Hemagglutinin

Hemagglutinin is a type of protein found on the surface of influenza viruses. It plays a crucial role in the virus infection process by enabling the virus to bind to and enter host cells. Hemagglutinin is also a primary target for the immune response to influenza infection and is the main component of most influenza vaccines.

Structure and Function

Hemagglutinin is a glycoprotein that forms a trimeric complex on the surface of the influenza virus. Each monomer of the complex consists of a long, rod-like stem and a globular head. The head contains the binding site for sialic acid, a component of the receptors on the surface of host cells.

Upon binding to sialic acid, hemagglutinin undergoes a conformational change that allows the virus to fuse with the host cell membrane and release its genetic material into the cell. This process is essential for the virus to establish an infection.

Immune Response and Vaccination

The immune system recognizes hemagglutinin as a foreign substance and produces antibodies against it. These antibodies can neutralize the virus by blocking its ability to bind to host cells.

Most influenza vaccines are designed to stimulate an immune response against hemagglutinin. They typically contain purified hemagglutinin from several different strains of influenza virus, chosen based on predictions of which strains will be most prevalent in the upcoming flu season.

Variation and Antigenic Drift

Influenza viruses are classified based on the type of hemagglutinin they express. There are 18 known types of hemagglutinin, designated H1 through H18.

The hemagglutinin protein is subject to frequent mutation, a process known as antigenic drift. This allows the virus to evade the immune response and is one of the reasons why a new influenza vaccine must be formulated each year.

See Also

• Influenza virus
• Influenza vaccine
• Antigenic drift
• Neuraminidase

Hemagglutinin Resources
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