文章来源:未知 文章作者:enread 发布时间:2011-01-05 03:40 字体: [ ]  进入论坛

About one-third of the human population is infected with a parasite1 called Toxoplasma gondii(弓形虫) , but most of them don't know it. Though Toxoplasma causes no symptoms in most people, it can be harmful to individuals with suppressed immune systems, and to fetuses3(胎儿) whose mothers become infected during pregnancy4. Toxoplasma spores5 are found in dirt and easily infect farm animals such as cows, sheep, pigs and chickens. Humans can be infected by eating undercooked meat or unwashed vegetables. Jeroen Saeij, an assistant professor of biology at MIT is investigating a key question: why certain strains of the Toxoplasma parasite (there are at least a dozen) are more dangerous to humans than others. He and his colleagues have focused their attention on the type II strain, which is the most common in the United States and Europe, and is also the most likely to produce symptoms. In a paper appearing in the Jan. 3 online edition of the Journal of Experimental Medicine, the researchers report the discovery of a new Toxoplasma protein that may help explain why type II is more virulent6(剧毒的,恶性的) than others.

Toxoplasma infection rates vary around the world. In the United States, it's about 10 to 15 percent, while rates in Europe and Brazil are much higher, around 50 to 80 percent. However, these are only estimates — it is difficult to calculate precise rates because most infected people don't have any symptoms.

After an infection is established, the parasite forms cysts(囊肿) , which contain many slowly reproducing parasites7, in muscle tissue and the brain. If the cysts rupture8(破裂) , immune cells called T cells will usually kill the parasites before they spread further. However, people with suppressed immune systems, such as AIDS patients or people undergoing chemotherapy, can't mount an effective defense9.

"In AIDS patients, T cells are essentially10 gone, so once a cyst ruptures11, it can infect more brain cells, which eventually causes real damage to the brain," says Saeij.

The infection can also cause birth defects, if the mother is infected for the first time while pregnant. (If she is already infected before becoming pregnant, there is usually no danger to the fetus2.)

There are drugs that can kill the parasite when it first infects someone, but once cysts are formed, it is very difficult to eradicate12(根除,消灭) them.

A few years ago, Saeij and colleagues showed that the Toxoplasma parasite secretes13 two proteins called rhoptry18 and rhoptry16 into the host cell. Those proteins allow the parasite to take over many host-cell functions.

In the new study, the MIT team showed that the parasite also secretes(隐匿,分泌) a protein called GRA15, which triggers inflammation in the host. All Toxoplasma strains have this protein, but only the version found in type II causes inflammation, an immune reaction that is meant to destroy invaders14 but can also damage the host's own tissues if unchecked. In the brain, inflammation can lead to encephalitis(脑炎) . This ability to cause inflammation likely explains why the type II strain is so much more hazardous15 for humans, says Saeij.

Saeij and his team, which included MIT Department of Biology graduate students Emily Rosowski and Diana Lu, showed that type II GRA15 leads to the activation16 of the transcription factor known as NF-kB, which eventually stimulates17 production of proteins that cause inflammation. The team is now trying to figure out how that interaction between GRA15 and NF-kB occurs, and why it is advantageous18 to the parasite.

Ultimately, Saeij hopes to figure out how the parasite is able to evade19 the immune system and establish a chronic20 infection. Such work could eventually lead to new drugs that block the parasite from establishing such an infection, or a vaccine21 that consists of a de-activated form of the parasite.


1 parasite U4lzN     
  • The lazy man was a parasite on his family.那懒汉是家里的寄生虫。
  • I don't want to be a parasite.I must earn my own way in life.我不想做寄生虫,我要自己养活自己。
2 fetus ekHx3     
  • In the fetus,blood cells are formed in different sites at different ages.胎儿的血细胞在不同时期生成在不同的部位。
  • No one knows why a fetus is not automatically rejected by the mother's immune system. 没有人知道为什么母亲的免疫系统不会自动排斥胎儿。
3 fetuses eae25b106f4ed68558631a5bf44c9293     
n.胎,胎儿( fetus的名词复数 )
  • DNA was extracted from fetuses at mid-gestation, about 10 days past conception. DNA从受孕大约10天后的中期妊娠胚胎中提取。 来自互联网
  • Brucellosis is a disease that causes fetuses to abort in cattle. 普鲁士菌病是一种可以导致牲畜胎儿夭折的疾病。 来自互联网
4 pregnancy lPwxP     
  • Early pregnancy is often accompanied by nausea.怀孕早期常有恶心的现象。
  • Smoking during pregnancy increases the risk of miscarriage.怀孕期吸烟会增加流产的危险。
5 spores c0cc8819fa73268b5ec019dbe33b798c     
n.(细菌、苔藓、蕨类植物)孢子( spore的名词复数 )v.(细菌、苔藓、蕨类植物)孢子( spore的第三人称单数 )
  • Ferns, mosses and fungi spread by means of spores. 蕨类植物、苔藓和真菌通过孢子传播蔓生。
  • Spores form a lipid membrane during the process of reproducing. 孢于在生殖过程中形成类脂膜。 来自英汉非文学 - 生命科学 - 预防生物武器
6 virulent 1HtyK     
  • She is very virulent about her former employer.她对她过去的老板恨之入骨。
  • I stood up for her despite the virulent criticism.尽管她遭到恶毒的批评,我还是维护她。
7 parasites a8076647ef34cfbbf9d3cb418df78a08     
寄生物( parasite的名词复数 ); 靠他人为生的人; 诸虫
  • These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的,而与寄生虫无关。
  • Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。
8 rupture qsyyc     
  • I can rupture a rule for a friend.我可以为朋友破一次例。
  • The rupture of a blood vessel usually cause the mark of a bruise.血管的突然破裂往往会造成外伤的痕迹。
9 defense AxbxB     
  • The accused has the right to defense.被告人有权获得辩护。
  • The war has impacted the area with military and defense workers.战争使那个地区挤满了军队和防御工程人员。
10 essentially nntxw     
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
11 ruptures 932414a52fbd26f128186a952208af3a     
n.(体内组织等的)断裂( rupture的名词复数 );爆裂;疝气v.(使)破裂( rupture的第三人称单数 );(使体内组织等)断裂;使(友好关系)破裂;使绝交
  • Fault ruptures may consist of a single narrow main break. 断层破裂可能只包括单独一条狭窄的主裂隙。 来自辞典例句
  • The dry seed ruptures and the green leaf uncurls. 干瘪的种子裂开了,卷曲的绿叶伸展了。 来自辞典例句
12 eradicate Ui1zn     
  • These insects are very difficult to eradicate.这些昆虫很难根除。
  • They are already battling to eradicate illnesses such as malaria and tetanus.他们已经在努力消灭疟疾、破伤风等疾病。
13 secretes b951c7cca7237b8e550dc03599b78b6f     
v.(尤指动物或植物器官)分泌( secrete的第三人称单数 );隐匿,隐藏
  • The pineal gland secretes melanin during times of relaxation and visualization. 松果体在放松时分泌黑色素是明白无误的。 来自互联网
  • For example, the archegonium (female organ) of the moss Funaria secretes sucrose. 例如藓类颈卵器(雌性器官)分泌蔗糖。 来自互联网
14 invaders 5f4b502b53eb551c767b8cce3965af9f     
入侵者,侵略者,侵入物( invader的名词复数 )
  • They prepared to repel the invaders. 他们准备赶走侵略军。
  • The family has traced its ancestry to the Norman invaders. 这个家族将自己的世系追溯到诺曼征服者。
15 hazardous Iddxz     
  • These conditions are very hazardous for shipping.这些情况对航海非常不利。
  • Everybody said that it was a hazardous investment.大家都说那是一次危险的投资。
16 activation 24eed33ee38027d124839f0fcdf6adcb     
n. 激活,催化作用
  • A computer controls the activation of an air bag.电脑控制着气囊的启动。
17 stimulates 7384b1562fa5973e17b0984305c09f3e     
v.刺激( stimulate的第三人称单数 );激励;使兴奋;起兴奋作用,起刺激作用,起促进作用
  • Exercise stimulates the body. 运动促进身体健康。 来自《简明英汉词典》
  • Alcohol stimulates the action of the heart. 酒刺激心脏的活动。 来自《现代英汉综合大词典》
18 advantageous BK5yp     
  • Injections of vitamin C are obviously advantageous.注射维生素C显然是有利的。
  • You're in a very advantageous position.你处于非常有利的地位。
19 evade evade     
  • He tried to evade the embarrassing question.他企图回避这令人难堪的问题。
  • You are in charge of the job.How could you evade the issue?你是负责人,你怎么能对这个问题不置可否?
20 chronic BO9zl     
  • Famine differs from chronic malnutrition.饥荒不同于慢性营养不良。
  • Chronic poisoning may lead to death from inanition.慢性中毒也可能由虚弱导致死亡。
21 vaccine Ki1wv     
  • The polio vaccine has saved millions of lives.脊髓灰质炎疫苗挽救了数以百万计的生命。
  • She takes a vaccine against influenza every fall.她每年秋季接种流感疫苗。