Different outcomes of immune cells exposed to eATP. Depending on the P2 receptor subtype expressed, the concentration in the extracellular milieu, and the duration of stimulation, eATP may induce pro- or anti-inflammatory responses. Millimolar concentrations of eATP open the P2X7 channel. Whereas the opening of the P2X7 channel for a short period of time leads to the activation of a number of mechanisms that sustain inflammation, prolonged stimulation of the P2X7 channel induces apoptosis of cells and consequent immune suppression. Relatively low (micromolar) concentrations of eATP activate the high-affinity receptor P2Y11, which is coupled to a G_s protein and induces an increase in intracellular concentration of cAMP, a well-known negative regulator of immune cells. Engagement of P2Y11 inhibits several effector mechanisms, including NK- and T-cell proliferation, cytokine production, and cytotoxic activity, thus contributing to the resolving phase of inflammation. In this model, ATP would act both as an initiator and terminator of immune response.