Innate Immune Recognition and Type I IFN Response to Cytosolic Pathogens

描述(申请人提供)：I型干扰素是宿主细胞对病原体作出反应时产生的一类分泌细胞因子，其产生受到严格的调控。I型干扰素控制着一大组抗感染重要基因的转录，也是激活先天免疫系统和获得性免疫系统的反应所必需的，包括抗原递呈和与T细胞、B细胞和自然杀伤细胞激活有关的细胞因子的产生。虽然I型干扰素信号被认为是一种重要的宿主防御机制，但对触发I型干扰素诱导的细菌配体和相应的宿主受体知之甚少。我们的长期目标是了解如何操纵I型干扰素的产生来预防和治疗自发性炎症和传染病。这项建议的目标，也是我们追求这一目标的下一步，是使用模式胞浆病原体Francisella来确定在细菌感染期间导致I型干扰素产生的宿主因素。我们假设多种刺激I型干扰素的胞浆受体被胞浆病原体Francisella的不同配体激活。最近的研究表明，免疫细胞表达几种胞浆感受器，可诱导I型IFN对DNA、RNA和环二核苷酸(CDN)等核酸配体的反应。到目前为止，已经描述了两种一般的激活机制。首先，活细菌可以通过特殊的分泌系统将刺激配体分泌到胞浆中。其次，可以从裂解或降解的细菌中检测到配体。根据初步实验，我们认为这两种激活机制都发生在方济各氏菌感染期间。这项建议中概述的实验将可能导致识别参与I型干扰素信号转导的新因素，并提供对分子的洞察。 寄主用来防御病原体的机制。我们建议通过以下三个目标来研究在感染弗朗西斯氏菌过程中导致I型干扰素产生的机制。目的1：确定CDN在弗朗西斯菌感染过程中是否对I型IFN的激活起重要作用。目的2：鉴定调节胞浆天然免疫反应的弗朗西塞氏菌因子。目的3：鉴定胞质感受器，该感受器调节对弗朗西塞氏菌的I型干扰素诱导。我们将采取有针对性的遗传和无偏见的正向遗传筛查方法来识别调节I型干扰素产生的弗朗西斯氏菌因子。此外，我们将采用遗传和生化方法来鉴定参与I型干扰素信号传递的胞质感受器。这项工作将增加我们对胞质检测、先天免疫和宿主-病原体相互作用的理解。

DESCRIPTION (provided by applicant): Type-I IFNs are a family of secreted cytokines made by host cells in response to pathogens and whose production is strictly regulated. Type I IFNs control the transcription of a large group of genes important in resisting infection and are also required to activate responses of the innate and adaptive immune systems including antigen presentation and production of cytokines involved in activation of T cells, B cells and natural killer cells. While type I IFN signaling is increasingly appreciated as an important host defense mechanism against invading pathogens, little is known about the bacterial ligands and respective host receptors that trigger type I IFN induction. Our long-term goal is to understand how type I IFN production can be manipulated to prevent and treat auto-inflammatory and infectious diseases. The objective of this proposal, which is our next step in pursuit of that goal is to determine the host factors that contribute to type I IFN production during bacterial infections, using the model cytosolic pathogen Francisella. We hypothesize that multiple type I IFN-stimulating cytosolic receptors are activated by diverse ligands from the cytosolic pathogen Francisella. Recent studies have demonstrated that immune cells express several cytosolic sensors that induce type I IFNs in response to nucleic acid ligands, including DNA, RNA and cyclic-di-nucleotides (CDNs). Thus far, two general mechanisms of activation have been described. First, viable bacteria can secrete stimulatory ligands into the cytosol through specialized secretion systems. Second, ligands can be detected from bacteria that are lysed or degraded. From preliminary experiments, we believe that both mechanisms of activation occur during a Francisella infection. The experiments outlined in this proposal will likely lead to the identification of new factors involved in type I IFN signaling and provide insight on the molecular mechanisms employed by the host to protect against pathogens. We propose to study the mechanisms that lead to type I IFN production during infections with Francisella by pursuing the following three aims. Aim 1: Determine if CDNs are important for activation of type-I IFNs during Francisella infection. Aim 2: Identify Francisella factors that modulate the cytosolic innate immune response. Aim 3: Identify cytosolic sensors that regulate type-I IFN induction in response to Francisella. We will take targeted genetic and unbiased forward genetic screen approaches to identify Francisella factors that modulate type I IFN production. Additionally, we will take genetic and biochemical approaches to identify cytosolic sensors that contribute to type I IFN signaling. This work will increase our understanding of cytosolic detection, innate immunity and host-pathogen interactions.