COMPLEMENT C5 AND C5A RECEPTOR--MOLECULAR GENETICS

补体的第五组分（C5）是一种糖蛋白， 蛋白水解活化成C5 a和C5 b多肽，介导重要的 炎症和细胞溶解过程。小的C5激活片段， C5 a是一种非常有效的炎性分子， C5 a-受体（C5 a-R），介导平滑肌的收缩， 血管舒张，趋化性和分泌颗粒酶从许多 此外，C5 a在增强体液和炎症细胞中起作用， 细胞介导的免疫反应。大的C5激活片段，C5 b， 启动C5 b-9膜溶解攻击复合物的组装， 直接负责补体介导的靶细胞溶解 细菌和病毒病原体。纯合子C5缺陷型血清 (C5D)个体缺乏杀菌活性， 诱导趋化性的能力受损;因此，C5 D个体具有 严重复发性细菌感染的倾向，特别是 奈瑟菌属，包括脑膜炎和生殖器外淋病。在 在某些病理条件下，健康组织的损伤发生在 C5活化是C5 b-9介导的非靶细胞裂解的结果 （旁观者）细胞和蛋白水解破坏的酶释放 中性粒细胞被C5 a募集和激活。例如，组织损伤 由C5激活多肽介导的是强烈牵连在 肺和心肌疾病的发病机制，动脉粥样硬化 病变和某些中枢神经系统疾病，包括 老年痴呆症此外，C5活化多肽发挥着重要作用。 在不协调异种移植物的过度反应性排斥中起关键作用。的 这项研究的长期目标是了解，从而 选择性调节炎症和细胞溶解作用， C5激活。 结构-功能的分子知识 补体C5激活和受体细胞 由C5 a切割多肽介导的相互作用是 这对实现这一目标至关重要。这是特别真实的， 非髓样组织细胞C5 a-R表达的发现 表明C5 a介导的生物学功能甚至更多， 比原先设想的多效性。我们的近期目标是： 1)确定人类C5的分子遗传和结构基础 缺乏DNA，RNA和蛋白质的研究，七个不同的C5- 缺陷的亲属，2）确定功能上重要的结合结构域 通过单克隆抗体的广泛作图研究， 合成肽，3）确定表达C5 a-1的组织细胞， 通过原位杂交和免疫组织化学研究， 4)确定所选细胞因子对C5 a-R的影响 使用适当的组织来源的细胞表达，和5）启动 研究C5 a-R介导的生物学功能， 通过检测急性时相蛋白、粘附 参与中性粒细胞迁移的分子，以及HLA I类和 II分子参与抗原呈递。

The fifth component of complement (C5) is a glycoprotein that, after proteolytic activation into C5a and C5b polypeptides, mediates important inflammatory and cytolytic processes. The small C5 activation fragment, C5a, is a very potent phlogistic molecule which, upon binding to the C5a-Receptor (C5a-R), mediates contraction of smooth muscle, vasodilation, and chemotaxis and secretion of granular enzymes from many inflammatory cells; moreover, C5a plays a role in augmenting humoral and cell mediated immune responses. The large C5 activation fragment, C5b, initiates the assembly of the C5b-9 membranolytic attack complex that is directly responsible for complement-mediated target cell cytolysis of bacterial and viral pathogens. Sera from homozygous C5-deficient (C5D) individuals lack bactericidal activity and have a severely impaired ability to induce chemotaxis; as a result, C5D individuals have a propensity for severe recurrent bacterial infections particularly to Neisserial species, including meningitis and extragenital gonorrhea. In certain pathological conditions, damage of healthy tissue occurs after C5 activation as a result of C5b-9 mediated lysis of non-target (bystander) cells and proteolytic destruction by enzymes released from neutrophils recruited and activated by C5a. For example, tissue damage mediated by C5 activation polypeptides is strongly implicated in the pathogenesis of pulmonary, and myocardial diseases, atherosclerotic lesions, and certain central nervous system disorders, including Alzheimer disease. Furthermore, C5 activation polypeptides play a critical role in the hyperactive rejection of discordant xenografts. The broad long-term goal of this study is to understand and thereby selectively modulate the inflammatory and cytolytic effects resulting from C5 activation. Molecular knowledge of the structural-functional aspects of complement C5 activation and the receptor-cellular interactions that are mediated by the C5a cleavage polypeptide are of paramount importance in achieving this goal. This is especially true as the discovery of C5a-R expression by non-myeloid tissue cells have indicated that the biological functions mediated by C5a are even more pleiotropic than originally assumed. Our immediate objectives are to: 1) determine the molecular genetic and structural basis of human C5 deficiency by DNA, RNA, and protein studies of seven different C5- deficient kindred, 2) determine functionally important binding domains in C5 by extensive mapping studies with monoclonal antibodies and synthetic peptides, 3) determine tissue cells expressing the C5a- receptor by in situ hybridization and immunohistochemistry studies, and 4) determine the effects that selected cytokines have on C5a-R expression using appropriate tissue derived cells, and 5) initiate investigations into the biological functions mediated by the C5a-R on tissue cells by examining expression of acute phase proteins, adhesion molecules involved in neutrophil emigration, and HLA class I and class II molecules involved in antigen presentation.