Innate immune-mediated control of pulmonary Legionella pneumophila infection

 描述（由申请方提供）：细胞内细菌病原体的清除需要启动有效的免疫应答。然而，病原体已经进化出毒力因子来使这种免疫应答失效。我们知识中的一个关键差距是了解如何在病原体颠覆的情况下成功地实现宿主防御。嗜肺军团菌是社区和医院获得性肺炎的重要原因，通过IV型分泌系统（T4 SS）递送细菌效应物，在肺泡巨噬细胞内解除武装和复制。几种T4 SS效应物有效地阻断宿主蛋白质合成。然而，宿主对军团菌T4 SS易位底物的感知矛盾地增强了细胞因子的产生。为了阐明这种宿主反应的分子和细胞基础，我们开发了一种强有力的方法，在单细胞水平上同时跟踪细菌效应子易位和细胞因子反应。我们发现，感染细胞产生的几个关键细胞因子很少，但仍然可以合成和释放IL-1家族细胞因子。此外，IL-1信号传导是未感染的免疫细胞产生细胞因子和肺上皮细胞产生嗜中性粒细胞趋化因子所必需的。我们的发现表明旁分泌IL-1信号传导 绕过病原体施加的翻译阻断，以协调未感染的旁观者细胞的快速免疫应答。虽然IL-1信号传导对于宿主防御的启动至关重要，但对IL-1应答的细胞类型以及这些细胞中IL-1α和IL-1β应答的具体结果尚不清楚。此外，缺乏IL-1信号传导的小鼠最终恢复了旁观者细胞因子应答、中性粒细胞募集和对感染的控制，这表明IL-1非依赖性免疫信号协调了另一层宿主防御。因此，我们提出了以下目标来定义IL-1依赖性和IL-1非依赖性免疫机制如何协作以产生成功的免疫。在目的1中，我们将检验IL-1α和IL-1β在不同细胞类型中调节不同免疫功能的假设。在目标2中，我们将检验以下假设：在军团菌感染的后期阶段，额外的IL-1非依赖性免疫信号确保旁观者细胞因子产生和中性粒细胞募集。总之，这些研究将确定新的先天免疫机制所采用的主机，以克服病原体编码的毒力活动。因此，拟议的研究将为宿主防御机制提供重要的见解，这些机制用于对抗广泛的微生物病原体，并有助于开发改进的抗微生物疗法和疫苗。

 DESCRIPTION (provided by applicant): Clearance of intracellular bacterial pathogens requires initiation of an effective immune response. However, pathogens have evolved virulence factors to disable such immune responses. A key gap in our knowledge is to understand how successful host defense can be achieved despite pathogen subversion. Legionella pneumophila, an important cause of community- and hospital-acquired pneumonia, disarms and replicates within alveolar macrophages by delivering bacterial effectors via a type IV secretion system (T4SS). Several T4SS effectors potently block host protein synthesis. However, host sensing of Legionella T4SS-translocated substrates paradoxically enhances cytokine production. To elucidate the molecular and cellular basis of this host response, we developed a powerful approach to simultaneously track bacterial effector translocation and cytokine responses at the single cell level. We found that infected cells poorly produced several key cytokines, but could still synthesize and release IL-1 family cytokines. Moreover, IL-1 signaling was required for robust production of cytokines by uninfected immune cells and neutrophil-attracting chemokines by lung epithelial cells. Our findings indicate that paracrine IL-1 signaling circumvents the pathogen-imposed translational block to orchestrate a rapid immune response by uninfected bystander cells. While IL-1 signaling is critical for the initiation of host defense,the cell types responding to IL-1 and the specific consequences of IL-1α and IL-1β responses in these cells are unclear. Moreover, mice lacking IL-1 signaling eventually recover bystander cytokine responses, neutrophil recruitment, and control over infection, suggesting that IL-1-independent immune signals coordinate an additional layer of host defense. Thus, we propose the following Aims to define how IL-1-dependent and IL-1-independent immune mechanisms collaborate to generate successful immunity. In Aim 1, we will test the hypothesis that IL-1α and IL-1β regulate distinct immune functions in different cell types. In Aim 2, we will test the hypothesis that additional IL-1-independent immune signals ensure bystander cytokine production and neutrophil recruitment at later stages of Legionella infection. Together, these studies will define novel innate immune mechanisms employed by the host to surmount pathogen-encoded virulence activities. The proposed research will therefore provide vital insight into mechanisms of host defense that are utilized against broad classes of microbial pathogens and aid development of improved anti-microbial therapeutics and vaccines.