CD200 Expression on Apoptotic DCs and Immune Tolerance

描述(申请人提供)：在细胞凋亡性死亡过程中，生化过程，包括半胱氨酸天冬氨酸氨基转移酶的作用，修饰自身蛋白质并产生潜在的自身抗原。为了在面对自然细胞更替的情况下保持稳定状态，免疫系统必须有一种机制来防止或控制对细胞死亡相关自身抗原或自身免疫风险的反应。CD200是一种跨膜糖蛋白，与T细胞共刺激分子B7家族具有相同的序列同源性，并被认为传递T细胞耐受信号。我们做了一个新的观察，在凋亡的小鼠树突状细胞(DC)中CD200的mRNA和蛋白的表达增加。我们鉴定了CD200基因中的功能性P53反应元件。我们发现了P53和caspase依赖的通路导致了凋亡DC上CD200表达的增加。凋亡DC表面的CD200显著改变了自体MLR培养中T细胞的增殖率和细胞因子谱。此外，使用CD200基因敲除的小鼠，我们发现CD200在接触性超敏反应中诱导UVB介导的对半抗原蛋白的免疫耐受是必不可少的。基于我们的小鼠数据，我们假设CD200在凋亡的DC上的表达有助于在体内诱导对caspase产生的自体肽的免疫耐受。我们建议使用已建立的对半抗原免疫耐受的小鼠模型在体内验证这一假设，并将我们的研究扩展到体外对人DC以及对caspase产生的自体肽和模型自身抗原的免疫反应。我们的具体目标是：(1)利用野生型和CD200基因敲除小鼠，确定输注或驻留DC上的CD200是否在诱导半抗原免疫耐受中发挥作用；(2)评估CD200 mRNA和蛋白在人DC亚群和原代角质形成细胞培养中的表达，以及(3)检测阻断CD200/CD200R相互作用对正常人和多发性硬化症患者PBMC产生的caspase产生的自肽、核组蛋白和髓鞘碱性蛋白的T细胞反应的影响。如果数据支持我们的假设，我们将确定CD200在凋亡树突状细胞上的表达是维持人类自我耐受的重要分子，可能还会限制自身免疫。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靶点提供新的分子途径。

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.