Innate Immunity in Pneumonic Sepsis

摘要 肺部感染是导致全球死亡率和发病率的败血症的主要原因。有效 病原体从肺中清除依赖于成功的先天免疫。了解 肺部的固有防御机制对于改进免疫疗法或疫苗至关重要，以减少 这种疾病的负担。触发先天免疫的信号级联由一种微妙的平衡组成 在促炎反应和抗炎反应之间。然而，它是 鲜为人知的是，这些先天免疫信号级联是如何汇聚在一起提供高效宿主的 在减轻炎症组织损伤的同时进行防御。来描述宿主防御机制 肺和肺外器官，我们关注的是一种主要的革兰氏阴性细胞外病原体， 肺炎克雷伯氏菌，因为这种细菌会导致严重的肺炎和败血症； 抗药性和超强毒力变种最近出现，导致毁灭性的肺脏和 全身感染。识别病原体是导致中性粒细胞流入的第一个关键步骤。 阿龙。关于细菌识别，核苷酸结合寡聚化结构域(NOD)样受体 (NLR)被牵连。然而，NLRs的作用，如Nod1和Nod2 S在宿主防御中的作用 肺炎克雷伯菌仍未被发现。Nod1/2信号级联涉及适配器蛋白RIP2。我们 现在提供初步证据表明，NOD2参与了肺炎克雷伯菌感染的宿主防御， 其中包括：1)缺乏RIP2的小鼠表现出存活率降低，细菌负荷增加，以及 减少中性粒细胞向肺和肺外器官的募集；2)NOD2缺陷小鼠表现出 减少中性粒细胞向肺的募集；3)NOD2基因缺陷的小鼠表现出caspase-1的降低。 4)IL-1β和IL-1β对宿主的重要作用 对肺炎克雷伯菌和RIP2的抵抗力调节肺内IL-23和IL-17的产生。这些 这些发现共同支持了肺炎克雷伯菌最初与肺的相互作用的假设 细胞导致NOD2活化，随后IL-1β和IL-18产生，进而诱导IL-17A- 介导的宿主中性粒细胞依赖的免疫。其目的是：(1)体内研究 肺炎脓毒症时NOD2调节中性粒细胞介导的宿主防御机制； 探讨肺炎脓毒症时NOD2促进IL-17A产生的体内机制； 以及(3)确定肺炎脓毒症时NOD2的调节是否改变了宿主的防御。独一无二的 体内和体外系统的结合，包括KO小鼠、过表达和过继转移 将采用各种战略来实现这些目标。我们认为，这在概念上、技术上和 翻译创新的提案将揭示NOD2作为肺炎脓毒症的主要调节器和 促进我们对NOD2如何促进肺炎败血症的有益反应的理解。

SUMMARY Lung infections are a leading cause of sepsis that poses global mortality and morbidity. Effective clearance of pathogens from the lung is dependent on successful innate immunity. Understanding the innate defense mechanisms in the lung is crucial for improved immunotherapeutics or vaccines to reduce this burden of disease. The signaling cascades triggering innate immunity consist of a delicate balance between pro-inflammatory responses, and counteracting anti-inflammatory responses. It is however poorly understood how these innate immune signaling cascades converge to provide efficient host defense while attenuating inflammatory tissue damage. To delineate the host defense mechanisms in the lungs and extrapulmonary organs, we have focused on a primary gram-negative extracellular pathogen, Klebsiella pneumoniae since this bacterium induces severe pneumonia followed by sepsis; and multiple drug-resistant and hypervirulent variants have recently emerged to cause devastating pulmonary and systemic infections. Recognition of pathogens is the first critical step leading to neutrophil influx in the lung. Regarding bacterial recognition, nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) were implicated. However, the role of NLRs, such as NOD1 and NOD2 s in host defense against K. pneumoniae remains unexplored. NOD1/2 signaling cascades involve the adaptor protein RIP2. We now provide preliminary evidence that NOD2 is involved in host defense during K. pneumoniae infection, which include: 1) Mice deficient in RIP2 demonstrate reduced survival, higher bacterial burden and decreased neutrophil recruitment to the lungs and extrapulmonary organs; 2) NOD2-deficient mice show attenuated neutrophil recruitment to the lungs; 3) NOD2-deficient mice demonstrate decreased caspase- 1 activation and interleukin (IL)-1β production in the lung; 4) Both IL-1β and IL-18 are important for host resistance against K. pneumoniae and 5) RIP2 regulates IL-23 and IL-17 production in the lungs. These findings collectively support the hypothesis that the initial interaction of K. pneumoniae with the lung cells leads to NOD2 activation followed by IL-1β and IL-18 production which then induces IL-17A- mediated neutrophil-dependent immunity in the host. The Aims are: (1) Investigate the in vivo mechanisms by which NOD2 modulates neutrophil-mediated host defense during pneumonic sepsis; (2) Explore the in vivo mechanisms by which NOD2 enhances IL-17A production during pneumonic sepsis; and (3) Determine if modulation of NOD2 alters host defense during pneumonic sepsis. A unique combination of in vivo and in vitro systems, including KO mice, overexpression and adoptive transfer strategies will be employed to address these aims. We believe that this conceptually, technically and translationally innovative proposal will reveal NOD2 as a master regulator for pneumonic sepsis and advance our understanding of how NOD2 promotes a beneficial response for pneumonic sepsis.