Mycobacterium tuberculosis evasion of CD4+ T cells in vivo

描述（由申请方提供）：开发抗结核病有效疫苗的最大障碍是结核分枝杆菌持续存在并导致进行性感染的能力，尽管出现了适应性免疫应答。虽然部分有效的疫苗可能来自抗原、佐剂和递送系统的最佳选择，但针对结核病的重大进展将需要基于克服或绕过M.结核病逃避适应性免疫反应。为了确定和表征这些机制，我们开发了新的工具，用于小鼠对M.结核病发现和表征机制，限制了适应性免疫反应的效力，以M。结核我们已经开发了一个系统，使用单克隆抗体，识别一个特定的肽：MHC II复合物和几个重组菌株的M。结核病，以检验假设，M。结核分枝杆菌在体内抑制MHCII抗原呈递，并检验结核分枝杆菌在体内抑制MHCII抗原呈递的假说。结核病将抗原转移到未感染的细胞作为免疫逃避策略。我们还开发了一个系统，使用来自一个独特的小鼠系的CD 4 + T细胞，该小鼠系具有对M特异的转基因T细胞抗原受体。结核分枝杆菌Ag 85 B的表达，并发现在结核分枝杆菌慢性期Ag 85 B基因表达下调。结核病感染伴随着对Ag 85 B的体内CD 4 + T细胞应答降低。综上所述，这些结果表明，M。结核病可能调节抗原基因的表达，作为避免被CD 4+效应T细胞识别和消除的手段。我们还开发了一种可视化和定位M。结核感染细胞和肺中的CD 4 + T细胞，并发现少数M.肺中的结核感染细胞与CD 4 + T细胞直接接触，这支持了CD 4 + T细胞识别M的假设。结核病感染的细胞在感染部位很差。在这个应用中，我们提出实验来检验一般假设，即M。肺中结核感染的细胞和抗原特异性CD 4 + T细胞是有缺陷的，这有助于感染的持续性。我们将测试特定的假设，即M之间的缺陷相互作用。结核感染细胞和慢性感染期间的CD 4 + T细胞是由于以下的组合：1）M.结核分枝杆菌抑制感染细胞的抗原提呈; 2）降低M.结核抗原在慢性感染阶段; 3）转移M.结核抗原从感染细胞转移到肉芽肿中邻近的未感染细胞，使未感染细胞作为诱饵激活远离感染细胞的T细胞。我们提出的研究将提供前所未有的深入了解所使用的机制M。这一发现将指导今后开发提高人类对结核病抵抗力的方法。

DESCRIPTION (provided by applicant): The greatest barrier to development of efficacious vaccines against tuberculosis is the ability of Mycobacterium tuberculosis to persist and to cause progressive infection despite development of an adaptive immune response. While partially-efficacious vaccines may result from optimal selection of antigens, adjuvants, and delivery systems, major progress against tuberculosis will require novel approaches to enhancing resistance, based on overcoming or bypassing the mechanisms used by M. tuberculosis to evade adaptive immune responses. To identify and characterize those mechanisms, we have developed novel tools for use in a mouse model of immunity to M. tuberculosis to discover and characterize mechanisms that limit the efficacy of the adaptive immune response to M. tuberculosis. We have developed a system using a monoclonal antibody that recognizes a specific peptide:MHC II complex and several recombinant strains of M. tuberculosis, to test the hypothesis that M. tuberculosis inhibits MHC II antigen presentation in vivo, and to test the hypothesis that M. tuberculosis transfers antigens to uninfected cells as an immune evasion strategy. We have also developed a system using CD4+ T cells from a unique line of mice with a transgenic T cell antigen receptor specific for M. tuberculosis Ag85B, and have discovered that downregulation of the gene encoding Ag85B during the chronic stage of M. tuberculosis infection is accompanied by diminished in vivo CD4+ T cell responses to Ag85B. Taken together, these results suggest that M. tuberculosis may modulate expression of antigen genes as a means of avoiding recognition and elimination by CD4+ effector T cells. We also developed a method for visualization and localization of M. tuberculosis-infected cells and CD4+ T cells in the lungs, and have found that a minority of M. tuberculosis-infected cells in the lungs are in direct contact with CD4+ T cells, which supports the hypothesis that CD4+ T cells recognize M. tuberculosis-infected cells poorly at the site of infection. In this application, we propose experiments to test the general hypothesis that interactions between M. tuberculosis-infected cells and antigen-specific CD4+ T cells in the lungs are defective, and that this contributes to persistence of the infection. We will test the specific hypothesis that defective interactions between M. tuberculosis-infected cells and CD4+ T cells during chronic infection are due to a combination of: 1) M. tuberculosis inhibition of antigen presentation by infected cells; 2) decreased expression of M. tuberculosis antigens during the chronic stage of infection; and 3) transfer of M. tuberculosis antigens from infected cells to neighboring uninfected cells in granulomas, allowing uninfected cells to act as decoys to activate T cells at a distance from infected cells. Our proposed studies will provide unprecedented insight into the mechanisms used by M. tuberculosis to evade elimination by the mammalian adaptive immune response, and will guide future efforts to develop the means to increase human resistance to tuberculosis.