Extracellular ATP was quantified by using the luminescent ATP detection assay from Abcam; the assay quantifies the amount of light emitted by luciferin when oxidized by luciferase in the presence of ATP and oxygen. Cells were plated into a 96-well plate and stimulated for different times with IL-4 or IFN-γ in triplicates, in complete medium (100 µl); for each time point untreated wells were used. At the end of the treatments the plate was centrifuged at 1,000 rpm for 5 min in order to pellet floating cells and 80 out of 100 µl were transferred in a black-plate for fluorimetric readings. ATP standards were loaded on the same plate as references. The following steps were performed according to the manufacturer’s instructions; light emission was quantified with Victor3 (Wallac).