Rapamycin(RAPA) is an immunosuppressive agent, it inhibits T lymphocyte activation and proliferation by suppressed antigen and cytokine(interleukin-2, interleukin-4 and interleukin-15), it was always used to treat autoimmune disease and graft versus host disease. RAPA can selectively expand mice CD4+CD25+FoxP3+ regulatory T cells in vitro, in this study, we demonstrated RAPA induce mice CD4+ CD25+FoxP3+ regulatory T cells proliferation in vivo. Balb/C mice were used between 8–10 weeks of age, weight was 20±2g, RAPA was given to Balb/C murine 0.4mg/day intragastric administration according to man dose, the same mice of age and weight were given with steriled water as the control, all mice were kept under specific pathogen-free conditions. Drinking water and food were steriled. After three weeks, peripheral blood was collected and spleen cells were prepared, CD4+CD25+T cells were detected with FCM(CD4-pcy5, CD25-FITC), the relative levels of foxp3 mRNA were determined by real-time quantitative RT-PCR in total splenocytes. The CD4+CD25+T cell of peripheral blood of experimental group and control group was (9.24±4.16)% and (4.32±1.26)%, respectively (P<0.01), and CD4+CD25+T cell of experimental mice splenocytes was (22.99±10.59)%, while control group was (7.37± 2.91)% (P<0.01). real-time quantitative RT-PCR showed that the levels of foxp3 mRNA of experimental mice splenocytes was 6 folds than control group(P<0.01). CD4+CD25+T cells and CD+CD25T cells were enriched with CD4+CD25+T regulate cells isolation kits from experimental Balb/C mice, we used mixed leukocyte reaction for CD4+CD25+T cells suppressor function. The CD4+CD25+T cells can inhibit the proliferation of CD4+CD25T cells and inhibition ratio was about 50%. Our result demonstrated that RAPA can induce Balb/C murine CD4+CD25+Foxp3+T cells proliferation in vivo, which suggested RAPA could increase CD4+CD25+Foxp3+T cells on the autoimmune disease and graft versus host disease treatment.

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