Transcription profiling of murine dendritic cells in the presence and absence of interferon (IFN)-gamma to identify a tolerogenic signature in IDO-competent dendritic cells

Although much is known on the transcriptional profiles of dendritic cells (DCs) during maturation, the molecular switches critical for the acquisition of a tolerogenic program by DCs are still obscure. In the present study, we explored the gene expression pattern of CD8+ DCs purified from the mouse spleen and treated with interferon (IFN)-gamma. The cytokine, indeed, potentiates the tolerogenic potential of this DC subset via induction of the immunosuppressive tryptophan catabolism mediated by indoleamine 2,3-dioxygenase (IDO). By comparing the expression of the IFN-gamma-modulated genes in IDO+ versus IDO- murine DCs, we found a consistent and selective association of the IDO-competent phenotype with the down-modulation of the Tyrobp gene, encoding the adapter molecule DAP12. IFN-gamma-mediated down-modulation of this gene involved IFN consensus sequence binding protein (ICSBP), a transcription factor also known as IRF-8. While silencing of Tyrobp conferred IDO functional competence on IDO- DCs, silencing of Icsbp1 in IDO+ cells completely abolished IDO expression and function. In parallel, silencing of TYROBP conferred IDO competence on human IDO- DCs while silencing of IRF8 impaired IDO expression and activity in human IDO+ DCs. Therefore, the same small set of molecular switches controls IDO competence in murine and human DCs. Experiment Overall Design: Labeled cRNA extracted from a a total of 8 samples was hybridized to the Affymetrix GeneChip MG-U74Av2 which contains 12,488 probe sets . The 4 control samples included 2 replicates each of RNA extracted from cells incubated in medium for 4 and 16 hours. Treated samples included 2 replicates each of RNA extracted from cells incubated in IFN-gammas for 4 and 16 hours.