Influenza A virus hemagglutinin (H1N1) (HA)

Influenza A virus hemagglutinin (H1N1) is a homotrimeric surface glycoprotein essential for the attachment and entry of the influenza virus into host cells (UniProt P03452). It acts as a lectin by binding to sialic acid receptors on the respiratory epithelium, initiating receptor-mediated endocytosis (Skehel & Wiley, 2000). Following endocytosis, the acidic environment of the endosome triggers a structural rearrangement in the hemagglutinin molecule, which facilitates the fusion of the viral and endosomal membranes (PubMed: 10857828). This process is vital for the release of the viral genome into the host cell cytoplasm, leading to infection and the clinical manifestation of influenza (CDC, 2023). In medical therapeutics, inactivated H1N1 hemagglutinin is the central component of seasonal influenza vaccines, acting as the primary antigen to stimulate an adaptive immune response (StatPearls: Influenza Vaccine). When administered, the protein is processed by dendritic cells and presented via MHC class II molecules to helper T-cells, which in turn activate B-cells to produce neutralizing antibodies (PubMed: 22226730). These antibodies target the hemagglutinin protein, effectively neutralizing the virus by preventing its attachment to host cells during subsequent exposures. Beyond vaccines, hemagglutinin is also a target for antiviral drugs like umifenovir, which inhibits the membrane fusion process, and various monoclonal antibodies currently in development (DrugBank DB13609). Due to the high mutation rate of the hemagglutinin gene, continuous surveillance and frequent vaccine updates are required to combat antigenic drift and maintain public health (NIH: NIAID).

Other names

HemagglutininH1 HAInfluenza A virus H1N1 surface glycoproteinHA1/HA2 subunitH1N1 antigen

The inactivated hemagglutinin antigen is processed by antigen-presenting cells and presented to T-cells and B-cells, inducing the production of neutralizing antibodies that block viral attachment and entry into host cells.