Influenza A virus hemagglutinin subtype 3 (HA (H3))

Influenza A virus hemagglutinin subtype 3 (H3 HA) is a trimeric glycoprotein embedded in the viral envelope. It is essential for the virus’s ability to bind sialic acid-containing receptors on host cells, mediating attachment and subsequent endosomal fusion to deliver viral RNA into the cell cytoplasm[1][2][4][5][7]. The protein consists of two major subunits: HA1 (forming the globular head, which contains the receptor-binding site) and HA2 (forming the stalk, which mediates membrane fusion). HA is the primary antigen recognized by the immune system, and its structure and sequence—especially in the head region—undergo frequent changes, enabling the virus to evade immune detection (antigenic drift and shift). H3 is particularly important because of its role in seasonal influenza epidemics and past pandemics. The protein is the main component of influenza vaccines and is a prime target for both neutralizing antibodies and efforts toward universal influenza vaccine designs[1][2][4][5][7].

Other names

Hemagglutinin (H3)H3 HAInfluenza hemagglutinin type 3HA subtype 3

Antibodies bind to HA head to block receptor attachment (preventing entry). Antibodies bind to stalk domain to block membrane fusion (preventing infection of new cells). Vaccine-induced antibodies neutralize virus by targeting HA head or stalk.