Receptor for interleukin-33 (IL-33); signaling requires association of the coreceptor IL1RAP. Its stimulation recruits MYD88, IRAK1, IRAK4, and TRAF6, followed by phosphorylation of MAPK3/ERK1 and/or MAPK1/ERK2, MAPK14, and MAPK8. Possibly involved in helper T-cell function. Inhibits IL-33 signaling. H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide Interacts with MYD88, IRAK1, IRAK4, and TRAF6. Bound to its ligand IL-33, interacts with IL1RAP to form the minimal interleukin-33 signaling complex with a 1:1:1 stoichiometry. Interacts with KIT (bound to KITLG/SCF). A mast cell-specific KITLG/SCF-induced interleukin-33 signaling complex contains IL1RL1, IL1RAP, KIT and MYD88. Interacts with TMED1 (PubMed:23319592). Highly expressed in kidney, lung, placenta, stomach, skeletal muscle, colon and small intestine. Isoform A is prevalently expressed in the lung, testis, placenta, stomach and colon. Isoform B is more abundant in the brain, kidney and the liver. Isoform C is not detected in brain, heart, liver, kidney and skeletal muscle. Expressed on T-cells in fibrotic liver; at protein level. Overexpressed in fibrotic and cirrhotic liver. The TIR domain mediates NAD(+) hydrolase (NADase) activity. Self-association of TIR domains is required for NADase activity. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the interleukin-1 receptor family.