Objective:To investigate the levels and correlation between myeloid-derived suppressor cell (MDSC) and T lymphocyte subsets in peripheral blood of patients with active pulmonary tuberculosis.Methods:A total of 38 patients with active pulmonary tuberculosis in Nanjing Second Hospital from February 2019 to June 2020 were selected as the tuberculosis group, and 23 healthy outpatient physical examination patients were selected as the healthy control group during the same period. The levels of MDSC, clinically related indicators, inflammatory cytokines and lymphocyte subsets were compared between each group, and the correlation between MDSC and lymphocyte subsets was analyzed. Meanwhile, the levels of MDSC and lymphocyte subsets before and after treatment were compared.Results:The MDSC and CRP in tuberculosis group were higher than those in healthy group: (16.41 ± 2.13)% vs. (1.82 ± 0.54)%, (25.42 ± 10.56) mg/L vs. (5.82 ± 1.39) mg/L ( P<0.05). Serum inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, IL-10 and interferon (IFN)-γ in tuberculosis group were significantly higher than those in healthy control group ( P<0.05). T lymphocyte subsets CD 3+ T cell, CD 4+ T cell, CD 8+ T cell and CD 16/56+ nature killer (NK) cell in tuberculosis group were significantly lower than those in healthy control group ( P<0.05), while the number of CD 19+ B cell was not statistically significant ( P>0.05). Correlation analysis showed that MDSC was negatively correlated with T lymphocyte subsets CD 3+ T cell ( r = -0.73, P<0.001), CD 4+ T cell ( r = -0.68, P<0.001) and CD 8+ T cell ( r = -0.53, P = 0.001), but had no significant correlation with CD 16/56+ NK cell ( r = -0.10, P = 0.561). CD 3+ T cell, CD 4+ T cell, CD 8+ T cell and CD 16/56+ NK cell were significantly different in peripheral blood MDSC before and after treatment ( P<0.05). Conclusions:MDSC, CD 3+ T cell, CD 4+ T cell, CD 8+ T cell and CD 16/56+ NK cell have a guiding role in the diagnosis and evaluation of the curative effect of active pulmonary tuberculosis, with high value in clinical application.