CD200 Expression on Apoptotic DCs and Immune Tolerance

描述（由申请人提供）：在凋亡细胞死亡过程中，生化过程，包括半胱天蛋白酶的作用，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自身抗原的反应或风险自身免疫。CD200是一种跨膜糖蛋白，与T细胞共刺激分子b7家族具有序列同源性，已知可传递T细胞耐受性信号。我们观察到CD200 mRNA和蛋白表达在凋亡的小鼠树突状细胞（dc）中增加。我们在CD200基因中发现了功能性p53-应答元件。我们发现p53和caspase依赖通路导致CD200在凋亡的dc上的表达增加。CD200对凋亡dc的影响显著改变了自体MLR培养中T细胞增殖率和细胞因子谱。此外，使用CD200敲除小鼠，我们发现CD200对于在接触超敏试验中诱导uvb介导的对偶联蛋白的免疫耐受是必不可少的。根据我们的小鼠数据，我们假设CD200在凋亡的dc上的表达有助于诱导对体内caspase产生的自肽的免疫耐受。我们建议在体内使用已建立的小鼠半抗原免疫耐受模型来验证这一假设，并将我们的研究扩展到人类dc和对caspase产生的自身肽和模型自身抗原的体外免疫反应。我们的具体目标是：(1)使用野生型和CD200敲除小鼠，确定输注或驻留dc上的CD200是否在诱导半抗原免疫耐受中起作用；(2)评估CD200 mRNA和蛋白在人dc亚群和诱导和不诱导凋亡的原代角质形成细胞培养中的表达；(3)利用正常人和多发性硬化症患者的PBMC，检测阻断CD200/CD200R相互作用对T细胞对caspase产生的自身肽、核组蛋白和髓鞘碱性蛋白反应的影响。如果数据支持我们的假设，我们将确定CD200在凋亡的dc上的表达是维持人类自我耐受性的重要分子，也许还可以限制自身免疫。这些研究还将为增强抗肿瘤免疫和预防移植物排斥反应的新分子途径提供新的见解。

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.