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细胞的单独的效应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。尽管IL-12诱导的针对共生细菌抗原的过度Th1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中起着关键作用。然而，肠道细菌抗原特异性Th17和Th1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。我们已经建立了一种针对CBir1鞭毛蛋白的TCR转基因小鼠系，CBir1鞭毛蛋白是这种共生细菌鞭毛蛋白之一。可以从这些CBir1转基因小鼠中分离出CBir1特异性的Th17和Th1细胞，并在免疫缺陷小鼠中传播疾病。肠道树突状细胞可能在宿主对这些共生鞭毛的免疫反应中发挥关键作用。固有层内存在多个DC亚群。LP DC，而不是脾DC，表达高水平的TLR5，并且在鞭毛刺激下，LP DC产生Th17发育所需的大量IL-6和IL-23，以及驱动Th1细胞发育的IL-12。我们假设：1)固有层DC和脾DC对CBir1鞭毛蛋白刺激的反应不同。固有层DC促进T细胞发育为Th1和Th17途径，而脾DC仅促进T细胞发育为Th1途径；2)髓系LPDCs优先诱导CBir1鞭毛蛋白特异的Th17细胞发育，而LPDC的另一亚群驱动Th1细胞途径；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。正常宿主的公共卫生相关性微生物区系、包括上皮细胞在内的先天免疫细胞和能够维持内稳态和预防炎症的获得性免疫细胞之间存在对话。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说是，正常的肠道微生物区系是驱动炎症性疾病的刺激因素，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，其中涉及的机制仍不明确。在小鼠和人类中发现的许多IBD易感基因位点似乎都与先天免疫系统有关。在天然免疫细胞中，树突状细胞(DC)在引导T细胞对包括共生菌在内的抗原反应中起着关键作用。树突状细胞的多个亚群存在于固有层。这个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的优势细菌抗原做出反应，以及它们如何指导肠道中致病效应T细胞的发育。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来改善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.