STAT1 and viral infectious disease: Three transcription factors, IFN regulatory factor (IRF)-3, IRF-7, and IFN-stimulated gene factor 3 (ISGF3) (a complex consisting of phospho-STAT1, phospho-STAT2, and IRF-9), are crucial in regulation of type I IFNs following virus infection IFNs [49,50]; IRF-3 is a constitutively expressed protein in most cell types that shuttles between the cytoplasm and nucleus.