Inferferon-gamma (IFN-gamma) is produced by lymphocytes activated by specific antigens or mitogens. IFN-gamma, in addition to having antiviral activity, has important immunoregulatory functions. IFN-gamma is a potent activator of macrophages and has antiproliferative effects on transformed cells. It can potentiate the antiviral and antitumor effects of the type I interferons. In Caucasians, genetic variation in IFN-gamma is associated with the risk of aplastic anemia, a rare disease in which th ereduction of the circulating blood cells results from damage to the stem cell pool in the bone marrow. IFN-gamma (Actimmune, Genentech) is used for reducing the frequency and severity of serious infections associated with chronic granulomatous disease.