Hemagglutinin protein of the influenza A virus subtype H3N2 (HA (H3N2))

The **hemagglutinin protein of the H3N2 subtype** is a surface glycoprotein and the principal antigen on the influenza A/H3N2 virus. It is a homotrimeric molecule composed of three identical subunits, each consisting of two domains: the globular head (responsible for binding sialic acid-containing receptors on host cells) and the stem (participating in membrane anchoring and fusion during viral entry)[2][5][6]. Upon viral contact with a host cell, the HA binds cell surface sialic acids, then, after endocytosis and acidification, mediates fusion of the viral and host membranes to facilitate infection[2][5]. The HA is highly mutable, particularly near its receptor-binding site, driving antigenic drift and making it both a challenge and a priority for influenza vaccine design[3][6]. It is exploited in diagnostic assays and is a target for vaccine and antibody therapies, although not for approved small-molecule drugs. The H3N2 HA is key in seasonal flu epidemiology and has been circulating in humans since 1968[3]. Its sequence and structure evolve rapidly, necessitating continual surveillance and vaccine adjustment to keep up with immune escape[4][6][8].

Other names

Influenza hemagglutinin H3N2H3N2 HAH3 hemagglutinininfluenza A hemagglutinin protein (H3N2)H3N2 surface glycoprotein

Antibodies: bind HA to block receptor binding and/or membrane fusion; neutralize virus[1][2] Vaccines: elicit immunity against HA, preventing infection