HLA-DRB1 and rheumatoid arthritis: Citrullinated vimentin-derived epitopes have been shown to stimulate T cell activation and enhance peptide-HLA (pHLA) binding affinity, especially with RA-predisposing HLA-DRB1 molecules such as HLA-DRB1*04:01, HLA-DRB1*04:04, and HLADRB1*04:05.