Effector Functions of Mucosal IgA

描述（由申请人提供）：本提案的长期目标是更好地了解人类粘膜免疫系统和IgA受体在粘膜免疫反应中的作用。口服疫苗比传统的肠外途径具有显著的优势。最值得注意的是，它刺激粘膜免疫反应，在入侵部位对抗病原体。然而，阻碍口服疫苗发展的一个主要限制是缺乏对如何有效地将疫苗抗原呈递到粘膜免疫系统的了解。目前正在研究的一种克服这一限制的有希望的方法是使用分泌IgA （SIgA）作为疫苗递送载体。SIgA在恶劣的胃肠道环境中非常稳定，并结合并被肠道微褶(M)细胞吸收，这些细胞专门用于通过Peyer's斑块的滤泡相关上皮运输腔内抗原。最近的一项研究表明，当给小鼠口服时，携带线性抗原表位的重组SIgA插入分泌成分诱导对抗原的免疫反应。研究还表明，SIgA与小鼠M细胞的结合是由一种新的IgA受体介导的。小鼠M细胞的分子特性目前尚不清楚。也不知道人类M细胞是否表达类似的IgA受体。因此，鉴定肠上皮Caco-2细胞与Raji B细胞共培养产生的人m细胞上表达的IgA受体是本项目的一个重要目标。由于小鼠和人类在IgA受体的表达和功能上存在重大差异，我们将首先确定人类M细胞是否也表达一种新的IgA受体，或者是否已知的IgA受体负责IgA与人类M细胞的结合。如果存在新的IgA受体，我们将使用两种不同的实验方法进行鉴定，即cDNA表达克隆和免疫沉淀。一旦我们确定了人m细胞IgA受体（新的或已知的），我们将分析其在人肠道活检样本中的表达及其在体外SIgA胞吞作用中的功能。该项目的另一个主要目标是了解人类M细胞如何调节SIgA胞吞作用。人IgA是一种高度复杂的糖蛋白，我们将生产定义明确的重组人IgA分子，每个分子都包含聚糖或蛋白质片段的特定修饰。利用这些抗体，我们将鉴定控制体外生成的人M细胞结合和转运效率的人SIgA的基序和表位。此外，我们还将确定SIgA与M细胞结合激活的细胞内信号通路，并确定其活性是否调节SIgA胞吞的效率。在小鼠中开发的M细胞靶向策略通常不适用于人类，因为这两种生物之间IgA生物学和M细胞表面特性的差异。拟用人类M细胞进行的研究将为开发实用的基于siga的人类口服疫苗提供必要的基础知识。

DESCRIPTION (provided by applicant): The long-term goal of this proposal is to gain a better understanding of the human mucosal immune system and the role of IgA receptors in the mucosal immune response. Oral vaccine delivery offers significant advantages over conventional parenteral routes. Most notably, it stimulates mucosal immune responses that combat pathogens at the sites of invasion. However, a major limitation that has hindered the development of oral vaccines has been a lack of understanding of how to effectively present the vaccine antigen to the mucosal immune system. One promising approach currently being investigated to overcome this limitation is the use of secretory IgA (SIgA) as a vaccine delivery vehicle. SIgA is extremely stable in the harsh gastrointestinal environment, and binds and is taken up by intestinal microfold (M) cells that are specialized for transporting luminal antigens across the follicle-associated epithelium of Peyer's patches. A recent study indicated that when administered orally to mice, recombinant SIgA carrying a linear antigenic epitope inserted into the secretory component induced immune responses against the antigen. Studies also showed that the binding of SIgA to mouse M cells is mediated by a novel IgA receptor. The molecular identity of the mouse M cell is currently unknown. It is also not known if human M cells express a comparable IgA receptor. Therefore, an important goal of this project is to identify the IgA receptor expressed on human M-cells generated by coculturing intestinal epithelial Caco-2 cells with Raji B cells. Since there are major differences between mice and humans in the expression and function of IgA receptors, we will first determine if human M cells also express a novel IgA receptor or if known IgA receptors are responsible for IgA-binding to human M cells. If the presence of a novel IgA receptor is suggested, we will identify it using two different experimental approaches, i.e., cDNA expression cloning and immunoprecipitation. Once we identify the human M-cell IgA receptor (novel or known), we will analyze its expression in human intestinal biopsy samples and its function in SIgA transcytosis in vitro. Another major goal of this project is to understand how human M cells regulate SIgA transcytosis. Human IgA is a highly complex glycoprotein and we will produce well-defined recombinant human IgA molecules each of which contains a specific modification in the glycan or protein moiety. Using these antibodies, we will identify the motifs and epitopes of human SIgA that control the efficiency of its binding and transport by human M cells generated in vitro. Furthermore, we will also identify intracellular signaling pathways activated by SIgA-binding to M cells and determine if their activities regulate the efficiency of SIgA transcytosis. M-cell targeting strategies developed in mice are often not applicable to humans because of the differences in IgA biology and the surface characteristics of M cells between these two organisms. The proposed studies using human M cells will provide the fundamental knowledge essential for the development of practical SIgA-based oral vaccines for humans. PUBLIC HEALTH RELEVANCE: Oral vaccines do not require sterile injection equipment or highly skilled medical personnel, thus significantly reducing the costs and workload necessary for immunization. The proposed studies will increase our understanding of how oral vaccines are taken up by the human intestine. They will also provide new strategies for the development of safe and efficient needle-free vaccines.