title: Kynurenine pathway enzymes in dendritic cells initiate tolerogenesis in the absence of functional IDO.
abstract: Dendritic cell (DC) tryptophan catabolism has emerged in recent years as a major mechanism of peripheral tolerance. However, there are features of this mechanism, initiated by IDO, that are still unclear, including the role of enzymes that are downstream of IDO in the kynurenine pathway and the role of the associated production of kynurenines. In this study, we provide evidence that 1) murine DCs express all enzymes necessary for synthesis of the downstream product of tryptophan breakdown, quinolinate; 2) IFN-gamma enhances transcriptional expression of all of these enzymes, although posttranslational inactivation of IDO may prevent metabolic steps that are subsequent and consequent to IDO; 3) overcoming the IDO-dependent blockade by provision of a downstream quinolinate precursor activates the pathway and leads to the onset of suppressive properties; and 4) tolerogenic DCs can confer suppressive ability on otherwise immunogenic DCs across a Transwell in an IDO-dependent fashion. Altogether, these data indicate that kynurenine pathway enzymes downstream of IDO can initiate tolerogenesis by DCs independently of tryptophan deprivation. The paracrine production of kynurenines might be one mechanism used by IDO-competent cells to convert DCs lacking functional IDO to a tolerogenic phenotype within an IFN-gamma-rich environment.
authors.affiliation: Department of Experimental Medicine, University of Perugia, Via del Giochetto, Perugia 06126, Italy.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Belladonna
authors.forename: Ursula
authors.initials: U
authors.lastname: Grohmann
authors.forename: Paolo
authors.initials: P
authors.lastname: Guidetti
authors.forename: Claudia
authors.initials: C
authors.lastname: Volpi
authors.forename: Roberta
authors.initials: R
authors.lastname: Bianchi
authors.forename: Maria C
authors.initials: MC
authors.lastname: Fioretti
authors.forename: Robert
authors.initials: R
authors.lastname: Schwarcz
authors.forename: Francesca
authors.initials: F
authors.lastname: Fallarino
authors.forename: Paolo
authors.initials: P
authors.lastname: Puccetti
mesh_terms: D000818:Animals; D016827:CD8 Antigens / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000276:immunology; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism / Q000637:transplantation; D005260:Female; D020868:Gene Silencing; D007108:Immune Tolerance / Q000235:genetics; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D007371:Interferon-gamma / Q000502:physiology; D007737:Kynurenine / Q000096:biosynthesis / Q000502:physiology*; D051379:Mice; D008811:Mice, Inbred DBA; D019899:Paracrine Communication / Q000235:genetics / Q000276:immunology; D011499:Protein Processing, Post-Translational; D034741:RNA, Small Interfering / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism / Q000502:physiology
chemical_list: D016827:CD8 Antigens; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D034741:RNA, Small Interfering; D007737:Kynurenine; D007371:Interferon-gamma; D014364:Tryptophan