The Interleukin 1 receptor family comprises at least nine members. All family members possess three immunoglobulin (Ig)-like domains in their extracellular region. Most members also have an intracellular TIR (Toll-like receptor/IL-1 receptor) signaling domain that is also conserved in the Toll-like receptor family. A subtype of the IL-1 R family, SIGIRR (single Ig domain-containing IL-1 R-related molecule) differs from the other nine members by having only one Ig domain.

IL-1 Rrp2, also known as IL-1 R6, is a transmembrane protein belonging to the IL-1 receptor family. It is a ligand binding subunit that associates with IL-1 RAcP to form a functional receptor complex for IL-1F6, IL-1F8, and IL-1F9.