Receptor-binding properties of influenza viruses isolated from gulls.

Ducks, gulls and shorebirds represent the major hosts of influenza A viruses (IAVs) in nature, but distinctions of IAVs in different birds are not well defined. Here we characterized the receptor specificity of gull IAVs with HA subtypes H4, H6, H14, H13 and H16 using synthetic sialylglycopolymers. In contrast to duck IAVs, gull IAVs efficiently bound to fucosylated receptors and often preferred sulfated and non-sulfated receptors with Galß1-4GlcNAc cores over the counterparts with Galß1-3GlcNAc cores. Unlike all other IAVs of aquatic birds, H16 IAVs showed efficient binding to Neu5Acα2-6Gal-containing receptors and bound poorly to Neu5Acα2-3Galß1-3-terminated (duck-type) receptors. Analysis of HA crystal structures and amino acid sequences suggested that the amino acid at position 222 is an important determinant of the receptor specificity of IAVs and that transmission of duck viruses to gulls and shorebirds is commonly accompanied by substitutions at this position.

Receptor specificity of influenza viruses from birds and mammals: new data on involvement of the inner fragments of the carbohydrate chain.

We studied receptor-binding properties of influenza virus isolates from birds and mammals using polymeric conjugates of sialooligosaccharides terminated with common Neu5Ac alpha2-3Gal beta fragment but differing by the structure of the inner part of carbohydrate chain. Viruses isolated from distinct avian species differed by their recognition of the inner part of oligosaccharide receptor. Duck viruses displayed high affinity for receptors having beta1-3 rather than beta1-4 linkage between Neu5Ac alpha2-3Gal-disaccharide and penultimate N-acetylhexosamine residue. Fucose and sulfate substituents at this residue had negative and low effect, respectively, on saccharide binding to duck viruses. By contrast, gull viruses preferentially bound to receptors bearing fucose at N-acetylglucosamine residue, whereas chicken and mammalian viruses demonstrated increased affinity for oligosaccharides that harbored sulfo group at position 6 of (beta1-4)-linked GlcNAc. These data suggest that although all avian influenza viruses preferentially bind to Neu5Ac alpha2-3Gal-terminated receptors, the fine receptor specificity of the viruses varies depending on the avian species. Further studies are required to determine whether observed host-dependent differences in the receptor specificity of avian viruses can affect their ability to infect humans.