疟原虫是导致疟疾的寄生虫。研究人员在5月在线出版的《自然—医学》期刊上报告，原有的疟疾能预防由另一种疟原虫所引发的再次感染，新发现可应用于疟疾流行地区治贫血的铁补充治疗。

尽管年幼的孩子对寄生虫有较低的免疫力，但因多种疟原虫引发的重复感染并没有普遍出现在他们身上。为了研究其中的原因，Maria Mota和同事合作，在小鼠体内模拟了疟原虫重复感染。

他们发现，在血液中疟原虫水平的域值以上，血液阶段的感染通过刺激宿主铁调素的上调抑制了肝脏阶段重复感染的发展，铁调素是一种铁调节激素。铁调素的增加减少了肝脏细胞中铁的可获得性，而这是肝脏中寄生虫成功发育的关键。相反，铁的补充增强了肝脏阶段疟原虫重复感染的进展。

原文出处：

Nature Medicine   DOI:10.1038/nm.2368

Host-mediated regulation of superinfection in malaria

Silvia Portugal; Celine Carret; Mario Recker; Andrew E Armitage; Ligia A Goncalves; Sabrina Epiphanio; David Sullivan; Cindy Roy; Chris I Newbold; Hal Drakesmith; Maria M Mota

In regions of high rates of malaria transmission, mosquitoes repeatedly transmit liver-tropic Plasmodium sporozoites to individuals who already have blood-stage parasitemia1. This manifests itself in semi-immune children (who have been exposed since birth to Plasmodium infection and as such show low levels of peripheral parasitemia but can still be infected) older than 5 years of age by concurrent carriage of different parasite genotypes at low asymptomatic parasitemias2. Superinfection presents an increased risk of hyperparasitemia and death in less immune individuals but counterintuitively is not frequently observed in the young3, 4. Here we show in a mouse model that ongoing blood-stage infections, above a minimum threshold, impair the growth of subsequently inoculated sporozoites such that they become growth arrested in liver hepatocytes and fail to develop into blood-stage parasites. Inhibition of the liver-stage infection is mediated by the host iron regulatory hormone hepcidin5, whose synthesis we found to be stimulated by blood-stage parasites in a density-dependent manner. We mathematically modeled this phenomenon and show how density-dependent protection against liver-stage malaria can shape the epidemiological patterns of age-related risk and the complexity of malaria infections seen in young children. The interaction between these two Plasmodium stages and host iron metabolism has relevance for the global efforts to reduce malaria transmission and for evaluation of iron supplementation programs in malaria-endemic regions.