Intestinal M Cells and Secretory IgA Response to Defined Gut Microbiota

说明(申请人提供)：IGA是人体内合成的主要免疫球蛋白分子。大部分IgA是由肠道固有层中的浆细胞产生的，并作为分泌型IgA跨上皮进入肠腔，帮助建立和维持与稳定驻留在人类胃肠道中的共生细菌的动态平衡。肠Peyer氏结是诱导IgA反应的重要解剖部位。为了刺激IgA的产生，共生菌和细菌抗原必须首先被抗原采样细胞摄取。有两种抗原采样途径可以解释细菌和细菌抗原最初是如何进入Peyer‘s斑块的：微折叠(M)细胞介导的摄取和单核吞噬细胞(包括树突状细胞和巨噬细胞)对管腔细菌的直接采样。M细胞是一种特殊的抗原采样上皮细胞，存在于滤泡相关上皮(FAE)中，覆盖着小肠和结肠中的有组织的淋巴结构，包括Peyer氏结和孤立的淋巴滤泡。这个项目的目标是使用小鼠模型系统来确定与其他潜在的抗原采样途径相比，M细胞是否在启动分泌IgA的过程中发挥主导作用。细胞因子RANKL是启动肠隐窝中未定位的上皮前体细胞向M细胞分化的必要条件和充分条件。因此，肠道上皮细胞RANK有条件缺失的小鼠(RANK IEC小鼠)在其Peyer氏结中缺乏肠道M细胞。初步研究表明，常规饲养的IEC级小鼠在肠道固有层中产生的粪便IgA量和IgA+浆细胞密度明显不足。该项目将使用无菌小鼠和用一组定义的厌氧肠道细菌(改变的Schaedler门或ASF)重新克隆的小鼠来确定这组定义的细菌的分泌IgA是否也依赖于M细胞对细菌的吸收。指导实验的中心假设是，M细胞介导的抗原采样占诱导肠道淋巴组织部位共生细菌的大部分，从而启动了正常分泌型IgA的有效诱导。 对细菌抗原的反应。该提案的第一个目的是确定肠道M细胞缺失对无菌小鼠分泌IgA的影响。第二个目的是描述在M细胞缺陷的IEC小鼠和对照仔鼠中引入一组确定的共生微生物区系(ASF)后的分泌性IgA反应。对肠道免疫系统M细胞介导的抗原采样如何促进肠道内稳态的机械性见解可能有助于开发改进的口服疫苗接种策略和治疗人类炎症性肠病的新方法。

DESCRIPTION (provided by applicant): 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 (RANK IEC mice) lack intestinal M cells in their Peyer's patches. Preliminary studies show that conventionally housed RANK IEC 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 RANK IEC 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.