Intestinal M Cells and Secretory IgA Response to Defined Gut Microbiota

项目总结/摘要 伊加是人体内合成的主要免疫球蛋白分子。大部分这种伊加是由 通过存在于肠固有层中的浆细胞，并通过上皮细胞转运到肠上皮细胞中。 管腔作为分泌型伊加，有助于建立和维持体内平衡与肠道细菌， 稳定地存在于人胃肠道中。小肠Peyer集合淋巴结是小肠淋巴结的重要解剖部位， 伊加反应的诱导。为了刺激伊加的产生，肠道细菌和细菌 抗原必须首先被抗原采样细胞吸收。有两种抗原采样途径， 解释细菌和细菌抗原最初如何进入派尔集合淋巴结的候选人：微折叠 (M)细胞介导的摄取和单核吞噬细胞对腔菌的直接取样（包括两者） 树突细胞和巨噬细胞）。M细胞是一种专门的抗原取样上皮细胞，存在于 小肠和结肠中覆盖有组织淋巴结构的滤泡相关上皮（FAE） 包括派伊尔淋巴结和孤立的淋巴滤泡。这个项目的目标是使用一个老鼠模型 系统，以确定M细胞是否发挥主导作用相比，其他潜在的抗原采样途径， 分泌型伊加产生的起始。细胞因子RANKL是启动M细胞增殖所必需的， 从肠隐窝中的未定型上皮前体细胞分化。结果， 肠上皮RANK的条件性缺失（RANKIEC小鼠）缺乏肠M细胞， 派伊尔淋巴结。初步研究表明，传统的安置RANKIEC小鼠具有显著的 产生的粪便伊加量和肠道中存在的伊加+浆细胞密度不足 固有层该项目将使用无菌小鼠和用一组确定的厌氧 肠细菌（Altered Schaedler植物群或ASF），以确定分泌型伊加的产生是否与此定义的 一组细菌也依赖于M细胞的细菌摄取。指导建议的中心假设 实验表明，M细胞介导的抗原采样占大多数采样的肠道细菌， 诱导肠淋巴组织的部位，从而启动正常分泌的有效诱导， 伊加对细菌抗原的反应。该提案的第一个目的是确定缺乏 肠M细胞对无菌小鼠分泌型伊加产生的影响。第二个目的是描述 分泌型伊加对将一组确定的肠道微生物群（ASF）引入M细胞缺陷型小鼠的应答 秩IEC小鼠和对照同窝仔。对M细胞介导的抗原采样如何通过 肠道免疫系统促进肠道内稳态可能有助于开发改善的口服 疫苗接种策略和治疗人类炎症性肠病的新方法。

Project Summary/Abstract IgA is the predominant immunoglobulin molecule synthesized in the human body. Most of this IgA is produced by plasma cells residing in the intestinal lamina propria and is transported across the epithelium and into the lumen as secretory IgA that helps to establish and maintain homeostasis with the commensal bacteria that stably reside in the human gastrointestinal tract. Intestinal Peyer's patches are important anatomic sites for the induction of IgA responses. In order to stimulate the production of IgA, commensal bacteria and bacterial antigens must first be taken up by antigen-sampling cells. There are two antigen-sampling pathways that are candidates to explain how bacteria and bacterial antigens are initially taken up into Peyer's patches: microfold (M) cell-mediated uptake and direct sampling of luminal bacteria by mononuclear phagocytes (including both dendritic cells and macrophages). M cells are specialized antigen-sampling epithelial cells that are found in the follicle-associated epithelium (FAE) covering organized lymphoid structures in the small intestine and colon including Peyer's patches and isolated lymphoid follicles. The goal of this project is to use a mouse model system to determine if M cells play a dominant role compared to other potential antigen-sampling pathways in the initiation of secretory IgA production. The cytokine RANKL is necessary and sufficient to initiate M cell differentiation from uncommitted epithelial precursor cells in intestinal crypts. As a result, mice with a conditional deletion of RANK in the intestinal epithelium (RANKIEC mice) lack intestinal M cells in their Peyer's patches. Preliminary studies show that conventionally housed RANKIEC mice have significant deficiencies in the amount of fecal IgA produced and the density of IgA+ plasma cells present in the intestinal lamina propria. This project will use germ-free mice and mice recolonized with a defined set of anaerobic enteric bacteria (Altered Schaedler Flora or ASF) to determine whether secretory IgA production to this defined set of bacteria is also dependent on bacterial uptake by M cells. The central hypothesis guiding the proposed experiments is that M cell-mediated antigen sampling accounts for most sampling of commensal bacteria at the site of inductive intestinal lymphoid tissues, thereby initiating the efficient induction of the normal secretory IgA response to bacterial antigens. The first aim of the proposal is to determine the impact of absence of intestinal M cells on secretory IgA production by germ-free mice. The second aim is to characterize the secretory IgA response to introduction of a defined set of commensal microbiota (ASF) into M cell-deficient RANKIEC mice and control littermates. Mechanistic insights into how M cell-mediated antigen sampling by the gut immune system promotes intestinal homeostasis may be useful in developing improved oral vaccination strategies and new approaches to the treatment of human inflammatory bowel disease.