Determinants of induced Treg and inflammatory Th17 cell balance in response to potentially pathogenic microbiota

肠道微生物群与免疫系统细胞的相互作用控制多种生理功能， 局部表现为肠屏障功能的调节，全身表现为自身免疫性疾病， 疾病和抗肿瘤免疫的调节。虽然互惠共生的微生物物种通常提供重要的 虽然它们对宿主的健康有益，但其中一些在某些情况下可能会有条件地造成伤害，例如 宿主遗传脆弱性或环境干扰。这些被称为 已经提出“致病菌”是炎症性肠病（IBD）的主要贡献者， 溃疡性结肠炎和克罗恩病，其特征在于肠道生态失调。更好的描述 这些细菌物种和它们与宿主在健康的稳态中相互作用的机制， 在IBD相关的炎症期间，治疗炎症对于开发更好的治疗方法至关重要。我们 研究了在健康人中诱导调节性T细胞（iTreg）的模型致病性肝螺杆菌（Helicobacter hepaticus）， 小鼠肠道，但促进Th 17-介导的炎症时，iT细胞受损。H.肝- 特异性幼稚T细胞被结肠引流肠系膜淋巴液中的抗原呈递细胞（APC）激活 淋巴结（mLN），并上调Foxp 3和RORgt，肠iTreg的特征性转录因子。 然而，当IL-10是有限的或当iTreg诱导以其他方式受损时，微生物特异性T细胞 表达RORgt并在固有层中采用致病性（p）Th 17细胞程序。本提案的目标 是鉴定与幼稚H相互作用的APC。mLN中的肝特异性T细胞编程iTreg 或pTh 17分化途径，阐明APC-T的参与分子和时间动力学 细胞相互作用，并确定不同类型的MHC II类表达细胞在肠道中的作用， 固有层促进iTreg和pTh 17细胞功能。在初步研究中，我们发现选择性损失 树突状细胞（DC）中的CCR 7或3型先天淋巴样细胞（ILC 3）中的MHC-II的缺失导致 iTreg细胞分化和扩增，而不是mLN和固有层中的pTh 17细胞。类似的iTreg 当参与TGF-β释放的分子在DC或ILC 3中突变时，观察到表型，表明 这种iTreg诱导细胞因子的受调节的局部释放需要幼稚T细胞与DC相互作用， ILC3.我们的第一个目标是通过遗传和转录组学方法精确地表征细胞类型， 在mLN中诱导iTreg所需的，并排除由于在mLN中表达Cre而引起的误解的可能性。 罕见的未表征的APC或细胞类型限制性突变的间接影响;并确定 细胞的时空相互作用，使用多光子显微镜。第二个目标是确定CCR 7- 在受损iTreg诱导的情况下，pTh 17细胞诱导所需的独立APC。第三个目标 就是利用H肝特异性系统，以研究多种非T细胞启动功能 肠固有层中表达MHC-II的细胞类型，包括上皮细胞和内皮细胞。

Interactions of the gut microbiota with cells of the immune system govern multiple physiological functions that are manifested locally, in the regulation of intestinal barrier functions, and systemically, in autoimmune diseases and modulation of anti-tumor immunity. Although mutualistic microbial species generally provide vital health benefits to the host, some of them can conditionally cause harm under some circumstances, such as host genetic vulnerabilities or following environmental perturbation. These bacterial species, known as “pathobionts”, have been proposed to be major contributors to inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn’s disease, which are characterized by intestinal dysbiosis. A better characterization of these bacterial species and the mechanisms by which they interact with the host in healthy homeostatic conditions and during IBD-associated inflammation is critical for developing better therapeutic approaches. We study the model pathobiont Helicobacter hepaticus, which induces regulatory T cells (iTreg) in the healthy murine gut, but promotes Th17-mediated inflammation when the iTregs are compromised. H. hepaticus- specific naïve T cells are activated by antigen-presenting cells (APCs) in colon-draining mesenteric lymph nodes (mLN), and up-regulate Foxp3 and RORgt, transcription factors characteristic of intestinal iTreg. However, when IL-10 is limiting or when iTreg induction is otherwise compromised, the microbe-specific T cells express RORgt and adopt a pathogenic (p)Th17 cell program in the lamina propria. The goals of this proposal are to identify the APCs that interact with naïve H. hepaticus-specific T cells in the mLN to program either iTreg or pTh17 differentiation pathways, elucidate the molecules involved and the temporal dynamics of the APC-T cell interactions, and determine the roles of the diverse types of MHC class II-expressing cells in the intestinal lamina propria in promoting iTreg and pTh17 cell functions. In preliminary studies, we found that selective loss of either CCR7 in dendritic cells (DCs) or MHC-II in type 3 innate lymphoid cells (ILC3) resulted in abrogation of iTreg cell differentiation and in expansion, instead, of pTh17 cells in mLN and lamina propria. A similar iTreg phenotype was observed when molecules involved in TGF-b release were mutated in DCs or ILC3, suggesting that regulated local release of this iTreg-inducing cytokine requires naïve T cells to interact with both DCs and ILC3. Our first aim is to precisely characterize, through genetic and transcriptomic approaches, the cell types required for iTreg induction in the mLN, and rule out potential for misinterpretation due to expression of Cre in rare uncharacterized APCs or to indirect effects of the cell type-restricted mutations; and determine the spatiotemporal interactions of the cells, using multiphoton microscopy. The second aim is to identify the CCR7- independent APC(s) required for pTh17 cell induction in settings of compromised iTreg induction. The third aim is to leverage the H. hepaticus-specific system to investigate potential non-T cell priming functions of diverse MHC-II-expressing cell types in the intestinal lamina propria, including epithelial and endothelial cells.