Influenza A virus H3 hemagglutinin (HA) (H3 HA)

Influenza A virus H3 hemagglutinin (HA) is a major surface glycoprotein of the H3N2 subtype, which is a primary cause of seasonal respiratory infections in humans [5, 13]. The protein exists as a homotrimer, where each monomer consists of two subunits, HA1 and HA2 [3, 5]. The receptor-binding region, located within the globular head of the HA1 subunit, is responsible for recognizing and binding to sialic acid receptors on the host cell surface, initiating viral entry [4, 8, 11]. Following attachment, the HA2 subunit undergoes a pH-dependent conformational change in the endosome to facilitate fusion between the viral and host membranes [5, 10]. Because of its essential role in the viral life cycle and its exposure on the virion surface, the H3 HA receptor-binding region is the primary target for neutralizing antibodies induced by seasonal vaccines [2, 9, 16]. It is also a focus for the development of novel entry inhibitors, including monoclonal antibodies and small-molecule drugs like umifenovir [1, 3, 7]. However, the high rate of antigenic drift in the receptor-binding region allows the virus to escape host immunity, necessitating frequent updates to vaccine compositions [15, 16]. Therapeutic challenges include the emergence of strain-specific resistance and the need for broadly neutralizing agents that can target conserved epitopes within the variable head domain [3, 11].

Other names

Hemagglutinin H3H3N2 hemagglutininHA1 subunitReceptor-binding domainRBDReceptor-binding siteRBSH3 HA receptor-binding region

Inhibition of viral attachment to host cell sialic acid receptors and prevention of hemagglutinin-mediated membrane fusion [3, 5, 7].