As SARS-CoV-2 may increase AhR ligands independently of IDO induction, it is proposed that SARS-CoV-2, like other viral infections, may be associated with the upregulation of IL4I1, and thereby with the driving of tryptophan to the production of other AhR ligands, viz I3P and I3A [16]. This evidence concerns the gene IL4I1 and viral infectious disease.