Human interferons are grouped into three major classes: interferon-alpha (IFN-alpha), interferon-beta (IFN-beta), and interferon-gamma (IFN-gamma). An extensive variety of biological effects have been observed for the interferon family including antiviral activity, anti-proliferative activity; stimulation of cytotoxic activities in lymphocytes, natural killer cells and macrophages, and modulation of the major histocompatibility complex.IFN-gamma is produced by only two cell types, T-cells and large granular lymphocytes.IFN-gamma probably exists in its native form as a dimer of the two active species of 20 and 25 kD respectively.Recombinant human IFN-gamma is purified from E.coli transfected with the human interferon gamma gene. One unit of Hycult Biotech Human Gamma Interferon approximates the bioactivity contained in one unit of the human gamma interferon standard prepared by NIH (Gg23-901-530).