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

项目总结 沙门氏菌血清型可导致人类严重的肠外疾病。而当 中性粒细胞通过NADPH氧化酶依赖的杀灭作用杀灭胞外细菌 巨噬细胞支持病原体在组织中的生长。主要毒力 促进细菌在肠外部位存活的因子，一种III型分泌系统 沙门氏菌致病岛(SPI)-2编码的(T3SS-2)在逃避中的作用 宿主吞噬细胞对NADPH氧化酶依赖的杀伤作用。矛盾的是，T3SS-2缺乏 突变株可以在小鼠肝和脾的巨噬细胞内生长，这表明 毒力因子不能逃避巨噬细胞对NADPH氧化酶依赖的杀伤 活着。我们的中心假设是鼠伤寒沙门氏菌在细胞内的捕获 死亡巨噬细胞的碎片(称为气孔诱导的细胞内陷阱或凹坑)保护 中性粒细胞NADPH氧化酶依赖性杀伤机制的病原体 含有活细菌的细胞碎片的胞吐作用。通过这个机制，T3SS- 小鼠伤寒沙门氏菌2依赖的巨噬细胞小坑形成使其能够逃避NADPH 当病原体从受感染的细胞退出时，中性粒细胞对氧化酶依赖的杀伤作用 形成新的感染源。我们将测试我们假设的关键方面，方法是确定 巨噬细胞小窝中的定位保护沙门氏菌免受中性粒细胞ROS的影响(特定目标 1)并通过阐明沙门氏菌T3SS-2如何使补体到达细胞内 坑内细菌(特定目标2)。成功完成拟议的实验将 建立新的概念，即巨噬细胞坑形成是一种毒力策略 细胞内病原体逃避中性粒细胞介导的宿主防御。

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.