Review Article

Children with frequent infections: A proposalfor a stepwise assessment and investigation ofthe immune system�The immune defense to foreign invaders�Symphony. Which instrument is out of tune?

The immune system (IS) is characterized byspontaneity and �educated� function regardingspecificity, diversity, and self-recognition. Itsstructure, organization and �harmonious� func-tion resemble a symphonic orchestra.The integrity of the human organism relies on

the prompt and adequate production of various

cells and proteins. The inability of the organismto respond satisfactorily by the production of allthe appropriate substances leads to an ineffectiveimmune response. This resembles an orchestra inwhich the various instruments are not�tuned� together with final result cacophony andturmoil.

Cassimos DC, Liatsis M, Stogiannidou A, Kanariou MG. Childrenwith frequent infections: A proposal for a stepwise assessment andinvestigation of the immune system. �The immune defense to foreigninvaders� Symphony. Which instrument is out of tune?Pediatr Allergy Immunol 2010: 21: 463–473.� 2009 John Wiley & Sons A/S

Although many children develop frequent infections, only a few have anunderlying immune disorder. Children with dysfunction of the immunesystem develop frequent infections and/or recurrent, persistent, severe,and rare infections. The aim of this review is to provide to the clinician avaluable tool for recognizing any �discords� of the �immune-systemsymphonic orchestra�. By following a reverse route, it will be possible tobrighten up the dark and winding road of immunodeficiencies andidentify the exact point of immune dysfunction. This is fundamentaland crucial to perceive etiologic management and subsequently achievethe best for these young patients and their families.

Dimitrios C. Cassimos1,2, ManolisLiatsis1, Anastasia Stogiannidou2 andMaria G. Kanariou1

1Department of Immunology-Histocompatibility,Center for Primary Immunodeficiencies – PaediatricImmunology, Aghia Sophia Children�s Hospital,Athens, Greece, 2Department of Pediatrics,Democritus University of Thrace, Alexandroupolis,GreeceKey words: infections; immune system; investigation;algorithm; immunodeficiencies

Maria G. Kanariou, Department of Immunology-Histocompatibility, Center for PrimaryImmunodeficiencies – Paediatric Immunology,Aghia Sophia Children�s Hospital, Athens, GreeceE-mail: mkanariou@hol.gr

Accepted 15 September 2009

Abbreviations: AFP, a-Fetoprotein; AH50, alternative hemolytic 50; AIDS, acquired immunodeficiency syndrome; ALPS,autoimmune lymphoproliferative syndrome; APC, antigen presenting cells; APECED, autoimmune polyendocrinopathy candidiasisectodermal dystrophy; AT, ataxia telangiectasia; BMT, bone marrow transplantation; CD, cluster differentiation; CEA, carcino-embryonic antigen; CGD, chronic granulomatous disease; CH50, classical hemolytic 50; CHS, Chediak-Higashi Syndrome; CID,combined immunodeficiencies; CMCC, chronic mucocataneous candidiasis; CMV, cytomegalovirus; CVID, common variableimmunodeficiency; DGS, Di George Syndrome; DHR, dihydrorhodamine; EBV, Epstein–Barr virus; FBC, full blood count; FcR, Fcportion of immunoglobulin receptor; GI, gastrointestinal system; GS, Griscelli Syndrome; GVHD, graft vs. host disease; HIES,hyper IgE syndrome; HSV, herpes simplex virus; IBD, inflammatory bowel disease; ICOS, inducible co-stimulation; ID, immuno-deficiency; IFN, interferon; Ig(s), immunoglobulin(s); IL-12R, interleukin-12 receptor; IPEX, immune dysregulation, polyendo-crinopathy, enteropathy X-Linked inheritance; IS, immune system; IVIG, intravenous immunoglobulin; LAD, leukocyte adhesiondeficiency; MHC major histocompatibility complex; NBT nitroblue tetrazolium test; NK natural killer cell; PID primary immun-odeficiencies; PRP pattern recognition receptors; SCID severe combined immunodeficiency; SCIG subcutaneous immunoglobulins;SLE systemic lupus erythematosus; TCR T-cell receptor; TLR Toll-like receptor; VZV Varicella Zoster Virus; WAS Wiskott AldrichSyndrome; WHIM warts, hypogammaglobulinemia, infections, myelokathexis; XLA, X linked agammaglobulinemia; XLP X linkedproliferative disease.

Pediatr Allergy Immunol 2010: 21: 463–473

DOI: 10.1111/j.1399-3038.2009.00964.x

� 2009 John Wiley & Sons A/S

PEDIATRIC ALLERGY AND

IMMUNOLOGY

463

Normally, all children have the experience ofinfections. The question that the clinician isfacing in his everyday practice is in which casesshould he suspect an underlying immune disor-der and how should he stratify the investigation.To answer these questions, it is important first ofall to review the structure and the function of theIS (1–8).Immune defense commences within hours with

an early (innate) non-specific response to foreigninvaders, continues with a slower specificresponse to certain molecules, and a non-specificaugmentation �crescendo� of this response. Thememory of the IS for specific antigens providesitself with the ability for a more immediateand vigorous response to a future challenge bythe same microorganism (adaptive-specificimmunity).The efficient immune response is completed in

two phases; the recognition and the effectorphases. The recognition of the foreign sub-stances is performed by PRP or TLR and thesubsequent binding to APC. Thereafter, thecascade of the immune response will follow.APC will process and present the antigentogether with MHC molecules to T cells viatheir receptors (TCR).Innate immunity, which is the first line defense

of the organism, is �performed� by cells (e.g., thephagocytes) and soluble components (e.g.,the complement) and in our metaphore is thebasic �tempo� of the orchestra. Specific immunity,the delicate complete immune response, derivedfrom the lymphocytes, that is of the �solo�instruments, which are mostly responsible forthe melody itself.

Phagocytic compartment

The phagocytic compartment of the immunesystem includes neutrophils, eosinophils, andmonocytes–macrophages. The latest migrate tothe tissues where they differentiate into specifictissue macrophages. The response of phagocytesagainst bacteria is integrated through phago-cytosis, which is accomplished in a stepwiseprocess. The first step in phagocytosis is chemo-taxis by which the phagocytic cells get attractedto the infected site moving towards bacteria andvarious substances that are produced in animmune response. The next step is adherence ofthe antigen to the phagocytic cell membrane. Thephagocytes have specific receptors at their cellu-lar membrane, thus enhancing the ability toattract antigens and bind to them more readily.By this process (opsonization), some antigens arerendered more susceptible to phagocytosis.

Complement system

The complement system participates, activates,and reinforces various immune functions likechemotaxis and opsonization. The complementactivates neutrophils and macrophages that sub-sequently induce lysis of bacteria and increasethe vascular permeability. Activation of eitherthe classical or the alternative pathway of thecomplement leads to C3 activation, consequentlyconverging to the same final route, ending to theproduction of the same biologic particles. Thecomplement functions as an autoregulated, auto-restricted system. In humans, deficiencies ofcomplement components are related to charac-teristic clinical syndromes. Patients with C1, C4,or C2 deficiency develop symptoms that resembleSLE and less frequently recurrent pyogenicinfections. Deficiencies of C3 and componentsof the final part of the complement (C5–9) arerelated with recurrent bacterial infections (9, 10).Nevertheless, hypocomplementemia can be the

final result of complement consumption, as mayoccur in autoimmune diseases or during aninfection (2, 11–13).

Lymphocytic system (LS)

The basic component of the LS is the lympho-cyte. The major populations of the lymphocytesare T, B, and Natural Killer (NK) cells. T and Bcells are further divided into subpopulations withdiscrete functions. The hallmark for differentiat-ing them is their immunophenotype that isdetermined in relation to specific markers (gly-coproteins) that they express on their surface andin the cytoplasm.T lymphocytes are divided into two main cell

types: CD4+ (T-helper – Th) and CD8+

(T-suppressor/cytotoxic-Ts/c). Th cells have acentral role in the immune response, as the�conductor� of the orchestra of the IS. Theyrecognize antigens, which are presented to themby APC in conjunction with MHC class IImolecules, and consequently they activate otherimmune cells inducing an immune response(Fig. 1). This process is enhanced by otherfunctioning molecules that are lymphocyte sur-face proteins, which increase binding, signaling,and homing of antigens. Th cells that are derivedfrom naı̈ve Th0 are divided into three distinctsubgroups depending on the cytokines theyproduce (Th1, Th2, and Th17). Th1 cells secreteIL-2 and IFN-c, which are favoring thedevelopment of cellular immunity. Th2 cellssecrete IL-4, IL-5, and IL-13 that regulate B-cellresponses, immunity against parasites, and are

Cassimos et al.

464

crucial for allergic diseases by the induction ofIgE production. Th17 cells play a key role inimmunoregulation (14). Ts/c cells restrict theimmune response and induce cytotoxicity totarget cells. They recognize viral antigens inconjunction with MHC class I molecules.B lymphocytes constitute the other major

lymphocytic population. After an antigenic stim-ulation, most of the B cells differentiate intoplasma cells that produce and secrete specificantibodies. Initially, these are IgM and later IgMand IgD and finally IgG, IgA, or IgE. Thisgradual process of Igs production that is knownas �isotype switching� requires the interaction ofseveral proteins, mainly CD40 on B-cell surfacewith its ligand (CD40L) on activated T cells. Bcells also function as APC in a secondaryimmune response.Some of the T and B cells differentiate to

memory cells that act as a reservoir of immuneresponse in a future antigenic challenge (Fig. 1).T cells are mostly responsible for the defenseagainst viruses, fungi, and parasites, as well astumors and foreign grafts while B cells towardsbacteria. There is also a great deal of interactionof these two populations to accomplish a satis-factory immune response. The communication ofthese and other cells of the IS is achieved by:(i) soluble mediators known as cytokines, mono-kines, or lymphokines, secreted by macrophages,monocytes, or lymphocytes, respectively. (Cyto-

kines that induce chemotaxis of leucocytes arereferred to as chemokines), (ii) specific cytokinereceptors on the surface of these cells (IL-12R,IFN-cR), and (iii) adhesion molecules.The NK cells form another part of the

lymphocytic population. They do not havememory and have limited specificity. Their actionagainst tumor cells and cells infected with virusesdoes not require the presence of antibodies orantigenic stimulation and therefore belongs tothe innate immunity.

Immunodeficiencies and time of onset

All children have the experience of infections.Children in playgroups – nurseries can develop8–10 upper respiratory tract infections and 1–2infections of the GI tract annually. Thereare some characteristics from the personaland family history that are more indicative ofan underlying immune disorder (Table 1) (15–18).The suspicion about an immune deficiency

should emerge in various clinical symptoms andsigns that the clinician comes across, and shouldbe able to identify (Table 2) (15, 16). It is alsoimportant to determine the time of onset ofthe disease (19). Inherited defective productionof antibodies become evident after the age of6 months, when antibodies of maternal originhave dissipated. On the other hand, SCID

ThB

memory

B

Teffector

NK

Tmemory

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CD80/CD86

CD28

CD40L

CD40Plasma

cell

MHC II

Cytokines

Antigen

TCR

CD80/CD86

CD28

Fig. 1. Schematic illustration ofthe immune response after anantigenic stimulation.

An immune investigation algorithm for children with frequent infections

465

presents soon after birth, while LAD causesdelay in the separation of the umbilical cordbeyond the age of 2 wk. Finally, CVID has noage preference and can present from late infancyto young adulthood with a broad spectrum ofsymptoms. The combination of various symp-toms and signs is pathognomonic of certainsyndromes or specific immunodeficiencies(Table 3) (19–40). Apart from the detailedmedical history, a thorough clinical examinationis a prerequisite for the objective evaluation ofthe problem.

Disease entity – epidemiology

Immunodeficiencies (IDs) are divided into pri-mary and secondary. In children, primary im-munodeficiencies (PID) are more common; whilein adults predominate the secondary. PID arevery rare, with an overall incidence one in 2000live births (41). In a recent publication, theprevalence of PID is estimated to be one in 1200persons. (42). Nevertheless, there is evidence thatPID are more common than what was previouslythought (43, 44).There is a lot of heterogeneity in the etiology

and the underlying genetic disorder of more than200 (45) known PID. Antibody deficiency is themost common type of PID, accounting for about2/3 of them, while complement deficiency com-prises <1%. Cellular and phagocytic defectsaccount for 20–30% of PID. There can also be agreat deal of variability in the clinical presenta-tion and the severity of the disease making thelong and winding pathway to the correct diag-nosis more difficult and more obscure (24, 41). Inregards to the immunologic pathway that isimpaired, PID are divided into eight groups ofsyndromes (Table 4) (46).

Table 1. Signals from history in children with possible immunodeficiency

Personal historyInfections Severe, recurrent, in multiple sites,

with prolonged duration, withpoor response to

treatment, with major complications,abscesses

Infective agents OpportunisticImmunizations With complication or disseminated

infection (e.g., BCG-itis)Dermatitis/eczema Severe and/or persistentBronchial asthma Severe, resistant, or corticoid dependentChronic lung diseaseAutoimmune manifestations Cytopenias, vasculitisDysmorphism, MicrocephalyDevelopmental delayChronic diarrheaDelayed separation of the

umbilical cord (>2 wk)Family history

Unexplained death in infancyKnown or possible immunodeficiencyParental consanguinityInfections at the home environment (HIV)Autoimmune diseases, SLELymphoma

Table 2. Clinical signs and symptoms in children with possible immunodefi-ciency

Failure to thriveDysmorphism, microcephalyExtremities, nails Digital clubbing, palenessMouth Periodonditis, gingivostomatitis,

delayed shedding of primary teethCardiovascular Congenital heart diseaseRespiratory Chronic lung disease,

bronchiectasis, pneumatocelesGastrointestinal Hepatosplenomegaly, IBDLymphatic tissue Absent or excessive proliferation

with lymphadenopathy, thymomaSkin, hair Eczema, petechiae, scars,

granullomas, angioedema, albinismPigmentary changes, severe

skin infections, abnormal hairEyes Retinal abnormalities, telangiectasiaSkeletal abnormalitiesNervous system Ataxia

Table 3. Characteristic clinical signs and/or laboratory findings in certainimmunodeficiencies

AT Cerebellar ataxia, oculocutaneous telangiectasia,elevated AFP and CEA

CGD Deep seated infections, abscesseswith granulomatous formation

CHS Partial oculocutaneous albinism, neurologic symptoms,and giant azurophil granules in neutrophils

CMCC Recurrent candidal infections of nails, skin, andmucous membranes, defective T-cell response

Complementdeficiency

Neisserial infection orautoimmune disorders

DGS Hypocalcaemic seizures, cardiacdisease, abnormal facies

GS Pigmentary dilution, neurologic abnormalities,pyogenic infections, and a hemophagocytic syndrome

HIES Failure to shed primary teeth, thickened skin,skin and lung infections, skeletal abnormalities

IFN-cR, IL-12R Atypical mycobacterial orSalmonella infections

LAD Delayed separation of the umbilical cord,chronic severe periodontitis, lack of pus

SCID Viral or fungal infections, chronic diarrhea,failure to thrive in early infancy

XLA Absent lymph nodes and tonsils,agammaglobulinaemia, and absence of B-cells

XLP Fulminant infectious mononucleosis,lymphoma and dysgammaglobulineamia

WAS Thrombocytopenia with small in size platelets,eczema, and recurrent infections by

encapsulated bacteriaWHIMS Warts, hypogammaglobulinemias,

immunodeficiency, and myelocathexis

Cassimos et al.

466

Diagnostic approach – stepwise evaluation andassessment

Although in the majority of children withfrequent infections, there is no underlyingimmune disorder, a delay in recognizing animmune dysfunction could be devastating forthese young patients. The earliest diagnosis iscrucial to pursue an etiologic management of thedisease and, subsequently, avoid the conse-quences of severe and/or recurrent infections.The recognition of the �damaged� immune path-way is substantial in identifying the possible�uninvited visitors�-microorganisms (Table 5)(2, 47–49). By following the reverse route, it ispossible to orientate to the possible implicatedimmune pathway. Functioning as a compass tothe clinician, are the presenting symptoms, thetype of infection(s), the severity of the diseaseand the microorganisms involved. Certainly, it isimportant to exclude secondary immunodeficien-cies and other causes of frequent infections(Table 6).The development of abscesses and deep sited

infections from Staphylococcus, Serratia, orAspergillus is consistent with neutrophils defi-ciency/dysfunction, as in CGD (50–53). Recur-rent infections from Neisseria (meningitidis orgonorrhoeae) emerge in patients with deficiencyof the final part of the complement (C5–C9) (12,54). Pyogenic bacteria (Haemophilus influenzaetype b, Pneumococcus, Pseudomonas) develop inpatients with deficient antibody response (55),whilst infections by intracellular organisms(Mycobacterium, Salmonella) and viruses aremore indicative of an underlying disorder of thecellular part of immunity and, more specifically,of the T cells and type 1 cytokine production (25,56). Recurrent and/or severe Herpes or Papil-loma virus infections may be seen in NKdysfunction. Patients with combined immunode-ficiencies (CID) can experience infections fromthe entire range of pathogens (2, 41).Although there are some outstanding proto-

cols for the diagnostic screening of PID, our

effort is to present a stepwise rational approachto the child with frequent infections, for a �handy�use in the �bed side� medicine (41, 47, 48, 57, 58).The initial investigation screening includes:

FBC, Igs (IgG, IgA, IgM, IgE), complement(CH50, C3, C4), and isohemmaglutinins(Table 7). From the FBC, it is possible to excludeneutropenia or lymphopenia. Neutropenia war-rants further investigation as well as lymphope-nia that can be the �prelude� of SCID.Nevertheless, marked leukocytosis and neutro-philia is almost always present in cases of LAD(41). White cells morphology can attribute to thediagnosis, like in CHS, where neutrophils havecharacteristic giant azurophil granules. Plateletsthat reflect the bone marrow function, can bediminished in WAS and in autoimmune diseases.Hb, Hct, and red cells morphology are goodmarkers for an underlying chronic disease.Cytopenias that are very alarming should bemonitored and investigated thoroughly (41, 46,59). CVID, one of the most common PID, exceptfrom autoimmune cytopenias and infections, canalso develop IBD and lymphomas (19). Erythro-phagocytosis can be the presenting feature ofsome PID (60). Evaluation of B-cell function, inthe first place, is assessed by measurement of Igs.The screening is extended in accordance withthe clinical picture and in conjunction withthe pathogenic microorganisms (Tables 6–8).The antibody function is further evaluated bymeasurement of specific antibodies, isohemmag-glutinins (anti-A, anti-B IgM antibodies), andIgG subclasses. (8, 61). However, infants 6–8 months old often develop transient hypo-

Table 4. Classification of PID (IUIS, 2007)

Combined T-cell and B-cell immunodeficienciesPredominantly antibody deficienciesOther well-defined immunodeficiency syndromesDiseases of immune dysregulationCongenital defects of phagocyte number, function, or bothDefects in innate immunityAutoinflammatory disordersComplement deficiencies

Table 5. Common pathogens related with infections in specific types of im-munodeficiencies

Immunodeficiencies Common pathogens

Antibody deficiency Bacteria: Staphylococcus aureus, StreptococcusHaemophilus influenza bEnteroviruses: polio, echo

T-cell deficiency Intracellular bacteria: Mycobacteriumspecies, listeria

VirusesFungi: Candida, Pneumocystis jiroveci

Combined T- andB-cell deficiency

BacteriaFungi: Pneumocystis jiroveci, Candida

Viruses: CMV, HSV, MeaslesParasites: Cryptococcus, Cryptosporidium

Phagocytes deficiency Bacteria: Staphylococcus aureus, Salmonella,Nocardia, Mycobacterium species-(atypical)

Fungi: AspergillusInnate immunity deficiency Bacteria: Staphylococcus aureus

Mycobacterium speciesHuman pappiloma virus (HPV)

Complement deficiency Bacteria: Streptococcus, Haemophilus influenza b,Neisseria meningitidis, Neisseria gonorrhoeae

An immune investigation algorithm for children with frequent infections

467

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tor

func

tion

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gammaglobulinemia and toddlers are notexpected to produce antibodies against polysac-charide antigens (e.g., Haemophilus influenzaetype b and/or Pneumonococcus). Responses topure polysaccharide antigens can be evaluated inpatients older than 2 yr of age (55, 62). Specificantibody levels are preferably interpreted 3 wkpost-vaccination and are expected to rise four-fold for protein antigens and two-fold for poly-saccharide antigens (41, 63). Specific antibodyresponses may be impaired as a result of a B-celldefect or a T-cell failure to help for antibodyproduction (2, 41, 62, 64). In cases with normallevels of Igs, impaired polysaccharide responsescould be due to IgG2 subclass deficiency orspecific antibody deficiency. (62, 64–67). Elevatedserum IgE levels matched with staphylococcus-binding IgE, and eosinophilia are characteristicof HIES.Cellular immunity is assessed by measurement

of the lymphocytes and their subpopulations.Also, with skin prick tests to antigens already�introduced� to the patient by vaccination(tetanus, mumps, diphtheria), or environmentally(Trichopyton, Candida, Proteus) cutaneousdelayed hypersensitivity, an in vivo T-cell specificantigenic response is evaluated (63, 68). A normalresponse is 2–5 mm of induration after 48–72 hof intracutaneous injection (12).The phagocytic part of immunity is assessed

primarily by white cells number and morphol-ogy. To investigate the phagocytic function, it isimportant to evaluate chemotaxis, phagocytosis,and neutrophil oxidative burst. The latter ismeasured by the nitroblue tetrazolium test(NBT) and by the dihydrorhodamine test(DHR), a flow cytometric assay (69, 70).The complement is evaluated initially by mea-

surement of CH50, C3, C4. In the case that thelevels of CH50 are low, the investigation has to

be extended to the other Complement compo-nents. If they are normal and the suspicion aboutcomplement deficiency remains strong, functionof the alternative pathway is further evaluatedwith measurement of AH50. This pathway canbe influenced in properdin or factor D deficiency(12, 41).If an allergic disease is considered as an

underlying cause for the clinical picture, beyondtotal IgE, specific IgE should be measured andin vivo allergic responsehas tobe acknowledgedbyskin prick and/or patch tests for certain allergens.If any of these first line investigations are

abnormal, more specific studies have to beorganized: immunophenotype of T and B cells,evaluation of the response to specific antigens,lymphocyte cultures, immunohistochemistry ofgranule contents, and, finally, measurement of allthe fractions of the complement (Table 8). Invery specific cases, it is required to pursue moreextended investigations with evaluation of theimmune cells communication, measurement ofspecific enzymes, and analysis of white cellglycoproteins. In cases in which certain syn-dromes are suspected, specific investigations areperformed (Table 3). Diagnosis at molecularlevel is mostly desired for the establishment ofunequivocal diagnosis, the identification of can-didates for gene specific therapy, and detection ofcarriers (69, 71–77). An online directory ofspecialized laboratory testing for immunodefi-ciencies has recently become available (78).

Prognosis

The prognosis of children with PID is consideredto be much better in the last two decades,something that is expected to improve even morewith the valuable input, assistance, and collabo-ration of the clinicians and scientists.Nevertheless, the key point for a favorable

prognosis is early diagnosis (15, 16, 48). With thesubsequent prompt etiologic and aggressivetreatment, it is possible to avoid permanent andlife-threatening complications and achieve longerand better quality of life (21, 41). There are threemajor categories of management:

1 Preventive: antimicrobial chemoprophylaxis,immunizations

2 Supportive: (i) replacement (IVIG, SCIG, etc),(ii) treatment of infections and complications

3 Curative: with the inclusion of hematopoieticstem cell transplantation and gene therapy inthe therapeutic repertoire of PID, it has beenachieved complete cure in cases of SCID andother PID (79–81)

Table 7. Investigation for possible immunodeficiency in children with frequentinfections

1st line diagnostic work outFull blood countImmunoglobulins: IgG, IgA, IgM, IgEIsohemagglutininsCH50, C3,C4

2nd line diagnostic work outImmunoglobulin subclasses In frequent bacterial infectionsComplement investigation In recurrent infections

by MeningococcusPhacocytic investigation In infections by Staphylococcus

aureus, gram negative bacteria, fungiLymphocytes subpopulations In severe viral or opportunistic

infectionsHIV investigation

3rd line or specialized diagnosticinvestigation

In opportunistic infections, TBC

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Finally, family counseling is an important issue,which can be extremely facilitated with geneticdiagnosis.

Conclusions

PID are a challenge for the clinical pediatrician(4, 43, 81, 82). The immune system resembles anorchestra that comprises many instruments andcan produce �melodies� balsam for the earsequivalent to – complete and effective immuneresponse(s), balsam for the �wounded� organism.A trained pediatrician enjoys the melody ofa �natural normal immune response�, but hasalso the trained �musical ear� that enables him/herto recognize any �discords� equivalent to aninconclusive immune response. The isolation ofthese �discords� will give him/her the hint aboutthe �instrument� – immune pathway, that is �outof tune� – dysfunctioning. The appropriateinvestigation – screening for a possible PID willthereafter be organized, brightening up theobscure pathways of immunodeficiencies (47,48, 83).

In conclusion, this review is intended to be avaluable tool for the clinical pediatrician. Theidentification of signs of PID will be the crucialpoint for the ignition of the diagnostic �mara-thon�. In collaboration with immunologic cen-ters, it will facilitate the revelation of the hiddenimmunopathogenetic route and identify the ID.With the diagnosis of a certain PID, the mostappropriate treatment is organized at specializedcenters and genetic counseling is obtainedaccomplishing the best for these young trouble-some patients and their families.

AcknowledgmentsWe would like to thank Mrs. Kelly Chorafopoulou,Mrs. Penio Kassari, Mr. Sotirios Livas & Mrs. Efi Symeo-nov for their support and contribution.

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