<p>Interleukin-1 alpha and interleukin-1 beta (IL-1 alpha and IL-1 beta) are cytokines that participate in the regulation of immune responses, inflammatory reactions, and hematopoiesis [<cite idref="PUB00007346"/>]. Two types of IL-1 receptor, each with three extracellular immunoglobulin (Ig)-like domains, limited sequence similarity (28%) and different pharmacological characteristics have been cloned from mouse and human cell lines: these have been termed type I and type II receptors [<cite idref="PUB00007347"/>]. The receptors both exist in transmembrane (TM) and soluble forms: the soluble IL-1 receptor is thought to be post-translationally derived from cleavage of the extracellular portion of the membrane receptors.</p><p>Both IL-1 receptors appear to be well conserved in evolution, and map to thesame chromosomal location. The receptors can both bind all three forms of IL-1 (IL-1 alpha, IL-1 beta and IL-1RA) [<cite idref="PUB00007348"/>]. The mature type I IL-1 receptor consists of (i) a ligand binding portion comprising three Ig-likedomains; (ii) a single TM domain; and (iii) a large cytoplasmic domain of ~215 amino acids. This domain is shared by a number of other proteins, including the rat FIT-1M precursor, the murine ST2L protein precursor, human oligophrenin-4 and interleukin-18 receptor accessory protein, and Drosophila toll-like proteins.</p> Interleukin-1 receptor, type I/Toll precursor