Within the IL18 receptor complex, responsible for the binding of the pro-inflammatory cytokine IL18, but not IL1A nor IL1B (PubMed:14528293, PubMed:25261253, PubMed:25500532, PubMed:37993714, PubMed:8626725). 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). {ECO:0000250|UniProtKB:Q61098, ECO:0000269|PubMed:10653850, ECO:0000269|PubMed:14528293, ECO:0000269|PubMed:25261253, ECO:0000269|PubMed:25500532, ECO:0000269|PubMed:37993714, ECO:0000269|PubMed:8626725}. This is the function of Ensembl gene identifier ENSG00000115604 (IL18R1, interleukin 18 receptor 1).