Mice devoid of interferon regulatory factor 1 (IRF‐1) show normal expression of type I interferon genes

The transcription factor interferon regulatory factor 1 (IRF‐1) binds tightly to the interferon (IFN)‐beta promoter and has been implicated in the induction of type I IFNs. We generated mice devoid of functional IRF‐1 by targeted gene disruption. As reported by others, IRF‐1‐deficient mice showed a discrete phenotype: the CD4/CD8 ratio was increased and IFN‐gamma‐induced levels of macrophage iNO synthase mRNA were strongly diminished. However, type I IFN induction in vivo by virus or double‐stranded RNA was unimpaired, as evidenced by serum IFN titers and IFN mRNA levels in spleen, liver and lung. There was also no impairment in the response of type I IFN‐inducible genes. Therefore, IRF‐1 is not essential for these processes in vivo.