Macrophage transcriptional responses to Legionella pneumophila

描述(由申请人提供)：嗜肺军团菌是一种新出现的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)是感染许多(如果不是全部)细胞内病原体的重要标志。我们的假设是，胞液监测途径在胞浆中检测到军团菌衍生的配体，导致I型IFN和共同调节基因的转录诱导。初步数据表明，I型干扰素是由军团菌以依赖于嗜肺乳杆菌IV型(Dot/ICM)分泌系统的方式诱导的。我们还发现，需要I型干扰素来限制军团菌的细胞内复制。刺激宿主产生干扰素的军团菌衍生配体尚不清楚，但我们的初步研究已确定MDA5是嗜肺乳杆菌的关键宿主传感器。由于MDA5是RNA的胞浆传感器，我们的发现表明嗜肺乳杆菌可能将细菌RNA转移到宿主细胞胞浆中，这是一种令人兴奋的可能性。即使MDA5感知到嗜肺乳杆菌的非RNA配体，我们的结果也挑战了现有的范式，因为人们普遍认为MDA5只是病毒的传感器，而不是细菌的传感器。因此，我们的具体目标是：1.鉴定和鉴定嗜肺乳杆菌能够积极或消极地调节宿主产生I型干扰素的分子决定因素。2.确定在胞浆中感应嗜肺乳杆菌的宿主途径，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，确定胞浆感觉和I型干扰素在抗嗜肺乳杆菌天然免疫中的作用。

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.