Abstract: Objective: To investigate the immunomodulatory effect of Schisandra chinensis lignans (SCL) in the cyclophosphamide (Cyp)-induced immunosuppressive mice, and to elucidate its related mechanisms.Methods: A total of 75 male ICR mice were divided in control group, model group,and low, middle,high doses (50, 100, and 200 mg·kg^-1) of SCL groups, 15 mice in each group. The mice in control and model groups were administered with distilled water intragastrically and the mice in SCL groups were administered with different doses of SCL intragastrically once a day for 21 d. After the successive administration for 17 d, the mice in model and SCL groups were intraperitoneally injected with Cyp (20 mg·kg^-1) once a day for 5 d. The thymus and spleen indexes were determined and the morphology of thymus and spleen tissues were observed. The phagocytic function of macrophages was estimated using carbon clearance test and the level of interferon-γ (IFN-γ) was measured by ELISA method. The spleen lymphocyte proliferation ability was measured by MTT method and the apoptotic rate of spleen lymphocyte was determined by flow cytometry.Results: Compared with control group, the thymus and spleen indexes,the phagocytic function of macrophages, the IFN-γ level, the spleen lymphocyte proliferation activity,and the early, late, total apoptotic rates of lymphocytes of the mice in model group were increased (P<0.05 or P<0.01). Compared with model group, the thymus and spleen indexes,the phagocytic function of macrophages, the IFN-γ levels, the spleen lymphocyte proliferation abilities,and the early, late, total apoptotic rates of lymphocytes of the mice in different doses of SCL groups were significantly decreased (P<0.05 or P<0.01). Compared with control group, the number of lymphocytes in the thymus cortex of the mice in model group was reduced, the number of splenic corpuscles was reduced and their volumes were obviously reduced. Compared with model group, the reducing of lymphocyte number in the thymus cortex and splenic corpuscles and atrophy of the mice in different doses of SCL groups were obviously improved.Conclusion: SCL can protect the mice with Cyp-induced immunodeficiency by regulating the cellular, humoral and non-specific immune functions of the mice.

Key words: Schisandra chinensis, lignans, cyclophosphamide, immunomodulation