IDO1 and tuberculosis: It is reported that HIV/Mtb coinfected patients display higher plasma IDO activity and more rapid TB disease progression from latent to active TB, than do those with TB infection alone (Collins et al., 2020), suggesting that high IDO activity and Kyn-related metabolites are still maintained at high levels in HIV/Mtb coinfected individuals (du-Gyamfi et al., 2017), presumably generating similar function of Kyn metabolites to the HIV or Mtb infection.