IL-1 Receptor Antagonist, also known as IL-1RA, ICIL-1RA, IRAP and IL-1RN, is a member of the interleukin 1 cytokine family. It is expressed by monocytes, neutrophils, macrophages, epithelial cells and fibroblasts. IL-1RA inhibits the activity of both IL-1alpha and IL-1beta, and modulates a variety of IL-1 related immune and inflammatory responses. It inhibits the activity of IL-1 by binding to the receptor IL-1R1 and preventing its association with the coreceptor IL-1RAP for signaling. Clinical studies are being conducted to investigate the use of IL-1RA in the treatment of sepsis, rheumatoid arthritis and chronic myelogenous leukemia.