Interferon gamma (IFN-gamma) is the major interferon produced by stimulated lymphocytes. IFN-gamma is structurally different from type I interferon and its major activity is immunoregulation. It has been implicated in the expression of class II histocompatibility antigens in cells that do not normally produce them, leading to autoimmune disease. IFN-gamma is mainly produced by T-cells and natural killer cells activated by antigens, mitogens, or alloantigens. It is produced by lymphocytes expressing the surface antigens CD4 and CD8. The synthesis of IFN-gamma is induced by Interleukin-2, FGF-basic, and EGF. Recombinant Rat IFN-gamma produced in E. coli is a single non-glycosylated polypeptide chain containing 135 amino acids with a MW of 15,609 Da.