Hemagglutinin H5 antigen (H5 HA)

Hemagglutinin H5 antigen is the major envelope glycoprotein of influenza A viruses of the H5 subtype and functions as the principal viral protein mediating attachment to and entry into host cells. It exists as a homotrimeric, integral membrane class I fusion protein, with each monomer consisting of HA1 (receptor binding) and HA2 (fusion) subunits generated by cleavage of the HA0 precursor. H5 HA recognizes sialic acid residues on host epithelial cells, prompting endocytosis and subsequent viral-host membrane fusion triggered by acidic pH-induced conformational changes in HA2. H5 HA is the major target of host neutralizing antibodies, is highly variable (leading to antigenic drift and immune escape), and is central to the pathogenesis, epidemiology, and control of avian and zoonotic influenza. Neutralizing monoclonal antibodies and vaccines targeting the H5 HA head or stem domains are in clinical and preclinical use; repeated antigenic change is a key challenge for durable protection. If you need specific protein/gene accession numbers or additional molecular detail (e.g., Uniprot, NCBI gene), clarify which influenza strain as H5 is a subtype defined by its antigenicity.

Other names

H5 hemagglutininInfluenza A virus H5 hemagglutininH5N1 hemagglutinin

Neutralizing antibodies bind and block receptor binding or fusion function by stabilizing critical domains of H5 HA, preventing conformational changes required for membrane fusion. Vaccination induces neutralizing antibodies that target major antigenic sites, thereby blocking viral entry.