title: IDO activates regulatory T cells and blocks their conversion into Th17-like T cells.
abstract: TLR ligands are effective vaccine adjuvants because they stimulate robust proinflammatory and immune effector responses and they abrogate suppression mediated by regulatory T cells (Tregs). Paradoxically, systemic administration of high doses of CpGs that bind to TLR9 ligands stimulated Tregs in mouse spleen to acquire potent suppressor activity dependent on interactions between programmed death-1 and its ligands. This response to CpG treatment manifested 8-12 h and was mediated by a rare population of plasmacytoid dendritic cells (CD19(+) pDC) induced to express the immunosuppressive enzyme IDO after TLR9 ligation. When IDO was blocked, CpG treatment did not activate Tregs, but instead stimulated pDCs to uniformly express the proinflammatory cytokine IL-6, which in turn reprogrammed Foxp3-lineage Tregs to express IL-17. Thus, CpG-induced IDO activity in pDCs acted as a pivotal molecular switch that induced Tregs to acquire a stable suppressor phenotype, while simultaneously blocking CpG-induced IL-6 expression required to reprogram Tregs to become Th17-like effector T cells. These findings support the hypothesis that IDO dominantly controls the functional status of Tregs in response to inflammatory stimuli in physiological settings.
authors.affiliation: Immunotherapy and Cancer Centers, Department of Pathology, Medical College of Georgia, Augusta, GA 30912, USA.
authors.forename: Babak
authors.initials: B
authors.lastname: Baban
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Chandler
authors.forename: Madhav D
authors.initials: MD
authors.lastname: Sharma
authors.forename: Jeanene
authors.initials: J
authors.lastname: Pihkala
authors.forename: Pandelakis A
authors.initials: PA
authors.lastname: Koni
authors.forename: David H
authors.initials: DH
authors.lastname: Munn
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Mellor
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000276:immunology; D002478:Cells, Cultured; D006131:Growth Inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D007113:Immunity, Innate; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000502:physiology*; D018836:Inflammation Mediators / Q000494:pharmacology; D020381:Interleukin-17 / Q000096:biosynthesis*; D015850:Interleukin-6 / Q000502:physiology; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology; D016192:Resting Phase, Cell Cycle / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000201:enzymology* / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000201:enzymology* / Q000276:immunology*
chemical_list: C408982:CPG-oligonucleotide; D006131:Growth Inhibitors; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D018836:Inflammation Mediators; D020381:Interleukin-17; D015850:Interleukin-6; D009838:Oligodeoxyribonucleotides