Abstract: OBJECTIVE To explore the expression of dendritic cell PD-L1 and immune response of mice with lipopolysaccharide (LPS)-induced bacterial sepsis. METHODS The dendritic cells of mice were stimulated by LPS so as to establish immune paralysis system of sepsis.The morphology of dendritic cells, expression of PD-L1 and SIINFEKL-specific T cell proliferation in vitro were detected by means of microscopic imaging technique, flow cytometry, immunofluorescence and BrdU cell proliferation assay kit. RESULTS The immature dendritic cells turned to be mature ones by the stimulation of LPS, and the average fluorescence intensity of positive PD-L1 cell was significantly increased from 4.91±0.04 in Control group to 26.56±0.39(P＜0.05); the percentage of positive SIINFEKL-H-2Kb was significantly increased from (19.08±0.86)% to (87.54±1.36)%(P＜0.05).The OD value of BrdU-labeled SIINFEKL-specific T cell proliferation was decreased to 0.358±0.030, however, the OD value of cell proliferation was significantly increased from 0.358±0.030 to 0.590±0.018 after the PD-L1 blocking(P＜0.05). CONCLUSION The high-expression co-inhibitory molecule PD-L1 in the dendritic cells may lead to the low immune response of T cells of the mice with LPS-induced sepsis, however, the PD-L1 blocking may improve the immune paralysis of the mice with bacterial sepsis.