IL-1β is also known as catabolin, and its precursor is cleaved by caspase 1. Cytosolic thiol protease cleaves the product to form mature IL-1β. IL1β are structurally related polypeptides that share approximately 21% aa identity in human. Both proteins are produced by a wide variety of cells in response to inflammatory agents, infections, or microbial endotoxins. IL1α and IL1β bind to the same receptor and exert identical biological effects. IL-1β is produced by activated macrophages as a proprotein, which is proteolytically processed to its active form by caspase 1 (CASP1/ICE). This cytokine is an important mediator of the inflammatory response, and is involved in a variety of cellular activities, including cell proliferation, differentiation, and apoptosis.