CHI3L1 and rheumatoid arthritis: Both are involved in the pathophysiology of the arthritic processes and reflect local disease activity.246 Moreover, CHI3L1 has been identified as a candidate autoantigen presented by HLA-DR in RA.247–250 Some patients with RA and OA possessed autoantibodies to CHI3L1.251,252 However, autoimmunity to CHI3L1 in patients with OA was present at equal or somewhat higher frequency than in patients with RA.