Hemagglutinin (H9N2 avian influenza virus) (HA)

The H9N2 avian influenza virus hemagglutinin (HA) is the primary surface glycoprotein of the H9N2 virus, playing an essential role in viral attachment and entry into host cells. As a class I fusion protein, it exists as a homotrimer on the viral envelope and mediates binding to host sialic acid receptors; specifically, avian-adapted H9N2 HA typically binds alpha-2,3-linked sialic acids, while mammalian adaptation often involves a switch to alpha-2,6-linked receptors [9, 12, 19]. Following receptor binding and endocytosis, HA undergoes a dramatic pH-triggered conformational change within the acidic environment of the endosome to facilitate the fusion of viral and host membranes [4, 14]. This molecule is the chief target of the host's neutralizing antibody response and is consequently the central component of influenza vaccines, including inactivated and recombinant formulations used in poultry and human clinical trials [18, 20]. Therapeutically, H9N2 HA is targeted by entry inhibitors such as umifenovir (arbidol), which stabilizes the pre-fusion state, and broad-spectrum neutralizing antibodies like MEDI8852 that target the conserved stem region [4, 6]. Because H9N2 viruses are endemic in global poultry and act as genetic donors for highly pathogenic reassortants like H7N9 and H10N8, the HA protein is a critical focus for surveillance and pandemic preparedness [1, 11, 17].

Other names

H9 HemagglutininHemagglutinin H9HAViral surface glycoprotein HAH9N2 HA

Inhibition of membrane fusion, Neutralization of viral infectivity, Receptor binding blockade