氏名:Thanyakorn Chalalai
所属:感染予防医学講座
修学指導教員氏名:花田 俊勝、研究指導教員氏名:小林 隆志
演題目:Physiological relevance of TRAF6 signaling in dendritic cells in controlling C. rodentium infection
座長:白石 裕士(細胞生物学講座)・松本 昂(環境予防医学講座)
【目 的】
Citrobacter rodentium (C. rodentium) has been used as a mouse infection model for studying human enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC). Upon ligation of pattern recognition receptors (PRRs), such as Toll-like-receptors by pathogen-associated molecular patterns (PAMPs), an intracellular molecule, tumor necrosis factor receptor-associated factor 6 (TRAF6) activates downstream signaling molecules required for inflammatory responses. However, physiological relevance of TRAF6 signaling in controlling C. rodentium infection remains unclear. Thus, we infected C. rodentium to dendritic cells-specific TRAF6-defifient (TRAF6D DC; CD11c-Cre Traf6 flox/flox) mice and analyzed the phenotype of the mice.
【方 法】
@ TRAF6D DC mice and wild-type (WT) mice were orally infected with 2 x 109 CFU of C. rodentium and monitored both survival rate and body weight changes. A Enumeration of the fecal and tissues bacterial load was performed after infection. B To assess the severity of the inflammation of the colon induced by C. rodentium infection, colon length was measured and, histological scores were calculated using H&E stained colonic tissue sections. C The expression levels of genes such as IL-12p40, IL-17 and IFN-γ which deeply correlated with both Th1 and Th17 responses in the colon were measured by real time PCR assay. D The population of Th17 cells and neutrophils in the colon were analyzed by flow cytometric analysis and immunohistochemistry, respectively.
【結 果】
@ TRAF6D DC mice showed body weight loss at 4 days post-infection (dpi), and started to die from 8 dpi, and approximately half of them survived. On the other hand, WT mice did not show body weight loss at all, and all mice survived. A An increased number of colonies was observed in the stool and colon of TRAF6D DC mice. B TRAF6D DC mice showed significantly shorter colon length, and higher histological scores than WT mice. C The expression levels of IL-12p40 and IFN-γ, but not IL-17 were reduced in TRAF6D DC mice. D In TRAF6D DC mice, both the number and proportion of Th17 cells were comparable with those of WT mice. Infiltration of neutrophils in the colon was rather enhanced in TRAF6D DC mice.
【考察(問題点等を含む)】
Here we found that TRAF6D DC mice were more susceptible to C. rodentium infection than WT mice. It has been reported that both Th1 and Th17 responses are important for the elimination of C. rodentium. In fact, bothIL-17, and IFN-γ-deficient mice were susceptible to C. rodentium infection. Given the decrease in IL-12p40, a common subunit of both IL-12 and IL-23, in TRAF6D DC mice, both Th1 and Th17 responses might be impaired in the mutant mice. Indeed, Th1 response as judged by increased levels of IFN-γ was impaired in TRAF6D DC mice. However, Th17 response as judged by IL-17 production was comparable between two groups and remarkable neutrophil infiltration was observed in the mutant mice. These results suggest that Th17 response inducing the recruitment of neutrophils is not sufficient for the eradication of C. rodentium.
【今後の計画】
To examine whether Th1 response inducing the activation of macrophages is responsible for the susceptibility to C. rodentium infection in TRAF6D DC mice, we well measure iNOS levels in macrophages using both immunohistochemical and flow cytometric analysis. |