The literature search was conducted within the PubMed database by using the keywords ‘peroxisome proliferator-activated receptor’ or ‘PPAR’ or ‘PGC-1’ or ‘kynurenine’ or ‘tryptophan’ or ‘IDO’ and ‘multiple sclerosis’ or ‘MS’ or ‘experimental autoimmune encephalomyelitis’ or ‘experimental allergic encephalomyelitis’ or ‘EAE’. Here, IDO1 is linked to myeloid sarcoma.