Classification of Interferons

Two different types of interferons can be described : type I (a, b, w) and type II (g) interferons, which differ in their interaction with distinct cell receptors and induce different biological effects.

Three main classes of interferons were initially differentiated on the basis of antigenicity, biochemical properties, and producer cell : IFN-a, IFN-b and IFN-g. 

IFN-a and –b, which have been grouped together as type I interferons, bind to the same receptor on the cell surface : the a/b receptor. On the other hand, IFN-g, known as type II interferon, binds to a different receptor, the g receptor.

In 1985, three groups reported the discovery of a novel type of interferon which is now termed IFN-omega (w). The sequence homology between IFN-w and IFN-a is of about 65% and it has been shown that Hu-IFN-w binds to the a/b receptor. IFN-w is the most recently discovered member of the type I superfamily. It is secreted by cells following viral infection, and displays antiviral, antiproliferative and immunomodulatory activities typical of a type I IFN.

The human interferon genes and proteins have been extensively studied. There are more than 20 human IFN-a genes but only one IFN-b gene and one single humanIFN-g gene. The major human a IFNs are not glycosylated whereas the b, w and g IFNs are often N-glycosylated.

IFNs exert their actions through species-specific cell surface receptors. Both the human IFN-a receptor and the human IFN-g receptor have been molecularly cloned between 1988 and 1990.