Influenza B Victoria lineage hemagglutinin antigen (HA (sometimes "IBV-HA" for B virus hemagglutinin))

The **influenza B Victoria lineage hemagglutinin antigen** is the principal surface glycoprotein of influenza B viruses in the Victoria lineage. Hemagglutinin (HA) is a homotrimeric, class I fusion protein that enables viral entry into host cells by binding sialic acid-containing receptors on the respiratory epithelium and mediating fusion of the viral envelope with the host endosomal membrane. The HA structure includes a globular head with the receptor-binding site and a stem region responsible for fusion activity[1][6][2]. The Victoria lineage is one of two current antigenically distinct influenza B virus lineages, the other being Yamagata[3][5]. The antigenicity of Victoria-lineage HA is defined mainly by several highly variable surface loops, such as the 120-loop, 150-loop, 160-loop, and the 190-helix, which represent major antigenic sites and are key determinants for immune recognition and vaccine formulation[3][5]. Drift variants arise from substitutions in these regions, which can diminish neutralization by pre-existing antibodies and thus challenge vaccine effectiveness[5][7]. HA from the Victoria lineage is a standard component of seasonal influenza vaccines to provide protection against circulating B/Victoria viruses. Antibodies against HA serve as both correlates of protection and tools for monitoring vaccine-induced immunity[7][3][5].

Other names

Influenza B virus hemagglutininIBV Victoria-lineage HAInfluenza B HA (Victoria lineage)Hemagglutinin protein (Influenza B, Victoria lineage)

Neutralizing antibodies bind to the hemagglutinin's receptor-binding site or stem, blocking viral attachment or membrane fusion[7][4] - Vaccines elicit an immune response that produces such neutralizing antibodies[7]