The target of ACPA might be not only an autoantigen but also a viral antigen such as the citrullinated form of Epstein-Barr virus encoded nuclear antigen (EBNA-1), suggesting a possible role of Epstein-Barr virus (EBV) infection in the induction of disease-specific antibodies in RA [16]. The gene discussed is PRTN3; the disease is rheumatoid arthritis.