免疫系统与众不同：蝙蝠经常接触传染病，确很少染病 - 动物新闻

蝙蝠与其他哺乳动物的免疫系统在工作方式上有着根本的不同。这个结论是由普朗克鸟类学研究所的科学家们在研究犬吻蝠时得出的。

虽然蝙蝠是许多传染病毒的携带者和宿主，但是目前对它们免疫系统的研究少之又有。马克斯普朗克鸟类学研究所，康士坦茨大学和位于巴拿马的史密森热带研究所的研究人员正试图填补这项研究上的空白。他们的研究显示蝙蝠与其它哺乳动物的免疫系统在工作方式上有着根本性的不同。这种动物的免疫系统能够提供如何避免某些传染病的线索。

已知的1300种蝙蝠中，有许多种蝙蝠的血液中存在抗体，以防止各种疾病的发生，但它们体内很少有病原体存在。这种动物似乎能够击退病原体而不生病。是什么使他们的免疫系统如此特殊?

科学家们研究了巴拿马帕氏犬吻蝠的免疫反应。这种动物遵循特定的日常活动：白天他们为了节约能量主要呆在栖息地从而减少能量消耗。在此期间，蝙蝠静止不动而且它们的体温下降。只有在日落时分，犬吻蝠才出门捕猎。这时，当它们在飞行过程中肌肉需要工作时，体温会上升到40摄氏度以上。

然而，高体温也有副作用：每天体温升高时，这就可以激活对抗病原体的免疫反应。相反，它们每天减缓新陈代谢速度也会抑制体内现有的病原体繁殖。

为了验证这个假设，研究人员给蝙蝠派发了一种脂多糖(LPS)，这是一种由脂类和糖组成的无害化合物。由于脂多糖也存在与许多病原体的外膜上，因此，蝙蝠的免疫系统会假定受到细菌的攻击而转换到防御模式。

科学家们证实，即使在给药之后，蝙蝠每天的体温波动仍然保持不变。因此虽然这种物质在其它哺乳动物身上有效，但却不会导致蝙蝠体温升高。此外，血液中的白细胞数量(免疫系统强弱的标志)没有增加。然而，蝙蝠在24小时内却失去的大量的白细胞，这个现象对研究人员来说，是动物动用了能量储备来进行免疫防御。

“这种大量的白细胞损失也发生在其它种类的蝙蝠身上，”该研究的主要作者Teague O’Mara说。“这个迹象表明它们的免疫系统被打开了。”直到现在为止，没有人确切地了解哪个细胞过程在起作用。“蝙蝠免疫系统与其它哺乳动物的工作方式不同，”马克斯普朗克鸟类研究所的Dina Dechmann说。“我们要了解是什么使蝙蝠如此与众不同。这能够帮助我们了解对人类构成威胁的疾病。”

因此，可以想见的是，蝙蝠为埃博拉病毒背了黑锅。在科赫罗伯特研究所和马克斯普朗克研究所的科学们做的一项调查中，系统分析了埃博拉病毒的起源。根据研究人员的说法，果蝠不是主要或很好的病毒宿主。蝙蝠身上没有埃博拉病毒的病原体。

迄今为止，埃博拉病毒抗体的证据链，已经在果蝠的血液中被发现。因此，这个动物可能频繁地接触了病毒但是却没有被传染。这种类似的情况也可能出现在其他由动物传染给人类的传染病上，如狂犬病。在这种情况下，有效的免疫系统可以保护蝙蝠不生病。“如果我们能够了解动物是如何应对疾病的，我们就可以利用这方面的知识来开发新的疫苗和药物，”O’Mara说。

Bats frequently come into contact with infectious diseases, but rarely suffer from them

The bat’s immune system works in a fundamentally different way to that of other mammals. This was the conclusion reached by scientists from the Max Planck Institute for Ornithology in a study of mastiff bats. The research could also be significant in the fight against viral diseases that can be transmitted from animals like bats to humans.

While bats qualify as carriers and reservoir hosts of a whole range of infectious diseases, very little research has been conducted on their immune system to date. Researchers from the Max Planck Institute for Ornithology in Radolfzell, the University of Konstanz and the Smithsonian Tropical Research Institute in Panama are now trying to bridge this gap. Their findings show that the immune system of bats may work in a way that is fundamentally different to that of other mammals. The immune defence of the animals could even provide clues as to how certain infectious diseases can be averted.

Many of the 1,300 known bat species have antibodies in their blood to protect against various diseases but rarely have the pathogens themselves. The animals seem to be able to fight off the pathogens without becoming ill themselves. But what makes their immune system so special?

The scientists studied the immune responses of Pallas’s mastiff bats (Molossus molossus) in Panama. The animals follow a specific daily routine: during the day they reduce their energy consumption in their roosts in order to save energy. During this period, the bats rest motionless and their body temperature drops. It’s only at sunset, when the mastiff bats set out for the hunt, that they come to life. Now, their body temperature rises to more than 40 degrees Celsius as their muscles need to work hard during their flight.

However, the high temperature could also have a side effect: it could activate the immune response against pathogens as a type of daily fever. Conversely, the daily slowdown in their metabolic rate could also inhibit the proliferation of existing pathogens in the body.

To test this hypothesis, the researchers administered a lipopolysaccharide (LPS) – a compound, harmless in itself, made up of lipid and sugar components – to the bats. As LPS is also found on the outer membrane of many pathogens, the bat’s immune system assumes a bacterial attack and switches to defence mode.

As the scientists demonstrated, however, the daily temperature fluctuations remained unchanged even after the administration of LPS. The material therefore does not trigger a fever in the bats, as it does in other mammals. Furthermore, the number of white blood cells in the blood – an indicator of the strength of the immune defence – did not increase. However, the bats did lose a significant amount of mass within 24 hours – a sign for the researchers that the animals mobilise energy reserves for the immune defence.