Hemagglutinin protein of Influenza A virus (HA) and Hemagglutinin protein of Influenza B virus (HA) (HA)

Hemagglutinin protein is a trimeric, integral membrane glycoprotein on the surface of Influenza A and B viruses[3][5]. It mediates two essential steps in the viral life cycle: **binding to host sialic acid receptors** on epithelial cells (attachment) and **fusion of the viral and cell membranes** in the endosome, triggered by acidic pH[3][5][2]. Hemagglutinin also acts as the main antigenic determinant for immune recognition and neutralization, driving both the need for influenza vaccine updates (due to frequent antigenic drift/shift) and the focus of therapeutic monoclonal antibody development[2]. Structural studies show that HA is synthesized as a precursor (HA0) and must be cleaved by host proteases into HA1 (receptor binding domain, head) and HA2 (membrane fusion domain, stalk) to be infectious[5][1]. Hemagglutinin is considered the principal target for vaccine and antiviral antibody strategies, given its fundamental role in viral entry and immune recognition[3][2][5].

Other names

Influenza hemagglutininViral hemagglutininHA glycoproteinHemagglutinin (influenza)

Inhibition of viral attachment (antibodies binding to HA head domain), blockade of membrane fusion (antibodies/stabilizing drugs binding to HA stalk domain), and other mechanisms.