IFNG and breast cancer: Furthermore, contrary to the syngeneic model of HER-2/neu-expressing mammary tumor rejection [49] where clear up-regulation of type I and type II IFNs could be documented, in this model ISG expression was not directly accompanied with the over expression of IFN-α, IFN-β or IFN-γ suggesting that, as recently demonstrated in a cytomegalovirus model [50], stimulation of interferon response genes could occur independently of de novo synthesis of IFNs through a direct interaction of viral proteins with cellular transcription factors.