Receptor for interleukin-33 (IL-33), 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 (By similarity). Inhibits IL-33 signaling. H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide Interacts with MYD88, IRAK1, IRAK4, and TRAF6 (By similarity). 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 (By similarity). Interacts with TMED1 (By similarity). Isoform A is detected in spleen, lung, bone marrow and lymh node. Isoform B is predominant in fibroblasts. By FOS. The TIR domain mediates NAD(+) hydrolase (NADase) activity. Self-association of TIR domains is required for NADase activity. Belongs to the interleukin-1 receptor family.