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Interferons
Interferon is most optimistic approach for antiviral therapy. They were first discovered by Isaacs in 1957. Isaacs and his co workers had incubated the chorioallaootic membrane from embryonated chicken eggs in a suspension of heat killed influenza virus and then transferred this membrane to buffer.

After storage for 24 hr. the membranes were discarded and the buffer tested for anti viral activity. This was done by placing a fresh piece of membrane in the buffer and then challenging the membrane with active influenza virus.

In 1980 a breakthrough came in interferon research when Swiss and Japanese scientists deciphered the genetic code for interferon, and spliced E. coli plasmids with the DNA code. Experiments showed that interferon from bacterial factories would reduce hepatitis symptoms, diminish the spread of herpes zoster, and shrink certain cancers. In 1984, a Swiss biotechnology firm received a patent for alpha interferon and began marketing its product using the trade name intron.

In 1986, the U.S. food & Drug Administration approved the sale of alpha interferon for use against a form of-leukemia. Alpha-and B-interferons are similar, the former synthesised by lymphoblas­toid cells and the latter (discovered by Isaacs) by fibroblastic cells, macrophages and others.

The anti viral activity of interferons can be measured by inhibition of the incorporation of radioactive uridine into viral RNA in cells infected by a togavirus. Activity is expressed in terms of the amount of interferon required to reduce the normal level of viral RNA by 50% and this is arbitrarily defined as one unit. Purified interferon has a high activity of around 10⁹ units per mg of protein. which is of the same order as the hormones.

The sequences of α, β and γ interferons has been determined through cloning. This has been shown that £ and 6 interferon have basic similarity (40% homology), and both are different from y interferon. In human genome, Band y interferons are represented by a single sequence, whereas at least 12 γ interferons differing in sequence are present. Interferon enhances the activation of natural killer (*NK) cells.