Abstract: Objective: To study the correlation between regulatory T cell subsets(Treg) and cytokines in patients with transfusion-related acute lung injury(TRALI).Methods: We collected 43 TRALI patients who admitted to our hospital from January 2020 to February 2021.At the same time, 40 cases of patients with no acute lung injury(non-TRALI group) and healthy volunteers(healthy group) in the physical examination department were selected during the same period. The peripheral venous blood of the subjects was collected and the T lymphocytes in the blood were measured by flow cytometry. Population distribution and CD4⁺CD25⁺Treg cytokine expression, and data analysis.Results: There was no significant difference in the distribution of CD3⁺, CD3⁺CD4⁺T cells in the 3 groups(P>0.05). There was no significant difference in the peripheral blood CD3⁺CD8⁺, CD4⁺CD25⁺Treg, CD4⁺/CD8⁺between the healthy group and the non-TRALI group(t=0.461, 0.240, 0.631, P>0.05). Compared with healthy group and non-TRALI group, the proportion of CD3⁺CD8⁺, CD4⁺CD25⁺Treg cells in TRALI group increased significantly(P<0.05), while CD4⁺/CD8⁺significantly reduced(P<0.05). The expression levels of TGF-β1 and IL-10 in the PBMNC supernatant of the healthy group and the non-TRALI group were not significantly different(P>0.05). Compared with the healthy group and the non-TRALI group, the TGF of the TRALI group-β and IL-10 levels were significantly increased(P<0.05). Compared with the survival group, the proportion of CD4⁺CD25⁺Treg in the peripheral blood of patients who died of TRALI and the expression of IL-10 and TGF-β1 significantly increased(P<0.05). Pearson correlation analysis showed that the distribution of CD4⁺CD25⁺Treg in the peripheral blood of the TRALI group was significantly positively correlated with TGF-β1 and IL-10(r=0.830, 0.159, P<0.05).Conclusion: The proportion of CD4⁺CD25⁺Treg cells in the peripheral blood of TRALI patients is increased, which exerts an immunosuppressive effect by up-regulating the expression of cytokines. Early monitoring of CD4⁺CD25⁺Treg cells and their cytokine expression can provide reference for prognostic evaluation of TRALI and clinical intervention measures.