McGill University, Department of Microbiology and Immunology, Montreal, Quebec, Canada H3A 2B4.
Exp Parasitol. 2012 Oct;132(2):109-15. doi: 10.1016/j.exppara.2012.06.001. Epub 2012 Jun 9.
Leishmania is an obligate intracellular protozoan parasite that infects cells of the reticulo-endothelial system. Host defences against Leishmania include fever and oxidant production, and the parasite has developed a number of defence mechanisms to neutralize the host response. The Leishmania donovani A2 family of proteins has been shown to be essential for survival in mammalian visceral organs. Here we provide evidence that A2 proteins protect the parasite against host defences, namely heat stress (fever) and oxidative stress. A2 is however unable to protect the cells from endoplasmic reticulum stress induced by dithiothreitol. To downregulate A2 protein expression, L. donovani was transfected with an A2 antisense RNA expressing-vector, resulting in significant reduction of A2 levels. The resulting A2-deficient cells were more sensitive to heat shock and this was associated with increased production of internal oxidants during heat shock. Moreover, axenic amastigotes with downregulated A2 expression had increased internal oxidants and decreased viability following treatment with hydrogen peroxide or a nitric oxide donor when compared to control cells. Overall, these results suggest that A2 protects L. donovani from a variety of stresses, thereby allowing it to survive in the internal organs of the mammalian host and to cause visceral disease.
利什曼原虫是一种专性细胞内原生动物寄生虫，感染网状内皮系统的细胞。宿主对利什曼原虫的防御包括发热和氧化剂的产生，寄生虫已经发展了许多防御机制来中和宿主的反应。已经表明，利什曼原虫 A2 家族蛋白对于在哺乳动物内脏器官中的生存是必需的。在这里，我们提供的证据表明 A2 蛋白保护寄生虫免受宿主防御，即热应激（发热）和氧化应激。然而，A2 不能保护细胞免受二硫苏糖醇诱导的内质网应激。为了下调 A2 蛋白表达，用 A2 反义 RNA 表达载体转染 L. donovani，导致 A2 水平显著降低。由此产生的 A2 缺陷细胞对热休克更敏感，并且在热休克期间产生更多的内部氧化剂。此外，与对照细胞相比，下调 A2 表达的无共生阿米巴原虫在用过氧化氢或一氧化氮供体处理后，内部氧化剂增加，存活能力降低。总的来说，这些结果表明 A2 保护利什曼原虫免受各种应激，从而使其能够在哺乳动物宿主的内脏器官中存活并引起内脏疾病。
