Macrophage transcriptional responses to Legionella pneumophila

描述（由申请人提供）：嗜肺军团菌是一种新兴传染病威胁的典型例子。最近来自几个实验室的令人兴奋的数据表明，I型干扰素（ifn）是许多（如果不是全部的话）细胞内病原体感染的重要标志。我们的假设是，胞质监测途径检测胞质中军团菌衍生的配体，导致I型ifn和协同调节基因的转录诱导。初步数据表明军团菌诱导I型干扰素的方式依赖于嗜肺乳杆菌的IV型（Dot/Icm）分泌系统。我们还发现需要I型干扰素来限制军团菌的细胞内复制。军团菌衍生的刺激宿主产生干扰素的配体尚不清楚，但我们的初步研究已经确定Mda5是嗜肺乳杆菌的关键宿主传感器。由于Mda5是RNA的细胞质传感器，我们的发现表明嗜肺乳杆菌可能将细菌RNA转运到宿主细胞的细胞质中。即使来自嗜肺乳杆菌的非rna配体被Mda5感知，我们的结果也挑战了现有的范式，因为Mda5被广泛认为仅仅是病毒的传感器，而不是细菌的传感器。因此，我们的具体目标是：1。鉴定和表征嗜肺乳杆菌的分子决定因素，积极或消极调节宿主生产I型干扰素。2. 表征宿主细胞质中感知嗜肺乳杆菌的途径，导致I型干扰素和其他基因的转录诱导。3. 利用体外和体内模型确定细胞质感应和I型干扰素在抗嗜肺乳杆菌先天免疫中的作用。公共卫生相关性：嗜肺军团菌是一种在宿主细胞巨噬细胞中复制的细菌，从而引起严重的、通常是致命的肺炎，称为军团病。在这项建议中，我们试图使用军团菌作为理解巨噬细胞如何感知和防御感染的模型，最终目标是利用这些信息开发更有效的治疗方法和疫苗。

DESCRIPTION (provided by applicant): Legionella pneumophila is a protypical example of an emerging infectious disease threat. Recent exciting data from several labs have indicated that type I interferons (IFNs) are an important signature of infection with many, if not all, intracellular pathogens. Our hypothesis is that a cytosolic surveillance pathway detects Legionella-derived ligands in the cytosol leading to the transcriptional induction of type I IFNs and coregulated genes. Preliminary data indicate that type I interferons are induced by Legionella in a manner dependent on L. pneumophila's type IV (Dot/Icm) secretion system. We also find that type I interferons are required to restrict intracellular replication of Legionella. The putative Legionella-derived ligand that stimulates host production of interferon is unknown, but our preliminary studies have identified Mda5 as a key host sensor of L. pneumophila. Since Mda5 is a cytosolic sensor of RNA, our finding suggests the exciting possibility that L. pneumophila may translocate bacterial RNA into the host cell cytosol. Even if a non-RNA ligand from L. pneumophila is sensed by Mda5, our results challenge existing paradigms since Mda5 is widely believed to be solely a sensor of viruses, rather than of bacteria. Thus, our specific aims are: 1. Identify and characterize molecular determinants of L. pneumophila that positively or negatively regulate host production of type I interferon. 2. Characterize the host pathways that sense L. pneumophila in the cytosol, leading to transcriptional induction of type I interferon and other genes. 3. Determine the role of cytosolic sensing and type I interferons in innate immunity against L. pneumophila using in vitro and in vivo models. PUBLIC HEALTH RELEVANCE: Legionella pneumophila is a bacterium that replicates in host cells called macrophages, thereby causing a severe, and often lethal, pneumonia called Legionnaires' Disease. In this proposal we seek to use Legionella as a model for understanding how macrophages sense and defend against infection, with the ultimate goal of using this information to develop more effective therapeutics and vaccines.