Active stage of autoimmune diabetes is associated with the expression of a novel cytokine, IGIF, which is located near Idd2

Interleukin-18 in metabolism: From mice physiology to human diseases

Interleukin-18 (IL-18) is a classical member of the IL-1 superfamily of cytokines. As IL-1β, IL-18 precursor is processed by inflammasome/caspase-1 into a mature and biologically active form. IL-18 binds to its specific receptor composed of two chains (IL-18Rα and IL-18Rβ) to trigger a similar intracellular signaling pathway as IL-1, ultimately leading to activation of NF-κB and inflammatory processes. Independently of this IL-1-like signaling, IL-18 also specifically induces IFN-γ production, driving the Th1 immune response. In circulation, IL-18 binds to the IL-18 binding protein (IL-18BP) with high affinity, letting only a small fraction of free IL-18 able to trigger receptor-mediated signaling. In contrast to other IL-1 family members, IL-18 is produced constitutively by different cell types, suggesting implications in normal physiology. If the roles of IL-18 in inflammatory processes and infectious diseases are well described, recent experimental studies in mice have highlighted the action of IL-18 signaling in the control of energy homeostasis, pancreatic islet immunity and liver integrity during nutritional stress. At the same time, clinical observations implicate IL-18 in various metabolic diseases including obesity, type 1 and 2 diabetes and nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). In the present review, we summarize and discuss both the physiological actions of IL-18 in metabolism and its potential roles in pathophysiological mechanisms leading to the most common human metabolic disorders, such as obesity, diabetes and NAFLD/NASH.

Association between IL-18 gene polymorphisms and Hashimoto thyroiditis

BACKGROUND

Hashimoto's thyroiditis (HT), which is also called lymphocytic thyroiditis, is the most frequent autoimmune thyroid disease (AITD), in which T helper-1 lymphocytes mediate the disease. IL-18 is expressed in thyroid follicular cells (TFCs) during HT. The findings of studies aimed at investigating the relationship between IL-18 and HT are highly contradictory. In this study, we aimed to investigate the association between IL-18 gene polymorphisms and HT.

METHODS AND RESULTS

The study included 97 patients diagnosed with HT and 86 volunteers in the healthy control group. The IL18-607C/A (rs1946518) and -137G/C (rs187238) genotypes were determined using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. No significant difference in the mean age or sex was observed between the groups (p = 0.763 and p = 0.658, respectively). The -137 IL18 CG genotype was more frequent in HT patients than in controls. In HT patients, the risk of the IL-18 CG genotype was more than 2.237 times higher (OR 2.237%95 Cl 1.195-4.187, p = 0.039) than that of the G/G genotype. Additionally, the -607 AC genotype was more frequent in the control group than in the HT group (in individuals with the IL18 CG genotype).

CONCLUSIONS

According to our results, the CG genotype might be a risk factor for HT. Conversely, there is a possibility that the AC genotype plays a protective role against the condition. However, further studies will contribute to new solutions by revealing the molecular and cellular mechanisms of HT.

Inflammasomes and Type 1 Diabetes

Microbiota have been identified as an important modulator of susceptibility in the development of Type 1 diabetes in both animal models and humans. Collectively these studies highlight the association of the microbiota composition with genetic risk, islet autoantibody development and modulation of the immune responses. However, the signaling pathways involved in mediating these changes are less well investigated, particularly in humans. Importantly, understanding the activation of signaling pathways in response to microbial stimulation is vital to enable further development of immunotherapeutics, which may enable enhanced tolerance to the microbiota or prevent the initiation of the autoimmune process. One such signaling pathway that has been poorly studied in the context of Type 1 diabetes is the role of the inflammasomes, which are multiprotein complexes that can initiate immune responses following detection of their microbial ligands. In this review, we discuss the roles of the inflammasomes in modulating Type 1 diabetes susceptibility, from genetic associations to the priming and activation of the inflammasomes. In addition, we also summarize the available inhibitors for therapeutically targeting the inflammasomes, which may be of future use in Type 1 diabetes.

100 years post-insulin: immunotherapy as the next frontier in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease characterised by T cell-mediated destruction of the insulin-producing β cells in the pancreas. Similar to other autoimmune diseases, the incidence of T1D is increasing globally. The discovery of insulin 100 years ago dramatically changed the outlook for people with T1D, preventing this from being a fatal condition. As we celebrate the centenary of this milestone, therapeutic options for T1D are once more at a turning point. Years of effort directed at developing immunotherapies are finally starting to pay off, with signs of progress in new onset and even preventative settings. Here, we review a selection of immunotherapies that have shown promise in preserving β cell function and highlight future considerations for immunotherapy in the T1D setting.

IL18 Gene Polymorphism Influences Age of Onset of DM1 in African Ancestry Brazilians

The aim of this study was to investigate the relationship of two single nucleotide polymorphisms (SNPs) in the interleukin-18 ( IL18 ) gene (rs187238, g.-137G > C; rs1946518, g.-607C > A) and one SNP of the IL12B gene (rs3212227 g.*159A > C, 3'UTR) with the age of onset for type 1 diabetes mellitus (DM1). A total of 1,101 patients with DM1 enrolled in 13 centers from different regions of Brazil were genotyped with TaqMan assay and classified according to the ancestry. Our results show that an SNP in IL18 gene could be associated with DM1 age onset, taking into account that this studied variation affects gene expression.

Expression of mRNA and protein of IL-18 and its receptor in human follicular granulosa cells

PURPOSE

There is no information available about the IL-18 receptor in ovarian follicles, so the present study attempts to demonstrate the expression of IL-18 and its receptor in human granulosa cells (GCs).

METHODS

To evaluate the concentration of IL-18 in serum and follicular fluid (FF), we collected serum and FF from 102 women undergoing oocyte retrieval. Also, to detect expression of IL-18 and its receptor by luteinized GCs, these cells were pooled six times from a total of twenty individual patients with 5-16 follicles each. The IL-18 concentration was determined by ELISA and the expression of IL-18 and its receptor by immunocytochemistry and reverse transcription polymerase chain reaction.

RESULTS

Our results showed that the median IL-18 concentration in serum, 159.27 pg/ml (IQR 121.41-210.1), was significantly higher than in FF, 142.1 pg/ml (IQR 95.7-176.5), p < 0.001. Moreover, we found that IL-18 and its receptor are expressed by GCs.

CONCLUSION

The presence of IL-18 in FF and the expression of IL-18 and its receptor by GCs suggest an important role for this cytokine in ovarian function.

Interleukin-18 deficiency protects against renal interstitial fibrosis in aldosterone/salt-treated mice

Interleukin (IL)-18 is a member of the IL-1 family of cytokines and was described originally as an interferon γ-inducing factor. Aldosterone plays a central role in the regulation of sodium and potassium homoeostasis by binding to the mineralocorticoid receptor and contributes to kidney and cardiovascular damage. Aldosterone has been reported to induce IL-18, resulting in cardiac fibrosis with induced IL-18-mediated osteopontin (OPN). We therefore hypothesized that aldosterone-induced renal fibrosis via OPN may be mediated by IL-18. To verify this hypothesis, we compared mice deficient in IL-18 and wild-type (WT) mice in a model of aldosterone/salt-induced hypertension. IL-18−/− and C57BL/6 WT mice were used for the uninephrectomized aldosterone/salt hypertensive model, whereas NRK-52E cells (rat kidney epithelial cells) were used in an in vitro model. In the present in vivo study, IL-18 protein expression was localized in medullary tubules in the WT mice, whereas in aldosterone-infused WT mice this expression was up-regulated markedly in the proximal tubules, especially in injured and dilated tubules. This renal damage caused by aldosterone was attenuated significantly by IL-18 knockout with down-regulation of OPN expression. In the present in vitro study, aldosterone directly induced IL-18 gene expression in renal tubular epithelial cells in a concentration- and time-dependent manner. These effects were inhibited completely by spironolactone. IL-18 may be a key mediator of aldosterone-induced renal fibrosis by inducing OPN, thereby exacerbating renal interstitial fibrosis. Inhibition of IL-18 may therefore provide a potential target for therapeutic intervention aimed at preventing the progression of renal injury.

Association of the interleukin-18 -137 C/G, -607 A/C polymorphisms with type 1 diabetes: A meta-analysis

Published data on the association between interleukin (IL)-18 gene polymorphisms (-137 C/G, -607 A/C) and type 1 diabetes (T1D) risk are inconclusive. To obtain a more precise estimation of the association between the IL-18 gene polymorphisms and T1D, a meta-analysis was performed. A total of 11 studies including 5,945 cases and 6,404 controls were included in the analysis of the association between -137 C/G and T1D risk. No significant association between -137 C/G and T1D risk was observed in the total population [C vs. G: odds ratio (OR)=1.02, 95% confidence interval (CI)=0.87-1.20; CC + CG vs. GG: OR=1.05, 95% CI=0.87-1.25; CC vs. CG + GG: OR=0.96, 95% CI=0.68-1.36]. No significant association was identified in the stratified analysis for all the genetic models in the European population. Concerning -607 A/C, 10 studies involving 3,048 patients and 3,377 controls were included in this meta-analysis. When all the studies were pooled, the results showed no evidence for a significant association between IL-18 -607 A/C polymorphism and T1D risk (A vs. C: OR=0.93, 95% CI=0.81-1.06; AA + AC vs. CC: OR=0.99, 95% CI=0.89-1.10; AA vs. AC + CC: OR=0.81, 95% CI=0.60-1.09). In addition, similar results were obtained in the subgroup analysis based on ethnicity. In summary, the present meta-analysis suggests a lack of association between the two polymorphisms (-137 C/G, -607 A/C) in the IL-18 gene and T1D. Due to the limitation of the number of the studies, the conclusions drawn should be considered with caution. Larger scale primary studies are required to evaluate the association between IL-18 gene polymorphisms and T1D.

IL-18 in inflammatory and autoimmune disease

Inflammation serves as the first line of defense in response to tissue injury, guiding the immune system to ensure preservation of the host. The inflammatory response can be divided into a quick initial phase mediated mainly by innate immune cells including neutrophils and macrophages, followed by a late phase that is dominated by lymphocytes. Early in the new millennium, a key component of the inflammatory reaction was discovered with the identification of a number of cytosolic sensor proteins (Nod-like receptors) that assembled into a common structure, the 'inflammasome'. This structure includes an enzyme, caspase-1, which upon activation cleaves pro-forms of cytokines leading to subsequent release of active IL-1 and IL-18. This review focuses on the role of IL-18 in inflammatory responses with emphasis on autoimmune diseases.

IL-18 105 A>C polymorphism contributes to renal manifestations in patients with SLE

Systemic lupus erythematosus (SLE) is a multisystem autoimmune connective tissue disorder characterized by various aberrations including increased production of IL-18. As IL-18 105 A>C polymorphic variants have been linked to increased production of this cytokine, we investigated the prevalence of IL-18 105 A>C (rs549908) polymorphic variants in SLE patients (n = 111) and controls (n = 152). There were no significant differences in the distribution of IL-18 105 A>C polymorphic variants in SLE patients and controls. However, there was a significant association between the IL-18 105 AA genotype (recessive model) and renal manifestations OR = 3.360 (1.523–7.415, P = 0.0039) and the P value remained statistically significant after Bonferroni correction (P corr = 0.0351).Our findings indicate that the IL-18 105 AA genotype variant can contribute to renal manifestations in patients with SLE.

IL-18 is required for self-reactive T cell expansion in NOD mice

IL-18 has a well-established role in pro-inflammatory responses in the islets in type 1 diabetes. Here, we identify a distinctive role for IL-18 in expanding pathogenic T cells in the periphery of NOD mice. Well in advance of disease onset, the periphery of IL-18-deficient mice exhibits reduced T cell turnover, an increased prevalence of naïve and quiescent T cells, emergence of fewer effector T cells, and disease protection. Islet-reactive T cells fail to become activated in the lymphoid organs of mice lacking IL-18 and their rapid expansion is inhibited. IL-18 secretion by antigen presenting cells increases with advancing disease and is required for expression of its receptor on T cells. Our results demonstrate that induction of the IL-18 receptor reflects a critical stage of autoreactive T cell activation and expansion on the pathway toward effector T cell differentiation. This study therefore assigns a novel role to IL-18 for expanding the pool of islet-destructive T cells during pre-diabetes. This report highlights a new basic mechanism in type 1 diabetes pathogenesis and suggests that targeting the IL-18 pathway should be explored as a potential treatment strategy.

Thyrocyte interleukin-18 expression is up-regulated by interferon-γ and may contribute to thyroid destruction in Hashimoto's thyroiditis

Interferon-γ (IFN-γ) has a direct role in thyroid destruction in autoimmune thyroiditis. Interleukin-18 (IL-18), a pro-inflammatory cytokine with potent IFN-γ inducing activities, may play an important role in Th1-mediated autoimmune diseases. The purpose of this study was to characterize the expression and localization of IL-18 in the thyroid tissues of Hashimoto's thyroiditis (HT) and to investigate the effect of IFN-γ on IL-18 expression in isolated human thyroid follicular cells (TFCs). Thyroid tissues obtained from six euthyroid patients with HT and six control subjects were used to detect IL-18 expression by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical staining. Human TFCs were isolated and incubated for 48 h with or without IFN-γ, tumour necrosis factor-α (TNF-α) or IL-1β. IL-18 expression was analysed by RT-PCR, immunofluorescent double staining and western blot. We found that IL-18 expression was increased in the thyroid tissues of HT compared with control thyroid tissues. TFCs were major cell types expressing IL-18 in the thyroid tissues of HT. IL-18 was constitutively expressed in isolated human TFCs, and the expression was significantly up-regulated by IFN-γ rather than TNF-α or IL-1β. Western bolt revealed that a 24-kDa band corresponding to pro-IL-18 was broadened in the lysates of IFN-γ-treated TFCs. Our results demonstrated that IL-18 expression is up-regulated in the TFCs of HT patients and in primary human TFCs exposed to IFN-γ. Therefore, intrathyroidal interaction between IL-18 and IFN-γ may have a role in promoting the local immune response, which contributes to the thyroid destruction seen in HT.

Genetic control of severe egg-induced immunopathology and IL-17 production in murine schistosomiasis

Infection with the trematode parasite Schistosoma mansoni results in a distinct heterogeneity of disease severity, both in humans and in an experimental mouse model. Severe disease is characterized by pronounced hepatic egg-induced granulomatous inflammation in a proinflammatory cytokine environment, whereas mild disease corresponds with reduced hepatic inflammation in a Th2 skewed cytokine environment. This marked heterogeneity indicates that genetic differences play a significant role in disease development, yet little is known about the genetic basis of dissimilar immunopathology. To investigate the role of genetic susceptibility in murine schistosomiasis, quantitative trait loci analysis was performed on F(2) progeny derived from SJL/J and C57BL/6 mice, which develop severe and mild pathology, respectively. In this study, we show that severe liver pathology in F(2) mice 7 wk after infection significantly correlated with an increase in the production of the proinflammatory cytokines IL-17, IFN-gamma, and TNF-alpha by schistosome egg Ag-stimulated mesenteric lymph node cells. Quantitative trait loci analysis identified several genetic intervals controlling immunopathology as well as IL-17 and IFN-gamma production. Egg granuloma size exhibited significant linkage to two loci, D4Mit203 and D17Mit82, both of which were inherited in a BL/6 dominant manner. Furthermore, a significant reduction of hepatic granulomatous inflammation and IL-17 production in interval-specific congenic mice demonstrated that the two identified genetic loci have a decisive effect on the development of immunopathology in murine schistosomiasis.

Association of single nucleotide polymorphisms in the IL-18 gene with production of IL-18 protein by mononuclear cells from healthy donors. Mediators Inflamm. 2008;2008:309721. [PMID: 18949051 PMCID: PMC2570435 DOI: 10.1155/2008/309721]

IL-18 has proinflammatory effects and participates in both innate and adaptive cellular and humoral immunity. A number of SNPs that influence IL-18 production are found in the gene promoter region. We investigated the association of SNPs in the IL-18 promoter at −607 and −137 with the level of IL-18 protein production by PBMC from healthy donors from Southwestern Siberia. The genetic distribution of these SNPs in the promoter site was established by PCR. IL-18 protein production was determined by ELISA. Our results showed that PBMC from donors carrying allele 137C have lower levels of both spontaneous and LPS-stimulated IL-18 production. In contrast, PBMC from donors carrying allele 607A showed significant increases in spontaneous and stimulated IL-18 production compared to wild type. Our study suggests that the SNPs −607 and −137 in the promoter region of the IL-18 gene influence the level of IL-18 protein production by PBMC from healthy donors in Southwestern Siberia.

Macrophage migration inhibitory factor (MIF) is necessary for progression of autoimmune diabetes mellitus

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine of the innate immune system that plays a major role in the induction of immunoinflammatory responses. To examine the role of endogenous MIF in the pathogenesis of type 1 diabetes (TID) we evaluated the effects of administration of neutralizing anti-MIF antibodies to NOD mice with accelerated forms of diabetes induced by injection of cyclophosphamide or by transfer of diabetogenic spleen cells. Both accelerated forms of diabetes were markedly reduced by anti-MIF antibody. Furthermore, MIF-deficient (MIF(-/-)) mice were less susceptible to the induction of immunoinflammatory diabetes, insulitis and apoptosis within the endocrine pancreas by multiple low doses of streptozotocin (MLD-STZ) than genetically matched wild type (WT) mice. MIF deficiency resulted in lower proliferation and lymphocyte adhesion, as well as reduced production from the spleens and peritoneal cells of a variety of inflammatory mediators typically associated with development of the disease including IL-12, IL-23, TNF-alpha, and IL-1beta. Furthermore, MIF deletion affected the production of IL-18, TNF-alpha, IL-1beta, and iNOS in the islets of Langerhans. These data, along with the higher expression of IL-4 and TGF-beta observed in the periphery and in the pancreas of MLD-STZ-challenged MIF(-/-) mice as compared to WT controls suggest that MIF deficiency has induced an immune deviation towards protective type 2/3 response. These results suggest that MIF participates in T1D by controlling the functional activity of monocytes/macrophages and T cells and modulating their secretory capacity of pro- and anti-inflammatory molecules.

Role of IL-18 in overt pain-like behaviour in mice

There are evidences that targeting IL-18 might be beneficial to inhibit inflammatory symptoms, including hypernociception (decrease in nociceptive threshold). The mechanism of IL-18 mechanical hypernociception depends on endothelin in rats and mice. However, the role of IL-18 in overt pain-like behaviour remains undetermined. Therefore, we addressed the role of IL-18 in writhing response induced by intraperitoneal (i.p.) injection of phenyl-p-benzoquinone (PBQ) and acetic acid in mice. Firstly, it was detected that PBQ and acetic acid i.p. injection induced a dose-dependent number of writhes in Balb/c mice. Subsequently, it was observed that the PBQ - but not the acetic acid-induced writhes were diminished in IL-18 deficient ((-/-)) mice. Therefore, considering that IFN-gamma, endothelin and prostanoids mediate IL-18-induced mechanical hypernociception, we also investigated the role of these mediators in the same model of writhing response in which IL-18 participates. It was noticed that PBQ-induced writhes were diminished in IFN-gamma(-/-) mice and by the treatment with bosentan (mixed endothelin ETA/ETB receptor antagonist), BQ 123 (cyclo[DTrp-DAsp-Pro-DVal-Leu], selective endothelin ETA receptor antagonist), BQ 788 (N-cys-2,6 dimethylpiperidinocarbonyl-l-methylleucyl-d-1-methoxycarboyl-d-norleucine, selective endothelin ETB receptor antagonist) or indomethacin (cycloxigenase inhibitor). Thus, IL-18, IFN-gamma, endothelin acting on endothelin ETA and ETB receptors, and prostanoids mediate PBQ-induced writhing response in mice. To conclude, these results further advance the understanding of the physiopathology of overt pain-like behaviour, and suggest for the first time a role for IL-18 in writhing response in mice.

Autoimmune diabetes mellitus with adult onset and type 1 diabetes mellitus in children have different genetic predispositions

Type 1 diabetes with manifestation after 35 years of age is defined by CP <200 pmol/L and institution of insulin therapy within 6 months after diagnosis. Latent autoimmune diabetes mellitus in adults (LADA) manifesting after 35 years of age is defined by minimum 6 months after diagnosis without insulin therapy and C peptide (CP) >200 pmol/L and antiGAD > 50 ng/mL. We aimed to find a possible genetic discrimination among different types of autoimmune diabetes. To accomplish this goal, we analyzed DNA samples from 31 LADA patients, 75 patients with adult-onset type 1 diabetes mellitus, 188 type 1 diabetic children, and 153 healthy adult individuals. We studied five genetic loci on chromosomes 6, 11, 4, and 14: HLA DRB1 and DQB1 alleles, major histocompatibility complex (MHC) class I-related gene-A (MIC-A) microsatellite polymorphism, interleukin (IL)-18 single nucleotide polymorphism, the microsatellite polymorphism of nuclear factor kappa B gene (NF-kappaB1), and the single nucleotide polymorphism of a gene for its inhibitor (NF-kappaBIA). HLA-DR3 was detected as the predisposition allele for LADA (OR = 4.94, P < 0.0001). Further we found a statistically significant increase of NF-kappaBIA AA genotype (OR = 2.68, P < 0.01). On the other hand, DRB1*04, which is linked with DQB1*0302, was observed as a risk factor in patients with type 1 diabetes mellitus (T1DM) onset after 35 years of age (OR = 10.47, P < 0.0001 and OR = 9.49, P < 0.0001, respectively). There was also an association with MIC-A5.1 (OR = 2.14, P < 0.01). Statistically significant difference was found in the distribution of IL-18 promoter -607 (C/A) polymorphism between LADA and T1DM in adults (P < 0.01). We conclude that all subgroups of autoimmune diabetes have partly different immunogenetic predisposition.

Interleukin-18 enhances glucose uptake in 3T3-L1 adipocytes

In order to characterize the potential causative effects of interleukin-18 (IL-18) on insulin resistance, we measured glucose uptake in 3T3-L1 adipocytes treated with mouse recombinant IL-18. IL-18 surprisingly enhanced, rather than reduced insulin-mediated glucose uptake in adipocytes. Moreover IL-18 could counteract the glucose uptake suppression caused by tumor necrosis factor alpha in 3T3-L1 adipocytes. The mechanism dissection showed that the IL-18 upregulated phosphorylated Akt and downregulated phosphorylated P38 MAPK. These findings indicated that the elevated serum IL-18 levels in obesity and diabetes might be a compensatory response to insulin resistance.

The role of interleukin-18 in renal injury

Interleukin (IL)-18 is a relatively new pro-inflammatory cytokine, formerly known as interferon-gamma-inducing factor, which induces interferon-gamma production in T cells and natural killer cells. It is synthesized as a biologically inactive precursor, which requires cleavage into an active molecule by an intracellular cysteine protease similar to IL-1beta. This review examines the pro-inflammatory role of IL-18 in various types of renal injury (i.e., endotoxemia, cisplatin toxicity, allograft rejection, and ischemia-reperfusion injury) and explores the integral role of IL-12 in IL-18 function and activity.

IL-18 gene promoter ?137C/G and ?607C/A polymorphisms in Chinese Han children with type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is a heterogeneous autoimmune disease, and both environmental and genetic factors play a role in its pathogenesis. Interleukin (IL)-18 is a potent pro-inflammatory cytokine capable of inducing interferon-gamma production that is associated with the development of T1DM. The gene for IL-18 is located on chromosome 11q22.2-q22.3 and has been reported to be associated with a susceptibility to T1DM. To test the putative involvement between IL-18 gene polymorphism and predisposition to T1DM, we conducted a case-control study in Chinese Han children. The single nucleotide polymorphisms at position -607(C/A) and -137(C/G) in the promoter region of the IL-18 gene were analysed by sequence-specific primers-polymerase chain reaction in 118 patients with T1DM and 150 healthy controls. (1) The allele frequency of -607A was 41.2% and 53.0%, respectively, in patients and in control subjects (P = 0.01), but the allele frequency of -137C/G was not statistically significant (P = 0.37). (2) The distribution of CC genotype at position -607 was significantly different between patients and normal controls (P = 0.03), while the distribution of AA genotype in patients was significantly lower than that in the controls (P = 0.03). (3) Furthermore, there was a significant increase in haplotype (-137C/-607G) and genotype combination (-137GG/ -607CC) in patients compared with controls (P = 0.03 and P = 0.04, respectively). The results of this study show that IL-18 gene promoter polymorphisms confer susceptibility to T1DM in Chinese Han children. Moreover, subjects carrying AA genotype at position -607 of the promoter of IL-18 gene may be a low risk of T1DM development.

Interleukin-18 Promoter Gene Polymorphisms in Chinese Patients With Systemic Lupus Erythematosus: Association With CC Genotype at Position –607

Introduction: Interleukin-18 (IL-18) is a Th1 cytokine, which is postulated to play a role in systemic lupus erythematosus (SLE). Two single nucleotide polymorphisms (SNPs) in the IL-18 promoter gene region were found to influence the quantitative expression of the IL-18 protein. The aim of this study was to determine whether IL-18 promoter gene polymorphisms are associated with SLE. Materials and Methods: One hundred and thirteen Chinese SLE patients and 218 Chinese healthy individuals were recruited. Genomic DNA was extracted from peripheral venous blood. Sequence-specific primer PCR and restriction fragment length polymorphism (RFLP) analysis were used to genotype the DNA samples for SNP-137 and SNP- 607. The following genotypes were obtained: SNP(-607) AA, AC, CC and SNP(-137) GG, GC, CC. Plasma IL-18 concentrations of patients and control subjects were measured by enzyme-linked immunosorbent assay. Results: the frequency of SNP-607/CC genotype was significantly higher in SLE patients (Pc < 0.05) while genotype SNP-607/AC was significantly decreased in SLE patients compared to the control group (Pc <0.05). Plasma IL-18 concentrations were significantly higher in SLE patients than in control subjects (P <0.05). Both patients and control subjects with CC and AC genotypes have significantly higher IL-18 concentrations than those with AA genotype. Conclusion: The IL-18 promoter gene polymorphism SNP–607 C allele is associated with SLE and may result in the enhanced production of IL-18 protein in SLE and normal individuals. Key words: Cytokines, Genotype, Single nucleotide polymorphisms

Interleukin-18 genetics and inflammatory disease susceptibility

IL18 was mapped to 11q22.2-22.3 in 1998. Owing to interleukin (IL)-18's important and novel role in immunomodulation, the gene itself has been subject to scrutiny, with the aim of discovering variants that may impact on disease susceptibility and/or progression. Despite being sequenced numerous times in different populations, no non-synonymous variants have been found. However, a number of polymorphisms within the proximal promoter have been verified that may interfere with transcription-factor-binding sites. Much of the subsequent association analyses have centred on these variants, but have yielded no consistent results, despite numerous different study populations being genotyped. IL18 has recently been resequenced in its entirety, enabling the tagging-single-nucleotide polymorphism (tSNP) methodology to be adopted. This approach has yielded interesting results, with genetic variation being shown to affect protein levels, and risk. This review aims to compile and reflect on the association data of interest published to date, with a focus on the diseases related to aberrant inflammatory control.

Interleukin-18 as a potential therapeutic target in chronic autoimmune/inflammatory conditions

Interleukin-18 (IL-18), a recently identified immunoregulatory and inflammatory cytokine, has attracted a profound interest as a potential therapeutic target in autoimmune/inflammatory disorders. In this review the authors focus on: IL-18 biology as an important link between innate and adaptive immunity; evidence of its pro-inflammatory role in several human autoimmune and chronic inflammatory disorders; and data indicating that IL-18 blockade in animal models results in prevention/amelioration of the disease process and preservation of the target tissue integrity and function. Finally, the authors analyse strategies presently under development to block IL-18 function and potential pitfalls resulting from IL-18 blockade that should be considered in ongoing/future clinical trials.

Analysis of polymorphisms of the interleukin-18 gene in type 1 diabetes and Hardy-Weinberg equilibrium testing

Recently, the interleukin-18 cytokine gene (IL18) was reported to be associated with type 1 diabetes. In the present report, we calculated that the reported genotypes of the two 5' region/promoter single nucleotide polymorphisms (SNPs), -607 (C-->A) (rs1946518) and -137 (G-->C) (rs187238), were not in Hardy-Weinberg equilibrium (HWE). We therefore investigated the association of the -607 and -137 SNPs in a U.K. type 1 diabetic Caucasian case-control collection (1,560 case and 1,715 control subjects tested at -607 and 4,323 case and 4,610 control subjects tested at -137) as well as a type 1 diabetic Caucasian collection comprised of families of European ancestry (1,347 families tested at -137 and 1,356 families tested at -607). No evidence for association with type 1 diabetes was found, including for the -607 A/A and C/A genotypes. To evaluate whether common variation elsewhere in the gene was associated with disease susceptibility, we analyzed eight IL18 tag SNPs in a type 1 diabetic case-control collection (1,561 case and 1,721 control subjects). No evidence for association was obtained (P = 0.11). We conclude that common allelic variation in IL18 is unlikely to contribute substantially to type 1 diabetes susceptibility in the populations tested and recommend routine application of tests for HWE in population-based studies for genetic association.

IL-18 gene polymorphism confers susceptibility to the development of anti-GAD65 antibody in Graves' disease

AIMS

This study aimed to investigate whether interleukin-18 (IL-18) gene polymorphisms are associated with the development of antibody against the 65-kDa isoform of recombinant human glutamic acid decarboxylase (GAD65Ab) in patients with Graves' disease.

METHODS

A total of 398 unrelated Japanese patients with Graves' disease, with and without GAD65Ab, were recruited. Three single nucleotide polymorphisms in the IL-18 gene were examined and the polymorphic allele and the genotype and haplotype frequencies calculated.

RESULTS

The frequency of the GG genotype at position -4675 of the IL-18 gene was significantly lower in Graves' disease patients with GAD65Ab than those without (4% vs. 24%, P = 0.0126). The -4675C allele frequency was significantly greater in patients with GAD65Ab than those without (69% vs. 53%, P = 0.0168). The homozygous -4675G/-607A/-137G haplotype was less common in Graves' disease patients with GAD65Ab than those without (4% vs. 23%, P = 0.0144).

CONCLUSIONS

These findings in a Japanese population indicate that Graves' disease patients carrying the GG genotype at position -4657 of the promoter of the IL-18 gene or a gene in linkage disequilibrium with the -4675G/-607A/-137G haplotype have a low risk for the development of GAD65Ab in Graves' disease.

Pathophysiological roles for IL-18 in inflammatory arthritis

IL-18 is a unique cytokine with prominently wide spectrum biological actions. Among these, its IFN-gamma/TNF-alpha-inducing activity primarily contributes to the development of various inflammatory diseases including inflammatory arthritis. IL-18 levels correlate with the disease activity of rheumatoid arthritis (RA) and osteoarthritis (OA). IL-18 is spontaneously released from RA synovial cells and OA chondrocytes and seems to participate in the development of the inflammatory and destructive alterations of joints via induction of TNF-alpha, a potent effector molecule. TNF-alpha, in turn, increases IL-18 expression in RA synovial cells. Recent clinical trials have revealed the efficacy of TNF-alpha in RA with a reduction in circulatory IL-18 levels. These may implicate the positive circuit between IL-18 and TNF-alpha for development of RA. As IL-18-deficient mice evade collagen-induced arthritis in a mouse RA model, therapeutics targeting IL-18 may be beneficial against RA/OA. Here, the authors review the possible roles of IL-18 in inflammatory arthritis.

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.

The proatherogenic cytokine interleukin-18 is secreted by human adipocytes

OBJECTIVE

Interleukin (IL)-18, an important mediator of innate immunity and strong risk factor for the development of cardiovascular disease, was shown recently to be elevated in obesity. The aim of our study was to investigate whether human adipocytes produce IL-18.

METHODS

Human adipose tissue was obtained from lean women undergoing elective plastic surgery and from obese individuals undergoing laparoscopic surgery (gastric banding). Preadipocytes from mammary adipose tissue were isolated and differentiated under defined adipogenic conditions. IL-18 expression was analyzed by real-time reverse transcriptase PCR, ELISA and immunocytochemistry.

RESULTS

Human preadipocytes of all differentiation stages spontaneously secreted IL-18. In parallel significant amounts of IL-18 mRNA were detected. Freshly isolated mature adipocytes from subcutaneous and omental depots also released IL-18. IL-18 release from adipocytes from obese donors was about 3-fold higher compared to adipocytes from non-obese donors.

CONCLUSIONS

We conclude that human adipose tissue produces IL-18 and thereby contributes to systemic IL-18 concentrations. This finding supports the concepts that adipocytes behave as primitive immune cells and that IL-18 may mediate some of the detrimental complications of obesity such as cardiovascular disease and type 2 diabetes.

Increased expression of caspase-1 and interleukin-18 in peripheral blood mononuclear cells in patients with multiple sclerosis

Multiple sclerosis (MS) is supposedly a T-cell mediated autoimmune disorder of the central nervous system. Cytokines and other molecules involved in the regulation of apoptosis are thought to be of importance for the pathogenesis of MS. In this study, the mRNA levels of interleukin 18 (IL-18), IL-1beta and their processing enzyme caspase-1 were quantified by a competitive RT-PCR method in unstimulated peripheral blood mononuclear cells (PBMCs) in MS patients never treated with disease modifying drugs. Western blot was used to support the expression pattern at the protein level. We found that the expression of caspase-1 and IL-18 was significantly increased in MS patients compared with healthy controls. Analysis of clinical subgroups revealed that caspase-1 was increased in all subgroups, whereas IL-18 was upregulated in chronic progression (P=0.001) and relapsing MS patients in remission (P=0.002) but not significantly during relapses (P=0.12). mRNA levels of IL-1beta were not significantly altered in MS except for a possible decrease in chronic progression (P=0.03). An increased IL-18 expression, potentially augmented at the mature protein level, may indicate a pathway worth considering in future therapeutic strategies in MS.

Interleukin 18 promoter polymorphisms are not strongly associated with type I diabetes in a UK population

Interleukin 18 (IL18) is a proinflammatory cytokine whose levels are increased in the subclinical stage of insulin-dependent (type I) diabetes mellitus. Previous case-control studies have reported associations between IL18 -607C>A and -137G>C promoter polymorphisms and type I diabetes. We performed case-control and family-based association studies employing Pyrosequencing to assess if these IL18 polymorphisms are also associated with the development of type I diabetes in the Northern Ireland population. The chi2 analysis of genotype and allele frequencies for the IL18 polymorphisms in cases (n=433) vs controls (n=426) revealed no significant differences (P>0.05). Assessment of allele transmission distortion from informative parents to affected offspring also failed to confirm previously reported associations. Stratification of these analyses for age-at-onset and HLA-DR type did not reveal any significance associations. In conclusion, our data do not support the strong positive associations of IL18 promoter polymorphisms with type I diabetes reported in previous smaller studies.

Interleukin-18: recent advances

PURPOSE OF REVIEW

Interleukin-18 (IL-18) has potent immunomodulatory effects. It is the only cytokine with a unique capacity to induce T helper 1 or T helper 2 polarization, depending on the immunologic context. Serum levels of IL-18 are increased in many human diseases and it has been implicated in the pathogenesis of several immune-mediated processes. Some of the recent key advances in the immunobiology of IL-18 are discussed in this review.

RECENT FINDINGS

Recent data from several laboratories have shed light on the structure of IL-18; the signaling cascades that are initiated; and its role on modulating T cells, dendritic cells, and natural killer cell function. Several new reports have expanded and delineated the role of IL-18 in a multitude of diseases, but only recent advances in the role of IL-18 in three disease processes (acute graft-versus-host disease, insulin-dependent diabetes, and sepsis), where it appears to play paradoxic roles are discussed.

SUMMARY

Although emerging data shed more light on the complex role of IL-18 in immune reactions, they also pose more questions. Given the pleiotropic, complex, and at times paradoxic effects of IL-18 in various disease processes, better understanding of its immunobiology might lead to the development of IL-18 and/or its antagonists as therapeutic agents against immune-mediated diseases.

Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice

Interleukin 15 (IL-15) and Interleukin 18 (IL-18) are key cytokines produced by macrophages during innate immune response. These cytokines can profoundly affect subsequent adaptive immune responses including autoimmunity. We have investigated the role of IL-15 and IL-18 in the development of autoimmune diabetes in mice induced by multiple low dose streptozotocin (MLD-STZ). To analyze the role of IL-15, we tested the effects of a soluble murine IL-15 receptor alpha-chain (smIL-15Ralpha), on the development of MLD-STZ in C57BL/6 mice. Animals were treated with 10 daily injections of 32 microg of smIL-15Ralpha starting on the first day of diabetes induction. This treatment significantly attenuated the development of diabetes as evaluated by significantly lower glycemia compared with control mice treated with an inactive mutant form of sIL-15Ra. To directly address the role of IL-18 in MLD-STZ we used IL-18 knockout (KO) mice on DBA/1 background. IL-18 deficient mice were significantly more resistant to the induction of diabetes compared with the wild-type controls and did not develop the typical mononuclear cell infiltrates in the islets. Taken together our data suggest that the innate mediators, IL-15 and IL-18, are essential for the development of diabetes and may be important targets in prevention and early treatment of autoimmune diabetes.

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.

Systemic administration of IL-18 promotes diabetes development in young nonobese diabetic mice

IL-18 is now identified as a pleiotropic cytokine that acts as a cofactor for both Th1 and Th2 cell development. Type 1 diabetes is considered a Th1-type autoimmune disease, and to date, the suppressive effect of exogenous IL-18 on the development of diabetes has been reported in 10-wk-old nonobese diabetic (NOD) mice. In the present study we administered exogenous IL-18 systemically in 4-wk-old NOD mice using i.m. injection of the IL-18 expression plasmid DNA (pCAGGS-IL-18) with electroporation. Contrary to previous reports, the incidence of diabetes development was significantly increased in NOD mice injected with pCAGGS-IL-18 compared with that in control mice. Systemic and pancreatic cytokine profiles deviated to a Th1-dominant state, and the the frequency of glutamic acid decarboxylase-reactive IFN-gamma-producing CD4(+) cells was also high in the IL-18 group. Moreover, it was suggested that the promoting effect of IL-18 might be associated with increased peripheral IL-12, CD86, and pancreatic IFN-inducible protein-10 mRNA expression levels. In conclusion, we demonstrate here that IL-18 plays a promoting role as an enhancer of Th1-type immune responses in diabetes development early in the spontaneous disease process, which may contribute to elucidating the pathogenesis of type 1 diabetes.

Association between IL-18 gene promoter polymorphisms and CTLA-4 gene 49A/G polymorphism in Japanese patients with type 1 diabetes

Interleukin-18 (IL-18) is a potent proinflammatory cytokine which is strongly associated with the development of diabetes in NOD mice. To test the putative involvement of IL-18 gene polymorphism in predisposition to human type 1 diabetes, the SNPs at position -607 (C/A) and -137 (G/C) in the promoter region of IL-18 gene were analyzed by sequence-specific PCR in 116 patients with type 1 diabetes and 114 normal controls. A linkage disequilibrium found only three of the four possible haplotypes defined by these SNPs. The distribution of the IL-18 gene genotypes at position -607 was significantly different between patients with type 1 diabetes and normal controls (P=0.023). Furthermore, there was a significant increase in haplotype 1 (-607C/-137G) in the patients compared with controls (P=0.006). The association study of the susceptible CTLA-4 genotype (GG at nucleotide position 49 in exon 1) or HLA-DR4-DQB1*0401 and type 1 diabetes showed that the predisposing IL-18 gene haplotype modulates the risk on CTLA-4 GG genotype, but not on HLA-DR4-DQB1*0401 haplotype. Among subjects carrying the CTLA-4 GG genotype, the frequency of IL-18 haplotype 1 in patients with type 1 diabetes was significantly higher than that in controls (91% vs. 71%, P=0.012). However, IL-18 haplotype 1 was not frequent in patients who do not exhibit the CTLA-4 high-risk genotype. These results suggest that the IL-18 gene polymorphism is associated with a type 1 diabetes susceptibility, and there might be a gene-gene interaction between IL-18 gene with susceptible CTLA-4 gene.

Mutation scan of a type 1 diabetes candidate gene: the human interleukin-18 binding protein gene

Type 1 (insulin-dependent) diabetes, T1DM, is the result of an immune-mediated destruction of the pancreatic beta cells dependent mainly on T helper cells and macrophages. Interleukin-18 (IL-18) is a proinflammatory cytokine produced mainly by macrophages. IL-18 is capable of inducing T lymphocyte synthesis of IFNgamma, thereby skewing the T helper response toward a T helper type 1 (Th1) profile. IL-18 binding protein (IL18BP) neutralizes IL-18 and leads to a reduced Th1 response. Polymorphisms in IL18BP may affect the activity of IL-18 and the magnitude of the Th1 response and may play a role in the pathogenesis of T1DM. The aim of the study was therefore to identify polymorphisms in IL18BP and to test these for association with T1DM. We evaluated the human IL18BP gene on chromosome 11q13 as a candidate susceptibility gene for T1DM and scanned the entire IL18BP (promoter, exons 1-6, and 3'UTR) for polymorphisms using single-strand conformational polymorphism analysis and direct sequencing. We identified a total of 11 polymorphisms, all having allele frequencies ranging between 0.05 and 0.10. Four were in the 5'UTR: -257G-->T, -78C-->T, -65G-->A, and -59A-->G. Three were in intron 3: IVS3+140A-->C, IVS4-147G-->T, and IVS4-59G-->T. The last four, 38*A-->T, 48*T-->A, 388*C-->G, and 440*_441*insG, were in the 3'UTR of IL18BP. However, none of these were frequent enough to permit association studies in T1DM and we conclude that IL18BP does not contribute to the overall genetic susceptibility to type 1 diabetes.

Caspase-1 is not required for type 1 diabetes in the NOD mouse

Interleukin (IL)-1 beta and IL-18 are two cytokines associated with the immunopathogenesis of diabetes in NOD mice. Both of these cytokines are cleaved by caspase-1 to their biologically active forms. IL-1 is a proinflammatory cytokine linked to beta-cell damage, and IL-18 stimulates production of interferon (IFN)gamma in synergy with IL-12. To examine the effects produced by caspase-1 deficiency on diabetes development in NOD/Lt mice, a disrupted Casp1 gene was introduced by a speed congenic technique. Casp1(-/-) bone marrow-derived macrophages stimulated with lipopolysaccharide produced no detectable IL-18, fourfold lower IL-1 beta, and 20-30% less IL-1 alpha than macrophages from wild-type Casp1(+/+) or Casp1(+/-) controls. Unexpectedly, despite reduced IL-1 and IL-18, there was no change in the rate of diabetes or in total incidence as compared with that in wild-type NOD mice. IL-1 reportedly makes an important pathological contribution in the multidose streptozotocin model of diabetes; however, there was no difference in sensitivity to streptozotocin between NOD mice and NOD.Casp1(-/-) mice at 40 mg/kg body wt or at 25 mg/kg body wt dosage levels. These findings show that caspase-1 processing of IL-1 beta and IL-18 is not absolutely required for mediation of spontaneous or chemically induced diabetes pathogenesis in the NOD mouse.

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.

Association of Interleukin-18 Gene Promoter Polymorphisms in Type 1 Diabetes and Autoimmune Thyroid Disease

Type 1 diabetes is a heterogeneous autoimmune disease and is often associated with other organ-specific autoimmune diseases, including autoimmune thyroid disease (AITD). IL-18 is a potent proinflammatory cytokine capable of inducing IFN-gamma production that is associated with the development of type 1 diabetes and AITD. The gene for IL-18 is located near Idd2 and has been reported to be associated with a susceptibility to type 1 diabetes. To test the putative involvement of IL-18 gene polymorphism in predisposition to type 1 diabetes and AITD, we conducted a case-control study in Japanese population. The SNPs at position -607 (C/A) and -137 (G/C) in the promoter region of the IL-18 gene were analyzed by sequence-specific PCR in 74 nondiabetic patients with AITD, 47 type 1 diabetic patients with AITD, and 114 normal controls. There was no significant increase in the genotype and allele frequencies not only in nondiabetic patients with AITD compared with normal controls, but also in type 1 diabetic patients with AITD compared with normal controls. The distribution of IL-18 gene haplotypes was also similar between both patient groups and normal controls. These results suggest that polymorphisms of the IL-18 gene are not associated with a susceptibility to AITD and type 1 diabetes coexistent with AITD in Japanese population.