Modulation of phenotype, cytokine production and stimulatory function of CD34+-derived DC by NiCl(2) and SDS

Improvement of human cell line activation test (h-CLAT) using short-time exposure methods for prevention of false-negative results

Recently, animal testing has been affected by increasing ethical, social, and political concerns regarding animal welfare. Several in vitro safety tests for evaluating skin sensitization, such as the human cell line activation test (h-CLAT), have been proposed. However, similar to other tests, the h-CLAT has produced false-negative results, including in tests for acid anhydride and water-insoluble chemicals. In a previous study, we demonstrated that the cause of false-negative results from phthalic anhydride was hydrolysis by an aqueous vehicle, with IL-8 release from THP-1 cells, and that short-time exposure to liquid paraffin (LP) dispersion medium could reduce false-negative results from acid anhydrides. In the present study, we modified the h-CLAT by applying this exposure method. We found that the modified h-CLAT is a promising method for reducing false-negative results obtained from acid anhydrides and chemicals with octanol-water partition coefficients (LogK_ow) greater than 3.5. Based on the outcomes from the present study, a combination of the original and the modified h-CLAT is suggested for reducing false-negative results. Notably, the combination method provided a sensitivity of 95% (overall chemicals) or 93% (chemicals with LogK_ow > 2.0), and an accuracy of 88% (overall chemicals) or 81% (chemicals with LogK_ow > 2.0). We found that the combined method is a promising evaluation scheme for reducing false-negative results seen in existing in vitro skin-sensitization tests. In the future, we expect a combination of original and modified h-CLAT to be applied in a newly developed in vitro test for evaluating skin sensitization.

Nature and kinetics of redox imbalance triggered by respiratory and skin chemical sensitizers on the human monocytic cell line THP-1

Low molecular weight reactive chemicals causing skin and respiratory allergies are known to activate dendritic cells (DC), an event considered to be a key step in both pathologies. Although generation of reactive oxygen species (ROS) is considered a major danger signal responsible for DC maturation, the mechanisms leading to cellular redox imbalance remain poorly understood. Therefore, the aim of this study was to unveil the origin and kinetics of redox imbalance elicited by 1-fluoro-2,4-dinitrobenzene (DNFB) and trimellitic anhydride chloride (TMAC), two golden standards of skin and chemical respiratory allergy, respectively. To track this goal, we addressed the time course modifications of ROS production and cellular antioxidant defenses as well as the modulation of MAPKs signaling pathways and transcription of pathophysiological relevant genes in THP-1 cells. Our data shows that the thiol-reactive sensitizer DNFB directly reacts with cytoplasmic glutathione (GSH) causing its rapid and marked depletion which results in a general increase in ROS accumulation. In turn, TMAC, which preferentially reacts with amine groups, induces a delayed GSH depletion as a consequence of increased mitochondrial ROS production. These divergences in ROS production seem to be correlated with the different extension of intracellular signaling pathways activation and, by consequence, with distinct transcription kinetics of genes such as HMOX1, IL8, IL1B and CD86. Ultimately, our observations may help explain the distinct DC phenotype and T-cell polarizing profile triggered by skin and respiratory sensitizers.

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Distinctive ROS origin and kinetics elicited by skin and respiratory sensitizers.

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ROS production elicited by DNFB results primarily from direct GSH haptenation.

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Distinct expression of genes involved in DC maturation and T-cell polarizing capacity.

Human Monocytoid THP-1 Cell Line versus Monocyte-Derived Human Immature Dendritic Cells as in Vitro Models for Predicting the Sensitising Potential of Chemicals

Immature dendritic cells (DCs) modulate differentiation markers following in vitro exposure to chemicals generating contact allergies. THP-1 is a monocytoid cell line maintaining some differentiating plasticity. In this study, human DCs and THP-1 cells were compared as in vitro models to predict contact sensitisation of chemicals with different sensitising potential. Expression of CD80 and CD86 was assessed by flow cytometry after exposure to subtoxic concentrations of potent (2,4-dinitrochlorobenzene, DNCB and p-phenylendiamine, PPD), strong (thimerosal, TMS), moderate (sodium tetrachloroplatinate, Na2PtCl4) sensitising compounds as well as of non-sensitising, irritating sodium dodecyl sulphate (SDS) as compared to a vehicle of sensitising substances (dimethyl sulphoxide, DMSO). Up-regulation of CD86 following in vitro incubation of DCs and THP-1 cells with DNCB, PPD, TMS and Na2PtCl4 but not with SDS, was observed. The CD80 membrane marker was up-regulated on DCs following in vitro incubation with DNCB and PPD, but not with TMS, Na2PtCl4 and SDS. On THP-1 cells, only DNCB up-regulated CD80 expression. In conclusion, both the cell line THP-1 and DCs are promising in vitro models for assays aiming at predicting the sensitisation potential of chemicals. THP-1 cell line is by far easier to handle and offers relevant advantages from the practical point of view.

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.

The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

This is the report of a workshop organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods that are of importance to the biosciences and which replace, reduce or refine the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organization of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (Anonymous, 1994). The workshop on "The use of in vitro systems for evaluating Immunotoxicity" was held at ECVAM (Ispra), Italy, on 24th-26th November 2003. The participants represented academia, national organizations, international regulatory bodies and industry. The aim of the workshop was to review the state-of-the-art in the field of in vitro immunotoxicology, and to develop strategies towards the replacement of in vivo testing. At the end of this report are listed the recommendations that should be considered for prevalidation and validation of relevant and reliable procedures, that could replace the use of animals in chemical and cosmetics toxicity testing.

Dendritic cells and the assessment in vitro of skin sensitizing potential

It is now well established that dendritic cells (DC) play pivotal roles in the initiation and orchestration of adaptive immune responses, including cutaneous immune responses to chemical allergens that drive the acquisition of skin sensitization. It is not unexpected, therefore, that a large number, and wide variety, of proposed approaches for the identification of skin sensitizing chemicals in vitro are based upon the use of cultured DC or DC-like cells. The use of DC in this context is legitimate. However, with our rapidly increasing understanding of the diversity of cutaneous DC with respect to both phenotype and function, it is timely now to review briefly the potential limitations and interpretive difficulties that are associated with the use of DC-based assays. Among the important considerations are the fact that chemical-induced changes in the characteristics and function of cultured DC will not necessarily reflect accurately the events that that support the development of skin sensitization in vivo. In addition, most DC-based assays are predicated on a view that cutaneous DC have as their primary function the initiation of adaptive immune responses. However, it is now appreciated that cutaneous DC, and in particular epidermal Langerhans cells (LC), may also play important immunoregulatory roles that serve to limit and contain skin immune responses. Notwithstanding these considerations there is reason to believe that at least some in vitro DC-based assays are of value, and indeed some are currently the subject of a formal validation process. However, it is appropriate that such assays are configured and interpreted carefully, and with an appreciation of the complexity of DC biology.

Chemical sensitization and allergotoxicology

Chemical sensitization remains an important environmental and occupational health issue. A wide range of substances have been shown to possess the ability to induce skin sensitization or respiratory sensitization. As a consequence, there is a need to have appropriate methods to identify sensitizing agents. Although a considerable investment has been made in exploring opportunities to develop methods for hazard identification and characterization, there are, as yet, no validated nonanimal methods available. A state of the art of the different in vitro approaches to identify contact and respiratory capacity of chemicals is covered in this chapter.

An in vitro test to screen skin sensitizers using a stable THP-1-derived IL-8 reporter cell line, THP-G8

Several studies have suggested that interleukin (IL)-8 can serve as a biomarker for discrimination of skin sensitizers from nonsensitizers. We established a stable THP-1-derived IL-8 reporter cell line, THP-G8, which harbors SLO and SLR luciferase genes under the control of IL-8 and glyceraldehyde 3-phosphate dehydrogenase promoters, respectively. After 6 h treatment with chemicals, normalized SLO luciferase activity (nSLO-LA) was calculated by dividing SLO-LA by SLR-LA, and the fold induction of nSLO-LA (FInSLO-LA) was calculated by dividing nSLO-LA of chemically treated cells by that of nontreated cells. The nSLO-LA of THP-G8 cells increased in response to lipopolysaccharide (LPS) and several sensitizers. The FInSLO-LA in THP-G8 cells induced by LPS or sensitizers positively correlated with their induction of IL-8 messenger RNA in THP-1 cells. The nSLO-LA value of THP-G8 cells was significantly increased (FInSLO-LA ≥ 1.4) by 13 of the 15 sensitizers as well as by 5 of the 7 nonsensitizers. Interestingly, pretreatment with N-acetylcysteine suppressed the increase in FInSLO-LA induced by all sensitizers (inhibition index (II) ≤ 0.8) but did not suppress that induced by most of the nonsensitizers. We then evaluated the performance of this assay using values of FInSLO-LA ≥ 1.4 and II ≤ 0.8 in at least two of three independent experiments as the criteria of a sensitizer, which resulted in test accuracies of 82% for the 22 chemicals used and of 88% for the chemicals proposed by European Center for the Validation of Alternative Methods. This newly developed assay is a candidate replacement for animal tests of skin sensitization because of its accuracy, convenience, and high throughput performance.

DNA microarrays provide new options for allergen testing

Microarray studies are increasingly used for toxicological research and even for the development of new toxicological test methods. Since gene-expression changes in cultured cells can be conveniently measured with microarrays, this method might be of use for in vitro toxicity testing, for example, in the field of contact sensitization. Allergic contact dermatitis, the clinical manifestation of contact sensitization, may occur when sensitizing chemicals enter the skin and get in contact with epidermal and dermal antigen-presenting cells. The resulting maturation process in these cells can be measured by employing gene-expression analysis. Biomarkers currently known seem to be insufficient to identify all kinds of contact sensitizers, which may partly activate different signaling pathways (e.g., metal or organic sensitizers). Therefore, genome-wide screenings using whole-genome DNA microarrays and extensive data analysis can be performed in order to identify additional genes. Ultimately, marker genes detected in whole-genome experiments can be included in small-scale-targeted microarrays in order to establish the final test method.

Immunotoxicology: Opportunities for Non-animal Test Development

At present, several animal-based assays are used to assess immunotoxic effects such as immunosuppression and sensitisation. The use of whole animals, however, presents several secondary issues, including expense, ethical concerns and relevance to human risk assessment. There is a growing belief that non-animal approaches can eliminate these issues without impairing human safety, provided that biological markers are available to identify the immunotoxic potentials of new chemicals to which humans may be exposed. Driven by the 7th Amendment to the EU Cosmetics Directive, the new EU policy on chemicals (the REACH system), proposals to update the European legislation on the protection of animals used in research, and emerging visions and strategies for predicting toxicity, such in vitro methods are likely to play a major role in the near future. The realisation that the immune system can be the target of many chemicals, resulting in a range of adverse effects on the host's health, has raised serious concerns from the public and within the regulatory agencies. Hypersensitivity and immunosuppression are considered the primary focus for developing in vitro methods in immunotoxicology. However, in vitro assays to detect immunostimulation and autoimmunity are also needed. This review of the state-of-the-art in the field of in vitro immunotoxicity, reveals a lack of cell-based immunotoxicity assays for predicting the toxicity of xenobiotics toward the immune system in a simple, fast, economical and reliable way.

Processing and presentation of variant surface glycoprotein molecules to T cells in African trypanosomiasis

Th1 cell responses to the variant surface glycoprotein (VSG) of African trypanosomes play a critical role in controlling infection through the production of IFN-gamma, but the role of APCs in the induction and regulation of T cell-mediated protection is poorly understood. In this study, we have investigated the Ag presentation capabilities of dendritic cells (DCs) and macrophages during early trypanosome infection in relatively resistant responder and susceptible nonresponder mouse strains. Splenic DCs appeared to be the primary cell responsible for activating naive VSG-specific Th cell responses in resistant responder animals through the coordinated up-regulation of costimulatory molecules, secretion of IL-12, and presentation of VSG peptides to T cells in vivo. Splenic DC depletion and the down-regulation of costimulatory markers on splenic macrophages were observed in susceptible animals and may be associated with the inability of these animals to elicit a significant VSG-specific T cell response. In contrast to splenic APCs, peritoneal macrophages secreted NO, failed to activate naive Th cells in vitro, and presented relatively low levels of VSG peptides to T cells in vivo. Thus, VSG-specific Th1 cell responses may be determined by tissue- and cell-specific differences in Ag presentation. Additionally, all APCs from resistant and susceptible strains displayed a reduced ability to process and present newly encountered exogenous Ag, including new VSG molecules, during high parasitemia. Thus, initial uptake of VSG (or other trypanosome factors) may interfere with Ag presentation and have dramatic consequences for subsequent T cell responses to other proteins.

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.

Cell types involved in allergic asthma and their use in in vitro models to assess respiratory sensitization

This review first describes the mechanism and cell types involved in allergic asthma, which is a complex clinical disease characterized by airway obstruction, airway inflammation and airway hyperresponsiveness to a variety of stimuli. The development of allergic asthma exists of three phases, namely the induction phase, the early-phase asthmatic reaction (EAR) and the late-phase asthmatic reaction (LAR). In the induction phase, antigen-presenting cells play a major role. Most important cells in the EAR are mast cells, and during the LAR, various cell types, such as eosinophils, neutrophils, T cells, macrophages, dendritic cells (DCs), and cells that endow structure are involved. In occupational asthma, this immunological mechanism is involved in 90% of the cases. The second part of this review gives an overview of in vitro models to assess the hazardous potential of high- and low-molecular weight chemicals on the respiratory system. In order to develop a good in vitro model for respiratory allergy, the choice of appropriate cell types is important. Epithelial cells, macrophages and DCs are currently the most used models in this field of research.

NF-kappaB plays a major role in the maturation of human dendritic cells induced by NiSO(4) but not by DNCB

Dendritic cell (DC) activation is a critical event for the induction of an immune response to haptens. Although signaling pathways such as mitogen-activated protein kinase (MAPK) family members have been reported to play a role in DC activation by haptens, little is known about the implication of the nuclear factor kappa B (NF-kappaB) pathway. In this work, we showed that NiSO(4) induced the expression of HLA-DR, CD83, CD86, and CD40 and the production of interleukin (IL)-8, IL-6, and IL-12p40 in human DCs, whereas DNCB induced mainly the expression of CD83 and CD86 and the production of IL-8. NiSO(4) but not DNCB was able to activate the degradation of IkappaB-alpha leading to the binding of the p65 subunit of NF-kappaB on specific DNA probes. Inhibition of the NF-kappaB pathway using BAY 11-7085 prevents both CD40 and HLA-DR expression and cytokine production induced by NiSO(4). However, BAY 11-7085 only partially inhibited CD86 and CD83 expression induced by NiSO(4). In addition, p38 MAPK and NF-kappaB were independently activated by NiSO(4) since SB203580 did not inhibit NF-kappaB activation by NiSO(4). Interestingly, we also showed that DNCB inhibited the degradation of IkappaB-alpha induced by tumor necrosis factor-alpha leading to alteration of CD40, HLA-DR, and CD83 expression but not of CD86 and CCR7. Extensive modifications of DC phenotype by NiSO(4) in comparison to DNCB are probably the consequence of NF-kappaB activation by NiSO(4) but not by DNCB.

Dendritic cells and skin sensitization: Biological roles and uses in hazard identification

Recent advances have been made in our understanding of the roles played by cutaneous dendritic cells (DCs) in the induction of contact allergy. A number of associated changes in epidermal Langerhans cell phenotype and function required for effective skin sensitization are providing the foundations for the development of cellular assays (using DC and DC-like cells) for skin sensitization hazard identification. These alternative approaches to the identification and characterization of skin sensitizing chemicals were the focus of a Workshop entitled "Dendritic Cells and Skin Sensitization: Biological Roles and Uses in Hazard Identification" that was given at the annual Society of Toxicology meeting held March 6-9, 2006 in San Diego, California. This paper reports information that was presented during the Workshop.

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.

Respiratory immunotoxicity: An in vitro assessment

As yet, in vitro assessment of the immunotoxic potency of respiratory agents is not possible. The complexity of the endpoint and the respiratory tract, and the limited availability of well-documented respiratory agents are the main reasons. The evidence that epithelial cells (ECs) are triggered by compounds to express in vitro surface proteins and soluble mediators, has stimulated their use for developing tests for respiratory immunotoxicity. A variety of airway ECs and EC-lines have been assessed, but the available information seems to point at human alveolar cells (e.g., A549) as the most convenient cell type. EC-based test formats with various degrees of complexity have been assessed. Sofar, promising results were obtained using a 3D model using the human A549 lung cell line. Dendritic cells (DCs) have been subjected to intensive research. However, currently available tests are not well suited to discern among the potency of sensitizers. Potential explanations include the lack of standardised protocols for the generation of DCs, no good standards for estimating the quality of in vitro derived DC-cultures, and limited dynamics of the currently used end-points. Alveolar macrophages (AMs) have so far received less attention. This may proof unjustified as macrophages may link innate responses to adaptive immunity. The observation that ECs, DCs and AMs affect each other, suggests that test formats are required combining at least two of these cell types if ranking of compounds according to their sensitising potency is the aim. In addition, the capacity of compounds to cross a cellular membrane is an important property of an immunotoxic compound, which can be assessed only in 3D reconstituted human tissue models. While promising data have been reported for the skin, immunocompetent 3D reconstituted human lung remains to be evaluated for respiratory immunotoxicity. Obviously, the success of any of these simplified test (as compared to the complexity of the immune response) is highly dependent on the availability of early stage biomarkers (expressed at mucosal barrier level) that are predictive for relevant immunotoxicity mechanisms occurring down-stream of the immune response. As yet, such biomarkers are not yet available.

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.

The Sensitizers Nickel Sulfate and 2,4-dinitrofluorobenzene Increase CD40 and IL-12 Receptor Expression in a Fetal Skin Dendritic Cell Line

Dendritic cells (DCs) are antigen-presenting cells (APCs) capable of capturing haptens and to process and present them to T lymphocytes. In order to sensitize T cells for contact hypersensitivity (CHS), skin DCs suffer a maturation process with modifications on their surface molecules. The aim of this work was to evaluate changes induced by two contact sensitizers, 2,4-dinitrofluorobenzene (DNFB) and nickel sulfate (NiSO4), and a non-sensitizer 2,4-dichloronitrobenzene (DCNB), on the protein levels of two activation markers, CD40 and IL-12 receptor (IL-12R), in a mouse skin dendritic cell line (FSDC). The expression of CD40 and IL-12R proteins was evaluated by western blot assay and direct immunofluorescence microscopy. The results showed that CD40 and IL-12R expression increased significantly after cell exposure to NiSO4 and DNFB, although DNFB exhibited a stronger activity. There was no effect with DCNB. The epidermal cytokine granulocyte–macrophage colony-stimulating factor (GM-CSF), also used in the experiments, slightly increased the expression of both CD40 and IL-12R and when tested together with the sensitizers the effect was partially additive. The results suggest that the sensitizers DNFB and NiSO4 are directly involved on the changes of the surface markers CD40 and IL-12R in skin DCs, during the sensitization phase of CHS, and this effect may be enhanced by GM-CSF. In contrast, no effect was observed with DCNB.

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.

Redox Imbalance Induced by Contact Sensitizers Triggers the Maturation of Dendritic Cells

Although p38 mitogen-activated protein kinases (MAPK) play a crucial role in the activation of monocyte-derived dendritic cells (MoDC) by contact sensitizers, the upstream signals of p38 MAPK remain undetermined. To examine whether sensitizers induce redox or oxidative stress in dendritic cells (DC), which subsequently stimulate p38 MAPK, we measured the ratio of the oxidized (GSSG) versus reduced (GSH) form of cellular glutathione in MoDC stimulated with five sensitizers including NiCl2 and 2,4-dinitrochlorobenzene (DNCB) and three non-sensitizers including sodium dodecyl sulfate using colorimetric assays. All the sensitizers, but none of the non-sensitizers at sublethal concentration, reduced the GSH/GSSG ratio, which was accompanied by phosphorylation of p38 MAPK. Treatment with the antioxidant, N-acetyl-L-cysteine, which suppressed the reduction of the GSH/GSSG ratio, abrogated both the phosphorylation of p38 MAPK and the augmentation of CD86 expression. A similar response pattern was observed in THP-1 macrophage-monocyte cells. Unexpectedly, however, formaldehyde (HCHO) reduced the GSH/GSSG ratio in MoDC, but not in THP-1. This finding, in conjunction with the observation that DNCB and NiCl2 reduced the GSH/GSSG ratio at different kinetics, indicated that the sensitizers reduced the GSH/GSSG ratio by a different mechanism. These data suggest that the GSH/GSSG imbalance plays a crucial role in triggering DC maturation by sensitizers.

Cytokine transcript profiling in CD34+-progenitor derived dendritic cells exposed to contact allergens and irritants

We here investigated wether genes encoding the interleukins IL-1beta, IL-6 and IL-8, and the chemokines CCL2, CCL3, CCL3L1 and CCL4 are useful markers for sensitization testing in CD34+-progenitor derived dendritic cells (CD34-DC). CD34-DC from at least three donors were exposed during 0.5 up to 24h to the chemical sensitizers nickel sulphate, oxazolone, 2,4-dinitrochlorobenzene (DNCB) and eugenol, and to the irritants sodium dodecyl sulphate (SDS) and benzalkonium sulphate (BC). mRNA expression was evaluated using real-time RT-PCR. We observed a large inter-individual variation in mRNA expression in CD34-DC exposed to the chemicals. No or limited effects on expression were observed for the irritant BC and the weak sensitizer eugenol. All other chemicals modulated the transcript levels of most cytokines that were investigated. Most of the time, no clear-cut distinctions could be made between the sensitizers and SDS. After 24 h, consistent upregulatory effects of all sensitizing compounds on transcript expression of CCL2, CCL3 and CCL4 were observed, whereas SDS (and BC) had no effect. Our findings suggest that the CCL2, CCL3 and CCL4 genes may be selective end-point markers in the CD34-DC model to discern chemical sensitizers from irritants.

Nickel and DNCB induce CCR7 expression on human dendritic cells through different signalling pathways: role of TNF-alpha and MAPK

After application of haptens on the skin, immature dendritic cells (DC), also named Langerhans cells (LC), migrate to the draining lymph node to sensitize naïve T-lymphocytes. Migration of DC involves many factors including the Cys-Cys chemokine receptor, CCR7. We investigated the effects of two well-known haptens, dinitrochlorobenzene (DNCB) and nickel (NiSO(4)), on the expression of CCR7 on human DC derived from CD34(+) progenitor cells. Both haptens were able to induce CCR7 expression and DC migration in response to Cys-Cys chemokine ligand, CCL19. Since interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha have been shown to participate in LC migration during contact hypersensitivity, we tested the effect of their neutralization on CCR7 expression. Neutralization of IL-1beta activity did not modify CCR7 expression in response to both haptens. CCR7 expression was strongly dependent on TNF-alpha in the case of DNCB, however, neutralization of TNF-alpha only partially reduced CCR7 expression upon NiSO(4) treatment. DNCB, NiSO(4) and TNF-alpha activated p38 mitogen-activated protein kinases (MAPK) and c-jun N-terminal kinase (JNK). Both p38 MAPK and JNK participated to TNF-alpha production induced by DNCB. Inhibition of both p38 MAPK and JNK affected significantly CCR7 expression upon nickel treatment whereas only inhibition of p38 MAPK but not of JNK downregulated CCR7 in the case of TNF-alpha stimulation. These results suggest that MAPK are necessary for haptens to induce CCR7 expression. NiSO(4), however, activates directly CCR7 expression through p38 MAPK and JNK activation whereas DNCB needs TNF-alpha whose secretion is also regulated by p38 MAPK and JNK.

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.

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.

Evaluation of the skin sensitization potential of chemicals using expression of co-stimulatory molecules, CD54 and CD86, on the naive THP-1 cell line

It has been known that dendritic cells (DCs) including Langerhans cells (LCs) play a critical role in the skin sensitization process. Many attempts have been made to develop in vitro sensitization tests that employ DCs derived from peripheral blood mononuclear cells (PBMC-DC) or CD34+ hematopoietic progenitor cells (CD34+ HPC) purified from cord blood or bone marrow. However, the use of the DCs in in vitro methods has been difficult due to the nature of these cells such as low levels in the source and/or donor-to-donor variability. In our studies, we employed the human monocytic leukemia cell line, THP-1, in order to avoid some of these difficulties. At the start, we examined whether treatment of the cells with various cytokines could produce DCs from THP-1. Treatment of THP-1 cells with cytokines such as GM-CSF, IL-4, TNF-alpha, and/or PMA did induce some phenotypic changes in THP-1 cells that were characteristic of DCs. Subsequently, responses to a known sensitizer, dinitrochlorobenzene (DNCB), and a non-sensitizer, dimethyl sulfoxide (DMSO) or sodium lauryl sulfate (SLS), on the expression of co-stimulatory molecules, CD54 and CD86, were examined between the naive cells and the cytokine-treated cells. Interestingly, the naive THP-1 cells responded only to DNCB and the response to the sensitizer was more distinct than cytokine-treated THP-1 cells. Similar phenomena were also observed in the human myeloid leukemia cell line, KG-1. Furthermore, with treatment of DNCB, naive THP-1 cells showed augmented expression of HLA, CD80 and secretion of IL-1 beta. The response of THP-1 cells to a sensitizer was similar to that of LCs/DCs. Upon demonstrating the differentiation of monocyte cells in our system, we then evaluated a series of chemicals, including known sensitizers and non-sensitizers, for their potential to augment CD54 and CD86 expression on naive THP-1 cells. Indeed, known sensitizers such as PPD and 2-MBT significantly augmented CD54 and CD86 expression in a dose-dependent manner while non-sensitizers, such as SLS and methyl salicylate (MS), did not. To note, the metal allergens such as (NH(4))(2)[PtCl(4)], NiSO(4) and CoSO(4) augmented significantly only CD54 expression. Taking advantage of a cultured cell line, measurement of the co-stimulatory molecules, CD54 and CD86, on naive THP-1 cells following chemical exposure shows promise for the development of a simple, short-term in vitro sensitization test.