B Cell Receptor Regulation of Antigen Processing

描述(由申请人提供)：B淋巴细胞捕获、处理抗原并将其呈递给T细胞的能力是正常体液免疫反应所必需的，也是B和T细胞介导的自身免疫性疾病的发病机制之一。B淋巴细胞优先捕获多价抗原，这些抗原通过聚集B细胞抗原受体(BCR)并启动信号级联反应，引发一系列协调的细胞反应，确保即使是低亲和力的抗原也能被有效捕获。抗原性多价极大地加速了参与的受体的内吞作用，并通过内吞途径将其传递到晚期的内体抗原处理室。与成熟的树突状细胞相似，BCR连接也会导致受体靶向抗原处理间隔的重塑，从而增强其处理多肽并将其加载到MHC II类分子上的能力。尽管BCR信号在决定抗原呈递给T细胞方面很重要，但人们对哪些信号通路有助于受体运输以及它们调节哪些特定的细胞过程知之甚少。在这个拨款申请中，我们证明了BCR成分Ig？在细胞表面被E3连接酶Itch泛素化，这是从早期到晚期内小体正常运输所必需的。在没有泛素化的情况下，受体循环回到细胞表面。再往下游，泛素连接酶Cbl-b需要进入抗原处理隔间。根据这些观察，我们提出了一个模型，在这个模型中，在BCR内吞运输中有两个不同的检查点，每个检查点都由不同的泛素连接酶控制。基于这个模型，我们预测，在每个检查点做出的受体转运决定决定了外周B细胞的反应。我们建议在以下特定目标上测试该模型：目的1.确定Itch泛素化Ig？的方式。目的2.测定免疫球蛋白Ig？泛素化。目的3.确定BLNK和Cbl-b在受体转运中的作用。目的4：探讨无能B细胞BCR转运异常的原因。

DESCRIPTION (provided by applicant): The ability of B lymphocytes to capture, process and present antigens to T cells is requisite for normal humoral immune responses and contributes to the pathogenesis of both B and T cell mediated autoimmune diseases. B lymphocytes preferentially capture polyvalent antigens which, by aggregating the B cell antigen receptor (BCR) and initiating signaling cascades, elicit a coordinated series of cellular responses that ensure that even low affinity antigens are productively captured. Antigenic polyvalency greatly accelerates both the endocytosis of engaged receptors and their transit through the endocytic pathway to the late endosomal antigen processing compartments. Similar to what has been described in maturing dendritic cells, BCR ligation also induces a remodeling of the receptor targeted antigen processing compartments which enhances their ability to process peptides and load them onto MHC class II. Despite the importance of BCR signaling in determining antigen presentation to T cells, relatively little is known about which signaling pathways contribute to receptor trafficking and what specific cellular processes they regulate. In this grant application, we demonstrate that the BCR constituent Ig? is ubiquitinylated at the cell surface by the E3 ligase Itch and that this is required for normal trafficking from early to late endosomes. In the absence of ubiquitinylation, the receptor recycles back to the cell surface. Farther downstream, the ubiquitin ligase Cbl-b is required for entry into the antigen processing compartments. From these observations, we propose a model in which there are two different checkpoints in BCR endocytic trafficking each controlled by different ubiquitin ligases. Based on this model, we predict that decisions in receptor trafficking made at each checkpoint determine peripheral B cell responses. We propose to test this model in the following Specific Aims: Aim 1. To determine how Itch ubiquitinylates Ig?. Aim 2. To determine the in vivo function of Ig? ubiquitinylation. Aim 3. To determine how BLNK and Cbl-b contribute to receptor trafficking. Aim 4: To determine why BCR trafficking is aberrant in anergic B cells.