B Cell Receptor Regulation of Antigen Processing

描述（由申请人提供）：B淋巴细胞捕获、加工和呈递抗原至T细胞的能力是正常体液免疫应答所必需的，并有助于B和T细胞介导的自身免疫性疾病的发病机制。B淋巴细胞优先捕获多价抗原，其通过聚集B细胞抗原受体（BCR）并引发信号级联，引发一系列协调的细胞应答，确保甚至低亲和力抗原也被有效捕获。抗原多价性极大地加速了接合受体的内吞作用及其通过内吞途径转运至晚期内体抗原加工区室。与成熟树突状细胞中所描述的相似，BCR连接也诱导受体靶向抗原加工区室的重塑，这增强了它们加工肽并将其加载到MHC II类上的能力。尽管BCR信号传导在决定抗原向T细胞呈递方面很重要，但对于哪些信号传导途径有助于受体转运以及它们调节哪些特定的细胞过程，人们知之甚少。在这个赠款申请，我们证明，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体的正常运输所必需的。在没有泛素化的情况下，受体回缩到细胞表面。在更下游处，需要泛素连接酶Cbl-b进入抗原加工区室。从这些观察，我们提出了一个模型，其中有两个不同的检查点在BCR内吞贩运每个控制不同的泛素连接酶。基于这个模型，我们预测，在每个检查点的受体贩运决定外周B细胞的反应。我们建议在以下具体目标中测试该模型：目标1。确定Itch如何泛素化IG？。目标2.确定IG？泛素化目标3.确定BLNK和Cbl-b如何促进受体转运。目的4：确定在无反应性B细胞中BCR运输异常的原因。

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.