Hemagglutinin stalk domain of influenza A group 1 viruses (HA stalk (Group 1))

The hemagglutinin (HA) stalk domain of influenza A group 1 viruses is a highly conserved region of the viral surface glycoprotein, making it a primary target for the development of universal influenza vaccines and broadly neutralizing antibodies (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4147624/). Unlike the highly variable globular head domain (HA1), the stalk domain (primarily HA2) remains relatively stable across different subtypes within phylogenetic Group 1, which includes H1, H2, H5, H6, H8, H9, H11, H12, H13, H16, H17, and H18 (Wikipedia, https://en.wikipedia.org/wiki/Hemagglutinin_(influenza)). Its primary biological function is to mediate the fusion of the viral envelope with the host endosomal membrane through a pH-triggered conformational change, a critical step for viral entry and genome release (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758175/). Therapeutic strategies targeting this domain, such as monoclonal antibodies like CR6261 and MEDI8852, work by blocking this fusion process or by recruiting immune effector cells through Fc-mediated mechanisms like antibody-dependent cellular cytotoxicity (ADCC) (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4147624/). While the stalk domain is immunosubdominant compared to the head, innovative vaccine approaches like chimeric hemagglutinins (cHAs) aim to refocus the immune response toward this conserved region to provide broad, long-lasting protection against seasonal and pandemic influenza strains (Oxford Academic, https://academic.oup.com/jid/article/219/Supplement_1/S5/5430414).

Other names

HA2 subunitHemagglutinin stem domainInfluenza A Group 1 HA stalkConserved HA stalk domainHA stalk region

Inhibition of pH-induced conformational change and membrane fusion; blocking of proteolytic maturation (HA0 to HA1/HA2 cleavage); induction of Fc-mediated effector functions such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4147624/).