Influenza virus hemagglutinin H5N1 antigen (HA (H5N1))

The influenza virus hemagglutinin H5N1 antigen is a trimeric glycoprotein found on the viral envelope of influenza A H5N1, a highly pathogenic avian influenza virus[3][1]. Hemagglutinin facilitates infectivity by binding to sialic acid receptors on host cell surfaces (via its HA1 subunit), then mediating fusion of the viral and host membranes (via HA2 subunit) to allow viral entry[1][2][3]. It is the primary antigen recognized by the host immune system, and thus a main target for vaccine development and therapeutic neutralizing antibodies. Neutralizing antibodies predominantly recognize epitopes on the globular head domain (e.g., receptor-binding site and defined vulnerable sites such as VS1), but some broadly neutralizing antibodies target more conserved sites in the HA stem region[1]. Mutations in hemagglutinin contribute to antigenic drift and shift, underlying the emergence of new viral strains and complicating vaccine design. Hemagglutinin is considered a principal therapeutic target in both prophylactic (vaccination) and therapeutic (antibody-based) strategies against influenza infection.

Other names

Hemagglutinin (H5N1)H5N1 HAInfluenza A H5 hemagglutininHA glycoprotein (H5N1)H5 subtype hemagglutinin

Most drug and antibody candidates block the receptor-binding site or interfere with membrane fusion by binding to critical hemagglutinin epitopes, preventing viral entry into host cells[1][3].