Dissecting Innate Immune Responses to Salmonella Enteritidis

项目概要和摘要 肠道沙门氏菌是美国食源性住院的主要原因。沙门氏菌 肠道菌包括超过2500种循环亚种或血清型，其引起的疾病范围从自身- 将胃肠炎限制为严重的全身性疾病和死亡。沙门氏菌的致病性和宿主研究 对沙门氏菌的免疫应答依赖于有限数量的常用参考沙门氏菌。伤寒 鼠伤寒（STm）或伤寒菌株。虽然这些研究已经确定了宿主的基本机制， 沙门氏菌的相互作用，它们不反映沙门氏菌之间广泛的基因型或表型多样性 enterica物种，这表明我们对宿主对沙门氏菌反应的理解存在重大差距。先天的 免疫系统识别和响应其他沙门氏菌血清型是特别感兴趣的，作为一个重要的 部分疾病是由伤寒或鼠伤寒以外的血清型引起的。先天性免疫系统发挥着 在宿主防御感染中起关键作用，因此代表了特别有吸引力的研究目标。 沙门氏菌在巨噬细胞内侵入和复制，并利用保守的III型分泌系统 由称为沙门氏菌致病岛2（SPI-2）的基因组区域编码，以注射毒力因子， 被称为“效应器”，进入宿主细胞质。这些效应器操纵宿主环境并允许 沙门氏菌维持细胞内生态位。SPI-2效应子显示血清型内和血清型间遗传 多样性，这有助于宿主对感染的反应的重要差异。虽然效应器很重要， 对于细菌毒力，它们还使宿主能够检测细胞内细菌。一种先天的 免疫识别涉及细胞溶质先天免疫传感器， 细胞质内激活炎性半胱天冬酶-1和/或-11（Casp 1/11）的效应物。Casp 1/11切割 并激活IL-1家族细胞因子和孔形成蛋白Gasdermin-D（GSDMD），导致 炎性细胞死亡称为焦亡。Casp 1/11是引起焦亡所必需的， 研究了S.鼠伤寒有趣的是，与先前的研究相比，我的初步研究显示， 第一次多个S。不同血清型的肠道临床分离株，包括S.肠道，触发Casp 1/11- 独立的GSDMD裂解、IL-1释放和细胞死亡。此外，我的初步研究进一步 证明S.肠杆菌和其他临床分离株在SPI中诱导这种Casp 1/11非依赖性细胞死亡， 2-依赖的方式。这些数据以及本提案中讨论的其他初步调查结果， 激发了沙门氏菌具有独特的SPI-2效应子的假设， Casp 8介导的焦亡。在这个提议中，我的目标是定义介导Casp 1/11的宿主途径- 响应于临床沙门氏菌分离株的独立细胞死亡（目的1），以及负责的细菌因子 引发这种细胞死亡（目标2）。拟议的项目将扩大我们对沙门氏菌的了解 致病机理和宿主对当前流行菌株的反应。

Project Summary and Abstract Salmonella enterica is the leading cause of food-borne hospitalizations in the United States. The Salmonella enterica species includes over 2500 circulating sub-species, or serovars, which cause disease ranging from self- limiting gastroenteritis to severe systemic disease and death. Studies of Salmonella pathogenicity and host immune responses to Salmonella rely on a limited number of commonly used reference S. enterica serovar Typhimurium (STm) or Typhi strains. While these studies have defined fundamental mechanisms of host- Salmonella interactions, they do not reflect the broad genotypic or phenotypic diversity among Salmonella enterica species, suggesting a crucial gap in our understanding of host responses to Salmonella. How the innate immune system recognizes and responds to other Salmonella serovars is of particular interest, as a significant fraction of disease is caused by serovars other than Typhi or Typhimurium. The innate immune system plays a crucial role in host defense against infection, and therefore represents a particularly attractive target for study. Salmonella invades and replicates within macrophages and utilizes a conserved type III secretion system encoded by a genomic region termed the Salmonella Pathogenicity Island 2 (SPI-2), to inject virulence factors, known as ‘effectors’, into the host cytosol. These effectors manipulate the host environment and permit Salmonella maintenance of an intracellular niche. SPI-2 effectors display intra- and inter-serovar genetic diversity, which contributes to important differences in host responses to infection. While effectors are important for bacterial virulence, they also enable the host to detect intracellular bacteria. One mechanism of innate immune recognition involves cytosolic innate immune sensors that detect bacterial ligands or the activity of effectors within the cytosol which activate the inflammatory caspases -1 and/or -11 (Casp1/11). Casp1/11 cleave and activate IL-1 family cytokines and the pore-forming protein Gasdermin-D (GSDMD), leading to an inflammatory cell death termed pyroptosis. Casp1/11 are necessary for pyroptosis in response to commonly studied strains of S. Typhimurium. Intriguingly, in contrast to prior studies, my preliminary studies show for the first time that multiple S. enterica clinical isolates of different serovars, including S. Enteritidis, trigger Casp1/11- independent GSDMD cleavage, IL-1 release, and cell death. Moreover, my preliminary studies further demonstrate that S. Enteritidis, and other clinical isolates, induce this Casp1/11-independent cell death in a SPI- 2-dependent manner. These data and as well as additional preliminary findings discussed in this proposal, provoke the hypothesis that Salmonella Enteritidis possesses a unique SPI-2 effector which triggers Casp8-mediated pyroptosis. In this proposal, I aim to define the host pathways mediating Casp1/11- independent cell death in response to clinical Salmonella isolates (Aim 1), and the bacterial factor(s) responsible for triggering this cell death (Aim 2). The proposed project will expand our understanding of Salmonella pathogenesis and host-responses to currently circulating strains.