Vaccines：A new health food

　　GETTING two for the price of one is always a good bargain. And according to a paper in this week’s Proceedings of the National Academy of Sciences, that is what Tomonori Nochi of the University of Tokyo and his colleagues have done. Using genetic engineering, they have overcome two of the limitations of vaccines. One is that they are heat-sensitive and thus have to be transported along a “cold chain” of refrigerators to the clinics where they are used. The other is that, although they stimulate immune responses inside the body, they often fail to extend that protection to the outside, where it might prevent bacteria and viruses getting inside in the first place.In this context, the outside is not the skin: that is dry and hostile to germs. It is the damp and welcoming surface of places such as the lung and the gut that are at risk. Although these are casually called internal, technically they are not. Any nasties in the gut or lungs have to cross the walls of those organs before they can multiply inside the body.

　　Dr Nochi’s genetic engineering involved growing the vaccine in rice. To prove the principle, he chose cholera, but it should work with other vaccines as well. With cholera, the immune response is induced by what is known as the cholera toxin B-subunit. This is a protein, and Dr Nochi took the gene that encodes it and inserted that gene into the genome of rice. Next to the B-subunit gene itself, he inserted a second piece of DNA called a promoter. This, as its name suggests, promotes activity in an adjacent gene. Promoters themselves are activated by other molecules, and whether they are switched on or not depends on whether the cell they are in provides the necessary stimulation. In this case Dr Nochi picked a promoter that is active in the tissue of rice grains.

　　It was then just a question of growing the rice and feeding the resulting grains to some experimental mice to find out what would happen. The first thing that happened was that the grains protected the B-subunit from being broken down in the stomach, thus overcoming one of the regular bugbears of protein-based drugs: that they cannot be given by mouth, because they will be digested. This is a problem with today’s cholera vaccine which is indeed taken by mouth and therefore affords poor protection. When the B-subunits got to the intestines they did exactly what Dr Nochi hoped and induced the production of antibodies and the secretion of those antibodies into the mucous coating of the intestinal wall. Dr Nochi’s mice really were protected. When he fed them cholera toxin, they did not get sick.

　　On top of all this, he got as good a response with rice that had been stored at room temperature for 18 months as he did when he used fresh grains. For a vaccine against a disease that is found predominantly in poor countries—places that tend to lack refrigerators and have only intermittent power to run those that do exist—that is an enormous advance. If Dr Nochi’s finding can be translated into a product that is safe and effective for people, it will be a big boost to the health of the world’s poor.

　　考研詞匯：

　　overcome[ˌəuvəˈkʌm]

　　v.戰(zhàn)勝，克服

　　[真題例句]If we do not confront and overcome these internal fears and doubts, if we protect ourselves too much, then we cease to grow.[1995年閱讀2]

　　[例句精譯] 如果我們不能去正視并克服這些內(nèi)在的恐懼和疑慮，如果我們過于自我保護(hù)，那么我們就會(huì)停止成長(zhǎng)。

　　hostile[ˈhɔstail]

　　a.敵對(duì)的，敵方的，敵意的

　　[真題例句]Stratford-on-Avon, as we all know, has only one industry—William Shakespeare—but there are two distinctly separate and increasingly hostile branches.[2006年閱讀2]

　　[例句精譯] 正如我們所知，埃文河上的斯特福特就只有一個(gè)行業(yè)——威廉·莎士比亞——但是卻有兩個(gè)界限清楚并各懷敵意的分支部門。

　　induce[inˈdju:s]

　　v.①引誘，勸使;②引起，導(dǎo)致;③感應(yīng)

　　[真題例句]Indeed, the mere presence of a grape in the other chamber (without an actual monkey to eat it) was enough to induce (②) sullen behaviour in a female capuchin.[2005年閱讀1]

　　[例句精譯] 事實(shí)上，一個(gè)籠舍里葡萄的存在(就算是沒有猴子在吃)，就足以引起另一只猴子憤憤不平了。

　　adjacent[əˈdʒeisənt]

　　a.(to)鄰近的，毗連的

　　mucous[ˈmju:kəs]

　　a.黏液的, 黏液似的

　　enormous[iˈnɔ:məs]

　　a.巨大的，龐大的

　　[真題例句]Of course, the use of the Internet isn�餿 the only way to defeat poverty.And the Internet is not the only tool we have.But it has enormous potential.[2001年閱讀2]

　　[例句精譯] 當(dāng)然，使用互聯(lián)網(wǎng)不是惟一消滅貧困的方法。互聯(lián)網(wǎng)也不是我們所擁有的惟一工具，但它卻有巨大的潛力。

　　背景常識(shí)介紹：

　　疫苗，是指為了預(yù)防、控制傳染病的發(fā)生、流行，而用于人體預(yù)防接種的疫苗類預(yù)防性生物制品。

　　疫苗是將病原微生物(如細(xì)菌、立克次氏體、病毒等)及其代謝產(chǎn)物，經(jīng)過人工減毒、滅活或利用基因工程等方法制成的用于預(yù)防傳染病的自動(dòng)免疫制劑。疫苗保留了病原菌刺激動(dòng)物體免疫系統(tǒng)的特性。當(dāng)動(dòng)物體接觸到這種不具傷害力的病原菌后，免疫系統(tǒng)便會(huì)產(chǎn)生一定的保護(hù)物質(zhì)，如免疫激素、活性生理物質(zhì)、特殊抗體等;當(dāng)

　　動(dòng)物再次接觸到這種病原菌時(shí)，動(dòng)物體的免疫系統(tǒng)便會(huì)依循其原有的記憶，制造更多的保護(hù)物質(zhì)來阻止病原菌的傷害。

　　疫苗的發(fā)現(xiàn)可謂是人類發(fā)展史上具有里程碑意義的事件。因?yàn)閺哪撤N意義上來說，人類繁衍生息的歷史就是人類不斷同疾病和自然災(zāi)害作斗爭(zhēng)的歷史。控制傳染性疾病比較主要的手段就是預(yù)防，而接種疫苗被認(rèn)為是比較行之有效的措施。

　　參考譯文：

　　疫苗：全新健康食品

　　“買一送一”一向都是筆好買賣。這個(gè)星期的《國(guó)家科學(xué)院學(xué)報(bào)》發(fā)表的論文中，東京大學(xué)的Tomonori Nochi和他的同事就公布了這樣一件好的成果。通過基因工程，他們突破了傳統(tǒng)疫苗的兩大局限。其一是疫苗往往是熱敏性的，因此在運(yùn)往臨床使用地的途中，疫苗必須通過“低溫運(yùn)輸系統(tǒng)”在冷藏庫(kù)中低溫運(yùn)輸。另一個(gè)則是盡管疫苗可以刺激人體內(nèi)部的免疫反應(yīng)，但他們往往不能將保護(hù)的范圍擴(kuò)大到外部，那里是能夠預(yù)防細(xì)菌和病毒進(jìn)入內(nèi)部的第一道防線。在這里，外部不是指皮膚(皮膚過于干燥不適合微生物生存)。而是指潮濕且細(xì)菌容易接觸的器官表面，例如肺和易感染的內(nèi)臟就很易受感染。盡管習(xí)慣上這些地方被稱為體內(nèi)，但在學(xué)術(shù)上并不是。任何細(xì)菌要進(jìn)入體內(nèi)繁殖必須首先通過這些器官的表面粘膜。

　　Nochi博士進(jìn)行的基因工程試驗(yàn)包括在大米中培育疫苗。為了證明這一原理可行，他選擇霍亂疫苗進(jìn)行試驗(yàn)，但這也應(yīng)該同樣適用于其他疫苗。應(yīng)對(duì)霍亂，引起免疫系統(tǒng)反應(yīng)的是被稱為霍亂毒素B亞單位的蛋白質(zhì)。Nochi博士分析出這種蛋白質(zhì)的基因，并且將其插入大米的染色體組中。他還在鄰近B亞單位基因處插入被稱為啟動(dòng)子的第二段DNA。就像這段DNA的名字一樣，它會(huì)激活鄰近基因的活性。啟動(dòng)子自身則由其他分子激活，這些啟動(dòng)子能否表達(dá)取決于其所在的細(xì)胞是否給其必要的刺激。在這個(gè)例子中，Nochi博士的啟動(dòng)子就是在大米組織中發(fā)揮作用。

　　現(xiàn)在，要做的就是種植這種大米并且用它們喂養(yǎng)一些試驗(yàn)用老鼠，以研究將會(huì)出現(xiàn)什么結(jié)果。首先，谷類糧食在胃中保護(hù)了B亞單位被直接消化，因此使傳統(tǒng)上一直困擾蛋白質(zhì)藥物的一大難題——蛋白質(zhì)藥物會(huì)在胃中被消化往往不能直接口服——得到解決。這同樣是霍亂疫苗的一大缺點(diǎn)，現(xiàn)今的霍亂疫苗實(shí)際上是口服的，因此往往只能起很小的作用。當(dāng)B亞單位順利進(jìn)入腸內(nèi)，大米疫苗實(shí)際上已經(jīng)完成Nochi博士所希望的工作，同時(shí)疫苗會(huì)使人體產(chǎn)生抗體并將這些抗體分泌入腸內(nèi)表面覆蓋的黏液中。Nochi博士的老鼠在實(shí)驗(yàn)中得到了保護(hù)，當(dāng)喂食它們霍亂毒素后，它們并沒有染病。

　　但比較關(guān)鍵的是，Nochi博士使用在室溫下保存了18個(gè)月的大米與使用新鮮大米所得到的實(shí)驗(yàn)結(jié)果是一樣良好的。由于需要疫苗來抵抗疾病的地方往往是那些貧窮國(guó)家，往往缺乏足夠的冷藏系統(tǒng)并且沒有足夠的穩(wěn)定電力來供這些系統(tǒng)運(yùn)行。因此相較傳統(tǒng)疫苗，大米疫苗的這一特點(diǎn)可以說是一個(gè)巨大的進(jìn)步。如果Nochi博士的發(fā)明可以制成安全且對(duì)人有效的產(chǎn)品，對(duì)世界上廣大貧窮人民的健康安全將會(huì)是一個(gè)巨大的推動(dòng)。