Regulatory polymorphisms modulate the expression of HLA class II molecules and promote autoimmunity.

Targeted sequencing of sixteen SLE risk loci among 1349 Caucasian cases and controls produced a comprehensive dataset of the variations causing susceptibility to systemic lupus erythematosus (SLE). Two independent disease association signals in the HLA-D region identified two regulatory regions containing 3562 polymorphisms that modified thirty-seven transcription factor binding sites. These extensive functional variations are a new and potent facet of HLA polymorphism. Variations modifying the consensus binding motifs of IRF4 and CTCF in the XL9 regulatory complex modified the transcription of HLA-DRB1, HLA-DQA1 and HLA-DQB1 in a chromosome-specific manner, resulting in a 2.5-fold increase in the surface expression of HLA-DR and DQ molecules on dendritic cells with SLE risk genotypes, which increases to over 4-fold after stimulation. Similar analyses of fifteen other SLE risk loci identified 1206 functional variants tightly linked with disease-associated SNPs and demonstrated that common disease alleles contain multiple causal variants modulating multiple immune system genes.

Fatty Acid Amide Hydrolase Regulates Peripheral B Cell Receptor Revision, Polyreactivity, and B1 Cells in Lupus.

C57BL/6 mice bearing the Sle2(z) lupus-susceptibility congenic interval on chromosome 4 display high titers of polyclonal autoantibodies with generalized B cell hyperactivity, hallmarks of systemic lupus erythematosus. In B6.Sle2(z)HEL(Ig).sHEL BCR-transgenic mice, Sle2(z) did not breach central tolerance, but it led to heightened expression of endogenous Ig H and L chains in splenic B cells, upregulation of RAG, and serological polyreactivity, suggestive of excessive receptor revision. Fatty acid amide hydrolase (FAAH), a gene in the minimal subcongenic interval generated through recombinant mapping, was found to be upregulated in Sle2(z) B cells by microarray analysis, Western blot, and functional assays. Pharmacological inhibition of FAAH reversed the increase in receptor revision, RAG expression, and polyreactive autoantibodies in lupus-prone mice. These studies indicate that increased peripheral BCR revision, or selective peripheral expansion of BCR-revised B cells, may lead to systemic autoimmunity and that FAAH is a lupus-susceptibility gene that might regulate this process.

Autoantibody profiling to identify individuals at risk for systemic lupus erythematosus.

The objective of this study was to determine the prevalence of lupus-related autoimmunity in a community-based cohort of over 3000 subjects, using a rheumatology registry as a comparison group. Measurements of ANA, anti-dsDNA and a panel of 8 other lupus-related autoantibodies were carried out in 176 subjects from the registry, including patients with SLE or with incomplete lupus (ILE) as well as in first degree relatives (FDRs) of these patients. Similar measurements were then carried out in 3470 samples from an unselected, urban community-based sample that included significant numbers of African-Americans and Hispanics. Correlations with demographic features including gender, race and ethnicity were determined for both groups. Autoantibody profiles in the community-based sample were further evaluated by comparison with diagnostic groups in the registry subjects. ILE patients were found to have autoantibody profiles similar to those seen in SLE patients with the exception of antibodies to dsDNA and chromatin. Some unaffected first degree relatives had multiple autoantibody specificities despite a lack of clinical symptoms. The population-based sample showed a 27% prevalence of ANA positivity, and high ANA levels, defined as greater than 2 standard deviations above the mean, were present in 2.5% of subjects. At least one additional potentially pathogenic autoantibody was present in 1.7%. The prevalence of autoreactivity observed in this population is strikingly similar to previous reports from geographically and ethnically diverse sources, suggesting that underlying genetic and environmental factors driving autoreactivity are widely shared in the human population. Identification of additional markers correlating with development of disease will be needed to determine objective and predictive measures of risk.