Individuals with IgA deficiency and common variable immunodeficiency share polymorphisms of major histocompatibility complex class III genes

Leveraging pleiotropy identifies common-variant associations with selective IgA deficiency

Selective IgA deficiency (SIgAD) is the most common inborn error of immunity (IEI). Unlike many IEIs, evidence of a role for highly penetrant rare variants in SIgAD is lacking. Previous SIgAD studies have had limited power to identify common variants due to their small sample size. We overcame this problem first through meta-analysis of two existing GWAS. This identified four novel common-variant associations and enrichment of SIgAD-associated variants in genes linked to Mendelian IEIs. SIgAD showed evidence of shared genetic architecture with serum IgA and a number of immune-mediated diseases. We leveraged this pleiotropy through the conditional false discovery rate procedure, conditioning our SIgAD meta-analysis on large GWAS of asthma and rheumatoid arthritis, and our own meta-analysis of serum IgA. This identified an additional 18 variants, increasing the number of known SIgAD-associated variants to 27 and strengthening the evidence for a polygenic, common-variant aetiology for SIgAD.

The Role of HLA in the Association between IgA Deficiency and Celiac Disease

Selective IgA deficiency (SIgAD) is the most frequent primary immune defect. Since SIgAD is not characterized by relevant infectious issues in most cases, it is often diagnosed during the diagnostic work up of several and different autoimmune disorders, which are associated with this primary immune defect. The genetic background of SIgAD is complex and three HLA haplotypes resulted to be more frequently associated with it; in detail, two of them include HLA-DQB1∗02 allelic variants, which are essential predisposing factors to develop Celiac Disease (CD). Here, we discuss the evidence regarding the role of HLA in the etiopathogenesis of SIgAD and its association with CD. Actually, the HLA region seems to play a modest role in the genetic predisposition to SIgAD and we may speculate that the association with the HLA-DQB1∗02 alleles (or haplotypes including them) could derive from its link with CD. Indeed, SIgAD and some related immunological alterations are likely to predispose to several autoimmune diseases (with and despite different HLA backgrounds), including CD, which is relatively common and directly associated with the HLA-DQB1∗02 allelic variants coding the DQ2 heterodimer. Further and specific studies are needed to make final conclusions in this regard.

Clinical and Laboratory Features of 184 Italian Pediatric Patients Affected with Selective IgA Deficiency (SIgAD): a Longitudinal Single-Center Study

PURPOSE

Selective IgA deficiency (SIgAD) is the most common humoral primary immunodeficiency. Long-term follow-up data in large cohort of pediatric patients are scarce.

METHODS

We report on a single-center cohort of 184 pediatric patients affected with selective IgA deficiency and describe the characteristics at diagnosis and during follow-up.

RESULTS

Respiratory infections were the most common clinical finding leading to the initial diagnosis (62%). Positive family history for antibody deficiencies (selective IgA deficiency, common variable immunodeficiency) led to SIgAD diagnosis in 16% of cases. During follow-up, while the incidence of respiratory infections was not particularly high, gastrointestinal symptoms were reported in 27% of patients. Allergic manifestations were found in 23% at diagnosis and an additional 16% of patients during follow-up, leading to a prevalence of atopy of 39% among SIgAD patients. Autoimmune manifestations, excluding celiac disease, were found in 9% of affected patients during follow-up. Celiac disease was found in a high prevalence (14%). Increase of serum IgA levels to partial deficiency (9%) and normal serum levels for age (4%) was observed during follow-up. A small percentage of patients (2%) progressed to common variable immunodeficiency (CVID).

CONCLUSIONS

In conclusion, this is the first study to describe a large single-center pediatric cohort of patients affected with SIgAD, revealing that overall most patients do well with regard to infections. Many develop CD, at a rate much higher than the general population. A few normalize their IgA levels. A few progress to CVID. Thus, careful follow-up is suggested to diagnose and treat potential complications earlier for avoiding potential morbidities.

Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most common primary immunodeficiency of young adolescents and adults which also affects the children. The disease remains largely under-diagnosed in India and Southeast Asian countries. Although in majority of cases it is sporadic, disease may be inherited in a autosomal recessive pattern and rarely, in autosomal dominant pattern. Patients, in addition to frequent sino-pulmonary infections, are also susceptible to various autoimmune diseases and malignancy, predominantly lymphoma and leukemia. Other characteristic lesions include lymphocytic and granulomatous interstitial lung disease, and nodular lymphoid hyperplasia of gut. Diagnosis requires reduced levels of at least two immunoglobulin isotypes: IgG with IgA and/or IgM and impaired specific antibody response to vaccines. A number of gene mutations have been described in CVID; however, these genetic alterations account for less than 20% of cases of CVID. Flow cytometry aptly demonstrates a disturbed B cell homeostasis with reduced or absent memory B cells and increased CD21(low) B cells and transitional B cell populations. Approximately one-third of patients with CVID also display T cell functional defects. Immunoglobulin therapy remains the mainstay of treatment. Immunologists and other clinicians in India and other South East Asian countries need to be aware of CVID so that early diagnosis can be made, as currently, majority of these patients still go undiagnosed.

High-density SNP mapping of the HLA region identifies multiple independent susceptibility loci associated with selective IgA deficiency

Selective IgA deficiency (IgAD; serum IgA<0.07 g/l) is the most common form of human primary immune deficiency, affecting approximately 1∶600 individuals in populations of Northern European ancestry. The polygenic nature of IgAD is underscored by the recent identification of several new risk genes in a genome-wide association study. Among the characterized susceptibility loci, the association with specific HLA haplotypes represents the major genetic risk factor for IgAD. Despite the robust association, the nature and location of the causal variants in the HLA region remains unknown. To better characterize the association signal in this region, we performed a high-density SNP mapping of the HLA locus and imputed the genotypes of common HLA-B, -DRB1, and -DQB1 alleles in a combined sample of 772 IgAD patients and 1,976 matched controls from 3 independent European populations. We confirmed the complex nature of the association with the HLA locus, which is the result of multiple effects spanning the entire HLA region. The primary association signal mapped to the HLA-DQB1*02 allele in the HLA Class II region (combined P = 7.69×10(-57); OR = 2.80) resulting from the combined independent effects of the HLA-B*0801-DRB1*0301-DQB1*02 and -DRB1*0701-DQB1*02 haplotypes, while additional secondary signals were associated with the DRB1*0102 (combined P = 5.86×10(-17); OR = 4.28) and the DRB1*1501 (combined P = 2.24×10(-35); OR = 0.13) alleles. Despite the strong population-specific frequencies of HLA alleles, we found a remarkable conservation of these effects regardless of the ethnic background, which supports the use of large multi-ethnic populations to characterize shared genetic association signals in the HLA region. We also provide evidence for the location of association signals within the specific extended haplotypes, which will guide future sequencing studies aimed at characterizing the precise functional variants contributing to disease pathogenesis.

Association of HLA-DRB1, DQA1 and DQB1 Alleles and Haplotypes with Common Variable Immunodeficiency in Iranian Patients

Common Variable Immunodeficiency (CVID) is an antibody deficiency syndrome that often co-occurs in families with selective IgA deficiency (IgAD). This study was designed to investigate the frequency of DR and DQ loci of HLA class II region in common variable immunodeficiency (CVID) patients. Fifteen Iranian patients with CVID or IgAD (mean age 14.6±5.4, range 4-25 years; 9 male and 6 female) and 63 healthy controls were studied. Establishment of B-lymphoblastoid cell lines was performed using Epstein-Barr-virus (EBV) immortalization technique and HLA alleles were typed using polymerase chain reaction based on sequence specific primers (PCR-SSP). DRB1 alleles including DRB1 *04 (p=0.03) and DRB1 *11 (p=0.01) significantly showed higher frequency in the studied subjects. In contrast, DRB1 *301 (p=0.04) and DRB1 *07 (p=0.02) alleles were negatively associated with CVID. For DQB1 and DQA1 loci, DQB1 *0302 (p=0.047) and DQA1 *03011 (p=0.001) demonstrated high frequency in cases, while DQB1 *0201 (p=0.02) and DQA1 *0201 (p=0.01) were detected to be low when compared to controls. Haplotype analysis indicated that frequency of DRB1*04-DQB1*03011-DQA1 *03011 (p=0.02), DRB1 *11-DQB1 *03011-DQA1 *0505 (p=0.047), DRB1 *11-DQA1 *0505 (p=0.04) and DRB1*04-DQA1*03011 (p=0.02) haplotypes were significantly higher in patient group, while only the frequency of the DRB1 *07-DQA1 *0201 haplotype gene was statistically lower in control group (p=0.02). According to the results, it could be deduced that the HLA-DR and DQ loci may contribute to the pathogenesis of CVID or they might be considered as suitable markers for the possibility of the occurrence of this genetic defect.

Parental consanguinity is associated with a severe phenotype in common variable immunodeficiency

The DEFI study has collected clinical data and biological specimens from kindreds with CVID. Patients with demonstrated parental consanguinity (cCVID group) were compared to patients without parental consanguinity (ncCVID). A total of 24 of the 436 patients with CVID had consanguineous parents. Age at first symptoms and age at diagnosis were comparable in the two groups. Some complications were more frequent in cCVID patients: splenomegaly (62.5% vs. 29%; p = 0.001), granulomatous disease (29% vs. 12%; p = 0.02), and bronchiectasis (58% vs. 29%; p = 0.003). A high incidence of opportunistic infections was also observed in this population (29% vs. 5%; p < 0.001). Distribution of B-cell subsets were similar in the two groups. Naïve CD4+ T cells were decreased in cCVID patients (15% vs. 28%; p < 0.001), while activated CD4 + CD95+ (88% vs. 74%; p = 0.002) and CD8 + HLA-DR + T cells (47% vs. 31%; p < 0.001) were increased in these patients when compared to ncCVID patients. Parental consanguinity is associated with an increased risk of developing severe clinical complications in patients with CVID. Most of these patients presented with severe T-cell abnormalities and should be considered with a diagnosis of late-onset combined immune deficiency (LOCID). Systematic investigation for parental consanguinity in patients with CVID provides useful information for specific clinical care and genetic screening.

The influence of MHC and immunoglobulins a and e on host resistance to gastrointestinal nematodes in sheep

Gastrointestinal nematode parasites in farmed animals are of particular importance due to their effects on production. In Australia, it is estimated that the direct and indirect effects of parasite infestation cost the animal production industries hundreds of millions of dollars each year. The main factors considered by immunologists when studying gastrointestinal nematode infections are the effects the host's response has on the parasite, which immunological components are responsible for these effects, genetic factors involved in controlling immunological responses, and the interactions between these forming an interconnecting multilevel relationship. In this paper, we describe the roles of immunoglobulins, in particular IgA and IgE, and the major histocompatibility complex in resistance to gastrointestinal parasites in sheep. We also draw evidence from other animal models to support the involvement of these immune components. Finally, we examine how IgA and IgE exert their influence and how methods may be developed to manage susceptible animals.

Pathogenesis and treatment of gastrointestinal disease in antibody deficiency syndromes

Primary humoral immune deficiencies are characterized by limited antibody responses secondary to either impaired B-lymphocyte development or B-cell responses to T-lymphocyte signals. Given that the gastrointestinal tract is the largest lymphoid organ in the body, it is not surprising that intestinal diseases are common in immunodeficiency. These gastrointestinal diseases can be classified into one of 4 groups, infection, malignancy, inflammatory, and autoimmune, and can mimic other known disease processes, such as inflammatory bowel disease and celiac sprue. The exact pathogenesis of these gastrointestinal disorders in the setting of systemic immunodeficiency is still under investigation. However, studies suggest that defects in antibody deficiency alone do not result in gastrointestinal disease but rather that defects in cellular immunity are also involved. Treatment is difficult given an already immunocompromised state, and often therapy with immunomodulators is required for more severe processes.

Genetics of hypogammaglobulinemia: what do we really know?

In the past, immunodeficiencies were categorized based on clinical and laboratory findings in the affected patient. Now we are more likely to define them based on the specific gene involved. One might expect this shift to increase the precision and clarity of diagnosis but in the last few years it has become increasingly clear that identification of a mutation in a specific gene may not tell the whole story. Some gene defects may reliably result in clinical disease, others may act as susceptibility factors that are more common in patients with immunodeficiency but can also be found in otherwise healthy individuals. Distinguishing between these two types of gene defects is essential for informative genetic counseling.

Role of polymorphisms in the TNFRSF13B (TACI) gene in Spanish patients with immunoglobulin A deficiency

Mutations in the TNFRSF13B (TACI) gene have been associated with common variable immunodeficiency, and a role in immunoglobulin A deficiency (IgAD) has also been suggested. We aimed at studying the role of several polymorphisms along this gene in IgAD susceptibility. Three TNFRSF13B mutations (C104R, A181E and R202H) and eight additional single nucleotide polymorphisms in the gene were genotyped in 338 Spanish IgAD patients and 553 ethnically matched healthy controls and tested for association. Data from parents of 114 IgAD patients were also collected and used for additional analysis. No statistically significant differences were observed after comparing patients and controls for any single nucleotide polymorphism analysed. Therefore, our work seems to discard a role of TNFRSF13B mutations in IgAD, concordantly with the most recent published studies.

Primary B cell immunodeficiencies: comparisons and contrasts

Sophisticated genetic tools have made possible the identification of the genes responsible for most well-described immunodeficiencies in the past 15 years. Mutations in Btk, components of the pre-B cell and B cell receptor (lambda5, Igalpha, Igbeta), or the scaffold protein BLNK account for approximately 90% of patients with defects in early B cell development. Hyper-IgM syndromes result from mutations in CD40 ligand, CD40, AID, or UNG in 70-80% of affected patients. Rare defects in ICOS or CD19 can result in a clinical picture that is consistent with common variable immunodeficiency, and as many as 10% of patients with this disorder have heterozygous amino acid substitutions in TACI. For all these disorders, there is considerable clinical heterogeneity in patients with the same mutation. Identifying the genetic and environmental factors that influence the clinical phenotype may enhance patient care and our understanding of normal B cell development.

Primary antibody deficiency syndromes

The primary antibody deficiency syndromes are a group of rare disorders characterized by an inability to produce clinically effective immunoglobulin responses. Some of these disorders result from genetic mutations in genes involved in B cell development, whereas others appear to be complex polygenic disorders. They most commonly present with recurrent infections due to encapsulated bacteria, although in the most common antibody deficiency, Common Variable Immunodeficiency, systemic and organ-specific autoimmunity can be a presenting feature. Diagnostic delay in this group of disorders remains a problem, and the laboratory has a vital role in the detection of abnormalities in immunoglobulin concentration and function. It is critical to distinguish this group of disorders from secondary causes of hypogammaglobulinaemia, in particular lymphoid malignancy, and appropriate laboratory investigations are of critical importance. Treatment of primary antibody deficiencies involves immunoglobulin replacement therapy, either via the intravenous or subcutaneous route. Patients remain at risk of a wide variety of complications, not all linked to diagnostic delay and inadequate therapy. In common variable immunodeficiency (CVID) in particular, patients remain at significantly increased risk of lymphoid malignancy, and regular clinical and laboratory monitoring is required. This review aims to give an overview of these conditions for the general reader, covering pathogenesis, clinical presentation, laboratory investigation, therapy and clinical management.

Screening of functional and positional candidate genes in families with common variable immunodeficiency

Background

Common variable immunodeficiency (CVID) comprises a heterogeneous group of primary antibody deficiencies with complex clinical and immunological phenotypes. The recent discovery that some CVID patients show monogenic defects in the genes encoding ICOS, TACI or CD19 prompted us to investigate several functional candidate genes in individuals with CVID.

Results

The exonic, protein coding regions of the genes encoding: APRIL, BCMA, IL10, IL10Rα, IL10Rβ, IL21, IL21R, and CCL18, were analyzed primarily in familial CVID cases, who showed evidence of genetic linkage to the respective candidate gene loci and CVID families with a recessive pattern of inheritance. Two novel SNPs were identified in exon 5 and exon 8 of the IL21R gene, which segregated with the disease phenotype in one CVID family. Eleven additional SNPs in the genes encoding BCMA, APRIL, IL10, IL10Rα, IL21 and IL21R were observed at similar frequencies as in healthy donors.

Conclusion

We were unable to identify obvious disease causing mutations in the protein coding regions of the analyzed genes in the studied cohort.

Common variable immunodeficiency in children

PURPOSE OF REVIEW

Common variable immunodeficiency is the most common primary immunodeficiency that needs medical attention. Symptoms may occur at any time, with two major peaks of onset at 5-10 and 20-30 years. We present the different clinical phenotypes of common variable immunodeficiency, review recent genetic findings and point to current treatment strategies.

RECENT FINDINGS

Five genes, ICOS, CD19, TNFRSF13B, TNFRSF13C and MSH5, have been found to be mutated in patients with common variable immunodeficiency. Additional possible genetic loci for autosomal dominant forms were detected on chromosomes 4q and 16q. These findings illustrate the heterogeneous molecular basis of common variable immunodeficiency and indicate the value of genetic linkage studies, thereby improving the genetic diagnosis.

SUMMARY

In young patients with unusually frequent bacterial infections, common variable immunodeficiency should always be considered as a differential diagnosis. The compulsory individual work-up should comprise a family history in order to document siblings and additional family members suffering from common variable immunodeficiency and/or selective IgA deficiency. Since the recently found gene defects affect a minority of patients with common variable immunodeficiency only, future genetic research is required to identify further susceptibility genes involved in the pathogenesis of this condition.

Deconstructing common variable immunodeficiency by genetic analysis

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency. Patients have recurrent bacterial infections and an increased risk of developing autoimmune diseases, lung damage, and selected cancers. Since 2003, four genes have been shown to be mutated in CVID patients: ICOS, TNFRSF13B (encoding TACI), TNFRSF13C (encoding BAFF-R) and CD19. Heterozygous mutations in TNFRSF13B are also associated with CVID, whereas the other three genes are purely recessive. Recent genetic linkage studies have also identified possible loci for dominant CVID genes on chromosomes 4q, 5p and 16q. These findings markedly improved the genetic diagnosis of CVID and point towards new strategies for future genetic studies. In addition, some CVID genes might be relevant to more common diseases such as asthma and stroke.

Role for Msh5 in the regulation of Ig class switch recombination

Ig class switch recombination (CSR) and somatic hypermutation serve to diversify antibody responses and are orchestrated by the activity of activation-induced cytidine deaminase and many proteins involved in DNA repair and genome surveillance. Msh5, a gene encoded in the central MHC class III region, and its obligate heterodimerization partner Msh4 have a critical role in regulating meiotic homologous recombination and have not been implicated in CSR. Here, we show that MRL/lpr mice carrying a congenic H-2(b/b) MHC interval exhibit several abnormalities regarding CSR, including a profound deficiency of IgG3 in most mice and long microhomologies at Ig switch (S) joints. We found that Msh5 is expressed at low levels on the H-2(b) haplotype and, importantly, a similar long S joint microhomology phenotype was observed in both Msh5 and Msh4-null mice. We also present evidence that genetic variation in MSH5 is associated with IgA deficiency and common variable immune deficiency (CVID) in humans. One of the human MSH5 alleles identified contains two nonsynonymous polymorphisms, and the variant protein encoded by this allele shows impaired binding to MSH4. Similar to the mice, Ig S joints from CVID and IgA deficiency patients carrying disease-associated MSH5 alleles show increased donor/acceptor microhomology, involving pentameric DNA repeat sequences and lower mutation rates than controls. Our findings suggest that Msh4/5 heterodimers contribute to CSR and support a model whereby Msh4/5 promotes the resolution of DNA breaks with low or no terminal microhomology by a classical nonhomologous end-joining mechanism while possibly suppressing an alternative microhomology-mediated pathway.

Common variable immunodeficiency: The power of co-stimulation

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immune deficiency in adults. CVID is characterized by the sequelae of an antibody deficiency syndrome: an impaired terminal B cell differentiation results in hypogammaglobulinemia and susceptibility to recurrent infections by encapsulated bacteria. The clinical course of CVID is complicated by a plethora of systemic immunopathology, including autoimmunity, lymphoproliferation, malignancy and sarcoid-like granulomas. Phenotypic and functional studies in CVID patients revealed multiple abnormalities within the innate and adaptive immune system. The recent description of monogenic defects in ICOS, TACI and CD19 focussed our interest to an impaired T cell-B cell collaboration within the germinal center and intrinsic B cell defects as possible explanations for the etiology of CVID.

Increased apoptosis of CD20+ IgA + B cells is the basis for IgA deficiency: the molecular mechanism for correction in vitro by IL-10 and CD40L

IgA deficiency is the most common primary immunodeficiency in humans. Comparative analysis of gene expression in PBMC from IgA-deficient (IgAd) and normal donors using functional multiplex panels showed overexpression of the Caspase-1 (CASP-1) gene. Cells from all the IgAd donors (n=7) expressed 4-10-fold caspase-1 mRNA over normal controls (n=5). CD19(+) B cells from all IgAd donors produced IgA in cultures following IL-10 and CD40L with Staphylococcus aureus (Cowan) (SAC) or tetanus toxoid (TT) treatments. In CD19(+) B cells from IgAd donors, reconstitution of IgA secretion was associated with protection of the CD20(+) B cell population that underwent apoptosis in the absence of IL-10, CD40L, and TT (triple treatment). Caspase-1 gene expression was decreased in the reconstituted cells. Furthermore, treatment with a caspase-1 inhibitor also independently protected against B cell apoptosis in vitro. An apoptosis-specific cDNA array showed differential expression of 4 out of 96 genes and a shift towards survival-related gene expression from the apoptotic to the protected B cells after triple treatment. There was an increase in the expression of the IAP-2 (inhibitor of apoptosis) gene in the reconstituted cells. Upregulation of the IAP-2 gene protects B cells from deletion and allows for IgA secretion in this system. The inability to detect secreted IgA in IgAd patients could result from the loss of IgA-committed B cells that express high levels of caspase-1.

Linkage of autosomal-dominant common variable immunodeficiency to chromosome 4q

The phenotype of common variable immunodeficiency (CVID) is characterized by recurrent infections owing to hypogammaglobulinemia, with deficiency in immunoglobulin (Ig)G and at least one of IgA or IgM. Family studies have shown a genetic association between CVID and selective IgA deficiency (IgAD), the latter being a milder disorder compatible with normal health. Approximately 20-25% of CVID cases are familial, if one includes families with at least one case of CVID and one of IgAD. Nijenhuis et al described a five-generation family with six cases of CVID, five cases of IgAD, and three cases of dysgammaglobulinemia. We conducted a genome-wide scan on this family seeking genetic linkage. One interval on chromosome 4q gives a peak multipoint LOD score of 2.70 using a strict model that treats only the CVID patients and one obligate carrier with dysgammaglobulinemia as affected. Extending the definition of likely affected to include IgAD boosts the peak multipoint LOD score to 3.38. The linkage interval spans at least from D4S2361 to D4S1572. We extended our study to a collection of 32 families with at least one CVID case and a second case of either CVID or IgAD. We used the same dominant penetrance model and genotyped and analyzed nine markers on 4q. The 32 families have a peak multipoint LOD score under heterogeneity of 0.96 between markers D4S423 and D4S1572 within the suggested linkage interval of the first family, and an estimated proportion of linked families (alpha) of 0.32, supporting the existence of a disease-causing gene for autosomal-dominant CVID/IgAD on chromosome 4q.

Regulation of anti-cyclic citrullinated peptide antibodies in rheumatoid arthritis: contrasting effects of HLA-DR3 and the shared epitope alleles

OBJECTIVE

To examine the association between HLA-DRB1 alleles and the production of anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF) autoantibodies in patients with rheumatoid arthritis (RA).

METHODS

We studied 1,723 Caucasian RA patients enrolled in the North American Rheumatoid Arthritis Consortium (NARAC) family cohort and the Study of New Onset Rheumatoid Arthritis (SONORA) cohort. All patients were tested for anti-CCP antibodies (by enzyme-linked immunosorbent assay), RF (by nephelometry), and HLA-DR genotype (by polymerase chain reaction and sequence-specific oligonucleotide hybridization).

RESULTS

When controlled for the presence of RF, anti-CCP positivity was strongly associated with the HLA-DRB1 shared epitope (SE). In RF+ patients, the presence of the SE was very significantly associated with anti-CCP positivity, with an odds ratio (OR) of 5.8 and a 95% confidence interval (95% CI) of 4.1-8.3. This relationship was also seen in RF- patients (OR 3.1 [95% CI 1.8-5.3]). In contrast, RF positivity was not significantly associated with presence of the SE independently of anti-CCP antibodies. Strikingly, HLA-DRB1*03 was strongly associated with reduced anti-CCP titers, even after controlling for the presence of the SE and restricting the analysis to anti-CCP+ patients. HLA-DR3 was also associated with anti-CCP- RA in our population.

CONCLUSION

The HLA-DRB1 SE is strongly associated with the production of anti-CCP antibodies, but not RF. In contrast, HLA-DR3 alleles are associated with anti-CCP- disease and with lower levels of anti-CCP antibodies, even when controlling for the SE. These data emphasize the complexity of the genetic effects of the major histocompatibility complex on the RA phenotype.

Analysis of families with common variable immunodeficiency (CVID) and IgA deficiency suggests linkage of CVID to chromosome 16q

Common variable immunodeficiency (CVID) is an antibody deficiency syndrome that often co-occurs in families with selective IgA deficiency (IgAD). Vorechovský et al. (Am J Hum Genet 64:1096-1109, 1999; J Immunol 164:4408-4416, 2000) ascertained and genotyped 101 multiplex IgAD families and used them to identify and fine map the IGAD1 locus on chromosome 6p. We analyzed the original genotype data in a subset of families with at least one case of CVID and present evidence of a CVID locus on chromosome 16q with autosomal dominant inheritance. The peak (model-based) LOD score for the best marker D16S518 is 2.83 at theta=0.07, and a 4-marker LOD score under heterogeneity peaks at 3.00 with alpha=0.68. The (model-free) NPL score using the same markers peaks at the same location with a value of 3.38 (P=0.0001).

Common variable immunodeficiency: the immune system in chaos

Common variable immunodeficiency (CVID) is a heterogeneous disorder that is associated with low serum-immunoglobulin concentrations, defective specific-antibody production and an increased susceptibility to bacterial infections of the respiratory and gastrointestinal tracts. In spite of the identification of genes that are associated with several known primary immunodeficiencies, the basic immunologic and molecular defects of the majority of patients with CVID have remained obscure. Most of the studies aimed at understanding the immunopathogenesis of CVID suggest that this condition is primarily a T-cell disorder, although renewed attention on the genetic linkage and haplotype analysis in families of patients with CVID and on the role of dendritic cells and B cells has revealed several interesting features. This new information should assist in understanding the pathogenesis of CVID and improving the therapeutic strategies.

Confirmation of the association of the C4B null allelle in autism

The objective of this study was to examine and attempt to confirm our previous findings of an increased frequency of the C4B null allele (C4BQ0) in subjects with autism. Newly identified subjects from Utah and Oregon were studied. Families evaluated included 85 who had a child with autism and 69 control families. Of the subjects with autism studied, 42.4% carried at least one C4BQ0, compared with 14.5% of the control subjects (p = 0.00013), with a relative risk of 4.33. Over half of the C4B null alleles in the subjects with autism involved C4A duplications. A marked increase in the ancestral haplotype 44.1 that lacks a C4B gene and has 2 C4A genes was also observed. The results of this study suggest that the human leukocyte antigen class III C4BQ0 significantly increases the risk for autism.

Clinical and laboratory aspects of common variable immunodeficiency

Common variable immunodeficiency (CVID) is an immunological disorder characterized by defective antibody production, recurrent infections, most notably of the respiratory tract, autoimmune phenomena and cancer. Some CVID patients may also present disturbances of the cellular immune response such as a decrease in the number and proportion of different lymphocyte populations, diminished lymphoproliferative response to mitogens and antigens, altered production of cytokines, and deficient expression of cell-surface molecules. Most Brazilian CVID patients included in this study show a decrease in T and B lymphocyte counts in the peripheral blood. Furthermore, their lymphocytes are more susceptible to apoptosis following activation than normal individuals, and they have a decrease in the expression of activation molecules like CD25, CD69, CD40L and CD70. Moreover, they show a decreased synthesis of IL-4 and IL-5 in comparison with normal individuals. The increase in susceptibility to apoptosis following activation, may also be responsible for the decrease in the expression of activation molecules and CD40L, decrease in Th2 cytokines synthesis, and in the number of T and B circulating cells. In this study we discuss some of these immunological disturbances correlating them to the patients' clinical features and comparing our patients' findings to the literature.

Major histocompatibility complex haplotypes in Spanish immunoglobulin A deficiency patients: a comparative fine mapping microsatellite study

The most consistent finding in Immunoglobulin A deficiency (IgAD) genetics is the presence of susceptibility factors located in the major histocompatibility complex (MHC). We have described the existence of at least two distinct susceptibility genes in the MHC present in different haplotypes. The aim of the present study was to locate with precision the susceptibility genes present in DR1- and DR7-positive haplotypes, taking advantage of their structural diversity, as opposed to the conserved nature of the DR3-extended susceptibility haplotype (DR3/B8), that hampers a more exhaustive scrutiny. A detailed analysis with 20 markers along the MHC in the 400 haplotypes present in 100 IgAD families, with special density at Class II locations, was performed to define the minimal shared susceptibility region present in all haplotypes carrying DR1 and, on the other hand, in all DR7-positive haplotypes. A comparison of the fine microsatellite allele structure of DR-extended haplotypes in the Spanish population with those described for Swedish and British families revealed no difference in DRB1*0101 and DRB1*0102 haplotypes between both populations. Our data suggest that the etiologic mutation present in DRB1*0101 and DRB1*0102 in North Europe (Sweden and UK) is missing in the Spanish DRB1*0101 haplotypes but is present in the DQB1/DRB1 region in DRB1*0102 haplotypes. The results obtained also indicated that the most likely susceptibility gene in the DR7 haplotypes is either DQA1 or DRB1.

The genetics of hypogammaglobulinemia

Etiologies for human hypogammaglobulinemias are diverse and include genetic and nongenetic causes. Although recent reviews focus on the complex genetics of common variable immunodeficiency, in this review, we survey different causes of hypogammaglobulinemias and discuss possible mechanisms.

Autoimmune manifestations in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a disorder characterized by decreased serum immunoglobulin concentrations and increased incidence of recurrent infections. Interestingly 20-25% of patients with CVID develop clinical features suggestive of an autoimmune disease. Although this association is well established, the immunodeficiency background of CVID patients manifesting autoimmune disorders is often overlooked. This study describes three CVID patients displaying a variety of autoimmune manifestations. The pathophysiologic mechanisms of autoimmunity in CVID are also reviewed.

The Complex Genetics of Common Variable Immunodeficiency

Immunoglobulin (lg)A deficiency and common variable immunodeficiency (CVID) are the most common primary immunodeficiency disorders in North America and Europe. These diseases appear to comprise a familial spectrum of immunodeficiency that ranges from partial IgA deficiency to a complete absence of serum immunoglobulin. The CVID phenotype is typically acquired and can spontaneously revert to IgG and IgM sufficiency. Family studies suggest the presence of at least two susceptibility loci within the major histocompatibility complex on the short arm of chromosome 6: one located near the class II region and the other located near the junction between the class III and class I regions. Inheritance of these susceptibility genes may yield an additive risk for the development of immunodeficiency. First-degree family members of patients with CVID are at risk throughout their lives for the development of these diseases and should be monitored with a high index of suspicion.

Common variable immunodeficiency and IgG subclass deficiency in central Alabama hemochromatosis probands homozygous for HFE C282Y

Eight hemochromatosis probands with HFE C282Y homozygosity had frequent, severe, or unusual infections and common variable immunodeficiency (CVID) or immunoglobulin (Ig) G subclass deficiency (IgGSD). Thus, we performed serum Ig isotyping and other characterization of 43 additional unselected probands, 5 human leukocyte antigen (HLA)-identical siblings, and 240 consecutive CVID or IgGSD index patients. C282Y allele frequencies were estimated in 58 CVID or IgGSD index patients without hemochromatosis phenotypes and in 341 controls. HLA-A and -B haplotypes and frequencies were determined in all 51 probands, 186 CVID or IgGSD index patients without hemochromatosis phenotypes, and 751 controls. Thirteen unselected probands (30%) had CVID or IgGSD. Among all 21 hemochromatosis probands with CVID (n = 4) or IgGSD (n = 17), Ig subclass deficiency patterns were IgG(1) (n = 5), IgG(1) and IgG(3) (n = 6), IgG(3) (n = 9), and IgG(1), IgG(3), and IgG(4) (n = 1). IgG(2) or IgA deficiency was not detected; one proband had IgM deficiency. Mean values of total IgG, IgG(1), and IgG(3) were significantly lower in probands with CVID or IgGSD. Mean values of age, transferrin saturation, and ferritin at diagnosis and phlebotomy units required to induce iron depletion were similar in probands with or without CVID or IgGSD; phlebotomy had no apparent effect on IgG levels. C282Y frequencies were similar in CVID or IgGSD index cases without hemochromatosis phenotypes and in controls. There was concordance of Ig and hemochromatosis phenotypes in probands and respective HLA-identical siblings. Eight of 240 CVID or IgGSD index patients had hemochromatosis phenotypes and C282Y homozygosity (3 vs 0.7% and 0.2% controls; P < 0.0001, respectively). The frequency of A*03-B*07 was greater in CVID and IgGSD index cases without hemochromatosis phenotypes than in controls (0.0968 vs 0.0546, respectively; P = 0.0032). HLA-A*03-B*07 was the predominant haplotype in probands grouped by presence or absence of CVID or IgGSD. Some probands in each group were A*03-B*07 homozygotes; group A*03-B*07 frequencies were similar. We conclude that serum IgG abnormalities characteristic of CVID or IgGSD are common in hemochromatosis probands, and that the prevalence of hemochromatosis is increased in CVID and IgGSD index cases. These observations could be explained by the increased frequencies of HLA-A*03-B*07 in C282Y homozygotes and in CVID and IgGSD, and by the common occurrence of putative CVID or IgGSD allele(s) on haplotypes bearing C282Y.

Linkage of autosomal dominant common variable immunodeficiency to chromosome 5p and evidence for locus heterogeneity

Common variable immunodeficiency (CVID, OMIM 240500) and selective immunoglobulin A deficiency (IgAD) are the most frequent primary immunodeficiencies in humans. Of the cases with CVID/IgAD, 20%-25% are familial, but the only previous claims of linkage or association are to the HLA region on chromosome 6p. We report the results of a genome-wide scan in three multiplex families with CVID, IgAD, and dysgammaglobulinemia, where affection is inherited in an autosomal dominant pattern. Two of the families are consistent with linkage to the telomeric region of chromosome 5p, whereas the third is consistent with linkage to the HLA region. Using a locus heterogeneity model and a conservative penetrance model, we obtained a LOD score of 3.35 for the 5p region. We sequenced the exons of one promising candidate gene within this region (PDCD6, also known as ALG-2) but found no causative mutation.

Fine-scale mapping at IGAD1 and genome-wide genetic linkage analysis implicate HLA-DQ/DR as a major susceptibility locus in selective IgA deficiency and common variable immunodeficiency

Selective IgA deficiency (IgAD) and common variable immunodeficiency (CVID) are the most common primary immunodeficiencies in humans. A high degree of familial clustering, marked differences in the population prevalence among ethnic groups, association of IgAD and CVID in families, and a predominant inheritance pattern in multiple-case pedigrees have suggested a strong, shared genetic predisposition. Previous genetic linkage, case-control, and family-based association studies mapped an IgAD/CVID susceptibility locus, designated IGAD1, to the MHC, but its precise location within the MHC has been controversial. We have analyzed a sample of 101 multiple- and 110 single-case families using 36 markers at the IGAD1 candidate region and mapped homozygous stretches across the MHC shared by affected family members. Haplotype analysis, linkage disequilibrium, and homozygosity mapping indicated that HLA-DQ/DR is the major IGAD1 locus, strongly suggesting the autoimmune pathogenesis of IgAD/CVID. This is supported by the highest excess of allelic sharing at 6p in the genome-wide linkage analysis of 101 IgAD/CVID families using 383 marker loci, by previously reported restrictions of the T cell repertoires in CVID, the presence of autoantibodies, impaired T cell activation, and a dysregulation of a number of genes in the targeted immune system. IgAD/CVID may thus provide a useful model for the study of pathogenesis and novel therapeutic strategies in autoimmune diseases.

MHC susceptibility genes to IgA deficiency are located in different regions on different HLA haplotypes

Familial predisposition to IgA deficiency (IgAD) suggests that genetic factors influence susceptibility. Most studies support a polygenic inheritance with a susceptibility locus (designated IGAD1) in the MHC, but its exact location is still controversial. This study aimed to map the predisposing IGAD1 locus (or loci) within the MHC by investigating the pattern of association of the disease with several markers in the region. DNA-based techniques were used to type individual alleles of four polymorphic HLA genes (HLA-DR, -DQA1, -DQB1, and HLA-B), six microsatellites (all located between HLA-DR and HLA-B), and three single nucleotide polymorphisms on the TNF gene. The frequencies of these alleles were compared among ethnically matched populations comprising 182 patients and 343 controls. Additionally, we investigated parents and siblings of 100 of these patients. All four parental haplotypes were established in each family (n = 400), and transmission disequilibrium tests were performed. Surprisingly, our results did not support the hypothesis of a unique susceptibility gene being shared by all MHC susceptibility haplotypes. On HLA-DR1 and -DR7-positive haplotypes IGAD1 mapped to the class II region, whereas on haplotypes carrying HLA-DR3 the susceptibility locus mapped to the telomeric end of the class III region, as reported previously. Our results show how, in complex diseases, individuals may be affected for different genetic reasons and a single linkage signal to a region of a chromosome may actually be the result of disease-predisposing alleles in different linked genes in different pedigrees.

Panhypopituitarism in a child with common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) represents a group of heterogeneous, still undifferentiated, syndromes that are all characterized by defective antibody formation. It is often associated with autoimmune disease.

METHODS

An African-American girl was diagnosed with CVID at age 3 years. She was seen during an adrenal crisis precipitated by pneumonia at the age of 8 years and 10 months. The diagnosis of panhypopituitarism was established soon after.

RESULTS

Panhypopituitarism in this patient was believed to be the result of the autoimmune process known as lymphocytic hypophysitis. This hypothesis was suggested by the results of magnetic resonance imaging.

CONCLUSIONS

Awareness of the possibility of this process in children or adults with CVID may lead to earlier diagnosis of panhypopituitarism. These patients also have failure to thrive, and earlier diagnosis may avoid a life-threatening event.

Primary immunodeficiency diseases: dissectors of the immune system

The past 50 years have seen enormous progress in this field. An unknown concept until 1952, there are now more than 100 different primary immunodeficiency syndromes in the world's literature. Each novel syndrome has shed new insight into the workings of the immune system, dissecting its multiple parts into unique functioning components. This has been especially true over the past decade, as the molecular bases of approximately 40 of these diseases have been identified in rapid succession. Advances in the treatment of these diseases have also been impressive. Antibody replacement has been improved greatly by the development of human immunoglobulin preparations that can be safely administered by the intravenous route, and cytokine and humanized anticytokine therapies are now possible through recombinant technologies. The ability to achieve life-saving immune reconstitution of patients with lethal severe combined immunodeficiency by administering rigorously T-cell-depleted allogeneic related haploidentical bone marrow stem cells has extended this option to virtually all such infants, if diagnosed before untreatable infections develop. Finally, the past 3 years have witnessed the first truly successful gene therapy. The impressive results in X-linked severe combined immunodeficiency offer hope that this approach can be extended to many more diseases in the future.

Central MHC genes affect IgA levels in the human: reciprocal effects in IgA deficiency and IgA nephropathy

This study investigates the hypothesis that alternative alleles of one or more genes in the central major histocompatibility complex (MHC) predispose carriers to IgA deficiency (IgAD) or IgA Nephropathy (IgAN). Australian caucasian IgAD, IgAN patients, and controls were typed at HLA loci, single nucleotide polymorphisms, and microsatellites in the MHC. Alleles of the D6S273 microsatellite exhibited strong associations with IgAD and IgAN. D6S273*129 and *139 were more frequent in IgAD and less frequent in IgAN patients than controls. The reverse was true for D6S273*133 and *131. Alleles of other microsatellites exhibited weak associations with IgAD or IgAN. D6S273*129 is found on the 65.1 ancestral haplotype [HLA-B14(65),DR1], which has been reported to be increased in IgAD, but the majority of IgAD patients with D6S273*129 did not have other alleles of the haplotype. D6S273*139 is characteristic of the 8.1 ancestral haplotype (HLA-A1,B8,DR3), which was common in IgAD and rare in IgAN patients. Further studies of the 8.1 haplotype in Australian, German and Spanish caucasian subjects revealed that HLA-DR3, in the absence of -B8, is not associated with IgAD. However -B8 is associated with IgAD in the absence of -DR3, consistent with a susceptibility locus in the central MHC. Provisional mapping within this region is discussed.

Neutropenia associated with primary immunodeficiency syndromes

The primary immunodeficiency diseases are a heterogeneous group of more than 75 disorders characterized by intrinsic defects in the functions of the immune system. Many are associated with abnormalities of hematopoiesis as well. This article will review those primary immunodeficiency syndromes in which neutropenia is a prominent finding, including X-linked agammaglobulinemia (XLA), hyper IgM syndrome, common variable immunodeficiency (CVID), IgA deficiency, cartilage-hair hypoplasia (CHH), and reticular dysgenesis, with regards to pathophysiologic findings and treatment.

Primary immunodeficiency disorders: antibody deficiency

As a group, antibody deficiencies represent the most common types of primary immune deficiencies in human subjects. Often symptoms do not appear until the latter part of the first year of life, as passively acquired IgG from the mother decreases to below protective levels. As with the T-cell immune deficiencies, the spectrum of antibody deficiencies is broad, ranging from the most severe type of antibody deficiency with totally absent B cells and serum Igs to patients who have a selective antibody deficiency with normal serum Ig. In addition to the increased susceptibility to infections, a number of other disease processes (eg, autoimmunity and malignancies) can be involved in the clinical presentation. Fortunately, the availability of intravenous immune serum globulin has made the management of these patients more complete. Recently, molecular immunology has led to identification of the gene or genes involved in many of these antibody deficiencies. As discussed in this review, this has led to a better elucidation of the B-cell development and differentiation pathways and a more complete understanding of the pathogenesis of many of these antibody deficiencies.

Giant cell myocarditis in a 12-year-old girl with common variable immunodeficiency

Giant cell myocarditis (GCM) is a rare and often fatal disease that infrequently affects children. Common variable immunodeficiency (CVID) describes a heterogeneous group of disorders characterized by hypogammaglobulinemia and poor specific antibody responses. To our knowledge, CVID and GCM have not been reported together in 1 patient. We describe a 12-year-old girl with CVID who developed acute severe GCM that necessitated cardiac transplantation. Histopathological and immunohistochemical studies of the endomyocardial biopsy specimen and the explanted heart revealed numerous histiocytes, eosinophils, T cells, and multinucleated giant cells. Both CVID and GCM are thought to involve dysregulation of T-cell function and have been associated with a similar spectrum of autoimmune conditions. The coincidence of CVID and GCM in a single patient may reflect a pathophysiologic connection.

Terminal defects of B lymphocyte differentiation

In humans several abnormalities can occur during terminal B cell differentiation, leading to primary humoral immunodeficiencies. A recent study provided evidence of a qualitative defect of the affinity antibody maturation in some patients affected with common variable immunodeficiency syndrome, the molecular basis of which remains unknown. Several genetic defects in class switch recombination leading to a hyper-IgM syndrome have recently been delineated. Besides the well-known role of CD40-CD40 ligand interaction, they definitively demonstrate the requirement of CD40-mediated nuclear factor kappa B activation and the essential role of a newly described molecule, the activation-induced cytidine deaminase, in B cell terminal differentiation.

Analysis of SWAP-70 as a candidate gene for non-X-linked hyper IgM syndrome and common variable immunodeficiency

SWAP-70 is a recently identified protein that functions as the only B cell-specific component of an isotype switch recombination complex called SWAP. The SWAP complex has specificity for the switch regions upstream of the constant region immunoglobulin genes and it facilitates the transfer of DNA between switch regions. These features suggested that mutations in the gene encoding SWAP-70 might result in humoral immunodeficiency. To test this hypothesis we determined the genomic structure of this gene and used single-stranded conformational polymorphism (SSCP) analysis to screen DNA from 38 patients with either non-X-linked hyper IgM syndrome or common variable immunodeficiency. The results demonstrated that SWAP-70 consists of 12 exons spread over 89 kb at chromosome 11p15.2. SSCP analysis of the patient population revealed five polymorphic variants in the gene, one of which (Q505E) is an amino acid substitution in the putative nuclear export signal of SWAP-70. However, none of the alterations appeared to be associated with disease in the patients screened.

G6b, a novel immunoglobulin superfamily member encoded in the human major histocompatibility complex, interacts with SHP-1 and SHP-2

The G6b gene, located in the class III region of the human major histocompatibility complex, has been suggested to encode a putative receptor of the immunoglobulin superfamily. Genomic sequence information was used as a starting point to clone the corresponding cDNA. Reverse transcriptase polymerase chain reaction showed that expression of the gene is restricted to certain hematopoietic cell lines including K562, Molt 4, and Jurkat. Several splice variants were detected, varying only in their C-terminal parts. One of the potential membrane-bound isoforms contained two immunoreceptor tyrosine-based inhibitory motifs in its cytoplasmic tail. Four of the isoforms were expressed as epitope-tagged proteins in the cell lines K562 and COS-7. The two splice isoforms lacking the hydrophobic transmembrane segment were secreted from the cell. Glycosidase treatment of the four recombinant proteins provided evidence for N- and O-glycosylation. Immunofluorescence studies indicated that the spliced isoforms having a transmembrane segment were directed to the cell membrane. The G6b isoform containing two immunoreceptor tyrosine-based inhibitory motifs in its cytoplasmic tail was found to be phosphorylated on tyrosine residues after pervanadate treatment of cells and, subsequently, interacts with the SH2-containing protein-tyrosine phosphatases SHP-1 and SHP-2. Mutagenesis studies showed that phosphorylation of tyrosine 211 is critical for the interaction of G6b with SHP-1 and SHP-2.