Genetic susceptibility confers significant risk for systemic lupus erythematosus (SLE). The MHC region and other polymorphic loci have been associated with SLE. Because more compelling evidence for an involvement of a genetic locus includes linkage, we tested a candidate region homologous to a murine SLE susceptibility region in 52 SLE-affected sibpairs from three ethnic groups. We analyzed seven microsatellite markers from the human chromosome 1q31-q42 region corresponding to the telomeric end of mouse chromosome 1, the region where specific manifestations of murine lupus, including glomerulonephritis and IgG antichromatin, have been mapped. Comparing the mean allele sharing in affected sibpairs of each of these seven markers to their expected values of 0.50, only the five markers located at 1q41-q42 showed evidence for linkage (P = 0.0005-0.08). Serum levels of IgG antichromatin also showed evidence for linkage to two of these five markers (P = 0.04), suggesting that this phenotype is conserved between mice and humans. Compared to the expected random distribution, the trend of increased sharing of haplotypes was observed in affected sibpairs from three ethnic groups (P < 0.01). We concluded that this candidate 1q41-q42 region probably contains a susceptibility gene(s) that confers risk for SLE in multiple ethnic groups.
Systemic lupus erythematosus (SLE) is a complex autoimmune disorder with multiple susceptibility genes. We have previously reported suggestive linkage to the chromosomal region 14q21-q23 in Finnish SLE families.
Genetic fine mapping of this region in the same family material, together with a large collection of parent affected trios from UK and two independent case-control cohorts from Finland and Sweden, indicated that a novel uncharacterized gene, MAMDC1 (MAM domain containing glycosylphosphatidylinositol anchor 2, also known as MDGA2, MIM 611128), represents a putative susceptibility gene for SLE. In a combined analysis of the whole dataset, significant evidence of association was detected for the MAMDC1 intronic single nucleotide polymorphisms (SNP) rs961616 (P –value = 0.001, Odds Ratio (OR) = 1.292, 95% CI 1.103–1.513) and rs2297926 (P –value = 0.003, OR = 1.349, 95% CI 1.109–1.640). By Northern blot, real-time PCR (qRT-PCR) and immunohistochemical (IHC) analyses, we show that MAMDC1 is expressed in several tissues and cell types, and that the corresponding mRNA is up-regulated by the pro-inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) in THP-1 monocytes. Based on its homology to known proteins with similar structure, MAMDC1 appears to be a novel member of the adhesion molecules of the immunoglobulin superfamily (IgCAM), which is involved in cell adhesion, migration, and recruitment to inflammatory sites. Remarkably, some IgCAMs have been shown to interact with ITGAM, the product of another SLE susceptibility gene recently discovered in two independent genome wide association (GWA) scans.
Further studies focused on MAMDC1 and other molecules involved in these pathways might thus provide new insight into the pathogenesis of SLE.
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by various autoantibodies that recognize autoantigens displayed on the surface of cells undergoing apoptosis. The genetic contribution to SLE susceptibility has been widely recognized. We previously reported evidence for linkage to SLE of the human chromosome 1q41–q42 region and have now narrowed it from 15 to 5 cM in an extended sample using multipoint linkage analysis. Candidate genes within this region include (a) PARP, poly(ADP-ribose) polymerase, encoding a zinc-finger DNA-binding protein that is involved in DNA repair and apoptosis; (b) TGFB2, encoding a transforming growth factor that regulates cellular interactions and responses; and (c) HLX1, encoding a homeobox protein that may regulate T-cell development. Using a multiallelic, transmission-disequilibrium test (TDT), we found overall skewing of transmission of PARP alleles to affected offspring in 124 families (P = 0.00008), preferential transmission of a PARP allele to affected offspring (P = 0.0003), and lack of transmission to unaffected offspring (P = 0.004). Similar TDT analyses of TGFB2 and HLX1 polymorphisms yielded no evidence for association with SLE. These results suggest that PARP may be (or is close to) the susceptibility gene within the chromosome 1q41–q42 region linked to SLE.
The NZM2410-derived Sle2 lupus susceptibility locus induces an abnormal B cell differentiation which most prominently leads to the expansion of autoreactive B1a cells. We have mapped the expansion of B1a cells to three Sle2 sub-loci, Sle2a, Sle2b, and Sle2c. Sle2 also enhances the breach of B cell tolerance to nuclear antigens in the 56R anti-DNA immunoglobulin transgenic (Tg) model. This study used the Sle2 sub-congenic strains to map the activation of 56R Tg B cells. Sle2c strongly sustained the breach of tolerance and the activation of anti-DNA B cells. The production of Tg-encoded anti-DNA antibodies was more modest in Sle2a expressing mice, but Sle2a was responsible for the recruitment for Tg B cells to the marginal zone, a phenotype that has been found for 56R Tg B cells in mice expressing the whole Sle2 interval. In addition, Sle2a promoted the production of endogenously encoded anti-DNA antibodies. Overall, this study showed that at least two Sle2 genes are involved in the activation of anti-DNA B cells, and excluded more than two-thirds of the Sle2 interval from contributing to this phenotype. This constitutes an important step toward the identification of novel genes that play a critical role in B cell tolerance.
Lupus; B cells; autoantibodies; marginal zone; genetics
Systemic lupus erythematosus (SLE) is a multifactorial disorder characterized by the presence of autoantibodies. We and others have implicated free radical mediated peroxidative damage in the pathogenesis of SLE. Since harmful free radical products are formed during this oxidative process, including 4-hydroxy 2-nonenol (4-HNE) and malondialdehyde (MDA), we hypothesized that specific HNE-protein adducts would be present in SLE red blood cell (RBC) membranes. Catalase is located on chromosome 11p13 where linkage analysis has revealed a marker in the same region of the genome among families with thrombocytopenia, a clinical manifestation associated with severe lupus in SLE affected pedigrees. Moreover, SLE afflicts African-Americans three times more frequently than their European-American counterparts. Hence we investigated the effects of a genetic polymorphism of catalase on risk and severity of SLE in 48 pedigrees with African American ancestry.
Tryptic digestion followed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis was used to identify the protein modified by HNE, following Coomassie staining to visualize the bands on the acrylamide gels. Genotyping analysis for the C → T, -262 bp polymorphism in the promoter region of catalase was performed by PCR-RFLP and direct PCR-sequencing. We used a "pedigree disequilibrium test" for the family based association analysis, implemented in the PDT program to analyze the genotyping results.
We found two proteins to be HNE-modified, migrating around 80 and 50 kD respectively. Tryptic digestion followed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the Coomassie stained 80 kD band revealed that the target of HNE modification was catalase, a protein shown to associate with RBC membrane proteins. All the test statistics carried out on the genotyping analysis for the C → T, -262 bp polymorphism in the promoter region of catalase were non-significant (p > 0.05) in our data, which suggested that this SNP is not associated with SLE.
Our results indicate that catalase is one of the proteins modified due to oxidative stress. However, catalase may not be a susceptibility gene for SLE. Nonetheless, catalase is oxidatively modified among SLE patients. This suggests a possible role between oxidative modification of catalase and its affects on enzymatic activity in SLE. An oxidatively modified catalase could be one of the reasons for lower enzymatic activity among SLE subjects, which in turn could favor the accumulation of deleterious hydrogen peroxide. Furthermore, HNE-products are potential neoantigens and could be involved in the pathogenesis of SLE. Decrease in catalase activity could affect the oxidant-antioxidant balance. Chronic disturbance of this balance in patients with SLE may work favorably for the premature onset of atherogenesis with severe vascular effect.
The 129-derived Sle16 is a susceptibility locus for systemic autoimmunity when present on the C57BL/6 (B6) background. Genetic analysis of a (129×B6)F2 cross identified a region from the B6 chromosome 3 (Sle18) with positive linkage to anti-nuclear antibodies. Here we have generated a B6 congenic strain harbouring the 129 allele of Sle18 and intercrossed this line with the lupus-prone B6.129-Sle16 strain. The presence of the 129-Sle18 allele in the B6.129-Sle16Sle18 double congenic mice suppressed the development of Sle16-mediated autoantibody production and ameliorated the renal pathology. The 129-Sle18 locus rectified the B cell abnormalities detected in the B6.129-Sle16 mice, such as the reduction in the percentage of marginal zone B and B1a cells and the increased number of germinal centers. The B6.129-Sle16Sle18 spleens still displayed an increased percentage of activated T and B cells. However, in the B6.129-Sle16Sle18 strain the percentage of naïve T cells was equivalent to that in B6.129-Sle18 and B6 mice and these cells showed a reduced proliferative response to anti-CD3 stimulation compared to B6.129-Sle16 T cells. There was a significant increase in the percentage of CD4+FoxP3+regulatory T cells in all congenic strains. These cells had normal regulatory function when tested in vitro. Thus 129-Sle18 represents a novel, non-MHC lupus-suppressor locus probably operating as a functional modifier of B cells that, in combination with other factors, leads to lupus resistance. Further characterisation of this locus will help to uncover the immune mechanism(s) conferring protection against lupus.
systemic lupus erythematosus; autoantibodies; rodent; congenic
Sle3 is an NZM2410-derived lupus susceptibility locus on murine chromosome 7. Congenic recombination has resulted in a novel mouse strain, B6.Sle3, associated with serum antinuclear autoantibodies (ANAs), T cell hyperactivity, and elevated CD4/CD8 ratios. An OVA-specific TCR transgene was used as a tool to demonstrate that Sle3 facilitated heightened T cell expansion in vitro, and in vivo, following antigen challenge. Indeed, continued T cell expansion was noted even in response to a tolerogenic signal. However, these phenotypes did not appear to be T cell intrinsic but were dictated by hyperstimulatory B6.Sle3 APCs. Importantly, B6.Sle3-derived DCs and macrophages appeared to be significantly more mature/activated, less apoptotic, and more proinflammatory and were better at costimulating T cells in vitro, compared with the B6 counterparts. Finally, the adoptive transfer of B6.Sle3-derived DCs into healthy B6 recipients elicited increased CD4/CD8 ratios and serum ANAs, 2 cardinal Sle3-associated phenotypes. We posit that their heightened expression of various costimulatory molecules, including CD80, CD106, I-Ab, and CD40, and their elevated production of various cytokines, including IL-12 and IL-1β, may explain why Sle3-bearing DCs may be superior at breaching self tolerance. These studies provide mechanistic evidence indicating that intrinsic abnormalities in DCs and possibly other myeloid cells may dictate several of the phenotypes associated with systemic lupus, including ANA formation and T cell hyperactivity.
Sle3 is an NZM2410/NZW-derived lupus susceptibility interval on murine chromosome 7, that is associated with spontaneous lupus nephritis, and also anti-GBM induced glomerulonephritis. The tissue kallikrein gene cluster is located within the Sle3 interval and constitutes potential candidate genes for this locus. We have recently reported that renal kallikrein expression was up-regulated by anti-GBM antibody challenge in a strain-specific manner and that it was significantly under-expressed in the anti-GBM sensitive strains, including B6.Sle3. Further sequencing and functional studies reported previously provided evidence that kallikreins could constitute disease genes in lupus. In the present report, we have used an adenoviral vector to deliver the klk1 gene to B6.Sle3 congenics to directly test if kallikreins might have a protective effect against anti-GBM induced nephritis. Our data shows that klk1 gene delivery ameliorated anti-GBM induced nephritis in B6.Sle3 congenics. Taken together with previous studies, these findings indicate that kallikreins play an important protective role in autoantibody-initiated glomerulonephritis, and could constitute potential candidate genes for anti-GBM induced and spontaneous lupus nephritis.
Kallikrein; anti-GBM; glomerulonephritis; adenovirus; lupus
The NZM2410-derived Sle1a lupus susceptibility locus induces activated autoreactive CD4+ T cells and reduces the number and function of Foxp3+ regulatory T cells. In this study, we first showed that Sle1a contributes to autoimmunity by increasing anti-nuclear antibody production when expressed on either NZB or NZW heterozygous genomes, and by enhancing the chronic graft vs. host disease response indicating an expansion of the autoreactive B cell pool. Screening two non-overlapping recombinants, the Sle1a.1 and Sle1a.2 intervals that cover the entire Sle1a locus, revealed that both Sle1a.1 and Sle1a.2 were necessary for the full Sle1a phenotype. Sle1a.1, and to a lesser extent Sle1a.2, significantly affected CD4+ T cell activation as well as Treg differentiation and function. Sle1a.2 also increased the production of autoreactive B cells. Since the Sle1a.1 and Sle1a.2 intervals contain only one and 15 known genes, respectively, this study considerably reduces the number of candidate genes responsible for the production of autoreactive T cells. These results also demonstrate that the Sle1 locus is an excellent model for the genetic architecture of lupus, in which a major obligate phenotype results from the co-expression of multiple genetic variants with individual weak effects.
Lupus; T cells; Treg; autoantibodies; genetics
Systemic lupus erythematosus (SLE) is the paradigm of a multisystem autoimmune disease in which genetic factors strongly influence susceptibility. Through genome scans and congenic dissection, numerous loci associated with lupus susceptibility have been defined and the complexity of the inheritance of this disease has been revealed. In this review, we provide a brief description of animal models of SLE, both spontaneous models and synthetic models, with an emphasis on the B6 congenic model derived from analyses of the NZM2410 strain. A hypothetical model of disease progression that organizes many of the identified SLE susceptibility loci in three distinct biological pathways that interact to mediate disease pathogenesis is also described. We finally discuss our recent fine mapping analysis, which revealed a cluster of loci that actually comprise the Sle1 locus.
antinuclear autoantibodies; autoimmunity; congenic dissection; murine lupus; SLE
Sle2 is a lupus susceptibility locus that has been linked toglomerulonephritis in the NZM2410mouse. Byitself, Sle2 does not induce any autoimmune pathology, but results into the accumulation of B1a cells. This study was designed to assess the contribution of Sle2 to autoimmune pathogenesis.
Sle2 or its sub-congenic intervals (Sle2a, Sle2b and Sle2c) were bred to Fas-deficient B6.lpr mice. Lymphoid phenotypes, focused on T cells, were assessed by flow cytometry, and histopathology was compared between cohorts of B6.Sle2.lpr congenics and B6.lpr mice aged up to 6 mo old.
Sle2 synergized with lpr, resulting in a greatly accelerated lymphadenopathy that largely targeted T cells, and mapped to the Sle2c1 locus. This locus has been identified as the main contributor to B1a cell expansion. Further analyses showed that Sle2c1 expression skewed the differentiation and polarization of Fas-deficient T cells, with a reduction of the CD4+ CD25+ Foxp3+ regulatory T cell subset and an expansion of the TH17 cells. This was associated with a high level of T cell infiltrates that promoted severe nephritis and dermatitis in the B6.Sle2c1.lpr mice.
These results show that Sle2c1 contributes to lupus pathogenesis by affecting T cell differentiation in combination with other susceptibility loci such as lpr. The significance of the co-segregation of this phenotype and B1a cell expansion in Sle2c1-expressing mice for lupus pathogenesis is discussed.
lupus; T lymphocytes; genetics; Fas; nephritis
Both genetic and environmental factors contribute to the development and progression of systemic lupus erythematosus (SLE), a complex autoimmune disease. The disease exhibits a strong gender bias and develops predominantly in females. Additionally, most SLE patients exhibit increased serum levels of interferon-α (IFN-α) and the “IFN signature”. Studies using the mouse models of lupus have identified several lupus susceptibility loci, including the New Zealand Black (NZB)-derived autoimmunity 2 (Nba2) interval on the chromosome 1. The interval, which is syntenic to the human chromosome 1q region, harbors the FcγR family, SLAM/CD2-family, and the IFN-inducible Ifi200-family genes (encoding for the p200-family proteins). Studies involving the B6.Nba2 congenic mice revealed that the development of antinuclear autoantibodies (ANAs) depends on the age, gender, and activation of type I IFN-signaling. Interestingly, recent studies involving the generation of Nba2 subcongenic mouse lines and generation of mice deficient for the Fcgr2b or Aim2 gene within the interval have provided evidence that epistatic interactions among the Nba2 genes contribute to increased lupus susceptibility. Given that the expression of some of the p200-family proteins is differentially regulated by sex hormones and these proteins differentially regulate cytosolic DNA-induced production of type I IFN and proinflammatory cytokines (IL-1β and IL-18), the major known contributors of SLE-associated inflammation, we discuss the recent advancements in our understanding of the role of p200-family proteins in lupus susceptibility modification. An improved understanding of the role of p200-family proteins in the development of autoimmunity is likely to identify new approaches to treat SLE patients.
Lupus susceptibility; Nba2 locus; Interferons; Sex hormones; Ifi200-family genes
OBJECTIVES--To determine whether the TAP2 transporter gene, which lies between HLA-DP and HLA-DQ, is involved in determining susceptibility to systemic lupus erythematosus (SLE). METHODS--TAP2 types were determined by ARMS-PCR in 89 white patients with SLE and 156 control subjects. RESULTS--No particular TAP2 dimorphism or allele was associated with SLE or with any clinical/immunological subgroup of SLE. Furthermore, there was no evidence for significant linkage disequilibrium between TAP2 and HLA-DQ/DR in SLE. CONCLUSIONS--These data suggest that TAP2 is not a disease susceptibility gene for SLE and that the disease-predisposing haplotypes do not extend as far as TAP2. This indicates that any HLA-DP association with SLE must be independent of other class II (DQ/DR) associations.
Sle1c is a sublocus of the NZM2410-derived Sle1 major lupus susceptibility locus. We have previously shown that Sle1c contributes to lupus pathogenesis by conferring increased CD4+ T cell activation and increased susceptibility to chronic graft-versus-host disease (cGVHD), which mapped to the centromeric portion of the locus. In this study, we have refined the centromeric sublocus to a 675Kb interval, termed Sle1c2. Mice from recombinant congenic strains expressing Sle1c2 exhibited increased CD4+ T cell intrinsic activation and cGVHD susceptibility, similar to mice with the parental Sle1c. In addition, B6.Sle1c2 mice displayed a robust expansion of IFNγ expressing T cells. NZB complementation studies showed that Sle1c2 expression exacerbated B cell activation, autoAb production, and renal pathology, verifying that Sle1c2 contributes to lupus pathogenesis. The Sle1c2 interval contains two genes, only one of which, Esrrg, is expressed in T cells. B6.Sle1c2 CD4+ T cells expressed less Esrrg than B6 CD4+ T cells, and Esrrg expression was negatively correlated to CD4+ T cell activation. Esrrg encodes for an orphan nuclear receptor that regulates oxidative metabolism and mitochondrial functions. In accordance with a reduced Esrrg expression, B6.Sle1c2 CD4+ T cells present reduced mitochondrial mass and altered mitochondrial functions, as well as altered metabolic pathway utilization when compared to B6. Taken together, we propose Esrrg as a novel lupus susceptibility gene regulating CD4+ T cell function through their mitochondrial metabolism.
Systemic lupus erythematosus (SLE) is a chronic multisystem genetically complex autoimmune disease characterised by the production of autoantibodies to nuclear and cellular antigens, tissue inflammation and organ damage. Genome-wide association studies have shown that variants within the major histocompatibility complex (MHC) region on chromosome 6 confer the greatest genetic risk for SLE in European and Chinese populations. However, the causal variants remain elusive due to tight linkage disequilibrium across disease-associated MHC haplotypes, the highly polymorphic nature of many MHC genes and the heterogeneity of the SLE phenotype.
A high-density case-control single nucleotide polymorphism (SNP) study of the MHC region was undertaken in SLE cohorts of Spanish and Filipino ancestry using a custom Illumina chip in order to fine-map association signals in these haplotypically diverse populations. In addition, comparative analyses were performed between these two datasets and a northern European UK SLE cohort. A total of 1433 cases and 1458 matched controls were examined.
Using this transancestral SNP mapping approach, novel independent loci were identified within the MHC region in UK, Spanish and Filipino patients with SLE with some evidence of interaction. These loci include HLA-DPB1, HLA-G and MSH5 which are independent of each other and HLA-DRB1 alleles. Furthermore, the established SLE-associated HLA-DRB1*15 signal was refined to an interval encompassing HLA-DRB1 and HLA-DQA1. Increased frequencies of MHC region risk alleles and haplotypes were found in the Filipino population compared with Europeans, suggesting that the greater disease burden in non-European SLE may be due in part to this phenomenon.
These data highlight the usefulness of mapping disease susceptibility loci using a transancestral approach, particularly in a region as complex as the MHC, and offer a springboard for further fine-mapping, resequencing and transcriptomic analysis.
We previously established an 80 kb haplotype upstream of TNFSF4 as a susceptibility locus in the autoimmune disease SLE. SLE-associated alleles at this locus are associated with inflammatory disorders, including atherosclerosis and ischaemic stroke. In Europeans, the TNFSF4 causal variants have remained elusive due to strong linkage disequilibrium exhibited by alleles spanning the region. Using a trans-ancestral approach to fine-map the locus, utilising 17,900 SLE and control subjects including Amerindian/Hispanics (1348 cases, 717 controls), African-Americans (AA) (1529, 2048) and better powered cohorts of Europeans and East Asians, we find strong association of risk alleles in all ethnicities; the AA association replicates in African-American Gullah (152,122). The best evidence of association comes from two adjacent markers: rs2205960-T (P = 1.71×10−34, OR = 1.43[1.26–1.60]) and rs1234317-T (P = 1.16×10−28, OR = 1.38[1.24–1.54]). Inference of fine-scale recombination rates for all populations tested finds the 80 kb risk and non-risk haplotypes in all except African-Americans. In this population the decay of recombination equates to an 11 kb risk haplotype, anchored in the 5′ region proximal to TNFSF4 and tagged by rs2205960-T after 1000 Genomes phase 1 (v3) imputation. Conditional regression analyses delineate the 5′ risk signal to rs2205960-T and the independent non-risk signal to rs1234314-C. Our case-only and SLE-control cohorts demonstrate robust association of rs2205960-T with autoantibody production. The rs2205960-T is predicted to form part of a decameric motif which binds NF-κBp65 with increased affinity compared to rs2205960-G. ChIP-seq data also indicate NF-κB interaction with the DNA sequence at this position in LCL cells. Our research suggests association of rs2205960-T with SLE across multiple groups and an independent non-risk signal at rs1234314-C. rs2205960-T is associated with autoantibody production and lymphopenia. Our data confirm a global signal at TNFSF4 and a role for the expressed product at multiple stages of lymphocyte dysregulation during SLE pathogenesis. We confirm the validity of trans-ancestral mapping in a complex trait.
Systemic lupus erythematosus (SLE/lupus) is a complex disease in which the body's immune cells cause inflammation in one or more systems to cause the associated morbidity. Hormones, the environment and genes are all causal contributors to SLE and over the past several years the genetic component of SLE has been firmly established. Several genes which are regulators of the immune system are associated with disease risk. We have established one of these, the tumour-necrosis family superfamily member 4 (TNFSF4) gene, as a lupus susceptibility gene in Northern Europeans. A major obstacle in pinpointing the marker(s) at TNFSF4 which best explain the risk of SLE has been the strong correlation (linkage disequilibrium, LD) between adjacent markers across the TNFSF4 region in this population. To address this, we have typed polymorphisms in several populations in addition to the European groups. The mixed ancestry of these populations gives a different LD pattern than that found in Europeans, presenting a method of pinpointing the section of the TNFSF4 region which results in SLE susceptibility. The Non-European populations have allowed identification of a polymorphism likely to regulate expression of TNFSF4 to increase susceptibility to SLE.
Anti-nuclear antibodies constitute the hallmark of lupus. The NZM2410-derived Sle1 lupus susceptibility interval on murine chromosome 1 breaches tolerance, leading to the emergence of anti-nuclear autoantibodies targeting nucleosomes. However, little is known about the molecular structure of the anti-nucleosome autoantibodies from this genetically simplified mouse model of lupus. In this study, the immunoglobulin heavy chain and light chain sequences of 50 anti-nuclear monoclonal antibodies derived from five B6.Sle1z mice were compared to non-nuclear antibody controls. Compared to 2 different sets of non-nuclear antibodies, anti-nucleosome antibodies derived from B6.Sle1z congenic mice exhibited a high degree of clonal expansion and 3 distinct sequence motifs in their heavy chains–cationic CDR3 stretches, non-anionic CDR2 regions, and an increased frequency of aspartate residues at H50, which together increased the likelihood of an antibody being chromatin-reactive by ~4-fold.
Autoimmunity; B-cells; autoantibodies; genetics; immunoglobulin repertoire
Autoimmune diseases are complex and have genetic and environmental susceptibility factors. The objective was to test the genetic association of systemic lupus erythematosus (SLE) and anti-neutrophil cytoplasmic antibody (ANCA) – associated systemic vasculitis (AAV) with SNPs in the IL2RA region and to correlate genotype with serum levels of IL-2RA.
Using a cohort of over 700 AAV patients, two SLE case-control studies and an SLE trio collection (totalling over 1000 SLE patients), and a TaqMan genotyping approach, we tested 3 SNPs in the IL2RA locus, rs11594656, rs2104286 & rs41295061, each with a prior association with autoimmune disease; rs11594656 and rs41295061 with type 1 diabetes (T1D) and rs2104286 with multiple sclerosis (MS) and T1D.
We show that SLE is associated with rs11594656 (P = 3.87 × 10-7) and there is some evidence of association of rs41295061 with AAV (P = 0.0122), which both have prior association with T1D. rs2104286, an MS and T1D – associated SNP in the IL2RA locus, is not associated with either SLE or AAV.
We have confirmed a previous suggestion that the IL2RA locus is associated with SLE and showed some evidence of association with AAV. Soluble IL-2RA concentrations correlate with rs11594656 genotype in quiescent disease in both AAV and SLE. Differential association of autoimmune diseases and SNPs within the IL2RA locus suggests that the IL2RA pathway may prove to play differing, as yet undefined, roles in each disease.
The gene coding for C-reactive protein (CRP) is located on chromosome 1q23.2, which falls within a linkage region thought to harbor a systemic lupus erythematosus (SLE) susceptibility gene. Recently, two SNPs in the CRP gene (+838, +2043) have been shown to be associated with CRP levels and/or SLE risk in a British family-based cohort. The current study was done to confirm the reported association in an independent population-based case-control cohort, and also to investigate the impact of three additional CRP tagSNPs (-861, -390, +90) on SLE risk and serum CRP levels.
DNA from 337 white women who met the ACR criteria for definite (n = 324) or probable (n = 13) SLE and 448 white female healthy controls was genotyped for five CRP tagSNPs (-861, -390, +90, +838, +2043). Genotyping was performed using PCR-RFLP, pyrosequencing or TaqMan assays. Serum CRP levels were measured using ELISA. Association studies were performed using the χ2 distribution, Z-test, Fisher's exact test and ANOVA. Haplotype analysis was performed using EH software and haplo.stats package in R 2.1.2.
While none of the SNPs were found to be associated with SLE risk individually, there was an association with the five-SNP haplotypes (p<0.000001). Three SNPs (-861, -390, +90) were found to significantly influence serum CRP level in SLE cases, both independently and as haplotypes.
Our data suggests that unique haplotype combinations in the CRP gene may modify the risk of developing SLE and influence circulating CRP levels.
Sle1 and Sle3 are 2 loci that confer susceptibility to lupus nephritis in the NZM2410 strain of mice. Our previous work has shown that B6.NZMc1 mice, congenic for Sle1, exhibit loss of tolerance to chromatin but do not develop any pathogenic autoantibodies or disease. B6.NZMc7 mice, congenic for Sle3, exhibit low-grade polyclonal B- and T-cell activation, elevated CD4/CD8 ratios, and mildly penetrant glomerulonephritis. In contrast to these monocongenics, the present study reveals that B6.NZMc1|c7 mice, bicongenic for Sle1 and Sle3, exhibit splenomegaly, significantly expanded populations of activated B and CD4+ T cells, and a robust, variegated IgG autoantibody response targeting multiple components of chromatin (including double-stranded DNA), intact glomeruli, and basement membrane matrix antigens. As one might predict, these mice, particularly the females, exhibit highly penetrant glomerulonephritis.
These findings lend strong support to a two-step epistatic model for the formation of pathogenic, nephrophilic autoantibodies in lupus. Whereas loci such as Sle1 may serve to breach tolerance to chromatin, full-blown pathogenic maturation of the autoantibody response appears to require additional input from other loci (such as Sle3) and gender-based factors.
J. Clin. Invest. 103:1685–1695 (1999).
One of the hallmarks of SLE is the loss of tolerance to chromatin. The genes and mechanisms that trigger this loss of tolerance remain unknown. Our genetic studies in the NZM2410 lupus strain have implicated genomic intervals on chromosomes 1 (Sle1), 4 (Sle2), and 7 (Sle3) as conferring strong lupus susceptibility. Interestingly, B6 mice that are congenic for Sle1 (B6.NZMc1) have elevated IgG antichromatin Abs. This study explores the antinuclear antibody fine specificities and underlying cellular defects in these mice. On the B6 background, Sle1 by itself is sufficient to generate a robust, spontaneous antichromatin Ab response, staining Hep-2 nuclei homogeneously, and reacting primarily with H2A/H2B/DNA subnucleosomes. This targeted immune response peaks at 7-9 mo of age, affects both sexes with equally high penetrance (> 75%), and interestingly, does not "spread" to other subnucleosomal chromatin components. Sle1 also leads to an expanded pool of histone-reactive T cells, which may have a role in driving the anti-H2A/H2B/DNA B cells. However, these mice do not exhibit any generalized immunological defects or quantitative aberrations in lymphocyte apoptosis. We hypothesize that Sle1 may lead to the presentation of chromatin in an immunogenic fashion, or directly impact tolerance of chromatin-specific B cells.
Recently, a new genetic factor within the interferon regulatory factor 5 (IRF5) gene was demonstrated for systemic lupus erythematosus (SLE) through linkage and association: the rs2004640‐T allele. IRF5 is involved in the production of rheumatoid arthritis (RA) cytokines, and SLE already shares with RA one genetic factor within the tyrosine phosphatase PTPN22 gene.
To test the hypothesis that the SLE IRF5 genetic factor could also be shared with RA.
Patients and methods
100 French Caucasian trio families with RA were genotyped and analysed with the transmission disequilibrium test, the frequency comparison of the transmitted and untransmitted alleles, and the genotype relative risk. 97% power was available to detect at least a trend in favour of a factor similar to that reported for SLE.
The analysis showed the absence of linkage and association globally and in “autoimmune” RA subsets, with a weak non‐significant trend against the IRF5rs20046470‐T allele. Given the robustness of familial‐based analysis, this slight negative trend provided strong evidence against even a weaker factor than that reported for SLE.
Our results exclude the IRF5rs2004640‐T allele as a major genetic factor for RA in this French Caucasian population.
Lupus erythematosus (LE) is a heterogeneous disease ranging from mainly skin-restricted manifestations (discoid LE [DLE] and subacute cutaneous LE) to a progressive multisystem disease (systemic LE [SLE]). Genetic association studies have recently identified several strong susceptibility genes for SLE, including integrin alpha M (ITGAM), also known as CD11b, whereas the genetic background of DLE is less clear.
To specifically investigate whether ITGAM is a susceptibility gene not only for SLE, but also for cutaneous DLE, we genotyped 177 patients with DLE, 85 patients with sporadic SLE, 190 index cases from SLE families and 395 population control individuals from Finland for nine genetic markers at the ITGAM locus. SLE patients were further subdivided by the presence or absence of discoid rash and renal involvement. In addition, 235 Finnish and Swedish patients positive for Ro/SSA-autoantibodies were included in a subphenotype analysis. Analysis of the ITGAM coding variant rs1143679 showed highly significant association to DLE in patients without signs of systemic disease (P-value = 4.73×10−11, OR = 3.20, 95% CI = 2.23–4.57). Significant association was also detected to SLE patients (P-value = 8.29×10−6, OR = 2.14, 95% CI = 1.52–3.00), and even stronger association was found when stratifying SLE patients by presence of discoid rash (P-value = 3.59×10−8, OR = 3.76, 95% CI = 2.29–6.18).
We propose ITGAM as a novel susceptibility gene for cutaneous DLE. The risk effect is independent of systemic involvement and has an even stronger genetic influence on the risk of DLE than of SLE.
OBJECTIVES--To determine whether HLA-DP genes are involved in determining susceptibility to systemic lupus erythematosus (SLE). METHODS--HLA-DPA1 and DPB1 genes were amplified by PCR of DNA samples from a panel of patients with SLE and normal controls. Amplified DNA was blotted on to nylon filters and probed with sequence-specific oligonucleotide (SSO) probes. RESULTS--No DPA1 or DPB1 allele was significantly associated with SLE, or with any immunological or clinical subset of SLE. Evidence was found for only limited linkage disequilibrium between HLA-DP and HLA-DQ/DR variants, and none between HLA-DP and the TAP2 gene. CONCLUSIONS--These data indicate that HLA-DP genes do not contribute towards determining susceptibility to SLE.
Systemic lupus erythematosus (SLE) is a complex autoimmune disease involving critical genetic and environmental risk factors. SLE is a relatively common disease among African American women, affecting as many as one in 250. A collection of more than 250 African American and European American pedigrees multiplex for SLE have been collected in Oklahoma over the past decade for the purpose of identifying the genetic risk factors involved in the pathogenesis of SLE. A genome scan has been performed, and interestingly, the linkage results usually dominate in families from one or the other of these ethnicities. For example, the linkage effect at 1q21-22 near FcgammaRIIA is much stronger in the African American pedigrees than in the European American pedigrees. On the other hand, a gene near the top of chromosome4 (at 4p l6-15) contributes to SLE in the European American pedigrees, but not in the African American pedigrees. The racially-specific results lead to the tentative conclusion of genetic differences associated with SLE in African Americans and European Americans. The identification of the genes responsible for the observed linkage effects will provide fundamental knowledge concerning SLE and may even provide new targets for therapy and strategies to defeat this enigmatic and difficult disease.