Interleukin-1 receptor antagonist protein (Il1rn), also known as IL-1ra, IRAP or IL1 inhibitor, is a member of the interleukin 1 cytokine family. This protein inhibits the activities of interleukin 1 alpha (IL1A) and interleukin 1 beta (IL1B), and modulates a variety of interleukin 1 related immune and inflammatory responses. The mouse Il1rn gene encodes a 178 amino acids (aa) protein with a 26 aa signal peptide. Mouse Il1rn protein shares 26% and 19% identity with its homologues IL-1 beta and IL-1 alpha, respectively. Il1rn can Inhibits the activity of interleukin-1 by binding to receptor IL1R1 and preventing its association with the coreceptor IL1RAP for signaling, but has no interleukin-1 like activity. Recently, an recombinant human Il1rn protein is used in the treatment of rheumatoid arthritis, an autoimmune disease in which IL-1 plays a key role.