Within the IL18 receptor complex, responsible for the binding of the pro-inflammatory cytokine IL18, but not IL1A nor IL1B. Involved in IL18-mediated IFNG synthesis from T-helper 1 (Th1) cells (By similarity). Contributes to IL18-induced cytokine production, either independently of SLC12A3, or as a complex with SLC12A3 (PubMed:26099046). H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide Forms a ternary complex with IL18 and IL18RAP (By similarity). Within this complex, IL18R1 is involved in ligand-binding and IL18RAP in signaling leading to NF-kappa-B and JNK activation (By similarity). Interacts with SLC12A3 in peritoneal macrophages; this interaction is increased by IL18 treatment (PubMed:26099046). 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.