生物谷報道：美國科學(xué)家最近驚奇地發(fā)現(xiàn),，一種古老的生物——變形蟲（social amoeba,，學(xué)名Dictyostelium discoideum,，又稱阿米巴蟲）體內(nèi)存在著免疫系統(tǒng),。除本身的重要性外,，該發(fā)現(xiàn)還有望加深人們對單細(xì)胞生物向多細(xì)胞生物轉(zhuǎn)變的認(rèn)識。相關(guān)論文發(fā)表在8月3日的《科學(xué)》雜志上,。
單個變形蟲一般是單細(xì)胞的,，而當(dāng)它們面臨生存壓力（比如饑餓）時,，這些單細(xì)胞生物會結(jié)合起來，形成可以移動的多細(xì)胞生物——蛞蝓（slug）,。蛞蝓能夠制造新的細(xì)胞并完成特定的孢子生殖功能,。
在最新的研究中，美國貝勒醫(yī)學(xué)院（Baylor College of Medicine）的生物學(xué)家Adam Kuspa和同事在蛞蝓體內(nèi)發(fā)現(xiàn)了一種新的具有免疫功能的噬菌細(xì)胞，他們稱之為“崗哨細(xì)胞”（sentinel cell）,。
研究表明,，崗哨細(xì)胞在蛞蝓體內(nèi)循環(huán)流通，吞噬入侵的細(xì)菌并且“扣押”毒素,，并最終將它們排出體外,。而崗哨細(xì)胞的這種作用是基于細(xì)胞內(nèi)Toll/Interleukin-1受體蛋白（簡稱TirA）的調(diào)控,。研究人員表示，蛞蝓體內(nèi)的這種信號路徑與植物和動物中的十分類似,，而在真菌中尚沒有發(fā)現(xiàn)該調(diào)控機(jī)制,。
Kuspa表示,，“近十年來,，變形蟲逐漸被認(rèn)為是最主要的四類真核生物形式之一（分別是植物、動物,、真菌和變形蟲）,。而這四類生物中已有三類被證實(shí)存在類似的免疫系統(tǒng)，因此我相信,，所有多細(xì)胞動物的祖先都具有這一免疫機(jī)制,。”
研究人員推測,，從另一方面而言,，單細(xì)胞生物轉(zhuǎn)變?yōu)槎嗉?xì)胞生物的一個特性很可能就是要識別自己，排除異己,，而識別自己的“標(biāo)志”很可能就是免疫系統(tǒng),。
進(jìn)一步的研究有望檢驗(yàn)這一推測。Kuspa表示,，“如果所有進(jìn)化為多細(xì)胞生物的早期生物都發(fā)展出了類似的免疫信號系統(tǒng),，那無疑將大大支持我們的論斷。”（科學(xué)網(wǎng) 任霄鵬/編譯）
原始出處:
Science 3 August 2007:
Vol. 317. no. 5838, pp. 678 - 681
DOI: 10.1126/science.1143991
Immune-like Phagocyte Activity in the Social Amoeba
Guokai Chen,1* Olga Zhuchenko,1* Adam Kuspa1,2,3
Social amoebae feed on bacteria in the soil but aggregate when starved to form a migrating slug. We describe a previously unknown cell type in the social amoeba, which appears to provide detoxification and immune-like functions and which we term sentinel (S) cells. S cells were observed to engulf bacteria and sequester toxins while circulating within the slug, eventually being sloughed off. A Toll/interleukin-1 receptor (TIR) domain protein, TirA, was also required for some S cell functions and for vegetative amoebae to feed on live bacteria. This apparent innate immune function in social amoebae, and the use of TirA for bacterial feeding, suggest an ancient cellular foraging mechanism that may have been adapted to defense functions well before the diversification of the animals.
1 Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
2 Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
3 Program in Developmental Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: [email protected]
