Lack of Interferon-γ Production Despite the Presence of Interleukin-18 During Cutaneous Wound Healing

Wound Healing Impairment in Type 2 Diabetes Model of Leptin-Deficient Mice—A Mechanistic Systematic Review

Type II diabetes mellitus (T2DM) is one of the most prevalent diseases in the world, associated with diabetic foot ulcers and impaired wound healing. There is an ongoing need for interventions effective in treating these two problems. Pre-clinical studies in this field rely on adequate animal models. However, producing such a model is near-impossible given the complex and multifactorial pathogenesis of T2DM. A leptin-deficient murine model was developed in 1959 and relies on either dysfunctional leptin (ob/ob) or a leptin receptor (db/db). Though monogenic, this model has been used in hundreds of studies, including diabetic wound healing research. In this study, we systematically summarize data from over one hundred studies, which described the mechanisms underlying wound healing impairment in this model. We briefly review the wound healing dynamics, growth factors’ dysregulation, angiogenesis, inflammation, the function of leptin and insulin, the role of advanced glycation end-products, extracellular matrix abnormalities, stem cells’ dysregulation, and the role of non-coding RNAs. Some studies investigated novel chronic diabetes wound models, based on a leptin-deficient murine model, which was also described. We also discussed the interventions studied in vivo, which passed into human clinical trials. It is our hope that this review will help plan future research.

Role of Inflammasomes in Keloids and Hypertrophic Scars-Lessons Learned from Chronic Diabetic Wounds and Skin Fibrosis

Keloids and hypertrophic scars are pathological cutaneous scars. They arise from excessive wound healing, which induces chronic dermal inflammation and results in overwhelming fibroblast production of extracellular matrix. Their etiology is unclear. Inflammasomes are multiprotein complexes that are important in proinflammatory innate-immune system responses. We asked whether inflammasomes participate in pathological scarring by examining the literature on scarring, diabetic wounds (also characterized by chronic inflammation), and systemic sclerosis (also marked by fibrosis). Pathological scars are predominantly populated by anti-inflammatory M2 macrophages and recent literature hints that this could be driven by non-canonical inflammasome signaling. Diabetic-wound healing associates with inflammasome activation in immune (macrophages) and non-immune (keratinocytes) cells. Fibrotic conditions associate with inflammasome activation and inflammasome-induced transition of epithelial cells/endothelial cells/macrophages into myofibroblasts that deposit excessive extracellular matrix. Studies suggest that mechanical stimuli activate inflammasomes via the cytoskeleton and that mechanotransduction-inflammasome crosstalk is involved in fibrosis. Further research should examine (i) the roles that various inflammasome types in macrophages, (myo)fibroblasts, and other cell types play in keloid development and (ii) how mechanical stimuli interact with inflammasomes and thereby drive scar growth. Such research is likely to significantly advance our understanding of pathological scarring and aid the development of new therapeutic strategies.

Specific mesoderm subset derived from human pluripotent stem cells ameliorates microvascular pathology in type 2 diabetic mice

Human induced pluripotent stem cells (hiPSCs) were differentiated into a specific mesoderm subset characterized by KDR+CD56+APLNR+ (KNA+) expression. KNA+ cells had high clonal proliferative potential and specification into endothelial colony-forming cell (ECFCs) phenotype. KNA+ cells differentiated into perfused blood vessels when implanted subcutaneously into the flank of nonobese diabetic/severe combined immunodeficient mice and when injected into the vitreous of type 2 diabetic mice (db/db mice). Transcriptomic analysis showed that differentiation of hiPSCs derived from diabetics into KNA+ cells was sufficient to change baseline differences in gene expression caused by the diabetic status and reprogram diabetic cells to a pattern similar to KNA+ cells derived from nondiabetic hiPSCs. Proteomic array studies performed on retinas of db/db mice injected with either control or diabetic donor-derived KNA+ cells showed correction of aberrant signaling in db/db retinas toward normal healthy retina. These data provide "proof of principle" that KNA+ cells restore perfusion and correct vascular dysfunction in db/db mice.

Bifunctional Peptide that Anneals to Damaged Collagen and Clusters TGF-β Receptors Enhances Wound Healing

Transforming growth factor-β (TGF-β) plays important roles in wound healing. The activity of TGF-β is initiated upon the binding of the growth factor to the extracellular domains of its receptors. We sought to facilitate the activation by clustering these extracellular domains. To do so, we used a known peptide that binds to TGF-β receptors without diminishing their affinity for TGF-β. We conjugated this peptide to a collagen-mimetic peptide that can anneal to the damaged collagen in a wound bed. We find that the conjugate enhances collagen deposition and wound closure in mice in a manner consistent with the clustering of TGF-β receptors. This strategy provides a means to upregulate the TGF-β signaling pathway without adding exogenous TGF-β and could inspire means to treat severe wounds.

Pyroptosis: Mechanisms and Links with Fibrosis

Fibrosis is responsible for approximately 45% of deaths in the industrialized world and has been a major global healthcare burden. Excessive fibrosis is the primary cause of organ failure. However, there are currently no approved drugs available for the prevention or treatment of fibrosis-related diseases. It has become evident that fibrosis is characterized by inflammation. In a large number of studies of various organs in mice and humans, pyroptosis has been found to play a significant role in fibrosis. Pyroptosis is a form of programmed cell death mediated by the N-terminal fragment of cysteinyl aspartate-specific proteinase (caspase)-1-cleaved gasdermin D (GSDMD, producing GSDMD-N) that gives rise to inflammation via the release of some proinflammatory cytokines, including IL-1β, IL-18 and HMGB1. These cytokines can initiate the activation of fibroblasts. Inflammasomes, an important factor upstream of GSDMD, can activate caspase-1 to trigger the maturation of IL-1β and IL-18. Moreover, the inhibition of inflammasomes, proinflammatory cytokines and GSDMD can prevent the progression of fibrosis. This review summarizes the growing evidence indicating that pyroptosis triggers fibrosis, and highlights potential novel targets for antifibrotic therapies.

Cutaneous innervation in impaired diabetic wound healing

Type 2 diabetes is associated with several potential comorbidities, among them impaired wound healing, chronic ulcerations, and the requirement for lower extremity amputation. Disease-associated abnormal cellular responses, infection, immunological and microvascular dysfunction, and peripheral neuropathy are implicated in the pathogenesis of the wound healing impairment and the diabetic foot ulcer. The skin houses a dense network of sensory nerve afferents and nerve-derived modulators, which communicate with epidermal keratinocytes and dermal fibroblasts bidirectionally to effect normal wound healing after trauma. However, the mechanisms through which cutaneous innervation modulates wound healing are poorly understood, especially in humans. Better understanding of these mechanisms may provide the basis for targeted treatments for chronic diabetic wounds. This review provides an overview of wound healing pathophysiology with a focus on neural involvement in normal and diabetic wound healing, as well as future therapeutic perspectives to address the unmet needs of diabetic patients with chronic wounds.

The imbalance of peripheral interleukin-18 and transforming growth factor-β1 levels in patients with cirrhosis and esophageal varices

INTRODUCTION

The presence of esophageal varices in liver cirrhosis indicates clinically significant portal hypertension (PH), that results from structural and dynamic changes in the liver and systemic circulation including the activation of several fibrotic and inflammatory pathways. We assessed if interleukin-18 (IL-18) and transforming growth factor-β1 (TGF-β1) serum levels can be used as PH markers and reflect its severity.

MATERIAL AND METHODS

IL-18 and TGF-β1 peripheral blood levels were analyzed in 83 cirrhotic patients with esophageal varices compared to healthy individuals, in relation to MELD and Child-Pugh scores, laboratory and Doppler ultrasound parameters, and non-selective beta-blocker therapy (NSBB).

RESULTS

IL-18 concentration was significantly higher in cirrhotic patients, while TGF-β1 concentration was lower than in controls. MELD score correlated positively with IL-18 levels and negatively with TGF-β1 levels. IL-18 levels correlated positively with bilirubin, INR, ALT and AST levels, and negatively with albumin levels and erythrocyte count. TGF-β1 levels correlated positively with platelet count, leukocyte, and erythrocyte count, and negatively with bilirubin levels and prothrombin time. Moreover, significant correlations were found: between IL and 18 levels and portal, mesenteric superior, and splenic vein velocity, and between TGF-β1 levels and splenic vein diameter and spleen size. In a subgroup of patients, IL-18 levels significantly decreased after NSBB.

CONCLUSION

The observed imbalance of peripheral IL-18 and TGF-β1 levels indicates clinically significant PH associated with the presence of esophageal varices in cirrhosis. The correlation of IL-18 levels with liver failure indicators and decrease with NSBB suggest an important role of IL-18 in disease progression and its potential use as noninvasive test for PH assessment.

Extremely low-frequency electromagnetic fields accelerates wound healing modulating MMP-9 and inflammatory cytokines

OBJECTIVES

In our previous reports, we have demonstrated that extremely low-frequency electromagnetic fields (ELF-EMF) exposure enhances the proliferation of keratinocyte. The present study aimed to clarify effects of ELF-EMF on wound healing and molecular mechanisms involved, using a scratch in vitro model.

MATERIALS AND METHODS

The wounded monolayer cultures of human immortalized keratinocytes (HaCaT), at different ELF-EMF and Sham exposure times were monitored under an inverted microscope. The production and expression of IL-1β, TNF-α, IL-18 and IL-18BP were measured by enzyme-linked immunosorbent assay and quantitative real-time PCR. The activity and the expression of matrix metalloproteinases (MMP)-2/9 was evaluated by zymography and Western blot analysis, respectively. Signal transduction proteins expression (Akt and ERK) was measured by Western blot.

RESULTS

The results of wound healing in vitro assay revealed a significant reduction of cell-free area time-dependent in ELF-EMF-exposed cells compared to Sham condition. Gene expression and release of cytokines analysed were significantly increased in ELF-EMF-exposed cells. Our results further showed that ELF-EMF exposure induced the activity and expressions of MMP-9. Molecular data showed that effects of ELF-EMF might be mediated via Akt and ERK signal pathway, as demonstrated using their specific inhibitors.

CONCLUSIONS

Our results highlight ability of ELF-EMF to modulate inflammation mediators and keratinocyte proliferation/migration, playing an important role in wound repair. The ELF-EMF accelerates wound healing modulating expression of the MMP-9 via Akt/ERK pathway.

High serum concentration of interleukin-18 in diabetic patients with foot ulcers

BACKGROUND

It is well known that interleukin-18 (IL-18) plays a key role in the inflammatory process. However, there are limited data on the role IL-18 plays with diabetic foot ulcers, an acute and complex inflammatory situation. Therefore, we aimed to evaluate serum IL-18 levels of diabetic patients with foot ulcers.

METHODS

Twenty diabetic patients with acute foot ulcers, 21 diabetic patients without a history of foot ulcers, and 21 healthy volunteers were enrolled in our study. Circulating levels of IL-18, and other biochemical markers are parameters of inflammation and were measured in all three groups.

RESULTS

Diabetic patients both with and without foot ulcers had high IL-18 concentrations (P < 0.001 and P = 0.020, respectively) when compared with the nondiabetic volunteers. Those with foot ulcers had higher levels of IL-18 level (P < 0.001), high-sensitivity C-reactive protein (hsCRP) (P = 0.001), and erythrocyte sedimentation rate (ESR) (P < 0.001) than those without foot ulcers.

CONCLUSIONS

We found that serum IL-18 concentrations were elevated in diabetic patients with acute diabetic foot ulcers. However, these findings do not indicate whether the IL-18 elevation is a cause or a result of the diabetic foot ulceration. Further studies are needed to show the role of IL-18 in the course of these ulcers.

Macrophage activation syndrome and cytokine-directed therapies

Macrophage activation syndrome (MAS) is an episode of overwhelming inflammation that occurs most commonly in children with systemic juvenile idiopathic arthritis (SJIA). It is characterized by expansion and activation of T lymphocytes and hemophagocytic macrophages and bears great similarity to hemophagocytic lymphohistiocytosis (HLH). This disorder has substantial morbidity and mortality, and there is frequently a delay in recognition and initiation of treatment. Here, we will review what is known about the pathogenesis of MAS and, in particular, its similarities to HLH. The development of MAS is characterized by a cytokine storm, with the elaboration of numerous pro-inflammatory cytokines. We will examine the evidence for various cytokines in the initiation and pathogenesis of MAS and discuss how new biologic therapies may alter the risk of MAS. Finally, we will review current treatment options for MAS and examine how cytokine-directed therapy could serve as novel treatment modalities.

Roles of lactoferrin on skin wound healing1This article is part of Special Issue entitled Lactoferrin and has undergone the Journal's usual peer review process

Skin wound healing is a complex biological process that requires the regulation of different cell types, including immune cells, keratinocytes, fibroblasts, and endothelial cells. It consists of 5 stages: hemostasis, inflammation, granulation tissue formation, re-epithelialization, and wound remodeling. While inflammation is essential for successful wound healing, prolonged or excess inflammation can result in nonhealing chronic wounds. Lactoferrin, an iron-binding glycoprotein secreted from glandular epithelial cells into body fluids, promotes skin wound healing by enhancing the initial inflammatory phase. Lactoferrin also exhibits anti-inflammatory activity that neutralizes overabundant immune response. Accumulating evidence suggests that lactoferrin directly promotes both the formation of granulation tissue and re-epithelialization. Lactoferrin stimulates the proliferation and migration of fibroblasts and keratinocytes and enhances the synthesis of extracellular matrix components, such as collagen and hyaluronan. In an in vitro model of wound contraction, lactoferrin promoted fibroblast-mediated collagen gel contraction. These observations indicate that lactoferrin supports multiple biological processes involved in wound healing.

[Inflammatory bowel diseases and inflammasome]

Inflammatory bowel disease (IBD), the most important entities being ulcerative colitis and Crohn's disease, are chronic, relapsing and remitting inflammatory conditions that result from chronic dysregulation of the mucosal immune system in the intestinal tract. Although the precise pathogenesis of IBD is still incompletely understood, increased levels of proinflammatory cytokines, including interleukin (IL)-1b, IL-18 and tumor necrosis factor-a, are detected in active IBD and correlate with the severity of inflammation, indicating that these cytokines may play a key role in the development of IBD. Recently, the intracellular nucleotide-binding oligomerization domain-like receptor (NLR) family members, including NLRP1, NLRP3, NLRC4 and NLRP6, are emerging as important regulators of intestinal homeostasis. Together, one of those aforementioned molecules or the DNA sensor absent in melanoma 2 (AIM2), apoptosis-associated speck-like protein containing 'a caspase recruitment domain (CARD)' (ASC) and caspase-1 form a large (> 700 kDa) multi-protein complex called the inflammasome. Stimulation with specific microbial and endogenous molecules triggers inflammasome assembly and caspase-1 activation. Activated caspase-1 leads to the secretion of proinflammatory cytokines, including IL-1b and IL-18, and the promotion of pyroptosis, a form of phagocyte cell death induced by bacterial pathogens, in an inflamed tissue. Therefore, inflammasomes are assumed to mediate host defense against microbial pathogens and gut homeostasis, so that their dysregulation might contribute to IBD pathogenesis. This review focuses on recent advances of the role of NLRP3 inflammasome signaling in IBD pathogenesis. Improving knowledge of the inflammasome could provide insights into potential therapeutic targets for patients with IBD.

Inflammasomes in intestinal inflammation and cancer

Inflammasomes are multi-protein complexes that mediate activation of caspase-1, which promotes secretion of the proinflammatory cytokines interleukin-1β and interleukin-18 and pyroptosis, a form of phagocyte cell death induced by bacterial pathogens. Members of the Nod-like receptor family (including Nlrp1, Nlrp3, and Nlrc4), the DNA sensor Aim2, the adaptor apoptosis-associated speck-like protein (ASC), and pro-caspase-1 are important components of inflammasomes. Stimulation with specific microbial and endogenous molecules leads to inflammasome assembly and caspase-1 activation. Inflammasomes are believed to mediate host defense against microbial pathogens and tissue homeostasis within the intestine, and their dysregulation might contribute to inflammatory diseases and intestinal cancer. Improving our understanding of inflammasome signaling pathways could provide insights into the pathogenesis of many gastrointestinal disorders and the development of therapeutic targets and approaches to treat diseases such as inflammatory bowel diseases and gastrointestinal cancers.

Innate immune mechanisms of colitis and colitis-associated colorectal cancer

The innate immune system provides first-line defences in response to invading microorganisms and endogenous danger signals by triggering robust inflammatory and antimicrobial responses. However, innate immune sensing of commensal microorganisms in the intestinal tract does not lead to chronic intestinal inflammation in healthy individuals, reflecting the intricacy of the regulatory mechanisms that tame the inflammatory response in the gut. Recent findings suggest that innate immune responses to commensal microorganisms, although once considered to be harmful, are necessary for intestinal homeostasis and immune tolerance. This Review discusses recent findings that identify a crucial role for innate immune effector molecules in protection against colitis and colitis-associated colorectal cancer and the therapeutic implications that ensue.

MyD88-mediated signaling prevents development of adenocarcinomas of the colon: role of interleukin 18

Signaling through the adaptor protein myeloid differentiation factor 88 (MyD88) promotes carcinogenesis in several cancer models. In contrast, MyD88 signaling has a protective role in the development of azoxymethane (AOM)/dextran sodium sulfate (DSS) colitis-associated cancer (CAC). The inability of Myd88(-/-) mice to heal ulcers generated upon injury creates an altered inflammatory environment that induces early alterations in expression of genes encoding proinflammatory factors, as well as pathways regulating cell proliferation, apoptosis, and DNA repair, resulting in a dramatic increase in adenoma formation and progression to infiltrating adenocarcinomas with frequent clonal mutations in the beta-catenin gene. Others have reported that toll-like receptor (Tlr) 4-deficient mice have a similar susceptibility to colitis to Myd88-deficient mice but, unlike the latter, are resistant to CAC. We have observed that mice deficient for Tlr2 or Il1r do not show a differential susceptibility to colitis or CAC. However, upon AOM/DSS treatment Il18(-/-) and Il18r1(-/-) mice were more susceptible to colitis and polyp formation than wild-type mice, suggesting that the phenotype of Myd88(-/-) mice is, in part, a result of their inability to signal through the IL-18 receptor. This study revealed a previously unknown level of complexity surrounding MyD88 activities downstream of different receptors that impact tissue homeostasis and carcinogenesis.

Enhanced expression of interleukin-18 in serum and pancreas of patients with chronic pancreatitis

AIM: To investigate interleukin-18 (IL-18) in patients with chronic panreatitis (CP).

METHODS: We studied 29 patients with CP and 30 healthy controls. Peripheral blood mononuclear cells (PBMC) were isolated and incubated with 50 mmol/L ethanol, lipopolysaccharide (LPS) (doses 25 g/L, 250 g/L, 2500 g/L) and both agents for 24 h. Levels of IL-18 in the supernatants, and levels of IL-18, IL-12, interferon (IFN)-γ and soluble CD14 in the serum were analysed by ELISA technique. Expression of IL-18 in PBMC was investigated by reverse-transcription (RT)-PCR. IL-18 protein levels in CP tissue and in normal pancreas were studied by ELISA technique. IL-18 levels in PBMC and pancreatic tissue were determined by Westernblot. Immunohistochemistry for pancreatic IL-18 expression was performed.

RESULTS: In patients, IL-18 serum levels were significantly enhanced by 76% (mean: 289.9 ± 167.7 ng/L) compared with controls (mean: 165.2 ± 43.6 ng/L; P < 0.0005). IL-12 levels were enhanced by 25% in patients (18.3 ± 7.3 ng/L) compared with controls (14.7 ± 6.8 ng/L, P = 0.0576) although not reaching the statistical significance. IFN-γ and soluble CD14 levels were not increased. In vitro, LPS stimulated significantly and dose-dependently IL-18 secretion from PBMC. Incubation with ethanol reduced LPS-stimulated IL-18 secretion by about 50%. The mRNA expression of IL-18 in PBMC and the response of PBMC to ethanol and LPS was similar in CP patients and controls. In PBMC, no significant differences in IL-18 protein levels were detected between patients and controls. IL-18 protein levels were increased in CP tissues compared to normal pancreatic tissues. IL-18 was expressed by pancreatic acinar cells and by infiltrating inflammatory cells within the pancreas.

CONCLUSION: IL-18 originates from the chronically inflammed pancreas and appears to be involved in the fibrotic destruction of the organ.

The suppressor of cytokine signaling-3 is upregulated in impaired skin repair: implications for keratinocyte proliferation

In this study, we determined regulation and function of the suppressor of cytokine signaling (SOCS)-3 in acute and impaired murine skin repair. Upon skin injury, SOCS-3 was induced and expressed during the inflammatory phase of repair. SOCS-3 protein expression was localized in a subset of non-proliferating keratinocytes within the developing wound margin epithelia. Growth factors (EGF, transforming growth factor-alpha), nitric oxide (NO), and pro-inflammatory cytokines were inducers of SOCS-3 mRNA and protein expression in cultured human (HaCaT) and primary murine keratinocytes. Stable overexpression of SOCS-3 in HaCaT keratinocytes interfered with cytokine-induced signal transducers and activators of transcription-3 phosphorylation and inhibited serum-stimulated proliferation of the cells. Moreover, overexpression of SOCS-3 led to final differentiation of keratinocytes, which was comparable to the Ca(2+)-induced differentiation process in the cells. Finally, we determined SOCS-3 expression in two models of impaired skin repair: NO-deficient and diabetic wound healing. In line with observations from normal repair and SOCS-3 overexpression experiments, reduced keratinocyte proliferation within atrophied neo-epithelia in both models of impaired healing was associated with a marked increase in SOCS-3-expressing wound keratinocytes. In summary, this study suggests a potential novel function of SOCS-3 in regulating keratinocyte proliferation and differentiation in vitro and during skin repair in vivo.

Cytokine gene expression in a murine wound healing model

Inflammatory mediators have been shown to play a major role in the complex series of co-ordinated events that occur in wound healing responses following injury. However, to date most of the studies carried out have addressed the expression, interactions and role of only one or two cytokines that are thought to be involved in wound repair. This study has evaluated, in murine skin samples taken at 0, 3, 12, 18, 24, 48, 72, 120 and 168 h post-wounding, the expression of a wide range of cytokines with potential for a role in wound repair. Various techniques (reverse transcription polymerase chain reaction (RT-PCR), bioassays and ELISA) were used to evaluate cytokine expression in these samples at both the mRNA and protein expressions level. Semi-quantitative analysis using RT-PCR revealed that IL-1beta, IP10, bFGF, and TGFbeta3 up-regulated in wounded samples, compared to non-injured control samples. Expression of mRNA for other cytokines and inflammatory mediators, IL-1alpha, IL-6, TGFbeta1, TNFalpha, MIP-1alpha, MIP-2, JE, KC, PDGFalpha and PDGFbeta, were found to be down-regulated in injured adult murine samples compared to normal control samples. Interestingly we failed to find evidence of mRNA expression for the cytokines IL-2, IL-4, IL-12, GM-CSF, IFNgamma and RANTES, in both non-injured and injured samples. These observations were also generally supported by the results obtained using bioassays for IL-1 and IL-6 and ELISA for IL-1alpha, IL-1beta, IL-6, TNFalpha, and IFNgamma.

Increased interleukin-18 content and angiogenic activity of sera from diabetic (Type 2) patients with background retinopathy

Hyperglycaemia increases inflammatory cytokine concentration in the blood. Elevated levels of interleukin-18 (IL-18), a cytokine belonging to the interleukin-1 (IL-1) family, were recently reported in patients with Type 2 diabetes mellitus (DM2) and nephropathy. The aim of the present work was an examination of IL-18 concentration in the sera of elderly DM2 patients with nonproliferative retinopathy and age-matched control people and an estimation whether this cytokine plays pro- or anti-angiogenic role in in vivo angiogenic activity of their sera in mice cutaneous angiogenesis test. Recombinant human IL-18 injected intradermally to murine skin induced significant neovascular reaction. DM2 patients sera contained higher concentration of IL-18 and induced stronger neovascular reaction in mice skin than did the sera of corresponding control people. Sera from both groups of people after neutralization with antihuman IL-18 antibodies lost substantial part of their angiogenic activity.

Vital role of the itch-scratch response in development of spontaneous dermatitis in NC/Nga mice

BACKGROUND

The itch sensation and the resultant response, scratching, are important symptoms of atopic dermatitis (AD) and have a significant impact on the quality of life of affected patients. However, the influence of the itch-scratch response on the pathology of AD has not been precisely elucidated.

OBJECTIVES

To investigate the role of scratching behaviour in the development of spontaneous dermatitis using conventionally raised NC/Nga mice (Conv-NC mice), which are known to be an animal model for human AD.

METHODS

Capsaicin-sensitive sensory nerves of the mice were ablated by neonatal capsaicin treatment (Cap-NC mice), and the development of spontaneous dermatitis in the Cap-NC mice was compared chronologically with that in Conv-NC mice.

RESULTS

Scratching behaviour was almost completely prevented in Cap-NC mice raised for 84 days under conventional conditions, and the development of dermatitis and elevation of the serum IgE level were significantly suppressed. Histological analysis revealed that the numbers of infiltrating eosinophils and mast cells in the lesional skin of Cap-NC mice were lower than those in Conv-NC mice. Immunological studies showed that the capability of spleen T cells to produce both T-helper (Th) 1 (interferon-gamma) and Th2 [interleukin (IL)-5 and IL-13] cytokines was diminished in Cap-NC mice. Furthermore, serum levels of IL-18 were approximately twice higher in Conv-NC mice than in Cap-NC mice.

CONCLUSIONS

These observations suggest that scratching behaviour contributes to the development of dermatitis by enhancing various immunological responses in the murine AD model, implying that prevention of the itch sensation and/or itch-associated scratching behaviour is an effective treatment for AD.

Administration of exogenous interleukin-18 and interleukin-12 prevents the induction of oral tolerance

Interleukin-18 (IL-18), a pro-inflammatory member of the IL-1 family, has been associated with autoimmunity and allergic disease. This type of pathology is thought to be the result of a defect in immunological tolerance and is often observed in inflammatory disorders of the gut such as coeliac disease, Crohn's disease and ulcerative colitis. IL-18 has been implicated in a number of mucosal immune disorders, where it synergizes with IL-12 to induce the production of interferon-gamma (IFN-gamma). We have therefore investigated the effects of IL-18 and IL-12 administration on the induction of oral tolerance to ovalbumin. The suppression of specific Ig G2a production, delayed-type hypersensitivity responses and IFN-gamma production by antigen-specific T cells were all abrogated by the presence of exogenous IL-12 and IL-18, suggesting that oral tolerance was broken. The expression of the co-stimulatory molecule CD80 on dendritic cells was also shown to be increased by this combination of cytokines. As dendritic cells are thought to be of major importance in the induction of tolerance, this suggests a mechanism by which tolerance to mucosal antigens may be broken in vivo.

Interleukin-18 expression after focal ischemia of the rat brain: association with the late-stage inflammatory response

Interleukin-18, previously designated interferon gamma-inducing factor, is a proinflammatory cytokine structurally related to interleukin-1beta and is therefore considered a member of the growing family of interleukin-1-like cytokines. Both interleukin-18 and -1beta are synthesized as inactive precursors that necessitate cleavage by caspase-1 for functional activity. In this study, the authors analyzed the expression pattern of interleukin-18, -1beta, and caspase-1 in focal brain ischemia induced in rats either by permanent middle cerebral artery occlusion or by photothrombosis of cortical microvessels. Using reverse transcriptase-polymerase chain reaction, they found a delayed increase of interleukin-18 mRNA starting at 48 hours and reaching its peak between 7 and 14 days after ischemia. In contrast, interleukin-1beta mRNA peaked within 16 hours and was downregulated thereafter. The time course of caspase-1 mRNA expression paralleled that of interleukin-18, but not of interleukin-1beta mRNA. Immunocytochemically, interleukin-18 expression was localized to ED1-positive phagocytic microglia/macrophages infiltrating the necrotic lesion between 3 and 6 days after ischemia. In contrast, interleukin-1beta immunoreactivity was expressed by ramified microglia in the infarct border zone and remote ipsilateral cortex during the first 16 hours postlesion. Induction of interleukin-18 was not accompanied by detectable expression of interferon-gamma mRNA. Their data show spatial and temporal diversity in interleukin-1 and -18 cytokine family expression in brain ischemia, and suggest a role of the interleukin-18/caspase-1 pathway in late-stage inflammatory responses to focal brain ischemia.