IDO1 and tuberculosis: With an unbiased metabolomics approach, Collins et al. (2020) recently studied the metabolic profiles of plasma samples of HCs, HHCs, LTBI, and patients with drug-sensitive (DS)-TB or MDR-TB, and reported that the tryptophan pathway is highly regulated throughout the spectrum of TB infection and disease, which was characterized by increased catabolism of tryptophan to kynurenine in both active TB and LTBI, along with simultaneous increase in the expression of IDO-1.