摘要: 蝙蝠與其他哺乳動物的免疫系統(tǒng)在工作方式上有著根本的不同。這個結(jié)論是由普朗克鳥類學(xué)研究所的科學(xué)家們在研究犬吻蝠時得出的。 雖然蝙蝠是許多傳染病毒的攜帶者和宿主，但是目前對它們免疫系統(tǒng)的研究少之又有。馬克斯普朗克鳥類學(xué)研究所，康士坦茨大學(xué)和位于巴拿馬的史密森熱帶...
蝙蝠與其他哺乳動物的免疫系統(tǒng)在工作方式上有著根本的不同。這個結(jié)論是由普朗克鳥類學(xué)研究所的科學(xué)家們在研究犬吻蝠時得出的。
雖然蝙蝠是許多傳染病毒的攜帶者和宿主，但是目前對它們免疫系統(tǒng)的研究少之又有。馬克斯普朗克鳥類學(xué)研究所，康士坦茨大學(xué)和位于巴拿馬的史密森熱帶研究所的研究人員正試圖填補這項研究上的空白。他們的研究顯示蝙蝠與其它哺乳動物的免疫系統(tǒng)在工作方式上有著根本性的不同。這種動物的免疫系統(tǒng)能夠提供如何避免某些傳染病的線索。
已知的1300種蝙蝠中，有許多種蝙蝠的血液中存在抗體，以防止各種疾病的發(fā)生，但它們體內(nèi)很少有病原體存在。這種動物似乎能夠擊退病原體而不生病。是什么使他們的免疫系統(tǒng)如此特殊?
科學(xué)家們研究了巴拿馬帕氏犬吻蝠的免疫反應(yīng)。這種動物遵循特定的日常活動：白天他們?yōu)榱斯?jié)約能量主要呆在棲息地從而減少能量消耗。在此期間，蝙蝠靜止不動而且它們的體溫下降。只有在日落時分，犬吻蝠才出門捕獵。這時，當(dāng)它們在飛行過程中肌肉需要工作時，體溫會上升到40攝氏度以上。
然而，高體溫也有副作用：每天體溫升高時，這就可以激活對抗病原體的免疫反應(yīng)。相反，它們每天減緩新陳代謝速度也會抑制體內(nèi)現(xiàn)有的病原體繁殖。
為了驗證這個假設(shè)，研究人員給蝙蝠派發(fā)了一種脂多糖(LPS)，這是一種由脂類和糖組成的無害化合物。由于脂多糖也存在與許多病原體的外膜上，因此，蝙蝠的免疫系統(tǒng)會假定受到細菌的攻擊而轉(zhuǎn)換到防御模式。
科學(xué)家們證實，即使在給藥之后，蝙蝠每天的體溫波動仍然保持不變。因此雖然這種物質(zhì)在其它哺乳動物身上有效，但卻不會導(dǎo)致蝙蝠體溫升高。此外，血液中的白細胞數(shù)量(免疫系統(tǒng)強弱的標(biāo)志)沒有增加。然而，蝙蝠在24小時內(nèi)卻失去的大量的白細胞，這個現(xiàn)象對研究人員來說，是動物動用了能量儲備來進行免疫防御。
“這種大量的白細胞損失也發(fā)生在其它種類的蝙蝠身上，”該研究的主要作者Teague O’Mara說?！斑@個跡象表明它們的免疫系統(tǒng)被打開了?！敝钡浆F(xiàn)在為止，沒有人確切地了解哪個細胞過程在起作用?！膀鹈庖呦到y(tǒng)與其它哺乳動物的工作方式不同，”馬克斯普朗克鳥類研究所的Dina Dechmann說。“我們要了解是什么使蝙蝠如此與眾不同。這能夠幫助我們了解對人類構(gòu)成威脅的疾病?！?/p>
因此，可以想見的是，蝙蝠為埃博拉病毒背了黑鍋。在科赫羅伯特研究所和馬克斯普朗克研究所的科學(xué)們做的一項調(diào)查中，系統(tǒng)分析了埃博拉病毒的起源。根據(jù)研究人員的說法，果蝠不是主要或唯一的病毒宿主。蝙蝠身上沒有埃博拉病毒的病原體。
迄今為止，埃博拉病毒抗體的證據(jù)鏈，已經(jīng)在果蝠的血液中被發(fā)現(xiàn)。因此，這個動物可能頻繁地接觸了病毒但是卻沒有被傳染。這種類似的情況也可能出現(xiàn)在其他由動物傳染給人類的傳染病上，如狂犬病。在這種情況下，有效的免疫系統(tǒng)可以保護蝙蝠不生病?！叭绻覀兡軌蛄私鈩游锸侨绾螒?yīng)對疾病的，我們就可以利用這方面的知識來開發(fā)新的疫苗和藥物，”O(jiān)’Mara說。
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.
