Role of autoantibody isotype in pemphigus pathogenesis

描述（由申请人提供）：天疱疮是一组潜在致命的水疱疾病，其特征是抗粘粒蛋白（Dsg）细胞粘附蛋白的自身抗体。目前的治疗需要一般的免疫抑制，这有致命感染和继发性癌症的风险。自身免疫研究的一个主要前沿是仅针对致病抗体。我们的总体目标是更好地确定天疱疮的致病抗体群，并设计合理的靶向治疗的长期目标。我们率先在天疱疮中使用抗体克隆技术来识别引起疾病的患者自身抗体的可变和恒定区域的特征。我们已经确定了致病自身抗体的可变区基因使用模式，即使在不同的患者中也是共享的。在定义了足以引起皮肤起泡的抗dsg可变区子集后，我们现在独特地定位于解决抗体恒定区（Fc）在天疱疮发病机制中的作用。我们假设IgG4， IgA和IgE是天疱疮的关键致病亚型，占疾病的全部临床和组织学谱。抗dsg IgG1存在于缓解期患者及其健康亲属中，而活动性疾病患者表现出IgG4自身抗体。在IgA天疱疮中，中性粒细胞性皮肤脓肿是由抗dsg IgA与白细胞Fc受体结合引起的，与此类似，抗dsg IgE可能引起嗜酸性天疱疮。由于慢性抗原刺激促进从IgG1到IgG4、IgA和IgE的类转换，这些同型可以作为区分疾病特异性抗体与其他IgG亚类的临床标记，而其他IgG亚类对提供感染免疫更重要。在Aim 1中，我们将从天疱疮患者中克隆IgG1和IgG4抗dsg单克隆抗体（mab），以确定是否在IgG1， IgG4或两种同型中发现致病性抗体。如果在IgG1和IgG4中都有发现，我们将确定抗dsg IgG4是来自IgG1的类转换还是来自单独的B细胞群，从而深入了解天疱疮中IgG4类转换的机制。在目标2和目标3中，我们将分别从嗜中性粒细胞和嗜酸性粒细胞型天疱疮患者中克隆抗dsg IgA和IgE单抗。我们将评估抗dsg IgA和IgE是否会在相关Fc受体人源化的小鼠中再现炎症性水疱病，并通过Fc效应功能抑制剂治疗小鼠，证明水疱和/或炎症对Fc的依赖性。通过系统地描述天疱疮单抗同型的可变和恒定区域的致病性，我们可以确定哪些结构特征导致疾病。这些研究将为预测不同形式的天疱疮对治疗的反应建立一个合理的框架，描述新的小鼠模型来评估fc介导的疾病，并可能确定新的治疗策略，如同型特异性靶向。由于类天疱疮、获得性大疱性表皮松解症和其他慢性自身免疫性疾病中也存在类似的同型谱，因此我们的研究可能对广泛的自身抗体介导的疾病具有治疗相关性。

DESCRIPTION (provided by applicant): Pemphigus is a group of potentially fatal blistering diseases characterized by autoantibodies against desmoglein (Dsg) cell adhesion proteins. Current therapy requires general immune suppression, which risks fatal infection and secondary cancers. A major frontier for autoimmunity research is to target only disease- causing antibodies. Our overall aim is to better define this pathogenic antibody population in pemphigus, with the long term goal of designing rational, targeted therapies. We have pioneered the use of antibody cloning technology in pemphigus to identify features of variable and constant regions of patient autoantibodies that cause disease. We have identified a pattern of variable region gene usage for pathogenic autoantibodies, which is shared even among different patients. Having defined a subset of anti-Dsg variable regions sufficient for skin blistering, we are now uniquely situated to address the role of the antibody constant region (Fc) in pemphigus pathogenesis. We hypothesize that IgG4, IgA and IgE are the critical pathogenic isotypes in pemphigus, accounting for the full clinical and histologic spectrum of disease. Anti-Dsg IgG1 is found in patients in remission and their healthy relatives, while patients with active disease exhibit IgG4 autoantibodies. In IgA pemphigus, neutrophilic skin abscesses are caused by anti-Dsg IgA binding to leukocyte Fc receptors, and anti-Dsg IgE may cause eosinophilic forms of pemphigus by analogy. Because chronic antigen stimulation promotes class switching from IgG1 to IgG4, IgA, and IgE, these isotypes may serve as clinical markers to distinguish disease-specific antibodies from the other IgG subclasses that are more important for providing immunity from infection. In Aim 1 we will clone IgG1 and IgG4 anti-Dsg monoclonal antibodies (mAbs) from pemphigus patients to determine whether pathogenic antibodies are found in IgG1, IgG4, or both isotypes. If found in both IgG1 and IgG4, we will determine whether anti-Dsg IgG4 result from class switching from IgG1 or arise from separate B cell populations, lending insight into mechanisms of IgG4 class switching in pemphigus. In Aims 2 and 3 we will clone anti-Dsg IgA and IgE mAbs from patients with neutrophilic and eosinophilic forms of pemphigus, respectively. We will evaluate whether anti-Dsg IgA and IgE reproduce inflammatory blistering disease in mice humanized for the relevant Fc receptor and demonstrate the Fc-dependence of blistering and/or inflammation by treating mice with inhibitors of Fc effector function. By systematically characterizing the pathogenicity of the variable and constant regions of pemphigus mAb isotypes, we can define which structural features cause disease. These studies will create a rational framework for predicting the response of different forms of pemphigus to therapy, describe novel mouse models for evaluating Fc-mediated disease, and may identify novel therapeutic strategies, such as isotype-specific targeting. As similar isotype profiles occur in pemphigoid, epidermolysis bullosa acquisita, and other chronic autoimmune conditions, our studies may have therapeutic relevance for a broad range of autoantibody-mediated diseases. PUBLIC HEALTH RELEVANCE: We propose to use antibody cloning technology as a novel approach to identify features within patient autoantibodies that cause pemphigus, a potentially fatal autoimmune blistering skin disorder. We hypothesize that IgG4, IgA, and IgE are the critical pathogenic antibody isotypes in pemphigus, and as such may serve as clinical markers to distinguish disease-specific antibodies from the other IgG subclasses that are important for providing immunity from infection. Our studies will create a rational framework for predicting the response of different forms of pemphigus to therapy, describe novel mouse models for evaluating disease, and may suggest novel and potentially safer therapeutic strategies, such as isotype-specific targeting.