Mechanisms of microbiota induced IL-23/Th17 immune responses in chronic colitis

复杂的调节机制共同维持肠道内稳态，这些途径的破坏可能最终导致炎症性肠病（IBD）。我们目前对肠道稳态的大部分理解是建立在微生物群不断与肠道免疫系统相互作用以及微生物群组成调节促炎和耐受性免疫反应之间的精细平衡的概念之上的。然而，在IBD中发生的与疾病相关的微生物群组成变化是直接导致疾病，还是反映了细菌群落对炎症或肠道环境中宿主基因型相关变化的适应，目前仍不完全清楚。IL-23R基因和其他编码IBD中IL-23/TH17通路相关蛋白的区域的遗传多态性以及小鼠研究表明，适当调节IL-23依赖性免疫反应对肠道免疫稳态至关重要。另一方面，IL-23/TH17轴可能在胃肠道感染的保护性免疫中发挥核心作用。在这个项目中，我们将从机制上研究IL-23产生细胞、IL-23R+免疫细胞群、它们的效应细胞因子和共生菌群之间的串扰。一个IL-23报告鼠菌株将用于分析IL-23在无菌条件下和在常规或定义的微生物群重新定植后的时空表达。利用IL-23依赖性自发性结肠炎小鼠模型，我们将对结肠炎发病前后肠道组织中的肠道T细胞和先天淋巴样细胞（ILC）池进行表征；这些结果将与IBD患者的情况进行比较。同时，通过16S rRNA宏基因组研究对肠道微生物群进行组成分析将有助于表征从健康到炎症过渡阶段微生物群/免疫系统的相互作用。此外，由于TH17细胞和RORγt+ ILC以IL-23依赖的方式产生的细胞因子IL-17和IL-22是肠上皮细胞（IEC）抗菌肽产生的重要调节因子，我们将确定细胞因子诱导的抗菌肽产生如何影响肠道微生物组成和多样性。据此，我们将在感染性结肠炎模型中分析IEC中IL-23依赖性抗菌因子的产生如何促进宿主对肠道病原体的生理反应。

Complex regulatory mechanisms work together to maintain intestinal homeostasis, and a breakdown in these pathways may finally result in inflammatory bowel disease (IBD). Much of our present understanding of intestinal homeostasis is built around the concept that the microbiota continuously interacts with the intestinal immune system and that the microbiota composition regulates the fine equilibrium between pro-inflammatory and tolerogenic immune responses. However, whether disease related shifts in microbiota composition that were shown to occur in IBD directly cause disease or reflect the adaptation of bacterial communities to inflammation or host genotype related changes in the intestinal environment is still incompletely understood. Genetic polymorphisms in the IL-23R gene and other regions that encode proteins implicated in the IL-23/TH17 pathway in IBD as well as murine studies suggest that appropriate regulation of IL-23 dependent immune responses is critical for intestinal immune homeostasis. On the other hand the IL-23/TH17 axis may play a central role in protective immunity to gastrointestinal infections. In this project, we will mechanistically investigate the crosstalk between IL-23 producing cells, IL-23R+ immune cell populations, their effector cytokines and the commensal flora. An IL-23 reporter mouse strain will be used to analyze the spatiotemporal expression of IL-23 under germfree conditions and after re-colonization with conventional or defined microflora. Using a mouse model of IL-23 dependent spontaneous colitis, we will characterize the intestinal T cell and innate lymphoid cell (ILC) pool in intestinal tissues before and after onset of colitis; these results will be compared to the situation in IBD patients. In parallel, the compositional analysis of the intestinal microbiota by 16S rRNA metagenomic studies will help to characterize the microbiota/immune system interactions in the transition phase from healthy to inflammatory settings. Moreover, as the cytokines IL-17 and IL-22 that are particularly produced by TH17 cells and RORγt+ ILC in an IL-23 dependent manner are important regulators of antimicrobial peptide production in intestinal epithelial cells (IEC), we will determine how cytokine induced antimicrobial peptide production affects microbial composition and diversity in the gut. In line with this, we will analyze in models of infectious colitis, how IL-23 dependent production of antimicrobial factors in IEC contribute to physiological host responses to intestinal pathogens.