| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 98 === Salmonella is a facultative intracellular pathogen that causes disease in a variety of hosts. Salmonella is capable of escaping phagocyte killing by delaying phagosome formation. In epithelial cells, S. Typhimurium was reported to damage Salmonella-containing vesicles (SCV) through a type III secretion system (TTSS) in Salmonella pathogenicity island 1 (SPI-1), thereby activating autophagosome formation. Base on our previous data, some intracellular Salmonella was engulfed by autophagosomes in human macrophage-like THP-1 cells at 24 hrs post-infection in electron microscopy. The mechanism of autophagy in Salmonella-infected macrophages was evaluated in this study. The protein expression ratio of LC3II/LC3I was used as an indicator of autophagy activation. Our data showed that S. Typhimurium induced autophagy after 2 hrs post-infection in THP-1 cells. Besides, Salmonella colocalized with autophagosome at 3 hrs post-infection in Raw264.7 cells with confocal analysis. It was known that host cells secrete several inflammatory cytokines to activate innate immunity system after bacterial infection. To clarify which cytokine may be involved in the activation of autophagy, cytokine expression profile was analyzed by an inflammatory cytokine array. At 4 hrs post-infection, S. Typhimurium induced high level of IL-1β, IL-6, IL-8, and TNF-α secretion. To figure out the effect of these cytokines in Salmonella-induced autophagy, cells were pretreated with these cytokines in starvation condition. The results showed that both IL-1β and IL-6 decreased the expression ratio of LC3II/ LC3I, while IL-8 and TNF-α had no effect. In Salmonella-infected macrophages, the autophagy activation also decreased with the pretreatment of IL-6. The results showed that inflammatory cytokines, especially IL-6, may play a role in regulating autophagy activation induced by Salmonella infection.
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