ANTIGEN HANDLING AND CYTOKINE PHENOTYPE REGULATION IN NORMAL AND INFLAMED COLON

炎症性肠病(IBD)炎症的发病机制涉及免疫、遗传和环境因素之间的复杂相互作用。来自越来越多的IBD小鼠模型的证据支持，作为一种常见的疾病机制，失控的CD4T细胞对肠道细菌菌群的反应是一种核心作用。虽然这些模型将注意力集中在特定的T细胞亚群和细胞因子作为疾病的媒介和驻留在粘膜免疫组织中的CD4T细胞，特别是结肠。引发和维持慢性肠炎的特异性抗原(S)和细菌种群尚不清楚。同样，正常和失控的CD4T细胞群的抗原特异性和表型也是未知的或特征不佳的。这项建议将使用抗原特异性模型来研究克隆性CD4T细胞群体与其在肠道中的同源抗原之间的相互作用，以研究慢性结肠炎的发生和发展。利用特征良好的卵清蛋白(OVA)特异性DO11.10 TCR转基因小鼠模型，将描述结肠中CD4T细胞对游离或细菌相关的OVA的识别和反应机制，并确定这种反应的特定干扰如何导致结肠炎。我们推测，盲肠和近端结肠细菌菌群的周转产生了三种常见的抗原：濒死生物释放的游离、胞浆和胞质相关抗原；细胞膜或细胞壁相关抗原：濒死生物释放的游离、胞质和胞质周围抗原；濒死生物释放的细胞膜或细胞壁相关抗原，以及完整的活生物。这些不同形式的细菌抗原在结肠淋巴滤泡或更远端的免疫组织中的摄取，推动了不同谱系的CD4T细胞的分化。游离细菌抗原是一种耐受性物质，有利于调节型(如Th1)细胞的发育，而膜相关抗原和活体生物由于是具有炎症性质的颗粒抗原，优先诱导促炎效应细胞(如Th1细胞)。正是肠道淋巴组织处理的抗原负载的混合性质刺激了促炎和抗炎的CD4T细胞表型的分化，从而维持了体内平衡。在第一个目标中，我们将检验这样一个假设，即在体内，TR1型调节性T细胞的发育是由对游离抗原的识别诱导的，而导致结肠炎的促炎效应细胞的发展需要对细菌相关抗原的识别。在第二个目标中，我们将检验这一假设，即在缺乏调节的CD4T细胞群的情况下，效应器CD4T细胞诱导由细菌相关抗原驱动的抗原特异性结肠炎。

The pathogenesis of inflammatory of inflammatory bowel disease (IBD) involves complex interactions among immune, genetic, and environmental factors. Evidence from a growing number of mouse models of IBD support a central role for disregulated CD4 T cell responses to the enteric bacterial flora as a common disease mechanism. While these models have directed attention to specific T cell subpopulations and cytokines as mediators of disease and CD4 T cells resident in mucosal immune tissues, particular the colon. The specific antigen(s) and bacterial populations that initiate and sustain chromic intestinal inflammation are unknown. Similarly, the antigenic specificity and phenotypes of normal and disregulated CD4 T cell population are unknown or poorly characterized. This proposal will examine the initiation and progression of chronic colonic inflammation using an antigen-specific model for study of interactions between clonal CD4 T cell populations with their cognate antigen in the intestine. The well- characterized, ovalbumin (OVA)-specific DO11.10 TCR transgenic mouse model will be used to delineate the mechanism of CD4 T cell recognition and response to free or bacterially associated OVA in the colon, and to determine how specific disruptions of this response lead to colitis. We postulate that turnover of the bacterial flora in the cecum and proximal colon generate three general types of antigens: free, cytosolic and periplasmic antigens released by dying organisms; cell membrane or cell wall associated antigens: free, cytosolic and periplasmic antigens released by dying organisms; cell membrane or cell wall associated antigens released by dying organisms, and intact, viable organisms. Uptake of these different forms of bacterial antigens in the colonic lymphoid follicles, or more distal immune tissues, drive differentiation of distinct lineages of CD4 T cells. Free bacterial antigens are toleragens that favor development of regulatory type (e.g. Th1) cells, whereas membrane associated antigens and live organisms, because they are particulate antigens with phlogistic properties, preferentially induce pro-inflammatory effector CD4 cells (e.g. Th1 cells). It is the mixed nature of the antigenic load handled by the intestinal lymphoid tissues that stimulates differentiation of pro- and anti-inflammatory CD4 T cell phenotypes that maintain homeostasis. In the first aim, we will test the hypothesis that in vivo development of Tr1-type regulatory T cells is induced by recognition of free antigen whereas development of pro-inflammatory effector cells that cause colitis requires recognition of bacterially associated antigen. In the second aim, we will test the hypothesis that in the absence of a regulatory CD4 T cell population, effector CD4 T cells induce an antigen-specific colitis driven by bacterially associated antigen.