Interferon-gamma induces expression of interleukin-18 binding protein in fibroblast-like synoviocytes.

OBJECTIVE: To investigate expression of the endogenous antagonist of interleukin 18 (IL-18) bioactivity, IL-18 binding protein isoform a (IL-18BPa), in fibroblast-like synoviocytes (FLS). METHODS: Long-term cultured FLS from rheumatoid arthritis (RA), osteoarthritis (OA) and spondylarthropathy patients were analysed for spontaneous and cytokine-induced IL-18BPa expression. Messenger RNA and release of IL-18BPa were assessed by semi-quantitative and quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) as well as immunoblot analysis, respectively. RESULTS: All investigated FLS cultures expressed low amounts of IL-18BPa transcripts. However, there was no detectable release of IL-18BPa from unstimulated synoviocytes. Of the investigated cytokines, only interferon (IFN)-gamma markedly up-regulated IL-18BPa mRNA levels. Induction was accompanied by release of IL-18BPa immunoreactivity from FLS. Conditioned media from IFN-gamma-stimulated FLS cultures reduced IL-12/IL-18-dependent IFN- production by peripheral blood mononuclear cells. CONCLUSION: The present data imply that IFN--activated synoviocytes mediate a negative feedback loop via IL-18BPa, which may limit IL-18 biological activity in arthritis.

Expression and release of IL-18 binding protein in response to IFN-gamma.

IL-18 and IL-18 binding protein (IL-18BP) are two newly described opponents in the cytokine network. Local concentrations of these two players may determine biological functions of IL-18 in the context of inflammation, infection, and cancer. As IL-18 appears to be involved in the pathogenesis of Crohn's disease and may modulate tumor growth, we investigated the IL-18/IL-18BPa system in the human colon carcinoma/epithelial cell line DLD-1. In this study, we report that IFN-gamma induces expression and release of IL-18BPa from DLD-1 cells. mRNA induction and secretion of IL-18BPa immunoreactivity were associated with an activity that significantly impaired release of IFN-gamma by IL-12/IL-18-stimulated PBMC. Inducibility of IL-18BPa by IFN-gamma was also observed in LoVo, Caco-2, and HCT116 human colon carcinoma cell lines and in the human keratinocyte cell line HaCaT. Induction of IL-18BPa in colon carcinoma/epithelial cell lines was suppressed by coincubation with sodium butyrate. IFN-gamma-mediated IL-18BPa and its suppression by sodium butyrate were confirmed in organ cultures of intestinal colonic biopsy specimens. In contrast, sodium butyrate did not modulate expression of IL-18. The present data suggest that IFN-gamma may limit biological functions of IL-18 at sites of colonic immune activation by inducing IL-18BPa production. Down-regulation of IL-18BPa by sodium butyrate suggests that reinforcement of local IL-18 activity may contribute to actions of this short-chain fatty acid in the colonic microenvironment.

Nitric oxide augments release of chemokines from monocytic U937 cells: modulation by anti-inflammatory pathways.

Nitric oxide (NO) appears to act as an inflammatory mediator on monocytic cells. Exogenous NO augmented release of chemokines from human promonocytic U937 cells and peripheral blood mononuclear cells. Pharmacological strategies aiming at modulation of NO-induced release of interleukin-8 (IL-8) were investigated in U937 cells in detail. Release of IL-8 was down-regulated by transforming growth factor beta2 (TGF-beta2), by the protein tyrosine-kinase inhibitor genistein, and via rises in intracellular cyclic AMP, generated by prostaglandin E(2), rolipram, pentoxifylline, forskolin, or dibutyryl-cyclic AMP. In addition, incubation with the synthetic glucocorticoid dexamethasone or suppression of activity of p38 mitogen-activated protein (MAP) kinases by SB-203580 modulated release of IL-8. Activation of p38 MAP kinases was confirmed by the demonstration of an augmented appearance of phosphorylated p38 in the presence of NO. The present data suggest that exposure to exogenous NO resembles activation of U937 cells by proinflammatory stimuli. The anti-inflammatory cytokine TGF-beta2, as well as anti-inflammatory or immunosuppressive agents such as genistein, pentoxifylline, rolipram, dexamethasone, and SB-203580 modulate inflammatory, chemokine-inducing actions of NO.

Lack of interferon-gamma production despite the presence of interleukin-18 during cutaneous wound healing.

BACKGROUND: Recently, we have reported a rapid and strong induction of interleukin-18 (IL-18) upon cutaneous injury in mice. In this paper, we investigated a possible role of IL-18 in triggering interferon-gamma (IFN-gamma) production at the wound site. MATERIALS AND METHODS: Expression of IFN-gamma during cutaneous wound healing was analyzed by RNase protection assay, Western blot, ELISA, and immunohistochemical techniques in a murine model of excisional skin repair. RESULTS: We could not detect any IFN-gamma mRNA and protein expression during normal skin repair. Additionally, impaired healing in the genetically diabetic db/db mouse, which was used as a model for a prolonged inflammatory phase of repair, was characterized by largely elevated levels of IL-18 during the late phase of repair and an absence of IFN-gamma. Western blot analysis for T-cell- and monocyte/macrophage-specific marker proteins (CD4, F4/80) clearly revealed the presence of these subsets of leukocytic cells at the wound site, that are known to produce IFN-gamma in response to IL-18. Furthermore, we provide evidence that the presence of transforming growth factor-beta1 (TGF-beta1) at the wound site might reflect a counterregulatory mechanism in IL-18-induced IFN-gamma production, as TGF-beta1 strongly suppressed IL-18/phytohaemagglutinin (PHA)-induced IFN-gamma production by peripheral blood mononuclear cells (PBMC) in vitro. CONCLUSIONS: Normal tissue regeneration processes after cutaneous injury were not dependent on the presence of IFN-gamma in vivo, and IL-18 must serve additional roles rather than inducing IFN-gamma during the healing process.