Simple chemicals can induce maturation and apoptosis of dendritic cells

In vitro characterisation of a novel rubber contact allergen in protective gloves

BACKGROUND

Allergic contact dermatitis (ACD) from protective gloves is often caused by rubber additives, such as accelerators. However, while accelerator-free rubber gloves are available, they still cause ACD in some individuals.

OBJECTIVES

A new allergen, 2-cyаnоethyl dimethyldithiocarbamate, (CEDMC), has recently been identified in accelerator-free gloves, and we here provide a first in vitro characterisation of CEDMC in a dendritic cell (DC)-like cell model along with three reference sensitizer rubber chemicals, consisting of tetraethylthiuram disulfide (TETD) and two xanthogenates.

METHODS

Cellular responses after the exposure to the rubber chemicals were assessed using a transcriptomic approach, multiplex cytokine secretion profiling, and flow cytometry to determine DC model activation marker expression and apoptosis induction.

RESULTS

CEDMC and all other sensitizers were classified as strong skin sensitizers with the transcriptomic approach. They all significantly increased IL-8 secretion and exposure to all except one increased CD86 DC activation marker expression. When tested, CEDMC induced apoptosis, however, delayed compared to TETD.

CONCLUSIONS

The in vitro data corroborate CEDMC, TETD, and investigated xanthogenates as skin sensitizers. Transcriptomic analyses further reveal unique cellular responses induced by CEDMC, which together with future study can contribute to better understanding of cellular mechanisms underlying the sensitising capacity of rubber chemicals.

Chitosan-Poly(Acrylic Acid) Nanoparticles Loaded with R848 and MnCl2 Inhibit Melanoma via Regulating Macrophage Polarization and Dendritic Cell Maturation

Purpose

Since immune cells in the tumor microenvironment (TME) can affect the development and progression of tumors, strategies modulating immune cells are considered to have an important therapeutic effect. As a TLR7/8 agonist, R848 effectively activates the innate immune cells to exert an anti-tumor effect. Mn²⁺ has been reported to strongly promote the maturation of antigen-presenting cells (APCs), thereby enhancing the cytotoxicity of CD8⁺ T cells. Thus, we tried to investigate whether chitosan-poly(acrylic acid) nanoparticles (CS-PAA NPs) loaded with R848 and MnCl₂ (R-M@CS-PAA NPs) could exert an anti-tumor effect by regulating the function of immune cells.

Methods

R-M@CS-PAA NPs were prepared, and their basic characteristics, anti-tumor effect, and potential mechanisms were explored both in vitro and in vivo.

Results

R-M@CS-PAA NPs easily released MnCl₂ and R848 at low pH. In B16F10 mouse melanoma model, R-M@CS-PAA NPs exerted the most significant anti-melanoma effect compared with the control group and CS-PAA NPs loaded with R848 or MnCl₂ alone. FITC-labeled R-M@CS-PAA NPs were displayed to be accumulated at the tumor site. R-M@CS-PAA NPs significantly increased the infiltration of M1 macrophages and CD8⁺ T cells but reduced the number of suppressive immune cells in the TME. Moreover, in vitro experiments showed that R-M@CS-PAA NPs polarized macrophages into the M1 phenotype to inhibit the proliferation of B16F10 cells. R-M@CS-PAA NPs also enhanced the killing function of CD8⁺ T cells to B16F10 cells. Of note, R-M@CS-PAA NPs not only promoted the maturation of APCs such as dendritic cells and macrophages by STING and NF-кB pathways, but also enhanced the ability of dendritic cells to present ovalbumin to OT-I CD8⁺ T cells to enhance the cytotoxicity of OT-I CD8⁺ T cells to ovalbumin-expressing B16F10 cells.

Conclusion

These data indicate that the administration of R-M@CS-PAA NPs is an effective therapeutic strategy against melanoma.

The IL-1 promoter-driven luciferase reporter cell line THP-G1b can efficiently predict skin-sensitising chemicals

IL-1 functions as an essential pro-inflammatory mediator for the sensitisation of allergic contact dermatitis (ACD). However, studies conducted to date have typically used a limited number of haptens and examined their effects only on murine ACD or murine dendritic cells (DCs). It therefore remains unclear whether IL-1α and/or IL-1β is produced in ACD induced by haptens other than those commonly used in mouse ACD models, and whether they are essential for sensitisation leading to ACD in humans. In addition, it is unclear whether human DCs also produce IL-1α or IL-1β after stimulation by haptens in general. Here, we first demonstrated that 10 haptens (3 extreme, 1 strong, 3 moderate and 3 weak) increased both IL-1α mRNA and IL-1β mRNA expression by the human monocyte cell line THP-1, a commonly used surrogate of DCs in in vitro skin sensitisation tests. Next, we constructed an in vitro skin sensitisation test using a stable IL-1β reporter cell line, THP-G1b, and evaluated whether 88 haptens and 34 non-haptens increase IL-1β reporter activity. We found that 94% of 77 haptens evaluated after considering their applicability domain and solubility in the chosen media stimulated reporter activity. These studies demonstrated that most haptens, irrespective of their potency, increased IL-1β mRNA expression by THP-1 cells, confirming that human DCs also produce IL-1β after stimulation by most haptens. The luciferase assay using THP-G1b cells is thus another skin sensitisation test based on the adverse outcome pathway with reasonable performance.

Human monocyte-derived dendritic cells as an in vitro alternative model cell to evaluate the immunotoxicity of 2, 4-Dinitrochlorobenzene

Improvements in science and technology have led to the increasing threats of new chemicals to the public health. It is crucial to evaluate the toxicity, especially immunotoxicology. Dendritic cells (DCs) are believed to be more favorable choices in immunotoxicity evaluations. To obtain and evaluate the value of human monocyte-derived immature DCs (imDCs) in vitro applications in immunotoxicology, compared the results in vitro. DCs were obtained from enriched leukocytes of peripheral blood by using magnetic cell sorting and cytokine (rhGM-CSF + rhIL-4) co-induction. imDCs function in vitro and the surface antigens changes both in imDCs and THP-1 after 24 h of 2,4-dinitrochlorobenzene (DNCB) exposure were determined. The results were compared with those of DNCB-induced rats. The feasibility of imDCs applications in immunotoxicology was evaluated. In vivo, the splenic nodules, lymphocytes, and CD103+DC surface antigen expression were altered in the spleen of DNCB-induced rats. Moreover, DNCB exposure increased CD8+ T cell numbers both in peripheral blood and in the spleen of DNCB-induced rats. In vitro, DNCB exposure reduced the antigen uptake capacity and enhanced the T cell proliferative capacity of imDCs. The results are consistent with in vivo, but superior to that of the THP-1. Our results suggest that human monocyte-derived DCs may have potential applications as an attractive in vitro alternative cell model to evaluate the sensitization of DNCB.

Immunoproteomic identification and characterization of Ni2+-regulated proteins implicates Ni2+ in the induction of monocyte cell death

Nickel allergy is the most common cause of allergic reactions worldwide, with cutaneous and systemic effects potentially affecting multiple organs. Monocytes are precursors of not only macrophages but also dendritic cells, the most potent activators of nickel hypersensitivity. Monocytes are themselves important antigen-presenting cells, capable of nickel-specific T-cell activation in vivo and in vitro, in addition to being important for immediate innate immune inflammation. To elucidate early Ni²⁺-dependent inflammatory molecular mechanisms in human monocytes, a Ni²⁺-specific proteomic approach was applied. Quantitative two-dimensional (2D) differential gel electrophoresis and Delta2D software analyses coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) revealed that Ni²⁺ significantly regulated 56 protein species, of which 36 were analyzed by MALDI-MS. Bioinformatics analyses of all identified proteins resulted in Ni²⁺-associated functional annotation clusters, such as cell death, metal ion binding, and cytoskeletal remodeling. The involvement of Ni²⁺ in the induction of monocyte cell death, but not T-cell death, was observed at Ni²⁺ concentrations at or above 250 μM. Examination of caspase activity during Ni²⁺-mediated cell death revealed monocytic cell death independent of caspase-3 and -7 activity. However, confocal microscopy analysis demonstrated Ni²⁺-triggered cytoskeletal remodeling and nuclear condensation, characteristic of cellular apoptosis. Thus, Ni²⁺-specific peripheral blood mononuclear cell stimulation suggests monocytic cell death at Ni²⁺ concentrations at or above 250 μM, and monocytic effects on immune regulation at lower Ni²⁺ concentrations.

Can the KG1 cell line be used as a model of dendritic cells and discriminate the sensitising potential of chemicals?

The KG1 myeloid leukaemia was used as source of dendritic cells (DC) to discriminate between respiratory and contact sensitising chemicals. A cocktail of cytokines was used to differentiate KG1 to dendritic like cells (termed dKG1) and the effects of nine chemicals (respiratory and contact sensitisers) and an irritant control on surface marker expression, 'antigen presenting' function and cytokine expression investigated. The stability of these chemicals when dissolved was characterised using MALDI ToF MS. A Hill plot model was used with the cellular viability data to quantify the lethal dose 50% (LD50) and a maximum sub toxic concentration of each chemical defined. Cytokine expression by the treated dKG1 was quantified using multiplex immunobead analysis. Whilst dKG1 cells were morphologically similar to DCs, expression of specific surface markers was not typical for DCs derived from healthy precursor cells. When the chemicals were applied at defined sub toxic doses no effects on dKG1 phenotype, function, or cytokine expression, attributable to the sensitisation properties were discriminated. However, dKG1 cells were much more sensitive to the toxic effects of these chemicals compared to the parent KG1 cells. Only 4 of the 9 chemicals tested were stable when dissolved indicating that the effect of sensitising chemicals on antigen presenting cells may be related to species other than the parent compound.

Oxazolone-induced contact hypersensitivity reduces lymphatic drainage but enhances the induction of adaptive immunity

Contact hypersensitivity (CHS) induced by topical application of haptens is a commonly used model to study dermal inflammatory responses in mice. Several recent studies have indicated that CHS-induced skin inflammation triggers lymphangiogenesis but may negatively impact the immune-function of lymphatic vessels, namely fluid drainage and dendritic cell (DC) migration to draining lymph nodes (dLNs). On the other hand, haptens have been shown to exert immune-stimulatory activity by inducing DC maturation. In this study we investigated how the presence of pre-established CHS-induced skin inflammation affects the induction of adaptive immunity in dLNs. Using a mouse model of oxazolone-induced skin inflammation we observed that lymphatic drainage was reduced and DC migration from skin to dLNs was partially compromised. At the same time, a significantly stronger adaptive immune response towards ovalbumin (OVA) was induced when immunization had occurred in CHS-inflamed skin as compared to uninflamed control skin. In fact, immunization with sterile OVA in CHS-inflamed skin evoked a delayed-type hypersensitivity (DTH) response comparable to the one induced by conventional immunization with OVA and adjuvant in uninflamed skin. Striking phenotypic and functional differences were observed when comparing DCs from LNs draining uninflamed or CHS-inflamed skin. DCs from LNs draining CHS-inflamed skin expressed higher levels of co-stimulatory molecules and MHC molecules, produced higher levels of the interleukin-12/23 p40 subunit (IL-12/23-p40) and more potently induced T cell activation in vitro. Immunization experiments revealed that blockade of IL-12/23-p40 during the priming phase partially reverted the CHS-induced enhancement of the adaptive immune response. Collectively, our findings indicate that CHS-induced skin inflammation generates an overall immune-stimulatory milieu, which outweighs the potentially suppressive effect of reduced lymphatic vessel function.

Hapten-induced contact hypersensitivity, autoimmune reactions, and tumor regression: plausibility of mediating antitumor immunity

Haptens are small molecule irritants that bind to proteins and elicit an immune response. Haptens have been commonly used to study allergic contact dermatitis (ACD) using animal contact hypersensitivity (CHS) models. However, extensive research into contact hypersensitivity has offered a confusing and intriguing mechanism of allergic reactions occurring in the skin. The abilities of haptens to induce such reactions have been frequently utilized to study the mechanisms of inflammatory bowel disease (IBD) to induce autoimmune-like responses such as autoimmune hemolytic anemia and to elicit viral wart and tumor regression. Hapten-induced tumor regression has been studied since the mid-1900s and relies on four major concepts: (1) ex vivo haptenation, (2) in situ haptenation, (3) epifocal hapten application, and (4) antigen-hapten conjugate injection. Each of these approaches elicits unique responses in mice and humans. The present review attempts to provide a critical appraisal of the hapten-mediated tumor treatments and offers insights for future development of the field.

Identification of a new phenotype of tolerogenic human dendritic cells induced by fungal proteases from Aspergillus oryzae

We characterized a new pathway to induce tolerogenic dendritic cells (DCs) following treatment of human monocyte-derived DCs with proteases from the fungus Aspergillus oryzae (ASP). ASP-treated DCs (ASP-DCs) exhibit a CD80(-)CD83(-)CD86(-)Ig-like transcript (ILT)2(-)ILT3(-)ILT4(+) phenotype, do not secrete cytokines or chemokines, and express tolerogenic markers such as glucocorticoid-induced leucine zipper, NO synthetase-2, retinaldehyde dehydrogenase-1 or retinaldehyde dehydrogenase-2. When cocultured with naive CD4(+) T cells, ASP-DCs induce an anergic state that can be reversed by IL-2. Generated T cells mediate a suppressive activity in third-party experiments that is not mediated by soluble factors. A comparison between dexamethasone-treated DCs used as a reference for regulatory T cell-inducing DCs and ASP-DCs reveals two distinct phenotypes. In contrast to dexamethasone, ASP treatment induces glucocorticoid-induced leucine zipper independently of glucocorticoid receptor engagement and leads to NF-κB p65 degradation. Abrogation of protease activities in ASP using specific inhibitors reveals that aspartic acid-containing proteases are key inducers of regulatory genes, whereas serine, cysteine, and metalloproteases contribute to NF-κB p65 degradation. Collectively, those features correspond to a previously unreported anergizing phenotype for human DCs. Such regulatory mechanisms may allow fungi to downregulate host immune responses and provide clues for new approaches to treat proinflammatory disorders.

Sensitization effect of thimerosal is mediated in vitro via reactive oxygen species and calcium signaling

Thimerosal, a mercury derivative composed of ethyl mercury chloride (EtHgCl) and thiosalicylic acid (TSA), is widely used as a preservative in vaccines and cosmetic products and causes cutaneous reactions. Since dendritic cells (DCs) play an essential role in the immune response, the sensitization potency of chemicals was studied in vitro using U937, a human promyelomonocytic cell line that is used as a surrogate of monocytic differentiation and activation. Currently, this cell line is under ECVAM (European Center for the Validation of Alternative Methods) validation as an alternative method for discriminating chemicals. Thimerosal and mercury derivatives induced in U937 an overexpression of CD86 and interleukin (IL)-8 secretion similarly to 1-chloro-2,4-dinitrobenzene (DNCB), a sensitizer used as a positive control for DC activation. Non-sensitizers, dichloronitrobenzene (DCNB), TSA and sodium dodecyl sulfate (SDS), an irritant, had no effect. U937 activation was prevented by cell pretreatment with N-acetyl-L-cysteine (NAC) but not with thiol-independent antioxidants except vitamin E which affected CD86 expression by preventing lipid peroxidation of cell membranes. Thimerosal, EtHgCl and DNCB induced glutathione (GSH) depletion and reactive oxygen species (ROS) within 15 min; another peak was detected after 2h for mercury compounds only. MitoSOX, a specific mitochondrial fluorescent probe, confirmed that ROS were essentially produced by mitochondria in correlation with its membrane depolarization. Changes in mitochondrial membrane permeability induced by mercury were reversed by NAC but not by thiol-independent antioxidants. Thimerosal and EtHgCl also induced a calcium (Ca2+) influx with a peak at 3h, suggesting that Ca2+ influx is a secondary event following ROS induction as Ca2+ influx was suppressed after pretreatment with NAC but not with thiol-independent antioxidants. Ca2+ influx was also suppressed when culture medium was deprived of Ca2+ confirming the specificity of the measure. In conclusion, these data suggest that thimerosal induced U937 activation via oxidative stress from mitochondrial stores and mitochondrial membrane depolarization with a primordial effect of thiol groups. A cross-talk between ROS and Ca2+ influx was demonstrated.

Effects of Degradable Mg-Ca Alloys on Dendritic Cell Function

Degradable magnesium alloys are new materials for implants used in orthopedic and trauma surgery. The aim of this study was to investigate the influence of degradable magnesium alloys on the function of dendritic cells (DC) as these cells represent the major antigen presenting cells of the body. MgP (pure magnesium), MgCa 0.6 (0.6% calcium), MgCa 0.8 (0.8% calcium), MgCa 1.0 (1% calcium), and MgCa 1.2 (1.2% calcium) alloys were degraded in cell culture medium. In parallel, murine bone marrow-derived DC were incubated with increasing concentrations (0.1—10 mmol/L) of magnesium chloride and calcium chloride, respectively. Incubation of DC with degradation media over 6 days had no influence on cell viability and only marginal influence on DC migration. Also, the production of TNFα and expression of CD86 was not enhanced by incubation with degraded magnesium alloys. The mixed leukocyte reaction revealed that there was also no increase of the T-cell proliferation in comparison to untreated controls. However, there was a trend toward macrophage development at the expense of DC expansion and an enhanced DC migration was induced by incubation with higher magnesium concentrations. Particularly the latter should be verified in in vivo experiments.

Activation of U937 cells by contact sensitizers: CD86 expression is independent of apoptosis

Among the different phenotypic changes induced by contact sensitizers in dendritic cells and myeloid cell lines, CD86 appears to be a consensus marker, since constantly described as systematically up-regulated. To evaluate the robustness of this marker, interference of cytotoxicity on CD86 expression was investigated in U937 myelomonocytic cell line. In this study, cytotoxicity observed at 48 hr (reading-time for CD86 expression) after treatment with DNCB, NiSO(4) and pPD was shown to result from apoptosis taking place at earlier time points. This allergen-induced apoptosis was at least partly caspase-dependent as demonstrated by caspase-3 activation in response to DNCB and NiSO(4) and inhibition of DNCB-induced apoptosis by Z-VAD-fmk. Inhibition of apoptosis did not modify the stimulation index of CD86 expression in DNCB-treated cells, indicating that apoptosis did not interfere with up-regulation of CD86 expression. In addition, similar CD86 expression level was found in DNCB-treated cells whether calculated from the whole non-necrotic cell population including apoptotic cells or from viable non-apoptotic cell population only. Altogether, these results brought evidence that the presence of cells engaged in death process are not a confusing factor for CD86 expression in response to contact sensitizers. They also pointed out apoptosis as another possible key marker of cellular response to contact sensitizers.

Glycosyltransferase-programmed stereosubstitution (GPS) to create HCELL: engineering a roadmap for cell migration

During evolution of the vertebrate cardiovascular system, the vast endothelial surface area associated with branching vascular networks mandated the development of molecular processes to efficiently and specifically recruit circulating sentinel host defense cells and tissue repair cells at localized sites of inflammation/tissue injury. The forces engendered by high-velocity blood flow commensurately required the evolution of specialized cell surface molecules capable of mediating shear-resistant endothelial adhesive interactions, thus literally capturing relevant cells from the blood stream onto the target endothelial surface and permitting subsequent extravasation. The principal effectors of these shear-resistant binding interactions comprise a family of C-type lectins known as 'selectins' that bind discrete sialofucosylated glycans on their respective ligands. This review explains the 'intelligent design' of requisite reagents to convert native CD44 into the sialofucosylated glycoform known as hematopoietic cell E-/L-selectin ligand (HCELL), the most potent E-selectin counter-receptor expressed on human cells, and will describe how ex vivo glycan engineering of HCELL expression may open the 'avenues' for the efficient vascular delivery of cells for a variety of cell therapies.

The role of mitogen-activated protein kinase-activated protein kinase 2 in the p38/TNF-alpha pathway of systemic and cutaneous inflammation

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) is a downstream molecule of p38, involved in the production of TNF-alpha, a key cytokine, and an established drug target for many inflammatory diseases. We investigated the role of MK2 in skin inflammation to determine its drug target potential. MK2 deficiency significantly decreased plasma TNF-alpha levels after systemic endotoxin application. Deficient mice showed decreased skin edema formation in chronic 2-O-tetradecanoylphorbol-13-acetate (TPA)-induced irritative dermatitis and in subacute 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity. Surprisingly, MK2 deficiency did not inhibit edema formation in subacute 2,4-dinitrochlorobenzene (DNCB)-induced contact allergy and even increased TNF-alpha and IL-1beta levels as well as granulocyte infiltration in diseased ears. Ear inflammation in this model, however, was inhibited by TNF-alpha neutralization as it was in the subacute DNFB model. MK2 deficiency also did not show anti-inflammatory effects in acute DNFB-induced contact hypersensitivity, whereas the p38 inhibitor, SB203580, ameliorated skin inflammation supporting a pathophysiological role of p38. When evaluating possible mechanisms, we found that TNF-alpha production in MK2-deficient spleen cells was strongly diminished after TLR stimulation but less affected after T-cell receptor stimulation. Our data suggest that MK2, in contrast to its downstream effector molecule, TNF-alpha, has a rather elusive role in T-cell-dependent cutaneous inflammation.

TGF-beta1 dampens the susceptibility of dendritic cells to environmental stimulation, leading to the requirement for danger signals for activation

In contrast to its favourable effects on Langerhans cell (LC) differentiation, transforming growth factor (TGF)-beta1 has been reported to prevent dendritic cells from maturing in response to tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, or lipopolysaccharide (LPS). We first characterized the effects of TGF-beta1 on dendritic cell function by testing the response of TGF-beta1-treated monocyte-derived dendritic cells (MoDCs) to maturation stimuli that LCs receive in the epidermis, namely, haptens, ATP and ultraviolet (UV). TGF-beta1 treatment, which augmented E-cadherin and down-regulated dendritic cell-specific ICAM3-grabbing non-integrin on MoDCs, significantly suppressed their CD86 expression and hapten-induced expression of IL-1beta and TNF-alpha mRNA and protein. As TGF-beta1-treated MoDCs lacked Langerin expression, we demonstrated the suppressive effects of TGF-beta1 on haematopoietic progenitor cell-derived dendritic cells expressing both CD1a and Langerin. These suppressive effects of TGF-beta1 increased with the duration of treatment. Furthermore, TGF-beta1-treated MoDCs became resistant to apoptosis/necrosis induced by high hapten, ATP or UV doses. This was mainly attributable to dampened activation of p38 mitogen-activated protein kinase (MAPK) in TGF-beta1-treated MoDCs. Notably, although ATP or hapten alone could only induce CD86 expression weakly and could not augment the allogeneic T-cell stimulatory function of TGF-beta1-treated MoDCs, ATP and hapten synergized to stimulate these phenotypic and functional changes. Similarly, 2,4-dinitro, 1-chlorobenzene (DNCB) augmented the maturation of TGF-beta1-treated MoDCs upon co-culture with a keratinocyte cell line, in which ATP released by the hapten-stimulated keratinocytes synergized with the hapten to induce their maturation. These data may suggest that TGF-beta1 protects LCs from being overactivated by harmless environmental stimulation, while maintaining their ability to become activated in response to danger signals released by keratinocytes.

Evaluation of changes of cell-surface thiols as a new biomarker for in vitro sensitization test

In order to find a novel biomarker for a simple assay to predict skin sensitization, we evaluated cell-surface thiols as a biomarker reflecting intracellular signaling in THP-1 cells (human monocytic cell line). First, we found that a decrease of cell-surface thiols on hapten-treated THP-1 cells was induced in parallel with phosphorylation of p38 MAPK. Next, we confirmed that 2-mercaptoethanol in the culture medium and the differentiation state of THP-1 cells did not affect the changes of cell-surface thiols by hapten. Changes of cell-surface thiols on THP-1 cells were detected after 2h treatment with most allergens (e.g., DNCB, NiSO(4)), as well as some non-allergens (e.g., Tween80, benzalkonium chloride), though other non-allergens (e.g., SDS, glycerol) had no effect. When either a significant decrease or increase of cell-surface thiols (more than 15% in each case) was used as a criterion, the results using 36 allergens and 16 non-allergens were in good accordance with those of in vivo assays. Finally, we confirmed that ATP, which is released as a consequence of cytotoxicity, did not affect the changes of cell-surface thiols. Our results suggest that changes of cell-surface thiols may be useful for an in vitro sensitization assay, which we designate as the SH test.

Effect of Skin Sensitizers on Inducible Nitric Oxide Synthase Expression and Nitric Oxide Production in Skin Dendritic Cells: Role of Different Immunosuppressive Drugs

Nitric oxide (NO) is involved in the pathogenesis of acute and chronic inflammatory conditions, namely in allergic contact dermatitis (ACD). However, the mechanism by which NO acts in ACD remains elusive. The present study focuses on the effects of different contact sensitizers (2,4-dinitrofluorbenzene, 1,4-phenylenediamine, nickel sulfate), the inactive analogue of DNFB, 2,4-dichloronitrobenzene, and two irritants (sodium dodecyl sulphate and benzalkonium chloride) on the expression of the inducible isoform of nitric oxide synthase (iNOS) and NO production in skin dendritic cells. It was also studied the role of different immunosuppressive drugs on iNOS expression and NO production. Only nickel sulfate increased the expression of iNOS and NO production being these effects inhibited by dexamathasone. In contrast, cyclosporin A and sirolimus, two other immunosuppressive drugs tested, did not affect iNOS expression triggered by nickel.

Activation of professional antigen presenting cells by acharan sulfate isolated from giant african snail, achatina fulica

Acharan sulfate isolated from the giant African snail, Achatina fulica, has been reported to have antitumor activity in vivo. In an effort to determine the mechanisms of its antitumor activity, we examined the effects of acharan sulfate on professional antigen presenting cells (APCs). Acharan sulfate increased the phagocytic activity, the production of cytokines such as TNF-alpha and IL-1beta, and the release of nitric oxide on a macrophage cell line, Raw 264.7 cells. In addition, acharan sulfate induced phenotypic and functional maturation of immature dendritic cells (DCs). Immature DCs cultured with acharan sulfate expressed higher levels of class II MHC molecules and major co-stimulatory molecules such as B7-1, B7-2, and CD40. Functional maturation of immature DCs cultured in the presence of acharan sulfate was confirmed by the increased allostimulatory capacity and IL-12 production. These results suggest that the antitumor activity of acharan sulfate is partly due to the activation of professional antigen presenting cells.

Phenotypic alterations and cytokine production in THP-1 cells in response to allergens

In the induction phase of allergic contact hypersensitivity, dendritic cells (DCs), including Langerhans cells (LCs) present in epidermis, can trigger an efficient T cell response once they have matured in response to an allergen. Upon maturation, DCs have been shown to induce expression of several surface molecules and the up-regulation of cytokine production. We have previously shown that THP-1 cells, human acute monocytic leukemia cell line, can discriminate between allergens and irritants by measuring expression of surface markers, CD86 and CD54, following chemical exposure. At the same time, we have also reported that augmented expression of HLA and CD80, and production of IL-1beta were up-regulated in THP-1 cells when treated with an allergen, 2,4-dinitrochlorobenzene (DNCB). In the present study, we first evaluated whether THP-1 cells induced the phenotypic changes and the production of cytokines, which are observed in the process of DC maturation, when treated with two known allergens, DNCB and nickel sulfate (NiSO(4)), and one irritant (sodium lauryl sulfate (SLS)). Exposure to DNCB and NiSO(4) induced significant augmentation of CD40 and CD83 expression as well as CD86 and CD54. Also, TNF-alpha and IL-8 secretion were markedly induced by DNCB and NiSO(4) in a dose-dependent manner. In addition, DNCB and NiSO(4) augmented CD1a expression and production of IL-6, respectively. On the contrary, SLS did not change any of these markers. We then evaluated a series of chemicals, including six known allergens (e.g., hydroquinone (HQ)) and two non-allergens (e.g., methyl paraben (MP)), in order to investigate the potential increase of CD86, CD54, CD40, and CD83 expression on THP-1 cells, and production of TNF-alpha and IL-8. Indeed, all tested allergens, except eugenol (EU), caused significant increased changes in at least four of the analyzed six markers, while non-allergens did not induce any changes. EU significantly augmented CD86, CD54 and CD40 expression. These results revealed that the wide variety of responses to allergens in THP-1 cells may emulate allergen-induced maturation processes of DCs. It is suggested that THP-1 cells, which could develop several DC-like properties, are suitable for identifying sensitizing potential of chemicals.

Angelan isolated from Angelica gigas Nakai induces dendritic cell maturation through toll-like receptor 4

During the evolution of neoplastic diseases, dendritic cell (DC) functions are usually attenuated, and this presents a problem to DC-based immunotherapies against cancer. Here, we investigated the effects of angelan, an acidic polysaccharide isolated from Angelica gigas Nakai, on DC maturation. Angelan efficiently increased the maturation of tlr4(+/+) DCs from C57BL/6 and C3H/HeN mice, but not tlr4(-/-) DCs from C3H/HeJ mice. Phenotypic maturation was confirmed by the elevated expressions of CD80, CD86, and MHC-class II molecules, and functional maturation by increased IL-12 production, enhanced allogenic T cell stimulation, and decreased endocytosis. Angelan was found to activate ERK and NF-kappaB, which are signaling molecules down-stream of toll-like receptor-4 (TLR4) receptors. Angelan-treated mature DC more effectively inhibited B16F10 tumor growth than immature DCs in syngenic murine tumor model. These results indicate that angelan induces DC maturation via TLR4 signaling pathways and suggest the possible use of angelan in DC-based immunotherapies.

Characterization of human metapneumovirus infection of myeloid dendritic cells

Recent in vivo studies suggest that hMPV is a poor inducer of inflammatory cytokines and that clinical symptoms may not be related to immune-mediated pathogenesis as it has been proposed for respiratory syncytial virus (RSV) and human parainfluenza 3 (HPF3). Dendritic cells (DCs) are specialized antigen presenting cells, and very effective at inducing specific CTLs after encountering invading viruses. Interactions of hMPV with DCs have not been characterized. We hypothesized that the relatively mild inflammatory responses observed in vivo after hMPV infection might be at least in part due to hMPV's poor ability to stimulate and activate DCs. hMPV actively infected immature monocyte-derived CD11c+/HLA-DR+ DCs. However, in contrast to RSV or HPF3, hMPV caused no gross cytopathic effects such as syncytia, lytic infection, or massive apoptosis. DCs exposed to hMPV show no cytopathic effects under tissue culture conditions permissive for viral replication. The surface maturation markers CD83 and CD86 were not significantly up-regulated in infected DCs as compared to uninfected controls, while expression of CD80 appeared increased. Stimulation of hMPV-infected DCs with LPS resulted in the enhanced expression of all these surface markers indicating that hMPV is not generally suppressing DC maturation. Overall, cytokine expression remained low. These results indicate that hMPV does not induce effective DC maturation in vitro and suggest that the weak stimulation of DCs may account for the overall low immunogenicity of this virus observed in vivo.

Role of bioactivation in drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are a major problem in both clinical treatment and drug development. This review covers recent developments in our understanding of the pathogenic mechanisms involved, with special focus on the potential role of metabolism and bioactivation in generating a chemical signal for activation of the immune system. The possible role of haptenation and neoantigen formation is discussed, alongside recent findings that challenge this paradigm. Additionally, the essential role of costimulation is examined, as are the potential points whereby costimulation may be driven by reactive metabolites. The relevance of local generation of metabolites in determining the location and character of a reaction is also covered.

CXCL8 secretion by dendritic cells predicts contact allergens from irritants

Monocyte-derived dendritic cell functions have been explored for identification of contact allergens in vitro. Current methods, including measurement of changes in cell surface marker expression (e.g. CD83, CD86) do not provide a sensitive method for detecting the sensitising potential of a chemical. In this study, we investigated whether chemokine production by monocyte-derived dendritic cells is increased upon maturation and whether chemokine production can provide methodology for the detection of allergens. Monocyte-derived dendritic cells were exposed to allergens (nickel sulphate, cobalt chloride, palladium chloride, copper sulphate, chrome-(III)-chloride, potassium dichromate, p-phenylenediamine and dinitrochlorobenzene) and irritants (sodium dodecyl sulphate, dimethylsulphoxide, benzalkoniumchloride and propane-1-ol). CD83 and CD86 expression was analysed by flow cytometry and chemokine production (CXCL8, CCL5, CCL17, CCL18, CCL19, CCL20, CCL22) was determined by ELISA. Significant up regulation of CD83 and CD86 expression could only be induced by three out of seven and five out of seven allergens, respectively. In contrast, CXCL8 production was significantly increased after stimulation with all allergens tested, whereas irritant exposure led to decreased CXCL8 production. All other chemokines tested, failed in identifying contact allergens. In conclusion, CXCL8 production, next to CD83 and CD86 up regulation, by monocyte-derived dendritic cells provides a promising in vitro tool for discrimination between allergens and irritants.

Relationship of CD86 surface marker expression and cytotoxicity on dendritic cells exposed to chemical allergen

Human peripheral blood-derived dendritic cells (DC) respond to a variety of chemical allergens by up-regulating expression of the co-stimulatory molecule CD86. It has been postulated that this measure might provide the basis for an in vitro alternative approach for the identification of skin sensitizing chemicals. We recently reported that DC, exposed in culture to the highest non-cytotoxic concentrations of various chemical allergens, displayed marginal up-regulation of membrane CD86 expression; the interpretation being that such changes were insufficiently sensitive for the purposes of hazard identification. For the work presented here, immature DC were derived from human monocytes and treated with the chemical allergens 2,4-dinitrobenzenesulfonic acid (DNBS), nickel sulfate (NiSO4), p-phenylenediamine (PPD), Bandrowski's base (BB), hydroquinone (HQ) and propyl gallate (PG) for 48 h at concentrations which induced both no to slight to moderate cytotoxicity. For comparison, DC were treated with the irritants sodium dodecyl sulfate (SDS), benzoic acid (BA), and benzalkonium chloride (BZC) at concentrations resulting in comparable levels of cytotoxicity. CD86 expression, as measured by flow cytometry, was consistently up-regulated (ranging from 162 to 386% control) on DC treated with concentrations of chemical allergens that induced approximately 10-15% cytotoxicity. The irritants BA and BZC did not induce up-regulation of CD86 expression when tested at concentrations that induced similar levels of cytotoxicity. SDS, however, up-regulated CD86 expression to 125-138% of control in 2/4 preparations when tested at concentrations which induced similar toxicity. Our results confirm that chemical allergens up-regulate CD86 expression on blood-derived DC and illustrate further that up-regulation of CD86 surface marker expression is more robust when DC are treated with concentrations of chemical allergen that induce slight to moderate cytotoxicity.

Contact sensitizers downregulate the expression of the chemokine receptors CCR6 and CXCR4 in a skin dendritic cell line

Chemokines are involved in the control of dendritic cell (DC) trafficking, which is critical for the immune response, namely in allergic contact dermatitis (ACD). In this work, we investigated by flow cytometry the effect of the contact sensitizers 2,4-dinitrofluorobenzene (DNFB), 1,4-phenylenediamine (PPD) and nickel sulfate (NiSO(4)), on the surface expression of the chemokine receptors CCR6 and CXCR4 in DC. As an experimental model of a DC we used a fetal skin-derived dendritic cell line (FSDC), which has morphological, phenotypical and functional characteristics of skin DC. Our results show that all the skin sensitizers studied decreased the membrane expression of the chemokine receptors CCR6 and CXCR4. In contrast, 2,4-dichloronitrobenzene (DCNB), the inactive analogue of DNFB without contact sensitizing properties, was without effect on the surface expression of these receptors. Lipopolysaccharide (LPS), which induces the maturation of DC, also reduced surface CCR6 and CXCR4 expression.

Efficient maturation and cytokine production of neonatal DCs requires combined proinflammatory signals

Specific functional properties of dendritic cells (DCs) have been suspected as being responsible for the impaired specific immune responses observed in human neonates. To analyze stimulatory requirements for the critical transition from immature, antigen-processing DCs to mature, antigen-presenting DCs, we investigated the effect of different proinflammatory mediators and antigens on phenotype and cytokine secretion of human neonatal DCs derived from hematopoietic progenitor cells (HPCs). Whereas single proinflammatory mediators were unable to induce the maturation of neonatal DCs, various combinations of IFNγ, CD40L, TNFα, LPS and antigens, induced the maturation of neonatal DCs documented by up-regulation of HLA-DR, CD83 and CD86. Combinations of proinflammatory mediators also increased cytokine secretion by neonatal DCs. Especially combined stimulation with LPS and IFNγ proved to be very efficient in inducing maturation and cytokine synthesis of neonatal DCs. In conclusion, neonatal DCs can be stimulated to express maturation as well as costimulatory surface molecules. However, induction of maturation requires combined stimulation with multiple proinflammatory signals.

Regulation by allergens of chemokine receptor expression on in vitro-generated dendritic cells

Immature dendritic cells (DCs) derived from CD34+ progenitor cells or peripheral monocytes, are used as in vitro sensitization models in many chemical allergen treatment studies. During the sensitization, DCs follow maturation process and gain the capacity to migrate to lymph nodes where they stimulate T cells. Chemokine receptor allows DCs to migrate along chemotactic gradients. In this work, we used immature DCs from peripheral monocytes to evaluate the influence of allergens on chemokine receptor and surface-marker expression. We tested the sensitizers dinitrochlorobenzene, Bandrowski's base, and coumarin, as well as the tolerogen dichloronitrobenzene, the irritant sodium dodecyl sulfate and the solvent dimethyl sulfoxide. All skin sensitizers up-regulated the co-stimulatory molecule CD86 and increased the CD83+ cell population. No expression of the chemokine receptors CCR2, CCR3, CCR6, or CXCR5 was observed on DCs exposed to the tested chemicals. The strong allergen dinitrochlorobenzene slightly increased CCR7 expression on DCs but down-regulated CCR1 surface expression. CCR1 down-regulation was not mediated by a classical maturation pathway, as it was unaffected by the corticosteroid dexamethasone.

Reactivity of Langerhans cells in human reconstructed epidermis to known allergens and UV radiation

Epidermal Langerhans cells are the outmost guards of our immune defence system. These cells are directly involved in phenomena such as contact hypersensitivity and UV-induced immunosuppression. Some years ago we succeeded in introducing CD34(+)-derived Langerhans cells into a reconstructed human epidermis. Here we describe their reactivity after topical exposure of the reconstructed epidermis to known allergens, allergen-inducible cytokines, irritants and UV irradiation. Exposure to allergens for 24 h resulted in an activated appearance of the Langerhans cells and in some cases a decrease in their number. Concomitantly, IL-1beta and CD86 mRNA over-expressions were detected in the reconstructed epidermis. A topical treatment with TNF-alpha or IL-1beta revealed that both cytokines induced an activated appearance of the Langerhans cells as early as 4 h following application. Irritants had no effect on the integrated Langerhans cells. Exposure of the reconstructed epidermis to Solar Simulated Radiation caused a dramatic decrease in the number of Langerhans cells and a loss of dendricity in the remaining cells 24 h after irradiation. The topical application of a large spectrum UVA/B filter before irradiation prevented these UV-induced alterations. In our hands, this model provides a promising tool to evaluate the sensitization potential of new compounds and to validate the efficacy of sunscreens to prevent UV-induced immunosuppression.

Capacity of CD34+ progenitor-derived dendritic cells to distinguish between sensitizers and irritants

In an attempt to develop an in vitro test to identify contact sensitizers, mostly dendritic cells (DCs) derived from monocytes (Mo-DC) have been used. Less is known about the potency of DC derived from CD34+ progenitors (CD34-DC) for in vitro allergen testing. CD34+ progenitor derived DC were exposed to nine well-known allergens (one weak, three moderate and five strong allergens) and two irritants. Surface marker expression (CD86, CD83 and HLA-DR) and cytokine production (IL-6, IL-12 and TNF-alpha) were analyzed after 24 h exposure to these chemicals. All allergens tested induced a significant increase in at least one of the DC surface markers. In contrast, none of the irritants tested were able to significantly upregulate membrane marker expression in exposed DC. The level of upregulation of CD86, CD83 and HLA-DR was dependent on the nature and concentration of the chemical, but not on the classification of the allergen. Changes in cytokine production (IL-6, IL-12 and TNF-alpha) were not consistently related to exposure to an allergen. Based on these results, we conclude that the in vitro test using CD34-DC has the capacity to distinguish between allergens and irritants based on altered phenotypic characteristics.

Vaccination with helper-dependent adenovirus enhances the generation of transgene-specific CTL

Recombinant adenoviral vectors (AdV) have been used experimentally as vaccines to present antigenic transgenes in vivo. However, administration of first-generation vectors (FG-AdV) is often limited by their induction of antiviral immunity. To address this limitation, helper-dependent vectors (HD-AdV) were developed that lack viral coding regions. While the administration of HD-AdV results in long-term gene expression in vivo, their utility as immunogens has never been examined. Direct vaccination with 10(8) blue-forming units (BFU) of HD-AdV injected into C57BL/6 mice lead to superior transgene-specific CTL and antibody responses when compared to the same amount of a FG-AdV. The antibody responses to viral antigens were high in response to both the vectors. As a mechanism to reduce viral exposure, dendritic cells (DC) were transduced with HD-AdV in vitro and then used as a cell-based vaccine. DC transduced with HD-AdV expressed higher levels of transgene-specific mRNA and up to 1200-fold higher levels of transgene protein than did DC transduced with a FG-AdV. In addition, HD-AdV-transduced DC stimulated superior transgene-specific CTL responses when administered in vivo, an effect that was further enhanced by maturing the DC with LPS prior to administration. In contrast to direct immunization with HD-AdV, vaccination with HD-AdV-transduced DC was associated with limited antibody responses against the AdV. We conclude that HD-AdV stimulates superior transgene-specific immune responses when compared to a FG-AdV, and that immunization with a DC-based vaccine maintains this efficacy while limiting antiviral reactivity.

p38 Mitogen-Activated Protein Kinase Mediates Dual Role of Ultraviolet B Radiation in Induction of Maturation and Apoptosis of Monocyte-Derived Dendritic Cells

Although ultraviolet B (UVB) induces apoptosis and functional perturbations in dendritic cells (DC), for example, Langerhans cells (LC), it also stimulates some LC into maturation after irradiation in vivo. To analyze its reciprocal effects on DC, we elucidated the direct effect of UVB on DC in vitro using human monocyte-derived DC (MoDC). UVB from 50 to 200 J per m2 stimulated the maturation of MoDC with (1) augmented expression of CD86 and HLA-DR, (2) enhanced production of IL-1beta, IL-6, IL-8, and TNF-alpha at both the mRNA and protein levels, and (3) enhanced allostimulatory capacity on a per-cell basis, whereas the exceeded doses induced apoptotic cell death. Western-blot analysis of MoDC after UVB demonstrated a concentration-dependent phosphorylation of p38- and c-JUN N-terminal kinase (JNK)-mitogen-activated protein kinases (MAPK), but not that of extracellular signal-regulated kinases. p38 MAPK-inhibitor, SB203580, inhibited both UVB-induced maturation and apoptosis of MoDC. Interestingly, MoDC that had undergone apoptosis exhibited an augmented expression of HLA-DR without upregulation of CD86 antigen, suggesting their tolerogenic phenotype. Thus, our study revealed a dual effect of UVB, to stimulate maturation or to induce apoptosis in MoDC, depending on the dosage, via p38 MAPK pathway.

Moderate skin sensitizers can induce phenotypic changes on in vitro generated dendritic cells

In the present study, we analyzed the phenotypic alterations induced by several allergens on immature dendritic cells (DC), with the aim to develop a potential in vitro alternative for predicting the sensitizing potential of chemicals. DC were generated from human monocytes cultured in the presence of GM-CSF, IL-4 and TGF-beta1 and treated for 2 or 4 days with different chemicals. Surface marker expression (HLA-DR, CD1a, CD40, CD54, CD83, CD86, CCR7 and E-cadherin) was analyzed by flow cytometry. Results showed that a 2-day treatment with the representative allergens DNCB and NiSO(4) induced significant changes of most antigens while other chemicals such as balm of Peru (strong allergen), kathon (moderate allergen), cinnamic aldehyde (mild allergen) or the irritant SLS had no significant effect. In contrast, the 4-day treatment with allergens substantially improved the results. Indeed, despite a large variability according to the donors, the number of modified antigens was significantly higher with all the tested chemicals, except kathon, as compared to that observed with the irritant SLS. The present study indicates that, in this model, the screening of mild or moderate allergens requires both the consideration of many antigens and a prolonged time of incubation with the chemicals.

T Lymphocyte-Mediated Immune Responses to Chemical Haptens and Metal Ions: Implications for Allergic and Autoimmune Disease

Chemical haptens and metal ions interact with proteins and thereby become recognizable by T and B lymphocytes. They induce the production of proinflammatory cytokines and chemokines by various cell types due to triggering of innate immune responses. This is an important prerequisite for the activation of the adaptive immune system and the development of diseases like allergic contact dermatitis and adverse drug and autoimmune reactions. Our increasing knowledge about the molecular basis of hapten and metal ion recognition by T cells and about the pathomechanisms of contact hypersensitivity and chemical-induced autoimmune reactions allows concomitant progress in the development of modern strategies for immunotherapy and will hopefully enable more specific intervention in hapten- and metal ion-induced human diseases in the future.

Modifying Adenoviral Vectors for Use as Gene-Based Cancer Vaccines

The past decade has produced significant advances in our understanding of antigen-presenting cells, tumor antigens, and other components of the immune response to cancer. Gene-based vaccination is emerging as one of the more promising approaches for loading dendritic cells (DC) with tumor-associated antigens. In this respect, it is proposed that adenoviral (AdV) vectors can deliver high antigen concentrations, promote effective processing and MHC expression, and stimulate potent cell-mediated immunity. While AdV vectors have performed well in pre-clinical vaccine models, their application to patient care has limitations. The in vivo administration of AdV vectors is associated with both innate and adaptive host responses that result in tissue inflammation and injury, viral neutralization, and premature clearance of AdV-transduced cells. A variety of strategies have been developed to address these limitations. The ideal vaccine would avoid vector-related immune responses, have relative specificity for transducing DC, and induce high levels of transgene expression. This review describes the range of host responses to AdV vaccines, identifies strategies to reduce viral recognition and enhance transgene antigen expression, and suggests future approaches to vector development and administration. There is every reason to believe that safer and more effective forms of AdV-based vaccines can be developed and applied to patient therapy.

Gene expression changes in peripheral blood-derived dendritic cells following exposure to a contact allergen

A critical step in the induction of allergic contact allergy is the activation and subsequent migration of Langerhans cells (LC), an important antigen presenting dendritic cell (DC) of the skin. As the Langerhans cells migrate, they undergo a maturation process. It has been proposed that contact allergen exposure can induce DC maturation. While changes in DC gene expression profiles induced by various maturation stimuli have been explored, there are no published reports describing genomic-scale analysis of the changes induced by chemical allergen exposure. Therefore, to explore the concept of chemical allergen-induced DC maturation and to identify genes that are regulated by exposure to allergens we examined, at the transcriptional level, the effects of exposure to a contact allergen on DC. Peripheral blood-derived DC were exposed for 24 h to either 1mM or 5 mM dinitrobenzenesulfonic acid (DNBS). Changes in gene expression were analyzed using Affymetrix U95Av2 GeneChip. Comparison of mean signal values from replicate cultures revealed 173 genes that were significantly different (P < or = 0.001) between 1 mM DNBS treated and untreated control DC and 1249 significant gene changes between 5 mM DNBS treated and control DC. Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) was used to evaluate the observed transcript changes for selected genes in DC derived from a second donor. Comparison of the fold-changes in transcript levels between the two platforms and donors revealed a good correlation in both direction and magnitude. RT-PCR analysis was also used to assess the allergen specificity of a selected number of genes in DC derived from a third donor. Many of the gene expression changes were found to be induced only by exposure to the allergen, DNBS, and not by exposure to a structurally similar non-allergen, benzenesulfonic acid. A number of gene expression changes induced by allergen exposure were found to be consistent with what is known of the DC maturation process, and thus provide support for the theory of contact allergen-induced DC maturation. Additionally, it is hoped that some of the transcript changes identified through this approach will be shown to be suitable for use in the development of an in vitro predictive assay for contact sensitization.

Antiapoptotic action of hypoxia-inducible factor-1 alpha in human endothelial cells

Hypoxia-inducible factor-1 (HIF-1) is the major transcription factor involved in the adaptive response to hypoxia and consists of HIF-1 alpha and HIF-1 beta subunits. Indirect evidence suggests that HIF-1 alpha may exert both proapoptotic and antiapoptotic actions in response to hypoxia. In this study, we evaluated the effects of RNA interference (RNAi) targeting HIF-1 alpha messenger RNA (mRNA) on apoptosis in primary cultured human umbilical vascular endothelial cells (HUVECs) exposed to anoxia and reoxygenation (A/R). HUVECs were transfected with specific 21-nt small interfering RNA (siRNA) duplexes targeting HIF-1 alpha mRNA sequences or scrambled RNA duplexes and subjected either to normoxia for 251/2 h or to anoxia for 11/2 h, and subsequently normoxia for 24 h (A/R). Control samples were subjected to A/R but not transfected. HUVECs apoptosis was evaluated by Tdt-mediated dUTP nick end-labeling (TUNEL) assay and by activated caspase-3 immunostaining and immunoblotting. The efficacy of RNAi was assessed by knockdown of HIF-1 alpha mRNA and protein expression via in situ hybridization, real-time quantitative PCR, immunohistochemistry, and Western blotting. When compared with normoxic cultures, A/R significantly upregulated HIF- 1 alpha mRNA and protein expression in HUVECs, but did not appreciably alter the percentage of apoptotic cells. In contrast, a significantly greater proportion of HUVECs transfected with specific siRNA duplexes and exposed to A/R demonstrated evidence of apoptosis when compared with nontransfected cells. Transfection with specific siRNA duplexes knocked down HIF-1 alpha mRNA and protein expression in A/R-treated cells by approximately 60%, whereas transfection with scrambled siRNA duplexes had no noticeable effect on HIF-1 alpha expression. These findings strongly suggest that HIF-1 alpha exerts an antiapoptotic role in HUVECs stressed by anoxia.

Contact sensitizer nickel sulfate activates the transcription factors NF-kB and AP-1 and increases the expression of nitric oxide synthase in a skin dendritic cell line

Nuclear factor kappa B (NF-kB) and activating protein-1 (AP-1) transcription factors are ubiquitously expressed signaling molecules known to regulate the transcription of a large number of genes involved in immune responses, namely the inducible isoform of nitric oxide synthase (iNOS). In this study, we demonstrate that a fetal skin-derived dendritic cell line (FSDC) produces nitric oxide (NO) in response to the contact sensitizer nickel sulfate (NiSO(4)) and increases the expression of the iNOS protein, as determined by immunofluorescence and Western blot analysis. The sensitizer NiSO(4) increased cytoplasmic iNOS expression by 31.9 +/- 10.3% and nitrite production, as assayed by the Griess reaction, by 27.6 +/- 9.5%. Electrophoretic mobility shift assay (EMSA), showed that 30 min of FSDC exposure to NiSO(4) activates the transcription factor NF-kB by 58.2 +/- 7.0% and 2 h of FSDC exposure to NiSO(4) activates the transcription factor AP-1 by 26.0 +/- 1.4%. Together, these results indicate that NiSO(4) activates the NF-kB and AP-1 pathways and induces iNOS expression in skin dendritic cells.