Influenza A H1 hemagglutinin (HA (H1 subtype))

Influenza A H1 hemagglutinin is a trimeric, integral viral surface glycoprotein essential for the infectivity of influenza A (H1 subtype) viruses[1][2][3][7]. Each monomer is made of two subunits, HA1 (globular head, binds sialic acid on host cells) and HA2 (stem domain, anchors to virus membrane and mediates fusion through conformational change at low endosomal pH)[1][2][3][7]. It enables viral attachment to host epithelial cells and, after initial endocytosis, drives viral and host membrane fusion to release the viral genome. HA is also the main viral antigen, making it a principle target for neutralizing antibodies, vaccine design, and antibody therapeutics[3][5][7]. The H1 subtype is historically significant—causing the 1918 and 2009 pandemics—and is a focus of influenza surveillance and therapeutic research. HA's high variability, especially in the head domain, complicates immune control and requires continual vaccine updates.

Other names

Hemagglutinin (influenza)Influenza virus hemagglutininH1 hemagglutininHA protein

Neutralizing antibodies block receptor binding or membrane fusion; Inhibitors prevent conformational changes required for fusion; Drugs may prevent viral attachment or entry via HA