Influenza A virus HA Antigen

Influenza hemagglutinin (HA) or haemagglutinin is a glycoprotein found on the surface of influenzaviruses. Being a class I fusion protein, it is responsible for binding the virus to cells with sialic acid on the 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. The name "hemagglutinin" comes from the protein's ability to cause red blood cells (erythrocytes) to clump together ("agglutinate") in vitro.