Intestinal M Cells and Secretory IgA Response to Defined Gut Microbiota

描述（由申请人提供）：IgA是人体内合成的主要免疫球蛋白分子。大多数IgA由居住在肠固有层的浆细胞产生，并作为分泌性IgA通过上皮运输进入管腔，帮助与稳定居住在人体胃肠道中的共生菌建立和维持稳态。肠道Peyer's补丁是诱导IgA反应的重要解剖部位。为了刺激IgA的产生，共生细菌和细菌抗原必须首先被抗原取样细胞吸收。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被吸收到Peyer's贴片中的：微褶(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）对腔内细菌的直接采样。M细胞是一种特殊的抗原取样上皮细胞，存在于覆盖小肠和结肠组织淋巴样结构的滤泡相关上皮（FAE）中，包括Peyer's斑块和分离的淋巴样滤泡。这个项目的目标是使用一个小鼠模型系统来确定M细胞是否比其他潜在的抗原采样途径在启动分泌性IgA生产中起主导作用。细胞因子RANKL是肠隐窝中启动M细胞从未确定上皮前体细胞分化的必要和充分条件。因此，肠上皮条件缺失RANK的小鼠（RANK IEC小鼠）在其Peyer's补丁中缺乏肠M细胞。初步研究表明，常规饲养的RANK IEC小鼠在产生粪便IgA的数量和存在于肠固有层的IgA+浆细胞密度方面存在显著不足。该项目将使用无菌小鼠和一组确定的厌氧肠道细菌（改变的Schaedler菌群或ASF）重新定植的小鼠来确定这组细菌的分泌IgA产量是否也依赖于M细胞的细菌摄取。指导本实验的中心假设是，M细胞介导的抗原取样占了诱导肠淋巴组织部位的大部分共生菌取样，从而启动了正常分泌IgA的有效诱导

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.