Objective:To investigate markers of regulatory T cells in the pathogenesis of systemic lupus erythematosus (SLE).Methods:Peripheral blood mononuclear cells (PBMCs) were isolated from SLE patients and healthy donors;Flow cytometry (FCS) was used to detect the expressions of CD25 and Foxp3 in CD4 and CD8 T subsets and analyze the changes in the ratios of Foxp3+/CD4+,CD25+Foxp3+/CD4+,Foxp3+/CD4+CD25+,Foxp3+/CD8+,CD25+Foxp3+/CD8+,Foxp3+/CD8+CD25+,and their relationships with SLEDAI,anti-dsDNA antibodies,complement C3/C4,serum IgG,kidney damage and leucopenia. Results:① Compared with healthy donors,the percentage of CD25+ cells in CD4+T cells did not change significantly in SLE patients,but the ratios of Foxp3+/CD4+,CD25+Foxp3+/CD4+ and Foxp3+/CD4+CD25+ significantly reduced in patients with mid- and high-active SLE,and the ratios were also negatively correlated to SLEDAI. Particularly,the ratio of CD25+Foxp3+/CD4+ in SLE patients was related with anti-dsDNA antibody,decrease of complement C3/C4 and increase of IgG;and the reduce of CD25+Foxp3+/CD4+ ratio was remarkable in SLE patients with renal damage or Leucopenia and patients in initial disease stage. ② Foxp3+ cells ratio of CD8+ cell population was similar between SLE patients and healthy controls,except that the ratio of Foxp3+/CD8+CD25+ decresed in mid- and high-active SLE patients,but had no relationship with disease activity. Conclusion:CD4+CD25+Foxp3+ is an important marker for evaluation of regulatory T cells,which reflects the deficient quantity of Treg,and might reflects the deficient function of Treg by the relationship between the cell percentage and SLE disease activity,immune disorder and tissue lesion. The study confirmed that CD4+CD25+Foxp3+ as the marker of Treg is significant for evaluation of immune system functional status of SLE patients in clinical.