Interleukin-1 receptor accessory protein (IL1RAP or IL-1RAcP) is also known as Interleukin-1 receptor 3 (IL-1R-3 or IL-1R3), C3orf13, which belongs to the interleukin-1 receptor family. IL1RAP contains three Ig-like C2-type (immunoglobulin-like) domains and one TIR domain. IL1RAP is detected in liver, skin, placenta, thymus and lung. Interleukin 1 induces the synthesis of the acute phase and proinflammatory proteins during infection, tissue damage, or stress, by forming a complex at the cell membrane with an interleukin 1 receptor and an accessory protein.