Rat Interleukin-1 beta (IL-1β) is a ~17 kDa protein composed of 153 amino acids. IL-1β along with IL-1α, is a member of the IL-1 superfamily. IL-1α and IL-β are pro-inflammatory cytokines involved in immune defense against infection. IL-1α and IL-1β, are the products of distinct genes, but recognize the same cell surface receptors. IL-1α and IL-1β are structurally related polypeptides that show approximately 25% homology at the amino acid level. Both proteins are produced by a wide variety of cells in response to stimuli such as those produced by inflammatory agents, infections, or microbial endotoxins. When stimulated by other cytokine growth factors, mRNA of IL-1β is present within 15 minutes and accumulates for 4 hours followed by a rapid fall that results in part from the synthesis of a transcriptional repressor as well as a decrease in mRNA half-life. IL-1β plays a role in signal transduction through its receptor, IL-1R. IL-1β is a converting enzyme, which plays an important role in apoptosis through nitric oxide