Hemagglutinin (Influenza A virus) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A virus and is essential for viral entry into host cells (UniProt: P03437). It functions as a homotrimeric protein that mediates two key processes: binding to sialic acid receptors on the host cell surface and facilitating the fusion of the viral envelope with the endosomal membrane following endocytosis (Gamblin & Skehel, 2010, PubMed: 20944003). The protein is divided into a globular head (HA1), which contains the receptor-binding site, and a stalk region (HA2), which contains the fusion machinery (NCBI: Influenza Virus). HA is the principal target for neutralizing antibodies and is the primary component of most influenza vaccines (CDC: Influenza Vaccines). Therapeutic interventions include monoclonal antibodies like MEDI8852 that target conserved epitopes in the stalk to provide broad-spectrum protection, as well as small-molecule inhibitors like umifenovir that prevent the conformational changes necessary for membrane fusion (DrugBank: DB06144). A major challenge in targeting HA is its high rate of mutation, or antigenic drift, which allows the virus to escape existing immunity and necessitates the annual reformulation of vaccines (WHO: Influenza).

Other names

Influenza A virus hemagglutininHA proteinHemagglutinin antigenH1-H18Hemagglutinin antigen of influenza A virus – immunological epitope complex