Interleukin-1 Receptor Accessory Protein (IL-1RAcP) is a member of the interleukin-1 receptor family. It contains three Ig-like C2-type domains in the extracellular region and a long cytoplasmic domain implicated in signal transduction. IL-1RAcP acts as a non-ligand binding accessory component of the receptors for IL1α, IL1βand IL33. IL-1RAcP mediates interleukin-1-dependent activation of NF-kappa-B. It is part of the membrane-bound form of the IL-1 receptor. IL-1 RAcP takes part in the Signaling ways by the formation of a ternary complex containing IL1R1, TOLLIP, MYD88, and IRAK1 or IRAK2. In addition, IL-1RAcP modulates the response to interleukins by associating with soluble IL1R1 and enhancing interleukin-binding to the decoy receptor.