Hemagglutinin antigen of Influenza A virus H3N2 subtype (HA)

Hemagglutinin antigen of Influenza A virus H3N2 subtype is a trimeric viral surface glycoprotein essential for infectivity of the influenza A virus. It mediates viral entry by binding sialic acid-containing receptors on host cells and fusing the viral envelope with the endosomal membrane following endocytosis[1][2][3][5][7]. HA exists as a precursor (HA0) that is cleaved into HA1 (receptor binding) and HA2 (fusion) subunits. The HA1 globular head contains the receptor binding domain, responsible for attachment to host cells, and is also the main site for antigenic variation, which enables the virus to escape immune detection[1][2][5]. HA2 contains the fusion machinery that is activated at low pH to mediate endosomal membrane fusion, permitting release of the viral genome into the cytoplasm[1][2][3][5][6]. The H3N2 subtype designation refers to a specific combination of hemagglutinin (H3) and neuraminidase (N2) antigens, with H3 HA being a major determinant of host specificity and immune response. HA is the principal target of neutralizing antibodies elicited by infection or vaccination, and its high variability is a central challenge for influenza vaccine design[3][5][7]. No direct small molecule therapeutics target HA in clinical use, but efforts to develop broadly neutralizing antibodies and next-generation vaccines are ongoing.

Other names

Influenza hemagglutinin H3Influenza A H3 hemagglutininHA (general abbreviation)H3N2 hemagglutininH3N2 influenza A virus hemagglutinin

Antibodies (or vaccines generating antibodies) block viral entry by: - Inhibiting HA binding to sialic acid receptors (blocking attachment) - Preventing HA-mediated membrane fusion (blocking endosomal fusion step)