Objective To study the effects of chimeric B7 antibodies on mononuclear cells from patients with ankylosing spondylitis (AS).Methods Chimeric antibodies of ch4E5 and chlD1 against B7 with a final concentration of 5 μg/ml were respectively added into culture media of mononuclear cells from patients with AS.Two other groups including huIgG-treated and untreated culture medium of mononuclear cells from patients with AS were set up as the controls.The culture medium of mononuclear cells from healthy subjects were prepared as normal control group.The disparities of mononuclear cell death in culture among each group were analyzed by using micro-lymphocyte cytotoxicity test (MLCT).The expression of membrane molecules were analyzed by FCM.The concentrations of cytokines in culture media were measured by ELISA.Results Both groups treated with the chimeric antibody showed lower scores for cell death than untreated group as indicated by MLCT (P＜0.01).FCM analysis demonstrated that both CD4/CD8 ratio (P ＜0.05) and membrane expression of CD154 (P＜0.01) decreased in chimeric antibody treated groups,but the number of CD4+CD25high Treg cells (P＜0.01) increased as compared with those in untreated group.The concentrations of IL-2 and TNF-α were down-regulated (P＜0.05) in chimeric antibody treated groups,while IL-4 and TGF-β were up-regulated (P＜0.02) as compared with those in untreated group.Conclusion Chimeric B7 antibodies might affect the expression of T cell membrane molecules and the cytokine production by mononuclear cells through B7/CD28 and CD4O/CD154 signaling pathways in patients with AS.