Genetic variation at the IRF7/PHRF1 locus is associated with autoantibody profile and serum interferon‐α activity in lupus patients

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Abstract
Objective Interferon‐α (IFNα) is a heritable risk factor for systemic lupus erythematosus (SLE). Genetic variation near IRF7 is implicated in SLE susceptibility. SLE‐associated autoantibodies can stimulate IFNα production through the Toll‐like receptor/IRF7 pathway. This study was undertaken to determine whether variants of IRF7 act as risk factors for SLE by increasing IFNα production and whether autoantibodies are important to this phenomenon. Methods We studied 492 patients with SLE (236 African American, 162 European American, and 94 Hispanic American subjects). Serum levels of IFNα were measured using a reporter cell assay, and single‐nucleotide polymorphisms (SNPs) in the IRF7/PHRF1 locus were genotyped. Results In a joint analysis of European American and Hispanic American subjects, the rs702966 C allele was associated with the presence of anti–double‐stranded DNA (anti‐dsDNA) antibodies (odds ratio [OR] 1.83, P = 0.0069). The rs702966 CC genotype was only associated with higher serum levels of IFNα in European American and Hispanic American patients with anti‐dsDNA antibodies (joint analysis P = 4.1 × 10−5 in anti‐dsDNA–positive patients and P = 0.99 in anti‐dsDNA–negative patients). In African American subjects, anti‐Sm antibodies were associated with the rs4963128 SNP near IRF7 (OR 1.95, P = 0.0017). The rs4963128 CT and TT genotypes were associated with higher serum levels of IFNα only in African American patients with anti‐Sm antibodies (P = 0.0012). In African American patients lacking anti‐Sm antibodies, an effect of anti‐dsDNA–rs702966 C allele interaction on serum levels of IFNα was observed, similar to the other patient groups (overall joint analysis P = 1.0 × 10−6). In European American and Hispanic American patients, the IRF5 SLE risk haplotype showed an additive effect with the rs702966 C allele on IFNα level in anti‐dsDNA–positive patients. Conclusion Our findings indicate that IRF7/PHRF1 variants in combination with SLE‐associated autoantibodies result in higher serum levels of IFNα, providing a biologic relevance for this locus at the protein level in human SLE in vivo.