The enhanced IL-18 production by UVB irradiation requires ROI and AP-1 signaling in human keratinocyte cell line (HaCaT)

Interleukin-18 and IL-18BP in inflammatory dermatological diseases

Interleukin (IL)-18, an interferon-γ inducer, belongs to the IL-1 family of pleiotropic pro-inflammatory factors, and IL-18 binding protein (IL-18BP) is a native antagonist of IL-18 in vivo, regulating its activity. Moreover, IL-18 exerts an influential function in host innate and adaptive immunity, and IL-18BP has elevated levels of interferon-γ in diverse cells, suggesting that IL-18BP is a negative feedback inhibitor of IL-18-mediated immunity. Similar to IL-1β, the IL-18 cytokine is produced as an indolent precursor that requires further processing into an active cytokine by caspase-1 and mediating downstream signaling pathways through MyD88. IL-18 has been implicated to play a role in psoriasis, atopic dermatitis, rosacea, and bullous pemphigoid in human inflammatory skin diseases. Currently, IL-18BP is less explored in treating inflammatory skin diseases, while IL-18BP is being tested in clinical trials for other diseases. Thereby, IL-18BP is a prospective therapeutic target.

Interleukin-18 cytokine in immunity, inflammation, and autoimmunity: Biological role in induction, regulation, and treatment

Interleukin-18 (IL-18) is a potent pro-inflammatory cytokine involved in host defense against infections and regulates the innate and acquired immune response. IL-18 is produced by both hematopoietic and non-hematopoietic cells, including monocytes, macrophages, keratinocytes and mesenchymal cell. IL-18 could potentially induce inflammatory and cytotoxic immune cell activities leading to autoimmunity. Its elevated levels have been reported in the blood of patients with some immune-related diseases, including rheumatoid arthritis, systemic lupus erythematosus, type I diabetes mellitus, atopic dermatitis, psoriasis, and inflammatory bowel disease. In the present review, we aimed to summarize the biological properties of IL-18 and its pathological role in different autoimmune diseases. We also reported some monoclonal antibodies and drugs targeting IL-18. Most of these monoclonal antibodies and drugs have only produced partial effectiveness or complete ineffectiveness in vitro, in vivo and human studies. The ineffectiveness of these drugs targeting IL-18 may be largely due to the loophole caused by the involvement of other cytokines and proteins in the signaling pathway of many inflammatory diseases besides the involvement of IL-18. Combination drug therapies, that focus on IL-18 inhibition, in addition to other cytokines, are highly recommended to be considered as an important area of research that needs to be explored.

Protective effect of isopsoralen on UVB-induced injury in HaCaT cells via the ER and p38MAPK signaling pathways

This study investigated the protective effect of isopsoralen on UVB-induced damage in HaCaT cells and its molecular mechanism. The cytotoxicity of isopsoralen and its effects on the viability of HaCaT cells were examined using the MTT assay. The effects of UVB irradiation and isopsoralen on the intracellular glutathione (GSH-PX), superoxide dismutase (SOD), malondialdehyde (MDA), and reactive oxygen species (ROS) content were examined using commercially available assay kits. Further, the effects of UVB irradiation and isopsoralen on the levels of the inflammatory cytokines TNF-α, IL-6, and IL-1α were examined using enzyme-linked immunosorbent assay. Finally, we examined the effect of adding the estrogen receptor (ER) antagonist ICI182780,780 and the p38MAPK antagonist SB203580 on the changes in inflammatory cytokines induced by isopsoralen treatment and UVB irradiation. Isopsoralen pretreatment markedly inhibited UVB-induced reduction in the viability and proliferation of HaCaT cells. Isopsoralen also reduced UVB-induced increase in the expression of the inflammatory cytokines and the level of free radicals (ROS and MDA), and reversed the UVB-induced suppression of antioxidant activity. Additionally, inhibition of ER and p38MAPK via the addition of their respective antagonists reversed the observed anti-inflammatory effects of Isopsoralen. Isopsoralen can efficiently provide protection against UVB-induced damage in HaCaT cells brought about via oxidation and inflammatory reactions, and the underlying mechanisms involve the ER and p38MAPK pathways. Therefore, Isopsoralen could be used in therapeutic solutions for UVB-induced skin conditions. PRACTICAL APPLICATIONS: Isopsoralen shows antioxidant and anti-inflammatory effects. As natural, healthy, and effective additives, isopsoralen has been widely used in cosmetics and botanical medicine products. The results of this study reveal the molecular mechanisms underlying isopsoralen effects, showing that isopsoralen reverses the effects of UVB irradiation regulating ER and p38MAPK signaling pathways. Consequently, isopsoralen regulates the expression of ER and p38MAPK signaling pathways, thereby reducing the activation of antioxidant and anti-inflammatory activity. These findings suggest that isopsoralen can be used as the base ingredient for antiphotoaging cosmetics and botanical medicine products. This study provides both theoretical and experimental background for isopsoralen deep processing and utilization.

Keratinocyte death by ferroptosis initiates skin inflammation after UVB exposure

The ultraviolet B radiation (UVB) causes skin inflammation, which contributes to the causality and the exacerbation of a number of cutaneous diseases. However, the mechanism of UVB-driven inflammation in the skin remains poorly understood. We show that ferroptosis, a non-apoptotic programmed cell death pathway that is promoted by an excessive phospholipid peroxidation, is activated in the epidermal keratinocytes after their exposure to UVB. The susceptibility of the keratinocytes to UVB-induced ferroptosis depends on the extent of pro-ferroptosis death signal generation and the dysregulation of the glutathione system. Inhibition of ferroptosis prevents the release of HMGB1 from the human epidermal keratinocytes, and blocks necroinflammation in the UVB-irradiated mouse skin. We show that while apoptosis and pyroptosis are also detectable in the keratinocytes after UVB exposure, ferroptosis plays a significant role in initiating UVB-induced inflammation in the skin. Our results have important implications for the prevention and the treatment of a broad range of skin diseases which are fostered by UVB-induced inflammation.

A short-term, hydroponic-culture of ginseng results in a significant increase in the anti-oxidative activity and bioactive components

Panax ginseng CA Meyer has a variety of biological effects, including antioxidant and antidiabetic activities. Ginseng requires long-term cultivation, but this can be shortened using hydroponic systems to facilitate the commercial development of ginseng as a functional food. However, the characteristics of short-term-cultured (< 30 days) hydroponic ginseng (sHCG) are unclear. We investigated the characteristics of 21-day-cultured sHCG compared 5-year-old normally cultured ginseng. The free radical-scavenging activity and total ginsenoside and phenolic contents were significantly higher in sHCG than in normally cultured ginseng. Fifteen ginsenosides were detected in sHCG, and the concentrations of most were higher in shoots than roots. These findings suggest that 21-day-cultured sHCG, due to its enhanced antioxidant activity and higher concentrations of total phenolics and ginsenosides (including Rd and Re), has potential as a functional food.

Secreted immunoregulatory proteins in the skin

The skin, thought initially to protect the body passively from pathogenic organisms and other environmental insults, is now recognised additionally as a sophisticated immune organ that actively regulates local immunity. Studies linking local innate and adaptive immunity to skin health and disease have revealed a complex network of cell communication and cytokine signalling. Here, we review the last 10 years of literature on this topic, and its relevance to skin immunity.

The pathogenic role of interleukin-22 and its receptor during UVB-induced skin inflammation

Recent studies show that IL-22, a cytokine produced by activated CD4+ T cells and NK cells, plays a pathogenic role in acute and chronic skin diseases. While IL-22 is produced by immune cells, the expression of IL-22Rα, the functional subunit of IL-22R, is mostly restricted to non-hematopoietic cells in organs such as the skin and pancreas. Although it is well known that ultraviolet B (UVB) radiation induces skin inflammation, there have been no reports regarding the effect of UVB on the expression of IL-22Rα. This study investigated IL-22Rα expression and IL-22-mediated proliferation and pro-inflammatory cytokine production by UVB-irradiated keratinocytes. IL-22Rα was increased in HaCaT and primary human keratinocytes after UVB irradiation through the translocation of IL-22Rα from the cytosol to the membrane. This increase in the expression of IL-22Rα was mediated by the PI3K/Akt pathway. Moreover, the suppression of keratinocyte proliferation by UVB irradiation was inhibited by treatment with IL-22. At the same time, IL-22 increased the production of IL-1α, IL-6, and IL-18 in UVB-irradiated HaCaT cells and primary human keratinocytes. Finally, IL-22Rα expression was increased in UVB-irradiated human and mouse skin by immunohistochemistry. The increased expression of IL-22Rα therefore promotes keratinocyte proliferation and pro-inflammatory cytokine production during UVB-induced skin inflammation, suggesting that UVB facilitates skin inflammation by increasing the responsiveness of keratinocytes to IL-22. This study provides a new insight into UVB-induced skin inflammation and the regulation of related inflammatory skin diseases.

Cross-talk between interferon-gamma and interleukin-18 in melanogenesis

Skin is the largest organ in our body and strategically placed to provide a metabolically active biological barrier against a range of noxious stressors. A lot of inflammatory cytokines, which are increased after ultraviolet (UV) irradiation produced by keratinocytes or other immunocytes, are closely related to pigmentary changes, including interleukin-18 (IL-18) and interferon-γ (IFN-γ). In this study, the effect of cross-talk between IL-18 and IFN-γ on melanogenesis was investigated. Treatment with IL-18 resulted in a dose-dependent increase of melanogenesis, while IFN-γ made an opposite effect. This influence of IL-18 and IFN-γ was mediated by regulations of microphthalmia-associated transcription factor (MITF) and its downstream enzymatic cascade expressions. Furthermore, IFN-γ inhibited basal and IL-18-induced melanogenesis. IFN-γ increased signal transducer and activator of transcription-1 (STAT-1) phosphorylation to play its position in regulating melanin pigmentation, and its inhibitory effect could be prevented by Janus Kinase 1 (JAK 1) inhibitor. IFN-γ could inhibit melanogenesis by decreasing melanocyte dendrite formation. In addition, IFN-γ inhibited the expressions of Rab Pases to suppress the mature and transport of melanosomes. IL-18 could rapidly induce Akt and PTEN phosphorylation and p65 expression in B16F10 cells. When treatment with IL-18 and IFN-γ together, the phosphorylation level of Protein Kinase B (Akt) and phosphatase and tensin homolog deleted on chromosome ten (PTEN) and expression of p65 NF-κB were inhibited, compared with treated with IL-18 only. Our studies indicated that IFN-γ could directly induce B16F10 cells apoptosis in vitro. Furthermore, we demonstrated that IFN-γ markedly up-regulated IL-18 binding protein (BP) production in normal human foreskin-derived epidermal keratinocytes in dose-dependent manner. UVB irradiation induced protease-activated receptor-2 (PAR-2) expression in NHEK, IFN-γ could inhibit this enhancement in a dose-dependent manner. These data suggest that IFN-γ plays a role in regulating inflammation- or UV-induced pigmentary changes, in direct/indirect manner.

The Role of Proinflammatory Cytokine Interleukin-18 in Radiation Injury

Massive radiation-induced inflammatory factors released from injured cells may cause innate and acquired immune reactions that can further result in stress response signal activity-induced local and systemic damage. IL-1 family members IL-1β, IL-18, and IL-33 play key roles in inflammatory and immune responses and have been recognized to have significant influences on the pathogenesis of diseases. IL-1β, IL-18, and IL-33 share similarities of cytokine biology, but differences exist in signaling pathways. A key component of the inflammatory reaction is the inflammasome, which is a caspase-1-containing multiprotein oligomer. Pathological stimuli such as radiation can induce inflammasome and caspase-1 activation, and subsequently cause maturation (activation) of pro-forms of IL-1 and IL-18 upon caspase-1 cleavage. This caspase-1 dependent and IL-1 and IL-18 associated cell damage is defined as pyroptosis. Activated IL-1 and IL-18 as proinflammatory cytokines drive pathology at different immune and inflammatory disorders through Toll-like receptor (TLR) signaling. While the mechanisms of IL-1β-induced pathophysiology of diseases have been well studied, IL-18 has received less attention. The author recently reported that gamma radiation highly increased IL-1β, IL-18 and IL-33 expression in mouse thymus, spleen and/or bone marrow cells; also circulating IL-18 can be used as a radiation biomarker to track radiation injury in mice, minipigs, and nonhuman primates. This mini-review focuses on the role of IL-18 in response to gamma radiation-induced injury.

IL-18 and Cutaneous Inflammatory Diseases

Interleukin (IL)-18, an IL-1 family cytokine, is a pleiotropic immune regulator. IL-18 plays a strong proinflammatory role by inducing interferon (IFN)-γ. Previous studies have implicated IL-18 in the pathogenesis of various diseases. However, it is not well understood biologic activities of IL-18 in the diverse skin diseases. Here, we have reviewed the expression and function of IL-18 in skin diseases including inflammatory diseases. This article provides an evidence-based understanding of the role of IL-18 in skin diseases and its relationship with disease activities.

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.

Interleukin-18 augments growth ability of primary human melanocytes by PTEN inactivation through the AKT/NF-κB pathway

Normal human skin relies on melanocytes to provide photoprotection and thermoregulation by producing melanin. The growth and behavior of melanocytes are controlled by many factors. Interleukin-18 (IL-18) is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the regulative roles of IL-18 in melanogenesis and growth of melanocytes have not been explored. The present study was conducted to investigate the effects of IL-18 on melanocytes and elucidate the underlying mechanisms. We proved that IL-18 increased the tyrosinase activity and melanin content in normal human foreskin-derived epidermal melanocytes (NHEM). Treatment with IL-18 (20 ng/ml) enhanced the expression of c-Kit, microphtalmia-associated transcription factor (MITF) and its downstream tyrosinase-related protein 1 (TRP-1), and TRP-2. In addition, IL-18 induced NHEM migration at concentration of 20 ng/ml. These results indicated a promotive action of IL-18 on melanogenesis in NHEM. Our data revealed that IL-18 stimulated ERK1/2 and NF-κB activation, improved p-Akt, p70 S6K and anti-apoptotic Bcl-2 levels, and deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in NHEM. Besides, IL-18 increased level of PTEN phosphorylation to protect NHEM from damage induced by H(2)O(2). These results in vitro showed the accommodation of IL-18 in melanocytes growth. Therefore, we suggested an important regulating action of IL-18 to melanogenesis and cell growth ability of skin melanocytes.

The anti-inflammatory effect of alloferon on UVB-induced skin inflammation through the down-regulation of pro-inflammatory cytokines

UVB irradiation can induce biological changes in the skin, modulate immune responses and activate inflammatory reactions leading to skin damage. Alloferon, which is isolated from the blood of an experimentally infected insect, the blow fly Calliphora vicina, is known for its anti-viral and anti-tumor activities in mice model. However, the effect of alloferon against UVB irradiation and its specific mechanism are still unknown. In this study, we investigated the effect of alloferon on UVB-induced cutaneous inflammation in a human keratinocyte cell line, HaCaT. RPA and ELISA data showed that alloferon decreased the production of UVB-induced pro-inflammatory cytokines, such as IL-1α, IL-1β, IL-6 and IL-18, both on the mRNA and protein level. Western blot analysis was done to determine if alloferon regulates the MAPK signaling pathway since the MAPK signaling pathway is activated by numerous inflammatory mediators and environmental stresses including UVB irradiation. Alloferon inhibited the activation of p38 mitogen-activated protein kinase (MAPK) induced by UVB irradiation. Furthermore, the topical application of alloferon on the UVB exposed skin of hairless mice showed that alloferon treatment significantly inhibited an increase in epithelial thickness in chronic UVB-irradiated mouse skin. These findings suggest that alloferon has significant anti-inflammatory effects not only on UVB-induced inflammation in the human keratinocyte cell line, HaCaT, but also on mouse skin.

Inflammasome activation of IL-1 family mediators in response to cutaneous photodamage

Although keratinocytes are relatively resistant to ultraviolet radiation (UVR) induced damage, repeated UVR exposure result in accumulated DNA mutations that can lead to epidermal malignancies. Keratinocytes play a central role in elaborating innate responses that lead to inflammation and influence the generation of adaptive immune responses in skin. Apart from the minor cellular constituents of the epidermis, specifically Langerhans cells and melanocytes, keratinocytes are the major source of cytokines. UVR exposure stimulates keratinocytes to secrete abundant pro-inflammatory IL-1-family proteins, IL-1α, IL-1β, IL-18, and IL-33. Normal skin contains only low levels of inactive precursor forms of IL-1β and IL-18, which require caspase 1-mediated proteolysis for their maturation and secretion. However, caspase-1 activation is not constitutive, but dependents on the UV-induced formation of an active inflammasome complex. IL-1 family cytokines can induce a secondary cascade of mediators and cytokines from keratinocytes and other cells resulting in wide range of innate processes including infiltration of inflammatory leukocytes, induction of immunosuppression, DNA repair or apoptosis. Thus, the ability of keratinocytes to produce a wide repertoire of proinflammatory cytokines can influence the immune response locally as well as systematically, and alter the host response to photodamaged cells. We will highlight differential roles played by each IL-1 family molecule generated by UV-damaged keratinocytes, and reveal their complementary influences in modulating acute inflammatory and immunological events that follow cutaneous UV exposure.

Naringin attenuates EGF-induced MUC5AC secretion in A549 cells by suppressing the cooperative activities of MAPKs-AP-1 and IKKs-IκB-NF-κB signaling pathways

Naringenin, the aglycone of naringin, has been reported to attenuate MUC5AC secretion by inhibiting activity of nuclear factor kappa B (NF-κB) via EGFR-PI3K-Akt/ERK MAPKinase signaling pathways. However, previous studies demonstrated that the MUC5AC promoter was located in two different regions: an activator protein-1 (AP-1) binding site and a NF-κB binding site. The current study comprehensively determined the involvement of MAPKs/AP-1 and IKKs/IκB/NF-κB in epidermal growth factor (EGF)-induced A549 cells, and sought to ascertain the signaling pathways of naringin imparted in suppression of EGF-induced MUC5AC secretion. The results showed that naringin of 100 μM not only significantly decreased EGF-induced overexpressions of both MUC5AC mucin and mRNA in A549 cells, but also suppressed the phosphorylation of EGF receptor, p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK1/2), and c-Jun N-terminal kinase (JNK), as well as nucleus NF-κB p65 and AP-1. Moreover, any of three MAPKs inhibitors (PD98059, SB203580, and SP600125) significantly inhibited EGF-induced MUC5AC secretion. And as compared to MG132, the inhibitor κB (IκB) phosphorylation inhibitor of SN50 was more effective in reducing EGF-induced MUC5AC secretion because of suppression of nucleus AP-1. Meanwhile, as compared to naringin, both SP600125 and azithromycin were less effective in suppressing EGF-induced secretion of MUC5AC because of the unchanged nucleus NF-κB p65. These results indicated that naringin attenuates EGF-induced MUC5AC secretion in A549 cells by suppressing the cooperative activities of MAPKs/AP-1 and IKKs/IκB/NF-κB signaling pathways.

Effect of IL-18 on expansion of gammadelta T cells stimulated by zoledronate and IL-2

Zoledronate (Zol) has recently been shown to expand gammadelta T cells that play important roles in host defenses against infection and tumors. In this study, we examined effects of interleukin-18 (IL-18) on expansion of gammadelta T cells in human peripheral blood mononuclear cells (PBMCs) stimulated by Zol and IL-2. The expansion of gammadelta T cells stimulated by Zol and IL-2 was strongly promoted by exogenous IL-18, and to the contrary, inhibited by neutralizing anti-IL-18 receptor antibody. The gammadelta T cells that expanded in the presence of Zol, IL-2, and IL-18 exhibited the phenotype of effector memory cells characterized by CD44 (+), CD27 (-), and CD45RA (-). In addition, they expressed NKG2D, perforin, CD94, CD25, and CD122, and 15% to 40% of them were positive for CD56. Incubation of gammadelta T cells in the presence with IL-18 produced GM-CSF, IFN-gamma, and TNF-alpha at much higher levels than those incubated without IL-18. They showed strong cytotoxicity against tumor cells including mesothelioma cells and inhibited growth of xenograft of mesothelioma in mice. These observations indicate that IL-18 can efficiently promote expansion of gammadelta T cells with potent antitumor activity.

Low-energy visible light irradiation modulates immune responses induced by epicutaneous sensitization with protein antigen

Epicutaneous sensitization has been an important route for protein allergen sensitization in atopic disease. Although the skin is irradiated by sunlight daily, the influence of visible light on epicutaneous sensitization has not been explored. In this study, by using a well-established murine protein-patch model, we show that low-energy visible light (LEVL) irradiation could differentially modulate the predominant Th2 immune response induced by epicutaneous sensitization with protein antigen. When the induced Th2 response was strong, as usually observed in BALB/c mice, LEVL irradiation suppressed the response. In contrast, LEVL irradiation enhanced the weaker Th2 response in C57BL/6 mice. Increased IL-18 and decreased TGF-beta expression in draining lymph nodes after LEVL irradiation was observed in BALB/c mice, but not in C57BL/6 mice. LEVL irradiation also enhanced IL-18 expression in skin and reduced the downregulation of CD24 expression on epidermal Langerhans cells in draining lymph nodes of BALB/c mice. Collectively, these results provide evidence for immunomodulatory effects of LEVL irradiation and will help us develop a useful strategy for prevention of allergen sensitization.

Clinical and experimental approaches to the pathophysiology of interleukin-18 in cancer progression

Interleukin-18 (IL-18, interferon [IFN]-gamma-inducing factor) is a proinflammatory cytokine converted to a biologically active molecule by interleukin (IL)-1beta converting enzyme (caspase-1). A wide range of normal and cancer cell types can produce and respond to IL-18 through a specific receptor (IL-18R) belonging to the toll-like receptor family. The activity of IL-18 is regulated by IL-18-binding protein (IL-18bp), a secreted protein possessing the ability to neutralize IL-18 and whose blood level is affected by renal function and is induced by IFNgamma. IL-18 plays a central role in inflammation and immune response, contributing to the pathogenesis and pathophysiology of infectious and inflammatory diseases. Because immune-stimulating effects of IL-18 have antineoplastic properties, IL-18 has been proposed as a novel adjuvant therapy against cancer. However, IL-18 increases in the blood of the majority of cancer patients and has been associated with disease progression and, in some cancer types, with metastatic recurrence risk and poor clinical outcome and survival. Under experimental conditions, cancer cells can also escape immune recognition, increase their adherence to the microvascular wall and even induce production of angiogenic and tumor growth-stimulating factors via IL-18-dependent mechanism. This is particularly visible in melanoma cells. Thus, the role of IL-18 in cancer progression and metastasis remains controversial. This review examines the clinical correlations and biological effects of IL-18 during cancer development and highlights recent experimental insights into prometastatic and proangiogenic effects of IL-18 and the use of IL-18bp against cancer progression.

UVB-induced IL-18 production in human keratinocyte cell line NCTC 2544 through NF-κB activation

In the present study, we investigated the implication of NF-kappaB in the production of pro-inflammatory cytokine IL-18 by human keratinocytes stimulated by UVB. We demonstrated that NCTC 2544 keratinocyte cell line irradiated by UVB enhanced the IL-18 mRNA and protein secretion under its bioactive form. Overexpression of IL-18 by UVB irradiation was accompanied by NF-kappaB transcription factor activation using specific IL-18 gene sequence corresponding to NF-kappaB DNA binding site. The relationship between these transcription factors and IL-18 expression was confirmed using curcumin and PDTC, two inhibitors of NF-kappaB. Our results show that UVB and curcumin or PDTC co-treatment led to a down-regulation of IL-18 expression associated with an inhibition of NF-kappaB DNA binding. Hence, our results demonstrated that this transcription factor is implicated in biologically active IL-18 production by human keratinocytes irradiated by UVB.

IL-18 enhances the migration ability of murine melanoma cells through the generation of ROI and the MAPK pathway

Interleukin-18 (IL-18) has multiple effects on various cells that are involved in immune escape of murine melanoma cells and in the inflammatory responses. This study investigated the effect of IL-18 on the ability of murine melanoma cells to migrate by using B16F10 cells and the IL-18 antisense transfectants of B16F10 cells (the B16F10/IL-18 antisense transfectant). The B16F10 cells were more able to migrate than were the B16F10/IL-18 antisense transfectants. An exogenous IL-18 treatment improved the ability of the B16F10/IL-18 antisense transfectant cells to migrate, indicating that IL-18 enhanced the migration ability of melanoma cells. To determine the signaling mechanisms involved in IL-18-enhanced migration, we measured the ROI levels. It was found that the ROI levels were increased by IL-18, and an antioxidant, N-acetyl-l-cystein (NAC), blocked the effect of IL-18 on migration, suggesting the involvement of ROI in the signal transduction of IL-18-enhanced cell migration. IL-18-enhanced cell migration was also reduced by PD98059. In addition, the level of ERK1/2 phosphorylation was markedly increased by treating with exogenous IL-18 at 20 min. These results suggest that IL-18 enhances the ability of melanoma cells to migrate via the generation of ROI and the MAPK pathway.

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.

UVB-induced interleukin-18 production is downregulated by tannic acids in human HaCaT keratinocytes

Tannic acids (TAs) are believed to be the key active components in plants, and are believed to be responsible for their anti-inflammatory, anti-viral effects and chemoprevention of cancer. However, the molecular mechanisms for the action of TA are unclear. This study examined the effects of TA on cutaneous inflammation with a human keratinocyte cell line (HaCaT). Interleukin-18 (IL-18) has multiple effects upon various cells involved in inflammatory response. In this study, the IL-18 mRNA expression and protein levels were reduced by a TA pretreatment. UV radiation can trigger the induction of the p38 mitogen-activated protein kinase (MAPK)-dependent signalling cascade. Immunoprecipitation and Western blot analysis was performed to determine if TA regulate the MAPK signalling pathway. TA significantly inhibited the activation of p38 MAPK and extracellular signal-regulated protein kinases. Moreover, TA-inhibited UVB enhanced the expression of the inflammatory mediators, IL-1, IL-6, tumor necrotic factor-alpha, cyclooxygenase-2 and prostaglandin E(2) in UVB-irradiated HaCaT cells. The topical application of TA on mouse skin treated with UVB irradiation has shown that TA inhibited the formation of erythema. These findings suggest that TA has significant anti-inflammatory effects on the UVB-induced response on the skin and may be a candidate natural compound for the regulation of cutaneous inflammation.

Assessment of potency of allergenic activity of low molecular weight compounds based on IL-1alpha and IL-18 production by a murine and human keratinocyte cell line

Assessment of allergenic potency of low molecular weight compounds is generally performed using animal models, such as the guinea pig maximisation test and the murine local lymph node assay (LLNA). Progress in unravelling the mechanisms of skin sensitisation, including effects on the production of cytokines by the different cell types of the skin, provides us with the opportunity to develop in vitro tests as an alternative to in vivo sensitisation testing. The aim of the present study was to establish an in vitro method to assess the potency of allergens, on the basis of their induction of cytokine production by murine and human keratinocytes. In the present study we used test systems comprised of the murine epidermal keratinocyte cell line HEL-30 and the human keratinocyte cell line HaCaT. We exposed these cell lines to the allergens ethyl-p-aminobenzoate (benzocaine), diethylamine (DEA), 2,4-dinitrochlorobenzene (DNCB), and phthalic anhydride (PA). IL-1alpha and IL-18 dose-response data were evaluated by non-linear regression analysis and at a stimulation index of 3 of cytokine production of treatment versus control, the corresponding allergen concentration was calculated. For HEL-30, for both cytokines DNCB showed the strongest potency followed in this order by PA, benzocaine, and DEA. This classification was similar to our previous findings obtained in the LLNA. For HaCaT, unfortunately, such ranking proved to be much less feasible. In conclusion, to assess the potency of allergens the murine keratinocyte cell line HEL-30 may be a useful in vitro test system, alternative to in vivo models, although this requires further testing using a much wider range of compounds.

Regulation of IL-18 expression by CRH in mouse microglial cells

Corticotropin releasing hormone (CRH) is a major regulator of the stress response. This study examined whether CRH regulates interleukin-18 expression on microglia, BV2. Our data show that CRH enhanced IL-18 expression and significantly induced the secretion of functional IL-18 protein. Furthermore, CRH induced IL-18 production could be blocked by N-acetyl-L-cystein (NAC), which suggests that reactive oxygen intermediates (ROI) may be involved in regulating IL-18. Indeed, it was also found that CRH increased the generation of ROI. Taken together, these results indicate that CRH is an important mediator that regulates IL-18 expression in the brain during stress.

Clinical improvement in chronic plaque-type psoriasis lesions after narrow-band UVB therapy is accompanied by a decrease in the expression of IFN-gamma inducers -- IL-12, IL-18 and IL-23

Type-1 cytokine-producing T cells are important in the pathogenesis of psoriasis vulgaris, for which efficient therapy is provided by means of narrow-band ultraviolet-B (NB-UVB). The expression of the type-1 cytokine interferon-gamma (IFN-gamma) is regulated by interleukin-12 (IL-12), IL-15, IL-18 and IL-23; however, not much is known about the effect of this therapy on the levels of these cytokines in lesional psoriatic skin in situ. In this study, we investigated the effects of NB-UVB therapy on the expression of IFN-gamma-inducing cytokines. Ten patients with chronic plaque-type psoriasis selected to be treated with NB-UVB therapy were recruited for these experiments and the expression of cytokines IL-12, IL-15, IL-18, IL-23 and IFN-gamma in lesional psoriatic skin before, during and after therapy was determined with the help of immunohistochemistry. Double staining was performed in order to determine the cell types expressing these cytokines. The decrease in the psoriasis area and severity index was accompanied by a significant decrease in the expression of IFN-gamma, and concomitantly, significant reduction of IFN-gamma inducers -- IL-12, IL-18 and IL-23. Thus, we concluded that the decrease of IFN-gamma expression in psoriasis lesions after NB-UVB therapy could be a result of diminished expression of IL-12, IL-18 and IL-23 in lesional skin. Therapies targeting these three cytokines should, therefore, be considered in the treatment of psoriasis.