Interleukin 36 Receptor Antagonist (IL-36Ra), also known as IL-1F5, FIL1 delta, IL-1HY1, IL-1H3, and IL-1L1, is a member of the IL-1 family of proteins. All family members show a 12 beta-strand, beta-trefoil configuration, and all are believed to have arisen from a common ancestral gene that underwent multiple duplications. The human IL-36Ra gene is in closest proximity to the gene for IL-1ra and is likely a relatively recent duplication of IL-1ra. Cells reported to express IL-36Ra include monocytes, B cells, dendritic cells/Langerhans cells, keratinocytes, and gastric fundus parietal and chief cells.