【#天文資訊】哺乳動物免疫系統對假想太空細菌的反應
人類一直努力不懈地尋找外星生命，科學家相信太陽系中可能有不止一個天體存在孕育生命不可或缺的液態水，加上在太空隕石中也不時能找到組成生命基本結構單元之一的胺基酸，外星微生物的存在看來也是有可能的。在將來，假如有太空人前往其他天體，甚至採集岩石樣本帶回地球，亦有可能接觸到由特殊胺基酸構成的外星微生物。如果這些微生物具侵襲性的話，人類的免疫系統是否有能力抵禦這些太空細菌呢？
科學家以小鼠為實驗對象，測試哺乳動物免疫系統對由隕石中兩種常見胺基酸組成的肽有何反應。結果發現當小鼠的T細胞（免疫反應的關鍵細胞）暴露於這種肽時，其活化度只有15%及61%，跟暴露於由地球常見胺基酸所組成的肽時的表現較差。這意味著當人類接觸到外星微生物時，免疫系統未必能有效地作出反應，增加外星探索任務的潛在風險。
【#Astronomyinfo】The Response of Mammalian Immune System to the Imaginary Space Germ
Humans have been working tirelessly to search for extraterrestrial life. Scientists believe liquid water may exist in more than one celestial body in the solar system. They also found amino acids, one of the basic building blocks of life, in meteorites from time to time. The existence of extraterrestrial microorganisms seems possible. In the future, if an astronaut travel to other celestial bodies, and even bring the collected rocks back to Earth, then it is possible to make contact with the extraterrestrial microorganisms composed of special amino acids. If these microorganisms are ingressive, can the human immune system respond effectively against them?
Scientists used mice as a test subject to examine the responses of mammalian immune systems to the peptides composed of two amino acids commonly found on meteorites. It was found that when mouse T cells, which are crucial to the immune responses, were exposed to the peptides, the activation level was only 15% and 61%, which was less efficient compared with their responses to peptides composed of common amino acids on Earth. This means that when humans come into contact with extraterrestrial microorganisms, the immune system may not be able to respond effectively, increasing the potential risks of space exploration missions.
圖片鳴謝Photo credit: NASA/JPL-Caltech
更多資料More information: http://www.exeter.ac.uk/news/homepage/title_807010_en.html
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