Influenza virus hemagglutinin and neuraminidase antigen (HA/NA)

Hemagglutinin and neuraminidase are **surface glycoprotein antigens of the influenza virus** essential for viral infectivity and are the primary targets of the host immune response and antiviral therapies. Hemagglutinin (HA) mediates *viral attachment to sialic acid-containing receptors on host cells* and triggers membrane fusion for viral entry; it is also the major antigen involved in neutralization by antibodies and has multiple subtypes (H1–H18 for influenza A)[5][7]. Neuraminidase (NA) is an *exosialidase enzyme* that cleaves sialic acid residues to release progeny virions from infected cells and prevent self-aggregation; it also exists in defined subtypes (N1–N11 for influenza A)[1][2][4]. Both proteins are highly variable, facilitating antigenic drift and shift, leading to recurrent seasonal epidemics and occasional pandemics. Current antiviral drugs (e.g., oseltamivir, zanamivir) target neuraminidase activity, while vaccines aim to elicit neutralizing anti-HA antibodies. Their centrality to the viral life cycle and immune evasion make them critical targets for influenza therapeutics and prevention[1][2][5][7][9].

Other names

HA (hemagglutinin)NA (neuraminidase)influenza virus HAinfluenza virus NAhemagglutinin antigenneuraminidase antigen

Neuraminidase inhibitors bind NA and block enzymatic cleavage of sialic acid, preventing viral release and spread[2][4]. Neutralizing antibodies bind HA (or its stem/receptor-binding domain), blocking viral entry or mediating immune clearance[5][7][9].