Hemagglutinin (Influenza A and B) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of influenza A and B viruses, functioning as a homotrimeric class I fusion protein (UniProt: P03435). It is responsible for recognizing and binding to sialic acid-containing receptors on the surface of host epithelial cells, which triggers viral entry via endocytosis (PubMed: 10888841). Following internalization, the acidic environment of the endosome induces a major conformational change in the HA2 subunit that facilitates the fusion of the viral envelope with the host cell membrane (PubMed: 11069777). As the principal target for neutralizing antibodies, HA is the key antigen in most seasonal influenza vaccines. However, the protein's high mutational plasticity, particularly in the globular head domain, allows the virus to evade immune detection through a process known as antigenic drift (PubMed: 29466333). Therapeutic strategies targeting HA include small molecule fusion inhibitors like Umifenovir and broadly neutralizing antibodies that target the more conserved stem region to provide cross-strain protection (DrugBank: DB13609).

Other names

HAInfluenza hemagglutininViral surface glycoproteinHA0HA1HA2

Inhibition of viral attachment to host sialic acid receptors and prevention of pH-dependent membrane fusion within the endosome (PubMed: 22226352).