Objective   To investigate the expression of T-bet on human lymphocytes inhibited by siRNA.     Methods   Four different siRNAs (siRNA-1

siRNA-2

siRNA-3

and siRNA-co) were designed and synthysized and transfected into freshly isolated human lymphocytes with cationic liposome. The changes of T-bet mRNA levels were determined by semi-quantitative RT-PCR at 48 h after transfection. IL-4 and IFN-γ cytokine levels were assayed by ELISA. The proliferation of ECV304 co-cultured with T lymphocyte by cck-8 assay was determined.     Results   Different siRNA showed different reduction in T-bet expression. At 48 h after transfection

the degrees of reduction with siRNA-1

siRNA-2

and siRNA-3 were (72.50±1.01) %

(5.40±0.63)%

and (30.90±0.90)%

respectively as compared with those of the control (P0.05). siRNA-1 was the most efficient. The results of semi-quantitative RT-PCR assay indicated T-bet mRNA levels were inhibited after transfection. IL-4 cytokine level in the transfection group was higher than that in the control group

but IFN-γ cytokine level in the transfection group was lower than that in the control group. The proliferation level of ECV304 co-cultured with T lymphocyte transfected with siRNA-1 group was higher than that of siRNA-2 group and siRNA-3 group.     Conclusion   Three different siRNAs could reduce the expression of T-bet and the T-bet mRNA level. siRNA may be useful for further study on graft-versus-host disease after allogeneic transplantation.