The founding members of the interleukin-1 (IL-1) superfamily include pro-inflammatory cytokines IL-1α, IL-1β and IL-1 receptor antagonist (IL-1RA). At least six similar proteins have been recently identified, including a homolog of IL-1RA (IL1F5). IL-1a, IL-1b and IL-1RA are mainly expressed in macrophages, monocytes, and dendritic cells. IL-1RA acts as an anti-inflammatory cytokine, binding the IL-1 receptor to limit the response to inflammation. Because it plays a key role in regulating the inflammatory response, recombinant IL-1RA is a therapeutic agent used in the treatment of diseases such as rheumatoid arthritis. Alternatively, mutation of the corresponding IL-1RA gene may be associated with susceptibility to the development of specific cancers.
