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Immunomodulators are substances that regulate or modify the function of the immune system. They may act as immunosuppressants by inhibiting the immune response or as immunostimulants by stimulating the immune response. Immunosuppressants are helpful in treating autoimmune diseases, such as Crohn’s disease, and in preventing the rejection of organ transplants. Immunostimulants are helpful in improving the immune function of people with chronic infectious diseases, immunodeficiency disorders, and cancers. Tolerogens, a substance that induces tolerance and makes certain tissues less responsive or nonresponsive to specific antigens, are the third type of immunomodulators.
It is unclear how immunomodulators work, but it is hypothesized that they act on certain points of the immune activation pathways. Cytokines are natural immunomodulators, and are produced by lymphoreticular cells. They have multiple interacting roles in the immune pathways.
Interferons (IFNs) are a group of cytokines with immune-enhancing properties and are thus called immunostimulants. Interferon-gamma increases antigen presentation to immune cells and stimulates the activation of various immune cells, including natural killer (NK) cells, macrophages, and cytotoxic T lymphocytes. It is used for the treatment of chronic granulomatous diseases. Interferon-alpha is used for the treatment of infections, such as hepatitis B and C, and cancers, such as chronic myelogenous leukemia, Kaposi’s sarcoma, hairy cell leukemia, and malignant melanoma. Interferons may cause side effects such as fever, chills, body pain, headache, and depression.
Other examples of immunostimulants include levamisole and thalidomide. Levamisole is a drug that was originally used for helminth infections, and are now used for colon cancer. Thalidomide was once used to control pregnancy-associated vomiting, but it was removed from the market because of its teratogenic effects. It has recently found a new use as an immunomodulator drug for rheumatoid arthritis, multiple myeloma, and erythema nodosum leprosum.
Immunomodulation therapy can control symptoms of inflammation. Those that inhibit the function of inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-alpha, can greatly benefit people suffering from chronic inflammatory conditions. For instance, azathioprine, 6-mercaptopurine, cyclosporine, and tacrolimus may be used to maintain remission in Crohn's disease and ulcerative colitis patients. Azathioprine, cyclophosphamide, methotrexate, and mycophenolate mofetil (MMF) are examples of antiproliferative or cytotoxic drugs, while cyclosporine and tacrolimus are examples of calcineurin inhibitors or specific T-cell inhibitors.
Immunomodulators act on the immune system. Blood tests are needed to monitor the effects of these drugs on the bone marrow, kidneys, and liver. Women who are pregnant or planning to get pregnant should consult their doctor regarding the use of immunomodulators because their use could lead to birth defects or miscarriage.