Hemagglutinin H3 (H3)

Hemagglutinin H3 is a primary surface glycoprotein of the Influenza A virus, most notably the H3N2 subtype which has circulated in humans since the 1968 pandemic (NCBI: TaxID 11320). It functions as a trimeric lectin that recognizes and binds to alpha-2,6-linked sialic acid receptors on human respiratory epithelial cells, triggering viral entry via endocytosis (UniProt: P03437). Following internalization, a pH-induced conformational change in the H3 protein mediates the fusion of the viral envelope with the host endosomal membrane, releasing the viral genome into the cytoplasm (PubMed: 30104375). As the principal target of the host immune response, H3 is the key antigen in seasonal flu vaccines; however, its rapid evolution through antigenic drift frequently necessitates vaccine reformulation (PubMed: 29439166). Therapeutic interventions targeting H3 include fusion inhibitors like umifenovir and various investigational broadly neutralizing antibodies, such as MEDI8852, designed to target the conserved stem region of the protein (PubChem CID: 131411; ClinicalTrials.gov: NCT02603952).

Other names

H3 hemagglutininInfluenza A virus H3N2 hemagglutininHA3Hemagglutinin protein H3Influenza A virus (A/Hong Kong/1/1968(H3N2)) hemagglutinin

Inhibition of viral attachment to host sialic acid receptors and prevention of pH-dependent membrane fusion within the endosome (PubMed: 28135201).