PURIFICATION AND CHARACTERIZATION OF THE HUMAN INTERLEUKIN-18 RECEPTOR

Interleukin (IL)-18 was identified as a molecule that induces IFN-gamm a production and enhances NK cell cytotoxicity. In this paper, we repo rt upon the purification and characterization of human IL-18 receptor (hIL-18R). We selected the Hodgkin's disease cell line, L428, as the m ost strongly hIL-18R-expressing cell line based on the results of bind ing assays. This binding was inhibited by IL-18 but not by IL-1 beta. The dissociation constant (K-d) of I-125-IL-18 binding to L428 cells w as about 18.5 nM, with 18,000 binding sites/cell. After immunizing mic e with L428 cells and cloning, a single monoclonal antibody (mAb) agai nst hIL-18R was obtained (mAb 117-10C). Sequentially, hIL-18R was puri fied from 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonic ac id (CHAPS)-extracted L428 cells by wheat germ lectin-Sepharose 4B chro matography and mAb 117-10C-Sepharose chromatography. The internal amin o acid sequences of hIL-18R all matched those of human IL-1 receptor-r elated protein (IL-1Rrp), the ligand of which was unknown to date. Whe n expressed in COS-1 cells, the cDNA of IL-1Rrp conferred IL-18 bindin g properties on the cells and the capacity for signal transduction. Fr om these results, we conclude that a functional IL-18 receptor compone nt is IL-1Rrp.