IFN gamma, also called Type II interferon, is a homodimeric glycoprotein containing approximately 21 to 24 kD subunits. In contrast to IFN alpha and IFN beta synthesis, which can occur in any cell, production of IFN gamma is a function of T cells and NK cells. IFNg is produced during infection by T cells of the cytotoxic/suppressor phenotype (CD8) and by a subtype of helper T cells, the Th1 cells. Th1 cells secrete IL-2, IL-3, TNF beta and IFN gamma, whereas Th4 cells mainly produce IL-3, IL-4, IL-5, and IL-10, but little or no IFNg (9). IFN gamma preferentially inhibits the proliferation of Th4 but not Th1 cells, indicating that the presence of IFNg during an immune response will result in the preferential proliferation of Th1 cells.
The role of IFNg as a disease marker has been demonstrated for a number of different pathological situations:

Infections: IFNg is produced during viral infections . IFN gamma is a diagnostic tool for distinguishing tuberculous from other nontuberculous ascites. IFN gamma values in pleural fluid are significantly higher in tuberculous pleuritis patients than those in non-tuberculous pleuritis patients, with a sensitivity and a specificity of 100%. Therapy-induced (treatment with thalidomide) alleviation of clinical symptoms of erythema nodosum leprosum correlates with IFN gamma and TNFa levels. Tuberculous leprosy patients show increased lymphocyte proliferation and IFNg production in response to stimulation with Mycobacterium leprae as compared to lepromatous leprosy patients and healthy individuals.

Autoimmune diseases: Accurate measurements of cellular production of cytokines, e.g. IFN gamma is important in the design and monitoring of immunotherapy of multiple sclerosis.

Transplant rejection: Intragraft IFNg mRNA expression occurs in active acute transplant rejection preceding clinical transplant rejection, thus offering an early diagnostic tool for detection of transplant rejection .

Allergy: IFN gamma production by isolated lymphocytes is not detectable in patients with cow's milk allergy as compared to control individuals. Infants who develop atopy produce significantly less IFN gamma at birth compared to infants who do not develop atopy.

Diabetes: Peripheral blood lymphomononuclear cells from newly diagnosed type I diabetes produce significantly less IFN gamma in comparison to controls and long-standing diabetes.

Synonyms: Type II IFN