Inhibition of T cell Responses by Bacteria

描述（由申请人提供）：我们已经开始研究CD8+ T细胞在细胞内细菌，福氏志贺氏菌免疫中的作用。在感染过程中，弗氏柔球菌进入细胞并逃逸到宿主细胞质中。我们预计从志贺氏菌中排泄的蛋白质会通过MHC-I加工途径被蛋白水解降解为肽，并且所产生的细胞表面肽：MHC-I复合物会刺激ecd8 + t细胞。在单核增生李斯特菌感染期间，另一种胞质细菌病原体，李斯特菌衍生的肽，与宿主MHC-I复合物，被CD8+ T细胞识别，并有助于产生保护性免疫。然而，我们发现CD8+ T细胞似乎在对弗氏沙门氏菌的保护性免疫中不起作用。即使志贺氏菌被设计成组成性地分泌异源表位，以刺激有效的CD8 + T细胞反应，这些反应也没有被检测到。我们还发现，当培养细胞被这些表位标记的flexneri菌株感染时，这些细胞不能被已建立的表位标签特异性t细胞克隆识别。这些发现提示我们，正常MHC-I加工途径中的一个步骤（或多个步骤）在感染flexneri的细胞中被抑制。本实验旨在识别和表征弗氏杆菌感染期间发生的MHC-I加工和/或表现的缺陷。具体而言：1)使用生化分析，我们将分析志贺菌感染期间MHC-I途径，以确定是否存在特定活性抑制；2)我们将使用两个平行的基因筛选来鉴定负责抑制的flexneri基因产物。通过这些实验，我们期望识别和描述mhc - 1加工和呈现的细菌抑制剂的活性。这种抑制剂可能代表了一类新的毒力决定因素，能够特异性地抑制宿主适应性免疫系统对病原体的识别。了解这种抑制如何影响细菌的毒力和获得性免疫，将进一步加深我们对这种细菌病原体及其哺乳动物宿主的复杂相互作用的理解。

DESCRIPTION (provided by applicant): We have initiated studies to characterize the role of CD8+ T cells in immunity to the intracellular bacterium, Shigella flexneri. During infection, S. flexneri enters cells and escapes into the host cell cytosol. We expected that proteins excreted from Shigella would be proteolytically degraded into peptides by the MHC-I processing pathway, and that the resulting cell-surface peptide:MHC-I complexes would stimulateCD8 + T-cells. During infection with Listeria monocytogenes, another cytosolic bacterial pathogen, Listeria-derived peptides, in complex with host MHC-I, are recognized by CD8+ T cells and contribute to the generation of protective immunity. However, we have found that CD8+ T cells do not appear to play a role in protective immunity to S. flexneri. Even when the Shigella have been engineered to constitutively secrete heterologous epitopes known to stimulate potent CD8 + T cell responses, those responses were not detected. We also found that when cultured cells were infected with these epitope-tagged S. flexneri strains, the cells were not recognized by established T-cell clones specific for the epitope tag. These findings have suggested to us that a step (or steps) in the normal MHC-I processing pathway is inhibited in cells infected with S. flexneri. The experiments in this proposal seek to identify and characterize the defect in MHC-I processing and/or presentation that occurs during S. flexneri infection. Specifically: 1) using biochemical assays, we will analyze the MHC-I pathway during Shigella infection to determine if there is inhibition of specific activities; and 2) we will use two parallel genetic screens to identify S. flexneri gene product(s) responsible for the inhibition. Through these experiments, we expect to identify and describe the activity of a bacterial inhibitor of MHC-I processing and presentation. Such an inhibitor might represent a novel class of virulence determinants specifically able to inhibit pathogen recognition by the adaptive immune system of the host. Understanding how this inhibition affects bacterial virulence and acquired immunity will further our understanding of the complex interaction of this bacterial pathogen and its mammalian host.