Hemagglutinin protein of influenza A and B virus (HA)

Hemagglutinin protein is a homotrimeric, viral surface glycoprotein integral to the infectivity of influenza A and B viruses. It is the primary antigen on the viral envelope and mediates attachment to sialic acid-containing receptors on host cells, followed by fusion of viral and host membranes in response to low pH in the endosome[1][3][5][7]. HA is synthesized as a single precursor (HA0) and cleaved into HA1 and HA2 subunits, forming a trimer where each monomer has a receptor-binding "head" and a fusion "stalk"[2][7]. There are multiple hemagglutinin subtypes in influenza A (H1–H18) and lineages in influenza B, corresponding to strain specificity and host adaptation[3][5]. HA is subject to frequent antigenic mutation, enabling immune evasion and posing challenges to vaccine efficacy and pandemic preparedness[3][5]. Therapeutic targeting of HA is achieved by neutralizing antibodies and vaccine-induced responses that prevent viral entry. The hemagglutinin titers in patient samples and vaccines are standard biomarkers for immunity verification and serological monitoring[3][6]. Major safety and therapeutic challenges include rapid evolution (antigenic drift and shift), potential for universal vaccine development, and rare but possible immune-related complications. Hemagglutinin remains a central therapeutic and diagnostic target in influenza research, vaccine formulation, and pandemic control[3][5][6][7].

Other names

Influenza hemagglutininHAhemagglutinin glycoprotein

- Inhibition of viral entry by steric blockade (antibodies) - Inhibition of membrane fusion (antibodies, fusion inhibitors) - Vaccine-induced neutralizing antibody production