Influenza A virus hemagglutinin protein H3 (Hemagglutinin H3 of Influenza A virus) (HA (specifically H3 subtype))

Hemagglutinin H3 is a **trimeric glycoprotein** found on the surface of the Influenza A virus, particularly the H3N2 subtype. It facilitates **viral entry into host cells** by binding to sialic acid–containing receptors on the cell surface and mediating the fusion of viral and host membranes after endocytosis. This dual function makes it essential for infectivity and pathogenicity. The HA protein is synthesized as a single precursor (HA0), which must be cleaved into HA1 and HA2 subunits for activation. HA is a major target of neutralizing antibodies, which block viral attachment and/or fusion. The H3 subtype is a major cause of **seasonal influenza** in humans and is associated with significant morbidity and mortality, especially among vulnerable populations. **Antigenic drift** in HA H3 enables the virus to evade preexisting immunity, necessitating frequent updates of influenza vaccines.

Other names

Hemagglutinin H3HA H3H3N2 hemagglutininInfluenza A HA H3Hemagglutinin (influenza)HA glycoprotein

Blocking viral attachment to host receptors (by antibodies); Inhibiting conformational changes required for membrane fusion (by antibodies)