Hemagglutinin protein of Influenza A virus subtype H3N2 (HA (Influenza A H3N2))

Hemagglutinin (HA) protein of Influenza A H3N2 is a trimeric surface glycoprotein essential for viral infectivity. Each HA monomer is composed of two subunits, HA1 and HA2, generated by proteolytic cleavage from a precursor HA0. The HA1 subunit mediates attachment to host cell sialic acid receptors, determining host range and cell tropism, while HA2 contains the fusion machinery required for viral–host membrane fusion after endosomal acidification. The globular head domain includes the main antibody target sites, whereas the stem domain is more conserved and enables membrane fusion. Through frequent genetic variation (antigenic drift), HA enables immune escape and periodic influenza outbreaks, with H3N2 being the predominant Influenza A subtype in humans for several decades. HA's biological activities—receptor binding, membrane fusion, and antigenicity—make it a primary target for vaccines and candidate therapeutic antibodies, although no approved drugs target HA directly. HA is also used diagnostically via its ability to agglutinate erythrocytes in vitro

Other names

Hemagglutinin (HA)Influenza hemagglutininH3 hemagglutininInfluenza A H3N2 hemagglutininHaemagglutinin (British English)

Neutralizing antibodies: Bind to HA, block receptor binding or fusion, preventing viral entry. Fusion inhibitors: Prevent conformational changes in HA necessary for membrane fusion. Vaccines: Induce immune memory targeting antigenic sites on HA, thus blocking infection.