Active Subversion of Innate Immunity by Bacterial LysM Protein

描述（由申请人提供）：细胞内病原体导致数量惊人的人类感染和死亡。破坏宿主先天免疫反应的能力是这些病原体建立感染的关键因素。单核细胞增生李斯特菌是人类和动物的兼性细胞内细菌病原体，经常被用作解剖免疫机制和发病机制的模型。我们之前对单核增生乳杆菌的研究发现了一种细菌蛋白p60，在小鼠全身感染模型中，细菌的表达和分泌是致病性所必需的。在培养细胞中，Lm感染不需要p60。我们发现p60刺激宿主自然杀伤细胞（NK）的激活，NK细胞是一种免疫细胞群，与宿主对单核增生乳杆菌和其他几种致病菌的易感性增加有关。我们已经证明p60通过结合树突状细胞刺激NK细胞，并引发IL-1和IL-18的产生。

DESCRIPTION (provided by applicant): Intracellular pathogens cause a staggering number of human infections and deaths. The ability to subvert host innate immune responses is a key factor in the establishment of infections by these pathogens. Listeria monocytogenes is a facultative intracellular bacterial pathogen of humans and animals and is frequently used as a model to dissect mechanisms of immunity and pathogenesis. Our prior studies with L. monocytogenes identified a bacterial protein, p60, whose expression and secretion from the bacterium is required for pathogenicity in the mouse model of systemic infection. p60 is not required for Lm infection in cultured cells. We found that p60 stimulates the activation of host natural killer (NK) cells, an immune cell population associated with increased host susceptibility to L. monocytogenes and several other pathogenic bacteria. We have shown that p60 stimulates NK cells by binding to dendritic cells, and eliciting the production of IL-1¿ and IL-18. The ability of p60 to activate DCs and NK cells maps to a region of the protein containing a LysM domain. Purified p60 protein, or just the region of p60 containing the LysM domain is sufficient to stimulate NK cell activation. The host factor NLRP3 is also required for IL-18 production and NK cell activation in cultures with DCs, NK cells, and p60. In our first Aim, we will further define the mechanisms by which the LysM domain containing peptide uniquely binds and stimulates DCs for IL-18 production and NK cell activation. Molecular, imaging, immunological, and cell biological approaches will be used. In our second Aim, we will investigate how NLRP3 impacts host resistance during systemic bacterial infections. In our third Aim, we will characterize NK cells producing IL-10 in response to L. monocytogenes infection and p60. We also test how IL-10 production by NK cells impacts host immune responses and susceptibility to bacterial infection. Together, our work will reveal how LysM-containing bacterial virulence factors subversively activate specific aspects of innate immunity in order to promote the establishment of systemic infections.