Variant surface antigens and immunity to malaria

描述（由申请人提供）：鉴于merozoites （MSPs）表面表达的抗原在红细胞入侵和血清抗体可及性方面的重要功能，许多注意力集中在血液期疟疾疫苗的开发和测试上。恶性疟原虫的体外研究和啮齿动物疟疾寄生虫的体内研究表明，抗体介导的抑制成熟红细胞的卵裂子入侵的努力已经指导了这些努力。然而，来自约氏疟原虫研究的数据表明，在体内，这些相同的抗体不足以阻止分裂子入侵网织红细胞。这似乎并不仅仅是由于不同的分裂子蛋白参与宿主红细胞上的受体的差异。如果要使基于msp的疫苗对间日疟原虫（一种网状细胞受限的疟疾寄生虫）有效，就必须解决这个问题。我们的假设是，被网织红细胞限制性疟疾寄生虫感染的红细胞在体内定位于红细胞生成位点，成熟并释放merozoite到一个有利于与新形成的网织红细胞相互作用的环境中，并减少接触merozoite中和抗体。为了验证这一假设，我们将对模仿人类疟疾寄生虫的限制性或非限制性宿主细胞偏好的约氏疟原虫血期寄生虫进行体外和体内研究。我们将重点关注网织细胞表面表达的疟原虫蛋白和变异表面抗原，它们在介导红细胞粘附血管内皮中的作用以及它们在免疫逃避中的作用。具体来说，我们将定义约氏疟原虫感染的粘附在血管内皮细胞上的网织红细胞中表达的疟原虫红细胞膜蛋白基因亚群，并监测它们在免疫压力下在寄生虫中的表达变化。我们将鉴定表面暴露的，P. yoelii网状细胞膜蛋白结合受体表达在血管内皮细胞。我们将确定在体外阻断约氏疟原虫感染的网织细胞粘附血管内皮的抗体是否也能在体内阻断寄生虫对红细胞生成组织的定位，从而增强基于msp的疫苗的效力。这些研究是建立在疟疾基因组测序工作的成功、通过微阵列分析监测大型多基因家族同时表达的能力以及利用定义良好的啮齿动物模型进行体内研究的基础上的。相关性：间日疟原虫每年导致7000万至8000万疟疾病例。开发疫苗以减少间日疟原虫疟疾的努力至关重要，但必须考虑到这种寄生虫在体内生长的独特方面。拟议的研究将增加我们对体内红细胞亚群寄生虫入侵因素的理解，以改进有效抑制这一过程的疫苗设计。

DESCRIPTION (provided by applicant): Much attention is focused on the development and testing of blood-stage malaria vaccines that target antigens expressed on the surface of merozoites (MSPs) given their functional importance in the invasion of erythrocytes and accessibility to serum antibodies. These efforts have been guided by in vitro studies of Plasmodium falciparum and in vivo studies of rodent malarial parasites that demonstrated the antibody- mediated inhibition of merozoite invasion of mature erythrocytes. However, data from studies of Plasmodium yoelii suggest that in vivo, these same antibodies are insufficient to prevent merozoites from invading reticulocytes. This does not appear to be due solely to differences in the receptors on host erythrocytes engaged by distinct merozoite proteins. This issue must be addressed if MSP-based vaccines are to be effective against Plasmodium vivax, a reticulocyte-restricted malaria parasite. Our hypothesis is that RBCs infected with reticulocyte-restricted malaria parasites localize to sites of erythropoiesis in vivo, mature and release merozoites into an environment that favors interaction with newly formed reticulocytes and reduces exposure to merozoite neutralizing antibodies. To test this hypothesis, we will conduct in vitro and vivo studies with P. yoelii blood-stage parasites that mimic the restricted or non-restricted host cell preferences of the human malarial parasites. We will focus on plasmodial proteins and variant surface antigens expressed on the reticulocyte surface, on their role in mediating adherence of pRBCs to vascular endothelium and on their role in immune evasion. Specifically, we will define the subset of plasmodial erythrocyte membrane protein genes expressed in P. yoelii infected reticulocytes which adhere to vascular endothelial cells and monitor changes in their expression in parasites under immune pressure. We will identify surface-exposed, P. yoelii reticulocyte membrane proteins that bind to receptors expressed on vascular endothelial cells. We will determine if antibodies that block adherence of P. yoelii infected reticulocytes to vascular endothelium in vitro also block localization of parasites to erythropoietic tissues in vivo and enhance the efficacy of MSP-based vaccines. These studies are built on the success of the malaria genome sequencing efforts, the ability to monitor the concurrent expression of large multigene families by microarray analysis, and the utilization of well-defined rodent models to conduct in vivo studies. Relevance: P. vivax causes 70-80 million cases of malaria each year. Efforts to develop vaccines to reduce P. vivax malaria are critical but must consider the unique aspects of the growth of this parasite in vivo. The proposed studies will increase our understanding of the factors that favor parasite invasion of subpopulations of erythrocytes in vivo to improve the design of vaccines that effectively inhibit the process.