Vaccination against encapsulated bacteria in hereditary C2 deficiency results in antibody response and opsonization due to antibody-dependent complement activation

Alternative pathway amplification and infections

The alternative pathway (AP) is the phylogenetically oldest arm of the complement system and may have evolved to mark pathogens for elimination by phagocytes. Studies using purified AP proteins or AP-specific serum showed that C3b amplification on bacteria commenced following a lag phase of about 5 min and was highly dependent on the concentration of complement. Most pathogens have evolved several elegant mechanisms to evade complement, including expressing proteases that degrade AP proteins and secreting proteins that block function of C3 convertases. In an example of convergent evolution, many microbes recruit the AP inhibitor factor H (FH) using molecular mechanisms that mimic FH interactions with host cells. In most instances, the AP serves to amplify C3b deposited on microbes by the classical pathway (CP). The role of properdin on microbes appears to be restricted to stabilization of C3 convertases; scant evidence exists for its role as an initiator of the AP on pathogens in the context of serum. Therapeutic complement inhibition carries with it an increased risk of infection. Antibody (Ab)-dependent AP activation may be critical for complement activation by vaccine-elicited Ab when the CP is blocked, and its molecular mechanism is discussed.

Inhibition of the different complement pathways has varying impacts on the serum bactericidal activity and opsonophagocytosis against Haemophilus influenzae type b

Defense against Haemophilus influenzae type b (Hib) is dependent on antibodies and complement, which mediate both serum bactericidal activity (SBA) and opsonophagocytosis. Here we evaluated the influence of capsule-specific antibodies and complement inhibitors targeting the central component C3, the alternative pathway (AP; fB, fD), the lectin pathway (LP; MASP-2) and the terminal pathway (C5) on both effector functions. Findings may be relevant for the treatment of certain diseases caused by dysregulation of the complement system, where inhibitors of complement factors C3 or C5 are used. Inhibitors against other complement components are being evaluated as potential alternative treatment options that may carry a reduced risk of infection by encapsulated bacteria. Serum and reconstituted blood of healthy adults were tested for bactericidal activity before and after vaccination with the Hib capsule-conjugate vaccine ActHIB. Most sera had bactericidal activity prior to vaccination, but vaccination significantly enhanced SBA titers. Independently of the vaccination status, both C3 and C5 inhibition abrogated SBA, whereas inhibition of the LP had no effect. AP inhibition had a major inhibitory effect on SBA of pre- vaccination serum, but vaccination mitigated this inhibition for all disease isolates tested. Despite this, SBA-mediated killing of some Hib isolates remained retarded. Even for the most serum-resistant isolate, SBA was the dominating defense mechanism in reconstituted whole blood, as addition of blood cells to the serum did not enhance bacterial killing. Limited Fc receptor-mediated opsonophagocytosis was unmasked when bacterial killing by the membrane attack complex was blocked. In the presence of C3 or C5 inhibitors, addition of post-vaccination, but not of pre-vaccination serum to the blood cells triggered opsonophagocytosis, leading to suppression of bacterial multiplication. Taken together, our data indicate that for host defense against Hib, killing by SBA is more efficient than by blood cell opsonophagocytosis. However, additional defense mechanisms, such as bacterial clearance by spleen and liver, may play an important role in preventing Hib-mediated sepsis, in particular for Hib isolates with increased serum-resistance. Results indicate potentially improved safety profile of AP inhibitors over C3 and C5 inhibitors as alternative therapeutic agents in patients with increased susceptibility to Hib infection.

Complement Genetics for the Practicing Allergist Immunologist: Focus on Complement Deficiencies

Complement deficiencies have been considered to be rare for many decades, but this assumption is changing year by year. Recognition of these conditions significantly increases thanks to the availability of different testing approaches and due to clinical awareness. Furthermore, sequencing technologies (including Sanger sequencing, targeted gene panels, and whole exome/genome sequencing) may facilitate the identification of the underlying disease-causing genetic background. On the other hand, functional characterization of the identified possibly pathogenic variations and performing family studies, as illustrated by some of our cases, remain similarly important to establish a precise clinical diagnosis facilitating the most appropriate management. Here, we present 4 illustrative cases with complement deficiencies of diverse etiologies and also provide an educative, step-by-step description on how to identify the underlying cause of complement deficiency based on the results of complement laboratory testing.

Increased serum bactericidal activity of autologous serum in C2 deficiency after vaccination against Haemophilus influenzae type b, and further support for an MBL-dependent C2 bypass mechanism

Deficiencies of C2 and other components of the classical pathway of complement are associated with increased risk of infections with encapsulated bacteria, such as Haemophilus (H.) influenzae. Defense against H. influenzae is dependent on specific antibodies and complement, which mediate serum bactericidal activity (SBA) and opsonization. Due to lack of normal classical and lectin complement pathway function in C2 deficiency (C2D), SBA would have to depend either on the alternative pathway or on C2 bypass mechanisms. Here we studied SBA against H. influenzae type b (Hib) before and after vaccination in a group of C2-deficient persons, as the bactericidal capacity of antibodies in autologous complement in relation to vaccination has not been investigated at group level in C2D. Sera from 22 persons with C2D and 26 healthy controls were available. Out of these, 18 persons with C2D and all controls had been vaccinated with Act-HIB®. SBA against Hib bacteria was analyzed with autologous serum as the only complement source. Antibodies to Hib capsular polysaccharide had been analyzed previously. Concentrations of mannose-binding lectin (MBL) and other complement components were measured in serum. SBA of both C2-deficient persons and controls was significantly more efficient after vaccination (p = 0.002 and p < 0.0001, respectively). After vaccination, all but two C2-deficient sera and one control serum showed sufficient SBA (<50% surviving bacteria). Before vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of MBL (lower proportion of surviving bacteria with higher MBL concentration; r = -0.55, p = 0.008). After vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of IgG Hib antibodies (r = -0.56, p = 0.01). In conclusion, SBA against Hib in autologous serum is increased after vaccination in persons with C2D. In unvaccinated C2-deficient persons SBA was correlated to MBL concentration, providing further support for an MBL-dependent C2 bypass mechanism operating in C2D.

Hereditary Deficiency of the Second Component of Complement: Early Diagnosis and 21-Year Follow-Up of a Family

Complement deficiencies are rare and often underdiagnosed primary immunodeficiencies that may be associated with invasive bacterial diseases. Serious infections with encapsulated organisms (mainly Streptococcus pneumoniae, but also Neisseria meningitides and Haemophilus influenzae type B) are frequent in patients with a deficiency of the second component of complement (C2), but no data are available on long-term follow-up. This study aimed to evaluate the long-term clinical outcome and the importance of an early diagnosis and subsequent infection prophylaxis in C2 deficiency. Here, we report the 21-year follow-up of a whole family which was tested for complement parameters, genetic analysis and biochemical measurements, due to recurrent pneumococcal meningitis in the elder brother. The two sons were diagnosed with homozygous type 1 C2 deficiency, while their parents were heterozygous with normal complement parameters. For the two brothers, a recommended vaccination program and antibiotic prophylaxis were prescribed. During the long-term follow-up, no severe/invasive infections were observed in either patient. At the age of 16, the younger brother developed progressive hypogammaglobulinemia of all three classes, IgA, IgM and IgG. A next generation sequencing panel excluded the presence of gene defects related to primary antibody deficiencies. Our data show that early diagnosis, use of vaccinations and antibiotic prophylaxis may allow a normal life in hereditary C2 deficiency, which can be characterized using functional and genetic methods. Moreover, a periodical check of immunoglobulin serum levels could be useful to detect a possible hypogammaglobulinemia.

Complement interactions with the pathogenic Neisseriae: clinical features, deficiency states, and evasion mechanisms

Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, while Neisseria meningitidis is an important cause of bacterial meningitis and sepsis. Complement is a central arm of innate immune defenses and plays an important role in combating Neisserial infections. Persons with congenital and acquired defects in complement are at a significantly higher risk for invasive Neisserial infections such as invasive meningococcal disease and disseminated gonococcal infection compared to the general population. Of note, Neisseria gonorrhoeae and Neisseria meningitidis can only infect humans, which in part may be related to their ability to evade only human complement. This review summarizes the epidemiologic and clinical aspects of Neisserial infections in persons with defects in the complement system. Mechanisms used by these pathogens to subvert killing by complement and preclinical studies showing how these complement evasion strategies may be used to counteract the global threat of meningococcal and gonococcal infections are discussed.

Prime-boost vaccination strategy enhances immunogenicity compared to single pneumococcal conjugate vaccination in patients receiving conventional DMARDs, to some extent in abatacept but not in rituximab-treated patients

OBJECTIVE

To explore whether a prime-boost vaccination strategy, i.e., a dose of pneumococcal conjugate vaccine (PCV) and a dose of 23-valent polysaccharide vaccine (PPV23), enhances antibody response compared to single PCV dose in patients with inflammatory rheumatic diseases treated with different immunosuppressive drugs and controls.

METHODS

Patients receiving rituximab (n = 30), abatacept (n = 23), monotherapy with conventional disease-modifying antirheumatic drugs (cDMARDs, methotrexate/azathioprine/mycophenolate mofetil, n = 27), and controls (n = 28) were immunized with a dose PCV followed by PPV23 after ≥ 8 weeks. Specific antibodies to 12 serotypes included in both vaccines were determined using a multiplex microsphere immunoassay in blood samples before and 4-8 weeks after each vaccination. Positive antibody response was defined as ≥ 2-fold increase from pre- to postvaccination serotype-specific IgG concentration and putative protective level as IgG ≥ 1.3 μg/mL. The number of serotypes with positive antibody response and IgG ≥ 1.3 μg/mL, respectively, after PCV and PCV + PPV23 were compared within each treatment group and to controls. Opsonophagocytic activity (OPA) assay was performed for serotypes 6B and 23F.

RESULTS

Compared to single-dose PCV, prime-boost vaccination increased the number of serotypes with positive antibody response in patients with abatacept, cDMARDs, and controls (p = 0.02, p = 0.01, and p = 0.01), but not in patients on rituximab. After PCV + PPV23, the number of serotypes with positive antibody response was significantly lower in all treatment groups compared to controls but lowest in rituximab, followed by the abatacept and cDMARD group (p < 0.001). Compared to PCV alone, the number of serotypes with putative protective levels after PCV + PPV23 increased significantly only in patients in cDMARDs (p = 0.03) and controls (p = 0.001). Rituximab treatment was associated with large reduction (coefficient - 8.6, p < 0.001) and abatacept or cDMARD with moderate reductions (coefficients - 1.9 and - 1.8, p = 0.005, and p < 0.001) in the number of serotypes with positive antibody response to PCV + PPV23 (multivariate linear regression model). OPA was reduced in rituximab (Pn6B and Pn23F, p < 0.001), abatacept (Pn23F, p = 0.02), and cDMARD groups (Pn6B, p = 0.02) compared to controls.

CONCLUSIONS

Prime-boost strategy enhances immunogenicity compared to single pneumococcal conjugate vaccination in patients with inflammatory rheumatic diseases receiving cDMARDs, to some extent in abatacept but not in patients on rituximab. Pneumococcal vaccination should be encouraged before the initiation of treatment with rituximab.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03762824. Registered on 4 December 2018, retrospectively registered.

Immunogenicity and safety of pneumococcal vaccination in patients with systemic sclerosis

Objective

To study the impact of disease and treatment with DMARDs on antibody response elicited by either pneumococcal conjugate vaccine (PCV13) or pneumococcal polysaccharide vaccine (PPV23) in patients with SSc.

Methods

Forty-four SSc patients and 49 controls received a dose of either PCV13 or PPV23. Twelve patients were treated with DMARDs. Antibody levels to pneumococcal polysaccharides 6B and 23 F were measured before and 4-6 weeks after vaccination using ELISA. Antibody functionality was studied using opsonophagocytic assay performed on serotype 23 F.

Results

Number of patients, percentage female and mean age (years) at vaccination were: 32, 94%, 57.5 years in SSc without DMARDs; 12, 100%, 55.5 years in SSc on DMARDs and 49, 63% and 50.6 years in controls. Post-vaccination antibody levels for both serotypes increased significantly in SSc without DMARDs and controls (P < 0.001), but in SSc on DMARDs only for 6B (P = 0.041). Compared with the other groups, patients with SSc receiving DMARDs had lower post-vaccination antibody levels for both serotypes. Opsonophagocytic assay increased significantly in all three groups. No significant difference in immunogenicity between PCV13 and PPV23 was seen.

Conclusion

Pneumococcal vaccination using either PCV13 or PPV23 yielded satisfactory antibody response in SSc patients without DMARD treatment, but a lower response in patients treated with synthetic DMARDs. Type of pneumococcal vaccine (conjugate or polysaccharide) did not significantly influence antibody response.

Trial registration

ClinicalTrials.gov, http://clinicaltrials.gov, NCT02240888.

Immune response to pneumococcal conjugate vaccine in patients with systemic vasculitis receiving standard of care therapy

AIM

To study the effect of standard of care therapy on antibody response and functionality following immunization with 13-valent pneumococcal conjugate vaccine (PCV13) in patients with primary systemic vasculitis compared to healthy controls.

METHODS

49 patients with vasculitis and 49 controls received a single dose (0.5ml) PCV13 intramuscularly. Ongoing treatments: azathioprine (AZA; n=11), cyclophosphamide (CYC; n=6), methotrexate (MTX; n=9), rituximab (n=3); anti-TNF (n=2), mycophenolate mofetil (n=2), prednisolone alone (n=15) and no active treatment (n=2). Specific antibody concentrations for serotypes 6B and 23F were determined using ELISA and opsonophagocytic activity (OPA) assay (23F) was performed, on serum samples taken immediately before and 4-6weeks after vaccination. Proportion of individuals with putative protective antibody concentration (≥1.0µg/mL) and positive antibody response (≥2-fold increase from prevaccination concentration) for both serotypes were calculated and groups were compared.

RESULTS

At baseline, 6 patients (12%) and 12 controls (24%) had protective antibody levels for both serotypes. After vaccination, antibodies increased for both serotypes in patients and controls (p<0.001), 32 patients (65%) and 35 controls (71%) reached protective level for 6B, and 32 patients (65%) and 37 controls (76%) for 23F. Compared to controls, patients had lower prevaccination geometric mean concentration (23F, p=0.01) and a numerical trend towards lower prevaccination level (6B) and postvaccination levels (both serotypes). Patients with prednisolone alone had lower prevaccination OPA (p<0.01) compared to controls. OPA increased after vaccination in both patients and controls (p<0.001), but improvement was better in controls (p=0.001). AZA, CYC or MTX, but not prednisolone alone, tended towards a lower proportion of patients reaching protective antibody levels (p=0.06), compared to controls.

CONCLUSIONS

Pneumococcal conjugate vaccine was safe and immunogenic in patients with established vasculitis. Treatment with DMARDs, mostly AZA, CYC and MTX but not systemic prednisolone may impair antibody response.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02240888. Registered 4 September, 2014.

Treatment with belimumab in systemic lupus erythematosus does not impair antibody response to 13-valent pneumococcal conjugate vaccine

Background/purpose The objective of this study was to explore the impact of systemic lupus erythematosus and belimumab given in addition to standard of care therapy on 13-valent conjugated pneumococcal vaccine (PCV13) response. Methods Forty-seven systemic lupus erythematosus patients and 21 healthy controls were immunized with a single dose of 13-valent conjugated pneumococcal vaccine. Forty systemic lupus erythematosus patients were treated with traditional disease-modifying anti rheumatic drugs, 11 of those received belimumab in addition, and 32 patients were treated with concomitant prednisolone. Quantification of serotype specific IgG levels to 12 pneumococcal capsular polysaccharides was performed in serum taken before and four to six weeks after vaccination using multiplex fluorescent microsphere immunoassay. IgG levels against serotypes 23F and 6B were also analyzed using standard enzyme-linked immunosorbent assays. Opsonophagocytic assay was performed on serotype 23F to evaluate the functionality of the antibodies. Pre- and post-vaccination log transformed antibody levels were compared to determine the impact of systemic lupus erythematosus diagnosis and different treatments on antibody response. Results Systemic lupus erythematosus patients as a group showed lower post-vaccination antibody levels and lower fold increase of antibody levels after vaccination compared to controls ( p = 0.02 and p = 0.009, respectively). Systemic lupus erythematosus patients treated with belimumab in addition to standard of care therapy or with only hydroxychloroquine did not differ compared to controls, whereas the other treatment groups had significantly lower fold increase of post-vaccination antibody levels. Higher age was associated with lower post-vaccination antibody levels among systemic lupus erythematosus patients. Conclusion Belimumab given in addition to traditional disease-modifying anti rheumatic drugs or prednisolone did not further impair antibody response to 13-valent conjugated pneumococcal vaccine.

Methotrexate reduces vaccine-specific immunoglobulin levels but not numbers of circulating antibody-producing B cells in rheumatoid arthritis after vaccination with a conjugate pneumococcal vaccine

BACKGROUND

Treatment with methotrexate (MTX) in patients with rheumatoid arthritis (RA) leads to decreased total immunoglobulin (Ig) levels and impairs vaccine-specific IgG antibody levels following pneumococcal vaccination. The mechanisms by which MTX exerts these effects in RA are unknown. We aimed to evaluate whether MTX reduces vaccine-specific serum Ig levels and their functionality in RA patients following vaccination with pneumococcal conjugate vaccine, and if numbers of antigen-specific circulating plasmablasts are affected.

METHODS

Ten patients with RA on MTX and 10 RA patients without disease modifying anti-rheumatic drug (DMARD) were immunized with a dose 13-valent pneumococcal conjugate vaccine (Prevenar13). Circulating plasmablasts producing total IgG and IgA as well as specific IgG and IgA against two pneumococcal capsular serotypes (6B and 23F) were enumerated using ELISPOT 6days after vaccination. IgG levels against both these serotypes were determined with ELISA before and 4-6weeks after vaccination. Positive antibody response was defined as ⩾2-fold increase of pre-vaccination antibody levels. The functionality of vaccine specific antibodies to serotype 23F was evaluated by measuring their ability to opsonize bacteria using opsonophagocytic assay (OPA) in 4 randomly chosen RA patients on MTX and 4 RA patients without DMARD.

RESULTS

After vaccination, RA patients on MTX showed significant increase in pre- to postvaccination antibody levels for 6B (p<0.05), while patients without DMARD had significant increases for both 6B and 23F (p<0.05 and p<0.01, respectively). Only 10% of RA on MTX and 40% of RA patients without DMARD showed positive post-vaccination antibody responses for both serotypes. Increased opsonizing ability after vaccination was detected in 1 of 4 RA patients on MTX and 3 of 4 patients on RA without DMARD. However, numbers of circulating total and vaccine-specific IgG- or IgA-producing plasmablasts did not differ between RA patients with or without MTX.

CONCLUSIONS

MTX treatment in RA leads to reduced vaccine-specific antibody responses and their functionality compared to untreated RA following pneumococcal vaccination using polysaccharide-protein conjugate vaccine. However, since there was no reduction in numbers of circulating total or vaccine-specific antibody-producing plasmablasts after vaccination this effect is probably not due to reduced activation of B cells in lymphoid tissue.

CLINICAL TRIAL REGISTRATION

NCT02240888.

Immunodeficiency among children with recurrent invasive pneumococcal disease

BACKGROUND

Recurrent invasive pneumococcal disease (rIPD) occurs mostly in children with an underlying disease, but some cases remain unexplained. Immunodeficiency has been described in children with rIPD, but the prevalence is unknown. We used a nationwide registry of all laboratory-confirmed cases of rIPD to identify cases of unexplained rIPD and examine them for immunodeficiency.

METHODS

Cases of rIPD in children 0-15 years of age from 1980 to 2008 were identified. Children without an obvious underlying disease were screened for complement function, T-cell, B-cell, natural killer--cell counts and concentration of immunoglobulins. B-cell function was evaluated by measuring antibody response to polysaccharide-based pneumococcal vaccination and the extent of fraction of somatic hypermutation. Toll-Like receptor (TLR) signaling function and mutations in key TLR-signaling molecules were examined.

RESULTS

In total, rIPD were observed in 54 children (68 cases of rIPD of 2192 IPD cases). Children with classical risk factors for IPD were excluded, and among the remaining 22 children, 15 were eligible for analysis. Of these 6 (40%) were complement C2-deficient. Impaired vaccination response was found in 6 children of whom 3 were C2 deficient. One patient had a severe TLR signaling dysfunction. No mutations in IRAK4, IKBKG or MYD88 were found.

CONCLUSION

Of an unselected cohort of children with rIPD at least 11% were C2 deficient. Data suggest that screening for complement deficiencies and deficient antibody response to pneumococcal vaccines in patients with more than 1 episode of IPD is warranted.

Classical pathway deficiencies - A short analytical review

Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency.

Immune responses following meningococcal serogroups A, C, Y and W polysaccharide vaccination in C2-deficient persons: evidence for increased levels of serum bactericidal antibodies

Complement C2 deficiency (C2D) is associated with immunological diseases and increased susceptibility to invasive infections caused by encapsulated bacteria such as Neisseria menigitidis. In this study we evaluate the immunogenicity of vaccination against N. menigitidis in C2D. C2D patients (n=22) and controls (n=52) were given a tetravalent meningococcal polysaccharide vaccine. Serum bactericidal antibody (SBA) titres (serogroups A, C, Y and W) were analysed using a rabbit complement source. Levels of IgG, IgM, and IgA, factor B, and factor H, polymorphisms of MBL and Fc-gamma receptors were determined. The C2D patients responded with an increased SBA titre to all four serogroups (p<0.001). The response rates define as SBA titres ≥8 were found to be between 85.7% and 92.5%. The post-vaccination titres for serogroups C, Y and W were equal to healthy controls. C2D patients with a history of invasive infection had a lower post-vaccination SBA titres both compared to healthy C2D persons (p=0.03) and compared to controls (p<0.0001). We found that the G2M*n/G2M*n genotype were associated with a higher SBA titres after immunization (p=0.03). None of the other investigated immunological factors appear to be important in influencing the vaccine responses. Autoimmune diseases in C2D did not affect the vaccine response. In general, vaccination against meningococci gave rise to antibody responses in the C2D patients that equal healthy controls. The response rate was lower to serogroup A and among C2D patients with history of invasive infections. The presence of G2M*n/G2M*n genotype was associated with higher SBA titres after immunization.

Primary immunodeficiency in infection-prone children in southern Sweden: occurrence, clinical characteristics and immunological findings

Background

Primary immunodeficiency diseases (PIDs) comprise a heterogeneous group of disorders mainly characterized by increased susceptibility to infections. The aims of this study were to estimate the occurrence rate of PID in the paediatric (age ≤ 18 years) population of southern Sweden (approx. 265,000 children) and to describe their demographic, clinical and immunological characteristics. During a period of 4 years, in four paediatric speciality clinics in Skåne County in southern Sweden, children being seen for infections and fulfilling specific criteria were evaluated according to a predefined examination schedule. The initial analysis consisted of complete blood counts with analysis of lymphocyte subpopulations (T, B, NK cells), measurement of immunoglobulins (IgG, IgA, IgM, IgE and IgG subclasses), and assessment of the complement system (classical, alternative and lectin pathways). In addition, results of these immunological analyses in other children from the same area and time period were evaluated.

Results

In total, 259 children (53.6% males) met the criteria and were included. The most common infection was recurrent otitis media. Immunological analyses results for about two thirds of the patients were outside age-related reference intervals. Further examination in this latter group identified 15 children with PID (9 males); 7 (2.7%) had genetically defined PID, representing 4 different diagnoses, and another 8 (3.1%) had a clinically defined PID - common variable immunodeficiency. No additional PID patient was identified from the evaluation of laboratory results in children not included in the study. The median age at diagnosis was 3.5 years (range 1–12 years).

Conclusions

The occurrence rate of PID was about 4 new cases per year in this population. Several different PID diagnoses were found, and the application of specified criteria to identify PID patients was useful. In children who are prone to infection, the use of a predefined set of immunological laboratory analyses at their first examination was beneficial for early identification of patients with PID.