Influenza A H3 hemagglutinin (HA (H3))

Influenza A H3 hemagglutinin is a homotrimeric, surface glycoprotein of influenza A viruses, specifically subtype H3, that mediates viral attachment and entry into host cells. Each monomer is synthesized as a precursor (HA0) and proteolytically cleaved into HA1 (head domain, mediating receptor binding) and HA2 (stem domain, mediating membrane fusion). The head region interacts with sialic acid-containing receptors on the host cell, facilitating viral entry via endocytosis, while the stem region enables low pH-triggered fusion of the viral and endosomal membranes[1][3][5]. H3 hemagglutinin is highly immunogenic and is the principal target for neutralizing antibodies, making it the focus for seasonal and pandemic influenza vaccines. Structural variability, especially in the receptor-binding domain, underlies immune evasion and vaccine escape. There are five major antigenic sites (A–E) on H3 hemagglutinin, all located in the head domain, with ongoing antigenic drift requiring continuous vaccine update[3][7]. The protein is essential for influenza virus infectivity and pathogenesis, and has served as a primary target for both prophylactic and therapeutic interventions.

Other names

influenza hemagglutininflu hemagglutininHAH3 HAH3 hemagglutininhemagglutinin H3

antibody-mediated receptor blockade (prevents binding to sialic acid receptors), inhibition of membrane fusion (antibody stabilization of pre-fusion state), target for vaccine-induced immune response