Cytoadherence and sequestration in malaria transmission stages

描述(由申请人提供)：细胞黏附和由此导致的被感染的红细胞的隔离是恶性疟原虫的一个特征。以前的研究强调了在恶性疟原虫无性发育的最后20小时内，纽结复合体，特别是主要的寄生虫抗原PfEMP1，在介导细胞黏附方面的主要贡献。恶性疟原虫的成熟性阶段只在发育8-10天后出现在外周血液中，而将未成熟性阶段隔离在解剖生态位中对于成功地将这些寄生虫传播到蚊媒是绝对关键的。这个解剖位置在哪里，有性阶段细胞黏附的分子基础是什么？本申请中概述的实验方法旨在区分发育的有性阶段引起细胞黏附的三种可能机制，并确定患者组织中相应的隔离特征：i)发育性阶段的细胞黏附通过与无性阶段相同的决定因素，即在感染的红细胞表面表达相同的PfEMP1。这将导致无性阶段和有性阶段的隔离档案在很大程度上重叠。Ii)它们在无性阶段的细胞黏附机制相同，但使用不同的决定因素，即性发育特有的PfEMP1。这种情况可能会导致配子体特异的隔离部位，类似于胎盘隔离表达保守的PfEMP1变体的寄生虫。Iii)它们通过完全不同的机制进行细胞黏附，即，PfEMP1以外的一个分子(或一类分子)。在这种情况下，隔离情况也不同于无性阶段。有性恶性疟原虫阶段是药物和疫苗战略的主要目标，以阻止该寄生虫在流行地区的传播。在目前使用的几乎完全针对红细胞内无性发育的药物制剂普遍存在耐药性的背景下，传播阻断战略重新引起了人们的兴趣，现在是世界范围内减轻疟疾负担的主要重点。拟议的实验与这些努力是一致的，因为它们旨在阐明对疟疾在人类宿主中传播阶段的生存和发展至关重要的机制。 公共卫生相关性： 旨在阻止疟疾寄生虫传播的战略在目前全世界根除疟疾的努力中发挥着核心作用。因此，了解人类宿主和蚊子媒介传播阶段的关键特性是至关重要的。这些特性之一是将发育中的性阶段隔离在深层组织中，然后最终以感染蚊子的成熟配子体的形式出现在血液循环中。在这里，我们提出了一个全面的分析机制的细胞黏附和隔离在发育阶段的传播在人类宿主。

DESCRIPTION (provided by applicant): Cytoadherence and the resulting sequestration of infected red blood cells are a hallmark of P. falciparum malaria. Previous studies have emphasized the major contribution of the knob complex and particularly the major parasite antigen, PfEMP1, in mediating cytoadherence during the last 20 hours of asexual development of P. falciparum parasites. Mature sexual stages of P. falciparum only appear in the peripheral blood after 8-10 days of development, and sequestration of immature sexual stages in anatomical niches must be absolutely crucial for successful transmission of these parasites to the mosquito vector. Where is that anatomical niche, and what is the molecular basis for cytoadherence in sexual stages? The experimental approaches outlined in this application aim to distinguish the three possible mechanisms by which developing sexual stages induce cytoadherence, and to identify the corresponding sequestration profiles in patient tissues: i) Developing sexual stages cytoadhere through the same determinants as asexual stages, i.e., the same PfEMP1 is expressed on the infected red blood cell surface. This would result in largely overlapping sequestration profiles for asexual and sexual stages. ii) They cytoadhere through the same mechanisms asexual stages, but using a different determinant, i.e., a PfEMP1 specific to sexual development. This situation would likely result in gametocyte-specific site of sequestration, similar to placental sequestration of parasites expressing a conserved PfEMP1 variant. iii) They cytoadhere through a different mechanism altogether, i.e., a molecule (or class of molecules) other than PfEMP1. In this case, the sequestration profile would also be different from that of asexual stages. Sexual P. falciparum stages are a major target for both drug- and vaccine-based strategies to block transmission of the parasite in endemic areas. In the context of widespread resistance against the currently used drug formulations that almost exclusively target asexual development within the red blood cell, transmission-blocking strategies have gained renewed interest and are now a major focus of worldwide efforts to reduce the burden of malaria. The proposed experiments are in line with these efforts as they aim to elucidate a mechanism crucial for the survival and development of malaria transmission stages in the human host. PUBLIC HEALTH RELEVANCE: Strategies aiming at blocking the transmission of malaria parasites play a central role in the current efforts to eradicate malaria worldwide. It is therefore crucial to understand the key properties of transmission stages in the human host and the mosquito vector. One of these properties is the sequestration of developing sexual stages in deep tissues, before they eventually emerge in the blood circulation as mosquito-infective mature gametocytes. Here we propose a comprehensive analysis of the mechanisms of cytoadherence and sites of sequestration of developing transmission stages in the human host.