IRF9 and cytomegalovirus infection: Our results revealed that several crucial signal transduction steps, such as the activation and phosphorylation of STAT1, nuclear localization of STAT1, and activity of the ISGF3-induced ISRE, are disrupted by UL23 during HCMV infection, which leads to the inhibition of transcription of downstream ISGs (CXCL10, MX1, and OAS1) as well as an increase in viral resistance to IFN-β.