antigen variation

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The sequential expression of a series of variable surface glycoproteins (VSGs) by trypanosomes while in the bloodstream of a mammalian host. The production of VSGs allows the parasite to evade the immune defenses of the host by keeping one step ahead of the antibodies the host raises against them. Trypanosomes contain hundreds of different genes for the individual VSGs, but in a single trypanosome only one of these genes is expressed at a given time. The switch from one VSG to another is accompanied by rearrangements of the DNA that generates additional copies of the genes being expressed. The glycoprotein being synthesized forms a macromolecular coating about 15 nanometers thick over the body and flagellum of the parasite. This coating functions only during the mammalian stage of the life cycle, since it is shed when the trypanosome enters the tsetse fly vector. See Glossina, Trypanosoma.

Subjects: Genetics and Genomics.

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