Summary of the production of active IL-1β. This process can be divided into 3 stages. Stage 1: LPS stimulates monocytes/macrophages (M∅) to produce pro-ICE and pro-IL-1β. Stage 2: ATP stimulates the P2X7R expressed on M∅ to cause a fall in intracellular K+ concentration ([K+]i) which in turn converts pro-ICE to ICE. Stage 3: LPS-primed M∅ following ATP stimulation results in activated ICE which converts inactive pro-IL-β to active IL-1β. It should be noted that this process is intracellular and the figure is for illustrative purposes only (see text for references).