Cytoadherence and sequestration in malaria transmission stages

描述（由申请人提供）：细胞粘附和由此产生的被感染红细胞的隔离是恶性疟原虫疟疾的标志。先前的研究强调了旋钮复合体的主要作用，特别是主要的寄生虫抗原PfEMP1，在恶性疟原虫无性发育的最后20小时中介导细胞粘附。恶性疟原虫的成熟性期在发育8-10天后才出现在外周血中，在解剖壁龛中隔离不成熟的性期对于这些寄生虫成功传播给蚊子载体至关重要。解剖学上的生态位在哪里？性阶段细胞粘附的分子基础是什么？本应用程序中概述的实验方法旨在区分性发育阶段诱导细胞粘附的三种可能机制，并确定患者组织中相应的隔离特征：i)性发育阶段的细胞粘附通过与无性发育阶段相同的决定因素，即在感染红细胞表面表达相同的PfEMP1。这将导致无性和有性阶段的大量重叠的隔离剖面。ii)它们通过相同的无性阶段的细胞粘附机制，但使用不同的决定因素，即特定于性发育的PfEMP1。这种情况可能导致配子细胞特异性的隔离位点，类似于表达保守的PfEMP1变体的寄生虫的胎盘隔离。iii)它们通过完全不同的机制（即PfEMP1以外的分子（或一类分子））进行细胞粘附。在这种情况下，隔离剖面也将不同于无性阶段。性恶性疟原虫阶段是在流行地区阻断寄生虫传播的药物和基于疫苗的战略的主要目标。在对目前使用的几乎完全针对红细胞内无性发育的药物配方产生广泛耐药性的背景下，传播阻断战略重新引起了人们的关注，现在是全世界减轻疟疾负担努力的一个主要重点。拟议的实验与这些努力是一致的，因为它们旨在阐明疟疾在人类宿主中传播阶段的生存和发展的关键机制。

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.