MHC Class II subsets in B Lymphocyte Biology

描述（由申请人提供）：除了介导CD 4 T细胞的活化外，抗原肽-MHC II类复合物还介导导致抗原呈递细胞活化的信号。我们最近使用已经有20多年历史的充分表征的抗I-Ak单克隆抗体（mAb），确定这些mAb在静息B细胞中引发II类信号传导的能力不同。具体地，结合1链Ia.2表位的mAb激活src家族激酶介导的钙信号传导，而结合2链Ia.17表位的两种mAb不激活。在本提案中提供的初步数据中，我们进一步证明了Ia.2表位并不像以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之外，I-Ak分子的Ia.2+亚组高度富集在脂筏中，关键地参与同源MHC限制的B细胞-T细胞相互作用的起始，并且独特地与低MW细胞表面蛋白相关。基于这些公开的和初步的结果，我们提出了这样的假设，即Ia.2表位代表了在具有信号传导能力的脂筏-嗜性I-Ak II类分子的子集上产生的或可接近的独特分子结构，其对于关键的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。为了验证这个假设，我们将完成两个具体目标。首先，我们将进一步建立Ia.2-轴承脂筏亲信号能力子集的I-Ak II类分子的分子结构。其次，我们将建立亚细胞区室，其中形成Ia.2-承载I-Ak II类分子。这些具体目标的完成将揭示Ia.2+ I-Ak II类分子独特信号传导特性背后的基本分子机制，建立控制Ia.2+ I-Ak II类分子选择性脂筏分配的分子机制（和其他MHC II类单倍型），为进一步研究Ia.2+等MHC Ⅱ类亚群在BCR介导的抗原加工/呈递中的作用奠定了基础。公共卫生相关性：B细胞和其它抗原呈递细胞（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类分子递送至这些细胞的细胞活化信号对于基于抗体的免疫（例如成功的疫苗接种）在生理学上是重要的。在治疗上，抗MHC II单克隆抗体已用于淋巴瘤患者，以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类信号传导的知识的增加将支持更大的利用MHC II类信号传导以改善免疫和抗肿瘤治疗的能力。

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.