Influenza virus hemagglutinin (HA) (HA)

Influenza virus hemagglutinin (HA) is a homotrimeric surface glycoprotein essential for the infectivity of influenza A and B viruses (UniProt: P03435). It serves two primary roles: recognizing and binding to sialic acid-containing receptors on the host cell surface to initiate infection, and facilitating the fusion of the viral envelope with the host endosomal membrane under acidic conditions (Gamblin & Skehel, 2010; PMID: 20959021). The protein is composed of a globular head (HA1), which contains the receptor-binding site, and a stalk region (HA2), which contains the fusion machinery. As the primary target of neutralizing antibodies, HA is the central antigen in most influenza vaccines, including inactivated, live-attenuated, and recombinant formulations (NIH, 2023). However, the high mutation rate of the HA head region, known as antigenic drift, allows the virus to escape host immunity, requiring continuous surveillance and annual vaccine updates. Therapeutic strategies targeting HA include small-molecule inhibitors like umifenovir that block membrane fusion and broadly neutralizing monoclonal antibodies that target the conserved stem region to provide protection against multiple viral subtypes.

Other names

HemagglutininHA proteinViral hemagglutininInfluenza HA antigenHA1/HA2 subunitInfluenza virus surface glycoprotein

Inhibition of viral entry by blocking the binding of the HA1 subunit to host sialic acid receptors or by preventing the pH-induced conformational change in the HA2 subunit required for membrane fusion (Skehel & Wiley, 2000; PMID: 10961938).