IDO2 and tuberculosis: Serum indoleamine 2,3-dioxygenase (IDO) activity was higher in active TB subjects than latently Mtb-infected individuals, which significantly declined in those after standard TB treatment, indicating that IDO might be a potential target in TB disease, and IDO activity and metabolite changes in tryptophan metabolism could be a predictor in the onset of TB disease [43, 45].