Cytosolic Immune Surveillance During Bacterial Infections

 描述(申请人提供)：败血症是一种高度致命的综合症，每年影响美国120多万人和全球1800万人。更好地了解潜在的免疫机制是开发特异和有效的药物所必需的。先天免疫系统是感知入侵病原体和激活宿主免疫反应的中心。一组不同的生殖系编码的先天性免疫受体调查几乎所有细胞隔间的病原体及其产物的存在。炎性小体是胞浆中的多蛋白支架，含有NLR受体、接头ASC和效应器caspase-1。炎性小体是胞浆免疫监视的重要组成部分。炎症体直接检测各种“标志性”微生物产物，或间接感觉与感染有关的征兆。虽然革兰氏阴性杆菌的脂多糖(LPS)被认为是通过Toll样受体-4(TLR4)在细胞表面特异性检测到的，但最近的研究表明，内毒素是通过炎症caspase-11以不依赖于TLR4的方式在胞浆中感受到的。内毒素激活Caspase-11导致Caspase-1蛋白水解性激活，进而激活IL-1β和IL-18。重要的是，活跃的caspase-11触发了一种炎症形式的细胞死亡(下垂)，并释放内源性警报或危险分子，使炎症反应永久化。胞浆内对内毒素的感知和随后的caspase-11激活是脓毒症的中心介质。尽管它具有深刻的临床意义，但关于内毒素进入胞浆的分子基础以及下游信号级联调控的机制细节仍很不清楚。这项研究试图在三个具体目标上全面解决这些关键的知识差距。目标1和目标2将确定内毒素如何进入胞浆并激活caspase-11，目标3将描述一种调节机制，该机制在小鼠和人类中控制炎症半胱氨酸酶介导的免疫反应。通过揭示人类胞浆内毒素感应驱动反应的分子细节，这项研究的发现可能提供新的免疫调节策略和靶点，以增强保护性免疫，并如传染病所希望的那样阻止有害的炎症。

 DESCRIPTION (provided by applicant): Sepsis is a highly lethal syndrome that affects more than 1.2 million people in the Unites States and 18 million globally each year. A better understanding of the underlying immune mechanisms is greatly needed to develop specific and effective drugs. Innate immune system is central to the sensing of invading pathogens and the activation of the host immune response. A diverse set of germ-line encoded innate immune receptors survey nearly all-cellular compartments for the presence of pathogens and their products. Inflammasomes are multi- protein scaffolds in the cytosol containing a NLR receptor, an adapter ASC, and an effector, caspase-1. Inflammasome is an integral part of the immunosurveillance of the cytosol. Inflammasomes directly detect various "signature" microbial products or indirectly sense signs associated with an infection. Although lipopolysaccharide (LPS) of Gram-negative bacteria was believed to be exclusively detected at the cell surface by Toll-like receptor-4 (TLR4), it has very recently been described that the LPS is sensed in the cytosol in a TLR4-independent manner by caspase-11, an inflammatory caspase. Activation of caspase-11 by intracellular LPS leads to the proteolytic activation of caspase-1, which then executes the activation of IL-1β and IL-18. Importantly, active caspase-11 triggers an inflammatory form of cell death (pyroptosis) and the release of endogenous alarmin or danger molecules that perpetuate the inflammatory reactions. Cytosolic sensing of LPS and the ensuing caspase-11 activation is the central mediator of sepsis. Despite its profound clinical implications the mechanistic details of this pathway regarding the molecular basis of cytosolic entry of LPS and the regulation of the downstream signaling cascade remains largely unknown. This study seeks to comprehensively address these critical knowledge gaps in three specific aims. Aim 1 and 2 will identify how LPS enters the cytosol and activates caspase-11 and Aim 3 will characterize a regulatory mechanism that keeps inflammatory caspases-mediated immune responses in check in mice and humans. By uncovering the molecular details of cytosolic LPS sensing-driven responses in humans, the findings from this study could offer new immunomodulatory strategies and targets to bolster protective immunity as well as block detrimental inflammation as desired in infectious diseases.