Innate immune-mediated control of pulmonary Legionella pneumophila infection

 描述(由申请人提供)：清除细胞内细菌病原体需要启动有效的免疫反应。然而，病原体已经进化出毒力因子来禁用这种免疫反应。我们知识中的一个关键差距是理解如何在病原体颠覆的情况下实现成功的宿主防御。嗜肺军团菌是社区和医院获得性肺炎的重要原因，它通过IV型分泌系统(T4SS)输送细菌效应物，解除武装并在肺泡巨噬细胞内复制。几个T4SS效应器可以有效地阻止宿主蛋白质的合成。然而，军团菌T4SS易位底物的宿主感应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，我们开发了一种强大的方法，在单细胞水平上同时跟踪细菌效应器易位和细胞因子反应。我们发现感染细胞很少产生几种关键的细胞因子，但仍能合成和释放IL-1家族的细胞因子。此外，IL-1信号是未感染的免疫细胞产生细胞因子和肺上皮细胞产生吸引中性粒细胞的趋化因子所必需的。我们的发现表明旁分泌IL-1信号 绕过病原体施加的翻译障碍，由未受感染的旁观者细胞协调快速免疫反应。虽然IL-1信号对宿主防御的启动至关重要，但对IL-1反应的细胞类型以及IL-1α和IL-1β反应在这些细胞中的具体后果尚不清楚。此外，缺乏IL-1信号的小鼠最终恢复旁观者细胞因子反应、中性粒细胞募集和对感染的控制，这表明IL-1独立的免疫信号协调了另一层宿主防御。因此，我们提出以下目标来定义IL-1依赖和IL-1非依赖的免疫机制如何协同产生成功的免疫。在目标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，我们将测试假设，额外的IL-1非依赖的免疫信号确保在军团菌感染的后期阶段旁观者细胞因子的产生和中性粒细胞的募集。总之，这些研究将确定宿主用来克服病原体编码的毒力活动的新的先天免疫机制。因此，拟议的研究将提供对宿主防御机制的重要洞察，这些机制可用于对抗广泛类别的微生物病原体，并有助于改进的抗微生物疗法和疫苗的开发。

 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.