A complex of the IL-1 homologue IL-1F7b and IL-18-binding protein reduces IL-18 activity.
IL-1F7 was discovered in expressed sequence tag databases as a member of the increasing family of proteins sharing sequence homology to IL-1alpha/beta, IL-1Ra, and IL-18. In the present study using immunohistochemical staining, IL-1F7 was localized in human peripheral monocytic cells, suggesting its role in immune regulation. Recombinant human IL-1F7b was shown to bind to the IL-18Ralpha but without IL-18 agonistic or antagonistic function. Using chemical cross-linking, we observed that, unlike IL-18, IL-1F7b fails to recruit the IL-18Rbeta chain to form a functionally active, ternary complex with the IL-18Ralpha chain. IL-1F7b shares two conserved amino acids with IL-18 (Glu-35 and Lys-124), which participate in the interaction of IL-18 with the IL-18Ralpha chain as well as the IL-18-binding protein (IL-18BP), a secreted protein that neutralizes IL-18 activity. In testing whether IL-1F7b interacts with IL-18BP, we unexpectedly observed that IL-1F7b enhanced the ability of IL-18BP to inhibit IL-18-induced IFNgamma by 25-30% in a human natural killer cell line. This effect was observed primarily at limiting concentrations of IL-18BP (3.12-12.5 ng/ml) and at a 50- to 100-fold molar excess of IL-1F7b. Similar results were obtained by using isolated human peripheral blood mononuclear cells. To study the molecular basis of this effect we performed binding studies of IL-1F7b and IL-18BP. After cross-linking, a high molecular weight complex consisting of IL-1F7b and IL-18BP was observed on SDS/PAGE. We propose that after binding to IL-18BP, IL-1F7b forms a complex with IL-18Rbeta, depriving the beta-chain of forming a functional receptor complex with IL-18Ralpha and thus inhibiting IL-18 activity.
Bufler
Philip
P
University of Colorado Health Sciences Center, Denver, CO 80262, USA. philip.bufler@uchsc.edu
Azam
Tania
T
Gamboni-Robertson
Fabia
F
Reznikov
Leonid L
LL
Kumar
Sanjay
S
Dinarello
Charles A
CA
Kim
Soo-Hyun
SH
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D015870:Gene Expression; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D007371:Interferon-gamma / Q000096:biosynthesis; D007375:Interleukin-1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020382:Interleukin-18 / Q000037:antagonists & inhibitors* / Q000235:genetics; D053727:Interleukin-18 Receptor alpha Subunit; D007694:Killer Cells, Natural / Q000276:immunology; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000276:immunology; D017434:Protein Structure, Tertiary; D018123:Receptors, Interleukin / Q000737:chemistry / Q000378:metabolism; D053724:Receptors, Interleukin-18; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D006023:Glycoproteins; C508572:IL18R1 protein, human; C508573:Il18r1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D007375:Interleukin-1; D020382:Interleukin-18; D053727:Interleukin-18 Receptor alpha Subunit; D046911:Macromolecular Substances; D018123:Receptors, Interleukin; D053724:Receptors, Interleukin-18; D011994:Recombinant Proteins; C118370:interleukin-18 binding protein; D007371:Interferon-gamma