Identification of Dual Receptor-binding Specific Strains of Human H5N1 Viruses in China

Objective Both the 2, 6 linkage and its topology on target cells are critical for the recognition by human influenza virus. The binding preference of avian flu virus H5N1 HA to the 2, 3-1inked sialylated glycans is considered the major factor limiting its efficient infection and transmission in humans. To monitor potential adaptation of H5N1 virus in human population, the surveillance of receptor-binding specificity was undertaken in China. Methods The binding specificity of 32 human H5N1 virus strains isolated from 2003 to 2009 was tested by 2, 3-specific sialidase-treated chicken red blood cell （CRBC） agglutination assay and a solid-phase direct binding assay with synthetic sialylglycopolymers. Results Dual binding preference to 2, 3 and 2, 6-glycans were found in two strains： A/Guangdong/1/06 （A/GD/1/06） and A/Guangxi/1/08 （A/GX/1/08）. Though minor effect of short-2, 6-binding was detected in A/GX/1/08 at a low virus titer, both showed high affinity to the oligosaccharide at a high load. Notably both are of the long-2, 6-recognition, with the same topology as that of human H1N1 and H3N2 viruses. Conclusion The findings suggest that human H5N1 virus in China likely acquired the potential human-adaptation ability. Further research and surveillance on receptor-binding specificity of H5N1 viruses are required.