Hemagglutinin protein of Influenza A virus; Hemagglutinin protein of Influenza B virus (HA)

The hemagglutinin protein (HA) is the principal surface glycoprotein of influenza A and B viruses, forming a homotrimeric spike on the viral envelope. It is a class I viral fusion protein responsible for key steps in the virus life cycle, including binding to sialic acid-containing receptors on host cells, facilitating viral entry by endocytosis, and mediating the fusion of the viral membrane with the endosomal membrane at low pH[2][4][6]. HA is highly immunogenic and serves as the primary antigenic target for neutralizing antibodies and vaccine design[3][4]. The protein consists of two subunits, HA1 (receptor binding domain) and HA2 (fusion domain), produced from cleavage of a precursor HA0. Genetic and antigenic variability in HA underlies the challenge of seasonal vaccine formulation and risk of pandemic emergence[3][4]. HA possesses multiple antigenic sites, and escape mutations drive antigenic shift and drift, enabling the virus to evade host immunity[1][3][4]. HA is considered a key therapeutic target for monoclonal antibodies, fusion inhibitors, and universal vaccine development.

Other names

Influenza hemagglutininViral hemagglutininHA proteinHemagglutinin (influenza)

Inhibition of receptor binding (by neutralizing antibodies); Blockade of membrane fusion (by stem-binding antibodies/fusion inhibitors); Prevention of viral entry; Antigen presentation and immune activation