Hemagglutinin protein of Influenza A H3N2 subtype (HA)

**Hemagglutinin protein of Influenza A H3N2 subtype** is a trimeric viral glycoprotein found on the surface of influenza A virus particles. It is classified as a viral surface protein responsible for two essential steps in virus infection: binding to sialic acid-containing receptors on the host cell surface and mediating the fusion of the viral and host cell membranes, enabling viral entry[1][2][4][5]. The protein is expressed as a precursor (HA0) that is cleaved by host proteases into two subunits, HA1 (receptor binding) and HA2 (membrane fusion), which remain linked via disulfide bonds[2][4][5]. Hemagglutinin is the primary antigen recognized by the immune system and a principal component of influenza vaccines, but its antigenic sites—especially in the globular head domain—are highly variable, facilitating immune escape and necessitating regular vaccine updates[1][5]. Changes in HA receptor binding properties have played a major role in host adaptation, pathogenicity, and pandemic potential. The H3N2 subtype hemagglutinin is a major cause of human epidemics and pandemics since its introduction in 1968, especially affecting elderly populations[3]. Hemagglutinin is routinely targeted by neutralizing antibodies (vaccine-induced or therapeutic), and the protein is under intense surveillance for mutations that may increase pathogenicity, alter receptor specificity, or contribute to resistance to antibody-based therapies[1][2][6].

Other names

Influenza A hemagglutininH3 hemagglutininH3N2 HAInfluenza A virus H3N2 hemagglutinin

Neutralization/blocking of receptor binding; Inhibition of membrane fusion; Immunization to induce protective antibodies