Effects of TNF-α knockout on liver and spleen neutrophil responses to Vibrio vulnificus bloodstream infection in a mouse model / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To investigate the effects of TNF-α knockout on liver and spleen neutrophil responses to Vibrio vulnificus bloodstream infection in a mouse model. Methods:(1) TNF-α-knockout (TNF-α -/-) and wild-type (WT) C57BL/6J mice aged 6-8 weeks were randomly divided into four groups with six in each group uninfected WT group, infected WT group, uninfected TNF-α -/- group and infected TNF-α -/- group. The mouse model of bloodstream infection was constructed by intraperitoneal injection of Vibrio vulnificus CGMCC1.1758 (2×10 8 CFU/200 μl), while the mice in the uninfected groups were injected intraperitoneally with equal amount of PBS. (2) Liver immune cells and splenocytes were isolated 4 h after infection and subjected to analyze the percentages and numbers of neutrophils, and the changes in cell viability, cellular reactive oxygen species (ROS) level and phagocytosis by flow cytometry. In addition, effects of Vibrio vulnificus bloodstream infection on mTOR signaling pathway in murine neutrophils were evaluated in vivo. Results:(1)Compared with the uninfected WT group, the percentages and numbers of neutrophils in liver and spleen tissues of the infected WT group increased significantly. The percentage and number of liver neutrophils were significantly higher in the infected TNF-α -/- group than in the infected WT group, but no significant difference in spleen neutrophils was detected between the two groups. (2) Compared with the infected WT group, the phagocytosis of liver neutrophils rather than that of spleen neutrophils was enhanced in the infected TNF-α -/- group. (3) The survival rates of neutrophils in both liver and spleen were decreased, while the cellular ROS level was significantly increased in the infected WT group compared with those of the uninfected WT group. Compared with the infected WT group, the infected TNF-α -/- group had increased survival rates of both liver and spleen neutrophils, but decreased level of ROS. (4) The levels of p-AKT (S473) in liver and spleen neutrophils of the infected WT group were lower than those of the uninfected WT group. Compared with the infected WT group, the infected TNF-α -/- group had lower level of p-AKT (S473) in liver neutrophils, but higher p-AKT (S473) level in spleen neutrophils. There were no significant differences in p-4E-BP1(T37/46) levels between the uninfected WT group and the infected WT group. The p-4E-BP1 (T37/46) level in liver neutrophils was lower in the infected TNF-α -/- group than in the infected WT group, but no significant difference in p-4E-BP1 (T37/46) levels in spleen neutrophils was observed between the two groups. Conclusions:TNF-α had different effects on the neutrophils in spleen and liver tissues of mice with Vibrio vulnificus bloodstream infection. It played a critical role in regulating the recruitment, phagocytic function and mTOR signaling of liver neutrophils after Vibrio vulnificus infection in vivo.