Influenza A virus (H1N1) hemagglutinin (HA)

The Influenza A 2009 hemagglutinin (HA) glycoprotein is the primary surface antigen of the H1N1 pandemic virus (H1N1pdm09), essential for viral attachment and entry into host cells (Xu et al., 2010, Science, PMID: 20300135). The HA molecule is a homotrimer where each monomer consists of a globular head domain (HA1) and a stalk domain (HA2). The HA head contains the receptor-binding site (RBS) that specifically targets alpha-2,6-linked sialic acids in the human respiratory tract and hosts five major antigenic sites: Sa, Sb, Ca1, Ca2, and Cb (Garten et al., 2009, Science, PMID: 19843921). These sites are the primary targets for neutralizing antibodies produced during infection or vaccination, making the HA head the focal point of seasonal vaccine development. However, the high rate of mutation in these antigenic sites, known as antigenic drift, necessitates frequent vaccine updates to maintain efficacy (Whittle et al., 2011, PNAS, PMID: 21835245). Therapeutic interventions include monovalent vaccines and investigational monoclonal antibodies like CH65 and 5J8, which bind specifically to the HA head to block receptor interaction. Monitoring the evolution of these antigenic sites is critical for global surveillance and pandemic preparedness.

Other names

H1N1pdm09 HAHemagglutininH1HA1HA2A/California/04/2009 HASurface glycoprotein

Neutralization of viral infectivity by binding to the globular head domain, thereby sterically hindering the interaction between the viral receptor-binding site and host cell sialic acid receptors (Xu et al., 2010, Science, PMID: 20300135).