The role of IL-18 in the modulation of matrix metalloproteinases and migration of human natural killer (NK) cells

Bioengineering strategies to enhance the interleukin-18 bioactivity in the modern toolbox of cancer immunotherapy

Cytokines are the first modern immunotherapeutic agents used for activation immunotherapy. Interleukin-18 (IL-18) has emerged as a potent anticancer immunostimulatory cytokine over the past three decades. IL-18, structurally is a stable protein with very low toxicity at biological doses. IL-18 promotes the process of antigen presentation and also enhances innate and acquired immune responses. It can induce the production of proinflammatory cytokines and increase tumor infiltration of effector immune cells to revert the immunosuppressive milieu of tumors. Furthermore, IL-18 can reduce tumorigenesis, suppress tumor angiogenesis, and induce tumor cell apoptosis. These characteristics present IL-18 as a promising option for cancer immunotherapy. Although several preclinical studies have reported the immunotherapeutic potential of IL-18, clinical trials using it as a monotherapy agent have reported disappointing results. These results may be due to some biological characteristics of IL-18. Several bioengineering approaches have been successfully used to correct its defects as a bioadjuvant. Currently, the challenge with this anticancer immunotherapeutic agent is mainly how to use its capabilities in a rational combinatorial therapy for clinical applications. The present study discussed the strengths and weaknesses of IL-18 as an immunotherapeutic agent, followed by comprehensive review of various promising bioengineering approaches that have been used to overcome its disadvantages. Finally, this study highlights the promising application of IL-18 in modern combinatorial therapies, such as chemotherapy, immune checkpoint blockade therapy, cell-based immunotherapy and cancer vaccines to guide future studies, circumventing the barriers to administration of IL-18 for clinical applications, and bring it to fruition as a potent immunotherapy agent in cancer treatment.

Comparative Evaluation of Gingival Crevicular Fluid Interleukin-17, 18 and 21 in Different Stages of Periodontal Health and Disease

Background and Objectives: The elicitation of a host’s immune−inflammatory responses to overcome oral bacterial biofilm challenges is mediated by numerous cytokines. We explored the role of three such cytokines, viz. interleukin (IL)-17, 18 and 21, by measuring their levels in the gingival crevicular fluid (GCF) of Indian individuals with healthy gingiva, chronic gingivitis, or chronic periodontitis. Materials and Method: Ninety systemically healthy individuals were enrolled in the study on the basis of predefined criteria and were categorized into three groups of 30 participants each. Groups A, B and C were composed of a control group with healthy gingiva, subjects with chronic gingivitis and subjects with chronic periodontitis, respectively. The periodontal disease status was assessed on the basis of a subject’s gingival index, probing pocket depth, clinical attachment loss and radiographic evidence of bone loss. After the complete history-taking and identification of gingival sulcus/pocket depth areas for GCF collection, a sample was collected from each subject in all groups for an estimation of the cytokine levels using ELISA. Statistical analysis was performed using SPSS v 21.0. Intergroup comparisons were conducted using a post hoc Tukey’s test. A value of p < 0.05 was considered to be statistically significant. Results: The mean IL-17, 18 and 21 concentrations in pg/mL was the greatest for Group C (99.67 ± 18.85, 144.61 ± 20.83 and 69.67 ± 12.46, respectively), followed by Group B (19.27 ± 2.78, 22.27 ± 2.43 and 22.74 ± 1.43, respectively) and finally by Group A (healthy control; 11.56 ± 0.99, 17.94 ± 1.24 and 12.83 ± 1.21 respectively). A statistically significant difference in the mean concentrations of two interleukins (IL-17 and IL-18) was observed between Groups A and C and also between Groups B and C. A statistically significant difference in the mean concentrations of IL-21 was observed between Groups B and C. Conclusions: Within the limitations of the present study, the findings revealed that the GCF levels of IL-17, IL-18 and IL-21 rose and correlated well with the severity of the disease. Thus, these cytokines present in GCF have the potential to be considered as biomarkers for periodontal tissue destruction. IL-21 in particular appears to be a promising biomarker for differentiating between gingivitis and periodontitis.

DPP inhibition alters the CXCR3 axis and enhances NK and CD8+ T cell infiltration to improve anti-PD1 efficacy in murine models of pancreatic ductal adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is projected to be the second leading cause of cancer death in the USA by 2030. Immune checkpoint inhibitors fail to control most PDAC tumors because of PDAC’s extensive immunosuppressive microenvironment and poor immune infiltration, a phenotype also seen in other non-inflamed (ie, ‘cold’) tumors. Identifying novel ways to enhance immunotherapy efficacy in PDAC is critical. Dipeptidyl peptidase (DPP) inhibition can enhance immunotherapy efficacy in other cancer types; however, the impact of DPP inhibition on PDAC tumors remains unexplored.

Methods

We examined the effects of an oral small molecule DPP inhibitor (BXCL701) on PDAC tumor growth using mT3-2D and Pan02 subcutaneous syngeneic murine models in C57BL/6 mice. We explored the effects of DPP inhibition on the tumor immune landscape using RNAseq, immunohistochemistry, cytokine evaluation and flow cytometry. We then tested if BXCL701 enhanced anti-programmed cell death protein 1 (anti-PD1) efficacy and performed immune cell depletion and rechallenged studies to explore the relevance of cytotoxic immune cells to combination treatment efficacy.

Results

In both murine models of PDAC, DPP inhibition enhanced NK and T cell immune infiltration and reduced tumor growth. DPP inhibition also enhanced the efficacy of anti-PD1. The efficacy of dual anti-PD1 and BXCL701 therapy was dependent on both CD8+ T cells and NK cells. Mice treated with this combination therapy developed antitumor immune memory that cleared some tumors after re-exposure. Lastly, we used The Cancer Genome Atlas (TCGA) to demonstrate that increased NK cell content, but not T cell content, in human PDAC tumors is correlated with longer overall survival. We propose that broad DPP inhibition enhances antitumor immune response via two mechanisms: (1) DPP4 inhibition increases tumor content of CXCL9/10, which recruits CXCR3+ NK and T cells, and (2) DPP8/9 inhibition activates the inflammasome, resulting in proinflammatory cytokine release and Th1 response, further enhancing the CXCL9/10-CXCR3 axis.

Conclusions

These findings show that DPP inhibition with BXCL701 represents a pharmacologic strategy to increase the tumor microenvironment immune cell content to improve anti-PD1 efficacy in PDAC, suggesting BXCL701 can enhance immunotherapy efficacy in ‘cold’ tumor types. These findings also highlight the potential importance of NK cells along with T cells in regulating PDAC tumor growth.

Stem cells-derived natural killer cells for cancer immunotherapy: current protocols, feasibility, and benefits of ex vivo generated natural killer cells in treatment of advanced solid tumors

Nowadays, natural killer (NK) cell-based immunotherapy provides a practical therapeutic strategy for patients with advanced solid tumors (STs). This approach is adaptively conducted by the autologous and identical NK cells after in vitro expansion and overnight activation. However, the NK cell-based cancer immunotherapy has been faced with some fundamental and technical limitations. Moreover, the desirable outcomes of the NK cell therapy may not be achieved due to the complex tumor microenvironment by inhibition of intra-tumoral polarization and cytotoxicity of implanted NK cells. Currently, stem cells (SCs) technology provides a powerful opportunity to generate more effective and universal sources of the NK cells. Till now, several strategies have been developed to differentiate types of the pluripotent and adult SCs into the mature NK cells, with both feeder layer-dependent and/or feeder laye-free strategies. Higher cytokine production and intra-tumoral polarization capabilities as well as stronger anti-tumor properties are the main features of these SCs-derived NK cells. The present review article focuses on the principal barriers through the conventional NK cell immunotherapies for patients with advanced STs. It also provides a comprehensive resource of protocols regarding the generation of SCs-derived NK cells in an ex vivo condition.

The Role of Interleukin-18 in the Development and Progression of Atherosclerosis

Atherosclerosis (AS), as a chronic inflammatory disorder of the cardiovascular system, is one of the leading causes of ischemic heart disease, stroke and peripheral vascular disease. There is growing evidence on the role of innate and adaptive immunity in the pathogenesis of atherosclerosis. Interleukin-18 is one of the novel proinflammatory cytokines involved in atherogenesis, atherosclerotic plaque instability and plaque rupture. In this review, we overview the findings of preclinical and clinical studies about the role and mechanism of action of IL-18 in the pathogenesis of AS, which could offer novel prognostic and therapeutic approaches.

Engineered Three-Dimensional Tumor Models to Study Natural Killer Cell Suppression

A critical hurdle associated with natural killer (NK) cell immunotherapies is inadequate infiltration and function in the solid tumor microenvironment. Well-controlled 3D culture systems could advance our understanding of the role of various biophysical and biochemical cues that impact NK cell migration in solid tumors. The objectives of this study were to establish a biomaterial which (i) supports NK cell migration and (ii) recapitulates features of the in vivo solid tumor microenvironment, to study NK infiltration and function in a 3D system. Using peptide-functionalized poly(ethylene glycol)-based hydrogels, the extent of NK-92 cell migration was observed to be largely dependent on the density of integrin binding sites and the presence of matrix metalloproteinase degradable sites. When lung cancer cells were encapsulated into the hydrogels to create tumor microenvironments, the extent of NK-92 cell migration and functional activity was dependent on the cancer cell type and duration of 3D culture. NK-92 cells showed greater migration into the models consisting of nonmetastatic A549 cells relative to metastatic H1299 cells, and reduced migration in both models when cancer cells were cultured for 7 days versus 1 day. In addition, the production of NK cell-related pro-inflammatory cytokines and chemokines was reduced in H1299 models relative to A549 models. These differences in NK-92 cell migration and cytokine/chemokine production corresponded to differences in the production of various immunomodulatory molecules by the different cancer cells, namely, the H1299 models showed increased stress ligand shedding and immunosuppressive cytokine production, particularly TGF-β. Indeed, inhibition of TGF-β receptor I in NK-92 cells restored their infiltration in H1299 models to levels similar to that in A549 models and increased overall infiltration in both models. Relative to conventional 2D cocultures, NK-92 cell mediated cytotoxicity was reduced in the 3D tumor models, suggesting the hydrogel serves to mimic some features of the biophysical barriers in in vivo tumor microenvironments. This study demonstrates the feasibility of a synthetic hydrogel system for investigating the biophysical and biochemical cues impacting NK cell infiltration and NK cell-cancer cell interactions in the solid tumor microenvironment.

Inflammatory activation and endothelial dysfunction markers in patients with permanent atrial fibrillation: a cross-sectional study

In recent years a growing body of evidence supported the role of inflammation in the initiation, maintenance and outcome of atrial fibrillation (AF). Nevertheless, despite a large amount of information, whether AF or the underlying structural heart disease (SHD) is the cause of the inflammatory process is still under debate. We, therefore, sought to determine if the inflammatory process reflect an underlying disease or the arrhythmia ‘per se’. We evaluated plasma levels of soluble Interleukin 2 Receptor Alpha (sIL-2Rα), TNF-α and IL-18 in 100 consecutive patients with permanent AF, (43 with a SHD and 57 without a SHD) compared to 121 age and sex-matched controls which had normal sinus rhythm. We also evaluated the endothelial function in both groups of patients using reactive hyperemia index (RHI) values measured by Endo-PAT2000. Compared to controls, AF patients showed higher circulating levels of inflammatory markers and a lower mean value of RHI. At multiple logistic regression analysis, the inflammatory markers and RHI were significantly associated with AF presence, whereas ROC curve analysis had good sensitivity and specificity in inflammatory variables and RHI for AF presence. No significant association was observed in the group of permanent AF patients, between inflammatory markers and the presence of an underlying SHD. These findings could help to clarify the role of inflammation in subjects with AF and suggest that the markers of systemic inflammation are not associated with the underlying cardiovascular disease, rather with the atrial fibrillation ‘per se’.

PD-1 immunobiology in autoimmune hepatitis and hepatocellular carcinoma

Disruption of liver immune tolerance allows for the development of autoimmune hepatitis (AIH) and hepatocellular carcinoma (HCC). AIH rarely progresses to HCC but the diseases similarly induce the production of IL-18 and matrix metalloproteinases. These molecules have distinct effects on the immune response, including the programmed cell-death 1 (PD-1) axis. In this review, differences in PD-1 function and possible cell signals in AIH and HCC are highlighted.

Interleukin-18, matrix metalloproteinase-22 and -29 are independent risk factors of human coronary heart disease

BACKGROUND

Coronary heart disease (CHD) is characterized by arterial wall inflammation and matrix degradation. Matrix metalloproteinase (MMP)-22 and -29 and pro-inflammatory cytokine interleukin-18 (IL18) are present in human hearts. IL18 may regulate MMP-22 and -29 expression, which may correlate with CHD progression.

METHODS AND RESULTS

Immunoblot analysis showed that IL18 induced MMP-22 expression in human aortic smooth muscle cells. The Mann Whitney test from a prospective study of 194 CHD patients and 68 non-CHD controls demonstrated higher plasma levels of IL18, MMP-22 and -29 in CHD patients than in the controls. A logistic regression test suggested that plasma IL18 (odds ratio (OR)=1.131, P=0.007), MMP-22 (OR=1.213, P=0.040), and MMP-29 (OR=1.198, P=0.033) were independent risk factors of CHD. Pearson's correlation test showed that IL18 (coefficient (r)=0.214, P=0.045; r=0.246, P=0.031) and MMP-22 (r=0.273, P=0.006; r=0.286, P=0.012) were associated with the Gensini score before and after adjusting for potential confounding factors. The multivariate Pearson's correlation test showed that plasma MMP-22 levels correlated positively with high-sensitive-C-reactive protein (hs-CRP) (r=0.167, P=0.023), and MMP-29 levels correlated negatively with triglyceride (r=-0.169, P=0.018). Spearman's correlation test indicated that plasma IL18 levels associated positively with plasma MMP-22 (r=0.845, P<0.001) and MMP-29 (r=0.548, P<0.001).

CONCLUSIONS

Our observations suggest that IL18, MMP-22 and -29 serve as biomarkers and independent risk factors of CHD. Increased systemic IL18 in CHD patients may contribute to elevated plasma MMP-22 and -29 levels in these patients.

Relation between Arterial Stiffness and Markers of Inflammation and Hemostasis - Data from the Population-based Gutenberg Health Study

The relation between inflammation, hemostasis and arterial stiffness is of pathophysiological relevance for the development of cardiovascular disease (CVD). Data investigating this interplay using stiffness index (SI) by digital photoplethysmography are not available yet. Therefore, sex-specific relation between SI and inflammatory and hemostatic biomarkers was investigated within 13,724 subjects from the population-based Gutenberg Health Study. C-reactive protein (CRP), white blood cell count (WBCC), neopterin, interleukin-18, interleukin-1 receptor antagonist (IL-1RA), fibrinogen and hematocrit were measured. Multivariable linear regression analysis with adjustment for cardiovascular risk factors, medication, and hormonal status (in females) revealed an independent association between SI and WBCC, IL-1RA and hematocrit in both sexes, and with fibrinogen in women. There was a joint effect of increasing tertiles of SI and biomarker concentrations for future CVD risk prediction. Subjects with both SI and biomarker concentration above the median had the worst overall survival and with both below the median the best survival during a follow-up period of 6.2 ± 1.7 years, except for hematocrit. The results support the relation between inflammation, hemostasis and arterial stiffness measured by digital photoplethysmography. Markers of inflammation and hemostasis modulate the ability of SI to identify subjects at risk for future CVD or higher mortality.

The Role of Interleukin-18, Oxidative Stress and Metabolic Syndrome in Alzheimer's Disease

The role of interleukins (ILs) and oxidative stress (OS) in precipitating neurodegenerative diseases including sporadic Alzheimer's disease (AD), requires further clarification. In addition to neuropathological hallmarks-extracellular neuritic amyloid-β (Aβ) plaques, neurofibrillary tangles (NFT) containing hyperphosphorylated tau and neuronal loss-chronic inflammation, as well as oxidative and excitotoxic damage, are present in the AD brain. The pathological sequelae and the interaction of these events during the course of AD need further investigation. The brain is particularly sensitive to OS, due to the richness of its peroxidation-sensitive fatty acids, coupled with its high oxygen demand. At the same time, the brain lack robust antioxidant systems. Among the multiple mechanisms and triggers by which OS can accumulate, inflammatory cytokines can sustain oxidative and nitrosative stress, leading eventually to cellular damage. Understanding the consequences of inflammation and OS may clarify the initial events underlying AD, including in interaction with genetic factors. Inflammatory cytokines are potential inducers of aberrant gene expression through transcription factors. Susceptibility disorders for AD, including obesity, type-2 diabetes, cardiovascular diseases and metabolic syndrome have been linked to increases in the proinflammatory cytokine, IL-18, which also regulates multiple AD related proteins. The association of IL-18 with AD and AD-linked medical conditions are reviewed in the article. Such data indicates that an active lifestyle, coupled to a healthy diet can ameliorate inflammation and reduce the risk of sporadic AD.

Estimation of interleukin-18 in the gingival crevicular fluid and serum of Bengali population with periodontal health and disease

Context:

Host's immune response elicits cytokines in response to bacterial challenge. We explore role of one such cytokine interleukin-18 (IL-18) in periodontal health and disease.

Aims:

IL-18 is a pro-inflammatory and tumor suppressive cytokine. Dental literatures suggest that IL-18 might have a role to play in the progression from oral health to periodontal disease. Therefore, this study was undertaken to elucidate the level and role of IL-18 in the gingival crevicular fluid (GCF) and serum of individuals with healthy gingiva, chronic gingivitis, chronic periodontitis, and aggressive periodontitis before and after periodontal therapy.

Settings and Design:

Eighty individuals chosen for the study were divided into healthy control group (1A), chronic gingivitis (2A), chronic periodontitis (3A), and aggressive periodontitis (4A) with twenty individuals each. Criteria for the division were the subject's gingival index, probing pocket depth, clinical attachment loss, and radiographic evidence of bone loss.

Materials and Methods:

The individuals underwent treatment (scaling in case of Groups 1A and 2A and scaling and root planing followed by flap surgery in Groups 3A and 4A) to form posttreatment Groups 1B, 2B, 3B, and 4B, respectively. Thus, a total of 160 GCF and 160 serum samples were collected and tested by ELISA.

Statistical Analysis Used:

Intergroup comparison was done by post hoc Tukey's test.

Results:

The mean IL-18 concentration was greatest in Group 3A (GCF 144.61 pg/μl, serum 55.12 pg/ml) followed by Group 4A (GCF 98.55 pg/μl, serum 39.06 pg/ml), Group 2A (GCF 22.27 pg/μl, serum 27.73 pg/ml) and lowest (GCF 17.94 pg/μl, serum 11.49 pg/ml) in Group 1A. Posttreatment groups (1B–4B) showed reduction in the mean IL-18 concentration in both GCF and serum.

Conclusions:

As the inflammation increased, there was a concomitant increase in the level of IL-18 and vice versa following periodontal therapy.

Interplay between Matrix Metalloproteinase-9, Matrix Metalloproteinase-2, and Interleukins in Multiple Sclerosis Patients

Matrix Metalloproteases (MMPs) and cytokines have been involved in the pathogenesis of multiple sclerosis (MS). However, no studies have still explored the possible associations between the two families of molecules. The present study aimed to evaluate the contribution of active MMP-9, active MMP-2, interleukin- (IL-) 17, IL-18, IL-23, and monocyte chemotactic proteins-3 to the pathogenesis of MS and the possible interconnections between MMPs and cytokines. The proteins were determined in the serum and cerebrospinal fluid (CSF) of 89 MS patients and 92 other neurological disorders (OND) controls. Serum active MMP-9 was increased in MS patients and OND controls compared to healthy subjects (p < 0.001 and p < 0.01, resp.), whereas active MMP-2 and ILs did not change. CSF MMP-9, but not MMP-2 or ILs, was selectively elevated in MS compared to OND (p < 0.01). Regarding the MMPs and cytokines intercorrelations, we found a significant association between CSF active MMP-2 and IL-18 (r = 0.3, p < 0.05), while MMP-9 did not show any associations with the cytokines examined. Collectively, our results suggest that active MMP-9, but not ILs, might be a surrogate marker for MS. In addition, interleukins and MMPs might synergistically cooperate in MS, indicating them as potential partners in the disease process.

Dendritic Cells Expressing Triggering Receptor Expressed on Myeloid Cells-1 Correlate with Plaque Stability in Symptomatic and Asymptomatic Patients with Carotid Stenosis

Atherosclerosis is a chronic inflammatory disease with atherosclerotic plaques containing inflammatory cells, including T-lymphocytes, dendritic cells (DCs) and macrophages that are responsible for progression and destabilization of atherosclerotic plaques. Stressed cells undergoing necrosis release molecules that act as endogenous danger signals to alert and activate innate immune cells. In atherosclerotic tissue the number of DCs increases with the progression of the lesion and produce several inflammatory cytokines and growth factors. Triggering receptor expressed on myeloid cells (TREM)-1 plays a crucial role in inflammation. However, relationship of DCs and the role of TREM-1 with the stability of atherosclerotic plaques have not been examined. In this study, we investigated the heterogeneity of the plaque DCs, myeloid (mDC1 and mDC2) and plasmacytoid (pDCs), and examined the expression of TREM-1 and their co-localization with DCs in the plaques from symptomatic (S) and asymptomatic (AS) patients with carotid stenosis. We found increased expression of HLA-DR, fascin, and TREM-1 and decreased expression of TREM-2 and α-smooth muscle actin in S compared to AS atherosclerotic carotid plaques. Both TREM-1 and fascin were co-localized suggesting increased expression of TREM-1 in plaque DCs of S compared to AS patients. These data were supported by increased mRNA transcripts of TREM-1 and decreased mRNA transcripts of TREM-2 in carotid plaques of S compared to AS patients. There was higher density of both CD1c+ mDC₁ and CD141+ mDC₂ in the carotid plaques from AS compared to S patients, where as the density of CD303+ pDCs were higher in the carotid plaques of S compared to AS patients. These findings suggest a potential role of pDCs and TREM-1 in atherosclerotic plaque vulnerability. Thus, newer therapies could be developed to selectively block TREM-1 for stabilizing atherosclerotic plaques.

Effect of polyclonal activators on cytokine production by blood cells and by malignant breast cancer cells

The production of cytokines by peripheral blood cells and biopsy specimens of tumors stimulated by polyclonal activators (PAs) was evaluated in 34 patients with invasive ductal breast carcinoma using enzyme-linked immunosorbent assay (ELISA). Positive correlation between the stimulation index of polyclonal activators (SIPA) for IL-18 production by the tumor and the relative content of poorly differentiated cells was revealed. The latter, in turn, was positively correlated with the numbers of normal and pathologic mitoses and the degree of malignancy. Cancer cells can produce IL-18, which is involved in the process of angiogenesis, stimulates invasion and metastasis. Decrease in SIPA for the production of IL-6 and GCSF by peripheral blood cells could serve as an indicator of malignant progression in invasive ductal breast carcinoma.

In Vitro Assessment of Human Natural Killer Cell Migration and Invasion

Cell invasion assays are important to obtain valuable functional data relating to tissue migration and invasion of effector lymphocytes. Boyden chamber invasion assays represent a reductionist system that allows for easy manipulation using various extracellular matrix (ECM) components addressing migratory functions or invasion into/through a three-dimensional matrix where migration and invasion inhibitors as well as stimulators can be added. Presented here is a description using the Transwell(®) system where invasion and migration can be studied. It constitutes an inner cell culture well with a (PET) polycarbonate filter with 3-8 μm pores that allow for cells to transverse to the bottom chamber where they can be recorded by various methods (Fig. 1). The polycarbonate filters may be coated with ECM proteins for migration and adhesive studies or covered with a thick layer that occludes the pores to address matrix degradation, i.e., invasion as described in this chapter.

Interlukin-18 Is a Pivot Regulatory Factor on Matrix Metalloproteinase-13 Expression and Brain Astrocytic Migration

The expression of matrix metalloproteinase-13 (MMP-13) has been shown to be elevated in some pathophysiological conditions and is involved in the degradation of extracellular matrix in astrocytes. In current study, the function of MMP-13 was further investigated. The conditioned medium (CM) collected from activated microglia increased interleukin (IL)-18 production and enhanced MMP-13 expression in astrocytes. Furthermore, treatment with recombinant IL-18 increased MMP-13 protein and mRNA levels in astrocytes. Recombinant IL-18 stimulation also increased the enzymatic activity of MMP-13 and the migratory activity of astrocytes, while administration of MMP-13 or pan-MMP inhibitors antagonized IL-18-induced migratory activity of astrocytes. In addition, administration of recombinant IL-18 to astrocytes led to the phosphorylation of JNK, Akt, or PKCδ, and treatment of astrocytes with JNK, PI3 kinase/Akt, or PKCδ inhibitors significantly decreased the IL-18-induced migratory activity. Taken together, the results suggest that IL-18-induced MMP-13 expression in astrocytes is regulated by JNK, PI3 kinase/Akt, and PKCδ signaling pathways. These findings also indicate that IL-18 is an important regulator leading to MMP-13 expression and cell migration in astrocytes.

Interleukin-18 alters protein expressions of neurodegenerative diseases-linked proteins in human SH-SY5Y neuron-like cells

Chronic inflammation and oxidative stress (OS) are present in Alzheimer's disease (AD) brains in addition to neuronal loss, Amyloid-β (Aβ) plaques and hyperphosphorylated tau-protein neurofibrillary tangles (NFTs). Previously we showed that levels of the pro-inflammatory cytokine, interleukin-18 (IL-18), are elevated in post-mortem AD brains. IL-18 can modulate the tau kinases, Cdk5 and GSK3β, as well as Aβ-production. IL-18 levels are also increased in AD risk diseases, including type-2 diabetes and obesity. Here, we explored other IL-18 regulated proteins in neuron-like SH-SY5Y cells. Differentiated SH-SY5Y cells, incubated with IL-18 for 24, 48, or 72 h, were analyzed by two-dimensional gel electrophoresis (2D-DIGE). Specific altered protein spots were chosen and identified with mass spectrometry (MS) and verified by western immunoblotting (WIB). IL-18 had time-dependent effects on the SH-SY5Y proteome, modulating numerous protein levels/modifications. We concentrated on those related to OS (DDAH2, peroxiredoxins 2, 3, and 6, DJ-1, BLVRA), Aβ-degradation (MMP14, TIMP2), Aβ-aggregation (Septin-2), and modifications of axon growth and guidance associated, collapsin response mediator protein 2 (CRMP2). IL-18 significantly increased antioxidative enzymes, indicative of OS, and altered levels of glycolytic α- and γ-enolase and multifunctional 14-3-3γ and -ε, commonly affected in neurodegenerative diseases. MMP14, TIMP2, α-enolase and 14-3-3ε, indirectly involved in Aβ metabolism, as well as Septin-2 showed changes that increase Aβ levels. Increased 14-3-3γ may contribute to GSK3β driven tau hyperphosphorylation and CRMP2 Thr514 and Ser522 phosphorylation with the Thr555-site, a target for Rho kinase, showing time-dependent changes. IL-18 also increased caspase-1 levels and vacuolization of the cells. Although our SH-SY5Y cells were not aged, as neurons in AD, our work suggests that heightened or prolonged IL-18 levels can drive protein changes of known relevance to AD pathogenesis.

Membrane-type matrix metalloproteinases: key mediators of leukocyte function

Leukocytes are major cellular effectors of the immune response. To accomplish this task, these cells display a vast arsenal of proteinases, among which, members of the MMP family are especially important. Leukocytes express several members of the MMP family, including secreted- and membrane-anchored MT- MMPs, which synergistically orchestrate an appropriate proteolytic reaction that ultimately modulates immunological responses. The MT-MMP subfamily comprises TM- and GPI-anchored proteinases, which are targeted to well-defined membrane microdomains and exhibit different substrate specificities. Whereas much information exists on the biological roles of secreted MMPs in leukocytes, the roles of MT-MMPs remain relatively obscure. This review summarizes the current knowledge on the expression of MT-MMPs in leukocyte and their contribution to the immune responses and to pathological conditions.

Matrix metalloproteinases in cytotoxic lymphocytes impact on tumour infiltration and immunomodulation

To efficiently combat solid tumours, endogenously or adoptively transferred cytotoxic T cells and natural killer (NK) cells, need to leave the vasculature, traverse the interstitium and ultimately infiltrate the tumour mass. During this locomotion and migration in the three dimensional environment many obstacles need to be overcome, one of which is the possible impediment of the extracellular matrix. The first and obvious one is the sub-endothelial basement membrane but the infiltrating cells will also meet other, both loose and tight, matrix structures that need to be overridden. Matrix metalloproteinases (MMPs) are believed to be one of the most important endoprotease families, with more than 25 members, which together have function on all known matrix components. This review summarizes what is known on synthesis, expression patterns and regulation of MMPs in cytotoxic lymphocytes and their possible role in the process of tumour infiltration. We also discuss different functions of MMPs as well as the possible use of other lymphocyte proteases for matrix degradation.

Effects of IL-2 on MMP expression in freshly isolated human NK cells and the IL-2-independent NK cell line YT

Interleukin-2 is an important activation factor for natural killer (NK) cells but its effect on NK cell matrix metalloproteinases (MMP) production and matrix degradation is less well investigated. We have used freshly isolated human NK cells and the IL-2-independent NK cell line, YT, to investigate the effects of IL-2 stimulation on NK cell invasion of Matrigel and on MMP expression and production. In YT cells, we found opposing early and late effects of IL-2 stimulation with an early (2 h) increase in MMP-9 protein level and enhanced migration in the Matrigel invasion assay and by 30 hours a decreased mRNA expression of MMP-2, MMP-9, MMP-13, MT3-MMP, and MT6-MMP. We also found a preculture period of 48 hours with IL-2 to negatively affect YT cell migration. We furthermore found that freshly isolated human NK cells Matrigel invasion was MMP-dependent and it increased in response to IL-2. Importantly, in freshly isolated human NK cells we did not see a downregulation of MMPs after 24 hours IL-2 stimulation, but instead a significant upregulation of MT6-MMP mRNA. Because of the cellular localisation of MT6-MMP, which ensures a focalized proteolytic activity, and its high expression compared with the other MMPs in freshly isolated human NK cells makes it of interest to study further.

Interleukin-18 among atrial fibrillation patients in the absence of structural heart disease

AIMS

Inflammation plays a role in the genesis and perpetuation of atrial fibrillation (AF). Interleukin (IL)-18 is a pleiotropic proinflammatory cytokine with a central role in the inflammatory cascade. We hypothesize that the circulating IL-18 concentration is elevated in AF patients.

METHODS AND RESULTS

In a case-control study design, 56 cases with AF and 26 controls were enrolled. All AF cases were categorized into paroxysmal and persistent AF or lone AF and AF with hypertension. Circulating levels of IL-18, tumour necrosis factor-α, high-sensitivity C-reactive protein, matrix metalloproteinase (MMP)-9, and tissue inhibitor of MMP-1 were measured. In adjusted analyses, only age, MMP-9, and IL-18 were independently associated with AF, in which IL-18 had the most significant association (P = 0.0011, standardized estimate &bgr = 1.76, OR = 1.02, 95% confidence interval: 1.01-1.03). Interleukin-18 levels in persistent AF patients were higher than those in paroxysmal ones (P = 0.0011). Patients who developed AF within 24 h prior to sampling displayed a higher level of IL-18 than those with sinus rhythm (P = 0.0027). Interleukin-18 was positively correlated with left atrial diameter (r = 0.33, P = 0.0117).

CONCLUSION

This study documents the elevated IL-18 in AF patients. Interleukin-18 may be superior to other inflammatory markers which are known to be elevated in AF.

Human NK cell lines migrate differentially in vitro related to matrix interaction and MMP expression

Matrix metalloproteinases (MMPs) are thought to be of importance for the migratory ability of natural killer (NK) cells. Their expression and production may influence the amount of tumour-infiltrating NK cells and thereby any therapeutic capability. In this study, we sought to investigate the importance of MMPs for human NK cells' ability to degrade and migrate through the extracellular matrix (ECM). The two human NK cell lines, NK-92 and YT, migratory ability, MMP expression and production as well as their morphological appearance when cultured in the ECM equivalent Matrigel were analysed and compared. The quantitatively more migratory NK-92 cells were found to express invadopodia/podosomes at a significantly higher degree when cultured in Matrigel and gave rise to a general disintegration of the Matrigel. The NK-92 cells had a higher mRNA expression of MMP-2, -9, -13, MT1-, MT3- and MT6-MMP and a significantly higher production of MMP-9 compared to YT cells. These differences could explain the substantial functional difference observed between the two cell lines with respect to migratory capacity. In addition, the number of Matrigel invading NK-92 cells decreased significantly in the presence of the MMP inhibitor GM6001, demonstrating that MMPs have a critical function in their migration.

Treg depletion-enhanced IL-2 treatment facilitates therapy of established tumors using systemically delivered oncolytic virus

There are several roadblocks that hinder systemic delivery of oncolytic viruses to the sites of metastatic disease. These include the tumor vasculature, which provides a physical barrier to tumor-specific virus extravasation. Although interleukin-2 (IL-2) has been used in antitumor therapy, it is associated with endothelial cell injury, leading to vascular leak syndrome (VLS). Here, we demonstrate that IL-2-mediated VLS, accentuated by depletion of regulatory T cells (Treg), facilitates localization of intravenously (i.v.) delivered oncolytic virus into established tumors in immune-competent mice. IL-2, in association with Treg depletion, generates "hyperactivated" natural killer (NK) cells, possessing antitumor activity and secreting factors that facilitate virus spread/replication throughout the tumor by disrupting the tumor architecture. As a result, the combination of Treg depletion/IL-2 and systemic oncolytic virotherapy was found to be significantly more therapeutic against established disease than either treatment alone. These data demonstrate that it is possible to combine biological therapy with oncolytic virotherapy to generate systemic therapy against established tumors.

Interleukin 18 and periodontal disease

Cytokines are of major importance in periodontal disease progression. It is generally agreed that control of the Th1/Th2 balance is central to the immunoregulation of periodontal disease. There is increasing evidence in humans that the stable periodontal lesion is mediated by Th1 cells, while the progressive lesion sees a shift toward Th2 cells. Equally, there is conflicting evidence, mainly in animal models, that bone loss is mediated by Th1 responses, and that Th2 responses are protective. In the presence of IL-12, IL-18 induces Th1 responses while, in the absence of IL-12, it promotes Th2 responses. It is clear, therefore, that since IL-18 has the ability to induce either Th1 or Th2 differentiation, it becomes important to consider its role in periodontal disease. This review endeavors to give an overview of this cytokine and its relevance for periodontal disease.

IL-18 is induced and IL-18 receptor alpha plays a critical role in the pathogenesis of cigarette smoke-induced pulmonary emphysema and inflammation

Th1 inflammation and remodeling characterized by local tissue destruction coexist in pulmonary emphysema and other diseases. To test the hypothesis that IL-18 plays an important role in these responses, we characterized the regulation of IL-18 in lungs from cigarette smoke (CS) and room air-exposed mice and characterized the effects of CS in wild-type mice and mice with null mutations of IL-18Ralpha (IL-18Ralpha(-/-)). CS was a potent stimulator and activator of IL-18 and caspases 1 and 11. In addition, although CS caused inflammation and emphysema in wild-type mice, both of these responses were significantly decreased in IL-18Ralpha(-/-) animals. CS also induced epithelial apoptosis, activated effector caspases and stimulated proteases and chemokines via IL-18Ralpha-dependent pathways. Importantly, the levels of IL-18 and its targets, cathepsins S and B, were increased in pulmonary macrophages from smokers and patients with chronic obstructive lung disease. Elevated levels of circulating IL-18 were also seen in patients with chronic obstructive lung disease. These studies demonstrate that IL-18 and the IL-18 pathway are activated in CS-exposed mice and man. They also demonstrate, in a murine modeling system, that IL-18R signaling plays a critical role in the pathogenesis of CS-induced inflammation and emphysema.

Effector and regulatory events during natural killer-dendritic cell interactions

The different cell types of the innate immune system can interact with each other and influence the quality and strength of an immune response. The cross talk between natural killer (NK) cells and myeloid dendritic cells (DCs) leads to NK cell activation and DC maturation. Activated NK cells are capable of killing DCs that fail to undergo proper maturation ('DC editing'). Encounters between NK cells and DCs occur in both inflamed peripheral tissues and lymph nodes, where both cell types are recruited by chemokines released in the early phases of inflammatory responses. Different NK cell subsets (CD56(bright)CD16(-) versus CD56(+)CD16(+)) differ in their homing capabilities. In particular, CD56(bright)CD16(-) NK cells largely predominate the lymph nodes. In addition, these two subsets display major functional differences in their cytolytic activity, cytokine production, and ability to undergo proliferation. NK cell functions are also greatly influenced by the presence of polarizing cytokines such as interleukin (IL)-12 and IL-4. The cytokine microenvironment reflects the presence of different cell types that secrete such cytokines in response to microbial products acting on different Toll-like receptors (TLRs). Moreover, NK cells themselves can respond directly to microbial products by means of TLR3 and TLR9. Thus, it appears that the final outcome of a response to microbial infection may greatly vary as a result of the interactions occurring between different pathogen-derived products and different cell types of the innate immunity system. These interactions also determine the quality and strength of the subsequent adaptive responses. Remarkably, NK cells appear to play a key role in this complex network.

Biomarkers of atherosclerotic plaque instability and rupture

Basic research over the last two decades has identified a large number of molecules pertinent to the atherosclerotic process, which have clearly improved our understanding of the underlying pathology. It is now well established that inflammation represents a major feature which is present in the vessel wall throughout all stages of the disease until the final pathophysiologic steps, representing plaque destabilization and eventually plaque rupture. Several cells typical for the atherosclerotic plaque, like monocyte-derived macrophages and T-lymphocytes are able to produce and secrete such mediator molecules, like cytokines, chemokines, growth-factors, enzymes, and disintegrins, which lead to activation of endothelial cells, proliferation of smooth muscle cells, lesion progression, and finally to the weakening of a vulnerable plaque by matrix degradation of its fibrous cap. Today, many of these molecules involved can be measured systemically by sensitive assays, and elevated concentrations in the circulation have been shown to be associated with future cardiovascular events. Determination of several of these molecules carries important prognostic information, independent of traditional risk factors, and may turn out to be useful in improving risk stratification. However, for most of these biomarkers the clinical utility has not yet been established.

Expression of interleukin-18 receptor mRNA in the mouse endometrium

Interleukin-18 (IL-18) is a proinflammatory cytokine involved in chronic inflammation, autoimmune diseases, and a variety of cancers, and is expressed in mouse uteri. Our previous study suggested that IL-18 acts as a paracrine factor, regulating endometrial function. To elucidate the physiological roles of IL-18 in the mouse endometrium, the expression of the IL-18 receptor (IL-18R) alpha subunit was analyzed. IL-18Ralpha mRNA was expressed in several mouse organs in addition to the endometrium. In situ hybridization analysis using a biotin-labeled mouse IL-18Ralpha riboprobe demonstrated that IL-18Ralpha mRNA expression was detected in glandular epithelial cells, stromal cells around uterine glands, and myometrial cells in the mouse uterus, suggesting that these cells are targets for IL-18. The uterine IL-18Ralpha mRNA expression level changed with the estrous cycle. The uterine IL-18Ralpha mRNA levels of estrous mice were higher than those of diestrous mice. In addition, the IL-18Ralpha mRNA levels in uteri at 3 and 14 days after ovariectomy were higher than those at diestrus and decreased following treatment with estradiol-17beta or progesterone. These findings suggest that IL-18Ralpha gene expression is regulated by estrogen and progesterone and that the uterine IL-18 system is involved in the regulation of uterine functions in a paracrine manner.

Increased concentrations of C-reactive protein and IL-6 but not IL-18 are independently associated with incident coronary events in middle-aged men and women: results from the MONICA/KORA Augsburg case-cohort study, 1984-2002

OBJECTIVE

We performed a prospective case-cohort study in initially healthy, middle-aged men and women from the MONICA/KORA Augsburg studies conducted between 1984 and 2002 to assess the role of IL-18 in comparison with IL-6 and CRP in the prediction of incident coronary heart disease (CHD).

METHODS AND RESULTS

Concentrations of IL-18 were measured in 382 case subjects with incident CHD and 1980 noncases. Mean follow-up was 11 years. Baseline concentrations of IL-18 were slightly higher in cases than in noncases (172.4 [1.0] versus 161.3 [1.0] pg/mL, respectively; P=0.114), but were clearly elevated for C-reactive protein (CRP) and IL-6 in cases compared with noncases. In multivariable analyses, accounting for classical cardiovascular risk factors and inflammatory markers, no statistically significant association was seen between increased concentrations of IL-18 and incident CHD both in men (hazard ratio [HR] and 95% confidence intervals [CIs] comparing extreme tertiles, 1.20; 95% CI, 0.85 to 1.69), and in women (HR, 1.25; 95% CI, 0.67 to 2.34). However, in this population increased concentrations of CRP and IL-6 were found to be independent predictors of future CHD events, even after multivariable adjustment.

CONCLUSIONS

Elevated concentrations of CRP and IL-6, but not IL-18, were independently associated with risk of CHD in subjects from an area with moderate absolute risk.

Interleukin-18 is a critical factor for vascular endothelial growth factor-enhanced migration in human gastric cancer cell lines

Cell migration and angiogenesis are key steps in tumor metastasis. However, the mechanism of migration regulated by vascular endothelial growth factor (VEGF), a potent regulator of angiogenesis, is not completely understood. This study examined the relationship between VEGF and migration, along with the mechanism involved in the VEGF-regulated migration of human gastric cancer cells. The level of cell migration was increased by recombinant human (rh)VEGF-165 in the VEGF receptor-2-expressing SNU-601 cells. Interleukin (IL)-18 is associated with the malignant progression of tumors. Accordingly, this study examined the effect of IL-18 on the migration of cancer cells in order to identify the factors involved in VEGF-enhanced migration. Inhibiting IL-18 markedly reduced the level of VEGF-enhanced migration, and IL-18 increased cell migration directly through filamentous-actin polymerization and tensin downregulation. It was confirmed that rhVEGF-165 increased IL-18 production significantly. An antioxidant and an extracellular signal-regulated kinase (ERK)1/2-specific inhibitor blocked rhVEGF-165-enhanced IL-18 production. Accordingly, rhVEGF-165 increased the generation of region of interest (ROI) and activated the ERK1/2 pathway. These results suggest that rhVEGF-165 enhances IL-18 production via the generation of ROI and ERK1/2 phosphorylation, which results in the increased migration of gastric cancer cells.

Matrix metalloproteinase-1 produced by human CXCL12-stimulated natural killer cells

Natural killer (NK) cells play a key role in inflammation and tumor regression through their ability to migrate into tissues. CXCL12 is a chemokine that promotes lymphocyte invasion and migration into tissues; however, the mechanism for this process remains incompletely understood. In this study, we show that CXCL12 significantly enhanced CD16(+)CD56(+) human peripheral NK-cell invasion into type I collagen by the catalytic activity of matrix metalloproteinase-1 (MMP-1). Confocal immunofluorescence and co-immunoprecipitation studies suggest that MMP-1 colocalized with alpha(2)beta(1) integrin on CXCL-12-stimulated NK-cell surface. The binding of pro-MMP-1 with alpha(2)beta(1) integrin required activation of G(i)-coupled pathway. However, the production of MMP-1 from CXCL12-stimulated NK cells was mediated by p38 and mitogen-activated or extracellular signal-regulation protein kinase kinase 1/2 in a manner independent of the G(i)-coupled pathway. These results suggest that CXCL12/CXCR4 interaction transduces the two signaling pathways to promote NK-cell invasion, which stimulates pericellular degradation of extracellular matrix proteins by membrane-associated MMP-1. The mechanisms would thus play a role in facilitating lymphocyte trafficking and accumulation in tissues during physiological and pathological processes.

Development and characterization of interleukin-18-loaded biodegradable microspheres

Immunostimulation represents a promising approach designed to specifically eradicate malignant cells. Since glioma tumour cells hole up in the central nervous system (CNS) in a particularly inauspicious milieu to antitumour immune reactions we here propose a new strategy to revert the properties of this microenvironment by administering an antitumour cytokine into the CNS tumour itself. Thus, biodegradable poly(D,L-lactide-co-glycolide) (PLGA) sustained-release microspheres for stereotaxic implantation loaded with interleukin-18 (IL-18), that is known to exert antitumour activity and trigger immune cell-mediated cytotoxicity, were developed. Different tests for assessing IL-18 bioactivity were set-up and evaluated. A specific bioassay was considered as the most reliable test. The stability and integrity of IL-18 was then verified during the encapsulation process. Consequently, two procedures of IL-18 encapsulation in PLGA microparticles (W/O/W and S/O/W) were investigated. As determined by radiolabelling studies using 125I-IL-18 and a continuous flow system, the in vitro release profile of IL-18 was optimum with S/O/W method with a moderate burst effect and a subsequent progressive discharge of 16.5+/-8.4 ng/day during the next 21 days against 6.1+/-4.2 ng/day with the W/O/W method. Considering analytical testing of IL-18 together with its preserved biological activity after release from microspheres, amounts of the active cytokine obtained with S/O/W method were relevant to plan in vivo evaluation to validate the therapeutic strategy.

In vitro investigation of lipid implants as a controlled release system for interleukin-18

Operating on the inductive and effective phases of an anti-tumor immune response and uncovering pivotal functions that may reduce cancer cell growth, interleukin-18 (IL-18) appears to be an attractive candidate for the sustained local adjuvant immunotherapeutic treatment of brain gliomas. The objective of this work was to develop IL-18 loaded lipid implants as a controlled delivery system. For the preparation of protein loaded triglyceride matrix material, a solid-in-oil (s/o) dispersion technique was chosen for which protein particles in the micrometer range were first prepared by co-lyophilization with polyethylene glycol (PEG). Implants of 1 mm diameter, 1.8 mm height and 1.8 mg weight were manufactured by compression of the powder mixture in a specially designed powder compacting tool. The in vitro release behavior of 125I-Bolton-Hunter-radiolabeled IL-18 was assessed in a continuous-flow system. A cell culture assay was established for the determination of bioactivity of released IL-18. Implants showed a continuous release of 10-100 ng IL-18 per day for 12 days. A progressive integrity loss was observed with ongoing release, which would be related to protein degradation during incubation. The initially released fraction proved complete retention of bioactivity, indicating that the manufacturing procedure had no detrimental effects on protein stability.

Association between IL-18 gene promoter polymorphisms and inflammatory bowel disease in a Japanese population

BACKGROUND

Interleukin-18 (IL-18) is a pleiotropic cytokine that induces the production of interferon (IFN)-gamma and also to regulate Th2 cytokines. Recently, association studies between IL-18 gene promoter polymorphisms and several Th1- or Th2-mediated inflammatory diseases were reported. In inflammatory bowel diseases (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), recent evidence suggests that IL-18 is involved in the pathogenesis.

METHODS

Using DNA direct sequencing, we investigated IL-18 gene promoter polymorphisms at -607C/A and -137G/C. Allele, genotype, and haplotype frequencies were determined in 210 Japanese patients with UC, 205 patients with CD, and 212 controls.

RESULTS

In UC, the -137C allele frequency was significantly higher in the proctitis-type patients than in controls (Pc = 0.0068). The -137 genotype frequency was also significantly different in the proctitis-type patients than in controls (Pc = 0.032). No other allele and genotype frequencies were significantly associated with UC after Bonferroni correction. Furthermore, the frequency of haplotype 2 (-607A, -137C), which had a lower promoter activity and IFN-gamma mRNA level than the other haplotypes as previously reported, was significantly higher in the proctitis-type patients than in controls (Pc = 0.01). In CD, we could not find any significant differences.

CONCLUSIONS

IL-18 gene promoter polymorphisms may not be associated with disease susceptibility but related to the extent of disease in UC.

Involvement of inflammation, degradation, and apoptosis in a mouse model of glaucoma

Glaucoma is a common cause of blindness affecting at least 66 million people worldwide. Pigmentary glaucoma is one of the most common forms of secondary glaucoma, and its pathogenesis remains unclear. Interleukin-18 (IL-18) is an important regulator of innate and acquired immune responses and plays an important role in inflammatory/autoimmunity diseases. Using the DBA/2J mouse as an animal model of human pigmentary glaucoma, we demonstrated for the first time that the expression of the IL-18 protein and gene in the iris/ciliary body and level of IL-18 protein in the aqueous humor of DBA/2J mice are dramatically increased with age. This increase precedes the onset of clinical evidence of pigmentary glaucoma, implying a pathogenic role of inflammation/immunity in this disease. We also observed that activated NF-kappaB and phosphorylated MAPK are increased in the iris/ciliary body of DBA/2J mice, suggesting that both signaling pathways may be involved in IL-18 mediated pathogenesis of pigmentary glaucoma in the eyes of DBA/2J mice. In addition, matrix metalloproteinase-2 (MMP-2) expression in the iris/ciliary body and the activity of MMP-2 in the aqueous humor are increased whereas tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) expression in the iris/ciliary body is decreased, indicating that the degradation process is involved in this mouse model of pigmentary glaucoma. Furthermore, the expressions of apoptosis-related genes, caspase-8, Fas, FADD, FAP, and FAF, and the activity of caspase-3 are increased in the iris/ciliary body of DBA/2J mice. Elucidation of biochemical and molecular mechanisms of IL-18 participation in the pathogenesis of pigmentary glaucoma should provide approaches for developing improved and targeted treatments to ameliorate this blinding disease. The possibility that altered IL-18 expression in the eye of DBA/2J mice initiates and/or amplifies the pathogenesis of pigmentary glaucoma requires further investigation.