Interleukin-1 receptor antagonist (IL-1RA) is a naturally occurring inflammatory inhibitor protein. It inhibits the activity of IL-1α and IL-1β by competitively blocking binding to their type I and type II receptors. IL-1Ra is produced by corneal epithelial cells, monocytes, neutrophils, macrophages, and fibroblasts. Therapeutically, IL-1Ra may help in the treatment of sepsis, cachexia, rheumatoid arthritis, chronic myelogenous leukemia, asthma, psoriasis, and inflammatory bowel disease. Recombinant human IL-1Ra is a 17.2 kDa protein consisting of 153 amino acid residues.