Influenza A virus hemagglutinin stem region (HA stem)

The Influenza A virus hemagglutinin stem region is the lower portion of the trimeric hemagglutinin (HA) glycoprotein present on the surface of influenza A virions. HA is vital for viral entry, mediating both host cell attachment (via its head domain) and fusion of viral and host membranes (via its stem region). The stem region, primarily composed of the HA2 subunit and portions of HA1, undergoes dramatic structural rearrangements after acidification in the endosome, driving the fusion of viral and host cell membranes—a crucial step for viral genome release into host cytoplasm[2][4][7]. While the HA head is highly variable and subject to immune evasion, the stem is relatively conserved across subtypes, making it an attractive target for the development of broadly neutralizing antibodies and universal influenza vaccines[3][6][7]. Therapeutic antibodies and immunogens directed at this region can block membrane fusion, thereby preventing infection by a broad range of influenza A virus subtypes, which include both circulating and emerging zoonotic strains[6][7]. The HA stem is a proven target for both therapy (antibodies) and for next-generation vaccine strategies aimed at overcoming strain variability.

Other names

Hemagglutinin stemHA stalkHA2 regionInfluenza A hemagglutinin stem

Inhibition of membrane fusion by blocking conformational changes in HA after endosomal acidification; Antibody-dependent cell-mediated cytotoxicity (when targeted by host immune response)