For instance, the Trp metabolic pathway crucially provides immune homeostasis in fungal infections by taming heightened inflammatory responses and inducing immune and tissue tolerance, an activity to which the host, fungi, and the microbiota cooperatively contributed.27, -29 On elucidating the relative contribution of the different mammalian dioxygenases in antifungal immunity and tolerance, it was found to be dependent on the combined effects of TDO2, IDO1, and AhR, a ligand-operated transcription factor activated by l-kynurenine. Here, IDO1 is linked to fungal infectious disease.