H9N2 HA

Influenza hemagglutinin (HA) is a glycoprotein found on the surface of influenza A viruses. It is responsible for binding the virus to cells with sialic acid on the host cell membranes, such as cells in the upper respiratory tract or erythrocytes. It is also responsible for the fusion of the viral envelope with the endosome membrane, after the pH has been reduced. H9 subtype influenza virus representing by H9N2 is widely prevalent in domestic poultry across Asia and Africa countries. Its avirulent phenotype makes them ignored by people and frequently provides internal genes for generating novel strains which caused human fatalities (such as H7N9 and H10N8). Current H9 HA has evolved into human-type receptor binding profile and could easily cross species barrier to infect human being.