InfluenzaHemagglutinin
Influenza hemagglutinin, commonly abbreviated HA, is a glycoprotein on the surface of influenza A and B viruses that drives entry into host cells and serves as a major target of the immune response. In influenza A, HA is a trimeric, single-pass transmembrane protein that anchors the viral envelope to the host.
HA is synthesized as a single precursor protein, HA0, which is cleaved by host proteases into two
During infection, HA binds to sialic acid receptors on target cells. The preference for sialic acid linkages
HA undergoes frequent genetic variation through antigenic drift—accumulation of mutations that alter antigenic sites—and, less commonly,
Influenza A viruses are categorized by HA subtypes (H1–H18) and neuraminidase subtypes (N1–N11), with common human