Effects Of Astragaloside On The Bactericidal Activity Of Neutrophils

When the body is exposed to acute infection,neutrophils are first raised to the site of infection.Neutrophils phagocytose and kill foreign microorganisms to release soluble inflammatory mediators,and then induce monocyte chemotaxis to the site of infection to play a synergistic effect.More and more studies have reported that the expression of CXCR2 on the surface of neutrophils is closely related to the migration and chemotaxis of the microbial infection in animal models and patients.Increasing studies have shown that astragaloside(AS-IV),as one of the main active constituents of Astragalus membranaceus,exhibits a wide range of biological and pharmacological activities and plays an important role in fungal,bacterial and viral-induced infections.In this study,we established the mouse model of intraperitoneal infection to observe the anti-infective immunoregulation effect of AS-IV and its potential mechanism,and provide new ideas for patients with clinical targeted therapy.Objective To investigate the effect of AS-IV on the bactericidal function of neutrophils,as well as its potential effect on neutrophil chemotaxis,phagocytosis and killing activity.Methods Two mice models of E.coli abdominal infection and caecal ligation and perforation(CLP)were established.After AS-IV administrated,the survival rate of mice was examined.The changes of bacterial quantity,the number of neutrophils,the expression of CXCR2 on the surface of neutrophils,the levels of inflammatory factors and chemokines were detected in bacterial-infected mice.The tissues were fixed and histopathologically examined.Flow cytometry,immunofluorescence and PCR were used to detect the mechanism of AS-IV on regulation of neutrophil bactericidal activities.Results 1.Protective effect of AS-IV on E.coli intraperitoneal infection The mice were treated with lethal dose of E.coli peritoneal infection.After AS-IV pretreatment,the mental state of mice improved and the survival rate in mice increased significantly.Meantime,the bacterial load in blood,peritoneal fluid and various organs was decreased.The expression of CXCR2 on the surface of neutrophils was significantly increased.The number of neutrophils in blood and peritoneal fluid were increased.The level of TNF-α was also decreased.2.Protective effect of AS-IV on CLP mice After treatment of AS-IV,the drinking water of mice was improved and the survival rate was significantly increased.The bacterial load in blood,peritoneal fluid and various organs was decreased.The number of neutrophils in peripheral blood and peritoneal fluid was increased.The pathological damage of lung tissues was alleviated.3.Effect of AS-IV on neutrophil bactericidal function AS-IV enhanced neutrophil chemotaxis,phagocytosis and killing function.AS-IV blocked the down-regulation of CXCR2 on neutrophil surface induced by LPS,and increases the chemotactic capacity of neutrophils to CXCL2.AS-IV inhibited the up-regulation of neutrophil Grk2 stimulated by LPS.AS-IV displays protective effects on bacterial-infected mice through Grk2-CXCR2 signaling.Conclusion AS-IV regulates neutrophil chemotaxis function through the Grk2-CXCR2 signal pathway,and then enhances the anti-infective immune response in bacteria-infected mice.