Salmonella pathogenicity island 2 triggers pore-induced intracellular trap formation to evade killing by neutrophils

项目摘要 沙门氏菌血清型可引起人类严重的肠外疾病。而 嗜中性粒细胞可使用NADPH氧化酶依赖性杀伤作用杀死细胞外细菌 巨噬细胞支持病原体在组织中的生长。主要毒力 促进肠外部位细菌存活的因子，III型分泌系统 （T3 SS-2）由沙门氏菌致病岛（SPI）-2编码，在逃避 宿主吞噬细胞的NADPH氧化酶依赖性杀伤。特别是，T3 SS-2缺陷 突变体可以在小鼠肝脏和脾脏的巨噬细胞内生长，这表明 毒力因子不能逃避巨噬细胞的NADPH氧化酶依赖性杀伤， vivo.我们的中心假设是S.细胞内的鼠伤寒 死亡巨噬细胞的碎片（称为孔诱导的细胞内陷阱或PIT） 病原体从中性粒细胞NADPH氧化酶依赖的杀伤机制， 含有活菌的细胞碎片的胞饮作用。通过这种机制，T3 SS- 2-依赖性巨噬细胞PIT形成使S.鼠伤寒逃避NADPH 当病原体从受感染的细胞中排出时，嗜中性粒细胞的氧化酶依赖性杀伤， 形成新的感染灶。我们将测试我们的假设的关键方面，确定是否 巨噬细胞PIT中的定位保护沙门氏菌免受嗜中性粒细胞ROS（特异性目的 1)并通过阐明沙门氏菌T3 SS-2如何使补体到达细胞内 PIT中的细菌（具体目标2）。成功完成拟议的实验将 建立了巨噬细胞PIT形成是一种毒力策略的新概念， 细胞内病原体逃避嗜热菌介导的宿主防御。

PROJECT SUMMARY Salmonella serovars can cause severe extraintestinal disease in humans. While neutrophils can kill extracellular bacteria using NADPH oxidase-dependent killing mechanisms, macrophages support growth of the pathogen in tissue. The main virulence factor promoting bacterial survival at extraintestinal sites, a type III secretion system (T3SS-2) encoded by Salmonella pathogenicity island (SPI)-2, functions in evading NADPH oxidase-dependent killing by host phagocytes. Paradoxically, T3SS-2-deficient mutants can grow within macrophages in the liver and spleen of mice, suggesting that the virulence factor does not evade NADPH oxidase-dependent killing by macrophages in vivo. Our central hypothesis is that entrapment of S. Typhimurium within the cellular debris of a dead macrophage (termed the pore-induced intracellular trap or PIT) protects the pathogen from neutrophil NADPH oxidase-dependent killing mechanisms during efferocytosis of cellular debris containing viable bacteria. Through this mechanism, T3SS- 2-dependent macrophage PIT formation enables S. Typhimurium to evade NADPH oxidase-dependent killing by neutrophils when the pathogen exits from infected cells to form new infection foci. We will test key aspects of our hypothesis by determining whether localization in macrophage PITs protects Salmonella from neutrophil ROS (Specific Aim 1) and by elucidating how Salmonella T3SS-2 enables complement to reach intracellular bacteria in PITs (Specific Aim 2). Successful completion of the proposed experiments will establish the novel concept that macrophage PIT formation is a virulence strategy of intracellular pathogens to evade neutrophil-mediated host defenses.