Characterization of the Brucella abortus virB Locus

描述(申请人提供)：流产布鲁氏菌是一种兼性细胞内病原体，通过气雾剂途径具有高度传染性，并导致一种慢性、衰弱的疾病。这种病原菌在寄主中存活的分子机制尚不清楚。我们最近发现，编码IV型分泌系统(T4SS)的VIRB基因对于流产杆菌在小鼠体内的持久性是必不可少的。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。本申请的目的是确定T4SS在逃避宿主免疫中的作用。这一应用的中心假设是，T4SS通过允许流产杆菌逃避适应性免疫的特定成分来调节持续的定植。这一假说是基于我们的初步数据提出的，这些数据表明：(I)VIRB突变株能够在小鼠体内定植，但随着适应性免疫的开始而被消除，(Ii)不能产生CD4+T细胞和B细胞依赖的适应性免疫的突变小鼠在清除VIRB突变株方面存在缺陷。我们为开展这项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)，并在布鲁氏菌病的体外和体内模型方面拥有经验。中心假说将得到检验，这项应用的目标将通过追求两个特定目标来实现：(1)确定T4SS介导逃逸CD4+T细胞和/或B细胞依赖的免疫反应的机制(2)确定T4SS是否能够使布鲁氏菌通过MHC II类逃避抗原递呈。这项研究具有创新性，因为它利用小鼠和细菌遗传学来确定特定毒力因子如何在逃避宿主免疫中发挥作用。我们希望这项工作的结果将确定B流产使用T4SS逃避的特定免疫机制。这些结果将具有重要意义，因为了解布鲁氏菌逃避哪些特定免疫机制将有助于开发治疗或预防布鲁氏菌病的新策略。

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.