HLA-DRB1 and rheumatoid arthritis: We and others have described antigen-specific responses to citrullinated peptides from several potential target molecules2–4, including a recent report on T cell reactivity against citrullinated Tenascin C (cit-TNC), where such T cell reactivities were prominent in both peripheral blood (PB) and synovial fluid (SF) of HLA-DRB1*04:01-positive RA patients5.