Hemagglutinin (H1N1) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the pandemic H1N1 influenza virus, playing a dual role in viral infection by mediating both host cell attachment and membrane fusion [12, 17]. It exists as a homotrimer on the viral envelope, where the HA1 subunit binds to sialic acid receptors on the host respiratory epithelium, and the HA2 subunit facilitates the fusion of the viral and endosomal membranes under acidic conditions [7, 12]. As the major target of the host's neutralizing antibody response, HA is the central component of most influenza vaccines, including those developed for the 2009 H1N1 pandemic [11, 18]. Beyond vaccines, HA is an attractive therapeutic target for small-molecule entry inhibitors like umifenovir and various broadly neutralizing monoclonal antibodies that target the conserved stalk region [2, 5, 11]. These therapeutics work by either masking the receptor-binding site or stabilizing the prefusion conformation to prevent the structural changes required for fusion [3, 15]. However, the protein's high rate of antigenic drift and shift necessitates frequent vaccine updates and poses a challenge for long-term therapeutic efficacy [11, 18]. Monitoring of hemagglutination inhibition (HAI) titers remains the gold standard for assessing vaccine-induced protection and viral neutralization [1, 13, 21]. Safety concerns include the potential for vaccine-associated enhanced respiratory disease (VAERD) and the emergence of escape mutants that bypass drug inhibition [10, 11].

Other names

HAH1Hemagglutinin surface glycoproteinH1N1 HASwine-origin influenza virus hemagglutininHA0

Inhibition of viral entry by blocking receptor binding or preventing pH-dependent membrane fusion