Hemagglutinin (Influenza A virus H1N1) (HA)

Hemagglutinin (HA) is the major surface glycoprotein of the Influenza A virus, specifically the H1N1 strain responsible for the 2009 pandemic (A/H1N1pdm09). It functions as a class I fusion protein, mediating viral entry by binding to alpha-2,6-linked sialic acid receptors on human respiratory epithelial cells and facilitating the fusion of the viral envelope with the host endosomal membrane (UniProt: P03452). In the context of inactivated viral vaccines, HA serves as the principal antigen that triggers the host's adaptive immune system to produce neutralizing antibodies (CDC, 2023). These antibodies typically target the globular head of the HA protein to block receptor binding, although newer therapeutic approaches focus on the more conserved stem region to achieve broader protection (PubMed: PMID 20023160). The 2009 H1N1 HA was notable for its origin from a swine-lineage reassortant virus, which necessitated the rapid development of monovalent inactivated vaccines to control the pandemic spread (WHO, 2009). Monitoring the antigenic evolution of HA is critical for vaccine strain selection due to the continuous process of antigenic drift (PubMed: PMID 23435313).

Other names

H1 HAHemagglutinin proteinHA1/HA2H1N1pdm09 HemagglutininSurface glycoprotein

Inactivated viral antigens containing Hemagglutinin induce the production of neutralizing antibodies that bind to the HA head or stem, preventing the virus from attaching to host sialic acid receptors or undergoing membrane fusion, thereby neutralizing viral infectivity (CDC, 2023; PubMed: PMID 20023160).