H2-O Mediated Antigen Focusing Modulates B Cell Immunity

描述(申请人提供)：MHC II类分子在内体隔间中装载它们的多肽货物。这一过程是由类11分子，人类白细胞抗原-DM(DM；在小鼠的H2-M)催化的。人类白细胞抗原DO(DO；在小鼠中为H2-O)是一种MHC编码的类似于11类分子的分子，在转运到内体隔室的过程中和之后都与DM相关。有趣的是，与II类加工途径的所有其他成分不同，DO的表达仅限于B细胞和胸腺上皮细胞。现在已经很清楚，DO可以改变DM的多肽负荷活性。不太清楚的是DO的净作用；DO可以促进或抑制II类多肽负荷取决于实验系统。DO/H2-O对B细胞的限制表达使我们假设H2-O主要作用于通过B细胞受体(BCR)内化的抗原(AGs)。我们的初步数据表明，BCR连接导致H2-O从H2-M迅速解离，并使游离H2-M与内化的BCR发生戏剧性的区隔。将银呈递的关键成分集中在一个隔室内显然表明了一种机制，即只有在BCR与银接触后，H2-O才能显著增强II类呈递。这种“抗原聚焦”机制似乎对T依赖的B细胞免疫反应至关重要，尤其是对表达低亲和力bcr的B细胞。这些概念将在本应用程序中直接进行检查。 在目标1中，我们将1)确认和扩展我们的研究，检查BCR连接的细胞中H2-O从H2-M解离；2)识别H2-O和H2-M交通到的亚细胞隔室；3)检查H2-O解离对II类呈现的影响。在目标2中，我们将确定H2-O在体内T细胞依赖的免疫反应中所起的作用。将检测H2-O表达对T细胞依赖、抗原特异性抗体反应和生发中心形成的影响。我们还将研究H2-O对体细胞超突变、亲和力成熟和B细胞阳性选择的影响。这项拟议的研究将阐明H2-O在体内免疫反应中II类抗原处理途径中的作用。这些研究与肿瘤免疫、自身免疫和疫苗开发有关。

DESCRIPTION (provided by applicant): MHC class II molecules are loaded with their peptide cargo in endosomal compartments. This process is catalyzed by the class ll-like molecule, HLA-DM (DM; H2-M in mice). HLA-DO (DO; H2-O in mice), an MHC-encoded, class ll-like molecule, associates with DM both during and after transport to endosomal compartments. Intriguingly, unlike all other components of the class II processing pathway, DO expression is restricted to B cells and thymic epithelial cells. It is now clear that DO modifies the peptide loading activity of DM. Less clear is the net effect of DO; DO can promote or inhibit class II peptide loading depending on the experimental system. The restricted expression of DO/H2-O to B cells has led us to hypothesize that H2-O exerts its affects predominantly on antigens (Ags) internalized via the B cell receptor (BCR). Our preliminary data shows that BCR ligation causes rapid dissociation of H2-O from H2-M and, also a dramatic compartmentalization of free H2-M with the internalized BCR. Focusing the critical components of Ag presentation within one compartment clearly suggests a mechanism by which H2-O substantially enhances class II presentation only after the BCR engagement of the BCR with Ag. Such an "Ag focusing" mechanism would appear to be critical for T-dependent B cell immune responses, particularly for B cells expressing low affinity BCR. These concepts will be directly examined in this application. In aim 1 we will 1) confirm and extend our studies examining H2-O dissociation from H2-M in BCR-ligated cells; 2) identify the subcellular compartments to which H2-O and H2-M traffic; and 3) examine the impact that H2-O dissociation has on class II presentation. In aim 2, we will determine the role H2-O plays in T cell-dependent immune response in vivo. The effect of H2-O expression on T cell-dependent, antigen specific antibody responses and germinal center formation will be examined. We will also study the impact of H2-O on somatic hypermutation, affinity maturation and B cell positive selection. The proposed studies will elucidate the role of H2-O in the class II antigen-processing pathway in vivo, during immune responses. These studies are relevant for tumor immunity, autoimmunity and vaccine development.