Following the recruitment and autophosphorylation of STAT1/2 (158), phosphorylated STAT1/2 forms a transcription factor complex with IRF-9, termed IFN-stimulated gene factor 3 (ISGF3; 159), which translocates from the cytosol to the nucleus and binds to IFN-stimulated response elements (ISREs) in the ISG promoters to initiate the transcription of genes against viral infection (160, 161). Here, STAT1 is linked to viral infectious disease.