Receptor for IL1A, IL1B and IL1RN. After binding to interleukin-1 associates with the coreceptor IL1RAP to form the high affinity interleukin-1 receptor complex which mediates interleukin-1-dependent activation of NF-kappa-B, MAPK and other pathways. Signaling involves the recruitment of adapter molecules such as TOLLIP, MYD88, and IRAK1 or IRAK2 via the respective TIR domains of the receptor/coreceptor subunits. Binds ligands with comparable affinity and binding of antagonist IL1RN prevents association with IL1RAP to form a signaling complex. Involved in IL1B-mediated costimulation of IFNG production from T-helper 1 (Th1) cells (By similarity). H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide The interleukin-1 receptor complex is a heterodimer of IL1R1 and IL1RAP. Interacts with PIK3R1. Interacts with IL1A (By similarity). The TIR domain mediates NAD(+) hydrolase (NADase) activity. Self-association of TIR domains is required for NADase activity. A soluble form (sIL1R1) is probably produced by proteolytic cleavage at the cell surface (shedding). Rapidly phosphorylated on Tyr-499 in response to IL-1, which creates a SH2 binding site for the PI 3-kinase regulatory subunit PIK3R1. Belongs to the interleukin-1 receptor family.