title: The combination of soluble IL-18Ralpha and IL-18Rbeta chains inhibits IL-18-induced IFN-gamma.
abstract: Although the beta chain of interleukin-18 receptor (IL-18Rbeta) is required for signaling, the soluble (extracellular) form does not bind IL-18, and its role in inhibiting IL-18 is unclear. In the present study, both the soluble human IL-18 ligand binding alpha chain (sIL-18Ralpha) and the sIL-18Rbeta chain were investigated for inhibition of IL-18-induced interferon-gamma (IFN-gamma) production in human peripheral blood mononuclear cells (PBMC), whole blood, and KG-1 macrophage and natural killer (NK) cell lines. Neutralization of IL-18 by soluble receptors was compared with that of the IL-18 binding protein (IL-18BP). An equimolar concentration IL-18BP inhibited 90% of IL-18 activity, whereas a 4-fold molar excess of sIL-18Ralpha had no effect. A dimeric construct of sIL-18Ralpha linked to the Fc domain of IgG1 (sIL-18Ralpha:Fc) increased IL-18 activity 2.5-fold. In PBMC stimulated with lypopolysaccharide (LPS) or in whole blood stimulated with Staphylococcus epidermidis, 3 nM IL-18BP reduced IFN-gamma by 80%, whereas IL-18Ralpha:Fc had no effect. A construct of the sIL-18Rbeta linked to Fc (sIL-18Rbeta:Fc) did not affect IL-18-induced IFN-gamma even at 80-fold molar excess of IL-18. However, the combination of both soluble receptors reduced IFN-gamma by 80%. In KG-1 cells, a 50% reduction in IL-18 activity was observed using an 80-fold molar excess of sIL-18Ralpha:Fc but only in the presence of sIL-18Rbeta:Fc. Similarly, a 50% reduction was observed using sIL-18Rbeta:Fc in the presence of a molar excess of sIL-18Ralpha:Fc. Similar inhibition was observed in NK cells. These studies reveal that the combination of the ligand-binding and the nonligand-binding extracellular domains of IL-18R is needed to inhibit IL-18, whereas IL-18BP neutralizes at equimolar concentration.
authors.affiliation: Department of Medicine, Division of Infectious Diseases, University of Colorado Health Sciences Center, Denver, CO 80262, USA. Leonid.Reznikov@uchsc.edu
authors.forename: Leonid L
authors.initials: LL
authors.lastname: Reznikov
authors.forename: Soo-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Li
authors.initials: L
authors.lastname: Zhou
authors.forename: Philip
authors.initials: P
authors.lastname: Bufler
authors.forename: Igor
authors.initials: I
authors.lastname: Goncharov
authors.forename: Monica
authors.initials: M
authors.lastname: Tsang
authors.forename: Charles A
authors.initials: CA
authors.lastname: Dinarello
mesh_terms: D000328:Adult; D002460:Cell Line; D006023:Glycoproteins / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D007371:Interferon-gamma / Q000096:biosynthesis*; D020382:Interleukin-18 / Q000008:administration & dosage / Q000494:pharmacology*; D053727:Interleukin-18 Receptor alpha Subunit; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology; D021122:Protein Subunits; D018123:Receptors, Interleukin / Q000008:administration & dosage* / Q000737:chemistry*; D053724:Receptors, Interleukin-18; D012995:Solubility; D013212:Staphylococcus epidermidis / Q000276:immunology
chemical_list: D006023:Glycoproteins; C508572:IL18R1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18; D053727:Interleukin-18 Receptor alpha Subunit; D008070:Lipopolysaccharides; D021122:Protein Subunits; D018123:Receptors, Interleukin; D053724:Receptors, Interleukin-18; C118370:interleukin-18 binding protein; D007371:Interferon-gamma