Mouse Interleukin-1 receptor type 1/IL-1 RI is a cytokine receptor that belongs to the interleukin-1 receptor family. This protein is a receptor for interleukin 1 alpha (IL1A), interleukin 1 beta (IL1B), and interleukin 1 receptor antagonist (IL1RA). It is an important mediator involved in many cytokine induced immune and inflammatory responses. An IL1 receptor accessory protein that can heterodimerize with the Type I receptor in the presence of IL1α or IL1βbut not IL1ra, was identified. This Type I receptor complex appears to mediate all the known IL1 biological responses. The receptor Type II has a short cytoplasmic domain and does not transduce IL1 signals. In addition to the membranebound form of IL1 RII, a naturallyoccurring soluble form of IL1 RII has been described. It has been suggested that the Type II receptor, either as the membranebound or as the soluble form, serves as a decoy for IL1 and inhibits IL1 action by blocking the binding of IL1 to the signaling Type I receptor complex.