Rat Interferon gamma (IFN-γ), also known as immune interferon, is a ~15 kDa protein of 137 amino acids (aa) after cleavage of a 19 aa signal peptide. It is presumed that Rat IFN-γ is a noncovalent homodimer. IFN-γ is the only member of the Type II class of interferons. It is produced by activated T, B and NK cells and is an important regulatory cytokine. IFN-γ plays a key role in host defense as it has antiviral, immunoregulatory, and anti-tumor properties. IFN-γ induces the production of cytokines and up-regulates the expression of various membrane proteins including class I and II MHC antigens, Fc receptors, leukocyte adhesion molecules, and B7 antigen. In the mature segment, rat IFN-γ is 87% identical to mouse IFN-γ and 40% identical to human IFN-γ.