Centre for Medical Parasitology at i, Faculty of Health and Medical Sciences, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
PLoS One. 2012;7(9):e45658. doi: 10.1371/journal.pone.0045658. Epub 2012 Sep 20.
The virulence of Plasmodium falciparum malaria is related to the parasite's ability to evade host immunity through clonal antigenic variation and tissue-specific adhesion of infected erythrocytes (IEs). The P. falciparum erythrocyte membrane protein 1 (PfEMP1) family expressed on dome-shaped protrusions called knobs on the IE surface is central to both. Differences in receptor specificity and affinity of expressed PfEMP1 are important for IE adhesiveness, but it is not known whether differences in the number and size of the knobs on which the PfEMP1 proteins are expressed also play a role. Therefore, the aim of this study was to provide detailed information on isolate- and time-dependent differences in knob size and density.
METHODOLOGY/PRINCIPAL FINDINGS: We used atomic force microscopy to characterize knobs on the surface of P. falciparum-infected erythrocytes. Fourteen ex vivo isolates from Ghanaian children with malaria and 10 P. falciparum isolates selected in vitro for expression of a particular PfEMP1 protein (VAR2CSA) were examined. Knob density increased from ∼20 h to ∼35 h post-invasion, with significant variation among isolates. The knob density ex vivo, which was about five-fold higher than following long-term in vitro culture, started to decline within a few months of culture. Although knob diameter and height varied among isolates, we did not observe significant time-dependent variation in these dimensions.
CONCLUSIONS/SIGNIFICANCE: The density of knobs on the P. falciparum-IE surface depends on time since invasion, but is also determined by the infecting isolate in a time-independent manner. This is the first study to quantitatively evaluate knob densities and dimensions on different P. falciparum isolates, to examine ex vivo isolates from humans, and to compare ex vivo and long-term in vitro-cultured isolates. Our findings contribute to the understanding of the interaction between P. falciparum parasites and the infected host.
恶性疟原虫疟疾的毒力与寄生虫通过克隆抗原变异和感染红细胞（IE）的组织特异性黏附来逃避宿主免疫的能力有关。在 IE 表面称为“钉状突起”的穹顶状突起上表达的恶性疟原虫红细胞膜蛋白 1（PfEMP1）家族是这两者的核心。表达的 PfEMP1 的受体特异性和亲和力的差异对 IE 黏附性很重要，但尚不清楚表达 PfEMP1 的钉状突起的数量和大小的差异是否也起作用。因此，本研究旨在提供关于分离株和时间依赖性钉状突起大小和密度差异的详细信息。
方法/主要发现：我们使用原子力显微镜对恶性疟原虫感染红细胞表面的钉状突起进行了表征。研究了来自加纳患有疟疾的儿童的 14 个体外分离株和 10 个体外选择表达特定 PfEMP1 蛋白（VAR2CSA）的恶性疟原虫分离株。从入侵后约 20 小时到 35 小时，钉状突起密度增加，分离株之间存在显著差异。体外长期培养后的钉状突起密度约为体外培养前的五倍，在培养后几个月内开始下降。尽管分离株之间的钉状突起直径和高度有所不同，但我们没有观察到这些维度的显著时间依赖性变化。
结论/意义：IE 表面 PfEMP1 上的钉状突起密度取决于入侵后的时间，但也以与时间无关的方式由感染的分离株决定。这是首次定量评估不同恶性疟原虫分离株上的钉状突起密度和尺寸、检测来自人类的体外分离株以及比较体外分离株和长期体外培养分离株的研究。我们的研究结果有助于理解恶性疟原虫寄生虫与受感染宿主之间的相互作用。
