Interleukin-1 receptor antagonist (IL-1RA) is an anti-inflammatory cytokine that inhibits the inflammatory responses of IL-1 through competitive binding of IL-1 type I receptors. IL-1RA is critical to the development and progression of diseases such as sepsis and rheumatoid arthritis. A recombinant form of IL-1RA has been investigated as a treatment for rheumatoid arthritis and a potential treatment for brain injury.