The interleukin-1 receptor antagonist (IL-1RA) is a protein that in humans is encoded by the IL1RN gene.IL-1RA was initially called the IL-1 inhibitor and was discovered separately in 1984 by two independent laboratories.IL-1RA is an agent that binds non-productively to the cell surface interleukin-1 receptor (IL-1R), the same receptor that binds interleukin 1 (IL-1), preventing IL-1 from sending a signal to that cell.A polymorphism of this gene is reported to be associated with increased risk of osteoporotic fractures and gastric cancer. Mutations in the IL1RN gene results in a rare disease called deficiency of the interleukin-1–receptor antagonist (DIRA).Variants of the IL1RN gene is also associated with risk of schizophrenia.Elevated levels of IL1RN has been found in serum of schizophrenia patients.An interleukin 1 receptor antagonist is used in the treatment of rheumatoid arthritis, an autoimmune disease in which IL-1 plays a key role. It is commercially produced as anakinra, which is a human recombinant form of IL-1RA. In terms of protein similarities, IL-1β is more closely related to IL-1RA than it is to IL- 1α. The amino acids that are identical between mature human IL-1α and mature IL-1β is 22% while it is 26% when comparing IL-1β to IL-1RA and only 18% when comparing IL-1α to IL-1RA.