title: Ligand and cytokine dependence of the immunosuppressive pathway of tryptophan catabolism in plasmacytoid dendritic cells.
abstract: Murine plasmacytoid dendritic cells (pDCs) have been credited with a unique ability to express indoleamine 2,3-dioxygenase (IDO) function and mediate immunosuppression in specific settings; yet, the conditions of spontaneous versus induced activity have remained unclear. We have used maneuvers known to up-regulate IDO in different cell types and have examined the relative efficacy and mechanisms of the induced activity in splenic pDCs, namely, after specific receptor engagement by CTLA-4-Ig, CD200-Ig or CD28-Ig, the latter in combination with silenced expression of the suppressor of cytokine signaling 3 (SOCS3) gene. We found that pDCs (CD11c+ mPDCA-1+ 120G8+) do not express IDO and are not tolerogenic under basal conditions. B7-1 engagement by CTLA-4-Ig, CD200R1 engagement by CD200-Ig and B7-1/B7-2 engagement by CD28-Ig in SOCS3-deficient pDCs were each capable of initiating IDO-dependent tolerance via different mechanisms. IFN-gamma was the major cytokine responsible for CTLA-4-Ig effects, and type I IFNs for those of CD200-Ig. Immunosuppression by CD28-Ig in the absence of SOCS3 required IFN-gamma induction and IFN-like actions of IL-6. Therefore, although pDCs do not mediate IDO-dependent tolerance constitutively, multiple ligands and cytokines will contribute to the expression of a tolerogenic phenotype by pDCs in the mouse.
authors.affiliation: Department of Experimental Medicine, Section of Pharmacology, University of Perugia, 06126 Perugia, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Fallarino
authors.forename: Ciriana
authors.initials: C
authors.lastname: Orabona
authors.forename: Carmine
authors.initials: C
authors.lastname: Vacca
authors.forename: Roberta
authors.initials: R
authors.lastname: Bianchi
authors.forename: Stefania
authors.initials: S
authors.lastname: Gizzi
authors.forename: Carine
authors.initials: C
authors.lastname: Asselin-Paturel
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Fioretti
authors.forename: Giorgio
authors.initials: G
authors.lastname: Trinchieri
authors.forename: Ursula
authors.initials: U
authors.lastname: Grohmann
authors.forename: Paolo
authors.initials: P
authors.lastname: Puccetti
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology; D016207:Cytokines / Q000276:immunology; D003713:Dendritic Cells / Q000166:cytology / Q000201:enzymology* / Q000276:immunology; D007108:Immune Tolerance; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000096:biosynthesis* / Q000276:immunology; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D010950:Plasma Cells / Q000166:cytology / Q000201:enzymology* / Q000276:immunology; D014364:Tryptophan / Q000276:immunology / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D016207:Cytokines; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D008024:Ligands; D014364:Tryptophan