The role of CBir1 flagellin-specific Th17 and Th1 effector cells in colitis

描述（由申请人提供）：产生il -17的CD4+ T （Th17）细胞最近被定义为不同于Th1和Th2细胞的单独效应T细胞谱系。在结肠炎动物模型和炎症性肠病（IBD）患者中，Th17和Th1反应均升高。虽然il -12驱动的Th1对共生细菌抗原的过度反应已被广泛认为是IBD发病的主要途径，但最近的研究表明IL-23-Th17细胞轴在实验性IBD中起关键作用。然而，肠道中共生细菌抗原特异性Th17和Th1效应细胞的分化和相互作用及其在IBD发病机制中的作用尚不清楚。我们最近发现肠道细菌鞭毛蛋白是实验性结肠炎和克罗恩病患者的免疫优势抗原。我们已经产生了一种TCR转基因小鼠系，对这种共生细菌鞭毛蛋白之一的CBir1鞭毛蛋白具有特异性。CBir1特异性Th17和Th1细胞可以从这些CBir1转基因小鼠中分离出来，并在免疫缺陷小鼠中转移疾病。肠道树突状细胞可能在宿主对这些共生鞭毛蛋白的免疫反应中发挥关键作用。在固有层中存在多个DC亚群。LP dc，而不是脾脏dc，表达高水平的TLR5，并且，在鞭毛蛋白刺激下，LP dc产生大量的IL-6和IL-23，这是Th17发育所需的，以及驱动Th1细胞发育的IL-12。我们假设1)固有层DC和脾脏DC对CBir1鞭毛蛋白刺激的反应不同。固有层dc驱动T细胞向Th1和Th17通路发展，而脾脏dc仅促进T细胞向Th1通路发展；2)髓系LPDC优先诱导CBir1鞭毛蛋白特异性Th17细胞发育，而LPDC的另一个亚群驱动Th1细胞通路；3) CBir1鞭毛蛋白激活TLR5信号，诱导LPDC产生TGF2和IL-23，从而驱动Th17细胞在固有层的发育和存活。在正常宿主中，微生物群、固有免疫细胞（包括上皮细胞）和适应性免疫细胞之间存在对话，适应性免疫细胞能够维持体内平衡并预防炎症。在IBD中，这种对话被干扰，从而导致炎症。关于IBD发病机制的主要工作假说是正常肠道菌群是驱动炎症性疾病的刺激物，适应性免疫CD4+ T细胞是介导遗传易感个体疾病的效应细胞。然而，所涉及的机制仍然不明确。在小鼠和人类中发现的许多IBD易感基因位点似乎与先天免疫系统有关。在先天免疫细胞中，树突状细胞（DC）是指导T细胞对抗原（包括共生细菌的抗原）反应的关键角色。在固有层存在多个DC亚群。本项目将探索不同的固有层DC亚群如何对最近定义的克罗恩病显性细菌抗原作出反应，以及它们如何指导肠道中致病性效应T细胞的发育。这些研究将为开发一种新的基于共生细菌抗原和细胞因子的治疗方法提供重要的理论依据，以改善IBD患者的生活。

DESCRIPTION (provided by applicant): IL-17-producing CD4+ T (Th17) cells have recently been defined as a separate effector T cell lineage distinct from Th1 and Th2 cells. Both Th17 and Th1 responses are elevated in animal models of colitis and in patients with inflammatory bowel disease (IBD). Although IL-12-driven excessive Th1 response against commensal bacterial antigen has been widely accepted as a major pathway in IBD pathogenesis, recent studies implicate a pivotal role for the IL-23-Th17 cell axis in experimental IBD. However, the differentiation and interaction of commensal bacterial antigen-specific Th17 and Th1 effector cells in intestine and their roles in pathogenesis of IBD remain undefined. We recently identified enteric bacterial flagellin as immunodominant antigen in experimental colitis and in patients with Crohn's disease. We have generated a TCR transgenic mouse line that is specific for CBir1 flagellin, one of such commensal bacterial flagellins. CBir1-specific Th17 and Th1 cells can be isolated from these CBir1 transgenic mice and transfer disease in immunodeficient mice. Intestinal dendritic cells likely play a critical role in the host immune response to these commensal flagellins. Multiple subsets of DC exist in lamina propria. LP DCs, but not spleen DCs, express high levels of TLR5, and, in response to flagellin stimulation, LP DCs produce high amounts of IL-6 and IL-23 which are required for Th17 development, as well as of IL-12 which drives Th1 cell development. We hypothesize that 1) Lamina propria DC and spleen DC respond differently to CBir1 flagellin stimulation. Lamina propria DCs drive T cell development into both Th1 and Th17 pathways whereas spleen DCs only promote T cell development into Th1 pathway; 2) Myeloid LPDCs preferentially induce CBir1 flagellin-specific Th17 cell development whereas another subset of LPDC drive Th1 cell pathway; 3) Activation of TLR5 signaling by CBir1 flagellin induces LPDC production of TGF2 and IL-23 which drive Th17 cell development and survival in lamina propria. PUBLIC HEALTH RELEVANCE In normal hosts there is a dialogue between the microbiota, innate immune cells, including epithelial cells, and the adaptive immune cells that is able to maintain homeostasis and prevent inflammation. In IBD this dialogue is disturbed such that inflammation results. The major working hypothesis concerning the pathogenesis of IBD is that the normal intestinal microbiota is the stimulus driving the inflammatory disease and that adaptive immune CD4+ T cells are the effector cells mediating disease in genetically susceptible individuals. However, the mechanisms involved are still undefined. Many of the IBD susceptibility gene loci identified in both mouse and humans appear to involve the innate immune system. Among innate immune cells, dendritic cells (DC) are the key players in directing T cell responses to antigens, including those of commensal bacteria. Multiple subsets of DC are present in lamina propria. This project will explore how different subsets of lamina propria DC respond to recently defined dominant bacterial antigens of Crohn's disease, and how they instruct pathogenic effector T cell development in the intestine. These studies will provide an important rationale to develop a novel, commensal bacterial antigen and cytokine based therapeutic approach to improve the lives of patients with IBD.