Whence Interferon? Variety in the Production of Interferon in Response to Viral Infection

The type I IFNs (IFN-α and IFN-β) were first characterized as cytokines capable of inducing an antiviral state in sensitive target cells (1). They were originally classified as leukocyte IFN and fibroblast IFN, respectively, to designate their distinct presumptive cellular origins. This designation has been replaced by a more precise nomenclature, based on molecular characterization after the isolation, cloning, and sequencing of the IFN multigene family. The originally detected IFN-α activity is encoded by a multigene family of closely related and clustered genes, while IFN-β is encoded by a single, somewhat more distantly related gene. It has also become clear that type I IFNs can be synthesized by many, if not all, nucleated cells, just as virtually all nucleated cells have the capacity to respond to secreted IFN to induce an antiviral state. This ability of most cells to secrete and respond to...