Characterization of the MHC Class II Peptide Loading Complex

描述（由申请人提供）：B细胞和CD4 T细胞之间的相互作用由肽- mhc II类复合物介导，并支持体液免疫反应的充分发展。B细胞是抗原特异性抗原提呈细胞，免疫相关抗原加工发生在B细胞受体（BCR）介导的结合和同源抗原内化之后。该实验室已经证实，bcr介导的抗原加工发生在抗原(Ag)-BCR泛素化之后，并导致具有独特功能和生化特性的衍生肽II类复合物（称为“I型”复合物）的表达。推动该项目的基本假设是，Ag-BCR复合物的加工发生在MHC II类肽装载复合物（PLC）内，该复合物位于MHC II类富集抗原加工室中。为了验证这一假设，我们将扩展我们新的初步数据，并采用生化方法进一步确定B细胞中II类PLC的分子组成，这些PLC通过bcr介导或液相内吞作用内化抗原（目的1）。我们还将利用“FRET显微镜”方法来研究完整B细胞中II类PLC形成的动力学（目的2）。总的目标是

DESCRIPTION (provided by applicant): Interactions between B cells and CD4 T cells are mediated by peptide-MHC class II complexes and support full development of a humoral immune response. B cells are antigen-specific antigen presenting cells, where immunologically relevant antigen processing occurs subsequent to B cell receptor (BCR)-mediated binding and internalization of cognate antigen. This laboratory has established that BCR-mediated antigen processing occurs subsequent to antigen (Ag)-BCR ubiquitination and results in expression of derivative peptide-class II complexes (termed "Type I" complexes) with unique functional and biochemical properties. The underlying hypothesis driving this project is that processing of Ag-BCR complexes occurs within an MHC class II peptide-loading complex (PLC) located in MHC class II enriched antigen processing compartments. To test this hypothesis, we will extend our new preliminary data and take a biochemical approach to further define the molecular composition of the class II PLC in B cells processing antigen internalized either via BCR-mediated or fluid-phase endocytosis (Aim 1). We will also utilize a "FRET microscopy" approach to study the dynamics of class II PLC formation in intact B cells (Aim 2). The overall goal of this proposal is to gain a better understanding of the molecular mechanism of class II peptide loading subsequent to BCR-mediated antigen processing, and to determine if class II peptide loading occurs within a PLC containing a dedicated source of antigenic peptide (i.e., Ag-BCR complexes). PUBLIC HEALTH RELEVANCE: Interactions between antigen specific B cells and CD4 helper T cells are restricted by B cell expressed peptide-MHC class II complexes. The goal of this project is to define the molecular mechanism by which antigen specific B cells generate these critical peptide-class II complexes. This information will be helpful in the design of new vaccines that enhance the production of these complexes or therapeutic protocols to dampen this mechanism in cases of autoimmunity.