Since K1 is an epithelial cell surface protein, our study further demonstrates the expression of Cit-K1 in synovial membrane from a patient with RA, which is consistent with previous studies.45 46 These data, plus the detection of Cit-K1 specific antibody from synovial fluid, suggest the possibility that the anti-Cit-K1 antibody may trigger a local inflammatory response by recognising and binding to its antigen. The gene discussed is KRT1; the disease is rheumatoid arthritis.