Influenza virus hemagglutinin (HA) stem domain (HA stem)

The influenza virus hemagglutinin (HA) stem domain is a highly conserved structural component of the primary surface glycoprotein of the influenza virus (UniProt, 2024). Unlike the globular head domain, which is subject to rapid antigenic drift, the stem domain is relatively invariant across multiple influenza subtypes, making it an ideal target for universal influenza vaccines and broadly neutralizing antibodies (NIH, 2023). Its primary biological function is to facilitate the fusion of the viral envelope with the host cell's endosomal membrane, a process triggered by the acidic environment of the endosome (PubMed, 2022). Therapeutic interventions targeting the HA stem typically function by binding to and stabilizing the pre-fusion conformation of the protein, effectively blocking the membrane fusion process and preventing the release of the viral genome into the host cytoplasm (Nature Communications, 2021). This target is central to efforts in developing long-lasting, cross-reactive immunity against both seasonal and pandemic influenza strains (Science, 2020). Broadly neutralizing antibodies (bnAbs) such as FI6 and CR9114 have demonstrated the ability to bind this region across diverse influenza A and B groups (Cell, 2019). Small molecule inhibitors like Umifenovir and JNJ-63623872 are also being developed or used to mimic the binding of these antibodies, providing a potential route for broad-spectrum antiviral therapy (Science, 2019). Despite its potential, the stem domain is less immunogenic than the head, presenting a challenge for vaccine design that requires specialized scaffolds to focus the immune response (Vaccines, 2021).

Other names

Hemagglutinin stalk domainHA2 subunitInfluenza HA fusion domainConserved stem regionHA stalk

Inhibition of pH-dependent conformational change and membrane fusion, preventing viral genome release into the host cytoplasm.