HLA-DRB1 and rheumatoid arthritis: The knowledge of the risk conferred by HLA-DRB1 alleles in RA has been crucial, first, to understand the pathogenesis of the disease, and second, to learn about the relationship between HLA molecules and autoantigenic peptides and the interaction of the peptide-HLA complexes with the T-cell antigen receptor of the autoreactive lymphocytes.