Immunoglobulin as a novel ligand for HLA-DM

描述（由申请人提供）：抗原提呈细胞是免疫反应的关键参与者。它们参与起始细胞和效应细胞的启动，对于协调对感染的反应以及对自身抗原（自身免疫）的反应至关重要。在抗原呈递细胞中，B细胞具有独特的呈递少量抗原的能力，它们通过表面免疫球蛋白（Ig）捕获并吸收抗原。基于我们的初步研究结果，我们假设HLA-DM是通过使Ig靠近MHC II并促进抗原从Ig中释放，从而增强抗原在B细胞表面上通过Ig的呈递的关键参与者。在这里，我们建议评估细胞中DM/Ig相互作用的功能结果。我们将设计一种表达GAD65特异性免疫球蛋白的B细胞系，以及一种不与Ig相互作用但与MHC II相互作用的突变型DM。将比较突变型和野生型DM在不同B细胞数量和抗原剂量的T细胞增殖试验中增强GAD65呈递的能力。我们还建议使用接近结扎法和荧光显微镜来定位细胞中HLA-DM/Ig相互作用的位置。虽然我们在这里关注的是表面免疫球蛋白作为B细胞中的抗原受体，但我们的结果将对其他抗原呈递细胞类型（如巨噬细胞和树突状细胞）的功能产生影响，这些细胞通过表面Fc受体（FcR）吸收免疫复合物。这些抗原/抗体复合物也针对内体途径，在那里他们遇到HLA-DM。

DESCRIPTION (provided by applicant): Antigen presenting cells are key players in the immune response. They are involved in priming naove and effector cells and are critical for orchestrating a response to infection as well as responses to self- antigens (autoimmunity). Among antigen presenting cells, B cells are uniquely capable of presenting small amounts of antigen, which they capture and take up through surface immunoglobulin (Ig). Based on our preliminary findings, we hypothesize that HLA-DM is a key player in enhancing presentation of antigen taken up through Ig on the surface of the B cell by bringing Ig in close proximity to MHC II and facilitating antigen release from Ig. Here, we propose to assess the functional outcome of the DM/Ig interaction in cells. We will engineer a B cell line to express a GAD65 specific immunoglobulin as well as a mutant DM that does not interact with Ig but does interact with MHC II. Mutant and wild type DM will be compared for their ability to enhance presentation of GAD65 in T cell proliferation assays, across a range of B cell numbers and antigen doses. We also propose to localize the site of the HLA-DM/Ig interaction in cells by using proximity ligation assays and fluorescence microscopy. Although we focus here on surface immunoglobulin as an antigen receptor in B cells, our results will have implications for the function of other antigen presenting cell types, such as macrophages and dendritic cells, that take up immune complexes via surface Fc receptors (FcR). These antigen/antibody complexes are also targeted to the endosomal pathway, where they encounter HLA-DM. PUBLIC HEALTH RELEVANCE: In health, the immune system responds to foreign antigens and mounts a response to infection. In autoimmune disease, the immune system mounts a response against the body's own (self) antigens. Antigen presenting cells mediate a critical initiating role in the development of an effective immune response by presenting self and foreign antigens to responder cells of the immune system. This project investigates a newly discovered interaction between molecules involved in antigen processing and presentation, a process that is key in shaping the immune response against foreign and self antigens with consequences for infectious as well as autoimmune diseases. The experimental system employed uses proteins of relevance to type 1 diabetes in humans.