Variant surface antigens and immunity to malaria

描述（由申请人提供）：鉴于裂殖子（MSP）表面上表达的抗原在红细胞侵入和血清抗体可及性中的功能重要性，大量注意力集中在靶向裂殖子（MSP）表面上表达的抗原的血液阶段疟疾疫苗的开发和测试上。这些努力是由恶性疟原虫的体外研究和啮齿类疟疾寄生虫的体内研究指导的，这些研究证明了抗体介导的裂殖子侵入成熟红细胞的抑制。然而，来自约氏疟原虫的研究数据表明，在体内，这些相同的抗体不足以防止裂殖子侵入网织红细胞。这似乎不仅仅是由于不同裂殖子蛋白参与的宿主红细胞受体的差异。如果基于MSP的疫苗要有效对抗间日疟原虫（一种网织红细胞限制性疟疾寄生虫），就必须解决这个问题。我们的假设是，红细胞感染网织红细胞限制性疟疾寄生虫定位于红细胞生成的网站在体内，成熟和释放裂殖子到一个环境，有利于与新形成的网织红细胞的相互作用，并减少暴露于裂殖子中和抗体。为了验证这一假设，我们将用约氏疟原虫血液期寄生虫进行体外和体内研究，这些寄生虫模拟人类疟疾寄生虫的限制性或非限制性宿主细胞偏好。我们将集中在疟原虫蛋白和变异的表面抗原表达的网织红细胞表面上，在介导粘附的pRBC血管内皮细胞的作用和它们在免疫逃避的作用。具体来说，我们将定义疟原虫红细胞膜蛋白基因的子集，表达约氏疟原虫感染的网织红细胞粘附血管内皮细胞和监测其表达的变化，在寄生虫免疫压力。我们将鉴定表面暴露的约氏疟原虫网织红细胞膜蛋白，其与血管内皮细胞上表达的受体结合。我们将确定在体外阻断约氏疟原虫感染的网织红细胞粘附于血管内皮的抗体是否也在体内阻断寄生虫定位于红细胞生成组织并增强基于MSP的疫苗的功效。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的多基因家族的同时表达的能力，以及利用明确定义的啮齿动物模型进行体内研究。相关性：间日疟原虫每年造成7000万至8000万例疟疾病例。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有利于寄生虫入侵体内红细胞亚群的因素的理解，以改进有效抑制该过程的疫苗设计。

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.