HLA-DRB1 and rheumatoid arthritis: In particular, the interaction of citrulline vimentin with the P4 pocket of HLA-DRB1*04:01/04, which is specific for RA and called the shared epitope, increased detection of CD4+ T-cells against citrullinated vimentins in the peripheral blood of RA patients and presence of plasma cells producing ACPA are the route of the classical RA autoimmunity (27, 28).