An antibody to a 17 amino acid synthetic peptide of the type I interleukin-1 receptor preferentially blocks interleukin-1 beta binding

Identification of a Critical Ig-Like Domain in IL-18 Receptor α and Characterization of a Functional IL-18 Receptor Complex

Steady state mRNA levels in various human tissues reveal that the proinflammatory cytokine IL-18 is constitutively and ubiquitously expressed. However, limited IL-18R alpha-chain (IL-18Ralpha) expression in tissues may restrict ligand-acting sites and contribute to a specific response for IL-18. To study the IL-18R complex, [(125)I]IL-18 was studied for binding to the cell surface receptors of IL-18-responsive NK and macrophagic KG-1 cells. After cross-linking, [(125)I]IL-18 formed three IL-18R complexes with sizes of approximately 93, 160, and 220 kDa. In KG-1 cells, Scatchard analysis revealed the presence of 135 binding sites/cell, with an apparent dissociation constant (K(d)) of 250 pM; in NK cells, there were 350 binding sites per cell with an apparent K(d) of 146 pM. Each domain of extracellular IL-18Ralpha was cloned and individually expressed in Escherichia coli. An mAb specifically recognized the membrane-proximal third domain; this mAb blocked IL-18-induced IFN-gamma production in NK cells. Furthermore, deletion of the membrane-proximal third domain of IL-18Ralpha prevented the formation of IL-18R ternary complex with IL-18R beta-chain. The present studies demonstrate that the biologically active IL-18R complex requires the membrane-proximal third Ig-like domain in IL-18Ralpha for the formation of IL-18R ternary complex as well as for signal transduction involved in IL-18-induced IFN-gamma in NK cells.

The role of neutral sphingomyelinase in interleukin-1beta signal transduction in mouse cerebral cortex cells

The cytokine interleukin-1 (IL-1) is an important mediator of neuroimmune interactions, though it has not been established precisely how the IL-lbeta signal is transmitted in nerve cells. This study demonstrates the involvement of the sphingomyelin cascade in IL-1beta signal transduction in the P2 membrane fraction of the mouse cerebral cortex. The key role of the membrane enzyme neutral sphingomyelinase in initiating the sphingomyelin signal transduction pathway for this cytokine is supported. The stimulating activity of IL-1beta on sphingomyelinase activity in the P2 fraction of the cerebral cortex was found to be dose-dependent. Studies using this membrane fraction from mice lacking the IL-1 type I receptor due to genomic mutations, along with studies using an IL-1 receptor antagonist. yielded data showing that IL-1beta binding with the type I receptor is a necessary event for activation of neutral sphingomyelinase. The results obtained here lead to the conclusion that the action of IL-1beta in the CNS is mediated by the IL-1 type I receptor and activation of neutral sphingomyelinase as the initiating enzyme of the sphingomyelin cascade.

Model of interaction of the IL-1 receptor accessory protein IL-1RAcP with the IL-1beta/IL-1R(I) complex

A preliminary model has been calculated for the activating interaction of the interleukin 1 receptor (IL-1R) accessory protein IL-1RAcP with the ligand/receptor complex IL-1beta/IL-1R(I). First, IL-1RAcP was modeled on the crystal structure of IL-1R(I) bound to IL-1beta. Then, the IL-1RAcP model was docked using specific programs to the crystal structure of the IL-1beta/IL-1R(I) complex. Two types of models were predicted, with comparable probability. Experimental data obtained with the use of IL-1beta peptides and antibodies, and with mutated IL-1beta proteins, support the BACK model, in which IL-1RAcP establishes contacts with the back of IL-1R(I) wrapped around IL-1beta.

Activation of neutral sphingomyelinase by IL-1beta requires the type 1 interleukin 1 receptor

The cytokine interleukin 1beta (IL-1beta) plays an important role in host defence reactions and neuro-immune interactions but it is still not clear which of the two interleukin 1 receptor subtypes is coupled to activation of neutral sphingomyelinase (nSMase) by IL-1beta. To investigate involvement of neutral sphingomyelinase (nSMase) in central IL-1beta effects we used P(2)fractions of brain cerebral cortex from wild-type mice and mice deficient in the type 1 IL-1 receptor. IL-1beta (human, recombinant) was shown to activate, in a dose-dependent manner, nSMase in the P(2)brain fraction of the wild-type mice while in the knock-out mice the stimulatory effect of IL-1beta on nSMase was absent. In the presence of an IL-1 receptor antagonist (IL-1ra), IL-1beta did not activate nSMase either in the cortex of wild-type or knock-out mice. These data suggest that nSMase, a key enzyme of the sphingomyelin signal transduction pathway, might be involved in IL-1beta signalling in the brain and that activation of the enzyme requires the IL-1 receptor type 1.

Structural requirements of six naturally occurring isoforms of the IL-18 binding protein to inhibit IL-18

A novel, constitutively expressed and secreted IL-18 binding protein (IL-18BP) neutralizes IL-18 and thereby suppresses the production of IFN-gamma, resulting in reduced T-helper type 1 immune responses. In the present study, four human and two mouse isoforms, resulting from mRNA splicing and found in various cDNA libraries, were expressed, purified, and assessed for binding and neutralization of IL-18 biological activities. Human IL-18BP isoform a (IL-18BPa) exhibited the greatest affinity for IL-18 with a rapid on-rate, a slow off-rate, and a dissociation constant (K(d)) of 399 pM. IL-18BPc shares the Ig domain of IL-18BPa except for the 29 C-terminal amino acids; the K(d) of IL-18BPc is 10-fold less (2.94 nM). Nevertheless, IL-18BPa and IL-18BPc neutralize IL-18 >95% at a molar excess of two. IL-18BPb and IL-18BPd isoforms lack a complete Ig domain and lack the ability to bind or neutralize IL-18. Murine IL-18BPc and IL-18BPd isoforms, possessing the identical Ig domain, also neutralize >95% murine IL-18 at a molar excess of two. However, murine IL-18BPd, which shares a common C-terminal motif with human IL-18BPa, also neutralizes human IL-18. Molecular modeling identified a large mixed electrostatic and hydrophobic binding site in the Ig domain of IL-18BP, which could account for its high affinity binding to the ligand. It is likely that preferential secretion of functional and nonfunctional isoforms of IL-18BP affect the immune response.