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托福阅读材料之艾滋病毒超级抗体

2015-01-14 17:20:57来源：网络

　　2015年托福考试已经来临，对于每一位参加托福考试的同学来说都是新的开始，那么我们对于托福听说读写都需要采取怎样的复习方法?这四项又需要注意些什么呢?我们分别谈一下。下面是新东方在线托福小编整理的托福阅读材料之艾滋病毒超级抗体，供同学们参考!

　　Scientists at the National Institutes of Health have identified long-sought and elusive broadly neutralizing antibodies to HIV in a pair of papers published in the July 9 issue of Science. These proteins produced by the immune system are crucial for creating a preventive vaccine, and could also have therapeutic uses developed in the coming years or decades.

　　Variations in individuals' immune systems can dramatically affect responses to infection—HIV is no exception. The result generally can be shown as a bell curve, with a group of people whose disease progresses rapidly, a broad middle segment who progress typically, and a small group of "elite controllers" whose immune systems are quite effective at containing HIV viral replication.

　　The quest to figure out why has focused primarily on the adaptive immune system, because CD4+ and CD8+ T cells have a clearly demonstrated capacity to kill cells infected with HIV. But that response only arises some days, weeks and even months after a person has been exposed to HIV and the virus has integrated itself into cellular DNA, establishing lifelong infection. The adaptive immune response can only contain an established infection, it cannot prevent that infection from occurring at its onset.

　　B cells are the first line of defense against infection. They attack at the initial exposure to a pathogen, and can prevent the establishment of infection—and HIV is no exception. But there are a number of reasons why it has proved difficult to identify their contribution to neutralizing the deadly virus.

　　HIV transmission is not very efficient. Exposed persons may avoid infection for a variety of mechanical (barrier) and biological reasons, such as the virus's failure to penetrate to the surface of mucosal tissue or dendritic cell difficulties in latching onto the virus to carry it to a lymph node. So it is challenging to conclusively identify the contribution of a specific immune response that can prevent an initial infection.

　　Over the years, it has become clear that there are factors other than CD4+ and CD8+ T cells that help to control the virus in at least a portion of those infected with HIV.


本文关键字: 托福阅读材料

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