Interferon is a protein molecule. It is produced by the cells when they are exposed to viral infection for the first time and protects the cells against the second viral infection. An interferon acts only in the same species in which it was produced.

In 1957 they are first isolated from the patients having viral attack, by Issacs and Linderman. They are of 20000-34000 daltons of molecular weight which suggests their small size.
Interferons have antiviral property. They inhibit the viral activities by inducing the biosynthesis of enzymes such as protein kinase and phosphodiesterase.The virus fails to multiply in the cells because these enzymes degrade the viral mRNAs and protein synthetic systems. They are used in the treatment of cancer because of the property of inhibition of abnormal cells multiplication. Interferons are produced against heat denatured viruses also.
On the basis of their antigenic and physiochemical properties they can be divided in to-

Alpha-Interferon- It is also called as leucocytic interferon, produced by virus infected leucocytes. It checks the viral multiplication during the second infection. There are eight subtypes- IFN1, IFN2, IFN3 etc.

Beta-Interferon- It is produced by the virus infected fibroblasts cells enhances the activity of T- cells, B-cells, macrophages(suppressor cells). pH 2 stabilizes it.

Gamma-Interferon- It binds with the cell surface antigen of virus infected cells or tumour cells, destroying the whole cells. It is produced by virus infected T-cells and natural killer cells and very sensitive to low pH.

In 1980, Gilbert and Wiesmann, produced genetically engineered human leucocytic interferon for the first time. They made complementary DNA from the mRNA and inserted it in a plasmid vector. The rDNA was introduced into E.coli which produced human leucocytic interferon in the culture. Biogen (US based company) started large scale production of Alpha-Inteferon.

Japanese workers isolated mRNA coding for human leucocytic interferon(Le IF-D) and cloned its c-DNA in E.coli. The transformed E.coli produces about 10,000 interferon molecules per cell. Another Japanese workers joined the cDNA of Le IF-D gene with alcohol dehydrogenase gene and introduced it in to Saccharomyces cerevisiae. The yeast could produce about a million molecules of interferon in a cell.. In 1982, the complete gene coding for human leucocytic interferon (IFN-alpa 1) was chemically synthesized for the first time. The gene is about 514 nucleotides long.

* They are used to treat commom cold, influenza etc. They can be injected intramuscularly or by nasal spray.

* Interferon A is used to treat hepatitis C.

* A bovine interferon improves the pregnancy rate in sheep.

* The Gamma-Interferon is used in the treatment of renal carcinoma in man.

* The Beta-Interferon is used in the treatment of cancers of lymph nodec and lymphoma.

* Leucocytic interferons are used in the treatment of breast cancer.

* The IFN- gamma is an active stimulator of the activity of macrophages that kill tumour cells and intracellular parasites.

The Alpha -Interferon is produced by leucocytes, Beta-Interferon is produced by fibroblast and the Gamma-Interferon is produced by T- lymphocytes.The cells are cultured in a nutrient medium for a week. Now the cell culture is treated with the virus against which interferon has to be produced. The virus multiplies inside the cell. Nutrient medium is removed and a fresh medium of polyinosine-cytosine RNA and diethylaminoethyl dextran is introduced to the culture, which enhances interferon production.After two days, half of the medium is removed and serum albumin or insulin and guanosine phosphate is added. These substances enhances the stability and production of interferons. After two days, interferons are extracted from the culture and fresh medium is added to the culture so that interferons production should be continued. Interferons is purified by immune affinity chromatography and freezed for future use.

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