Extracellular ATP induces a distorted maturation of dendritic cells and inhibits their capacity to initiate Th1 responses

Dendritic cells (DCs) express functional purinergic receptors, but the effe cts of purine nucleotides on DC functions have been marginally investigated . In this study, we report on the ability of micromolar concentrations of A TP to affect the maturation and Ag-presenting function of monocyte-derived DCs in vitro. Chronic stimulation (24 h) of DCs with low, noncytotoxic ATP doses increased membrane expression of CD54, CD80, CD86, and CD83, slightly reduced the endocytic activity of DCs, and augmented their capacity to pro mote proliferation of allogeneic naive T lymphocytes. Moreover, ATP enhance d LPS- and soluble CD40 ligand-induced CD54, CD86, and CD83 expression. On the other hand, ATP markedly and dose-dependently inhibited LPS- and solubl e CD40 ligand-dependent production of IL-1 alpha, IL-1 beta, TNF-alpha, IL- 6, and IL-12, whereas IL-1 receptor antagonist and IL-10 production was not affected. As a result, T cell lines generated from allogeneic naive CD45RA (+) T cells primed with DCs matured in the presence of ATP produced lower a mounts of IFN-gamma and higher levels of IL-4, IL-5, and IL-10 compared wit h T cell lines obtained with LPS-stimulated DCs, ATP inhibition of TNF-alph a and IL-12 production by mature DCs was not mediated by PGs or elevation o f intracellular cAMP and did not require ATP degradation. The inability of UTP and the similar potency of ADP to reproduce ATP effects indicated that ATP could function through the P2X receptor family. These results suggest t hat extracellular ATP may serve as an important regulatory signal to dampen IL-12 production by DCs and thus prevent exaggerated and harmful immune re sponses.