Hemagglutinin (H9) of Influenza A virus (HA)

The Hemagglutinin (HA) protein of the H9N2 influenza virus is a major surface glycoprotein essential for the viral life cycle, specifically mediating host cell entry. It functions as a lectin, binding to sialic acid-linked receptors on the host cell surface—preferring alpha 2-3 linkages in avian hosts and increasingly showing affinity for alpha 2-6 linkages in human-like receptors (PMID: 21107321). Following endocytosis, the HA protein undergoes a critical pH-dependent conformational change that triggers the fusion of the viral envelope with the host endosomal membrane, releasing the viral genome into the cytoplasm (PMID: 11017100). H9N2 is considered a low pathogenic avian influenza (LPAI) virus but is a significant public health threat due to its widespread endemicity in poultry and its potential for zoonotic transmission to humans (WHO). It also serves as a frequent donor of internal genes for other highly pathogenic influenza viruses, such as H5N1 and H7N9 (PMID: 24048893). Therapeutically, HA is the primary target for neutralizing antibodies induced by vaccination and is the focus of small-molecule inhibitors like Umifenovir, which blocks the fusion process (PMID: 30854234). Monitoring the antigenic evolution of the H9 protein is vital for the development of effective vaccines and diagnostic tools to prevent a potential pandemic.

Other names

HAH9HemagglutininSurface glycoproteinH9 HA

Inhibition of viral entry by blocking receptor binding or preventing the pH-dependent conformational change required for membrane fusion.