Abstract: Objective To explore the relationship between Toll-like receptor 4(TLR4) and Legionella infection in a mouse model.Methods TLR4 gene mutant mice of C3H/HeJ and control mouse C3H/HeN were used as experimental animals.The C3H/HeJ and C3H/HeN mice of infection group were treated with tracheal injection of bacterial suspension to make a mouse Legionella pneumophila infection model.The C3H/HeN mice in the control group were treated with tracheal injection of sterile saline.TLR4 protein expression level in peripheral blood mononuclear cells(PBMCs) of the mice were detected with flow cytometry.Results Pathological examination showed that lung tissue of C3H/HeJ and C3H/HeN infection group presented infiltration of inflammatory cells and alveolar vascular bleeding,while the mice of control group showed no inflammatory reaction.The lung and spleen coefficients of infection group were obviously higher than those in the control group.Legionella pneumonia model was established successfully.In 12 hours,TLR4 protein expression of C3H/HeJ infection group was relatively lower than that of C3H/HeN infection group (P<0.001),but there was no significant difference in the expression between C3H/HeN infection group and C3H/HeN control group(P>0.05).Conclusion The TLR4 gene mutations could decrease the reaction to Legionella in mice.However,the anti-inflammatory effect of TLR4 on Legionella needs further study.