At low IFNγ concentrations acute infections typically occur, whereas persistence and clearance of Chlamydia infection occurs at medium and high IFNγ concentrations, respectively, possibly through the depletion of host tryptophan needed for bacterial growth owing to induction of indoleamine 2,3-dioxygenase expression by IFNγ [37]. This evidence concerns the gene IDO2 and chlamydia infectious disease.