The interferon alpha group contains about 20 different proteins. Regular white blood cells do not produce the interferon alphas until they are infected by a virus. The infected cell then releases the alpha proteins into the area outside the infected cell. The proteins then attach to receptors on other cells and signal to the cell that viruses are in the vicinity. The cell then adapts itself to become more resistant to viral infection. The cell alters itself by changing the expression of the genes in its nucleus. For example, the interferon alpha can signal the cell to make more enzymes that can break down viral products and stop the virus from replicating.
Interferon beta has similar effects to interferon alpha but is produced when a virus infects a cell that is not part of the dedicated immune system, such as a skin cell. The infected cells that produce interferon alpha and interferon beta may themselves die after releasing the proteins. The type I interferons also increase antigen recognition in other cells and improve the rate at which the invaders are found and destroyed by the killer cells of the immune system.
Some T-cells and Natural Killer (NK) cells of the immune system produce Interferon gamma when the cells recognize viral antigens or another lymphocyte cell reacts to a invading stimulus. Interferon gamma acts on other cells to build more molecules on the outside of the cell that recognize antigens and present them to other cells that destroy them. This increases the chance that the invader will be caught and destroyed before doing any damage to the body. This is a similar mechanism to the type I interferons but works on slightly different molecules. Interferon gamma can also signal cells to become more resistant to viruses and even signal other cells to kill infected cells to stop the virus spreading.
The beneficial immune system effects of interferons are sometimes used to treat illness. Interferon alpha is part of a treatment regimen for Hepatitis C and Hepatitis B. Interferon beta also has useful medical antiviral properties but can also help treat multiple sclerosis (MS), a disease of the nervous system. Interferon gamma can have beneficial effects in patients with diseases such as leprosy, toxoplasmosis and skin cancers.