Objective:To observe the influence of rapamycin on the differentiation and proliferation of CD4+ CD25+ Treg cells,so as to lay a foundation for further studying its role in inducing immune tolerance.Methods: The spleens were taken from C57BL/6 mice under sterile condition and the mononuclear cells were isolated.CD4+ T cells were isolated by immunomagnetic beads (negative) and were divide into normal control group,rapamycin (0.1 μmol/L,for 7 days) group and cyclosporine (0.5 μmol/L,for 7 days) group.Flow cytometry was used to determine the proportions of CD4+CD25+ Treg cells,and RT-PCR was used to examine the expression of Foxp3 mRNA.Results: Compared with the control group,the proportion of CD4+CD25+ Treg cells in the CD4+T cells was significantly decreased (\[7.42±0.82\]% vs \[3.72±0.74\]%,P<0.01) in the cyclosporine group and was significantly increased (\[7.42±0.82\]% vs \[11.47±1.08\]%,P<0.01) in the rapamycin group.Expression of Foxp3 mRNA in rapamycin group was significantly higher than that in the other 2 groups(P<0.01); expression of Foxp3 mRNA in the cyclosporine group was significantly lower than that in the control group (P<0.05).Conclusion: Rapamycin can promote the proliferation and growth of CD4+CD25+Foxp3+Treg cells in vitro, and facilitate the development of immune tolerance.It has a different immune suppression mechanism with cyclosporine A.