Studies of Fc-epsilon-RI as an antigen presentation structure at mucosal surfaces

描述（由申请方提供）：本研究项目的目的是检验胃肠道树突状细胞（DC）通过Fc-γ-RI-IgE介导的摄取处理腔内抗原，从而影响肠道炎症反应和I型超敏反应的假设。Fc-RI是高亲和力IgE Fc受体，是一种多聚体免疫识别受体，通过其α链中的单价表位结合IgE。抗原诱导的IgE-Fc-ε-RI复合物交联通过受体的信号亚基（Fc-ε-RI-β和共同γ链的二聚体）引起细胞活化。Fc-γ- RI的独特特征是其细胞类型和物种特异性表达模式。在小鼠中，受体仅在肥大细胞和嗜碱性粒细胞上表达为异源四聚体（α、β和两个γ链）。在人类中，Fc-γ-RI作为异源四聚体在肥大细胞和嗜碱性粒细胞上组装，但另外也作为缺乏β亚基的异源三聚体组装。独特地，人异源三聚体形式的Fc-RI-RI在抗原呈递细胞上表达，包括肠中的DC。受体的表面表达与过敏性疾病相关，并在过敏反应期间控制IgE介导的细胞活化。与其他多聚体免疫识别受体不同，表面表达在内质网中亚基的共翻译组装水平上受到调控;但调控机制仍不清楚。目的1将阐明单个Fc ε RI亚基的结构特征，其决定受体组装并因此决定Fc ε RI复合物的表面表达。目的2将确定人三聚体Fc-γ-RI是否通过IgE介导的摄取途径在DC或巨噬细胞上发挥呈递抗原的功能。这组实验将使用表达Fc-ε-RI的鼠细胞，其允许我们研究受体介导的抗原呈递对MHC II类和MHC I类途径中的T细胞活化的功能后果。目的3利用在DCs上条件性表达人α链Fc-γ-RI的转基因动物研究IgE介导的肠道免疫应答。公共卫生相关性：胃肠道粘膜必须平衡对病原体的反应能力，同时保持对食物和环境抗原以及肠道微生物菌群的不反应。越来越多的人患有食物过敏和慢性肠道炎症。IgE和Fc-γ-RI-IgE如何影响这些疾病尚不清楚。更好地了解控制Fc-γ-RI-IgE介导的免疫系统激活的机制将为过敏和抗原诱导的胃肠道粘膜炎症提供新的治疗策略。

DESCRIPTION (provided by applicant): The goal of this research program is to test the hypothesis that dendritic cells (DCs) of the gastro intestinal tract process lumenal antigens by Fc-epsilon-RI-IgE mediated uptake, thereby affecting the intestinal inflammatory response and type I hypersensitivity. Fc-epsilon-RI, the high affinity IgE Fc-receptor, is a multimeric immune recognition receptor that binds IgE through a monovalent epitope in its alpha chain. Antigen-induced crosslinking of the IgE-Fc-epsilon-RI complex causes cell activation via the signaling subunits of the receptor (Fc-epsilon-RI-beta and a dimer of the common gamma chain). A unique feature of Fc-epsilon- RI is its cell type- and species-specific expression pattern. In mice, the receptor is expressed only as a heterotetramer (alpha, beta, and two gamma chains) on mast cells and basophils. In humans, Fc-epsilon-RI assembles as a heterotetramer on mast cells and basophils, but additionally also as a heterotrimer lacking the beta subunit. Uniquely, the human heterotrimeric form of Fc-epsilon-RI is expressed on antigen presenting cells, including DCs in the intestine. Surface expression of the receptor correlates with allergic diseases, and controls IgE-mediated cell activation during the allergic response. Unlike other multimeric immune recognition receptors, surface expression is regulated at the level of co-translational assembly of subunits in the endoplasmic reticulum; but the mechanism of regulation remains unknown. Aim 1 will elucidate structural features of individual Fc-epsilon-RI subunits that dictate receptor assembly and thus surface expression of Fc- epsilon-RI complexes. Aim 2 will determine if the human trimeric Fc-epsilon-RI functions on DCs or macrophages to present antigen via IgE-mediated uptake pathways. This set of experiments will use Fc- epsilon-RI-expressing murine cells that allow us to study functional consequences of receptor-mediated antigen presentation for T cell activation in the MHC class II and the MHC class I pathways. Aim 3 will investigate IgE-mediated intestinal immune responses in vivo using a transgenic animal conditionally expressing the human alpha-chain of Fc-epsilon-RI on DCs. PUBLIC HEALTH RELEVANCE: The GI mucosa must balance the ability to respond to pathogens while remaining unresponsive to food and environmental antigens and the commensal microflora. Rising numbers of individuals suffer from food allergies and chronic intestinal inflammation. How IgE and Fc-epsilon-RI-IgE affect these diseases is unknown. A better understanding of the mechanisms that control Fc-epsilon-RI-IgE-mediated activation of the immune system will point towards new treatment strategies for allergy and antigen-induced mucosal inflammation in the GI tract.