The interleukin-1beta (IL-1beta) converting enzyme (ICE) processes the inactive IL-1beta precursor to the proinflammatory cytokine. ICE was also shown to cleave the precursor of interferon-gamma inducing factor (IGIF) at the authentic processing site with high efficiency, thereby activating IGIF and facilitating its export. Lipopolysaccharide-activated ICE-deficient (ICE-/-) Kupffer cells synthesized the IGIF precursor but failed to process it into the active form. Interferon-gamma and IGIF were diminished in the sera of ICE-/- mice exposed to Propionibacterium acnes and lipopolysaccharide. The lack of multiple proinflammatory cytokines in ICE-/- mice may account for their protection from septic shock.

The novel cytokine interferon-gamma-inducing factor (IGIF) augments natural killer (NK) cell activity in cultures of human peripheral blood mononuclear cells (PBMC), similarly to the structurally unrelated cytokine interleukin (IL)-12. IGIF has been found to enhance the production of interferon-gamma (IFN-gamma) and granulocyte/macrophage colony-stimulating factor (GM-CSF) while inhibiting the production of IL-10 in concanavalin A (Con A)-stimulated PBMC. In this study, when anti-CD3 monoclonal antibody (mAb)-stimulated human enriched T cells were exposed to IGIF, the cytokine dose-dependently enhanced the proliferation of the cells and this could be completely inhibited by a neutralizing antibody against IL-2 at lower concentrations of IGIF. Neutralizing antibody against IFN-gamma had only insignificant inhibitory effects on T cell proliferation at higher concentrations of IGIF. Enzyme-linked immunosorbent assays (ELISA) revealed that, like PBMC, T cells exposed to IGIF produced large amounts of IFN-gamma; however, changes in the production of IL-4 and IL-10 were minimal. IGIF, but not IL-12, significantly enhanced IL-2 and GM-CSF production in T cell cultures, as determined by CTLL-2 bioassay and ELISA, respectively; however, both IGIF and IL-12 enhanced IFN-gamma production by the T cells. When T cells were exposed to a combination of IGIF and IL-12, a synergistic effect was observed on the production of IFN-gamma, but not on production of IL-2 and GM-CSF. In conclusion, IGIF enhances T cell proliferation apparently through an IL-2-dependent pathway and enhances Th1 cytokine production in vitro and exhibits synergism when combined with IL-12 in terms of enhanced IFN-gamma production but not IL-2 and GM-CSF production. Based on structural and functional differences from any known cytokines, it was recently proposed that this cytokine be designated interleukin-18.

No abstract

Interleukin (IL)-18 was identified as a molecule that induces IFN-␥ 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. Murine interleukin-18 (mIL-18) 1 was identified in the livers of mice sequentially injected with heat-killed Propionibacterium acnes and with lipopolysaccharide (1). Murine IL-18 cDNA was cloned from murine liver mRNA, and the factor was provisionally termed IFN-␥-inducing factor because it was first identified as an IFN-␥ inducer in mice. Consequently, human interleukin-18 (hIL-18) was cloned from normal human liver mRNA (2). 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-␥ (IFN-␥), and granulocyte-macrophage colony-stimulating factor production by activated T cells and promotion of Th1-type helper (Th1) clone responses (1-4). 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 (5). 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 (2). 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-␥ production (1, 4). Interestingly, the amino acid sequence of IL-18 includes the IL-1 signature-like sequence (2) and has been shown to have 15% homology at the amino acid level with the IL-1␤ protein, but does not bear significant functional resemblance to the IL-1 family (2).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. EXPERIMENTAL PROCEDURES Cell Lines and ReagentsC5/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% CO 2 air mixture in RPMI 1640 medium supplemented with 10% heat-inactivated fetal bovine serum (BioWhittaker Inc.). Recombinant human IL-1␤ (R&D Systems) and 125 -I-IL-1␤ (Amersham) were obtained commercially. Recombinant IL-18Recombinant human IL-18 (rhIL-18) was produced by cu...

We have established by differential display polymerase chain reaction of mRNA that interleukin (IL)-18 is expressed by osteoblastic stromal cells. The stromal cell populations used for comparison differed in their ability to promote osteoclast-like multinucleated cell (OCL) formation. mRNA for IL-18 was found to be expressed in greater abundance in lines that were unable to support OCL formation than in supportive cells. Recombinant IL-18 was found to inhibit OCL formation in cocultures of osteoblasts and hemopoietic cells of spleen or bone marrow origin. IL-18 inhibited OCL formation in the presence of osteoclastogenic agents including 1α,25-dihydroxyvitamin D3, prostaglandin E2, parathyroid hormone, IL-1, and IL-11. The inhibitory effect of IL-18 was limited to the early phase of the cocultures, which coincides with proliferation of hemopoietic precursors. IL-18 has been reported to induce interferon-γ (IFN-γ) and granulocyte/macrophage colony-stimulating factor (GM–CSF) production in T cells, and both agents also inhibit OCL formation in vitro. Neutralizing antibodies to GM–CSF were able to rescue IL-18 inhibition of OCL formation, whereas neutralizing antibodies to IFN-γ did not. In cocultures with osteoblasts and spleen cells from IFN-γ receptor type II–deficient mice, IL-18 was found to inhibit OCL formation, indicating that IL-18 acted independently of IFN-γ production: IFN-γ had no effect in these cocultures. Additionally, in cocultures in which spleen cells were derived from receptor-deficient mice and osteoblasts were from wild-type mice and vice versa, we identified that the target cells for IFN-γ inhibition of OCL formation were the hemopoietic cells. The work provides evidence that IL-18 is expressed by osteoblasts and inhibits OCL formation via GM–CSF production and not via IFN-γ production.