Recent results indicate that coherent models of how multiple interferons (I
FN) are recognized and signal selectively through a common receptor are now
feasible, A proposal is made that the IFN receptor, with its subunits IFNA
R-1 and IFNAR-2, presents two separate ligand binding sites, and this doubl
e structure is both necessary and sufficient to ensure that the different I
FN are recognized and can act selectively. The key feature is the duplicati
on of the extracellular domain of the IFNAR-1 subunit and the configuration
al geometry that this imposes on the intracellular domains of the receptor
subunits and their associated tyrosine kinases.