hemagglutiniini

Hemagglutinin (often abbreviated as "hemagglutiniini" in some languages) is a glycoprotein found on the surface of influenza viruses. It plays a critical role in the virus's ability to infect host cells. Hemagglutinin facilitates the initial step of infection by binding to sialic acid residues on the surface of target cells, primarily respiratory epithelium in humans. This binding allows the virus to attach firmly to the cell membrane.

Following attachment, hemagglutinin mediates the fusion of the viral envelope with the host cell membrane. This fusion process enables the viral genetic material to enter the host cell, initiating infection. Hemagglutinin's structure is typically a trimer, composed of identical subunits, each containing a receptor-binding site and a fusion peptide that becomes active under acidic conditions within endosomes.

Hemagglutinin is also a primary target for the immune response; antibodies directed against it can neutralize the virus and prevent infection. Consequently, it is a key component of influenza vaccines, with vaccine strains often selected based on the circulating hemagglutinin variants. Hemagglutinin proteins are classified into different subtypes, such as H1, H2, H3, and others, which are used to categorize various influenza A virus strains.

The antigenic properties of hemagglutinin are subject to frequent changes through mutations, a process known as antigenic drift, which necessitates regular updates of influenza vaccines. Understanding the structure and function of hemagglutinin is crucial for developing effective antiviral strategies and vaccines against influenza viruses.