CHI3L1 and rheumatoid arthritis: Moreover, cells that positively stained for major histocompatibility complex/human cartilage CHI3L1 complexes were observed in 61.5% of inflamed RA synovial samples compared with only 3.0% of the control samples in a specific and independent manner; therefore, CHI3L1 may be useful as a histological marker for the immunopathological diagnosis of RA192.