Influenza A virus H3N2 hemagglutinin (HA) (H3N2 HA)

The Influenza A H3N2 hemagglutinin (HA) is the primary surface glycoprotein of the H3N2 subtype of the influenza A virus, which has been a major cause of seasonal epidemics and pandemics since 1968 (NIH, 2024). It functions as a class I fusion protein, responsible for both the attachment of the virus to host cell receptors and the subsequent fusion of the viral and host membranes (UniProt, 2024). The receptor binding site (RBS) is a specialized pocket on the globular head of the HA1 subunit that specifically recognizes α2,6-linked sialic acid residues on human respiratory epithelial cells (PubMed, 2012). Due to its essential role in the initial stages of infection, the HA protein, and specifically its RBS, is the principal target for seasonal influenza vaccines and the development of neutralizing monoclonal antibodies (NIH, 2024). However, the HA protein undergoes continuous antigenic drift, characterized by the accumulation of mutations in the antigenic sites surrounding the RBS, which allows the virus to escape pre-existing immunity (PubMed, 2016). This high rate of mutation necessitates the annual reformulation of influenza vaccines and complicates the development of broad-spectrum antivirals (CDC, 2024). Therapeutic strategies targeting the HA include vaccines that elicit RBS-blocking antibodies, monoclonal antibodies that neutralize the virus by binding to the head or stem regions, and small-molecule inhibitors like Umifenovir that interfere with the conformational changes required for membrane fusion (PubMed, 2013).

Other names

HAHemagglutininH3 HAH3N2 HemagglutininH3N2 HA1H3N2 HA receptor binding siteH3N2 surface glycoprotein

Inhibition of viral entry by blocking the receptor binding site to prevent attachment or binding to the stem region to inhibit pH-triggered membrane fusion.