The role of the terminal complement pathway in experimental cerebral malaria.

描述(申请人提供)：疟疾仍然是整个发展中国家最致命的传染病之一，特别是在儿童中[1]。尽管作出了数十年的努力，但通过疫苗开发对这种寄生虫进行免疫控制的尝试并未成功。这一失败在很大程度上是由于我们在先天性免疫和获得性免疫水平上对宿主对寄生虫的免疫反应缺乏了解[2]。脑型疟疾是恶性疟最严重的临床并发症之一，病死率很高。 15-30%的CM幸存者和10%的CM幸存者有永久性的神经后遗症。在CM中，脑微血管系统的特征是激活的内皮，血管被寄生虫感染的红细胞(IRBC)、血小板和白细胞堵塞[3-5]。除了微血管病理学，我们最近还观察到了显著的神经变性的证据，表现为浦肯野细胞的结构和转录变化，以及在ECM期间小脑的髓鞘形成中断。许多促炎介质已被证明有助于CM的发展[3，4，6]，但缺乏对这些免疫成分如何相互作用并导致中枢神经系统(CNS)疾病的全面了解。由于炎症是CM的中心病理生理学原则，我们开始使用伯氏疟原虫(PBA)模型系统[3，5，6]研究补体系统在实验性脑疟疾(ECM)的发展和发病机制中的作用。我们最近报道，由于C5a受体缺陷(C5aR-/-)小鼠对ECM完全易感，C5-/-小鼠由于失去了膜攻击形成[14]，而不是像以前报道的那样，由于C5a受体缺陷(C5aR-/-)小鼠而失去了C5a介导的作用[29，30]，从而显著地保护了C5-/-小鼠免受ECM的伤害。我们的初步结果表明，抑制经典和替代补体途径(分别通过C4-/-和B-/-小鼠)不会改变ECM的敏感性。重要的是，我们还观察到C3-/-小鼠的ECM临床症状明显比C5-/-小鼠严重。综上所述，这些数据表明，在ECM中，C5裂解不需要经典和替代途径C5转换酶(两者都包含源于C3裂解的C3b)。相反，我们的数据表明，最近描述的补体“外源性蛋白酶激活途径”可能负责在ECM中将C5裂解为功能活跃的C5a和C5b[15，17，18]。这些发现提出了关于补体在ECM中的作用的重要问题。例如，C5如何机械地促进ECM的发展和进展？在ECM中，外源性蛋白水解酶激活途径(通过凝血酶和纤溶酶等酶)对C5介导的炎症有何相对重要性？根据我们的初步观察，我们假设C5是ECM中关键的补体炎症效应分子，C5通过外源性蛋白酶激活途径激活导致ECM中补体介导的病理。 与公共卫生有关：疟疾仍然是整个发展中世界最致命的传染病之一，尤其是在儿童中[1]。尽管经过几十年的努力，但通过疫苗开发对这种寄生虫进行免疫控制的尝试并不成功，这种失败在很大程度上是因为我们对宿主在先天免疫和获得性免疫水平上对寄生虫的免疫反应缺乏了解[2]。脑型疟疾是恶性疟最严重的临床并发症之一，病死率很高。 15-30%的CM幸存者和10%的CM幸存者有永久性的神经后遗症。

DESCRIPTION (provided by applicant): Malaria remains one of the most deadly infectious diseases throughout the developing world especially among children [1]. Despite decades of effort, attempts at immunological control of this parasite through vaccine development have not been successful. This failure is, in large part, due to our poor understanding of the host immune response to the parasite both at the level of innate and adaptive immunity [2]. Cerebral malaria (CM) is one of the most severe clinical complications of P. falciparum malaria with a fatality rate of 15-30% and 10% of CM survivors have permanent neurological sequelae. In CM the brain microvasculature is characterized by an activated endothelium, occlusion of vessels with parasite-infected RBCs (iRBCs), platelets and leukocytes [3-5]. In addition to microvasculature pathology, we have recently observed evidence of significant neurodegeneration manifested by structural and transcriptional changes in Purkinje cells and disruptions in myelination in the cerebellum during ECM. Numerous proinflammatory mediators have been shown to contribute to the development of CM [3, 4, 6] but a comprehensive understanding of how these immune components interact and lead to central nervous system (CNS) disease is lacking. Since inflammation is a central pathophysiological tenet of CM, we began examining the role of the complement system in the development and pathogenesis of experimental cerebral malaria (ECM) using the Plasmodium berghei ANKA (PbA) model system [3, 5, 6]. We have recently reported that C5-/- mice are significantly protected from ECM due to the loss of membrane attack formation [14], not to the loss of C5a-mediated effects as previously reported [29, 30], since C5a receptor-deficient (C5aR-/-) mice are fully susceptible to ECM. Our preliminary results now demonstrate that inhibition of the classical and alternative complement pathways (via C4-/- and factor B-/- mice, respectively) does not alter ECM susceptibility. Importantly we have also observed that clinical signs of ECM in C3-/- mice are significantly more severe than in C5-/- mice. Together these data indicate that the classical and alternative pathway C5 convertases (both of which contain C3b derived from C3 cleavage) are not required for C5 cleavage in ECM. Rather our data suggest that the more recently described complement "extrinsic protease activation pathway" may be responsible for cleaving C5 to functionally active C5a and C5b in ECM [15, 17, 18]. These findings raise important questions regarding the role of complement in ECM. For example, how does C5 mechanistically contribute to ECM development and progression? What is the relative importance of extrinsic protease activation pathway (via proteases such as thrombin and plasmin) to C5- mediated inflammation in ECM? Based on our preliminary observations, we hypothesize that C5 is the critical complement inflammatory effector molecule in ECM and that activation of C5 via the extrinsic protease activation pathway leads to complement-mediated pathology in ECM. PUBLIC HEALTH RELEVANCE: Malaria remains one of the most deadly infectious diseases throughout the developing world especially among children [1]. Despite decades of effort, attempts at immunological control of this parasite through vaccine development have not been successful, and this failure is, in large part, due to our poor understanding of the host immune response to the parasite both at the level of innate and adaptive immunity [2]. Cerebral malaria (CM) is one of the most severe clinical complications of P. falciparum malaria with a fatality rate of 15-30% and 10% of CM survivors have permanent neurological sequelae.