ATP is released by human periodontal ligament cells (hPDLCs) and has been shown to regulate PDL regeneration and responses to mechanical stress through activation of P2Y receptors. This nucleotide, however, has also been reported to trigger the pro-inflammatory cascade by inducing the maturation and/or release of chemokines/cytokines from various cell types mainly via P2X7 receptors. Much less is known on the possible role of ATP in stem cells deriving from PDL (hPDLSCs) which are considered to be a promising tool for cell-based therapy to restore lesions. Given the role played by P2X7 in pathophysiological conditions, in this study we investigated the expression of P2X7 ATP receptors in hPDLSCs. The results obtained showed that hPDLSCs express P2X7 receptors evaluated by means of cytofluorimetric, immunohistochemistry, reverse transcriptase-PCR, and Western blot analyses. P2X7 ligation by 2′,3′-(benzoyl-4-benzoyl)-ATP (BzATP), a specific receptor agonist, was followed by an increase in intracellular Ca2+ and in the uptake of ethidium bromide. These effects were dramatically reduced by oxidized ATP (oATP), the P2X7 irreversible inhibitor, suggesting that the P2X7 is the functional receptor involved. At 24 h treatment of hPDLSCs with BzATP it enhanced the release of the pro-inflammatory agents IL8 and CCL20, without influencing cell viability. These effects were counteracted by pre-treating the cells with oATP or with A-740003, a selective and potent P2X7 competitive antagonist. Collectively, these results indicated that extracellular ATP mediate a pro-inflammatory response via P2X7 receptors in hPDLSCs opening a further approach to control hPDLSCs behavior in their possible application as therapeutic tool. J. Cell. Biochem. 115: 1138–1146, 2014. © 2013 Wiley Periodicals, Inc.