Objective To investigate the relationship between the helper T cell 17 (TH 17)/ Regulatory T cells (Treg cells) balance in peripheral blood with acute graft-versus-host reaction (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT),as well as the impact of anti-thymocyte immunoglobulin (ATG) on helper T cells in peripheral blood.Method Seventyeight hematologic patients underwent allo-HSCT,conditioning with or without ATG.Ten healthy volunteers severed as a control group.The helper T and regulatory T cells in peripheral blood were detected by flow cytometry.Enzyme-linked irnmunosorbent assay (ELISA) was used to detect serum concentrations of interleukin(IL)-17,IL-21,IL22,IL23,γ interferon (IFN-γ),and transforming growth factor β1 (TGF-β1).Result The percentage of Treg cells,TH17 cells and ratio of TH17/Treg cells in patients without aGVHD showed no significant difference from the healthy controls (P＞ 0.05).As compared with control group and non aGVHD group,the ratio of Treg cells was increased,the percentage of TH 17 cells,and TH 17/Treg cells were significantly increased in 1-2-degree aGVHD group (P＜0.01).With increased degree of aGVHD,the difference as above was more significant in 3-4-degree aGVHD recipients (P＜0.01).In aGVHD group,the IL-17,IL-23,IL-21 and IFN-γ concentrations were higher than the healthy group (P＜0.01) and non-aGVHD group (P＜0.05).Serum TGF-β1 level in aGVHD group was significantly decreased as compared with healthy group and non-GVHD group (P＜0.05),while IL-22 concentrations showed no statistically significant difference among three groups (P＞0.05).In anti-thymocyte immunoglobulin (ATG) pretreatment group,the absolute count of peripheral blood lymphocytes was less than in healthy control group (P＜0.01).In ATG group,the absolute counts of TH1 cells,TH17 cells,CD3+ CD4+ cells and non-TH1/17 cells were less than in non-ATG group (P =0.0000),while the absolute counts of lymphocytes,CD3+ CD4-cells,and TH 1/17 cells were less than in non-ATG group,but there was significant difference (P＞0.05).Conclusion The balance of TH 17/Treg cells and related cytokines were closely associated with aGVHD after allo-HSCT,and ATG influences the reconstruction of TH 17 and Th1 cells at early stage.