ATP induces IL-1β secretion in both monocytes and macrophages. (A) Human monocytes and macrophages were incubated with RPMI, LPS (1 μg/mL), or a combination of LPS and MDP (10 μg/mL) for 24 hours. Intracellular pro-IL-1β or secreted mature IL-1β were measured by specific ELISA kits (n = 6, mean ± SEM). (B) Monocytes or macrophages were incubated with RPMI or LPS for 4 hours, followed by ATP (1 mM) for 15 minutes (RPMI/ATP or LPS/ATP). Mean levels of mature IL-1β secreted in the supernatant were measured by ELISA (n = 6, mean ± SEM). (C) Western blots of caspase-1 in lysates after stimulation of monocytes with RPMI, LPS (1 μg/mL), ATP (1 mM), or a combination of LPS and ATP. (D) Monocytes and macrophages were incubated with RPMI or LPS (1 μg/mL) for 4 hours, and ATP was measured in the supernatant using a luciferase assay (n = 6, mean ± SEM, *P < .05 compared with monocytes). (E) Human monocytes and macrophages were incubated with RPMI or LPS (1 μg/mL) for 4 hours, and P2X7 receptors were blocked by adding oxidized ATP (oATP, 300 μM). Concentrations of mature IL-1β were measured in the supernatants by ELISA (n = 6, mean ± SEM, *P < .05 compared with RPMI). (F) Macrophages (Mf) differentiated in the presence of 10 ng/mL IFN-γ were stimulated for 24 hours with LPS (1 μg/mL), MDP (10 μg/mL), or heat-killed S epidermidis (10⁶ organisms/mL). IL-1β in the supernatant was measured by ELISA (n = 6, mean ± SEM). (G) Macrophages differentiated for 5 days in RPMI with 10% plasma while in rotating (4 rpm) in 50-mL polypropylene tubes were stimulated for 24 hours with LPS, MDP, or heat-killed S epidermidis. IL-1β in the supernatant was measured by ELISA (n = 6, mean ± SEM). (H) Western blot of the active caspase-1 p10 fragment in macrophages differentiated in the absence (RPMI) or presence (IFN-γ) of IFN-γ. Data from 2 volunteers (1 and 2) are presented. (I) ATP release from macrophages differentiated in the absence or presence of IFN-γ (n = 5, mean ± SEM, *P < .05 compared with macrophages without IFN-γ).