The type I interferons (IFNs), ? and , are a group of structurally and functionally related proteins that are induced by either viruses or double stranded RNA and defined by their ability to confer an antiviral state in cells. The ? and IFNs appear to compete with one another for binding to a common cell surface receptor, while immune IFN (IFN?) binds to a distinct receptor. The latter protein, IFN-?R, is only weakly responsive to type I interferons in contrast to IFN-?/R, which binds to and responds effectively to IFN- and to several of the IFN-? subtypes. Moreover, IFN-?/R is physically associated with the cytoplasmic tyrosine kinase JAK1 and thus, in addition to ligand binding, appears to be functionally involved in signal transduction. IFN-?R1 is a receptor for IFN-?/ and is present as the full chain (IFN-?R1a) and as a splice-variant (IFN-?R1). The IFN-? receptor complex consists of an alpha subunit (IFN-?R?) and a beta subunit that is 332 amino acids in length (mouse) and 337 amino acids in length (human).
