Interferons are natural proteins produced by the immune systems of many animals in response to a challenge by a foreign agent. In humans, there are 4 major classes of interferon: alpha, beta, gamma, and omega. Interferon classes alpha and beta have many subtypes (with slightly different specifities), and homologous molecules are found in many species, including rats and mice.

Interferon alpha and beta are produced by many cell types, including T-cells and B-cells, and are an imporant component of the anti-viral response. They stimulate both macrophages and NK cells. Interferons alpha and beta are also active against tumors.

Interferon was scarce and expensive until 1980 when the Interferon gene was inserted into bacteria using genetic engineering, allowing mass cultivation and purification from bacterial cultures. Several different types of interferon are now approved for use in humans, and interferon therapy is now used (in combination with chemotheraphy and radiation) as a treatment for many types of systemic cancer. Unfortunately, interferon delivered intravenously is not very effective, and often causes undesirable side effects at high doses.

Interferon-alpha was cleared by the United States Food and Drug Administration in February 25 1991 as a treatment for hepatitis C. Several different forms of interferon alpha, including interferon alpha-2a, interferon alpha-2b, and interferon alfacon-1 are approved for the treatment of viral hepatitis.

Interferon beta is used in the treatment and control of the neurological disorder multiple sclerosis.

About half of hepatitis C patients treated with interferon respond, with better blood tests and better liver biopsies. Half the patients who respond relapse once the interferon is stopped, for a total cure rate of about 25%. There is some evidence that giving interferon immediately following infection can prevent hepatitis C; unfortunately, people infected by hepatitis C often do not display systoms until months of years later, when it is too late.

Interferon-gamma is involved in the regulation of the immune and inflammatory responses; in humans, there is only one type of interferon-gamma. Interferon-gamma has has some anti-viral and anti-tumor effects, but these are generally weak; however, interferon-gamma potentiates the effects of interferon-alpha and interferon-beta. Unfortunately, interferon-gamma needs to be released at the site of a tumor in very small doses; at this time, interferon-gamma is not very useful for treating cancer.

Inteferon-gamma is also released by Th1 cells, and recruits leukocytes to a site of infection, resulting in increased inflammation. It also stimulates macrophages to kill bacteria that have been engulfed. The interferon-gamma released by Th1 cells is also important in regulating the Th2 response.

Interferon-omega is released by leukocytes at the site of viral infection or tumors.

see also: Immunotherapy