CD200 Expression on Apoptotic DCs and Immune Tolerance

描述（由申请方提供）：在凋亡性细胞死亡期间，生化过程（包括半胱天冬酶的作用）修饰自身蛋白并产生潜在的自身抗原。为了在面对自然细胞更新时保持稳定状态，免疫系统必须有一种机制来预防或控制对细胞死亡相关的自身抗原的反应或自身免疫的风险。CD 200是与T细胞共刺激分子的B7家族共享序列同源性的跨膜糖蛋白，并且已知其赋予T细胞致耐受性信号。我们发现凋亡的小鼠树突状细胞（DCs）中CD 200 mRNA和蛋白表达增加。我们确定了CD 200基因内的功能性p53反应元件。我们确定了p53和半胱天冬酶依赖的途径，导致CD 200的表达增加凋亡的DC。凋亡DC上的CD 200显著改变了自体MLR培养物中T细胞增殖的速率和细胞因子谱。此外，使用CD 200基因敲除小鼠，我们发现，CD 200是必不可少的诱导UVB介导的免疫耐受的半抗原蛋白在接触超敏反应试验。基于我们的小鼠数据，我们假设凋亡DC上的CD 200表达有助于诱导体内对胱天蛋白酶产生的自身肽的免疫耐受。我们建议使用已建立的半抗原免疫耐受小鼠模型在体内测试这一假设，并将我们的研究扩展到人类DC和半胱天冬酶产生的自身肽和模型自身抗原的免疫反应。我们的具体目标是：（1）使用野生型和CD 200敲除小鼠确定输注或驻留DC上的CD 200是否在诱导对半抗原的免疫耐受中起作用;（2）评估在诱导和不诱导凋亡的情况下，人DC亚群和原代角质形成细胞培养物中CD 200 mRNA和蛋白的表达;（3）用正常人和多发性硬化患者的PBMC检测阻断CD 200/CD 200 R相互作用对T细胞对半胱天冬酶产生的自身肽、核组蛋白和髓鞘碱性蛋白的反应的影响。如果数据支持我们的假设，我们将确定CD 200表达凋亡的DC作为一个重要的分子，在维持自身耐受性的人，也许，在限制自身免疫。这些研究也将提供新的见解，一个新的分子途径，是一个目标，增强抗肿瘤免疫和预防移植排斥反应。

DESCRIPTION (provided by applicant): During apoptotic cell death, biochemical processes, including the action of caspases, modify self-proteins and create potential autoantigens. To maintain a steady-state in the face of natural cell turnover, the immune system must have a mechanism to prevent or control responses to cell death-associated autoantigens or risk autoimmunity. CD200 is a transmembrane glycoprotein that shares sequence homology with the B7-family of T cell costimulatory molecules and is known to impart a T cell tolerogenic signal. We made the novel observation that CD200 mRNA and protein expression was increased in apoptotic murine dendritic cells (DCs). We identified functional p53-response elements within the CD200 gene. We identified both p53- and caspase-dependent pathways leading to increased expression of CD200 on apoptotic DCs. CD200 on apoptotic DCs significantly altered the rate of T cell proliferation and the cytokine profile in autologous MLR cultures. Furthermore, using CD200 knockout mice, we found that CD200 was essential for induction of UVB-mediated immune tolerance to haptenated proteins in contact hypersensitivity assays. Based on our mouse data, we hypothesize that CD200 expression on apoptotic DCs contributes to the induction of immune tolerance to caspase-generated self-peptides in vivo. We propose to test this hypothesis in vivo using an established mouse model of immune tolerance to hapten and to extend our studies to human DCs and immune responses to both caspase-generated self-peptides and model autoantigens in vitro. Our Specific Aims are: (1) To determine whether CD200 on infused or resident DCs plays a role in the induction of immune tolerance to hapten using wild-type and CD200 knockout mice; (2) To assess the expression of CD200 mRNA and protein in subsets of human DCs and in cultures of primary keratinocytes with and without induction of apoptosis; and (3) To test the effect of blocking CD200/CD200R interaction on T cell responses to caspase-generated self-peptides, nucleohistone and myelin basic protein using PBMC from normal individuals and multiple sclerosis patients. If the data support our hypothesis, we will have identified CD200 expression on apoptotic DCs as an important molecule in maintaining self-tolerance in humans and, perhaps, in limiting autoimmunity. These studies will also provide new insight into a novel molecular pathway that is a target for enhancement of antitumor immunity and for prevention of graft rejection.