GAN and rheumatoid arthritis: Pathologically, the antibodies to citrullinated proteins are expected to be produced in the synovial compartment [13] given that the anti-CCP antibodies constituted a higher proportion of immunoglobulin (Ig) G) in synovial fluid (SF) than that in serum of patients with RA [13,14] and given that B cells producing the anti-CCP antibodies have been isolated from RA synovium [14].