sentences:  Type I IFN binding to IFNAR1 was less strongly impacted by mutating single amino acids to alanine.Importantly, structural studies have not revealed differences in ternary complex structures with IFNAR and various type I IFN subtypes, despite differences in ligand affinities.The evolutionary conservation of type I IFN subtypes binding the same IFNAR receptor at the same site with differing affinities suggests that type I IFNs are nonredundant and potentially regulate different cellular responses.