Object To study the therapeutic effect and the possible mechanism of F 1C, a tannin fraction with immunosuppressive effect isolated from Cornus officinalis Sieb. et Zucc., in the treatment of adjuvant arthritis (AA) rats. Methods AA rat model was reproduced to observe the effect on immune function both in vivo and in vitro and compare with Cyclosporine (CsA) and Tripterygium wilfordii (TW). The effect of F 1C on joint swelling and the immune respones of AA rats were evaluated by lymphocytotic reaction, flow...