ANTIGEN HANDLING AND CYTOKINE PHENOTYPE REGULATION IN NORMAL AND INFLAMED COLON

炎症性肠病（IBD）的发病机制涉及免疫、遗传和环境因素之间复杂的相互作用。来自越来越多的IBD小鼠模型的证据支持CD4 T细胞对肠道细菌菌群的失调反应作为一种常见的疾病机制发挥核心作用。虽然这些模型已经将注意力转向了作为疾病介质的特定T细胞亚群和细胞因子，以及驻留在粘膜免疫组织（特别是结肠）中的CD4 T细胞。引发和维持慢性肠道炎症的特定抗原和细菌种群是未知的。同样，正常和失调的CD4 T细胞群的抗原特异性和表型是未知的或缺乏特征。本研究将利用抗原特异性模型研究慢性结肠炎症的发生和进展，以研究克隆CD4 T细胞群与其在肠道中的同源抗原之间的相互作用。这种特性良好的卵白蛋白（OVA）特异性DO11.10 TCR转基因小鼠模型将用于描述CD4 T细胞识别和对结肠中游离或细菌相关OVA的反应机制，并确定这种反应的特异性中断如何导致结肠炎。我们假设盲肠和近端结肠细菌菌群的周转产生三种一般类型的抗原：死亡生物体释放的游离抗原、胞质抗原和质周抗原；细胞膜或细胞壁相关抗原：死亡生物体释放的游离抗原、胞质抗原和质周抗原；细胞膜或细胞壁相关抗原，由濒死生物体和完整的活生物体释放。在结肠淋巴滤泡或更远的免疫组织中摄取这些不同形式的细菌抗原，驱动不同谱系的CD4 T细胞分化。游离细菌抗原是有利于调节性细胞（如Th1）发育的耐受性抗原，而膜相关抗原和活生物体，因为它们是具有炎症特性的颗粒抗原，优先诱导促炎效应CD4细胞（如Th1细胞）。肠道淋巴组织处理的抗原负荷的混合性质刺激了促炎性和抗炎性CD4 T细胞表型的分化，维持了体内平衡。在第一个目标中，我们将验证tr1型调节性T细胞的体内发育是通过识别游离抗原诱导的，而导致结肠炎的促炎效应细胞的发育需要识别细菌相关抗原的假设。在第二个目标中，我们将验证在缺乏调节性CD4 T细胞群的情况下，效应CD4 T细胞诱导由细菌相关抗原驱动的抗原特异性结肠炎的假设。

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.