Dissecting the role of the Leishmania flagellum in pathogenicity

利什曼原虫是通过沙蝇叮咬传播的寄生虫。感染利什曼原虫的人可能出现轻微症状，伴有局部皮肤损伤，或危及生命的全身感染。目前全世界约有1200万人感染；每年大约有3万人死于这种疾病，而那些幸存下来的人往往会留下毁容的伤疤。利什曼原虫是一种小的单细胞，在人体内，它们生活在称为巨噬细胞的血细胞中。巨噬细胞最重要的工作之一是发现并消灭致病微生物。简单地说，巨噬细胞吞噬并消化一些入侵的微生物，然后通知免疫系统的其他细胞发动协同攻击并摧毁微生物。当巨噬细胞吞下利什曼原虫时，寄生虫不会死亡。相反，它会改变自己的形状，繁殖，然后扩散感染其他细胞。我们想知道寄生虫是如何与巨噬细胞沟通，阻断其杀伤机制，促进自身生存的。我们认为寄生虫上有一种薄薄的突起，叫做鞭毛，可以起到“细胞天线”或信号装置的作用。我们现在想要发现这种鞭毛的组成部分（蛋白质）是什么，以及为什么它似乎是寄生虫在宿主细胞中生存所必需的。我们已经生成了鞭毛蛋白质的列表，现在将使用一种称为基因编辑的新技术来产生一组数百种突变寄生虫，其中鞭毛的不同部分被破坏。然后我们将这些突变寄生虫与巨噬细胞在实验室混合，几天后观察哪些突变体成功进入巨噬细胞，哪些没有进入。那些没有感染的将被详细研究，以发现鞭毛的哪些部分是感染所必需的，以及鞭毛及其连接如何帮助寄生虫在巨噬细胞的破坏机制中存活下来。

Leishmania are parasites that are transmitted by the bite of the sand fly. A person infected with Leishmania can develop mild symptoms, with localized skin lesions, or a life-threatening infection of the whole body. About 12 million people across the world are currently infected; about 30,000 people die every year from the disease and those that survive are often left with disfiguring scars. Leishmania parasites are small single cells and in the human body they live inside blood cells called macrophages. One of the most important jobs of the macrophage is the discovery and destruction of microbes that cause disease. Simply put, macrophages swallow and digest some of the invading microbes and then inform other cells of the immune system to mount a coordinated attack and destroy the microbes. When a macrophage swallows a Leishmania parasite, the parasite does not die. Instead it changes its shape, multiplies and then spreads to infect other cells. We want to find out how the parasites communicate with the macrophage to block its killing mechanisms and promote their own survival. We think a thin projection on the parasite, called the flagellum, could function as a 'cellular antennae' or signalling device. We now want to discover what the building blocks (proteins) of this flagellum are and why it appears to be required for parasite survival in the host cell. We have generated a list of flagellar proteins and will now use a new technology called gene editing to produce a set of several hundred mutant parasites, where different parts of the flagellum are disrupted. We will then mix these mutant parasites with macrophages in the laboratory and look a few days later to see which mutants were successful in entering the macrophages and which ones didn't make it. Those that fail to infect will be studied in detail to discover which parts of the flagellum are required for infection and how the flagellum and the connections it makes help the parasite to survive the destruction mechanisms of the macrophage.