Cytosolic sensing of intracellular Brucella infection

描述（由申请人提供）：布鲁氏菌病是最广泛的人畜共患感染之一，每年有超过50万新病例。该疾病主要由细菌病原体布鲁氏菌和流产布鲁氏菌引起，通过食用未经巴氏消毒的乳制品或与受感染的动物接触而获得。布鲁氏菌病是一种多系统疾病，其特征是发热，并经常出现骨关节疾病。由于据估计只有4%的布鲁氏菌病病例得到报告，实际数字可能要大得多。该疾病的一个重要特征是其延续性，其结果是网状内皮系统的持续细菌定植和全身传播。然而，导致免疫系统成功定植和逃避清除的病原体和宿主之间的特定相互作用在很大程度上是未知的。虽然布鲁氏菌似乎缺乏大多数经典的毒力因子，但我们的工作已经表明，编码IV型分泌系统（T4SS）的virB位点对于单核吞噬细胞的存活和小鼠感染模型中的毒力至关重要。虽然T4SS介导的细胞内持久性的分子机制尚不清楚，但我们最近已经确定了(i) T4SS的第一个底物，以及（ii） T4SS在体内触发肉芽肿炎症中的作用。我们的长期目标是确定布鲁氏菌与宿主相互作用导致疾病的分子机制。本应用程序的目的是在细胞水平上查明T4SS如何与先天免疫信号通路相互作用以触发有利于定植的反应。该应用的中心假设是，T4SS通过在感染细胞中引发caspase-1依赖性促炎反应，在宿主中建立一个生态位。通过(1)鉴定检测胞内布鲁氏菌感染的细胞质传感器和(2)确定分泌的T4SS底物在调节caspase-1炎性体中的作用，将对中心假设进行验证，并实现本应用的目标。我们期望这项工作的结果将为T4SS如何引发细胞反应以促进布鲁氏菌在其宿主生态位中的建立建立新的范例，从而显著影响推动该领域的概念和方法。

DESCRIPTION (provided by applicant): Brucellosis is a one of the most widespread zoonotic infection, with over 500,000 new cases each year. The disease, caused primarily by the bacterial pathogens Brucella melitensis and Brucella abortus, is acquired by consumption of unpasteurized dairy products or by contact with infected animals. Brucellosis is a multisystem disease characterized by fever, and frequently, osteoarticular disease. Since it has been estimated that only 4% of brucellosis cases are reported, the actual number is likely to be much larger. An important feature of the disease is its protracted nature that results from persistent bacterial colonization of the reticuloendothelial system and systemic dissemination. However, the specific interactions between pathogen and host that result in successful colonization and evasion of clearance by the immune system are largely uncharacterized. While Brucella spp. appear to lack most classical virulence factors, our work has shown that the virB locus, encoding a Type IV secretion system (T4SS), is essential for survival in mononuclear phagocytes and virulence in a mouse infection model. While the molecular mechanisms underlying T4SS-mediated intracellular persistence are unknown, we have recently identified (i) the first substrates of the T4SS, and (ii) a role for the T4SS in triggering granulomatous inflammation in vivo. Our long-range goal is to define molecular mechanisms of Brucella interaction with the host that lead to disease. The objective of this application is to pinpoint at the cellular level, how the T4SS interacts with innate immune signaling pathways to trigger a response that is favorable for colonization. The central hypothesis of this application is that the T4SS functions in establishing a niche in the host by eliciting caspase-1 dependent proinflammatory responses in infected cells. The central hypothesis will be tested and the objectives of this application accomplished by (1) Identifying the cytosolic sensors that detect intracellular Brucella infection and (2) Determining the role of secreted T4SS substrates in modulating the caspase-1 inflammasome. We expect that the results of this work will establish new paradigms of how the T4SS elicits cellular responses to promote establishment of Brucella in its host niche, thereby significantly influencing concepts and methods driving the field.