Purification and Characterization of the Human Interleukin-18 Receptor (1997)

Interleukin (IL)-18 was identified as a molecule that induces IFN-γ production and enhances NK cell cytotoxicity. In this paper, we report upon the purification and characterization of human IL-18 receptor (hIL-18R). We selected the Hodgkin's disease cell line, L428, as the most strongly hIL-18R-expressing cell line based on the results of binding assays. This binding was inhibited by IL-18 but not by IL-1β. The dissociation constant (K d) of125I-IL-18 binding to L428 cells was about 18.5 nm, with 18,000 binding sites/cell. After immunizing mice with L428 cells and cloning, a single monoclonal antibody (mAb) against hIL-18R was obtained (mAb 117-10C). Sequentially, hIL-18R was purified from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS)-extracted L428 cells by wheat germ lectin-Sepharose 4B chromatography and mAb 117-10C-Sepharose chromatography. The internal amino acid sequences of hIL-18R all matched those of human IL-1 receptor-related protein (IL-1Rrp), the ligand of which was unknown to date. When expressed in COS-1 cells, the cDNA of IL-1Rrp conferred IL-18 binding properties on the cells and the capacity for signal transduction. From these results, we conclude that a functional IL-18 receptor component is IL-1Rrp. Interleukin (IL)-18 was identified as a molecule that induces IFN-γ production and enhances NK cell cytotoxicity. In this paper, we report upon the purification and characterization of human IL-18 receptor (hIL-18R). We selected the Hodgkin's disease cell line, L428, as the most strongly hIL-18R-expressing cell line based on the results of binding assays. This binding was inhibited by IL-18 but not by IL-1β. The dissociation constant (K d) of125I-IL-18 binding to L428 cells was about 18.5 nm, with 18,000 binding sites/cell. After immunizing mice with L428 cells and cloning, a single monoclonal antibody (mAb) against hIL-18R was obtained (mAb 117-10C). Sequentially, hIL-18R was purified from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS)-extracted L428 cells by wheat germ lectin-Sepharose 4B chromatography and mAb 117-10C-Sepharose chromatography. The internal amino acid sequences of hIL-18R all matched those of human IL-1 receptor-related protein (IL-1Rrp), the ligand of which was unknown to date. When expressed in COS-1 cells, the cDNA of IL-1Rrp conferred IL-18 binding properties on the cells and the capacity for signal transduction. From these results, we conclude that a functional IL-18 receptor component is IL-1Rrp. Murine interleukin-18 (mIL-18) 1The abbreviations used are: mIL-18, murine interleukin-18; rhIL-18, recombinant human interleukin-18; hIL-18R, human interleukin-18 receptor; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid; mAb, monoclonal antibody; IL-1RI, interleukin 1 receptor type I; IL-1RII, interleukin 1 receptor type II; IL-1Rrp, interleukin-1 receptor-related protein; IL-1RAcp, IL-1 receptor accessory protein; WGL, wheat germ lectin; IFN, interferon; PBS, phosphate-buffered saline; PAGE, polyacrylamide gel electrophoresis; RT-PCR, reverse transcriptase-polymerase chain reaction; BS3, bis(sulfosuccinimidyl) substrate; CBB, Coomassie Brilliant Blue. 1The abbreviations used are: mIL-18, murine interleukin-18; rhIL-18, recombinant human interleukin-18; hIL-18R, human interleukin-18 receptor; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid; mAb, monoclonal antibody; IL-1RI, interleukin 1 receptor type I; IL-1RII, interleukin 1 receptor type II; IL-1Rrp, interleukin-1 receptor-related protein; IL-1RAcp, IL-1 receptor accessory protein; WGL, wheat germ lectin; IFN, interferon; PBS, phosphate-buffered saline; PAGE, polyacrylamide gel electrophoresis; RT-PCR, reverse transcriptase-polymerase chain reaction; BS3, bis(sulfosuccinimidyl) substrate; CBB, Coomassie Brilliant Blue. was identified in the livers of mice sequentially injected with heat-killed Propionibacterium acnes and with lipopolysaccharide (1Okamura H. Tsutui H. Komatsu T. Yatsudo M. Hakura A. Tanimoto T. Torigoe K. Okura T. Nukada Y. Hattori K. Akita K. Namba M. Tanabe F. Konishi K. Fukuda S. Kurimoto M. Nature. 1995; 378: 88-91Crossref PubMed Scopus (2392) Google Scholar). Murine IL-18 cDNA was cloned from murine liver mRNA, and the factor was provisionally termed IFN-γ-inducing factor because it was first identified as an IFN-γ inducer in mice. Consequently, human interleukin-18 (hIL-18) was cloned from normal human liver mRNA (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). IL-18 is a non-N-linked, glycosylated, 18.3-kDa cytokine in its mature form and exhibits biologic activities in the monomeric form. IL-18 has been found to have a variety of biologic actions, including the stimulation of the proliferation of activated T cells, enhancement of the lytic activity of NK cells, induction of interferon-γ (IFN-γ), and granulocyte-macrophage colony-stimulating factor production by activated T cells and promotion of Th1-type helper (Th1) clone responses (1Okamura H. Tsutui H. Komatsu T. Yatsudo M. Hakura A. Tanimoto T. Torigoe K. Okura T. Nukada Y. Hattori K. Akita K. Namba M. Tanabe F. Konishi K. Fukuda S. Kurimoto M. Nature. 1995; 378: 88-91Crossref PubMed Scopus (2392) Google Scholar, 2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar, 3Micallef M.J. Ohtsuki T. Kohno K. Tanabe F. Ushio S. Namba M. Tanimoto T. Torigoe T. Fujii M. Ikeda M. Fukuda S. Kurimoto M. Eur. J. Immunol. 1996; 26: 1647-1651Crossref PubMed Scopus (556) Google Scholar, 4Kohno K. Kataoka J. Ohtsuki T. Suemoto Y. Okamoto I. Usui M. Ikeda M. Kurimoto M. J. Immunol. 1997; 158: 1541-1550PubMed Google Scholar). It has also been reported that IL-18 inhibits osteoclast-like multinucleated cell formation in co-cultures of osteoblasts and hemopoietic cells of spleen or bone marrow origin (5Udagawa N. Horwood N.J. Elliot J. Mackay A. Owens J. Okamura H. Kurimoto M. Chambers T.J. Martin J. Gillespie M.T. J. Exp. Med. 1997; 185: 1005-1012Crossref PubMed Scopus (358) Google Scholar). Thus, it is very obvious that IL-18 plays an important role in the immune system. IL-18 shares some of its biologic activities with IL-12, although the primary structures of the two cytokines show no homology (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). In addition, in the experiments using murine Th1 clones and enriched human T cells, IL-18 and IL-12 acted on the T cells synergistically to induce IFN-γ production (1Okamura H. Tsutui H. Komatsu T. Yatsudo M. Hakura A. Tanimoto T. Torigoe K. Okura T. Nukada Y. Hattori K. Akita K. Namba M. Tanabe F. Konishi K. Fukuda S. Kurimoto M. Nature. 1995; 378: 88-91Crossref PubMed Scopus (2392) Google Scholar, 4Kohno K. Kataoka J. Ohtsuki T. Suemoto Y. Okamoto I. Usui M. Ikeda M. Kurimoto M. J. Immunol. 1997; 158: 1541-1550PubMed Google Scholar). Interestingly, the amino acid sequence of IL-18 includes the IL-1 signature-like sequence (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar) and has been shown to have 15% homology at the amino acid level with the IL-1β protein, but does not bear significant functional resemblance to the IL-1 family (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). The identification of the receptor for IL-18 is important for investigation of the physiological role of IL-18 in nature. In this report, we describe the purification and identification of hIL-18R from a Hodgkin's disease-derived cell line, L428, and present some characterization of this molecule. C5/MJ, CCRF-HSB-2, HPB-ALL, JM, MOLT-3, MOLT-4, MOLT-16, PEER, SKW-3 (human T cell leukemia), ARH-77, BALL-1 (human B cell leukemia), KG-1, HL-60, U-937 (human myelomonocytic cell leukemia), NALM-16, HEL (human non-T, non-B cell leukemia), and L-428 and HDLM (human Hodgkin's disease) cell lines were maintained in culture at 37 °C, in a 5% CO2 air mixture in RPMI 1640 medium supplemented with 10% heat-inactivated fetal bovine serum (BioWhittaker Inc.). Recombinant human IL-1β (R&D Systems) and 125-I-IL-1β (Amersham) were obtained commercially. Recombinant human IL-18 (rhIL-18) was produced by culture of Escherichia coli transformed with an expression vector containing hIL-18 cDNA. Purification of rhIL-18 to homogeneity from culture broths of transformed E. coli was as described elsewhere (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). The purified rhIL-18 had a specific activity of 1 × 105 units/mg of protein (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). One unit of IL-18 is that amount of protein which induces 160 IU/ml IFN-γ production from 0.75 × 106 peripheral blood mononuclear cells in the presence of ConA. Radioiodination of rhIL-18 using Bolton-Hunter reagent (ICN) was performed according to the manufacturer's instructions (6Calderon J. Sheehan K.C.F. Chance C. Thomas M.L. Schreiber R.D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 4837-4841Crossref PubMed Scopus (55) Google Scholar). Specific radioactivity of the preparations was in the range of 5–7 × 104 cpm/ng of protein. All human cell lines were suspended in RPMI 1640 medium containing 0.1% bovine serum albumin, 0.1% NaN3, and 100 mm HEPES (binding medium). The binding reactions were performed on 2 × 106 cells for 1 h at 4 in 150 μl of binding medium containing various concentrations of125I-IL-18 or 125-I-IL-1β with or without 500 nm unlabeled rhIL-18 or IL-1β. After incubation, the mixture was layered over 200 μl of phthalate oil (dibutylphthalate:dioctylphthalate = 1:1), centrifuged at 6,000 × g for 5 min at 15 °C, and cell-bound125I-IL-18 or 125-I-IL-1β of the cell pellet was determined using a γ-counter. Receptor binding data of cell lines with high specific binding were analyzed by the Scatchard coordinate system. L428 cells (5 × 107) were incubated for 1 h at 4 °C in binding medium containing 125I-IL-18 or125I-IL-1β with or without unlabeled rhIL-18 or IL-1β. The cells were suspended in 1 ml of PBS containing 1 mmbis(sulfosuccinimidyl) substrate (BS3, Pierce) and incubated for 1 h on ice. After the addition of 50 μl of 1m Tris-HCl (pH 7.4), the cells were lysed by the addition of 100 μl of PBS containing 12 mm CHAPS. After incubation at 4 °C for 3 h, the lysates were centrifuged at 10,000 ×g for 30 min at 4 °C and the supernatants were electrophoresed on a 2–15% SDS-PAGE (Daiichi Chemicals Co.) under reducing conditions. After electrophoresis, the gel was dried and exposed to x-ray film for 4 days. The assay used to semi-quantitate the extracted hIL-18R was modified from the solubilized granulocyte colony-stimulating factor receptor binding assay developed by Fukunaga et al. (7Fukunaga R. Ishizaka-Ikeda E. Nagata S. J. Biol. Chem. 1990; 265: 14008-14015Abstract Full Text PDF PubMed Google Scholar). The CHAPS-extracted receptor (50 μl) or partially purified hIL-18R preparations were mixed with 1 nm125I-IL-18 (1–2 × 105 cpm) in 100 μl of PBS containing 0.1% bovine serum albumin in the presence or absence of 500 nmunlabeled rhIL-18. The binding reaction was performed for 1 h at 4 °C. After incubation, 50 μl of PBS containing 200 μg of bovine γ-globulin (Sigma) was added and the receptor-ligand complex was precipitated from the solution by the addition of 250 μl of PBS containing 20 (w/v) polyethylene glycol. Precipitates were collected by centrifugation at 10,000 × g for 5 min at 4 °C. The radioactivity of the pellet was quantitated as described above. BALB/c mice were immunized through the intraperitoneal route with L428 cells at 2 × 107 cells/mouse. Mice received 11–12 booster injections of 2 × 107 cells over a 6-month period. For preparation of activated spleen cells, mice were injected intravenously with a partially purified hIL-18R preparation, on 2 consecutive days, starting 3 days prior to spleen cell harvest. Spleen cells were fused with SP2/O cells according to the methods of Uchiyama et al. (8Uchiyama T. Broder S. Waldmann T.A. J. Immunol. 1981; 126: 1387-1393PubMed Google Scholar). Hybridoma supernatant reactivities were assayed by the system of inhibition of 125I-IL-18 binding to L428 cells. Antibodies were purified from murine ascites fluids by hydroxyapatite gel chromatography, since the mAb of interest, 117-10C, was of the IgM subclass. mAb 117-10C was conjugated to CNBr-Sepharose for hIL-18R purification by chromatography according to the manufacturer's a of L428 cells as a of hIL-18R, we used the cell proliferation this is a to human cells in the of of cell culture methods T. K. T. C. M. K. T. Fujii M. Fukuda S. Kurimoto M. PubMed Scopus Google Scholar). was as described S. K. Y. K. M. T. Kurimoto M. 1997; PubMed Scopus Google Scholar) with to a pellet of L428 cells × cells, 100 was added 500 ml of mm Tris-HCl (pH and 1 and cells were on for 30 of mm Tris-HCl (pH containing and 1 was added to the which was centrifuged at × g for was obtained by centrifugation of the supernatant at ×g for The pellet was suspended in ml of PBS containing 12 mm CHAPS, 1 mm and mm and at 4 °C for The was centrifuged at × g for and the supernatant was used as the starting for the The described was used to of The CHAPS-extracted from from a of × cells, were and used for of were to ml of the extracted After the protein was with PBS containing 12 mm and The hIL-18R preparations from were against PBS containing 2 purified by mAb 117-10C-Sepharose chromatography, and with mm (pH containing 2 mm CHAPS. The were with 1m HEPES (pH and with an The from mAb 117-10C-Sepharose chromatography were and The was electrophoresed on a a and with according to the methods of et al. J. Biol. Chem. Full Text PDF PubMed Google Scholar). were and to J. Biol. Chem. Full Text PDF PubMed Google Scholar). For by the the were electrophoresed on a gel in the presence of a reducing After the gel with CBB, to the receptor were and with according to the methods of et al. U. C. J. 1995; PubMed Scopus Google Scholar). The extracted from the gel were injected a in a system were to amino acid using a protein From the results of internal amino acid and with the internal of the purified hIL-18R were found to to We to a expression vector for cDNA. cDNA was from L428 cell as a specific cDNA amino of were cloned and the expression K. T. T. T. S. PubMed Scopus Google Scholar). COS-1 cells were by with expression and h of incubation as described Biol. 1995; PubMed Google Scholar). the COS-1 cells as binding and gel were performed S. K. Y. K. M. T. Kurimoto M. 1997; PubMed Scopus Google Scholar). the purification and cDNA of the hIL-18R, the was to cells that high expression of hIL-18R on the cell human cell lines of including and myelomonocytic cell were for hIL-18R expression by binding assay shown in specific binding of rhIL-18 was to L428 cells and to HDLM cells, with found in C5/MJ, MOLT-16, PEER, and cells, and also found in CCRF-HSB-2, MOLT-3, MOLT-4, and cells, From these results, we selected L428 cells as the primary for hIL-18R of hIL-18R on human cell used as normal Hodgkin's non-B used as normal Hodgkin's in a 1 results of binding of 125I-IL-18 to L428 cells. of the data in the Scatchard coordinate system a line, that a single of a binding for IL-18 on L428 cells. The dissociation constant (K d) from the data was about 18.5 nm with 18,000 binding sites/cell. at this that IL-18 and IL-1β not the were performed on L428 cells and shown in on the of L428 cells, specific binding of 125I-IL-18 and was The binding of 125I-IL-18 to L428 cells was not inhibited by the addition of unlabeled and the specific binding of to L428 cells was not inhibited by the addition of unlabeled rhIL-18, for IL-18 on L428 cells the formation of a complex which was at and which was to have a of of the was inhibited by the addition of unlabeled rhIL-18 binding of125I-IL-18 to L428 cells. the of rhIL-18 is about the of the complex that hIL-18R as a single of In with the results of binding the formation of the complex was not inhibited by the addition of unlabeled IL-1β. In the of formation of a complex was at a range to a of which range was from that of and hIL-18R cytokines have the and for IL-18 and results that on the cell of L428 cells, hIL-18R is from the of hIL-18R and expression on L428 cells by with 125I-IL-18 or125I-IL-1β in the presence of unlabeled rhIL-18 or IL-1β. L428 cells were incubated with nm125I-IL-18 or in the presence or absence of a of unlabeled rhIL-18 or IL-1β. and were performed as described under were analyzed by on 2–15% SDS-PAGE and of the dried The show the of the IL-18 complex and the IL-1β After of BALB/c mice with L428 cells, spleen cells were fused to SP2/O cells and supernatants were assayed for by inhibition of 125I-IL-18 binding to L428 cells. After clones were After a clone of the IgM (mAb was which inhibited 125I-IL-18 binding to L428 cells. In addition, the mAb was for and inhibited the activity of the mAb was not for in the presence of reducing not Purification of the hIL-18R from extracted L428 was by an assay that is based on the of the complex by polyethylene The of extracted hIL-18R in the was from the of the a starting for purification of the hIL-18R, of L428 cells were extracted with 12 mm and the solubilized were to shown in about of the binding activity of the solubilized was in the of in about a against 2 mm in PBS to the was to mAb 117-10C-Sepharose and with as described under of the binding activity from chromatography was in the from mAb in about a of human were from × L428 were from × L428 cells. in a When the preparation was analyzed by SDS-PAGE in the presence of reducing a with a in the range of for the for the purified hIL-18R, the is hIL-18R protein is and has a of The purification is in which that the purification of hIL-18R was about of the CHAPS-extracted with a of From × L428 cells, an μg of hIL-18R protein was from the μg of purified hIL-18R were used for amino acid sequence The results of amino acid at 1 and 3 in 4 the the amino acid sequence at 2 was because the sequences of 2 the the of the purified hIL-18R preparation was used for and internal were From the results of a homology in the and data it was that the amino acid sequences of hIL-18R all matched those of the sequence We to clone the cDNA and a expression vector for to is a functional cDNA was by and a expression vector and was expressed in COS-1 cells Specific binding of125I-IL-18 to the COS-1 cells was The expressed an of nm and × 104 specific binding This was to the for IL-18 binding to L428 cells. the expressed signal IL-18 protein to the COS-1 cells, we performed experiments to the factor was activated or because it has been reported that the of IL-1Rrp was of binding J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). shown in the hIL-18R is of binding in to stimulation with rhIL-18. IL-1β with COS-1 cells, the induction of to binding of the and COS-1 cells in to IL-1β stimulation was also were no in the of the and COS-1 cells in to IL-1β. cytokine present at on the cell a chain and a high most it to receptor this we for hIL-18R-expressing cell lines by binding assay and to an mAb by of mice with the selected hIL-18R-expressing cells. The selected Hodgkin's disease cell line, L428 cells expressed hIL-18R at about 18,000 sites/cell. The in expression with cell lines the preparation of of purified protein for amino acid The results of of hIL-18R-expressing cells from human cell lines of and myelomonocytic cell origin that expression of the hIL-18R was but was expressed at by Hodgkin's disease cell results that hIL-18R is expressed in a of as is the which is in with the results of for IL-1Rrp mRNA expression J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). these lines of to the of hIL-18R in normal no IL-18 and IL-1 cells and actions, the amino acid sequence of IL-18 includes an IL-1 signature-like sequence (2Ushio S. Namba M. Okura T. Hattori K. Nukada Y. Akita K. Tanabe F. Konishi K. Micallef M. Fujii M. Torigoe K. Tanimoto T. Fukuda S. Ikeda M. Okamura H. Kurimoto M. J. Immunol. 1996; 156: 4274-4279PubMed Google Scholar). of the IL-18 and IL-1 a over the of the sequences that the 12 of the Nature. 1996; PubMed Scopus Google Scholar). it was that was that IL-18 and IL-1 the the results of binding and that IL-18 and IL-1β not the receptor expressed by L428 cells 2 and In addition, using human cells, which 1996; PubMed Google we also that IL-18 does not for the expressed on cells by binding assay not From the results of hIL-18R on L428 cells by the of the hIL-18R was to in the range of in with the of purified hIL-18R determined as shown in the cell of L428 cells, to a single of which and in the form binding some cell that homology to the amino acid sequence of have been the murine IL-1 receptor accessory protein amino acid homology to murine amino acid homology to and IL-1Rrp amino acid homology to J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, K. T. T. T. S. PubMed Scopus Google Scholar). murine a ligand for has been cloned S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, T. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google and as IL-1RAcp, it has been reported that a complex with or to or but not M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). IL-1Rrp, IL-1Rrp cDNA has been cloned by methods using for amino acid sequences in the sequence J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). not IL-1Rrp, for which the ligand unknown to date. It has been reported that a in which the IL-1Rrp was fused to the and of the IL-1 to IL-1 COS-1 cells by of and induction of J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). In this report, we that COS-1 cells with expression vector containing the IL-1Rrp cDNA conferred not IL-18 binding but also the capacity of In addition, in experiments using the mAb, this mAb inhibited the activities of IL-18 on normal human peripheral blood mononuclear cells, and the cells were by K. S. T. H. T. M. H. and M. in From these results, we conclude that a functional IL-18 receptor component is IL-1Rrp. It has been reported that murine Th1 clones to IL-18 in the of IFN-γ production and or no proliferation in to was in murine clones in which was expressed K. Kataoka J. Ohtsuki T. Suemoto Y. Okamoto I. Usui M. Ikeda M. Kurimoto M. J. Immunol. 1997; 158: 1541-1550PubMed Google Scholar, 1996; PubMed Google Scholar). amino acid sequences of the of show high homology to those of the of signal by IL-18 to to that by we that the of cells the the of IL-18 and In in the of murine mRNA of the were in the Th1 clones and not in clones as determined by methods not results that in Th1 type cells and not in type cells. In addition, from the results of binding assay on L428 cells using IL-18 or to to does not to with In we have that hIL-18R molecule has been purified from of L428 cells using a of internal amino acid sequences of the purified matched those of and expressed in COS-1 cells, the cDNA of IL-1Rrp conferred IL-18 binding properties and the capacity of signal transduction. From these results, we conclude that IL-1Rrp is a functional receptor component of We M. Micallef for and