Opposite effect of Interferon-gamma on PGE2 release from Interleukin-1-stimulated human monocytes or fibroblasts

Interleukin-18 and the pathogenesis of inflammatory diseases

Several autoimmune diseases are thought to be mediated in part by interleukin (IL)-18. Many are those with associated increased interferon-gamma (IFNgamma) levels such as systemic lupus erythematosus, macrophage activation syndrome, rheumatoid arthritis, Crohn's disease, psoriasis, and graft-versus-host disease. In addition, ischemia, including acute renal failure in human beings, appears to involve IL-18. Animal studies also support the concept that IL-18 is a key player in models of lupus erythematosus, atherosclerosis, graft-versus-host disease, and hepatitis. Unexpectedly, IL-18 plays a role in appetite control and the development of obesity. IL-18 is a member of the IL-1 family; IL-1beta and IL-18 are related closely, and both require the intracellular cysteine protease caspase-1 for biological activity. The IL-18 binding protein, a naturally occurring and specific inhibitor of IL-18, neutralizes IL-18 activities and has been shown to be safe in patients. Other options for reducing IL-18 activities are inhibitors of caspase-1, human monoclonal antibodies to IL-18, soluble IL-18 receptors, and anti-IL-18 receptor monoclonal antibodies.

Interleukin 1 and interleukin 18 as mediators of inflammation and the aging process

In this review, 2 cytokines are discussed with respect to the inflammatory processes that are fundamental to aging and mortality. Both interleukin (IL)-1 and IL-18 are members of the same structural family (IL-1 family, or IL-F); there are presently 9 members of this family, but with the exception of IL-1alpha, IL-1beta, and IL-18, the others are antagonists or remain without known function. IL-1alpha is an intracellular cytokine with properties of both a cytokine and a transcription factor. IL-1beta and IL-18 are closely related; both possess a similar three-dimensional structure, and their respective precursor forms are inactive until cleaved by the intracellular cysteine protease caspase-1. Patients with mutations in the NALP3 gene, which controls the activity of caspase-1, readily secrete more IL-1beta and IL-18 and suffer from systemic inflammatory diseases. Patients with defects in this gene have high circulating concentrations of IL-6, serum amyloid A, and C-reactive protein, each of which decrease rapidly upon blockade of the IL-1 receptor, which suggests that IL-1beta contributes to the elevation of these markers of the inflammatory mechanisms of aging. Animal studies support the concept that IL-1beta and IL-18 participate in the pathogenesis of atherosclerosis. For example, overexpression of the IL-18 binding protein, a naturally occurring, specific inhibitor of IL-18, prevents the spontaneous development of atherosclerosis in apolipoprotein E-deficient mice. From human and animal studies, one may conclude that IL-1beta and IL-18 participate in fundamental inflammatory processes that increase during the aging process.

IL-18 binding protein increases spontaneous and IL-1-induced prostaglandin production via inhibition of IFN-gamma

IL-18 shares with IL-1 the same family of receptors and several identical signal transduction pathways. Because of these similarities, IL-18 was investigated for its ability to induce prostaglandin E(2) (PGE(2)) synthesis in human peripheral blood mononuclear cells (PBMC), a prominent, proinflammatory property of IL-1. IL-18 was highly active in PBMC by inducing the synthesis of the chemokine IL-8; however, no induction of PGE(2) synthesis nor cyclooxygenase type-2 gene expression was observed in PBMC stimulated with IL-18. In the same cultures, IL-1beta induced a 12-fold increase in PGE(2). Although IL-1beta-induced IL-8 synthesis was augmented 3-fold by IL-18, IL-18 suppressed IL-1beta-induced PGE(2) production by 40%. The suppressive effect of IL-18 on PGE(2) production was mediated by interferon (IFN)-gamma because anti-human IFN-gamma-antibody prevented IL-18-induced reduction in PGE(2). Consistent with these observations, IL-12, a known inducer of IFN-gamma, augmented IL-1beta-induced IFN-gamma but suppressed IL-1beta-induced PGE(2) by 75%. IL-18 binding protein (IL-18BP) is a naturally occurring and specific inhibitor of IL-18. When recombinant IL-18BP was added to PBMC cultures, unexpectedly, spontaneous PGE(2) production increased. PGE(2) production was also increased by the addition of IL-18BP to PBMC stimulated with either IL-1beta or IL-12 and also in whole blood cultures stimulated with Staphylococcus epidermidis. These studies demonstrate that IL-18BP decreases endogenous IL-18 activity by reducing IFN-gamma-mediated responses.

Cytokine-dependent synergistic regulation of interleukin-8 production from human gingival fibroblasts

Human Gingival Fibroblasts (HGF) may have an important role in the orchestration of immuno-participant cells infiltrating the gingiva in response to continuously recurring bacterial infection. To examine the cytokine network regulating HGF-derived interleukin (IL)-8, a potent neutrophil chemotactic cytokine, we analyzed the effects of inflammatory cytokines alone and in combination on IL-8 production by HGF. IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-6, and IL-8 were used as stimulants. HGF secreted IL-8 in a dose-dependent manner after stimulation with either IL-1 beta or TNF-alpha, but not with IFN-gamma or IL-6. Furthermore, IL-8 itself did not affect IL-8 mRNA accumulation in HGF in an autocrine manner. The combination of IL-1 beta and TNF-alpha synergistically enhanced the secretion of IL-8, whereas IFN-gamma suppressed IL-8 secretion by IL-1 beta- or TNF-alpha-stimulated HGF. These effects were also observed at each level of IL-8 mRNA expression in HGF. IL-8 secretion by cytokine-stimulated HGF was not influenced by the inhibition of PGE2 synthesis with indomethacin, indicating that endogenous PGE2 was not involved in IL-8 production by HGF. These results indicate that IL-8 production by HGF is synergistically stimulated by specific cytokines, IL-1 beta and TNF-alpha, and suggest that these stimulatory effects are down-regulated by IFN-gamma at the transcriptional level through PGE2-independent pathways. Thus, neutrophil-mediated processes in periodontal disease may be regulated in part by HGF in the cytokine network of immuno-participant cells.

Substance P gene expression is regulated by interleukin-1 in cultured sympathetic ganglia

We have investigated the effects of interleukin-1 beta (IL-1 beta) on the induction of substance P (SP) in cultured sympathetic ganglia. Northern blot analysis reveals that SP increases are secondary to an increase in mRNA coding for the preprotachykinin (PPT) precursor of SP. Nuclear transcription assays detect an early increase in PPT-specific nascent transcripts, suggesting that the ultimate effect of IL-1 is on transcription itself. Depolarizing agents, interferon-gamma, glucocorticoid hormones, and prostaglandin synthesis inhibitors all diminish the induction of SP and PPT mRNA by IL-1. Since SP has stimulatory effects on the immune system, the IL-1-induced increase in ganglionic SP may be one means by which the nervous and immune systems interact during an acute response to ganglionic injury.

Effects of murine recombinant interferon-gamma on rat liver fat storing cell proliferation, cluster formation and proteoglycan synthesis

Rat liver fat storing cells (FSC, perisinusoidal lipocytes, Ito cells) in primary culture were exposed to various concentrations of murine recombinant interferon-gamma (rIFN-gamma) in the range of 1 to 50 units/mL medium for 72 hr. FSC kept in complete medium (10% fetal calf serum) showed a dose-dependent increase of both [3H]thymidine incorporation (up to 2.3-fold) and DNA content of culture. Reverse (inhibitory) effects were obtained with cells kept under serum-reduced (0.5% fetal calf serum) conditions. The synthesis of medium proteoglycans and of total cellular protein was not affected by rIFN-gamma. By bromodeoxyuridine-staining (BrdUrd) and phase contrast microscopy it is shown that rIFN-gamma stimulates strongly the cluster growth of FSC in culture. The cluster forming cells differ in their morphology and their cytoskeleton-staining from typical FSC. They were found to be mostly desmin and alpha-actin negative or weakly positive but highly proliferative. Because no contaminating fibroblasts and other cell types were detected in any appreciable amounts in the early cultures we conclude that the clustered cells might be a rapidly proliferating subpopulation of FSC, which is promoted by rIFN-gamma.

Bone-resorbing activity and prostaglandin E produced by human periodontal ligament cells in vitro

Human periodontal ligament (PDL) cells were derived from healthy premolars extracted for orthodontic treatment and were utilized for in vitro experiments in passages 4-6. Human PDL cells were seeded in tissue culture tubes and incubated with interleukin-1 alpha (IL-1 alpha), IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), indomethacin, parathyroid hormone (PTH), or their combinations, for 1 h. The medium was then replaced with serum-free BGJb medium and incubated for 24 h without further additions. Prostaglandin E (PGE) concentrations in the conditioned media (CM) were measured by radioimmunoassay, and bone-resorbing activity was measured using 45Ca-labeled neonatal mouse calvariae. The results of this study indicated that (1) unstimulated cultured PDL cells produced PGE, and PDL CM stimulated bone resorption; (2) cytokine-treated (IL-1 alpha, IL-1 beta, and TNF-alpha) PDL cells had increased production of PGE and bone-resorbing activity compared to unstimulated PDL cells; (3) indomethacin completely inhibited PGE production from unstimulated PDL cells but only partially inhibited bone-resorbing activity, indicating that PDL cells produced nonprostaglandin bone-resorbing factor(s); (4) IFN-gamma did not change PGE or bone-resorbing activity production by cytokine-stimulated PDL cells; and (5) PTH treatment of PDL cells in addition to cytokines (IL-1 alpha, IL-1 beta, and TNF-alpha) had additive effects on the production of bone-resorbing activity and synergistic effects on PGE production compared to cytokine treatment alone.

Synergistic, additive, and antagonistic effects of interleukin-1 beta, tumor necrosis factor alpha, and gamma-interferon on prostaglandin E, hyaluronic acid, and collagenase production by cultured synovial fibroblasts

The effects of binary combinations of the recombinant human cytokines, interleukin-1 beta (rHuIL-1 beta), tumor necrosis factor alpha (rHuTNF alpha), and gamma-interferon (rHu gamma-IFN) on the production of prostaglandin E (PGE), hyaluronic acid (HA), and collagenase by human synovial fibroblasts in culture were investigated. All 3 were stimulated by rHuIL-1 beta and rHuTNF alpha alone, but not by rHu gamma-IFN. Stimulation with rHuIL-1 beta and rHuTNF alpha occurred at femtomolar and picomolar concentrations, respectively, and maximal stimulation by rHuIL-1 beta was several times greater than that by rHuTNF alpha. Stimulation of PGE and collagenase production with rHuIL-1 beta or rHuTNF alpha was depressed by rHu gamma-IFN, depending on the concentration used. In contrast, stimulation of HA production with rHuIL-1 beta or rHuTNF alpha was unaffected or increased somewhat with rHu gamma-IFN. Combinations of rHuIL-1 beta or rHuTNF alpha had marked synergistic effects on PGE and collagenase production. However, when rHuIL-1 beta effects were maximal, rHuTNF alpha had an additive effect. These cytokines had only additive effects on HA production, however, and when rHuIL-1 beta effects were maximal, rHuTNF alpha produced no further stimulation. These data suggest that the secretory activities of synovial fibroblasts can be influenced by a combination of cytokines and is dependent on the type of cytokine present and its concentration.

Interactive effects between cytokines on PGE production by human periodontal ligament fibroblasts in vitro

Mononuclear cell production of cytokines that stimulate fibroblast production of prostaglandin E (PGE) is an important mechanism by which mononuclear cells regulate fibroblast function. The objective of this investigation was to determine the effects of the cytokines interleukin 1 beta (IL-1 beta), interleukin 1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma), alone or in paired combinations, on PGE production by near-confluent human periodontal ligament (PDL) fibroblasts in vitro. Premolars extracted in the course of orthodontic treatment were used for this study. Fibroblast cultures, free of epithelial cells, were obtained after the fourth subculture by the use of accurately-timed trypsin treatment. Cells in the fourth to sixth passage, incubated in DMEM supplemented with 10% equine serum, were used for these experiments. Cells (1 x 10(5)) were seeded in 12- x -75-mm tissue culture tubes and incubated with various doses of IL-1 beta, IL-1 alpha, TNF-alpha, and IFN-gamma, alone or in specific combinations, for 15 min, two, 12, 24, and 72 h. PGE concentrations in the media were measured by radio-immunoassay. The results showed that human PDL fibroblasts responded to the administration of cytokines by an elevation in the synthesis of PGE in a dose- and time-related fashion. The increase in PGE production was inhibited by the addition of indomethacin. The interactions between these cytokines varied in degree, depending on the particular combinations of cytokines. In addition, the administration of cytokine combinations was found to be additive, synergistic, subtractive, or suppressive on the production of PGE by PDL fibroblasts, depending on the duration of incubation. These experiments demonstrate the importance of the consideration of the interplay between cytokines produced by mononuclear cells on the mechanisms that regulate the functions of PDL fibroblasts.