Innate Immunity in Pneumonic Sepsis

总结 肺部感染是脓毒症的主要原因，脓毒症造成全球死亡率和发病率。有效 病原体从肺中的清除依赖于成功的先天免疫。了解 肺中的先天防御机制对于改进的免疫治疗剂或疫苗至关重要， 这种疾病负担。触发先天免疫的信号级联由微妙的平衡组成 在促炎反应和对抗抗炎反应之间。然而， 对这些先天免疫信号级联如何汇聚以提供有效的宿主 防御，同时减轻炎症组织损伤。为了描述宿主防御机制， 肺和肺外器官，我们集中在一个主要的革兰氏阴性细胞外病原体， 肺炎克雷伯氏菌，因为该细菌诱导严重肺炎，随后是败血症;以及 最近出现了耐药性和高毒力的变异体， 全身感染病原体的识别是导致中性粒细胞流入的第一个关键步骤， 肺。关于细菌识别，核苷酸结合寡聚化结构域（NOD）样受体 （NLR）有牵连。然而，NLR，如NOD 1和NOD 2在宿主防御中的作用， K. pneumoniae肺炎remains保持unexplored探索. NOD 1/2信号级联涉及衔接蛋白RIP 2。我们 现在提供了初步证据表明，NOD 2参与宿主防御K。肺炎感染， 其包括：1）RIP 2缺陷的小鼠表现出降低的存活率、更高的细菌负荷， 减少中性粒细胞向肺和肺外器官的募集; 2）NOD 2缺陷型小鼠显示 减弱中性粒细胞向肺的募集; 3）NOD 2缺陷小鼠表现出减少的半胱天冬酶- IL-1β和IL-18在肺组织中均起重要作用 对K. 5）RIP 2调节肺中IL-23和IL-17的产生。这些 研究结果共同支持的假设，K.肺炎伴肺 细胞导致NOD 2活化，随后产生IL-1β和IL-18，然后诱导IL-17 A-1 β和IL-18。 介导宿主中的嗜中性粒细胞依赖性免疫。目的：（1）研究体内 NOD 2调节肺炎脓毒症期间嗜中性粒细胞介导的宿主防御的机制;（2） 探索NOD 2在肺炎脓毒症期间增强IL-17 A产生的体内机制; 和（3）确定在肺炎脓毒症期间NOD 2的调节是否改变宿主防御。一个独特 体内和体外系统的组合，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 创新的提案将揭示NOD 2作为肺炎脓毒症的主要调节因子， 推进我们对NOD 2如何促进肺炎脓毒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.