Hemagglutinin protein of Influenza A virus subtype H5N1 (HA)

The **hemagglutinin protein** of Influenza A virus subtype H5N1 (**HA**) is a surface glycoprotein and class I viral fusion protein essential for viral infectivity. It mediates binding of the influenza virus to sialic acid-containing receptors on host cells, triggering endocytosis and facilitating viral entry through pH-dependent membrane fusion in the endosome[2][3][4][6]. HA is the primary antigenic determinant of influenza viruses, inducing robust antibody responses and serving as the main target for vaccine and antibody-based therapies. Structural variation and antigenic drift in HA enable viral immune evasion and play a central role in influenza pathogenicity and epidemiology, particularly in highly virulent strains such as H5N1[3][4].

Other names

hemagglutininHAinfluenza hemagglutininhaemagglutinin (British English)Influenza A hemagglutinin

Neutralizing antibodies block receptor binding and prevent viral entry; Fusion inhibitors prevent the conformational changes required for membrane fusion; Vaccines induce antibody responses against HA, preventing infection