IDO1 and Cognitive impairment: IDO is thought to be critical for tryptophan metabolism to cause cognitive deficits in septic encephalopathy, and in the study by Gao et al., L-kynurenine, a metabolite of IDO, induced cognitive deficits similar to those in septic mice after injection; these deficits were subsequently relatively ameliorated by administration of the inhibitor of IDO, 1-methyl-D, L-tryptophan (Gao et al., 2016).