Defining human noncanonical inflammasome responses to Legionella pneumophila

 描述(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。未能控制感染可能导致脓毒症，这是一种严重的病理，由对内毒素(LPS)和其他微生物产品的免疫反应失调所致。败血症可发展为多器官衰竭、血压严重下降和感染性休克。革兰氏阴性菌感染每年导致全球1000多万败血症病例，死亡率超过30%。关键的是，一百多项成功治疗小鼠败血症的免疫调节剂临床试验都失败了，导致人类败血症缺乏有效的治疗方法。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到重要作用。我们的长期目标是阐明人类对感染的特异性先天免疫反应的分子机制，因为这一知识对于开发新的脓毒症治疗方法至关重要。为此，我们对革兰氏阴性杆菌嗜肺军团菌进行了研究。军团菌会导致严重的肺炎军团病，如果不及时治疗，可能会发展为败血症。军团菌通过将细菌毒力因子输送到宿主细胞胞浆中，在巨噬细胞内感染和复制，从而引发疾病。 易位细菌产物的胞浆免疫检测触发炎性小体的组装，多蛋白复合体激活半胱氨酸酶诱导宿主细胞死亡，并释放IL-1家族细胞因子。我们和其他团队最近在小鼠细胞中发现了两种类型的炎症体，它们对军团菌和其他革兰氏阴性病原体有反应：典型的炎症体激活caspase-1(CASP1)，而非典型性的炎症体与caspase-11(MCASP11)结合，后者直接检测胞液中的内毒素。虽然mCASP11在宿主防御中起关键作用，但mCASP11也介导内毒素休克。有趣的是，人类表达两个mCASP11同源基因，hCASP4和hCASP5，这两个同源基因都能识别内毒素，但它们如何控制细菌感染引起的炎症体反应却知之甚少。我们最近发表的新发现揭示了小鼠和人类非典型炎症体的主要差异，并表明hCASP4和hCASP5具有不同的作用。因此，我们假设hCASP4和hCASP5介导的对细菌感染的反应驱动人类特有的炎症反应。因此，我们将追求两个目标，即研究hCASP4和hCASP5如何调节人类对感染的炎症体反应，以及确定在原代人类巨噬细胞中非典型性炎症体激活所需的细菌和宿主因素。这些研究将为非规范炎症体在人类细胞中的功能提供基本的见解，并将为调节抗细菌免疫反应和脓毒症的人类特有机制提供关键信息。

 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.