Defining human noncanonical inflammasome responses to Legionella pneumophila

 描述（由申请人提供）：革兰氏阴性细菌感染仍然是一个巨大的公共卫生挑战。未能控制感染可导致脓毒症，这是一种由对脂多糖（LPS）和其他微生物产物的免疫应答失调驱动的严重病理。脓毒症可发展为多器官衰竭、血压严重下降和脓毒性休克。革兰氏阴性菌感染每年造成全球超过1000万例败血症，死亡率超过30%。重要的是，超过一百项成功治疗小鼠脓毒症的免疫调节剂临床试验失败，导致缺乏有效的人类脓毒症治疗方法。这些失败的基础尚不清楚，但人类和小鼠对感染的先天免疫反应的根本差异可能起着重要作用。我们的长期目标是阐明人类特异性先天免疫反应对感染的分子机制，因为这些知识对于开发脓毒症的新治疗方法至关重要。为此，我们研究了革兰氏阴性病原体嗜肺军团菌。军团菌引起严重的肺炎军团菌病，如果不及时治疗，可发展为败血症。为了引发疾病，军团菌通过将细菌毒力因子递送到宿主细胞胞质溶胶中来感染巨噬细胞并在巨噬细胞内复制。 易位的细菌产物的细胞溶质免疫检测触发炎性体、多蛋白复合物的组装，所述多蛋白复合物激活半胱天冬酶以诱导宿主细胞死亡和IL-1家族细胞因子的释放。我们和其他研究小组最近在鼠细胞中发现了两种类型的炎性小体，它们对军团菌和其他革兰氏阴性病原体有反应：典型炎性小体激活caspase-1（CASP 1），而非典型炎性小体参与caspase-11（mCASP 11），它直接检测细胞溶质LPS。虽然mCASP 11对宿主防御至关重要，但mCASP 11也介导内毒素休克。有趣的是，人类表达两种mCASP 11直系同源物，hCASP 4和hCASP 5，它们也识别LPS，但它们如何控制对细菌感染的炎性反应却知之甚少。我们最近发表的新发现揭示了小鼠和人类非典型炎性小体的主要差异，并表明hCASP 4和hCASP 5具有不同的作用。因此，我们假设hCASP 4和hCASP 5介导的对细菌感染的反应驱动人类特异性炎症反应。因此，我们将追求两个目标，将检查hCASP 4和hCASP 5如何调节人类炎性小体对感染的反应，并确定在原代人类巨噬细胞中非典型炎性小体激活所需的细菌和宿主因子。这些研究将为非典型炎性小体如何在人类细胞中发挥作用提供基本的见解，并将为调节抗菌免疫反应和败血症的人类特异性机制提供重要的启示。

 DESCRIPTION (provided by applicant): Gram-negative bacterial infections remain an enormous public health challenge. Failure to control infection can lead to sepsis, a severe pathology driven by dysregulated immune responses to lipopolysaccharide (LPS) and other microbial products. Sepsis can progress to multi-organ failure, a severe drop in blood pressure, and septic shock. Gram-negative infections are responsible for over 10 million cases of sepsis worldwide each year, with a greater than 30% mortality rate. Critically, more than a hundred clinical trials of immunomodulators that successfully treat sepsis in mice have failed, resulting i a shortage of effective treatments for human sepsis. The basis for these failures is unclear, but fundamental differences in human and mouse innate immune responses to infection likely play an important role. Our long-term goal is to elucidate the molecular mechanisms underlying human-specific innate immune responses to infection, as this knowledge is essential for developing new treatments for sepsis. To this end, we study the gram-negative pathogen Legionella pneumophila. Legionella causes the severe pneumonia Legionnaires' disease, which can develop into sepsis if not promptly treated. To initiate disease, Legionella infects and replicates within macrophages by delivering bacterial virulence factors into the host cell cytosol. Cytosolic immune detection of translocated bacterial products triggers assembly of inflammasomes, multiprotein complexes that activate caspases to induce host cell death and release of IL-1 family cytokines. We and other groups recently identified two types of inflammasomes in murine cells that respond to Legionella and other gram-negative pathogens: canonical inflammasomes activate caspase-1 (CASP1), while noncanonical inflammasomes engage caspase-11 (mCASP11), which directly detects cytosolic LPS. Although mCASP11 is critical for host defense, mCASP11 also mediates endotoxic shock. Intriguingly, humans express two mCASP11 orthologs, hCASP4 and hCASP5, both of which also recognize LPS, but how they control inflammasome responses to bacterial infection is poorly understood. Our recently published and new findings reveal major differences in mouse and human noncanonical inflammasomes and indicate that hCASP4 and hCASP5 have distinct roles. We thus hypothesize that hCASP4- and hCASP5-mediated responses to bacterial infection drive human-specific inflammatory responses. Thus, we will pursue two aims that will examine how hCASP4 and hCASP5 regulate human inflammasome responses to infection and define the bacterial and host factors required for noncanonical inflammasome activation in primary human macrophages. These studies will provide fundamental insight into how noncanonical inflammasomes function in human cells, and will shed critical light on human-specific mechanisms that regulate anti-bacterial immune responses and sepsis.