Antigen-specific CD4+T cells, recognising citrullinated self-peptides (eg, citrullinated α-enolase, vimentin and tenascin-C) presented by HLA-DRB1*04:01, constitute a small population of T cells in both peripheral blood12, 17 and synovial fluid of RA patients17 18 at time of diagnosis and during the disease course. The gene discussed is CD4; the disease is rheumatoid arthritis.