Characterization of the Brucella abortus virB Locus

描述（由申请人提供）：流产布鲁氏菌是一种兼性细胞内病原体，通过气溶胶途径具有高度传染性，引起慢性衰弱性疾病。这种病原体在宿主体内持续存在的分子机制尚不清楚。我们最近的研究表明，编码IV型分泌系统（T4SS）的virB基因对流产芽孢杆菌在小鼠体内的持久性至关重要。我们的长期目标是阐明T4SS介导流产杆菌持续感染的分子机制。本应用的目的是表征T4SS在逃避宿主免疫中的作用。该应用的中心假设是T4SS通过允许B. abortus逃避适应性免疫的特定成分来介导持续定植。这一假设是根据我们的初步数据制定的，这些数据表明：(1)virB突变体能够在小鼠体内定植，但随着适应性免疫的开始而被消除；(2)突变小鼠不能产生CD4+ T细胞和B细胞依赖性适应性免疫，在清除virB突变体方面存在缺陷。我们为开展拟议的研究做好了独特的准备，因为我们已经确定了免疫逃避所需的毒力因子（T4SS），并且在布鲁氏菌病的体外和体内模型方面具有工作经验。中心假设将被检验，本应用的目标将通过追求两个特定目标来实现：(1)确定T4SS介导CD4+ T细胞和/或B细胞依赖性免疫应答逃避的机制(2)确定T4SS是否启用；布鲁氏菌通过MHC II类逃避抗原呈递。这项研究具有创新性，因为它采用小鼠和细菌遗传学来确定特定的毒力因子如何在逃避宿主免疫中起作用。我们期望这项工作的结果将确定利用T4SS逃避的流产B的特定免疫机制。这些结果将具有重要意义，因为了解布鲁氏菌避开哪些特定免疫机制将有助于制定治疗或预防布鲁氏菌病的新战略。

DESCRIPTION (provided by applicant): Brucella abortus is a facultative intracellular pathogen that is highly infectious by the aerosol route and causes a chronic, debilitating disease. The molecular mechanisms employed by this pathogen to persist in the host are unknown. We have recently shown that the virB genes, encoding a Type IV secretion system (T4SS), are essential for persistence of B. abortus in mice. Our long-range goal is to elucidate the molecular mechanism by which the T4SS mediates persistent infection by B. abortus. The objective of this application is to characterize the role of the T4SS in evading host immunity. The central hypothesis of this application is that the T4SS mediates persistent colonization by allowing B. abortus to evade a specific component of adaptive immunity. This hypothesis has been formulated on the basis of our preliminary data showing that (i) virB mutants are able to colonize the mouse, but are eliminated with the onset of adaptive immunity, and (ii) mutant mice that are unable to generate CD4+ T cell and B cell dependent adaptive immunity, are defective in clearing a virB mutant. We are uniquely prepared to undertake the proposed research, because we have identified a virulence factor (T4SS) required for immune evasion and have experience in working with in vitro and in vivo models of brucellosis. The central hypothesis will be tested and the objectives of this application accomplished by pursuing two specific aims: (1) Identify the mechanism by which the T4SS mediates evasion of CD4+ T cell- and/or B cell-dependent immune responses (2) Determine whether the T4SS enables; Brucella to evade antigen presentation via MHC class II. This research is innovative since it employs both mouse and bacterial genetics to identify how a specific virulence factor functions in evasion of host immunity. We expect that the results of this work will identify specific immune mechanisms evaded by B abortus using the T4SS. These results will be significant, because knowing which specific immune mechanisms are evaded by Brucella will facilitate the development of new strategies to treat or prevent brucellosis.