Table 2.

Pathways of immunomodulation by IDO1 and kynurenine pathway metabolites.

Pathway	Functional consequence	Reference
IDO1 acting as a signaling molecule by complex formation with SHP-1 and SHP-2	Long-term tolerance in plasmacytoid DC	(98)
Depletion of Trp, activation of GCN2 kinase, and inhibition of mTOR in IDO-expressing cells	Cell-cycle arrest and functional anergy in CD8+ T cells	(92, 93)
Binding of kynurenine to AhR in DC and T cells	Decrease in immunogenicity of DC, and generation of Treg cells	(86, 89)
3-HAA acting on DC (possibly via blocking the JNK and p38 MAPK pathways)	Decrease in expression of pro-inflammatory cytokines, increase in expression of TGF-β, and induction of Treg cells	(90, 91)