Influenza B virus hemagglutinin (HA) (HA)

Influenza B virus hemagglutinin (HA) is a major surface glycoprotein and a primary target for the host immune response and therapeutic intervention [2, 11]. It exists as a homotrimer on the viral envelope, composed of two subunits, HA1 and HA2, which are generated by the cleavage of a precursor protein, HA0 [8, 16]. The HA1 subunit forms the globular head and is responsible for binding to sialic acid receptors on host respiratory epithelial cells, while the HA2 subunit forms the stalk and mediates the fusion of the viral and endosomal membranes under acidic conditions [4, 11]. This dual functionality makes HA essential for viral entry and a critical determinant of host range and virulence [8, 15]. In the context of disease, HA is the principal antigen in seasonal influenza vaccines, which aim to induce neutralizing antibodies that block viral attachment or fusion [14, 21]. However, the protein undergoes frequent antigenic drift, particularly in the HA1 head region, necessitating regular updates to vaccine compositions to match circulating Victoria and Yamagata lineages [15, 18]. Therapeutic strategies targeting HA include broadly neutralizing monoclonal antibodies and small-molecule fusion inhibitors, which often target the more conserved HA2 stalk region to provide broader protection across different strains [3, 20]. Despite its potential, the high rate of mutation remains a significant challenge for developing universal vaccines and long-lasting antiviral therapies [12, 21].

Other names

HemagglutininHAInfluenza B HAHA0HA1HA2Viral hemagglutinin

Inhibition of viral attachment to host cell sialic acid receptors and blockade of acid-induced conformational changes required for membrane fusion [5, 6, 11].