Influenza A virus hemagglutinin H3 (HA (H3))

Influenza A virus hemagglutinin H3 is a homotrimeric glycoprotein on the virus surface, consisting of HA1 and HA2 subunits linked by disulfide bonds, with a globular head domain for sialic acid receptor binding and a stem domain for membrane anchoring and pH-triggered fusion of viral and host endosomal membranes during entry.[2][3][4][5] The head (HA1) enables attachment to sialic acid on host cells like respiratory epithelium, while the stem (HA2) drives fusion at low pH (5.0-6.0), releasing viral genome.[2][3][4] H3 is one of 16 HA subtypes, key in H3N2 strains causing seasonal influenza and pandemics like 1968 Hong Kong flu; it evolves via mutations and N-glycosylation to evade immunity.[1][2][3] The receptor binding site shows variations for α2,6-linked sialic acid preference in human strains.[3] HA is the primary antigen, targeted by neutralizing antibodies, with conserved stem epitopes for broad protection efforts.[1][3][6]

Other names

H3 hemagglutininH3 HAInfluenza hemagglutinin subtype H3