ĭnˌtərfērˈŏn, any of a group of proteins produced by cells in the body in response to an attack by a virus. A cell infected by a virus releases minute amounts of interferons, which attach themselves to neighboring cells, prompting them to start producing their own protective antiviral enzymes. The result is impairment of the growth and replication of the attacking virus. Interferon has also been shown to have some antitumor properties. There are three known classes of interferons: alpha-, beta-, and gamma-interferons.

Although they were discovered in the 1950s, the medical use of interferons was impractical until the recombinant DNA techniques of genetic engineering made it possible to mass produce them. Interferons used as drugs include alpha-interferon, for hepatitis B and C, human papillomavirus, hairy-cell leukemia, and Kaposi's sarcoma (a cancer associated with AIDS), and beta-interferon, for multiple sclerosis.

See also immunity.

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