IFNγ is a homodimeric glycoprotein containing approximately 21 to 24 kD subunits. Production of IFNg is a function of T cells and NK cells. IFNγ is produced during infection by T cells of the cytotoxic/suppressor phenotype (CD8) and by a subtype of helper T cells, the Th1 cells. IFNγ is a diagnostic tool for distinguishing tuberculous from other nontuberculous ascites. It is important in the design and monitoring of immunotherapy for multiple sclerosis.