Seasonal influenza virus hemagglutinin and neuraminidase antigens (HA/NA)

Seasonal influenza virus hemagglutinin (HA) and neuraminidase (NA) are the primary surface glycoproteins of influenza A and B viruses, playing critical roles in the viral life cycle and serving as the principal targets for vaccines and antiviral drugs (Source: CDC). HA is a trimeric lectin responsible for viral attachment to sialic acid-containing receptors on the host cell surface and subsequent membrane fusion within the endosome, while NA is a tetrameric enzyme that facilitates the release of progeny virions by cleaving sialic acid residues that would otherwise tether the virus to the cell or cause viral aggregation (Source: UniProt). Because these proteins are under constant evolutionary pressure from the host immune system, they undergo 'antigenic drift,' characterized by the accumulation of point mutations that can lead to the emergence of new seasonal strains capable of evading prior immunity (Source: WHO). Most current seasonal vaccines are designed to elicit neutralizing antibodies against the HA protein to prevent infection, while therapeutic strategies like neuraminidase inhibitors (NAIs) target the enzymatic activity of NA to limit the spread of the infection within the respiratory tract (Source: PubMed).

Other names

Influenza surface glycoproteinsHA and NA antigensFlu antigensHemagglutinin and Neuraminidase

Neuraminidase inhibitors (e.g., oseltamivir) competitively bind to the active site of the NA enzyme, preventing the cleavage of sialic acid and thus inhibiting the release of new viral particles from the host cell (Source: StatPearls). Hemagglutinin-targeted interventions, primarily vaccines, work by inducing antibodies that bind to the HA protein, blocking viral attachment to host receptors or preventing the conformational change required for membrane fusion (Source: Nature Reviews Microbiology).