Hemagglutinin protein of H9N2 avian influenza virus (HA)

The **hemagglutinin protein of H9N2 avian influenza virus** is a type I viral envelope glycoprotein that mediates the initial attachment of the virus to host cell receptors and facilitates fusion between the viral and host membranes. Hemagglutinin (HA) recognizes sialic acid-containing receptors on the surface of host epithelial cells; in avian H9N2 viruses, HA generally prefers α2-3-linked sialic acids but certain mutations (such as Q226L and I155T) can shift preference toward human-type α2-6-linked sialic acids, increasing zoonotic potential and posing a pandemic risk[2][3][4][6][8]. HA is the primary target for neutralizing antibodies and is responsible for viral antigenicity, but undergoes rapid genetic and antigenic evolution, contributing to immune escape and complicating effective vaccine design[5][8]. The biological roles of HA include host range determination, infectivity, and adaptation; its structure and sequence are closely monitored as molecular markers for epidemic and pandemic surveillance[2][5]. Therapies are under investigation to target HA-mediated entry, using neutralizing antibodies or receptor analog inhibitors, but no direct HA inhibitors are currently in clinical use. Rapid mutation and host adaptation are major safety and public health concerns.

Other names

Hemagglutinin (HA)H9N2 HAInfluenza A virus hemagglutininH9N2 Influenza hemagglutininAvian influenza H9N2 HA

Viral entry inhibitors: Block HA binding to sialic acid receptors or interfere with membrane fusion Neutralizing antibodies: Prevent HA from binding host cells or mediate immune clearance[5][8]