Objective To prepare the anti-TLR4 C-terminal domain monoclonal antibody and investigate its effect in treatment of sepsis.Methods TLR4 C-terminal polypeptide (amino acid sequence:368-579,named as TLR4-C) was obtained through prokaryotic expression and Sephacryl S-100 gel purification,and then was used to immunize female Balb/c mice (6-8 weeks old).After cell fusion,antibody screening and purification,monoclonal antibody specific for the C terminal of TLR4 was obtained.Specificity of monoclonal antibody was detected by Western blot and cell immunofluorescence.In vitro antibody activity test,NR8383 was cultured for 1 h with adding antibody (100 μg/ml) and then 12 h after adding lipopolysaccharide (LPS) (10 ng/ml),and level of tumor growth factor (TNF)-α in the culture medium was tested by ELISA.In vivo septic animal experiment,40 SD rats were assigned to control antibody group (n =20) and anti-TLR4 monoclonal antibody group (n =20) according to the random number table.Each group was rejected 50 mg/kg corresponding antibodies via caudal vein for 1 h,and then LPS (10 mg/kg) via intraperitoneal injection for 4 h.Blood samples from caudal vein of ten rats in each group were collect to test the serum level of TNF-α.The rest rats in each group were used to measure the animal survival rate within 72 h.Results Three highly specific anti-TLR4 monoclonal antibodies were obtained and could combined with TLR4-C and TLR4 holoprotein.In vitro cell activity study indicated only one monoclonal antibody could obviously inhibit the release of TNF-α.In vivo animal experiment showed serum TNF-α level in anti-TLR4-C antibody group was (1.54 ± 0.18) ng/ml,significantly lower than (0.51 ± 0.10) ng/ml in antibody control group (P ＜ 0.01).Animal survival rate in anti-TLR4-C antibody group was 70％,higher than 30％ in antibody control group (P ＜ 0.05).Conclusion Anti-TLR4-C monoclonal antibodies have great capacity to neutralize TLR4 and good protective effect on LPS-induced sepsis.