Influenza A virus group 1 hemagglutinin stem region (HA stem (Group 1))

The Influenza A virus group 1 hemagglutinin stem region is a highly conserved structural domain of the hemagglutinin (HA) glycoprotein, which serves as the primary surface antigen for influenza A viruses. While the globular head of the HA protein undergoes rapid antigenic drift to escape host immunity, the stem region remains nearly invariant across the diverse subtypes within Group 1, including H1, H2, H5, and H9 (Ekiert et al., 2009, Science). This high level of conservation makes the stem region a premier target for the development of universal influenza vaccines and broadly neutralizing antibodies (bnAbs) capable of protecting against both seasonal and pandemic strains (Sui et al., 2009, Nature). Biologically, the stem region is responsible for mediating the fusion between the viral envelope and the host endosomal membrane, a process triggered by the acidic environment of the endosome (Harrison, 2008, Nature Reviews Microbiology). Therapeutic antibodies such as CR6261 bind to a hydrophobic pocket in the stem and sterically block the pH-induced conformational changes required for membrane fusion (Throsby et al., 2008, PLoS ONE). By preventing this fusion event, these agents effectively neutralize the virus and prevent the release of the viral genome into the host cell cytoplasm (Impagliazzo et al., 2015, Science). Consequently, targeting the HA stem offers a robust strategy for broad-spectrum antiviral intervention that is less susceptible to the resistance mechanisms typically seen with head-directed antibodies.

Other names

Hemagglutinin stalk regionHA2 subunit stemConserved HA stem domainGroup 1 HA stalkHemagglutinin fusion domain

Inhibition of pH-dependent membrane fusion by stabilizing the pre-fusion conformation of the hemagglutinin protein and preventing the structural rearrangement of the HA2 subunit.