Objective To investigate the expression of OX40 on CD4+T cells in patients with ulcerative colitis (UC)and the role of OX40/OX40L interaction for the cytokine production of lamina propria(LP)-CD4+T cells from UC.Methotis LP-CD4+T cells were purified.The expression of OX40 molecule was measured with FACS.LP-CD4+T cells were cultured with different stimuli and proliferation was assessed.The cytokines concentrations of the culture supernatant were detected.Results No difference of the OX40 expression was observed among the CD4+T cells from peripheral blood(PB)of UC patients,LP of non-inflammatory colonic tissue in UC patients and control PB.However.the expression of OX40 was significantly higher on LP-CD4+T cells from inflammatory colonic tissue in UC patients.In vitro culture with antigen presenting cells,the levels of IFNγ and TNFα secreted by LP-CD4+T cells from the inflammatory colonic tissue were significantly higher than those from the non-inflammatory colonic tissue(both P＜0.01).The levels of IFNγ and TNFα secreted by LP-CD4+T cells from the inflammatory colonic tissue were further increased by anti-OX40 MoAb stimulation.but suppressed significantly by adding anti-OX40L MoAb (compared with non stimulation,P＜0.01,respectively).The IFNγ and TNFα secretion of the LP-CD4+T cells from the non-inflammatory colonic tissue were not significantly different with and without anti-OX40 or anti-OX40L MoAbs stimulation.IL-4 and IL-10 produced by LP-CD4+T cells from the inflammatory or non-inflammatory colonic tissue were not significantly changed when adding different stimuli.Conclusions OX40 is highly expressed on LP-CD4+T cells from inflammatory colonic tissue in patients with UC.AntiOX40L MoAb can inhibit the proinflammatory cytokines secreted by these cells.It is indicated that OX40+T cells are involved in the immunopathological process in UC and blockage of the interaction of OX40 and OX40Lis a new strategy to be considered for the treatment of the disease.