Abstract: Objective: To investigate the regulation of transcription factor RORγt on the IFN-γ production in different T cell subpopulations.Methods: Peripheral blood mononuclear cells were isolated from peripheral blood of healthy donors by density gradient centrifugation,and were stimulated with CD3 monoclonal antibody and cultured in IL-2 containing medium for 12 days.The activated T cells were transfected with chemical synthesized small interfering RNA(siRNA) sequences for RORγt gene using liposomes.The expression of RORγt gene was detected in RORγt-siRNA transfected T cells by RT-PCR assay.The percentages of IFN-γ producing cells in total T cells,CD4⁺ and CD8⁺ T cells were measured in the transfected T cells by flowcytometry.Results: By using semi-quantity RT-PCR assay,the RORγt gene expression was inhibited in activated T cells that transfected with RORγt-siRNA-1026 and^-1197,but not inhibited in that with RORγt-siRNA-982.Among the RORγt-siRNA-1026 transfected activated T cells,the percentage of IFN-γ producing cells in CD4⁺ T cells(32.78±3.41) significantly decreased,compared to untransfected group(44.54±1.75) (P<0.01).Conclusions: Transcription factor RORγt is involved in the positive regulation for IFN-γ production in CD4⁺ T cells.