Influenza A virus Hemagglutinin (HA) (HA)

Influenza A virus Hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus and a critical mediator of viral entry into host cells. It is synthesized as a precursor polypeptide (HA0) that is subsequently cleaved into two subunits: HA1, which forms the distal globular head, and HA2, which forms the proximal stalk or stem region (Gamblin & Skehel, 2010). The head region (HA1) contains the receptor-binding site (RBS) that specifically recognizes and binds to sialic acid residues on host cell glycoproteins and glycolipids, initiating the process of receptor-mediated endocytosis (UniProt P03435). As the most exposed and immunodominant portion of the virus, the head region is the primary target for neutralizing antibodies induced by seasonal influenza vaccines (CDC, 2023). However, the head is highly plastic and undergoes rapid evolution through a process known as antigenic drift, which allows the virus to escape pre-existing host immunity (Wiley & Skehel, 1987). This variability necessitates the annual reformulation of vaccines to match circulating strains. While the head region remains a major focus for vaccine development, its high mutation rate presents a significant challenge for achieving broad-spectrum or universal protection against diverse influenza strains.

Other names

HA1 subunitGlobular head domainReceptor-binding domainHemagglutinin subunit 1Viral hemagglutinin

Inhibition of viral attachment to host cell sialic acid receptors by binding to the globular head domain, thereby neutralizing viral infectivity.