A study of the association of HLA DR, DQ, and complement C4 alleles with systemic lupus erythematosus in Iceland

TScan-II: A genome-scale platform for the de novo identification of CD4+ T cell epitopes

CD4+ T cells play fundamental roles in orchestrating immune responses and tissue homeostasis. However, our inability to associate peptide human leukocyte antigen class-II (HLA-II) complexes with their cognate T cell receptors (TCRs) in an unbiased manner has hampered our understanding of CD4+ T cell function and role in pathologies. Here, we introduce TScan-II, a highly sensitive genome-scale CD4+ antigen discovery platform. This platform seamlessly integrates the endogenous HLA-II antigen-processing machinery in synthetic antigen-presenting cells and TCR signaling in T cells, enabling the simultaneous screening of multiple HLAs and TCRs. Leveraging genome-scale human, virome, and epitope mutagenesis libraries, TScan-II facilitates de novo antigen discovery and deep exploration of TCR specificity. We demonstrate TScan-II's potential for basic and translational research by identifying a non-canonical antigen for a cancer-reactive CD4+ T cell clone. Additionally, we identified two antigens for clonally expanded CD4+ T cells in Sjögren's disease, which bind distinct HLAs and are expressed in HLA-II-positive ductal cells within affected salivary glands.

Impact of C4, C4A and C4B gene copy number variation in the susceptibility, phenotype and progression of systemic lupus erythematosus

BACKGROUND

Complement component 4 (C4) gene copy number (GCN) affects the susceptibility to systemic lupus erythematosus (SLE) in different populations, however the possible phenotype significance remains to be determined. This study aimed to associate C4A, C4B and total C4 GCN and SLE, focusing on the clinical phenotype and disease progression.

METHODS

C4, C4A and C4B GCN were determined by real-time PCR in 427 SLE patients and 301 healthy controls, which underwent a detailed clinical evaluation according to a pre-established protocol.

RESULTS

The risk of developing SLE was 2.62 times higher in subjects with low total C4 GCN (< 4 copies, OR = 2.62, CI = 1.77 to 3.87, p < 0.001) and 3.59 times higher in subjects with low C4A GCN (< 2 copies; OR = 3.59, CI = 2.15 to 5.99, p < 0.001) compared to those subjects with normal or high GCN of total C4 (≥4) and C4A (≥2), respectively. An increased risk was also observed regarding low C4B GCN, albeit to a lesser degree (OR = 1.46, CI = 1.03 to 2.08, p = 0.03). Furthermore, subjects with low C4A GCN had higher permanent disease damage as assessed by the Systemic Lupus International Collaborating Clinics - Damage Index (SLICC-DI; median = 1.5, 95% CI = 1.2-1.9) than patients with normal or high copy number of C4A (median = 1.0, 95% CI = 0.8-1.1; p = 0.004). There was a negative association between low C4A GCN and serositis (p = 0.02) as well as between low C4B GCN and arthritis (p = 0.02).

CONCLUSIONS

This study confirms the association between low C4 GCN and SLE susceptibility, and originally demonstrates an association between low C4A GCN and disease severity.

Association of HLA-DR3 and HLA-DR15 Polymorphisms with Risk of Systemic Lupus Erythematosus

Background:

Systemic lupus erythematosus (SLE) is an autoimmune disease under genetic control. Growing evidences support the genetic predisposition of HLA-DRB1 gene polymorphisms to SLE, yet the results are not often reproducible. The purpose of this study was to assess the association of two polymorphisms of HLA-DRB1 gene (HLA-DR3 and HLA-DR15) with the risk of SLE via a comprehensive meta-analysis.

Methods:

This study complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Case-control studies on HLA-DRB1 and SLE were searched from PubMed, Elsevier Science, Springer Link, Medline, and Cochrane Library database as of June 2018. Analysis was based on the random-effects model using STATA software version 14.0.

Results:

A total of 23 studies were retained for analysis, including 5261 cases and 9838 controls. Overall analysis revealed that HLA-DR3 and HLA-DR15 polymorphisms were associated with the significant risk of SLE (odds ratio [OR]: 1.60, 95% confidence interval (CI): 1.316–1.934, P = 0.129 and OR: 1.68, 95% CI: 1.334–2.112, P = 0.001, respectively). Subgroup analyses demonstrated that for both HLA-DR3 and HLA-DR15 polymorphisms, ethnicity was a possible source of heterogeneity. Specifically, HLA-DR3 polymorphism was not associated with SLE in White populations (OR: 1.60, 95% CI: 1.320–1.960, P = 0.522) and HLA-DR15 polymorphism in East Asian populations (OR: 1.65, 95% CI: 1.248–2.173, P = 0.001). In addition, source of control was another possible source for both HLA-DR3 and HLA-DR15 polymorphisms, with observable significance for HLA-DR3 in only population-based studies (OR: 1.65, 95% CI: 1.370–1.990, P = 0.244) and for HLA-DR15 in both population-based and hospital-based studies (OR: 1.38, 95% CI: 1.078–1.760, P = 0.123 and OR: 2.08, 95% CI: 1.738–2.490, P = 0.881, respectively).

Conclusions:

HLA-DRB1 gene may be a SLE-susceptibility gene, and it shows evident ethnic heterogeneity. Further prospective validations across multiple ethnical groups are warranted.

Low copy numbers of complement C4 and homozygous deficiency of C4A may predispose to severe disease and earlier disease onset in patients with systemic lupus erythematosus

Objectives Low copy numbers and deletion of complement C4 genes are potent risk factors for systemic lupus erythematosus (SLE). However, it is not known whether this genetic association affects the clinical outcome. We investigated C4 copy number variation and its relationship to clinical and serological features in a Northern European lupus cohort. Methods We genotyped the C4 gene locus using polymerase chain reaction (PCR)-based TaqMan assays in 169 patients with SLE classified according to the 1997 revised American College of Rheumatology (ACR) criteria and in 520 matched controls. In the patient group the mean C4 serum protein concentrations nephelometrically measured during a 12-month period prior to genetic analysis were compared to C4 gene copy numbers. Severity of disease was classified according to the intensity of the immunosuppressive regimens applied and compared to C4 gene copy numbers, too. In addition, we performed a TaqMan based analysis of three lupus-associated single-nucleotide polymorphisms (SNPs) located inside the major histocompatibility complex (MHC) to investigate the independence of complement C4 in association with SLE. Results Homozygous deficiency of the C4A isotype was identified as the strongest risk factor for SLE (odds ratio (OR) = 5.329; p = 7.7 × 10^-3) in the case-control comparison. Moreover, two copies of total C4 were associated with SLE (OR = 3.699; p = 6.8 × 10^-3). C4 serum levels were strongly related to C4 gene copy numbers in patients, the mean concentration ranging from 0.110 g/l (two copies) to 0.256 g/l (five to six copies; p = 4.9 × 10^-6). Two copies of total C4 and homozygous deletion of C4A were associated with a disease course requiring cyclophosphamide therapy (OR = 4.044; p = 0.040 and OR = 5.798; p = 0.034, respectively). Homozygous deletion of C4A was associated with earlier onset of SLE (median 24 vs. 34 years; p = 0.019) but not significant after correction for multiple testing. SNP analysis revealed a significant association of HLA-DRB1*0301 with SLE (OR = 2.231; p = 1.33 × 10^-5). Conclusions Our findings confirm the important role of complement C4 genes in the development of SLE. Beyond the impact on the susceptibility for lupus, C4 copy numbers may be related to earlier onset and a more severe course of the disease. The association of homozygous deletion of C4A and SLE is accompanied by the presence of HLA-DRB1*0301 without a proven pathophysiological mechanism.

Low C4, C4A and C4B gene copy numbers are stronger risk factors for juvenile-onset than for adult-onset systemic lupus erythematosus

OBJECTIVE

Complete deficiency of Complement C4 component is a strong genetic risk factor for SLE. C4 is encoded by two different genes, C4A and C4B, which show considerable gene copy number (GCN) variation. This study investigates the association of total C4, C4A and C4B GCN with JSLE.

METHODS

Ninety JSLE patients, 170 adult-onset SLE (aSLE) patients and 200 healthy individuals were evaluated for C4A and C4B GCN by quantitative real-time PCR.

RESULTS

JSLE patients had lower GCN for C4A (mean = 1.7; 95% CI: 1.5, 1.9) and C4B (mean = 1.5; 95% CI: 1.3, 1.6) compared with healthy individuals (mean C4A = 2.3; 95% CI: 2.2, 2.5, P < 0.001; C4B = 2.0; 95% CI: 1.8, 2.1; P < 0.001) or with aSLE patients (mean C4A = 1.9; 95% CI: 1.8, 2.1, P = 0.006; mean C4B = 1.8; 95% CI: 1.7, 1.9, P < 0.001). Low total C4 GCN (<4 copies) was more frequent in JSLE than in healthy individuals (59% vs 28%; P < 0.001). The same was observed for low C4A (⩽1 copy) (52% vs 18%; P < 0.001) and for low C4B (60% vs 31%; P < 0.001). JSLE had a stronger association with low total C4 (OR = 3.68, 95% CI: 2.19, 6.20), C4A (OR = 4.98, 95% CI: 2.88, 8.62) and C4B (OR = 3.26; 95% CI: 1.95, 5.47) than aSLE (C4 OR = 2.03; 95% CI: 1.32, 3.13; C4A OR = 2.36; 95% CI: 1.46, 3.81; C4B OR = 1.13; 95% CI: 0.73, 1.74). In addition, pericarditis in JSLE patients was associated with low C4 (OR = 4.13; 95% CI: 1.02, 16.68; P = 0.047) and low C4A (OR = 5.54; 95% CI: 1.37, 22.32; P = 0.016).

CONCLUSION

Low total C4, C4A and C4B GCN were associated with a stronger risk for developing JSLE than aSLE. Additionally, low total C4 and C4A GCN are risk factors for pericarditis in JSLE.

Value of HLA-DR genotype in systemic lupus erythematosus and lupus nephritis: a meta-analysis

AIM

Human leukocyte antigen (HLA)-DRB1 allele polymorphisms have been reported to be associated with systemic lupus erythematosus (SLE) susceptibility, but the results of these previous studies have been inconsistent. The purpose of the present study was to systematically summarize and explore whether specific HLA-DRB1 alleles confer susceptibility or resistance to SLE and lupus nephritis.

METHODS

This review was guided by the preferred reporting items for systematic reviews and meta-analyses (PRISMA) approach. A comprehensive search was made for articles from PubMed, Medline, Elsevier Science, Springer Link and Cochrane Library database. A total of 25 case-control studies on the relationship between gene polymorphism of HLA-DRB l and SLE were performed and data were analyzed and processed using Review Manager 5.2 and Stata 11.0.

RESULTS

At the allelic level, HLA-DR4, DR11 and DR14 were identified as protective factors for SLE (0.79 [0.69,0.91], P < 0.001; 0.72 [0.60, 0.85], P < 0.0001; 0.47 [0.59, 0.95], P < 0.05, respectively). HLA-DR3, DR9, DR15 were potent risk factors for SLE (1.88 [1.58, 2.23], P < 0.001; 1.24 [1.07, 1.45], P < 0.05; 1.25 [1.10, 1.43], P < 0.001, respectively). However, HLA-DR8 was not statistically significant between the SLE group and control group (OR, 1.11 [0.96, 1.30], P > 0.05). DR4 and 11 (OR, 0.55 [0.39, 0.79], P < 0.01; 0.60 [0.37, 0.96], P < 0.05, respectively) conferred a significant protective effect for lupus nephritis. DR3 and DR15 (OR, 2.00 [1.49, 2.70], P < 0.05; 1.60 [1.21, 2.12], P < 0.001, respectively) were at a high risk of developing lupus nephritis. HLA-DR8, DR9 and DR14 (OR, 1.47 [0.9, 2.33], P > 0.05; 0.90 [0.64, 1.27], P > 0.05; 0.61 [0.36, 1.03], P > 0.05, respectively) were not statistically significant between the lupus nephritis and control groups.

CONCLUSIONS

The HLA-DR4, DR11, DR14 alleles might be protective factors for SLE and HLA-DR3, DR9, DR15 were potent risk factors. In addition, HLA-DR4 and DR11 alleles might be protective factors for lupus nephritis and DR3 and DR15 suggest a risk role. These results proved that HLA-DR3, DR15, DR4 and DR11 might be identified as predictors for lupus nephritis and SLE.

Clearance of dying cells and systemic lupus erythematosus: the role of C1q and the complement system

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease of unknown etiology characterized by the presence of pathogenic high-titer autoantibodies to a diverse group of autoantigens. In 88% of patients, autoantibodies are present an average of 3.3 years before diagnosis. Antinuclear, anti-Ro, anti-La, and anti-phospholipid antibodies appear first, followed by anti-DNA, anti-Smith and anti-ribonucleoprotein. These autoantibodies have features of an antigen-driven, T-cell-dependent immune response. Once present, the course of SLE is characterized by disease flares and autoimmune dysregulation. Programmed cell death (PCD), an essential developmental and homeostatic mechanism, is the preferred physiological death processes for cells as well as an important immune response regulator. Appropriate clearance of apoptotic material completes the PCD process, and is essential for regulating of inflammation and maintaining self-tolerance. Early complement proteins are important in protecting humans against the development of SLE and the protective role of C1q and complement in SLE is mainly related to their role in clearance of dying cells. However, the complement system is also an important ingredient in inflammation, which mediates SLE pathogenesis. Thus, the question remains whether complement factors have either a protective or a destructive role, or a combination of both.

Primary immunodeficiency and autoimmunity: lessons from human diseases

Primary immunodeficiency diseases (PID) are a genetically heterogenous group of >150 disorders that affect distinct components of the innate and adaptive immune system and are often associated with autoimmune diseases. We describe PID affecting T-regulatory cells, complement and B cells or their products and discuss the possibility of a cause-effect relationship. The high concordance of T-regulatory cell defects to organ-specific autoimmune disease implies an obligatory role of these cells in maintaining tolerance to epithelial and endocrine tissues; the absence of central nervous system involvement may reflect immunological privilege. Congenital defects in C1q, C1r/s and C4 are strongly associated with systemic lupus erythematosus (SLE), and this pattern along with laboratory evidence suggests a major importance of classical pathway activity in safe elimination of immune complexes and prevention of immune complex disease (ICD). It is debatable whether this ICD is to be regarded as an autoimmune disease (resulting from a breakdown of immunological ignorance to antigens that are normally hidden), as autoantibodies may be absent, and tissue damage because of deposition of immune complexes could account for all of the pathology observed. Evidence for a causative link between primary antibody deficiencies and autoimmune disease is much less compelling and may in fact involve a common genetic background. However, arguments have also been made in favour of the notion that an intense antigen load as a result of recurrent or persistent infections may affect either tolerance or ignorance, e.g. by molecular mimicry or the presence of superantigens. Similar immunological mechanisms might account for the vast majority of autoimmune diseases.

Genetic aspects of rheumatic diseases

In this review on the genetic aspects of rheumatic diseases, the approach was taken (i) to discuss, in general, important principles in the identification of susceptibility genes and (ii) to focus on five autoimmune rheumatic diseases that have the characteristics of complex diseases and in which important advances have been made in the identification of the genetic component. A decade ago, most reviews on the genetics of rheumatic diseases focused almost exclusively on a discussion of the human leukocyte antigen (HLA) but in this fast-moving field it is now apparent that genes outside the HLA also contribute to susceptibility. Current hypotheses concerning the pathogenesis of autoimmunity have led to the inclusion of hundreds of genes as potential candidates. Almost any molecule involved in immune recognition, cell interaction, intracellular signalling, cytokine pathways or programmed cell death can be reasonably proposed. The identification of the genes involved in complex diseases will contribute to an understanding of disease mechanisms and disease biology. The disease pathways by which the genes exert their effects or functions could lead to the discovery of new therapeutic targets that may be modulated. An increased understanding of the interactions between genes and environment might also be attained.

A study of association of the complement C4 mutations with systemic lupus erythematosus in the Malaysian population

The aim of the present study was to investigate the association of C4 gene mutations with systemic lupus erythematosus, in 130 Malaysian SLE patients and 130 healthy controls. Generally, various PCR approaches were used to screen the mutations of the C4 genes, which included 2 bp (+TC) insertions at codon 1213 in exon 29, 1 bp deletions (-C) at codon 811 in exon 20, 1 bp (-C), 2 bp (-GT) deletions at codons 522 and 497 in exon 13 and null alleles. No mutations located at exons 13, 20 and 29 of the C4 gene, were detected amongst the patient and control samples in this study. C4A*Q0 was found in two out of the 130 control samples, while C4B*Q0 was present in two out of the 130 SLE patients. Overall, our results do not demonstrate a significant association to these known C4 mutations identified by previous studies, in the Malaysian scenario.

Defective prevention of immune precipitation in autoimmune diseases is independent of C4A*Q0

Increased prevalence of C4 null alleles is a common feature of autoimmune diseases. We have shown previously that complement-dependent prevention of immune precipitation (PIP) is defective in patients with systemic lupus erythematosus (SLE), and correlated this defect with C4A*Q0 and low levels of the C4A isotype. To further clarify the role of C4A in the aetiology of SLE, we now extend our studies to other diseases which have been associated with C4A*Q0. The frequency of C4A*Q0 was increased in Icelandic patients with coeliac disease (0.50; P < 0.001), Grave's disease (0.30; P = 0.002) and insulin-dependent diabetes mellitus (0.23; P = 0.04) and in British patients with dermatitis herpetiformis (0.42; P = 0.002) and this was reflected in low levels of C4A. In spite of this, PIP was normal in these patients, and in marked contrast to our previous observations on connective tissue diseases, PIP measurements in these patient groups correlated more strongly with levels of C4B (r = 0.51, P = 0.0000004) than C4A. Patients with increased levels of anti-C1q antibodies had significantly lower PIP than patients without such antibodies (P < 0.01) and a negative association of PIP with anti-C1q antibodies was also reflected in an increased prevalence (P = 0.006) and levels (P = 0.006) of anti-C1q antibodies in patients with subnormal PIP, as well as a negative correlation between PIP and anti-C1q antibodies (r = - 0.25, P = 0.02). These results show that the PIP defect cannot be explained by low levels of C4A alone and suggest that measurements of anti-C1q antibodies may be useful in future studies on the molecular cause of the PIP defect in autoimmune connective tissue disease.

A protective role for innate immunity in systemic lupus erythematosus

Clinical and genetic studies in humans and animal models indicate a crucial protective role for the complement system in systemic lupus erythematosus (SLE). This presents a paradox because the complement system is considered to be an important mediator of the inflammation that is observed in patients with SLE. One current view is that complement provides protection by facilitating the rapid removal of apoptotic debris to circumvent an autoimmune response. In this Opinion article, I discuss an alternative model in which complement - together with other components of the innate immune system - participates in the 'presentation' of SLE-inducing self-antigens to developing B cells. In this way, the complement system and innate immunity protect against responses to SLE (self) antigens by enhancing the elimination of self-reactive lymphocytes.

Patients with systemic lupus erythematosus are deficient in complement-dependent prevention of immune precipitation

OBJECTIVE

A functional deficiency of complement has been implicated but not conclusively demonstrated in the pathogenesis of systemic lupus erythematosus (SLE). To test this, we studied several aspects of complement in 44 patients with SLE, 46 patients with rheumatoid arthritis and 102 blood donors.

METHODS

Prevention of immune precipitation (PIP) was measured by an enzyme immunoassay, levels of C1q, C4 and C3 by rocket immunoelectrophoresis, C4A, C4B and C3d by enzyme-linked immunosorbent assay (ELISA), complement haemolysis (CH50) by standard methods and C4 allotypes by high-voltage agarose electrophoresis and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

PIP was significantly reduced in SLE (P<0.001); the defect was revealed by a sensitive assay measuring this function of complement but not by the other tests employed. The patients were clinically well at the time of study, and levels of C3d, which have been shown to correlate with disease activity, were normal. The defect was more common in patients with early disease (P = 0.009), supporting a role in aetiology or early pathophysiology. PIP was positively correlated with levels of C4 (P = 3 x 10(-5)) and in particular the C4A isotype (P = 9 x 10(-10)) whereas C4B was redundant.

CONCLUSIONS

Our results reveal a defect in prevention of immune precipitation in SLE that is apparent at an early stage in the disease and correlates with low levels of C4A. These results indicate that subtle deficiencies of complement may predispose to SLE.

The involvement of HLA -DRB1*, DQA1*, DQB1* and complement C4A loci in diagnosing systemic lupus erythematosus among Tunisians

BACKGROUND

Genetic susceptibility to systemic lupus erythematosus (SLE) varies among populations. Few data exist on associations of HLA class II and class III alleles of the major histocompatibility complex (MHC) and susceptibility to SLE in Tunisians.

PATIENTS AND METHODS

We compared HLA-DRB1*, DQA1, DQB1* and C4 allotypes in 62 Tunisian SLE patients and 100 matched controls. We also assessed the association of specific alleles with distinct autoantibody profiles in SLE patients.

RESULTS

HLA-DRB1*0301, -DRB1*1501 and C4AQO alleles were increased in the SLE patients, while the frequencies of HLA-DRB1*04 and DQB1*03 were decreased. HLA-DQA1*0102 and DQA1*0501 were significantly increased in the SLE patients. HLA-DQB1*0201 and DQB1*0602 were more frequent in the SLE patients. C4A*QO and C4B*QO were increased in frequency in the SLE patients compared to the controls, but only C4A null was significantly increased. Eleven of 17 SLE patients with the C4 null allele were HLA-DRB1*0301 positive. Three of 16 SLE patients with HLA-DRB1*1501 were associated with HLA-DQB1*0501 rather than DQB1*0602, as has been reported in European SLE patients.

CONCLUSIONS

The MHC class II alleles (DRB1, DQA1, DQB1) and C4 null associations noted in other ethnic groups are also found in Tunisians, suggesting shared susceptibility factors across ethnic lines in predisposition to SLE. In contrast to other ethnic groups, MHC class II alleles are not associated with the presence of specific autoantibodies in Tunisian SLE patients.

The genetics of systemic lupus erythematosus: putting the pieces together

With lambda(s) estimates of 10 to 20 and other evidence of familial aggregation, as well as a monozygotic twin concordance rate >20, systemic lupus erythematosus (SLE) would appear to be a very promising phenotype using modern genetic approaches. Indeed, genetic associations are already known at numerous candidate loci including various HLA alleles, complement component genes, Fcgamma receptors, and others, and murine genetic studies of lupus models have provided additional candidate genes and potential syntenic linkages to evaluate in man. The completed genetic linkage studies performed on various collections of pedigrees multiplex for SLE have identified 60 susceptibility loci with varying degrees of evidence for linkage in man. Seven of these meet or exceed the threshold for significant linkage (LOD > or = 3.3 or P < or = 0.00005) at 1q22-23, 1q41, 2q37, 4p16, 6p21-11, 16q13 and 17p13. In addition, these linkages usually dominate in one ethnicity or another, suggesting that the responsible polymorphisms, once identified, will also vary by ethnicity. Evidence that these linkages can be reproduced range from outright independent confirmation (1q41, 4p16 and 6p21) to additional suggestive evidence in the genomic region of the purported linkage (1q22-23 and 2q37). The results now available suggest that human lupus genetics are robust and that gene identification should be possible using existing genetic approaches and technologies.

Association between a catechol-o-methyltransferase polymorphism and obsessive-compulsive disorder in the Afrikaner population

BACKGROUND

It has been proposed that the catechol-o-methyl transferase gene (COMT) may play a role in the pathogenesis of obsessive-compulsive disorder (OCD). Whereas studies in a North American population showed that the low activity (L) allele of a functional polymorphism in COMT was associated with OCD in male patients, this result was not supported by studies in a Japanese population. The present association study assessed the risk for OCD conferred by this COMT polymorphism in a geographically different patient group, namely, the relatively genetically homogeneous Afrikaner population of South Africa.

METHODS

Fifty-four unrelated OCD patients and fifty-four sex-matched controls were recruited from the same Afrikaner community. Patients and controls were phenotyped (DSM-IV) and genotyped for a NlaIII polymorphism with H (high activity) or L (low activity) alleles in the COMT gene.

RESULTS

The H/L genotype was significantly more common than expected in the OCD patient group (P = 0.0017).

LIMITATIONS

Replication studies with related individuals may be useful in discovering factors underpinning the H/L genotype abundance in the Afrikaner population.

CONCLUSIONS

These results emphasise the need for further studies in genetically homogeneous populations to help define the complex etiology of this disease.

Long PCR detection of the C4A null allele in B8-C4AQ0-C4B1-DR3

The genes coding for the two components of complement 4 (C4), C4A and C4B, are located within the major histocompatibility complex (MHC) on the short arm of chromosome 6. Several studies have shown that deficiency of C4A is associated with systemic lupus erythematosus (SLE), rheumatoid arthritis and scleroderma. A large deletion covering most of the C4A gene and the 21-hydroxylase-A (21-OHA) pseudogene found on the extended haplotype B8-C4AQ0-C4B1-DR3 is estimated to account for approximately two-thirds of C4A deficiency in Caucasian SLE patients. Detection of this C4A null allele has been technically difficult due to the high degree of homology between C4A and C4B, with protein analysis and restriction fragment length polymorphism (RFLP) analysis using Southern blotting being the only approaches available. In this study, a long PCR strategy was used to rapidly genotype for the C4A deletion through specific primer design. The methodology makes use of the unique sequence of the G11 gene upstream of C4A and the sequence of a 6.4 kb retrotransposon, the human endogenous retrovirus HERV-K(C4), which is present in intron 9 of C4A but absent in the case of the deletion.

A susceptibility locus for human systemic lupus erythematosus (hSLE1) on chromosome 2q

To identify chromosomal regions containing susceptibility loci for systemic lupus erythematosus (SLE), we performed genome scans in families with multiple SLE patients from Iceland, a geographical and genetic isolate, and from Sweden. A number of chromosomal regions showed maximum lod scores (Z) indicating possible linkage to SLE in both the Icelandic and Swedish families. In the Icelandic families, five regions showed lod scores greater than 2.0, three of which (4p15-13, Z=3.20; 9p22, Z=2.27; 19q13, Z=2.06) are homologous to the murine regions containing the lmb2, sle2 and sle3 loci, respectively. The fourth region is located on 19p13 (D19S247, Z=2.58) and the fifth on 2q37 (D2S125, Z=2.06). Only two regions showed lod scores above 2.0 in the Swedish families: on chromosome 2q11 (D2S436, Z=2. 13) and 2q37 (D2S125, Z=2.18). The combination of both family sets gave a highly significant lod score at D2S125 of Z=4.24 in favor of linkage for 2q37. This region represents a new locus for SLE. Our results underscore the importance of studying well-defined populations for genetic analysis of complex diseases such as SLE.