HLA-DRB1 and rheumatoid arthritis: We analyzed the expression data with regard to several parameters related to the risk of RA or disease activity, including gender, age at disease onset, rheumatoid factor (RF) and ACPA status, smoking, the HLA-DRB1 SE, polymorphisms in the PTPN22 locus, DAS28 at baseline and type of medication for cohort I.