PURPOSE: The current study aimed to elucidate the role of peritoneal fluid IL-17A in septic mice, and the effects of intraperitoneal or intravenous blockade of the IL-1 7A pathway by anti-IL17A antibody on survival, plasma, and peritoneal cavity cytokine profile in a murine caecal ligation and puncture (CLP) sepsis model.The main source of peritoneal fluid IL-17A in septic mice was identified.METHODS: Male C57BL/6 mice that underwent severe CLP or sham surgery were intraperitoneally or intravenously administered anti-IL17A antibodies or isotype antibodies.The survival rates were observed.IL-17A, TNF-α, and IL-6 cytokine levels were measured by ELISA.Surface and intracellular IL-17A immunofluorescence stains were detected by flow cytometry to identify the IL-17A-producing cells.RESULTS: The IL-17A level was elevated much higher and earlier in peritoneal fluid than in the blood of the CLP mice.The intraperitoneal IL-17A blockade more significantly protects against CLP-induced mortality than intravenous blockade because of decreased TNF-α and IL-6 levels both in peritoneal fluid and blood, neutrophil infiltration in the peritoneal cavity, and lung injury, γδ T lymphocytes were identified to be the main source of IL-17A in the peritoneal fluid of septic mice.CONCLUSIONS: The earlier and higher elevated IL-17A derived from γδ T cells in peritoneal fluid plays a critical role during polymicrobial severe sepsis and effect of intraperitoneal IL-17A antibody administration superior to intravenous administration on survival of severe CLP-induced septic mice.The intraperitoneal blockade of IL-17A decreases proinflammatory cytokine production, neutrophil infiltration, and lung injury, thereby improving septic mice survival, which provides a new potential therapy target for sepsis.