The adaptive immune system consists of B cells,T cells, and their products. T cells or lymphocyteclones each bear a unique T-cell receptor (TCR)which recognizes peptides, derived from foreignor self-proteins, bound in a molecular complex tothe major histocompatibility complex (MHC) pro-teins on the surface of other cells. T cells aredivided into subsets based on their expression ofdifferent proteins, which are assigned cluster dif-ferentiation (CD) numbers. Killer T cells expressCD8 and are important to kill virally infectedcells. Helper T cells express CD4 and orchestratethe overall immune response by secreting cyto-kines and providing co-stimulatory signals toCD8+ cells and B cells.

The basis of an adequate immune responseresides in the capacity of individual cells of theimmune system to recognize and react to the myr-iad antigens in the environment. The hemopoieticsystem of pluripotent stem cells is the source of all

6 S. Aslam et al.

the major cell types, which are involved in theimmune response. These cells include variouslymphocyte subsets, macrophages, natural killercells, monocytes, and polymorphonuclear leuko-cytes. These cells are involved in a complex reg-ulatory network of cell interactions whichconstitute an immune response and whose func-tion is to eliminate both self-aberrant moleculesand cells as well as to protect the host from micro-bial attack (Fig. 2).

Lymphocyte development occurs along twodistinct pathways leading to the production ofthe two major lymphocyte populations, T cellsand B cells, which have very different biologicaleffector functions. The thymus is the site of devel-opment of T cells, which are responsible for therange of effector functions collectively termedcell-mediated immunity. Cell-mediated immunity

ranges from the release of soluble factors such ascytokines, which regulate the activity of all cellsof the immune system, to direct cytopathic effectof cytotoxic lymphocytes on viruses or tumorcells. B lymphocytes, on the other hand, have amore restricted effector function, confined to thesynthesis and secretion of humoral antibodies ineach of the immunoglobulin classes, IgG, IgA,IgM, IgD, and IgE.

The heterogeneity of cell types forms the basisfor an international leukocyte typing classificationsystem (CD, cluster differentiation), utilizingmonoclonal antibodies which recognize specificcell-surface markers in order to define individualleukocyte subsets. The more widely used CDantigens, for classifying immune effector celltypes, are described in Table 1.

BLOOD STEM CELL

Myeloid Stem CellLymphoid Stem Cell

LymphoblastMyeloblast

Granulocytes

Red bloodcells

Platelets

B Lymphocyte

T Lymphocyte

Natural killercell

White blood cells

Basophil

Eosinophil

Neutrophil

Fig. 2 Blood cell development. Blood stem cells releasedfrom the bonemarrow develop into mature blood cells overtime. The blood stem cell may become a myeloid stem cellor a lymphoid stem cell. The myeloid stem cell can furtherdifferentiate into either red blood cells, white blood cells,

or platelets. The lymphoid stem cell becomes a lympho-blast which then differentiates into one of the followinglymphocyte types: B lymphocyte, T lymphocyte, naturalkiller cell

Immunology and Immunodeficiencies in Children 7

It is now well established that T lymphocytesdo not recognize native antigen on any pathogen,but rather a processed form of the antigen, inassociation with self-major histocompatibilityantigens (MHCs), class I (HLA-A, HLA-B,HLA-C), or class II (HLA-DR/Ia) molecules.This important processing of foreign antigen iscarried out by one of a group of antigen-presenting cells which include macrophages, den-dritic cells, Kupffer cells, and some B cells. Theproper functioning of these accessory cells istherefore as central to an adequate immuneresponse as that of specific effector cells, such asthe T lymphocytes. When antigen becomes local-ized and processed by the antigen-presenting cell(APC), the complex interaction of APC, T cells,and B cells begins, which eventually leads tospecific immunological memory, both of T cellsand B cells as well as to antibody production.Although B cells can be directly activated byantigen, under experimental conditions, concom-itant activation of T cells is required for the clonal

expansion of antigen-specific B cells, leading tothe generation of long-lived memory B cells andimmunoglobulin-secreting plasma cells.

As already mentioned, the difference betweenneonatal and pediatric immune responses is theskewed response from Th1 to Th2. There isdecreased production of interferon (Cant et al.2003); as a result, there is decreased Th1 cyto-kines (IL-1 and IL-12) with decreased cell-mediated immunity in neonates. There are differ-ent theories as to why there is skewed Th2response. We know with certainty that it is relatedto decreased production of IL-12. Although Th1response can be induced in neonates by usingexogenous IL-12 or using adult rather than neo-natal APC (antigen-presenting cells) which sig-nifies that the rate-limiting step is the maturity ofAPC. If neonatal APC are stimulated by an effec-tive antigen, these cells are able to produce IL-12,e.g., in response to BCG vaccination. Whileresponse to DPT is Th2 skewed.

Several studies in the literature havequestioned the stage of maturity of circulatinglymphocytes in the newborn. Some parametersof T-cell function in cord blood, however, havebeen shown to be normal or similar to those ofhealthy older children. These include the quantityand proportion of T lymphocytes, lymphocyteresponse to mitogens, and production of certaincytokines such as IL-2.

Lymphocyte Phenotype

There has been a reported incidence of up to 25%of cord blood lymphocytes co-expressing bothCD4 helper T-cell and CD8 suppressor T-cellsurface markers. Cells of this double-positive phe-notype are common in the thymus, where they areconsidered to be the precursors of mature helperand suppressor T cells. The CD38 antigen, whichis a marker of immature thymus-derived Tcells, aswell as activated lymphocytes, is present in themajority of newborn cord blood lymphocytes.This thymocyte-like membrane phenotype canbe modulated by the influence of thymic hor-mones in vitro. In addition to the presence ofCD38 thymocyte-associated antigen, human

Table 1 Cell-surface antigens which identify leukocytesubtypes in the newborn

Antigen Function

T cells

CD2 LFA-3 receptor (adhesion)

CD3 Associated with cell receptor

CD4 Class II and HIV receptor

CD5 Co-stimulatory

CD7 Unknown

CD8 Class I receptor

B cells

CD19 Signal transduction

CD20 Unknown

CD21 C3d and EBV receptor (CR2)

CD72 Ligand for CD5

NK cells

CD16 IgG receptor (FcRIII)

CD56 Isoform of N-CAM

CD94 Unknown

Myeloid/monocytic cells

C14 Unknown

C15 Unknown

CD32 IgG receptor (FcRII)

CD35 C3b receptor (CRI)

IFN interferon, IL interleukin

8 S. Aslam et al.

cord blood contains T cells of the unusual pheno-type which include peanut agglutinin-positive/CD8-positive as well as some CD3-positiveCD1a-positive lymphocytes. Like CD38, CD1ais a marker present on early thymocytes. CD1a-positive cells are especially present in preterm andantenatally stressed infants. While the neonate hasadequate numbers of CD4 helper T cells, cordblood T cells are deficient in their ability to pro-vide help for antibody production, probably at thelevel of altered cytokine production. The cellularbasis for this functional defect is reflected in otherphenotypic markers of functional activity. Morethan 90% of cord blood T cells carry the CD45RA+ “virgin” cell phenotype marker, compared with50% of adult T cells which express CD45RA+. Incontrast, less than 10% of cord blood lymphocytesexpress the CD45RA “memory” T-cell markercompared to a 50% level of expression in adultT cells. This major imbalance in the ratio ofCD45RA+/CD45RA, CD4-positive T cells in thenewborn compared to adults may help explainsome of the functional differences of newborncells compared to adult lymphocytes (Crespoet al. 2012).

B-Cell Responses

The newborn’s capacity to produce antibody issignificantly reduced, both quantitatively andqualitatively, compared to that of an adult. New-born B lymphocytes poorly differentiate intoimmunoglobulin-producing cells. The mecha-nisms controlling this aspect of B-cell immuno-competence in the newborn are unknown. Manystudies have focused on the ability of cord bloodlymphocytes to terminally differentiate into IgG-,IgA-, and IgM-producing plasma cells in responseto mitogens. However, a delay occurs in B-celldifferentiation, resulting in decreased productionof plasma cells, markedly diminishing the secretionof antibody and restriction of secreted antibody toIgM isotype. Cord blood B lymphocytes, unlikeadult B cells, usually are unable to differentiate intoimmunoglobulin plaque-forming cells when cul-tured with pokeweed mitogen alone or with killedStaphylococcus aureus alone. However, it appears

that these two stimuli can act synergistically toinduce a significant in vitro plaque-forming cellresponse in cord blood B cells.

Immunoglobulins

The presence of physiological hypo-gammaglobulinemia has been noted by severalinvestigators in preterm and term infants. Neonateshave low levels of IgA and IgM immunoglobulinsbecause of the poor ability of these immunoglobu-lin classes to cross the placenta. Furthermore, allIgG subclasses are not equally transferred acrossthe placenta, especially the IgG2 and IgG4 subclasslevels, which are therefore also relatively low in thenewborn. The neonate is consequently very sus-ceptible to pyogenic bacterial infections since mostof the antibodies that opsonize capsular polysac-charide are contained in the IgG2 subclass and IgM.Neonates, even during overwhelming sepsis, donot produce type-specific antibodies. This impair-ment in antibody production appears to be second-ary to the defect in the differentiation of Blymphocytes into immunoglobulin-secretingplasma cells and T-lymphocyte-mediated facilita-tion of antibody synthesis. There is a marked lim-itation in infant antibody responses to mostbacterial capsular polysaccharides. This limitationprevents successful infant immunization with Hibpolysaccharide vaccines, which fortunately can becircumvented by use of conjugate vaccines shownto be immunogenic in infants.

Cytokines

Among the major molecular components of theimmune system are the immunoglobulins, cyto-kines, and proteins of the acute-phase responseand complement system. The term “cytokine” isused to describe a group of peptides with potentimmunoregulatory effects, which are producedand utilized, by individual cells of the immunesystem, to communicate with each other and tocontrol the environment in which they operate. Adescription of some of the major characterizedcytokines is listed in Table 2.

Immunology and Immunodeficiencies in Children 9

Present evidence suggests that cytokines are ofimmense importance in controlling both local andsystemic immune responses, inflammation, andthe regulation of hematopoiesis. Their mostimportant function appears to be at local level,modulating the behavior of adjacent cells in aparacrine fashion, or the cells that secrete them,in an autocrine fashion. In addition, especially inthe case of TNF-α, IL-1, and IL-6, cytokines mayeffect endocrine-like activity on distant organs ortissues. Cytokines have important biologicalactivity, which can be of major clinical benefit,such as stimulation of antimicrobial function, pro-motion of wound healing, and myelostimulation.

With such diverse biological function, an exag-gerated or prolonged secretion of these peptidesmay be detrimental for the host. Specifically, aber-rant secretion of cytokines, such as TNF-α andIL-1, is thought to be responsible for the hemody-namic changes in the host during septic shock andin cachexia of chronic disease. The availability ofrecombinant DNA techniques to produce cyto-kines in almost unlimited quantities and the pro-duction of specific antagonists such as solublecytokine receptors and IL-1 receptor antagonistsare leading to new and exciting therapeutic poten-tial for these molecules.

The Inflammatory ResponseSyndromes

One reason for the failure of anti-inflammatorystrategies in patients with sepsis may be a changein the syndrome over time (Fig. 3). Initially, sepsismay be characterized by increases in inflamma-tory mediators; but as sepsis persists, there is ashift toward an anti-inflammatory immunosup-pressive state (Lederer et al. 1999). If the initialinsult is sufficiently severe, the pro-inflammatoryresponse can become intense and lead to a mas-sive systemic inflammatory response syndrome(SIRS) and disrupt homeostasis. If the delay isprolonged and the resolution of inflammation isblocked, the neutrophilia has a very high potentialfor causing extreme damage to healthy tissue dueto the concentrated release of ROS and proteases.This then forces the body to produce a massivecompensatory anti-inflammatory response syn-drome (CARS) that may be inappropriate andresult in tissue injury. If this occurs, the bodydevelops “immune paralysis” and is more suscep-tible to infection. The final stage occurs when theoverwhelming inflammation is not resolved causingmultiple organ dysfunction syndrome and death ofthe patient (Bone 1996). Adjunctive immunomodu-latory treatments for sepsis seek to balance theseresponses and restore homeostasis (Bone 1996).However discovering which inflammatory phase isdominant in the patient at a certain time pointremains difficult and hinders appropriate therapeuticimmunomodulation. Anti-inflammatory treatment

Table 2 Cytokines and their functions

NamePrincipal cellularsource

Principal cellulartarget

IL-1 Macrophages,fibroblasts,endothelial cells

Thymocytes,endothelial cells,neutrophils,T cells, B cells

IL-2 T cells T-cells, B-cells

IL-3 T cells Multipotentialstem cells

IL-4 T helper cells T cells, B cells,mast cells,macrophages

IL-5 T helper cells B cells,eosinophils

IL-6 Fibroblasts B cells,fibroblasts,hepatocytes

IL-7 Stromal cells B cells

IL-8 Macrophages Neutrophils

IL-10 T cells, activatedmonocytes

T-cell subsets,macrophages

IL-12 Macrophages T cells, NK cells

IL-13 T helper cells B cells

TNF-α Macrophages,fibroblasts

Many cell types

TNF-α T cells Many cell types

IFN-β Macrophages,fibroblasts

Many cell types

IFN-β Fibroblasts Many cell types

IFN-β T cells, NK cells Macrophages,T cells, B cells

TGF-β T cells, macrophages,platelets

Many cell types

GM-CSF T cells, endothelialcells

Multipotentialstem cells

10 S. Aslam et al.

can increase mortality. Following a cecal ligationand puncture model of sepsis in a murine modelmortality was increased in mice pretreated withinterleukin receptor antagonist (IL-1RA) increasedmortality (Gomez et al. 1998).

Fetal and neonatal inflammatory responses(FIRS and NIRS) have been described. A sys-temic fetal inflammatory response is determinedby increased IL-6, in an independent risk factorfor severe neonatal morbidity (Ashare et al. 2005).Preterm neonates with systemic infection haveelevated IL-6, IL-10, and TNF-α concentrations.Severe infection is signified by increased IL-10/TNF-α and IL-6/IL-10 ratios. Transiently elevatedIL-10 or IL-10/TNF-α levels are not invariablyassociated with a poor prognosis (Ng et al. 2003).

Clinical Outcomes in Neonatal Sepsisand Inflammation

Death and long-term complications are commonsequelae of bacterial infections in newborns. Neo-nates undergoing intensive care have infectionrates of 25–50% (Stoll et al. 2002), and mortalityhas not changed from 15% to 20% over the last20 years. Altered bactericidal mechanisms areresponsible for the increased vulnerability to sep-sis in this group and mirror the pattern seen ingrossly neutropenic patients. Neutropenia com-monly develops in neonatal sepsis in contrast to

the leukocytosis in septic adults (Carr 2000). Thismay be mediated by a decreased neutrophil stor-age pool and a limited capacity for increasedprogenitor production in newborns especiallypreterms.

There is increasing evidence that sepsis andinflammation are important in the pathogenesisof perinatal brain injury. In preterm infants, epi-sodes of sepsis are associated with poorerneurodevelopmental outcomes. In addition, anassociation between cerebral palsy and maternalperipartum infection in term infants has been welldocumented (Nelson and Willoughby 2000). Ele-vated pro-inflammatory cytokines have also beendemonstrated in retrospectively reviewed driedneonatal blood spots from children aged 3 yearswith cerebral palsy. Activated leukocytes andinfection have been implicated in the pathogene-sis of neonatal brain damage (Dammann et al.2001). Severe disruption of the blood-brain bar-rier in severe asphyxia may exacerbate neuronaldamage allowing infiltration of activated immunecells and cytokines.

Pediatric Sepsis

Sepsis is a major cause of admission to pediatricintensive care units (PICU) and is a leading causeof morbidity and mortality in children. In theUnited States, sepsis accounts for nearly 4,500

An

ti-in

flam

mat

ory

SIRSImmunostimulation

CARSImmunosuppression

INSULT

Fig. 3 Pro- and anti-inflammatory responses:these responses eventuallybalance to producehomeostasis and recovery.If one or other responsepredominates, it mayincrease morbidity andmortality. SIRS systemicinflammatory responsesyndrome, CARScompensatory anti-inflammatory responsesyndrome

Immunology and Immunodeficiencies in Children 11

deaths and costs almost 2 billion dollars per yearin health care. The incidence of sepsis is highest ininfants (5.16/1,000 per year), decreasing in olderchildren to 0.20/1,000 in 10–14-year-old children(Watson et al. 2003). In the United Kingdom, theunadjusted case fatality rate for children admittedto PICU is 4.1%. The cause of sepsis is multifac-torial but can include virtually any infectiousorganism, although bacterial infection is themost common. The most prevalent causes ofsevere sepsis and septic shock are Staphylococcaland fungal infections (Watson et al. 2003).

The pathophysiology of sepsis is characterizedby a complex systemic inflammatory response,endothelial dysfunction, and dysregulation ofcoagulation system. Sepsis in pediatric patientsfrequently manifests as disseminated intravascu-lar coagulation (DIC) with consumption of plate-lets and clotting proteins (Wheeler et al. 2011).The production of inflammatory cytokines duringSIRS has been associated with organ dysfunctionand hypoperfusion. Nadel et al. reported the con-sensus for definition of infection (InternationalConsensus of Sepsis) as evidence of pathogen-positive blood culture, tissue stain or polymerasechain reaction (PCR) test, or a clinical syndromeassociated with a high probability of infection(Nadel et al. 2007). SIRS is defined clinically bythe presence of physiologic signs and one labora-tory study that indicates activation of the immune/inflammatory response (Table 1; Standage andWong 2011). Sepsis is a syndrome rather than adiscreet pathologic entity with a clear, unified,maladaptive process at its core. Early recognition,appropriate therapeutic response, and effectiveantibiotic therapy are critical to prevent its pro-gression to severe sepsis and septic shock(Standage and Wong 2011).

Previous pediatric studies had defined theinclusion criteria for sepsis as hyperthermia orhypothermia, tachycardia (may be absent in thehypothermic patient), evidence of infection, andat least one of the following signs of new-onsetorgan dysfunction: altered mental status, hypox-emia, bounding pulses, or increased lactate(Carcillo 2003; Doughty et al. 1996; Proulx et al.1994).

Primary Immunodeficiencies

Primary immunodeficiencies (Cant et al. 2003;Bonilla et al. 2005, 2015) can be divided intofour major contributors of immune system, thatis, B cells, T cells, complement, and phagocytes(Table 2).

B-Cell Deficiencies

X-linked agammaglobulinemia (Cant et al. 2003;Bonilla et al. 2005, 2015) is a deficiency of allclasses of immunoglobulins along with deficiencyof B cells. The failure is due to mutation in a geneencoding for tyrosine kinase, which is an essentialsignal transduction protein. Recurrent pyogenicinfections occur from 6 month of age as mater-nally acquired antibodies at its lowest nadir. It isdiagnosed by measuring immunoglobulin levelsand B-cell numbers in blood. Treatment is life-long immunoglobulin replacement therapy and byusing prophylactic antibiotics to prevent or treatinfections. Patient on replacement immunoglobu-lin can lead to relatively normal lives. Selectiveimmunoglobulin deficiencies are also congenitalsuch as IgA deficiency, commoner than IgG andIgM deficiency. The failure to switch heavy chainbetween different classes of immunoglobulins isthe main cause of deficiency. IgA prevent infec-tion of mucous membrane lining mouth, airway,and GIT. IgA deficiency presents with suscepti-bility to recurrent sinopulmonary infections,although the vast majority of children are normalas immunity is conferred by IgG and IgM anti-bodies. Children with IgA deficiency are at higherrisk of autoimmune diseases.

T-Cell Deficiencies

22q11.2 deletion syndrome (previously known asDiGeorge syndrome) has varied spectra of presen-tation with different organs involved with varyingdegrees of severity. Infections occur in the infantsand children secondary to failure of third andfourth pharyngeal pouches to develop and presentwith dysmorphic features, abnormal gland

12 S. Aslam et al.

developments, and heart defects. There is either adefect in function or production of T cells.22q11.2 deletion syndrome (Cant et al. 2003;Bonilla et al. 2005, 2015) is a life-long condition,but recurrent infections mostly occur in infantsand children as the incidence of recurrent infec-tions decreases in late childhood and adulthood. Itis diagnosed at birth based on clinical observationand genetic testing. As the disease has variedspectrum, mild cases of immunodeficiency relatedto T cell can be managed by prophylactic antibi-otics and close follow-up. In severe cases, bonemarrow transplantation is the treatment of choice.Chronic mucocutaneous syndrome is one of therecognized T-cell deficiencies. In chronic muco-cutaneous syndrome, there is specific deficiencyin T cells directed toward candida which is nor-mally non-pathological in a normal host. As thename is self-explanatory, it presents with recurrentcandidal infection of skin and mucous mem-branes. The mainstay of treatment is antifungal.Hyper IgM syndrome patients have high concen-tration of IgM and lower concentration of IgG,IgA, and IgE. There is defect in the surface proteinof T helper cells that interact with CD40 receptorson the B cells and thus B cell inability to switchfrom production of IgM to other classes of anti-bodies. It presents with recurrent pneumonias,bronchiectasis, and sinusitis. Intravenous immu-noglobulin is the treatment of choice.

Combined B- and T-Cell Deficiencies

Severe combined immunodeficiency disease(SCID) in which both B and T cells are involved(Cant et al. 2003; Bonilla et al. 2005, 2015) andeither the number is reduced or the function isdefective. It is considered one of the most seriousprimary immune deficiencies. The main causesare defects in differentiation of early stem cells,and it can be X linked or autosomal dominant. InX-linked SCID, the commonest cause is the defectin IL-2 receptor in T cells. In the autosomal dom-inant forms there is defect in gene encoding tyro-sine kinase in T cells called ZAP 70. Other formsof SCID include adenosine deaminase and nucle-oside phosphorylase deficiency that affects bone

marrow differentiation as these enzymes areinvolved in making precursors for DNA. SCIDpresents with recurrent and severe respiratoryinfections, and other symptoms include failure tothrive, eczema like rashes, chronic diarrhea, andthrush infection in mouth. Early detection ofSCID is important and has positive effect onlong-term outcome. Diagnosis depends upon clin-ical suspicion, absence of thymus and lymphoidtissue, lymphopenia, panhypogammaglo-bulinemia, and poor response of T cells to anti-gens. Once diagnosis is established, the onlytreatment available is bone marrow transplanta-tion. Gene therapy for severe forms of SCID isbeing used in clinical trials.

Wiskott-Aldrich syndrome (WAS) is character-ized by recurrent, severe pyogenic infection,eczematous skin eruptions, and thrombocytopenia.There is T-cell lymphopenia and poor T-cellresponses. Both flow cytometry on lymphocytesfrom patient with suspected WAS and moleculardiagnosis are required. Bone marrow transplanta-tion (BMT) is the treatment of choice. BeforeBMT, intravenous immunoglobulins and prophy-lactic antibiotics are effective treatment of choice.Ataxia telangiectasia is characterized by ataxia,dilatation of blood vessels in skin and conjunctiva,and recurrent pyogenic infections. It is autosomalrecessive. Immunological abnormalities includelow or elevated level of immunoglobulin, poorspecific antibody response, and alteration in lym-phocyte proliferation. Diagnosis depends onestablishing the presence of chromosomal fragilityand pathognomonic increased level of oncofeto-proteins. The treatment as for any other primaryimmunodeficiency is antibiotic prophylaxis andgammaglobulin replacement therapy.

Complement Deficiencies

Hereditary angioedema (Cant et al. 2003; Bonillaet al. 2005, 2015) involves an absence of C1esterase inhibitor, it is not associated with anyimmune deficiency, and its deficiency does notpredispose to recurrent infections. A general defi-ciency of complement proteins is associated withrecurrent bacterial infections of respiratory

Immunology and Immunodeficiencies in Children 13

system, associated with antibody deficiency andhigher prevalence of autoimmune diseases, andespecially associated with C2 and C4 deficiency.For example, as all complement pathways acquireactive C3, its deficiency can present with samespectrum of disease as associated with severeantibody deficiency. Deficiency of C6, C7, andC8 can present with infections with neisserialgroup of organisms. Diagnosis of complementdeficiency for classical and alternate pathwaydepends on laboratory tests called CH50 andAH50, respectively. The treatment of choice islong-term antibiotic therapy.

Phagocytic Cell Deficiencies

Chronic granulomatous disease (Cant et al. 2003;Bonilla et al. 2005, 2015) is characterized byrecurrent infection with bacteria and fungi. Thereis lack of NADPH oxidase activity leading toreduction of reactive oxygen intermediates anddecreased phagocytic function. Diagnosisdepends on establishing the phagocytic oxidaseactivity. Prophylactic antimicrobial use, granulo-cyte transfusion in the presence of an active infec-tion, and surgical debridement if poor response tomedical therapy are the mainstay of treatment. Itcan be successfully treated with bone marrowtransplantation.

Chediak-Higashi syndrome is an autosomalrecessive disease caused by failure of lysosomesof neutrophils to empty their contents. It presentswith partial oculocutaneous albinism and neuro-logical symptoms. It is diagnosed by the presenceof giant azurophilic granules in neutrophils. Infec-tions associated with this syndrome are pyogenicand involve skin and respiratory tract. Bone mar-row transplantation is curative and improves theimmune deficiency but has no effect on albinismand neurologic manifestations.

In hyper IgE syndrome, the main defect is thefailure to produce IFN-γ by helper Tcells leading toincrease in TH2 cells and thus increase in IgE. IgEcauses histamine release and blocks certain aspectsof the inflammatory response; thus “cold abscesses”are characteristic for this disease. Patients are proneto infections with Staphylococcus aureus and

Aspergillus and suffer from chronic dermatitis.Patients with hyper IgE syndrome have involve-ment of skeletal system and dentition. High levelsof IgE, Staphylococcus aureus-binding IgE, andeosinophilia are characteristic of this disease butare not considered pathognomonic. The mainstayof treatment is aggressive prophylactic antibioticsand antifungals. The use of intravenous immuno-globulin (IVIG) and immunomodulation withIFN-γ is controversial in this disease. BMT is oflimited value as disease recurs posttransplant.

In leucocyte adhesion deficiency (LAD) syn-drome, there is absent or decreased expression ofCD18 (LAD1) and CD15 (LAD2) or decreasedupregulation in the presence of acute infection onthe surface of neutrophils. Patients suffer fromcellulitis, abscesses, and bacterial and fungal pul-monary infections. Patients with neutrophilia andrecurrent infections in the absence of pus forma-tion should be investigated for this disease. Theneutrophil count may be so high in acute infectionthat a possibility of leukemia or acute leukemoidreaction might be considered. The main treatmentstrategy is prevention by using prophylactic anti-biotics and aggressive treatment of acute infec-tions. Granulocyte transfusion and surgicaldebridement should be considered if medical ther-apy fails.

Acquired Immunodeficiency

Combined variable immunodeficiency (CVID) isan example of B-cell immunodeficiency of uncer-tain etiology. It should be considered if the patientsuffers from recurrent respiratory tract infections(Lougaris et al. 2016) with encapsulated organ-isms (Haemophilus influenza, Streptococcuspneumoniae) and atypical organisms such asmycoplasma. There is GIT involvement as well,and infections with Giardia, Campylobacter, andSalmonella are common. There is an increasedincidence of autoimmune diseases, nonmalignantlymphoproliferative disorders, and malignanciesin CVID (Xiao et al. 2014). Hypo-gammaglobulinemia and poor specific antibodyresponse are hallmark of CVID. The treatment ofchoice is prophylactic antibiotics and IVIG.

14 S. Aslam et al.

A general approach to treatment in primaryimmunodeficiencies is medical including antibi-otics, immunoglobulins, and immune modulation.In patients with humoral immune deficiency andcomplement deficiencies, the treatment of choiceis IVIG and prophylactic antibiotics. While com-bined and cellular immune deficiencies requirebone marrow transplantation, most of thesepatients might require IVIG and prophylactic anti-biotics as antibody function might not fullyrecover after BMT. Surgical treatment is requiredwhen medical treatment fails. Patients with recur-rent middle ear infections and rhinosinusitis mightbenefit from tympanostomy tube placement andadenotonsillectomy. Surgical drainage anddebridement might be required for infectionswith poor response to medical therapy. Thesepatients require more aggressive, prolongedcourse of combined antibiotics and at higherdoses post-surgery to reduce mortality and mor-bidity. Patients undergoing surgical proceduresshould be discussed with immunologist/infectiousdisease consultants with expertise to treat thesepatients prior to procedure. Other important clin-ical point is to avoid live vaccines in these immu-nodeficient patients such as BCG, oral poliovaccine, and MMR. These patients should bereviewed by an immunologist on regular basis.

Immunomodulation

Neonates especially those preterm are particularlyvulnerable to sepsis. Transplacental transfer ofimmunoglobulins from the mother to the fetusoccurs after 32weeks of gestation, and endogenousproduction commences at a few months of age.Administration of intravenous immunoglobulinprovides IgG that can bind to cell surface receptors,provide opsonic activity, activate complement, pro-mote antibody dependent cytotoxicity, andimprove neutrophilic chemoluminescence. Termneonates have low type-specific antibody andopsonin deficiencies. Preterm neonates also havesevere hypogammaglobulinemia and deficientcomplement activity.

Theoretically infectious morbidity and mor-bidity could be reduced by the administration of

intravenous immunoglobulin (IVIG). Meta-analysis of small trials has suggested that IVIGmay reduce the rate of neonatal death butCochrane reviews could not recommend routineuse of prophylaxis against nosocomial infectionsor for treatment in proven or suspected infection(Ohlsson and Lacy 2004, 2013). The InternationalNeonatal Immunotherapy Study (INIS) was aninternational multicenter randomized controlledtrial (RCT) studying the use of nonspecific IVIGin addition to antibiotics in babies with suspectedor proven sepsis. However, in this study and also asubsequent Cochrane analysis, IVIG had no effecton the rate of mortality and major morbidity (INISCollaborative Group et al. 2011; Ohlsson andLacy 2015).

Neonates often become neutropenic when sep-tic, and therefore the use of granulocyte colony-stimulating factor and granulocyte macrophagecolony-stimulating factors (GCSF and GM-CSF)has been studied on this population. The Cochranemeta-analysis of trials has found no significantimprovement in outcome when CSFs were usedfor prophylaxis or treatment of sepsis.

The program multicenter RCT of prophylacticGM-CSF to reduce systemic sepsis in pretermneonates included 280 infants <31 weeks. WhenGM-CSF 10 ug/kg/day was administered prophy-lactically for 5 days, neutrophil counts werehigher on days 3–12 than controls. There wereno significant differences in sepsis-free survivalin gnats who were neutropenic at recruitment, thenumber of infants experiencing one or more epi-sodes of culture-positive sepsis or survival to dis-charge. GM-CSF rapidly corrected neutropenia inpreterm, growth-restricted neonates. ProphylacticGM-CSF and correction of neutropenia, evenwhen severe, did not reduce sepsis or all-causemortality (Carr et al. 2009). Kuhn et al. describeda multicenter, randomized, double-blind, placebo-controlled trial of the prophylactic use of GCSF inneutropenic preterm infants<32 weeks (n= 200)and found no differences in survival free of con-firmed infection for 4 weeks after treatment witheither GCSF (10 mg/kg/day) or placebo for 3 days(Kuhn et al. 2009). However activated leukocytesmay mediate neonatal brain injury (Nelson andWilloughby 2000). GM-CSF stimulates neonatal

Immunology and Immunodeficiencies in Children 15

neutrophil activation unlike GCSF and both pro-long neutrophil survival (Molloy et al. 2005).However the 2-year developmental outcomeswere equal in both groups.

APC (drotrecogin alfa activated) was studied inthe RESOLVE (REsearching severe Sepsis andOrgan dysfunction in children: a gLobal perspec-tiVE) trial evaluated sepsis for safety, pharmacoki-netics, and pharmacodynamics of drotrecogin alfa(activated) in children with severe sepsis, and nobenefit was found (Nadel et al. 2007). The patientsstudied were from term newborn to 18 years, andalthough similar pharmacokinetic profiles werefound, bleeding rates were increased.

Prebiotics are unique oligosaccharides that arenot absorbed but facilitate colonization by probi-otic organisms (bifidobacteria and lactic acid-producing bacteria). Use of probiotics has beenshown to decrease the duration and severity ofrotavirus-induced diarrhea, allergies to cow milkprotein, atopic dermatitis, and some inflammatoryintestinal diseases. A relative reduction in the riskof NEC, late-onset sepsis, and mortality has beendemonstrated with probiotics (B. infantis, Strep-tococcus thermophilus, and B. bifidus in one studyand Lactobacillus acidophilus and B. infantis inanother) (Nadel et al. 2007; Neu 2007). A multi-center, double-blind, randomized, controlled trialof the probiotics B. bifidus and L. acidophilusshowed a lower incidence of NEC in the studygroup than controls, but sepsis was more frequentin the study group, although this difference wasnot significant on multivariate analyses, and noneof the affected patients developed sepsis withorganisms used as probiotics. There are persistentconcerns about the use of probiotics inimmunosuppressed infants as there have beenreports of preterm infants who had short gut syn-drome and developed Lactobacillus bacteremiawhile receiving this probiotic bacterium. A recentCochrane review has suggested that routine use ofprobiotics in less than 28weeks’ gestation neonatesis not useful; the results of further ongoing multi-center studies are awaited. In addition to theseimmediate concerns about sepsis, the long-termeffects of the use of probiotics, especially in pre-term infants in terms of immunemodulation in later

life, development of immune disorders (such asinsulin resistance, diabetes, obesity, and cancer),and neurodevelopmental outcomes are not known.

Conclusion and Future Directions

In fetal and neonatal life, many aspects of theimmune system are different to older children andadults. The molecular and cellular basis for theseabnormalities, while partially explained bymany ofthe observations described in this chapter, remainsrelatively unclear. The prospects for more specificand selective immunological intervention as part ofthe treatment of the immunocompromised neonateundergoing surgery will benefit enormously fromongoing research into the biological basis ofimmuno-incompetence of the newborn.

Designing new drugs to neutralize microbialproducts or block their interaction with specificreceptor on immune cells is an attractive concept(Wynn et al. 2009, 2010). Potential targets includeLPS-binding protein, CD14, TLR4, andMD-2 forGram-negative sepsis and CD14, TLR2, andTLR6 for Gram-positive sepsis. Monoclonal anti-bodies against CD14 are being evaluated in phaseII studies. Several intracellular signaling mole-cules such as MyD88 and the mitogen-activatedprotein kinase are other possible therapeutic tar-gets. However, inactivating molecules that arepivotal to innate immunity can be harmful, asshown by the increased sensitivity to bacterialsepsis in mice with mutations of the TLR4 gene.Careful selection of patients with severe infec-tions associated with a high probability of deathwill therefore be essential.

Cross-References

▶Chylothorax and Other Pleural Effusions▶Empyema▶Necrotizing Enterocolitis▶ Perinatal Physiology▶ Preoperative Assessment▶ Sepsis▶ Specific Risks for Preterm Infants

16 S. Aslam et al.

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