IRF9 and viral infectious disease: Binding of type I IFNs to their cognate dimeric receptor activates the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, leading to formation of Stat1/2/IRF9 complexes that induce expression of IFN-stimulated genes (ISGs), key players in the innate immune response to viral infection [19].