USP18 and rheumatoid arthritis: Our study has revealed significant hypomethylation of type I IFN-related genes annotated by GO (IFIT1, IRF7, MX1, OAS1, USP18, RSAD2, Table 2) in CD4+ T cells of GD/RA/SLE/SSc patients compared with controls, and we wanted to further evaluate their ability to distinguish the patients from healthy individuals to see if methylation levels of these genes can be of diagnostic value.