Mechanisms of antibody protection in pre-erythrocytic and blood stage malaria

描述(申请人提供)：疟疾的病原体--疟原虫感染是世界上最大的疾病负担之一，每年有多达3亿人感染，120万人死亡。这种寄生虫在蚊子媒介和哺乳动物宿主之间维持着令人难以置信的复杂生命周期。在传播后，它将以子孢子的形式通过皮肤和血液，感染肝细胞，然后发展为肝脏阶段，并以感染红细胞的裂殖子的形式回到血液中。红细胞前期(子孢子期和肝期)是疫苗开发的理想目标，因为它没有症状，寄生虫数量有限。然而，由于只有一种寄生虫可以引起暴发性血液期感染，用红细胞前免疫预防血液期疾病面临着挑战。在临床前和临床研究中，对入侵和感染肝脏但不能进展到血液期的减毒寄生虫进行免疫已取得了很高的效果。这个 传统的理解是，这种保护主要依赖于CD8+T细胞。然而，我已经证明，抗子孢子蛋白CSP的单抗(MAb)和通过全寄生虫免疫而产生的多克隆抗体(Pab)都能够提供强大的保护，以抵御传染性蚊子叮咬。由全寄生虫免疫(WPI)产生的抗体也可以控制不依赖T细胞帮助的直接血液期感染。关于抗体效应器在这两个阶段调节这种保护的机制知之甚少，但WPI提供的跨阶段保护为研究这些机制提供了一个理想的平台。我建议使用这个模型来研究抗体介导的保护下的中和、补体介导的裂解和调理作用在疟疾啮齿动物模型中的作用。目的1将重点放在通过被动转移缺乏Fc介导的特异性效应功能的突变型mAb来预防子孢子感染。这些突变单抗将与WT单抗进行比较，以了解它们在被蚊子叮咬感染后减轻肝脏阶段负担的能力。此外，在缺乏补体、Fc受体结合或两者都缺乏的小鼠中，被动转移WPI血清然后蚊子叮咬攻击，将阐明每种机制在WPI背景下的作用。目的2将扩展这一模型以检查抗体在疾病血液阶段的保护作用。同样，被动地将WPI血清转移到补体、Fc受体结合不足或两者都缺乏的小鼠之后，将出现直接的血液阶段挑战。通过监测随后的寄生虫血症，我们将能够确定每个效应机制对控制血液期疟疾的各自贡献(如果有的话)。本文提出的研究是对抗体介导的抗子孢子期和血液期疟原虫保护机制的首次全面和详尽的分析。了解在这些阶段进行有效保护所需的特定类型的抗体反应，将指导合理设计旨在预防感染的下一代疟疾疫苗。

DESCRIPTION (provided by applicant): Infections with Plasmodium parasites, the causative agents of malaria, constitute one of the world's largest disease burdens with up to 300 million infections and 1.2 million deaths each year. The parasite maintains an incredibly complex life cycle between mosquito vector and mammalian host. After transmission, it will pass through the skin and bloodstream as sporozoites, which infect liver hepatocytes, then develops as liver stages and emerges back into the blood as red blood cell-infective merozoites. The pre-erythrocytic (sporozoites and liver stages) phase is an ideal target for vaccine development as it is asymptomatic and has limited parasite numbers. However, as only one parasite can cause a fulminant blood stage infection, preventing blood stage disease with pre-erythrocytic immunity faces a challenge. Immunization with attenuated parasites which invade and infect the liver but fail to progress to blood stage have been highly effective in preclinical and clinical studies. The conventional understanding is that this protection relies predominantly by CD8+ T cells. However, I have shown that both monoclonal antibodies (mAb) against the sporozoite protein CSP and polyclonal antibodies (pAb) elicited by immunization with whole parasites are capable of providing robust protection against an infectious mosquito bite. The Abs elicited by whole parasite immunization (WPI) can also control a direct blood stage infection independent of T cell help. Little is known about the antibody effector mechanisms mediating this protection at either stage, but the cross-stage protection afforded by WPI provides an ideal platform on which to investigate these mechanisms. I propose to use this model to investigate the contributions of neutralization, complement-mediated lysis and opsonization underlying Ab-mediated protection in a rodent model of malaria. Aim 1 will focus on protection against sporozoite infection by passive transfer of mutant mAb which lack specific FC-mediated effector functions. These mutant mAb will be compared to WT mAb for their ability to reduce liver stage burden following infection by mosquito bite. Furthermore, passive transfer of WPI serum followed by mosquito bite challenge in mice deficient in complement, FC receptor binding or both will elucidate the role of each mechanism in the context of WPI. Aim 2 will expand this model to examine antibody-mediated protection in the blood stage of disease. Again, passive transfer of WPI serum to mice deficient in complement, FC receptor binding or both will be followed by direct blood stage challenge. By monitoring subsequent parasitemia, we will be able to determine the respective contributions (if any) of each effector mechanism to control of blood stage malaria. The studies proposed here represent the first comprehensive and exhaustive analysis of the mechanisms conferring antibody-mediated protection against both the sporozoite and blood stages of Plasmodium. Knowledge of the specific type of antibody response required for effective protection at these stages will guide the rational design of the next generation of malaria vaccines aimed at preventing infection.