Résumé : Extracellular adenosine triphosphate affects the maturation of human monocyte-derived dendritic cells (DCs), mainly by inhibiting T-helper 1 (Th1) cytokines, promoting Th2 cytokines, and modulating the expression of costimulatory molecules. In this study, we report that adenosine triphosphate (ATP) can induce immunosuppression through its action on DCs, defining a new role for extracellular nucleotides. Microarray analysis of ATP-stimulated human DCs revealed inter alia a drastic up-regulation of 2 genes encoding mediators involved in immunosuppression: thrombospondin-1 (TSP-1) and indoleamine 2,3-dioxygenase (IDO). The release of TSP-1 by DCs in response to ATP was confirmed at the protein level by enzyme-linked immunosorbent assay (ELISA), immunodetection, and mass spectrometry analysis, and has an antiproliferative effect on T CD4+ lymphocytes through TSP-1/CD47 interaction. Our pharmacologic data support the involvement of purinergic receptor P2Y11 in this ATP-mediated TSP-1 secretion. We demonstrate also that ATP significantly potentiates the up-regulation of IDO--a negative regulator of T lymphocyte proliferation--and kynurenine production initiated by interferon-gamma (IFN-gamma) in human DCs. Thus, extracellular ATP released from damaged cells and previously considered as a danger signal is also a potent regulator of mediators playing key roles in immune tolerance. Consequently, nucleotides' derivatives may be considered as useful tools for DC-based immunotherapies.