ObjectiveTo explore the expression of programmed death-1 ligand (PD-L1) on peripheral blood monocytes in septic mice, and analyze the difference between the mild and severe septic mice. MethodsFirstly, thirty C57 mice were randomly divided into a sham group, a mild sepsis group and a severe sepsis group. Sepsis model was induced by cecal ligation and puncture (CLP). The severity of sepsis was distinguished by length of cecum ligated. Survival rate was recorded after CLP and compared between three groups. Then sixty C57 mice were randomly divided into a sham group, a mild sepsis group and a severe sepsis group. Peripheral blood was obtained at 6 h and 24 h to detect PD-L1 expression on monocytes in peripheral blood by flow cytometry. Tumor necrosis factor-α(TNF-α) and interleukin-10 (IL-10) in serum were detected by enzyme-linked immunosorbent assay. ResultsThe survival rate in the mild sepsis group was higher than that in the severe sepsis group. TNF-αand IL-10 levels in the mild and severe sepsis groups were higher than those in the sham group at 6 h and 24 h (P < 0.01). PD-L1 expression on monocytes in the mild and severe sepsis groups was higher than that in the sham group at 6 h and 24 h (P < 0.05). The expression of PD-L1 in the severe sepsis group was higher than that in the mild sepsis group, however, there was no statistical difference between two groups (P > 0.05). ConclusionsPD-L1 expression on monocytes is increased in septic mice. PD-L1 expression tended to increase in severe sepsis compared with the mild sepsis.