Inhibition of T cell Responses by Bacteria

超出提供的空间。我们已经开始研究CD8+T细胞在细胞内细菌Shigellaflexneri免疫中的作用。在感染期间，福氏志贺菌进入细胞，然后逃逸到宿主细胞胞浆中。我们预计志贺氏菌分泌的蛋白质将通过MHC-I加工途径降解为多肽，产生的细胞表面多肽：MHC-I复合体将刺激CD8+T细胞。在感染单核细胞增多性李斯特菌的过程中，另一种胞质致病菌--李斯特菌衍生的多肽与宿主MHC-I形成复合体，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细胞似乎并不在对福氏志贺氏菌的保护性免疫中发挥作用。即使志贺氏菌已经被设计成结构性地分泌异源表位，以刺激强大的CD8+T细胞反应，这些反应也没有被检测到。我们还发现，当培养的细胞感染这些标记了表位的志贺氏菌株时，这些细胞不能被建立的针对表位标记的T细胞克隆识别。这些发现向我们表明，在感染福氏志贺氏菌的细胞中，正常的MHC-I处理途径中的一个或多个步骤受到抑制。这项建议中的实验试图识别和表征在福氏志贺氏菌感染期间发生的MHC-I处理和/或呈现方面的缺陷。具体地说：1)我们将使用生化分析方法，分析志贺氏菌感染过程中的MHC-I途径，以确定是否存在特定活性的抑制；以及2)我们将使用两个平行的遗传筛选来鉴定与抑制有关的福氏志贺菌基因产物(S)。通过这些实验，我们希望确定和描述一种MHC-I加工和呈递的细菌抑制剂的活性。这种抑制物可能代表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。了解这种抑制作用如何影响细菌的毒力和获得性免疫，将有助于我们进一步了解这种细菌病原体与其哺乳动物宿主之间的复杂相互作用。表演网站========================================Section End===========================================

EXCEED THE SPACE PROVIDED. We have initiated studies to characterize the role of CD8 + T cells in immunity to the intracellular bacterium, Shigellaflexneri. 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 stimulate CD8 + 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 dectected. 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. PERFORMANCE SITE ========================================Section End===========================================