HLA-DRB1 and rheumatoid arthritis: Susceptibility is strongly shaped by HLA variation, with class II alleles (e.g., HLA-DRB1 shared epitope in rheumatoid arthritis; HLA-DRB1/DQA1/DQB1 in systemic lupus erythematosus and Sjögren’s syndrome) dictating peptide presentation and T cell help to autoreactive B cells [3].