Synergistic extra and intracellular recognition of F. tularensis

描述（由申请人提供）：表面表达的toll样受体（TLRs）和一类新描述的细胞质模式识别受体（PRRs），是nod样受体（NLR）家族的成员，在天然宿主防御细胞内病原体土拉菌Francisella tularensis （a类生物威胁因子）中发挥重要作用。最近有研究表明，土拉螺旋体可触发免疫细胞中的TLR2信号，而这种PRR的突变与对感染的易感性增加有关。同样，通过含有caspase-募集结构域（ASC）、NLR接头分子的凋亡相关斑点样蛋白的信号传导，以及随后的caspase-1激活，被证明是诱发对土拉菌感染的保护性免疫所必需的。一个有趣的问题是TLR和NLR信号通路之间的确切关系，以及NLR对土拉菌的激活是发生在TLR的下游还是独立于TLR信号传导。此外，土拉菌触发下游信号事件的特定成分和NLR通路的受体尚不清楚。本研究旨在通过验证TLR2和NLR通路信号的整合是土拉菌感染先天免疫反应的最佳发展所必需的假设来解决这些问题，具体目的如下：1)鉴定激活NLR通路的土拉菌SchuS4组分，并评估选定的NLR在介导土拉菌感染的促炎反应中的作用。2)建立响应土拉菌SchuS4的TLR2和NLR信号通路整合的关键位点。本课题将研究先天免疫关键组分之间信号整合的细胞生物学，以及这些过程如何在细胞水平上促进宿主抵抗微生物挑战的能力。确定先天免疫的分子机制将是开发免疫治疗和有效疫苗策略以对抗各种细胞内细菌病原体的重要第一步。该建议具有创新性，因为它提供了一种全面的方法来探索在cdc批准的ABSL3/BSL3设施中，土拉菌SchuS4感染后细胞外和细胞内先天免疫机制之间相对未知的信号整合。本研究将确定土拉菌成分和受体，负责触发胞质机制，并阐明细胞外和细胞内信号整合以引发最佳先天免疫反应的分子机制。公共卫生相关性：本提案旨在研究土拉菌病的免疫病理机制，土拉菌病是由一类生物威胁因子土拉菌引起的人畜共患疾病。研究将集中在探索先天免疫关键组分之间信号整合的细胞生物学，以及这些过程如何在细胞水平上促进宿主抵抗微生物挑战的能力。确定先天免疫的分子机制将是开发免疫治疗和有效疫苗战略以对抗这一致命疾病的重要的第一步。

DESCRIPTION (provided by applicant): Surface-expressed Toll-like receptors (TLRs) and a newly described class of cytosolic pattern recognition receptors (PRRs), members of the Nod-like receptor (NLR) family, play a major role in innate host defense against the intracellular pathogen Francisella tularensis, a category A biothreat agent. Recently it was shown that F.tularensis triggers TLR2 signaling in immune cells and that mutation of this PRR is associated with greater susceptibility to infection. Similarly, signaling through apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), an NLR adaptor molecule, and subsequent caspase-1 activation were shown to be essential for eliciting protective immunity to F. tularensis infection. One intriguing question which remains unanswered is the precise relationship between the TLR and NLR signaling pathways and whether activation of NLRs in response to F. tularensis occurs downstream of TLRs or proceeds independent of TLR signaling. Furthermore, the specific component(s) of F. tularensis that triggers the downstream signaling events and the receptor(s) of the NLR pathways are not known. This proposal seeks to address these issues by testing the hypothesis that integration of signals transduced via the TLR2 and NLR pathway is required for the optimal development of innate immune responses to F. tularensis infection via the following Specific Aims: 1) Identify the F. tularensis SchuS4 component(s) activating the NLR pathway and evaluate the role of select NLRs in mediating the pro-inflammatory responses to F. tularensis. 2) Establish the key sites of integration between the TLR2 and NLR signaling pathways in response to F. tularensis SchuS4. This proposal will study the cell biology of signal integration between key components of innate immunity and how these processes at the cellular level contribute to the host's ability to resist microbial challenge. Defining the molecular mechanism(s) of innate immunity will be an essential first step towards development of immunotherapeutic, as well as effective vaccine strategies to combat a variety of intracellular bacterial pathogens. This proposal is innovative because it provides a comprehensive approach to explore the relatively unknown signal integration between extra- and intracellular innate immune mechanisms following F. tularensis SchuS4 infection in our CDC-approved ABSL3/BSL3 facility. This study will identify the F. tularensis component(s) and the receptor(s) responsible for triggering the cytosolic machinery and elucidate the molecular mechanisms by which extra- and intracellular signals are integrated to elicit an optimal innate immune response. PUBLIC HEALTH RELEVANCE: This proposal aims to investigate the immunopathologic mechanisms underlying tularemia, a zoonotic disease caused by Francisella tularensis, a Category A biothreat agent. The studies will focus on exploring the cell biology of signal integration between key components of innate immunity and how these processes at the cellular level contribute to the host's ability to resist microbial challenge. Defining the molecular mechanism(s) of innate immunity will be an essential first step towards development of immunotherapeutic, as well as effective vaccine strategies to combat this fatal disease.