A novel IFN-α/β independent ligand receptor system which upon engagement leads, among other things, to the establishment of an anti-viral state is disclosed. Further disclosed are three closely positioned genes on human chromosome 19 that encode distinct but highly homologous proteins, designated INF-λ1, IFN-λ2, IFN-λ3, based inter alia, in their ability to induce antiviral protection. Expression of these proteins is induced upon viral infection. A receptor complex utilized by all three IFN-λ proteins for signaling is also disclosed. The receptor complex is generally composed of two subunits, a novel receptor designated IFN-λR1 or CRF2-12, and a second subunit, IL-10R2 or CRF2-4, which is also a shared receptor component for the IL-10 and IL-22 receptor complexes. The gene encoding IFN-λR1 is generally widely expressed, including many different cell types and tissues. Expression of these proteins is induced by immune events, including, for example, upon viral infection. Apoptotosis may also be induced under effective conditions.
