The founding members of the interleukin-1 (IL-1) superfamily include pro-inflammatory cytokines IL-1α and IL-1β, and a third protein that acts as an IL-1 receptor antagonist (IL-1RA). At least six similar proteins have been recently identified, including a homolog of IL-1RA (IL1F5). The three better-characterized proteins (IL-1a, IL-1b and IL-1RA) are mainly expressed in macrophages, monocytes, and dendritic cells. IL-1a and IL-1b act as potent inflammatory cytokines that help regulate host defense and immune responses (1). Binding of these pro-inflammatory cytokines to an IL-1 receptor recruits adapter proteins (such as IRAK) to the receptor. Phosphorylation of these adaptor proteins promotes downstream signaling cascades associated with the immune response (2). Altered expression of both IL-1a and IL-1b is associated with an extensive list of human disorders, including Alzheimer's disease, rheumatoid arthritis, psoriasis and various forms of cancer (3,4). IL-1RA acts as an anti-inflammatory cytokine, binding the IL-1 receptor to limit the response to inflammation (5). 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 (6).
