Modulation of host innate immune response by Francisella tularensis

描述（由申请方提供）：历史上，吞噬细胞产生活性氧（ROS）主要是在细菌杀灭的背景下研究的。然后，确定了ROS控制许多细胞类型中被称为“氧化还原信号传导”的正常生理信号传导。最近出现的概念是，在产生ROS方面远不如嗜中性粒细胞有效的巨噬细胞通过由氧化还原信号传导协调的促炎细胞因子的产生获得其活化的杀微生物表型。另一方面，细菌抗氧化防御系统中和巨噬细胞衍生的ROS以在巨噬细胞中存活，并且这些机制已经很好地建立。然而，细菌抗氧化剂对氧化还原信号通路、促炎细胞因子产生和先天性免疫应答的ROS中和的影响仍未得到充分研究。这项研究的目的是建立一个新的作用，细菌抗氧化剂在调节宿主的先天性 使用A类选择剂土拉热弗朗西丝氏菌（Ft）SchuS 4作为模型的免疫应答。我们特别感兴趣的是研究Ft抑制宿主先天免疫防御的机制。我们在追求理解Ft的毒力机制方面的广泛工作为拟议的研究计划奠定了非常坚实的基础。我们已经证明，Ft SchuS 4具有强大的抗氧化防御机制，使其对氧化剂具有极强的抵抗力。通过产生Ft SchuS 4-活疫苗株（LVS）的密切替代物的点和多个基因缺失突变体，我们已经确定Ft抗氧化剂是重要的毒力因子，并在抑制激酶信号传导和巨噬细胞活化中发挥重要作用。在本申请中，我们希望更深入地挖掘Ft SchuS 4的有效ROS清除能力与其引起先天免疫抑制的能力之间的联系。我们已发表的和初步的研究提供了令人信服的证据，支持我们的假设，即“Ft抗氧化剂通过抑制氧化还原敏感性信号传导成分的激活和促炎细胞因子的产生来抑制先天免疫反应”。提出了以下具体目标：目标1：将研究Ft SchuS 4的抗氧化剂如何通过调节巨噬细胞氧化还原环境来破坏先天免疫功能。目标二：将研究摄取后立即对细胞内巨噬细胞ROS依赖性信号级联的Ft抗氧化防御的影响，而Aim 3将建立Ft抗氧化剂介导的细胞溶质氧化还原敏感性核苷酸结合寡聚化结构域（NOD）样受体（NLR）信号转导的颠覆机制。本申请的长期目标是为开发基于氧化还原的广谱治疗/预防方法建立强大的平台。细菌抗氧化剂除了其作为ROS/RNS的清除剂的既定作用之外还可以破坏宿主的先天免疫应答的概念是高度创新的，并且可能真正揭示细菌致病的新颖且保守的机制。

DESCRIPTION (provided by applicant): Historically, the production of reactive oxygen species (ROS) by phagocytes was mainly studied in the context of bacterial killing. Then, it was established that ROS controls normal physiologic signaling termed as "redox-signaling" in many cell types. The recent emerging concept is- macrophages that are far less potent than neutrophils at producing ROS, acquire their activated microbicidal phenotype through the production of proinflammatory cytokines which is orchestrated by redox-signaling. On the flip side, bacterial antioxidant defenses neutralize macrophage-derived ROS to survive in macrophages and these mechanisms have been well established. However, the impact of ROS neutralization by bacterial antioxidants on redox-signaling pathways, pro-inflammatory cytokine production, and innate immune responses remain understudied. The goal of the proposed research is to establish a novel role for bacterial antioxidants in the modulation of host's innate immune response using a category A select agent, Francisella tularensis (Ft) SchuS4 as a model. We are particularly interested in investigating the mechanisms by which Ft suppresses host's innate immune defenses. Our extensive work in the pursuit of understanding the virulence mechanisms of Ft lays a very solid foundation for the proposed research program. We have demonstrated that Ft SchuS4 possesses robust antioxidant defense mechanisms which render it extremely resistant to oxidants. By generating point and multiple gene deletion mutants of a close surrogate of Ft SchuS4- the live vaccine strain (LVS), we have established that Ft antioxidants are important virulence factors and play an essential role in the suppression of kinase signaling and macrophage activation. In this application, we wish to dig deeper to expose the link between efficient ROS scavenging capacity of Ft SchuS4 to its ability to cause innate immune suppression. Our published and preliminary studies provide compelling evidence in support of our hypothesis that "Ft antioxidants suppress innate immune responses by inhibiting the activation of redox-sensitive signaling components and production of pro-inflammatory cytokines". The following specific aims are proposed: Aim 1: will investigate how antioxidants of Ft SchuS4 subvert innate immune function by modulating macrophage redox-environment. Aim 2: will investigate the impact of Ft antioxidant defenses immediately upon uptake, on intracellular macrophage ROS-dependent signaling cascades, while Aim 3 will establish the mechanism of Ft antioxidant mediated subversion of cytosolic redox-sensitive nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) signaling. The long-term objective of this application is to build a strong platform for the development of redox- based broad-spectrum therapeutic/prophylactic approaches. The concept that bacterial antioxidants in addition to their established role as scavengers of ROS/RNS can subvert host's innate immune response is highly innovative and may truly uncover a novel and conserved mechanism of bacterial pathogenesis.