Influenza A H1N1 hemagglutinin (HA (H1N1))

Influenza A H1N1 hemagglutinin is a homotrimeric glycoprotein present on the surface of influenza A H1N1 virus particles and is essential for viral infectivity[3][1][4][5][7]. The HA protein has two main functional domains: a globular head containing the receptor-binding site (RBD) that attaches to sialic acid on host cell surfaces, and a stem region that contains the fusion machinery, enabling the viral and endosomal membranes to fuse after endocytosis, releasing viral RNA into the host cell[3][5][7][1]. HA is initially synthesized as an HA0 precursor and is activated by host proteases cleaving it into HA1 and HA2 subunits, which remain linked by a disulfide bond[1][5][7]. Its antigenic sites are the primary targets for neutralizing antibodies and host immune responses, and HA variability via antigenic drift or shift enables escape from immunity, making it a principal target for influenza vaccines and antiviral drug development[2][4][7]. Changes in HA (mutation, glycosylation, cleavage site composition) are associated with pandemic potential, altered immune recognition, and fluctuating vaccine effectiveness[5][4][2].

Other names

Influenza hemagglutinin H1H1 HAHemagglutinin of influenza A H1N1HA1/HA2H1 subtype HA

Neutralizing antibodies target the HA protein to block viral attachment or fusion; Antigenic drift and shift allow escape from existing immunity; Vaccines induce immunity by exposing the immune system to HA or its epitopes