IDO1 and cytomegalovirus infection: Moreover, recent reports have described the interplay between AHR signaling and HCMV replication: (i) HCMV infection of primary human fibroblasts triggers the persistent induction of AHR transcriptional activity; (ii) Sustained AHR activity is associated with tightly balanced IDO-1 activity; (iii) AHR signaling is required for the efficient replication of virus; (iv) HCMV induced G1/S cell cycle arrest depends on AHR activity; and (v) HCMV exploits AHR signaling to counteract the innate antiviral immune response, in a negative feedback loop containing IDO1-Kyn-AHR (129).