Influenza hemagglutinin protein subtype H3N2 (HA)

The influenza hemagglutinin protein (HA) of the H3N2 A subtype is a trimeric envelope glycoprotein found on the surface of influenza A viruses. It mediates viral entry into host cells by binding to sialic acid receptors and catalyzing membrane fusion upon acidic activation in endosomes. HA consists of a variable globular head domain (receptor-binding, major antigenic region) and a more conserved stem domain (fusion machinery). HA is the primary antigen recognized by host antibodies and thus the major vaccine component. The continuous antigenic evolution (“drift”) in HA requires annual strain selection for vaccine production and is central to influenza’s ability to evade immunity and cause recurrent epidemics. Therapeutics targeting HA include monoclonal antibodies and experimental drugs, but most clinical drugs target the neuraminidase enzyme. HA-induced hemagglutination is the basis of standard diagnostic assays. Safety and therapeutic challenges mainly stem from rapid mutation and antigenic drift leading to immune escape, requiring regular surveillance and vaccine updates.

Other names

Hemagglutinin (influenza)HA proteinInfluenza A H3N2 hemagglutininH3 hemagglutinin

Antibody-mediated neutralization: blocks receptor binding or fusion; Prevention of viral entry: inhibits membrane fusion; Induction of protective immunity: vaccine-generated immune responses against HA epitopes