Elevation of plasma interleukin-18 concentration is correlated with disease activity in systemic lupus erythematosus

Disease association of the interleukin-18 promoter polymorphisms in Taiwan Chinese systemic lupus erythematosus patients

Interleukin (IL)-18, an important mediator of innate and adaptive immunity, plays multiple roles in chronic inflammation, in autoimmune diseases, in a variety of cancers and in number of infectious diseases. IL-18 promoter polymorphisms have been also noted associated with various inflammatory diseases. We investigated the association of IL-18 promoter polymorphisms (-656T/G, -607A/C and -137C/G) with systemic lupus erythematosus (SLE) in Taiwan Chinese patients and controls. Six haplotypes (hts) were identified from the three promoter polymorphisms. The genotype distribution of the ht1 (GCC), ht2 (TAC), ht4 (GAC) and ht5 (TCC) were different in patients and controls (P<0.002). Moreover, the haplotype and genotype frequencies of ht1 were significantly increased in patients with discoid rash (P=0.045, odds ratio (OR): 2.01, 95% confidence interval (CI): 1.01-4.00; P=0.027, OR: 5.13, 95% CI: 1.41-18.68). In addition, the homozygous genotype ht1/ht1 was significant increased in patients with serositis (P=0.015, OR: 9.78, 95% CI: 1.55-61.73). These observations suggest that the three promoter polymorphisms contribute to the genetic background of SLE pathogenesis.

Arsenic trioxide: a promising novel therapeutic agent for lymphoproliferative and autoimmune syndromes in MRL/lpr mice

MRL/lpr mice develop a human lupuslike syndrome and, as in autoimmune lymphoproliferative syndrome (ALPS), massive lymphoproliferation due to inactivation of Fas-mediated apoptosis. Presently, no effective therapy exists for ALPS, and long term, therapies for lupus are hazardous. We show herein that arsenic trioxide (As2O3) is able to achieve quasi-total regression of antibody- and cell-mediated manifestations in MRL/lpr mice. As2O3 activated caspases and eliminated the activated T lymphocytes responsible for lymphoproliferation and skin, lung, and kidney lesions, leading to significantly prolonged survival rates. This treatment also markedly reduced anti-DNA autoantibody, rheumatoid factor, IL-18, IFN-γ, nitric oxide metabolite, TNF-α, Fas ligand, and IL-10 levels and immune-complex deposits in glomeruli. As2O3 restored cellular reduced glutathione levels, thereby limiting the toxic effect of nitric oxide, which is overproduced in MRL/lpr mice. Furthermore, As2O3 protected young animals against developing the syndrome and induced almost total disease disappearance in older affected mice, thereby demonstrating that it is a novel promising therapeutic agent for autoimmune diseases.

Elevated serum levels of interferon-regulated chemokines are biomarkers for active human systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is a serious systemic autoimmune disorder that affects multiple organ systems and is characterized by unpredictable flares of disease. Recent evidence indicates a role for type I interferon (IFN) in SLE pathogenesis; however, the downstream effects of IFN pathway activation are not well understood. Here we test the hypothesis that type I IFN-regulated proteins are present in the serum of SLE patients and correlate with disease activity.

METHODS AND FINDINGS

We performed a comprehensive survey of the serologic proteome in human SLE and identified dysregulated levels of 30 cytokines, chemokines, growth factors, and soluble receptors. Particularly striking was the highly coordinated up-regulation of 12 inflammatory and/or homeostatic chemokines, molecules that direct the movement of leukocytes in the body. Most of the identified chemokines were inducible by type I IFN, and their levels correlated strongly with clinical and laboratory measures of disease activity.

CONCLUSIONS

These data suggest that severely disrupted chemokine gradients may contribute to the systemic autoimmunity observed in human SLE. Furthermore, the levels of serum chemokines may serve as convenient biomarkers for disease activity in lupus.

Chloroquine treatment influences proinflammatory cytokine levels in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is an autoimmune disease with a complex pathogenesis. Published data have revealed that serum levels of proinflammatory cytokines are increased in SLE patients. The aim of our study was to evaluate whether monotherapy with chloroquine phosphate affects IL-1beta, IL-6, IL-18 and TNF-alpha serum levels in SLE patients. The study group consisted of 25 SLE patients with mild or moderate disease activity and 25 age- and sex-matched healthy control subjects. In SLE patients the cytokine levels were measured just before and three months after starting chloroquine treatment at a dose of 125 mg twice daily. Although the majority of SLE patients had a low systemic lupus activity measure (SLAM) index, the levels of IL-6, IL-18 and TNF-alpha were significantly higher than in the control group. After three-months of chloroquine therapy the mean level of IL-6, IL-18 and TNF-alpha decreased significantly. Minimal erythema doses (MEDs) were significantly increased in SLE patients after three months of chloroquine therapy. The results indicate that chloroquine treatment lowers some proinflammatory cytokines and may provide a photoprotective effect.

Blockade of TLR9 agonist-induced type I interferons promotes inflammatory cytokine IFN-gamma and IL-17 secretion by activated human PBMC

Type I interferons (IFN) (IFN-alpha/beta) are recognized as both inhibitors and effectors of autoimmune disease. In multiple sclerosis, IFN-beta therapy appears beneficial, in part, due to its suppression of autoimmune inflammatory Th cell responses. In contrast, in systemic lupus erythematosus (SLE) triggering of plasmacytoid DC (pDC) Toll-like receptors (TLRs) by autoimmune complexes (autoICs) results in circulating type I IFN that appear to promote disease by driving autoantigen presentation and autoantibody production. To investigate how pDC-derived type I IFN might regulate Th cells in SLE, we examined a model in which sustained pDC stimulation by autoICs is mimicked by pretreating normal human PBMC with TLR9 agonist, CpG-A. Subsequently, PBMC Th cells are activated with superantigen, and APC are activated with CD40L. The role of CpG-A/TLR9-induced type I IFN in regulating PBMC is determined by blocking with virus-derived soluble type I IFN receptor, B18R. In summary, pretreatment with either rhIFN-alpha/beta or CpG-A inhibits PBMC secretion of superantigen-induced IFN-gamma and IL-17, and CD40L-induced IL-12p70 and IL-23. B18R prevents these effects. Data indicate that CpG-A-induced type I IFN inhibit IL-12p70-dependent PBMC IFN-gamma secretion by enhancing IL-10. Our results suggest that in SLE, circulating type I IFN may potentially act to inhibit inflammatory cytokine secretion.

Characteristics and long-term outcome of 15 episodes of systemic lupus erythematosus-associated hemophagocytic syndrome

Reactive hemophagocytic syndrome (HS) occurs mainly in the setting of serious infections and lymphomas. HS can occur in the course of 2 active systemic diseases, without simultaneous infection: adult Still disease and systemic lupus erythematosus (SLE). Observations of specific lupus-associated HS are rare, and the long-term outcome of these patients with active SLE is unknown. We retrospectively studied 15 episodes of SLE-associated HS in 12 patients (10 women, 2 men) and noted the long-term outcome. HS occurred at a mean age of 25 years. All patients were febrile with >or=2 cytopenias, and bone marrow aspiration indicated hemophagocytosis. HS revealed SLE in 9 patients and recurred in 3. The main features of SLE-associated HS were a low frequency of hepatosplenomegaly, a high frequency of heart involvement (5 pericarditis, 4 myocarditis requiring transfer to intensive care unit), and a low C-reactive protein level (mean, 15 mg/L). Cutaneous-mucous symptoms of SLE, arthritis, and nephritis were present respectively in 8 (53%), 6 (40%), and 4 (27%) episodes, but symptoms of SLE were absent in 4 episodes at admission. All patients had anti-nuclear antibodies when the HS occurred. Anti-double-stranded DNA antibodies were present in 12 episodes. Treatment was steroids in 14 cases but cyclophosphamide was the only treatment able to control HS in 2 cases. All the cases of SLE-associated HS were controlled by the immunosuppressive regimen. Intravenous immunoglobulins seemed poorly effective. No infectious agent was found. Clinical presentations of the 23 patients with SLE-associated HS described in the literature were reviewed and were similar to those of the current series. The mean follow-up was 88 months (range, 7-240 mo). One patient died at 15 months (sepsis). Among the 5 patients with a follow-up >8 years, 4 always had active disease. During the follow-up of SLE, immunosuppressive drugs were added in 8 patients (cyclophosphamide in 7, azathioprine in 3, mycophenolate mofetil in 2) with significant adverse drug reactions. In the long-term, SLE-associated HS seems to define a severe SLE form with frequent flares, possible HS recurrences, and the need for prolonged immunosuppression.

Soluble Mediators as Therapeutic Targets in Systemic Lupus Erythematosus: Cytokines, Immunoglobulin Receptors, and the Complement System

After many years of anticipation, we have entered a period of promise for new lupus therapies; several clinical trials are planned or are in progress. The accelerated activity in systemic lupus erythematosus therapeutics has been driven by scientific advances. Enhanced understanding of the cells and mediators that drive autoimmunity and tissue damage has led to the identification of rational therapeutic targets. The conventional immunosuppressive therapies, including corticosteroids and cyclophosphamide, can be effective but at a high and unacceptable cost of adverse effects. There is high optimism that targeted therapies, including those that are specific for soluble mediators, will allow effective control of disease activity while sparing patients the damaging toxicities that are associated with traditional immunosuppressive agents.

New treatments for SLE: cell-depleting and anti-cytokine therapies

Although systemic lupus erythematosus (SLE) is indeed a complex autoimmune disease, recent advances in our understanding of lupus pathogenesis have suggested new, targeted approaches to therapy. The purpose of this review is to discuss the underlying scientific rationale and results of first clinical studies of new treatment approaches to SLE, with a focus on cell-depleting therapies and cytokine blockade. It has become clear that the B lymphocyte plays a key role in disease pathogenesis by both autoantibody-dependent and autoantibody-independent mechanisms. Additionally, aberrant interactions between B and T cells are critical to disease emergence and progression. New agents that directly target immune cells abnormal in SLE include the B-cell depleting or modulating antibodies, rituximab (anti-CD20) and epratuzumab (anti-CD22) and the anti-dsDNA tolerogen LJP394. Another promising approach has been to block co-stimulatory interactions between T and B cells, for example by inhibiting the CD40-CD40 ligand pathway with anti-CD40 ligand monoclonal antibody or the B7 pathway with CTLA-4Ig. Immune cells can also be manipulated indirectly through cytokine effects. For B cells, anti-BAFF (B-cell activation factor of the tumor necrosis family) provides an example of this approach. Other, more pleiotropic cytokines can likewise be blocked in SLE. In addition to the blockade of interleukin-10 (IL-10), the first anti-cytokine approach examined, it is mainly anti-tumor necrosis factor therapy that has come into focus, holding promise for some patients with lupus nephritis. The majority of the available data on these new treatment approaches stems from open-label trials, but controlled trials are under way. Moreover, many additional cytokines, such as interleukin (IL)-6, IL-18, and the type I interferons, represent interesting future targets.

The adrenal gland is a source of stress-induced circulating IL-18

The present study compared plasma IL-18 levels between sham-operated and adrenalectomized mice following stress to investigate whether the adrenal gland contributes to the elevation of circulating IL-18 during stress. Two hours of stress provoked a robust, stressor-dependent, elevation of IL-18 mRNA and peptide in the adrenal gland in sham-operated mice. Consistently, levels of circulating mature IL-18 increased during stress and remained elevated for up to 6 h after stress. The stress-induced increase in circulating IL-18 was abolished by adrenalectomy. These findings demonstrate that the adrenal gland is required to achieve elevation of circulating IL-18 during stress.

A role of the adrenal gland in stress-induced up-regulation of cytokines in plasma

To reveal a pathway by which psychological/physical stresses influence host defense capability, responses to immobilization stress in mice were investigated, focusing on a multifunctional cytokine, interleukin-18 (IL-18). Immobilization stress induced interleukin-18 accumulation in plasma and in the adrenal gland. Inhibition on ACTH resulted in suppressed levels of IL-18 both in plasma and the adrenal gland. In hemi-adrenalectomized mice, plasma IL-18 levels after stress were lower than in sham-operated mice. This, together with the observation in stressed hemi-adrenalectomized mice that IL-6 levels in plasma were suppressed but up-regulated by recombinant IL-18, showed that the adrenal gland plays a crucial role in stress-related elevation of IL-6 in plasma via IL-18. Adrenal gland is highlighted as an organ connecting the psychological, endocrine, and immune systems. Controlling the secretion of IL-18 from the adrenal gland may serve as a possible preventative means against a stress-related disruption of host defenses.

Rational design of an EGF-IL18 fusion protein: implication for developing tumor therapeutics

Interleukin-18 (IL-18) is a proinflammatory cytokine. This protein has a role in regulating immune responses and exhibits significant anti-tumor activities. Epidermal growth factor (EGF) is an important growth factor that plays a central role in the regulation of cell cycle and differentiation. It was proposed that a targeted delivery of IL-18 by generation of IL-18-EGF fusion protein might decrease adverse effects and result in enhancing cytotoxic and antitumor activities. In the present study, a fusion protein, consisting of EGFR binding domain fused to human IL-18 mature peptide via a linker peptide of (Gly(4)Ser) 3, was constructed and expressed in the insect cell line Sf9 using Bac-to-Bac baculovirus expression system. We showed that the purified recombinant fusion protein induced similar levels of IFN-gamma to that of native IL-18 protein in human PBMC in the presence of ConA. Furthermore, EGF receptor competitive test in human epithelial cancer A431 cell line showed that EGF-IL18 fusion protein can specifically bind with EGFR by competing with native EGF protein. These suggest that this rationally designed protein can be further developed as novel tumor therapeutics.

Interleukin-18 bioactivity: a novel target for immunopharmacological anti-inflammatory intervention

Interleukin-18 is a member of the interleukin-1 family of cytokines with pro-inflammatory and tumor-suppressive properties. Its ability to potently enhance the production of interferon-gamma indicates in particular the crucial function of interleukin-18 as an immunomodulatory molecule. In fact, high levels of interleukin-18 are detected in human diseases associated with immunoactivation including viral or bacterial infections and chronic inflammation. Animal models suggest suppression of interleukin-18 bioactivity as a novel therapeutic concept specifically for the treatment of chronic inflammatory diseases such as rheumatoid arthritis, Crohn's disease, and psoriasis. Here we introduce into the biology of interleukin-18 and review immunopharmacological strategies that aim at reducing interleukin-18 bioactivity in human disease.

Cys74 and Cys163 are necessary for IL-18 to elicit IFN-gamma production from peripheral blood lymphoid mononuclear cells

There are four cysteines (Cys74, Cys104, Cys112 and Cys163) in mature human IL-18 (hIL-18). These cysteines are highly conserved in IL-18s of 11 species cloned so far, suggesting that one or more of the cysteines may be important for hIL-18 function. In this study, each cysteine residue was individually replaced with serine by site-directed mutagenesis. The wild type and mutant IL-18s were expressed in Escherichia coli and renatured by two renaturing methods. The purified wild type and mutant rhIL-18s were assayed for their capacity of inducing IFN-gamma and activating NF-kappaB from ConA-stimulated PBMC. DNA binding activity of NF-kappaB was performed by electrophoretic mobility-shift analysis. Our results showed that the mutant rhIL-18C74S and C163S induced much less amount of IFN-gamma from PBMC and the decrement of NF-kappaB DNA binding activity was also observed from C74S and C163S treated PBMC. These results indicate that functional hIL-18 has an absolute requirement for residues Cys74 and Cys163.

Aberrant production of soluble costimulatory molecules CTLA-4, CD28, CD80 and CD86 in patients with systemic lupus erythematosus

OBJECTIVE

The costimulatory interactions of the B7 family molecules CD80 and CD86 on antigen-presenting cells with their T-cell counter-receptors CD28 and CTLA-4 modulate T lymphocyte-mediated immune responses in a reciprocal manner. We investigated the possible aberrant production of soluble (s) forms of the T-cell costimulatory molecules CD80, CD86, CD28 and CTLA-4 in plasma of patients with systemic lupus erythematosus (SLE), an autoimmune disease arising from T-lymphocyte dysregulation.

METHODS

Plasma concentration and ex vivo production of soluble costimulatory molecules of 79 SLE patients with or without active disease and 40 sex- and age-matched healthy subjects were measured by enzyme-linked immunosorbent assay.

RESULTS

Plasma sCTLA-4, sCD28, sCD80 and sCD86 concentrations of all SLE patients were significantly higher than concentrations in control subjects (all P<0.01). These increases were observed even in patients with inactive disease [SLE Disease Activity Index (SLEDAI) <3]. Plasma sCTLA-4 concentration in all SLE patients correlated significantly with SLEDAI score (r = 0.228, P = 0.043). Upon mitogen treatment of peripheral blood mononuclear cells, the percentage increases in ex vivo production of sCD28 and sCD80 and the percentage decrease in sCTLA-4 release were all significantly smaller in SLE patients with active disease than in healthy subjects (P<0.01, P<0.05 and P<0.0001, respectively).

CONCLUSION

The aberrant production of soluble T-cell costimulatory molecules is important in the immunopathogenesis of SLE, which occurs by the dysregulation of T-lymphocyte costimulation. Plasma sCTLA concentration could potentially serve as a surrogate marker of SLE disease activity.

Elevation of plasma osteopontin concentration is correlated with disease activity in patients with systemic lupus erythematosus

BACKGROUND

Osteopontin (OPN) is an extracellular matrix cell adhesion phosphoprotein with immunological activities including stimulation of macrophage chemotaxis, T-helper type 1 lymphocyte response and B-cell antibody synthesis. Overexpression of OPN has been associated with the development of the autoimmune/lymphoproliferative syndrome.

METHODS

We measured the plasma concentration and ex vivo production of OPN, and the plasma proinflammatory IL-18 concentration in 54 SLE patients with or without renal impairment (RSLE group and SLE group, respectively) and 26 sex- and age-matched control (NC) subjects using an enzyme-linked immunoabsorbent assay.

RESULTS

Plasma OPN concentrations were significantly higher in RSLE and SLE patients than in the NC group (both P<0.001). Increase in OPN concentration correlated positively and significantly with SLEDAI score in all SLE patients (r = 0.308, P = 0.023). The ex vivo production of OPN upon mitogen activation of peripheral blood mononuclear cells was significantly higher in the RSLE and SLE groups than in the NC group (both P<0.001). In RSLE patients, plasma OPN concentration showed a significant positive correlation with proinflammatory cytokine IL-18 concentration (r = 0.404, P = 0.037).

CONCLUSION

The above results suggest that the production of OPN is associated with the inflammatory process and SLE development, and may serve as a potential disease marker of SLE.

Up-regulation of IL-18 and predominance of a Th1 immune response is a hallmark of lupus nephritis

There is evidence that nephritis is dominated by a Th1 immune response in systemic lupus erythematosus. Since IL-18 promotes polarization of the immune response toward Th1, we investigated the role of this cytokine in lupus nephritis (LN). A total of 133 lupus patients and 44 healthy subjects were enrolled. Demographic and clinical characteristics with renal biopsy data were recorded. IL-18 along with IFN-gamma and IL-4, two prototypical of Th1 and Th2 cytokines, were measured in serum by ELISA. Peripheral blood lymphocytes were analysed by flow cytometry for IFN-gamma and IL-4. IL-18 expression was determined by immunohistochemistry in 13 renal biopsy specimens from patients with LN and 2 controls. Serum IL-18 was higher in lupus patients than in controls. Levels of IL-18 correlated with urinary microalbumin and were increased in patients with LN when compared to those without LN. IL-18 expression was also increased within the glomeruli of nephritic patients and was primarily detected within the mesangial matrix and in infiltrating mononuclear cells. Measurement of IFN-gamma and IL-4 in either sera or peripheral blood lymphocytes showed high IFN-gamma along with low IL-4 expression in LN patients compared to patients without nephritis. A positive correlation between serum IL-18 and IFN-gamma levels was found. IL-18 may play a prominent role in the pathogenesis of LN by promoting a cytokine imbalance towards a Th1 immune response. Measurement of IL-18 may be helpful for the early identification of lupus patients with LN and may help gauge the response to treatment in patients with active LN undergoing treatment.

Pathogenesis of hemophagocytic syndrome (HPS)

Hemophagocytic syndrome (HPS) is a clinicopathologic entity characterized by increased proliferation and activation of benign macrophages with hemophagocytosis throughout the reticuloendothelial system. Uncontrolled T-lymphocyte activation is responsible for increased T(H)1 cytokines secretion such as IFN-gamma, IL-12 and IL-18 that promotes macrophage activation. Genetic defects specific for cytotoxic T lymphocytes (CTL) and natural killer (NK) cells have been identified in patients with primary HPS that are responsible for altered cell death and apoptosis induction or target killing. HPS may be secondary to malignancy, infection or autoimmune disease, and mechanisms involved are poorly understood. However, in adult-onset Still's disease, juvenile chronic arthritis and probably systemic lupus erythematosus, IL-18 might play a role in initiating macrophage activation.

Increased circulating levels and salivary gland expression of interleukin-18 in patients with Sjögren's syndrome: relationship with autoantibody production and lymphoid organization of the periductal inflammatory infiltrate

IL-18, an immunoregulatory and proinflammatory cytokine, has been shown to play an important pathogenic role in Th1-driven autoimmune disorders. In this study, we evaluated the circulating levels and salivary-gland expression of IL-18 in patients with Sjögren's syndrome (SS), a mainly Th1-mediated disease. IL-18 serum levels were measured by ELISA in 37 patients with primary SS, 42 with rheumatoid arthritis, and 21 normal controls. We demonstrated high IL-18 serum levels in SS, similar to those in rheumatoid arthritis patients and significantly higher than in controls (P < 0.01). In addition, IL-18 serum concentrations were significantly higher in anti-SSA/Ro+ and anti-SSB/La+ than in anti-SSA/Ro- and anti-SSB/La- SS patients (respectively, P = 0.01, P < 0.01). Serum IL-18 correlated strongly with anti-SSA/Ro (P = 0.004) and anti-SSB/La (P = 0.01) titers. Salivary gland IL-18 expression was investigated by single/double immunohistochemistry in 13 patients with primary SS and in 10 with chronic sialoadenitis, used as controls. The expression of IL-18 was also examined in periductal inflammatory foci in relation to the acquisition of features of secondary lymphoid organs such as T-B compartmentalization, formation of follicular dendritic cell networks, and presence of germinal-center-like structures. IL-18 expression in SS salivary glands was detected in 28 of 32 periductal foci of mononuclear cells (87.5%), while no IL-18 production by infiltrating cells was detected in patients with chronic sialoadenitis. Within the inflammatory foci, IL-18 immunoreactivity co-localized almost exclusively with CD68+ macrophages. In addition, IL-18 was found in 15 of 19 foci (78.9%) with no evidence of T-B cell compartmentalization (nonsegregated) but in 100% of the segregated aggregates, both in T- and B-cell-rich areas. Strikingly, IL-18 was strongly expressed by CD68+ tingible body macrophages in germinal-centre-like structures both in SS salivary glands and in normal lymph nodes. IL-18 expression was observed in the ducts of all SS biopsies but in only 4 of 10 patients with nonspecific chronic sialoadenitis (P < 0.01). This study provides the first evidence of increased circulating levels and salivary gland expression of IL-18 in SS, suggesting an important contribution of this cytokine to the modulation of immune inflammatory pathways in this condition.

Elevated interleukin-18 levels correlated with disease activity in systemic lupus erythematosus

The aim of this study was to determine the serum interleukin-18 (IL-18) levels in patients with systemic lupus erythematosus (SLE) and to assess their relationship with disease activity. Thirty-five patients with SLE and 35 age- and sex-matched controls were enrolled in this study. Paired serum samples were collected from all the patients with SLE, both at active stage before treatment and at the stable stage after treatment. The serum IL-18 levels were determined using ELISA and their correlations with the disease activity, measured using the SLE Disease Activity Index (SLEDAI) and laboratory parameters such as anti-dsDNA antibody, CH50, C3, C4, and circulating immune complex levels, were analyzed. The serum IL-18 levels in patients with SLE were significantly higher than those in the controls, particularly when the disease status was active (mean+/-SD: active stage, 721.23+/-360.15 pg/ml; inactive stage, 343.68+/-317.78 pg/ml; controls, 113.98+/-13.22 pg/ml, p<0.05). The IL-18 levels measured at the active stage before treatment correlated well with SLEDAI (r=0.41, p<0.05) and anti-dsDNA antibody titer (r=0.35, p<0.05). When we compared the changes of the IL-18 level and those of parameters reflecting the disease activity between the active stage and the stable stage of the disease, it was found that the changes in IL-18 level correlated well with the changes of SLEDAI score during the patient's disease course (r=0.39, p<0.05). In conclusion, the serum IL-18 levels were elevated in patients with SLE, and these increased levels correlated well with SLE disease activity.

Interleukin-18 null mice show diminished microglial activation and reduced dopaminergic neuron loss following acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment

Recent reports have revealed an involvement of microglial cells in dopaminergic neurodegeneration. In the present study, we tested the hypothesis that interleukin-18 (IL-18) plays a role in the microglial activation. The present study investigated microglial activation and dopaminergic neurodegeneration in substantia nigra pars compacta (SNpc) following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in wild type (WT) and IL-18 knockout (KO) mice. The number of dopaminergic neuron loss in WT mice was significantly decreased 7 days after MPTP treatment compared with IL-18 KO mice. In WT mice microglial activation occurred in the SN at 1 day after MPTP treatment, progressively increased within the SNpc until 7 days post MPTP, and subsided by 14 days. In contrast, in IL-18 KO mice microglial activation occurred in the SN at 1 day post-MPTP, and decreased by 7 days, earlier than in WT mice. The lesser microglial activation and dopaminergic neurodegeneration in the SNpc following MPTP treatment in WT indicates the possibility that IL-18 may participate in microglial activation and dopaminergic neurodegeneration.

IL-18 cDNA vaccination protects mice from spontaneous lupus-like autoimmune disease

The lupus-like autoimmune syndrome of MRL/Mp-Tnfrsf6lpr (lpr) mice is characterized by progressive lymphadenopathy and autoantibody production, leading to early death from renal failure. Activation of T helper lymphocytes is one of the events in the pathogenesis of the disease in these mice and likely in human systemic lupus erythematosus. Among T helper lymphocyte-dependent cytokines, IFN-gamma plays a pivotal role in the abnormal cell activation and the fatal development of the lpr disease. IL-18, an inducer of IFN-gamma in T lymphocytes and natural killer cells, may contribute to the disease because cells from lpr mice are hypersensitive to IL-18 and express high levels of IL-18. To assess the contribution of IL-18 to the pathogenesis in the animal model, in vivo inhibition of IL-18 was attempted. Young lpr mice were vaccinated against autologous IL-18 by repeated administration of a cDNA coding for the murine IL-18 precursor. Vaccinated mice produced autoantibodies to murine IL-18 and exhibited a significant reduction in spontaneous lymphoproliferation and IFN-gamma production as well as less glomerulonephritis and renal damage. Moreover, mortality was significantly delayed in anti-IL-18-vaccinated mice. These studies support the concept that IL-18 plays a major role in the pathogenesis of the autoimmune syndrome of lpr mice and that a reduction in IL-18 activity could be a therapeutic strategy in autoimmune diseases.

Molecular mechanisms regulating Th1 immune responses

The T helper lymphocyte is responsible for orchestrating the appropriate immune response to a wide variety of pathogens. The recognition of the polarized T helper cell subsets Th1 and Th2 has led to an understanding of the role of these cells in coordinating a variety of immune responses, both in responses to pathogens and in autoimmune and allergic disease. Here, we discuss the mechanisms that control lineage commitment to the Th1 phenotype. What has recently emerged is a rich understanding of the cytokines, receptors, signal transduction pathways, and transcription factors involved in Th1 differentiation. Although the picture is still incomplete, the basic pathways leading to Th1 differentiation can now be understood in in vitro and a number of infection and disease models.

IL-18BPa:Fc cooperates with immunosuppressive drugs in human whole blood

The proinflammatory cytokine interleukin (IL)-18 appears to be involved in the pathogenesis of diseases associated with immunoactivation and inflammation. Consequently, blockage of IL-18 bioactivity by use of IL-18 binding protein (IL-18 BP) is likely a promising therapeutic concept. In the present study, we investigated immunomodulatory activities of IL-18 BPa:Fc in human whole blood cultures. We report that IL-18 BPa:Fc (200 ng/mL) significantly inhibited lipopolysaccharide (LPS, 10 ng/mL)/IL-12 (5 ng/mL)-induced release of interferon-gamma (IFNgamma) and matrix metalloproteinase-9 (MMP-9) from whole blood cultures of healthy donors. Notably, IL-18 BPa:Fc (200 ng/mL) further reinforced dexamethasone (5 nM)- or mycophenolic acid (2 microM)-mediated reduction of LPS/IL-12-induced IFNgamma production by an additional 50.5 or 49.9%, respectively. To investigate effects of IL-18 BP:Fc in the context of autoimmune diseases, experiments were performed with whole blood obtained from patients with systemic lupus erythematosus or Wegener's granulomatosis undergoing immunosuppressive therapy. After ex vivo stimulation with LPS (10 ng/mL), production of IFNgamma and MMP-9 was determined. Both mediators likely contribute to renal inflammation frequently seen in these diseases. In accord with the aforementioned data, LPS (10 ng/mL)-induced IFNgamma was significantly reduced by coincubation with IL-18 BPa:Fc at 200 ng/mL. IL-18 BPa:Fc also inhibited production of MMP-9. The present data demonstrate that IL-18 BPa:Fc has the potential to amplify anti-inflammatory actions of immunosuppressive drugs, and thus may prove to be a valuable novel pharmacological component in the treatment of human autoimmune diseases.

Elevated levels of interleukin-18 and tumor necrosis factor-alpha in serum of patients with type 2 diabetes mellitus: relationship with diabetic nephropathy

To compare levels of interleukin (IL)-18, tumor necrosis factor-alpha (TNF-alpha), and IL-6 in serum, we studied 151 type 2 diabetes mellitus patients with various degrees of nephropathy, as well as 80 healthy volunteers. IL-18, TNF-alpha, and IL-6 in serum were measured using an enzyme-linked immunosorbent assay (ELISA) with the respective mouse monoclonal antibodies. Significant differences in serum levels of IL-18 and TNF-alpha were observed between the patients and control subjects (IL-18, 278.0 +/- 11.9 pg/mL v 172.8 +/- 7.7 pg/mL, P <.0001; TNF-alpha, 2.41 +/- 0.18 pg/mL v 0.46 +/- 0.18 pg/mL, P <.0001), whereas that of IL-6 was not different between the two groups (0.73 +/- 0.10 pg/mL v 0.65 +/- 0.08 pg/mL, difference not significant [NS]), although patients with nephropathy showed higher levels. In addition, IL-18 levels were increased in diabetic patients with the development of urinary albumin excretion, with the highest found in those with microalbuminuria (<30 micro g/mg creatinine, 252.7 +/- 16.4 pg/mL; 30 to >300 micro g/mg creatinine, 352.7 +/- 35.2 pg/mL; >>300 micro g/mg creatinine, 350.0 +/- 16.0 pg/mL). Similarly, TNF-alpha and IL-6 in diabetic patients with microalbuminuria or clinical albuminuria were significantly increased as compared with those without albuminuria (TNF-alpha, 3.20 +/- 0.41 pg/mL v 1.94 +/- 0.18 pg/mL; IL-6, 1.64 +/- 1.11 pg/mL v 0.51 +/- 0.05 pg/mL, P <.05, respectively). These results suggest that serum levels of IL-18, TNF-alpha, and IL-6 may have some etiopathogenic roles in diabetic nephropathy.

Interleukin-18

Interleukin-18 (IL-18), a recently described member of the IL-1 cytokine superfamily, is now recognized as an important regulator of innate and acquired immune responses. IL-18 is expressed at sites of chronic inflammation, in autoimmune diseases, in a variety of cancers, and in the context of numerous infectious diseases. This short review will describe the basic biology of IL-18 and thereafter address its potential effector and regulatory role in several human disease states including autoimmunity and infection. IL-18, previously known as interferon-gamma (IFN-gamma)-inducing factor, was identified as an endotoxin-induced serum factor that stimulated IFN-gamma production by murine splenocytes [(1) ]. IL-18 was cloned from a murine liver cell cDNA library generated from animals primed with heat-killed Propionibacterium acnes and subsequently challenged with lipopolysaccharide [(2) ]. Nucleotide sequencing of murine IL-18 predicted a precursor polypeptide of 192 amino acids lacking a conventional signal peptide and a mature protein of 157 amino acids. Subsequent cloning of human IL-18 cDNA revealed 65% homology with murine IL-18 [(3) ] and showed that both contain an unusual leader sequence consisting of 35 amino acids at their N terminus.

Elevated production of interleukin-18 is associated with renal disease in patients with systemic lupus erythematosus

To investigate the production mechanism and proinflammatory role of the cytokine interleukin (IL-18) in lupus nephritis, we investigated the plasma concentrations of IL-18 and nitric oxide (NO) and the release of IL-18 and NO from mitogen-activated peripheral blood monomuclear cells (PBMC), in 35 SLE patients with renal disease (RSLE), 37 patients without renal disease (SLE) and 28 sex- and age-matched healthy control subjects (NC). IL-18 and NO concentrations were measured by ELISA and colourimetric non-enzymatic assay, respectively. Gene expressions of IL-18 and IL-18 receptor were analysed by RT-PCR. Plasma IL-18 and NO concentrations were significantly higher in RSLE than NC (both P < 0.01). Elevation of plasma IL-18 in RSLE correlated positively and significantly with SLE -disease activity index and plasma NO concentration (r = 0.623, P < 0.0001 and r = 0.455, P = 0.017, respectively), and the latter also showed a positive and significant correlation with plasma creatinine (r = 0.410, P = 0.034) and urea (r = 0.685, P < 0.0001). There was no significant difference in gene expressions of IL-18 and IL-18 receptor in PBMC among RSLE, SLE and NC. Percentage increase in culture supernatant IL-18 concentration was significantly higher in RSLE than SLE and NC (both P < 0.05). The basal NO release was significantly higher in RSLE than that in SLE and NC (both P < 0.005). IL-18 is therefore suggested to play a crucial role in the inflammatory processes of renal disease in SLE.

Circulating angiogenesis inhibitor endostatin and positive endothelial growth regulators in patients with systemic lupus erythematosus

Serum concentrations of three angiogenic cytokines: vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), interleukin-18 (IL-18) and antiangiogenic factor endostatin in the serum of 52 patients with systemic lupus erythematosus (SLE) and 20 healthy subjects were investigated. The possible association between serum levels of these proteins and SLE activity as well as correlation between the concentrations of angiogenic cytokines and the level of endostatin was also analyzed. VEGF and IL-18 were detectable in all SLE patients and healthy control group. bFGF was measurable in 71.2% of patients with SLE and 65% of healthy persons. Endostatin was detectable in 94.2% of SLE patients and 95% of normal subjects. The serum levels of endostatin and bFGF were not significantly different in SLE and healthy control (P > 0.05). The median concentration of VEGF was higher in active SLE (238.4 pg/ml) than in inactive disease (118.1 pg/ml, P < 0.05) or in control group (133.5 pg/ml, P < 0.04). The median serum level of IL-18 was higher in the SLE patients (595.2 pg/ml) than in the control group (252.7 pg/ml) (P < 0.001). The correlations between the levels of angiogenic cytokines and endostatin with clinical features, laboratory abnormalities and also with the type of treatment were analysed. We found a positive correlation between VEGF serum concentration and SLE activity according to SLAM score (p = 0.275, P < 0.05). The significant positive correlation was also found between IL-18 and endostatin (p = 0.289, P < 0.04). In contrast, the correlation between bFGF and endostatin was significantly negative (p = - 0.299, P < 0.04). In conclusion, serum levels of the angiogenic and antiangiogenic factors may play an important role in SLE pathogenesis.

Serum IL-12 in systemic lupus erythematosus: absence of p70 heterodimers but presence of p40 monomers correlating with disease activity

Biologically active IL-12 is a 70 kDa heterodimeric cytokine (IL-12 p70) mainly produced by antigen-presenting cells (APC) and made of disulfide-linked alpha (p35) and beta (p40) chains. Since the production of the p40 subunit is independently regulated from that of IL-12 p70, we compared levels of p40 and IL-12 p70 in the sera of patients with systemic lupus erythematosus (SLE). Sera obtained from rheumatoid arthritis (RA) patients and healthy subjects were used as controls. Serum p40 titers were significantly higher in SLE patients (mean +/- s.e.m.: 348 +/- 40 pg/ml) compared with patients with rheumatoid arthiritis (mean +/- s.e.m.: 116 +/- 18 pg/ml, P < 0.0001) or controls (mean +/- s.e.m.: 0 +/- pg/ml, P < 0.0001). By contrast, IL-12 p70 was not detected in any serum. In SLE patients, serum p40 levels were positively correlated with the SLEDAI (r = + 0.56, P = 0.02) and negatively with serum C3 levels (r = - 0.42, P = 0.03). Follow-up measurements indicated that serum p40 dropped significantly after immunosuppressive therapy. Finally, size exclusion chromatography with p40 immunoprecipitates obtained from SLE sera demonstrated that p40 was present as a monomer, and not as a homodimer, nor as a p19/p40 (IL-23) heterodimer. In conclusion, serum p40 monomers (but not IL-12 p70 titers) are elevated in the sera of SLE patients commensurate with disease activity. While the relevance of these observations needs to be further investigated, our results are consistent with the APC dysfunction described in SLE.

Plasma interleukin-18 levels in patients with psychiatric disorders

There are an increasing number of reports on an association between the alteration of circulating cytokine levels and pathophysiology of psychiatric disorders. Plasma concentrations of interleukin (IL)-18 were measured in 13 nonmedicated patients with psychiatric disorders. There was a significant elevation of IL-18 levels in patients with major depression (n = 8) and panic disorder (n = 5), compared with normal controls. The mean IL-18 value of our psychiatric patients was comparable with that of various somatic disorders reported. We suggest that the elevation of plasma IL-18 levels reflects the increased production and release of IL-18 in the central nervous system under stressful settings. We propose that the measurement of IL-18 plasma levels may provide a useful index for the involvement of immune system in psychiatric disorders.

Possible correlation between high levels of IL-18 in the cord blood of pre-term infants and neonatal development of periventricular leukomalacia and cerebral palsy

Periventricular leukomalacia (PVL) is a neonatal white matter damage of the brain of pre-term infants that often leads to cerebral palsy (CP). At present, diagnosis of PVL can be done by magnetic resonance imaging (MRI) and ultrasonography only when the infant is at least one week of age. No biochemical methods are available to identify high-risk infants at birth. Cytokines are usually not present in the cord blood but recently an elevation of IL-6 and TNF-alpha levels has been reported in amniotic fluid, cord blood and brain sections of infants with white matter damages. Levels of interleukin-18 (IL-18), a pleiotropic cytokines expressed in the brain and many other tissues, are highly sensitive to pathophysiological changes to raise the possibility that IL-18 may provide a useful indicator of PVL. The cord blood from 17 pre-term infants with PVL, 38 pre-term infants without PVL, and 30 normal full-term infants were retrospectively analysed for IL-18, IL-6, IL-1beta, and TNF-alpha. The possible factors involved in alteration of IL-18 concentration in relation to PVL and CP were examined. IL-18 is undetectable in the cord blood of normal full-term infants. However, high levels of IL-18 exist in the cord blood samples obtained from pre-term infants who neonatally developed PVL followed by CP. For pre-term infants under 35 weeks of gestation, seven out of eight showing more than 200 pg/ml of IL-18 (87.5%) developed PVL neonatally, with five of them subsequently developing CP. In contrast, only five out of 38 pre-term infants with less than 100 pg/ml of IL-18 (13.2%) developed PVL. For pre-term infants with less than 30 weeks of gestation, eight out of nine showing more than 100 pg/ml of IL-18 (88.9%) developed PVL, with six of these eight (75%) developing CP later. In conclusion, the presence of high levels of IL-18 in the cord blood of the pre-term infants is correlated with the incidence of PVL and CP and may provide a prognostic marker applicable at birth.

A proinflammatory role of IL-18 in the development of spontaneous autoimmune disease

Serum from patients with systemic lupus erythematosus (SLE) contained significantly higher concentrations of IL-18 than normal individuals. MRL/lpr mice, which develop spontaneous lupus-like autoimmune disease, also had higher serum levels of IL-18 than wild-type MRL/++ mice. Daily injections of IL-18 or IL-18 plus IL-12 resulted in accelerated proteinuria, glomerulonephritis, vasculitis, and raised levels of proinflammatory cytokines in MRL/lpr mice. IL-18-treated MRL/lpr mice also developed a "butterfly" facial rash resembling clinical SLE. In contrast, MRL/lpr mice treated with IL-18 plus IL-12 did not develop a facial rash. The facial lesion in the IL-18-treated mice showed epidermal thickening with intense chronic inflammation accompanied by increased apoptosis, Ig deposition, and early systemic Th2 response compared with control or IL-12 plus IL-18-treated mice. These data therefore show that IL-18 is an important mediator of lupus-like disease and may thus be a novel target for therapeutic intervention of spontaneous autoimmune diseases.

Interleukin-18 promotes sleep in rabbits and rats

Interleukin (IL)-1beta is involved in physiological sleep regulation. IL-18 is a member of the IL-1 family, and its signal-transduction mechanism is similar to that of IL-1. Therefore, we hypothesized that IL-18 might also be involved in sleep regulation. Three doses of IL-18 (10, 100, and 500 ng) were injected intracerebroventricularly (icv) into rabbits at the onset of the dark period. The two higher doses of IL-18 markedly increased non-rapid eye movement sleep (NREMS), accompanied by increases in brain temperature (Tbr). These effects were lost after the heat inactivation of IL-18. The 500 ng of IL-18 injection during the light period also increased NREMS and Tbr. Similar results were obtained after icv injection of 100 ng of IL-18 into rats. Furthermore, intraperitoneal injection of 30 microg/kg of IL-18 slightly, but significantly, increased NREMS, whereas it significantly decreased electroencephalogram slow-wave activity in rats. Intraperitoneal IL-18 failed to induce fever. An anti-human IL-18 antibody had little effect on spontaneous sleep in rabbits, although the anti-IL-18 antibody significantly attenuated muramyl dipeptide-induced sleep. These data suggest that IL-18 is involved in mechanisms of sleep responses to infection.

Osteoporosis in systemic lupus erythematosus: prevention and treatment

The patient with systemic lupus erythematosus (SLE) is at risk of osteoporosis through several factors: the inflammatory disease itself, disease-related co-morbidity, and its treatment. Bone loss is apparent early in the disease and this may be confounded primarily by treatment with corticosteroids. Patients should be assessed for additional risk factors for osteoporosis and general lifestyle measures adopted. Bone mineral density measurement should be considered in SLE patients at high risk of osteoporosis, particularly those starting corticosteroids and in postmenopausal women. Calcium and vitamin D supplementation provide general prophylaxis and are a suitable first-line option. Hormone replacement should be used in hypogondal subjects unless contra-indicated. In subjects at high fracture risk, particularly in postmenopausal women, bisphosphonate therapy should be considered as these agents have been shown to significantly reduce vertebral fracture risk. These measures should reduce the burden of osteoporosis and fracture in patients with lupus.

A novel IL-18BP ELISA shows elevated serum IL-18BP in sepsis and extensive decrease of free IL-18

IL-18 binding protein (IL-18BP) is a circulating antagonist of the proinflammatory Th1 cytokine IL-18. It effectively blocks IL-18 by forming a 1:1 high affinity (Kd=400 pM) complex, exhibiting a very low dissociation rate. We have developed a sandwich ELISA for IL-18BPa and determined its limit of detection (62 pg/ml). Interference by IL-18 and related cytokines, as well as cross reactivity with other IL-18BP isoforms (b, c, and d) were determined. Using this ELISA, we measured serum IL-18BPa in large cohorts of healthy individuals and in septic patients. Serum IL-18BPa in healthy individuals was 2.15+/-0.15 ng/ml (range 0.5-7 ng/ml). In sepsis, the level rose to 21.9+/-1.44 ng/ml (range 4-132 ng/ml). Total IL-18 was measured in the same sera by an electrochemiluminescence assay and free IL-18 was calculated based on the mass action law. Total IL-18 was low in healthy individuals (64+/-17 pg/ml) and most of it ( approximately 85%) was in its free form. Total IL-18 and IL-18BPa were both elevated in sepsis patients upon admission (1.5+/-0.4 ng/ml and 28.6+/-4.5 ng/ml, respectively). At these levels, most of the IL-18 is bound to IL-18BPa, however the remaining free IL-18 is still higher than in healthy individuals. We conclude that IL-18BPa considerably inhibits circulating IL-18 in sepsis. Yet, exogenous administration of IL-18BPa may further reduce circulating IL-18 activity.