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CD 4 + T（Th 17）细胞最近被定义为不同于Th 1和Th 2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，Th 17和Th 1应答均升高。虽然IL-12驱动的针对肠道细菌抗原的过度Th 1应答已被广泛接受为IBD发病机制的主要途径，但最近的研究暗示IL-23-Th 17细胞轴在实验性IBD中起关键作用。然而，肠道细菌抗原特异性Th 17和Th 1效应细胞在肠道中的分化和相互作用及其在IBD发病机制中的作用尚不清楚。我们最近确定肠道细菌鞭毛蛋白作为免疫显性抗原在实验性结肠炎和克罗恩病患者。我们已经产生了一个TCR转基因小鼠系，是特定的CBir 1鞭毛蛋白，这样的细菌鞭毛蛋白之一。CBir 1特异性Th 17和Th 1细胞可以从这些CBir 1转基因小鼠中分离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鞭毛蛋白的免疫应答中起关键作用。固有层中存在多个DC亚群。LP DC，而不是脾DC，表达高水平的TLR 5，并且响应于鞭毛蛋白刺激，LP DC产生大量的IL-6和IL-23，其是Th 17发育所需的，以及驱动Th 1细胞发育的IL-12。我们假设1）固有层DC和脾DC对CBir 1鞭毛蛋白刺激的反应不同。固有层DCs驱动T细胞向Th 1和Th 17途径发育，而脾DCs仅促进T细胞向Th 1途径发育：2）髓样LPDC优先诱导CBir 1鞭毛蛋白特异性Th 17细胞发育，而另一个LPDC亚群驱动Th 1细胞途径; 3）CBir 1鞭毛蛋白激活TLR 5信号传导诱导LPDC产生TGF 2和IL-23，其驱动Th 17细胞在固有层中发育和存活。在正常宿主中，微生物群、先天免疫细胞（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，这种对话被扰乱，从而导致炎症。关于IBD发病机制的主要工作假设是，正常肠道微生物群是驱动炎性疾病的刺激物，并且适应性免疫CD 4 + T细胞是介导遗传易感个体疾病的效应细胞。然而，所涉及的机制仍不明确。在小鼠和人类中鉴定的许多IBD易感基因位点似乎涉及先天免疫系统。在先天性免疫细胞中，树突状细胞（DC）是指导T细胞对抗原（包括肠道细菌的抗原）应答的关键参与者。固有层中存在多个DC亚群。该项目将探索固有层DC的不同子集如何响应最近定义的克罗恩病的优势细菌抗原，以及它们如何指导肠道中的致病性效应T细胞发育。这些研究将为开发一种新的、基于细菌抗原和细胞因子的治疗方法以改善IBD患者的生活提供重要的理论基础。

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.