The invention relates to suppressors of endogenous human interferon-gamma (INF-γ) applicable in treatment of diseases associated with impaired activity of endogenous IFN-γ. The suppressors of the invention are useful in treating autoimmune diseases and for prevention of graft arteriosclerosis and rejection of organs in allograft transplanted patients. The invention includes inactive analogues or variants of IFN-γ having preserved affinity to the IFN-γ receptor, genetically modified in the domain responsible for triggering the signal transduction pathway.