Indoleamine 2,3-dioxygenase 1 (IDO1), the enzyme which catalyzes the catabolism of tryptophan, has been found to be significantly increased in the Mtb granuloma in non-human primate models (Mehra et al., 2013) and has been shown to be an effective biomarker for active tuberculosis infection (Adu-Gyamfi et al., 2017). The gene discussed is IDO1; the disease is Granuloma.