MHC Class II subsets in B Lymphocyte Biology

描述(由申请人提供)：除了介导CD4T细胞的激活外，抗原肽-MHC II类复合体还传递导致抗原提呈细胞激活的信号。利用已有20多年历史的抗I-AK单抗，我们最近证实，这些单抗在诱导静息B细胞中II类信号的能力上有所不同。具体地说，与1链Ia2表位结合的单抗可诱导src家族蛋白激酶介导的钙信号转导，而与2链Ia.17表位结合的单抗则不能。在这个提案中提供的初步数据中，我们进一步证明了Ia2表位并不像以前认为的那样存在于所有的I-AK分子上，而是标记了细胞表面I-AK II类分子的一个子集。此外，除了其独特的信号功能外，I-AK分子的Ia.2+亚群在脂筏中高度丰富，在启动同源MHC限制性B细胞-T细胞相互作用中起关键作用，并与低分子量细胞表面蛋白唯一相关。基于这些已发表的和初步的结果，我们提出假设，Ia2表位代表一个独特的分子结构，在具有信号功能的脂类亲水性I-AK II类分子的子集上产生或提供可访问的分子结构，这些分子对于关键的MHC II类功能至关重要，如B细胞信号转导和同源B细胞-T细胞相互作用的形成。为了验证这一假设，我们将实现两个具体目标。首先，我们将进一步建立I-AK II类分子的Ia2-脂筏亲脂信号功能亚集的分子结构。第二，我们将建立亚细胞室，在那里形成Ia2-AK II类分子。这些特定目的的完成将揭示Ia.2+I-AK II类分子独特的信号转导特性背后的基本分子机制，建立控制Ia.2+I-AK II类分子(和其他MHC II类单倍型)选择性脂筏分配的分子机制，并为进一步表征Ia.2+和其他MHC II类亚群在BCR介导的抗原处理/提呈中的作用奠定基础。公共卫生相关性：B细胞和其他抗原提呈细胞(APC)表达称为主要组织相容性复合体(MHC)II类分子的细胞表面蛋白。通过MHC II类分子传递给这些细胞的细胞激活信号对于基于抗体的免疫(例如，成功接种)具有重要的生理学意义。在治疗方面，抗MHC II单抗已用于淋巴瘤患者，通过引发细胞死亡来帮助消除恶性细胞。在这项研究项目中获得的关于B细胞MHC II类信号的更多知识将支持更大的能力来利用MHC II类信号来改进免疫和抗肿瘤治疗。

DESCRIPTION (provided by applicant): In addition to mediating activation of CD4 T cells, antigenic peptide-MHC class II complexes transduce signals leading to antigen presenting cell activation. Using well-characterized anti-I-Ak monoclonal antibodies (mAbs) that have been available for over 20 years, we recently established that these mAbs differ in their ability to elicit class II signaling in resting B cells. Specifically, a mAb that binds the 1 chain Ia.2 epitope elicits src family kinase-mediated calcium signaling, while two mAbs that bind the 2 chain Ia.17 epitope do not. In preliminary data presented in this proposal, we further demonstrate that the Ia.2 epitope is not present on all I-Ak molecules as previously thought, but rather marks a subset of cell surface I-Ak class II molecules. Further, in addition to its unique signaling capacity the Ia.2+ subset of I-Ak molecules is highly enriched in lipid rafts, critically involved in initiation of cognate MHC-restricted B cell-T cell interactions, and uniquely associated with a low MW cell surface protein. Based on these published and preliminary results, we put forth the hypothesis that the Ia.2 epitope represents a unique molecular structure generated, or rendered accessible, on a subset of signaling-competent lipid raft-tropic I-Ak class II molecules, which are critically important to key MHC class II functions such as B cell signaling and formation of cognate B cell-T cell interactions. To test this hypothesis, we will accomplish two Specific Aims. First, we will further establish the molecular structure of the Ia.2-bearing lipid raft-tropic signaling-competent subset of I-Ak class II molecules. Second, we will establish the sub-cellular compartment in which Ia.2- bearing I-Ak class II molecules are formed. Completion of these specific aims will reveal the basic molecular mechanism behind the unique signaling properties of Ia.2+ I-Ak class II molecules, establish a molecular mechanism controlling the selective lipid raft partitioning of Ia.2+ I-Ak class II molecules (and other MHC class II haplotypes), and lay the groundwork for the further characterization the role Ia.2+ and other MHC class II subsets in BCR-mediated antigen processing / presentation. PUBLIC HEALTH RELEVANCE: B cell and other antigen presenting cells (APCs) express cell surface proteins called major histocompatibility complex (MHC) class II molecules. Cellular activation signals delivered to these cells through MHC class II molecules are important physiologically for antibody-based immunity (e.g. successful vaccination). Therapeutically, anti-MHC II monoclonal antibodies have been used in lymphoma patients to help eliminate malignant cells by triggering cell death. The increased knowledge of B cell MHC class II signaling gained during this research project will support a greater ability to harness MHC class II signaling for improved immunization and anti-tumor therapy.