AHR and viral infectious disease: In this study, we reported that Kyn production triggered by SARS-CoV-2 leads to AhR activation, inhibition of IFN-I expression, and the transcriptional activation of ACE2, indicating that AhR is a proviral host factor for SARS-CoV-2 replication, similar to previous findings with respect to other viral infections (16, 18, 19).