?疟疾产生的最严重伤害就是对孕妇和儿童的伤害。瑞典Karolinska学院和乌干达Makerere大学的联合研究对于疟原虫本身是如何在胎盘中隐藏的现象有了一些重要的发现。
??Plasmodium falciparium是目前传染人类的最有毒力的4大疟原虫之一。他的极其危险性在于他也感染孕妇的胎盘，对孕妇和胎儿有致命的影响。因此，遭受疟疾国家的医疗资源常常也很薄弱，这样就造成了孕妇在分娩过程中死亡的严重后果。
??“由于某些原因，通常在成人中发现，怀第一胎的妇女丢失半免疫性，”一边工作一边学习的KI毕业生 Niloofar Rasti解释说，“胎盘似乎是诸虫亚群体最有利的解剖学环境。”
??在Mats Wahlgren教授领导下的Karolinska学院的研究小组和Uganda大学KI同事一起详细研究了寄生虫是如何感染胎盘的。他们的结果出版在美国科学杂志PNAS上，促进了抗严重疟疾感染的疫苗和治疗的研究。
??寄生虫在其生命的特定阶段进入人体红细胞，在红细胞里能够产生自身黏附的蛋白血脉壁的受体结合。这会引起红细胞在机体毛细管处聚积，产生危及生命的征兆。感染过几次疟原虫成人的防御系统开始逐渐识别寄生虫蛋白，变得部分免疫。然而，一旦胎盘形成，不同的受体就会诱导形成新的环境。这就意味着一个适合诸虫亚群体生存的环境形成。
??早期研究表明，寄生虫来源的每个蛋白只识别某个特异的胎盘蛋白受体。然而，Ms Rasti和他的同事怀疑天然机制比实验室的研究更复杂。因此，他们在乌干达对胎盘进行收集分析研究。
??“我们研究的大多数诸虫能结合胎盘上不同的受体，”她说，“这就意味着未来的疫苗不能只局限于以往研究的一个蛋白一个受体的原则。”
??既然科学家知道，几个胎盘受体结合的机制，那么研究就应该转移到寄生虫本身上来，看是否产生不同的表面蛋白，或者一个和一类蛋白是否能结合许多不同的宿主受体。
英文原文：
New findings could lead to vaccine for severe malaria
The most severe form of malaria hits pregnant women and children the hardest. A joint study between Karolinska Institutet in Sweden and Makerere University in Uganda has now produced some important findings on how the malaria parasite conceals itself in the placenta.
Plasmodium falciparium is the name of by far the most virulent of the four malaria parasites that infect man. It is particularly dangerous in that it also infects the placenta of pregnant women, with fatal consequences for both her and the foetus. This, combined with the often feeble medical resources of malaria-stricken countries, can lead to such serous complications that the mother dies during delivery.
"For some reason, women in their first pregnancy lose the semi-immunity that is normally found in adults," explains Niloofar Rasti, a KI graduate student who has been working with the study. "The placenta seems to be an anatomically favourable environment for a subpopulation of the parasites."
The research group from Karolinska Institutet, under the leadership of Professor Mats Wahlgren, has been working with colleagues from KI's partner university in Uganda to study in detail how the parasite infects the placenta. Their results, which are published in the American scientific journal PNAS, can enable the development of vaccines and therapies to combat severe malarial infections.
During one particular phase of its lifecycle, the parasite enters human red blood cells, where it produces proteins that attach themselves to receptors in the wall of the blood vessels. This causes the red blood cells to accumulate in organ capillaries, and gives rise to life-threatening symptoms. Adults who have been infected several times can become partly immune as their defence system gradually starts to recognise the parasite's proteins. When the placenta is formed, however, a new environment is introduced with a different set of receptors. This means that a new growth niche is made available to a subpopulation of the parasites.
Earlier studies have suggested that each protein from the parasite attaches to only one specific protein, a receptor, in the placenta. Ms Rasti and her colleagues suspected, however, that the natural mechanisms are more complex than laboratory studies have shown. They therefore collected and analysed placentas on site in Uganda.
"Most of the parasites we studied could bind to three different receptors in the placenta," she says. "This would mean that a future vaccine cannot be based on the principle of one protein-one receptor, as was previously believed."
Now that scientists know that several placental receptors are involved in the binding mechanism, attention will be shifted to the parasite itself, and whether it produces many different surface proteins or if one and the same protein is able to bind to many host receptors.
