USP18 and rheumatoid arthritis: In accordance with previous studies, we identified the hypomethylation of type I IFN-related genes annotated by GO, including IFIT1, IRF7, MX1, OAS1, USP18, and RSAD2 [which were also identified in SLE before (Absher et al., 2013)] at the epigenetic level in CD4+ T cells of GD/RA/SLE/SSc patients, indicating the aberration of DNA methylation profiles of these genes might play a role in the pathogenesis of the autoimmune diseases in this study.