Within the IL18 receptor complex, responsible for the binding of the pro-inflammatory cytokine IL18, but not IL1A nor IL1B (PubMed:8626725, PubMed:14528293, PubMed:25261253, PubMed:25500532). Involved in IL18-mediated IFNG synthesis from T-helper 1 (Th1) cells (PubMed:10653850). Contributes to IL18-induced cytokine production, either independently of SLC12A3, or as a complex with SLC12A3 (By similarity). H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide Forms a ternary complex with IL18 and IL18RAP (PubMed:14528293, PubMed:25500532). Within this complex, IL18R1 is involved in ligand-binding and IL18RAP in signaling leading to NF-kappa-B and JNK activation (Probable). Interacts with SLC12A3 in peritoneal macrophages; this interaction is increased by IL18 treatment (By similarity). Highly expressed in leukocytes, spleen, lung. Also expressed, but at lower levels, in liver, small intestine, colon, prostate, thymus, placenta, and heart. Specifically coexpressed with IL18R1 in Th1 cells (PubMed:10925275, PubMed:11046021, PubMed:10653850). Induced by IL12/interleukin-12 in T-cells. Proposed to be a phenotypic marker for T-helper 1 (Th1) cells. The TIR domain mediates NAD(+) hydrolase (NADase) activity. Self-association of TIR domains is required for NADase activity. N-glycosylated. N-linked glycosyl chains contribute to ligand recognition and intra-receptor interactions required for formation of an active ternary receptor complex. Belongs to the interleukin-1 receptor family.