\[Abstract\]ObjectiveTo observe the effect of Tongluo recipe(TLR) on CD4+CD25+ regulatory T cell in the thymus of experimental diabetic rats. MethodsTotally 112 SD rats were randomly divided into three groups: control group, diabetes mellitus(DM) group, and TLR treatment group. Rat diabetic model was induced by intraperitoneal injection of streptozotocin (60 mg/kg). The TLR treatment group was further divided into two subgroups: prevention group was given intragastric TLR (0.4 g·kg-1·d-1) for 12 weeks starting from the day of streptozotocin injection (TL-1 group), and the treatment group was given intragastric TLR (0.4 g·kg-1·d-1) for 12 weeks starting from 12 weeks after streptozotocin injection (TL-2). The animals were sacrificed at different time points (The control and DM group: 4, 8, 12, 16, 20, and 24 weeks; TLR group: 12 and 24 weeks after administration of TLR). Flow cytometry, H-E staining, and immunochemistry were performed to investigate the change of CD4+CD25+ regulatory T cell ratio in CD4+ T cells, the thymus morphology, and the expression of Foxp3 protein in the thymus.ResultsCompared with the normal control group, diabetic group had a gradually shrunk thymus, a decreased ratio of CD4+CD25+ regulatory T cells in CD4+ T cells, and a decreased expression of Foxp3. The ratios of CD4+CD25+ regulatory T cells and the thymus indices in the two TLR groups were significantly higher than those in the diabetic model group(P<0.05).ConclusionTongluo recipe can greatly increase the ratio of CD4+CD25+ regulatory T cells, thymus index, and Foxp3 expression in the thymus, and may protect the thymus CD4+CD25+ regulatory T cells in experimental diabetic rats.