Interferons,Virus Infection,Leucocytes,Fibroblasts,immune Interferon,Adenosine Polymerase,Large Granular Lymphocytes (LGL),Mammalian Cell Cultures

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	Interferons Interferons are proteins produced by a cell infected by a virus, and provide protection to other healthy cells from viruses. Interferon was discovered in 1957 when Issacs and Lindenmann observed that virus-free fluid obtained from cultured cells infected with virus protected other cells from virus infection. They called the substance present in these fluids, which interfered with virus infection, interferon. There are three major types of interferons:
(1) interferon-α (INF- α; produced by leucocytes or white blood cells), (2) interferon-β (INF- β; produced by fibroblasts), and (3) interferon-γ (INF- γ; produced by stimulated T-lymphocyte; also called immune interferon). The mechanism of protection by interferons appears to be as follows. When interferon reacts with the interferon receptors of a cell, the cell enters in a state called interferon induced antiviral state. In this state, a rapid degradation of mRNA occurs if the cell is infected by any virus.
Interferon induces in cells the production of 2, 5-adenosine polymerase. When such a cell is infected by a virus, the 2, 5-A polymerase is activated to produce 2, 5-adenosine (2, 5-A), which in turn activates preexisting but inactive molecules of ribonuclease-L. Activated ribonuclease-L degrades all mRNA (of host as well as virus origin) present in the cell bringing the protein synthesis to a halt in such cells. This interferes with multiplication of the virus so that virus infection is either stopped or sufficiently slowed down to allow the production of adequate antibodies against the invading virus.
The protection due to interferons is nonspecific in that interferon induced by anyone virus will provide protection against all viruses. It is possible that interferons modify ribosomes so that they no longer translate viral mRNAs, although they are fully capable of translating mRNAs of the host origin. Interferons enhance the cytotoxic activity of natural killer cells (NK cells), which are a type of lymphocytes identifiable as large granular lymphocytes (LGL). NK cells are cytotoxic to some types of tumour cells. Interferons are known to inhibit growth of some types of tumours; most of these tumours are also responsive to chemotherapy. Interferons, therefore, have been employed in treatment of the responsive tumours despite their prohibitive cost (initially, $50 million/g of commercial product).
	Interferons are produced from human leucocytes isolated from donor blood and cultured in vitro, and from mouse fibroblast cultures. The production scheme, in simple terms, is as follows. Large scale (l,000 I to 10,000 I) cell cultures are infected with Sendai virus, and incubated for 24 hr after which the supernatant (clear fluid) is collected, centrifuged, and used for interferon isolation. The amount of interferon recovered is relatively small (I g interferon of low purity from leucocytes separated from blood of about 90,000 donors), and the normal leucocytes are difficult to culture preventing scaling up from relatively small inocula. These contributed to the enormous price of the product. In view of the value of and demand for interferons, intensive efforts were made to produce it in genetically engineered organisms, e.g., E. coli, yeast, mammalian cell cultures and even in plants. These efforts have drastically reduced the cost (to less than 10% of the initial price) and improved the purity (by several orders of magnitude) of the product.