MHC Class II subsets in B Lymphocyte Biology

描述（由申请人提供）：除了介导CD4 T细胞的活化外，抗原肽- mhc II类复合物转导导致抗原提呈细胞活化的信号。使用已经存在超过20年的特性良好的抗i- ak单克隆抗体（mab），我们最近发现这些单克隆抗体在静止B细胞中诱导II类信号传导的能力不同。具体来说，结合1链Ia.2表位的单克隆抗体会引发src家族激酶介导的钙信号，而结合2链Ia.17表位的两种单克隆抗体则不会。在本提案提供的初步数据中，我们进一步证明了Ia.2表位并不像之前认为的那样存在于所有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，除了其独特的信号传导能力外，I-Ak分子的Ia.2+亚群在脂筏中高度富集，关键参与同源mhc限制性B细胞- t细胞相互作用的启动，并且独特地与低MW细胞表面蛋白相关。基于这些已发表的初步结果，我们提出了这样的假设，即Ia.2表位代表了一种独特的分子结构，这种分子结构是在一组具有信号能力的脂质筏性I-Ak II类分子上产生的，或者可以接近的，这些分子对关键的MHC II类功能（如B细胞信号传导和同源B细胞-t细胞相互作用的形成）至关重要。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类分子中携带ia .2的脂质筏性信号传导亚群的分子结构。其次，我们将建立亚细胞区室，在其中形成含i .2的I-Ak类分子。这些特定目标的完成将揭示Ia.2+ I-Ak II类分子独特信号特性背后的基本分子机制，建立控制Ia.2+ I-Ak II类分子（以及其他MHC II类单倍型）选择性脂质分流的分子机制，并为进一步表征Ia.2+和其他MHC II类亚群在bcr介导的抗原加工/递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（APCs）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基于抗体的免疫（例如成功接种疫苗）具有重要的生理意义。在治疗上，抗mhc II单克隆抗体已用于淋巴瘤患者，通过触发细胞死亡来帮助消除恶性细胞。在本研究项目中获得的对B细胞MHC II类信号的更多了解将支持更好地利用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.