Objective To study the changes of immune function of endotoxin tolerant dendritic cell (ETDC) and to observe its effect on sepsis in mouse model.Methods ETDC were prepared by pretreated bone marrow dendritic cells derived from BALB/c mice with lipopolysaccharide stimulation.The cells were collected and the expressions of surface markers including major histocompatibility complex ( MHC)Ⅱ, CD86 and CD11c were detected by flow cytometry.The proliferation rate of T lymphocytes was evaluated by cell counting kit-8 and the concentrations of cytokines in the supernatant were detected by enzyme linked immuno sorbent assay.Afterwards, 36 mice were randomly assigned into 4 groups.The blank control group did not receive any treatment, the sham-operated group underwent simple incision suture, the sepsis group and ETDC reinfusion group underwent cecal ligation and puncture to establish sepsis.Before sepsis model establishment, 0.9% sodium chloride solution or suspension of ETDC and 0.9%sodium chloride were reinfused by tail vein.The serum levels of alanine aminotransferase (ALT) and aspartate transaminase (AST), tumor necrosis factor (TNF)-α, interleukin(IL)-6 and IL-10, and the proportion of help T cell ( Th) 17/regulatory T cell ( Treg) in spleen of each group were detected.The pathological manifestations of liver, kidney and ileum in each group were observed.T test and χ2 test were used for comparisons between groups.Results The results of flow cytometry showed that MHCⅡ, CD86 and CD11c of ETDC were 70.4%, 43.1%, and 73.1%, respectively, which were significantly lower than those of mature dendritic cell (mDC) (96.1%, 89.5%, and 84.6%, respectively) (χ2 ＝56.47, 83.78, and 23.29, respectively, all P＜0.01).The concentrations of IL-10, TNF-αand IL-6 in the supernatant of ETDC were (978.04 ±56.70), (980.34 ±111.96) and (12 743.03 ±865.81) ng/L, respectively, and those of mDC were (741.35 ±99.23), (1 703.11 ±117.00) and (19 052.28 ±1 145.84) ng/L, respectively.The differences were all statistically significant (t＝5.073, 10.93, and 10.76, respectively, all P＜0.01).The proliferation rates of T lymphocytes co-cultured with ETDC in 1∶5 and 1∶10 ratio group were (676.95 ±85.99)%and (514.00 ±106.39)%, respectively, which were lower than those of the mDC group (956.25 ±127.12)%and (772.07 ±214.08)%, respectively.The pathological injuries of liver, kidney and ileum in ETDC treatment group were significantly lighter than those in sepsis group.Serum ALT and AST levels in the ETDC reinfusion group were (299.71 ±36.91) and (690.39 ±154.92) U/L, respectively, and TNF-α, IL-6 and IL-10 were (0.067 ±0.005), (0.428 ±0.051) and (0.058 ±0.005) ng/L, respectively.Serum ALT and AST levels in the sepsis group were (620.67 ±69.27) and (1 430.17 ±134.05) U/L, respectively, and TNF-α, IL-6 and IL-10 were (0.085 ±0.007), (0.774 ±0.088) and (0.036 ±0.005) ng/L, respectively.The differences were all statistically significant (t＝11.60, 10.96, 5.991, 8.657, and 8.04, respectively, all P ＜0.01).The proportion of Treg/Th17 in the ETDC reinfusion group was 23.4%, and that in the sepsis group was 60.8%(χ2 ＝28.69, P＜0.01).Conclusion The reinfusion of ETDC has a protective effect on sepsis in mouse model, which may play a negative immune regulatory role by regulating the differentiation of T cells.