Influenza A virus hemagglutinin 5 antigen (HA (H5))

Influenza A virus hemagglutinin 5 antigen is a trimeric glycoprotein found on the surface of influenza A viruses of the H5 subtype, including highly pathogenic avian strains such as H5N1. It is the principal viral antigen and facilitates two essential steps in the viral life cycle: binding to sialic acid–containing receptors on host cells and mediating fusion of the viral envelope with the host cell membrane[4][2][1]. HA is the major target of neutralizing antibodies and defines viral subtype specificity together with neuraminidase. The protein’s antigenic sites are highly variable, driving immune escape and necessitating frequent vaccine updates. Subtype H5 is of particular concern due to its pandemic potential and history of severe disease in humans and poultry. The hemagglutinin inhibition assay is a key tool for measuring immunity and vaccine match[6][5]. HA's structure and antigenicity are major research focuses for universal influenza vaccine and antibody therapy development[5][2][4].

Other names

Hemagglutinin type 5HA subtype H5H5 antigenH5 hemagglutinin

Neutralizing antibodies bind to HA, preventing receptor (sialic acid) binding or membrane fusion, thereby blocking viral entry[5][2][4]. Vaccines induce generation of such neutralizing antibodies targeting HA Small-molecule antivirals may not directly target HA, but reduction in viral replication advances HA-mediated effects