Abstract: AimTo observe the effects of sinomenine on the immune functions and apoptosis of murine lymphocyte as well as on human synovial fibroblast proliferation. MethodsBoth in vivo and in vitro tests were adopted. The lymphocyte proliferation induced by mitogens was assayed by MTT method. Spleen T lymphocyte subtypes were tested with flow cytometry. Spleen lymphocyte apoptosis was analyzed by flow cytometry and DNA ladder methods. In vitro test was adopted to observe the effects of sinomenine on the proliferation of human fibroblast of rheumatoid arthritis. ResultsSinomenine can inhibit the proliferation of mouse lymphocytes induced by ConA, LPS and anti-CD3 mAb but not PMA in vitro, and inhibit the proliferation induced by LPS and PMA in vivo. Sinomenine can reduce up-regulated CD4⁺/CD8⁺ ratio of T lymphocyte subtype in adjuvant arthritis rat. At the same concentration increased apoptosis ratio. As to human synovial fibroblast, sinomenine can significantly inhibit proliferation of human fibroblast. ConclusionSinomenine can inhibit the immunological function and correct imbalance of CD4⁺/CD8⁺ ratio of T lymphocyte subtype. It can also increase apoptosis ratio of spleen lymphocyte. This may be the mechanism of its immunological inhibitory effect.