HLA-DRB1 and rheumatoid arthritis: HLA‐DRB1*13 alleles were found to be protective in ACPA‐positive RA.172 This effect has been explained by specific properties of the DERAA sequence (located similarly to the “shared epitope”: positions 70‐74 of the beta chain), which has been proposed to function not as a presenting molecule, but as a self‐antigen.