Cryopyrin, also known as NALP3 or CIAS1, is essential for inflammasome activation in response to specific stimuli. The study shows that cryopyrin-deficient macrophages cannot activate caspase-1 in response to Toll-like receptor (TLR) agonists plus ATP, which activates the P2X7 receptor to decrease intracellular K+ levels. The release of IL-1β in response to nigericin, a potassium ionophore, and maitotoxin, a potent marine toxin, was also found to be dependent on cryopyrin. In contrast, cells deficient in cryopyrin (Cias1-/-) activated caspase-1 and secreted normal levels of IL-1β and IL-18 when infected with Gram-negative bacteria. However, macrophages exposed to Gram-positive bacteria required both ASC and cryopyrin to activate caspase-1 and secrete IL-1β. Cryopyrin-deficient mice were generated to investigate its role in inflammatory responses to pathogen-derived molecules. These mice showed normal NF-κB signaling in response to TLR2 and TLR4 agonists. Cryopyrin was essential for ATP-induced caspase-1 activation, as shown by the inability of Cias1-/- macrophages to cleave pro-IL-1β after ATP treatment. The study also demonstrated that cryopyrin is essential for inflammasome activation in response to signaling pathways triggered by specific bacterial infections and treatments that deplete intracellular K+. The study further showed that cryopyrin is essential for inflammation in vivo, as cryopyrin-deficient mice had markedly less serum IL-1β and IL-18 than wild-type mice after LPS injection. The results suggest that cryopyrin, like ASC, is an important mediator of LPS-induced endotoxic shock. The study also showed that cryopyrin is not essential for MDP-induced activation of NF-κB and ERK, but is crucial for ATP-induced activation of the macrophage inflammasome. The study concludes that the caspase-1 inflammasome is a dynamic entity that is assembled from different adaptor proteins in a stimulus-dependent manner. Cryopyrin is essential for inflammasome activation in response to specific bacterial infections and treatments that deplete intracellular K+. Ipaf and other members of the NALP family may substitute for cryopyrin upon infection with Gram-negative bacteria. The cryopyrin-dependent response to extracellular ATP may represent a physiological response that occurs when ATP is released by dying cells and degranulating platelets. Future studies will need to address how activating mutations in cryopyrin circumvent the normal regulation of the inflammasome to produce inflammatory diseases.Cryopyrin, also known as NALP3 or CIAS1, is essential for inflammasome activation in response to specific stimuli. The study shows that cryopyrin-deficient macrophages cannot activate caspase-1 in response to Toll-like receptor (TLR) agonists plus ATP, which activates the P2X7 receptor to decrease intracellular K+ levels. The release of IL-1β in response to nigericin, a potassium ionophore, and maitotoxin, a potent marine toxin, was also found to be dependent on cryopyrin. In contrast, cells deficient in cryopyrin (Cias1-/-) activated caspase-1 and secreted normal levels of IL-1β and IL-18 when infected with Gram-negative bacteria. However, macrophages exposed to Gram-positive bacteria required both ASC and cryopyrin to activate caspase-1 and secrete IL-1β. Cryopyrin-deficient mice were generated to investigate its role in inflammatory responses to pathogen-derived molecules. These mice showed normal NF-κB signaling in response to TLR2 and TLR4 agonists. Cryopyrin was essential for ATP-induced caspase-1 activation, as shown by the inability of Cias1-/- macrophages to cleave pro-IL-1β after ATP treatment. The study also demonstrated that cryopyrin is essential for inflammasome activation in response to signaling pathways triggered by specific bacterial infections and treatments that deplete intracellular K+. The study further showed that cryopyrin is essential for inflammation in vivo, as cryopyrin-deficient mice had markedly less serum IL-1β and IL-18 than wild-type mice after LPS injection. The results suggest that cryopyrin, like ASC, is an important mediator of LPS-induced endotoxic shock. The study also showed that cryopyrin is not essential for MDP-induced activation of NF-κB and ERK, but is crucial for ATP-induced activation of the macrophage inflammasome. The study concludes that the caspase-1 inflammasome is a dynamic entity that is assembled from different adaptor proteins in a stimulus-dependent manner. Cryopyrin is essential for inflammasome activation in response to specific bacterial infections and treatments that deplete intracellular K+. Ipaf and other members of the NALP family may substitute for cryopyrin upon infection with Gram-negative bacteria. The cryopyrin-dependent response to extracellular ATP may represent a physiological response that occurs when ATP is released by dying cells and degranulating platelets. Future studies will need to address how activating mutations in cryopyrin circumvent the normal regulation of the inflammasome to produce inflammatory diseases.