Hemagglutinin (HA) (H5 and H7 subtypes) (HA (H5/H7))

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza A virus, with the H5 and H7 subtypes being particularly significant due to their association with highly pathogenic avian influenza (HPAI) [1, 10]. HA plays a dual role in the viral life cycle: the HA1 subunit mediates attachment to host cell sialic acid receptors, while the HA2 subunit facilitates the fusion of the viral envelope with the host endosomal membrane following a low-pH-induced conformational change [1, 7]. In H5 and H7 strains, the presence of a polybasic cleavage site allows the protein to be processed by ubiquitous intracellular proteases like furin, leading to systemic infection and high mortality rates in avian species and posing a severe zoonotic threat to humans [7, 15]. As the major target for the host immune system, HA is the central component of both seasonal and pandemic vaccines, where the induction of neutralizing antibodies is the primary goal [1, 16]. Therapeutic interventions targeting HA include small molecules like umifenovir that inhibit membrane fusion and broadly neutralizing monoclonal antibodies that target the conserved stem region [3, 4]. Ongoing research focuses on developing "universal" vaccines by targeting these conserved regions to provide broad protection against diverse H5 and H7 lineages [1, 12]. Understanding the structural evolution and receptor specificity of H5 and H7 HA is critical for pandemic preparedness and the development of effective countermeasures [10, 14].

Other names

H5HAH7HAInfluenza A virus hemagglutinin H5Influenza A virus hemagglutinin H7HA0HA1HA2Hemagglutinin precursor

Inhibition of viral entry and membrane fusion by stabilizing the pre-fusion conformation, blocking the receptor-binding site, or preventing proteolytic cleavage of the HA0 precursor [1, 3, 7].