Influenza virus hemagglutinin (HA)

Influenza virus hemagglutinin (HA) is a major surface glycoprotein found on the envelope of influenza A and B viruses, functioning as a homotrimeric Class I fusion protein. Its primary biological role is to mediate the attachment of the virus to sialic acid-containing receptors on the surface of host epithelial cells and to facilitate the subsequent fusion of the viral envelope with the endosomal membrane following endocytosis (PubMed: 22976116). HA is the principal target of the host's neutralizing antibody response and is the primary component of seasonal influenza vaccines, which aim to induce antibodies that block the receptor-binding site (StatPearls: NBK459363). Due to the high rate of mutation in the HA gene, a process known as antigenic drift, the protein's structure constantly evolves, necessitating the annual reformulation of vaccines to match circulating strains (CDC: Antigenic Characterization). Beyond vaccines, HA is a target for therapeutic intervention, including small-molecule fusion inhibitors like Umifenovir and broadly neutralizing monoclonal antibodies designed to target the more conserved stem region of the protein (NCBI: PMC6136651).

Other names

HemagglutininHA proteinInfluenza A virus hemagglutininInfluenza B virus hemagglutininH1-H18 subtypesSurface glycoprotein HA

Inhibition of viral attachment to sialic acid receptors, blockade of pH-dependent conformational changes required for membrane fusion, and neutralization of viral entry via antibody-mediated interference.