IDO1 and multiple sclerosis: IFN beta induces indoleamine 2,3-dioxygenase (IDO), the enzyme responsible for tryptophan degradation into kynurenine and other metabolites (not FICZ), which have been implicated in IFN immune response, including that observed during IFN treatment of multiple sclerosis (Meyer et al., 1992; Durastanti et al., 2011).