Influenza A virus subtype H3N2 hemagglutinin (HA)

Influenza A virus subtype H3N2 hemagglutinin (HA) is a critical surface glycoprotein that mediates the initial stages of viral infection, including host cell attachment and membrane fusion [1, 2, 10]. It functions as a homotrimeric Class I fusion protein, where each monomer consists of two subunits, HA1 and HA2, produced by the proteolytic cleavage of a precursor HA0 [1, 10, 14]. The HA1 subunit contains the receptor-binding site that specifically recognizes α2,6-linked sialic acids on human respiratory epithelial cells, while the HA2 subunit facilitates the fusion of the viral envelope with the endosomal membrane following a low-pH-induced conformational change [1, 7, 12]. As the primary target of the host's neutralizing antibody response, HA is the key component of seasonal influenza vaccines [4, 11, 16]. However, H3N2 HA is subject to rapid antigenic drift, characterized by the accumulation of mutations in the globular head that allow the virus to evade pre-existing immunity and necessitate annual vaccine updates [5, 16, 17]. Therapeutic interventions targeting HA include fusion inhibitors like umifenovir and broadly neutralizing monoclonal antibodies that target the more conserved stalk region to provide broader protection across different influenza strains [8, 10, 12].

Other names

H3 HA [1, 4]Hemagglutinin protein [2, 10]HA1/HA2 [1, 10, 14]H3N2 HA [7, 13]Hemagglutinin (H3) [1, 9]

Inhibition of viral entry by blocking receptor binding or preventing the low-pH-induced conformational change required for membrane fusion [3, 8, 10, 12, 15].