Allergic contact dermatitis: epidemiology, molecular mechanisms, in vitro methods and regulatory aspects. Current knowledge assembled at an international workshop at BfR, Germany

Development of an in vitro method to estimate the sensitization induction level of contact allergens

No standardized in vitro methods to assess potency of skin sensitizers are available. Recently, we standardized a procedure which combines the epidermal equivalent potency assay with assessment of IL-18 to provide a single test for identification and classification of skin sensitizers. This current study aimed to extend tested chemicals, and to provide a simple in vitro method for estimation of the expected sensitization induction level interpolating in vitro EC50 and IL-18 SI2 values to predict LLNA EC3 and/or human NOEL from standards curves generated using reference contact allergens. Reconstituted human epidermis was challenged with 14 chemicals not previously tested benzoquinone, chlorpromazine, chloramine T, benzyl salicylate, diethyl maleate, dihydroeugenol, 2,4-dichloronitrobenzene, benzyl cinnamate, imidazolidinyl urea, and limonene as contact sensitizers while benzyl alcohol, isopropanol, dimethyl isophthalate and 4-aminobenzoic acid as non-sensitizers in the LLNA. Where for benzyl salicylate and benzyl cinnamate no sensitization was observed in human predictive studies, positive responses to benzyl alcohol and dimethyl isophthalate were reported. The proposed method correlates better with human data, correctly predicting substances incorrectly classified by LLNA. With the exception of benzoquinone (interference with both MTT and IL-18 ELISA), and chloramine T (underestimated in the interpolation), a good estimation of LLNA EC3 and in vivo available human NOEL values was obtained.

SkinSensDB: a curated database for skin sensitization assays

Skin sensitization is an important toxicological endpoint for chemical hazard determination and safety assessment. Prediction of chemical skin sensitizer had traditionally relied on data from rodent models. The development of the adverse outcome pathway (AOP) and associated alternative in vitro assays have reshaped the assessment of skin sensitizers. The integration of multiple assays as key events in the AOP has been shown to have improved prediction performance. Current computational models to predict skin sensitization mainly based on in vivo assays without incorporating alternative in vitro assays. However, there are few freely available databases integrating both the in vivo and the in vitro skin sensitization assays for development of AOP-based skin sensitization prediction models. To facilitate the development of AOP-based prediction models, a skin sensitization database named SkinSensDB has been constructed by curating data from published AOP-related assays. In addition to providing datasets for developing computational models, SkinSensDB is equipped with browsing and search tools which enable the assessment of new compounds for their skin sensitization potentials based on data from structurally similar compounds. SkinSensDB is publicly available at http://cwtung.kmu.edu.tw/skinsensdb.

Dermal γδ T Cells Do Not Freely Re-Circulate Out of Skin and Produce IL-17 to Promote Neutrophil Infiltration during Primary Contact Hypersensitivity

The role of mouse dermal γδ T cells in inflammatory skin disorders and host defense has been studied extensively. It is known that dendritic epidermal T cells (DETC) have a monomorphic γδ T cell receptor (TCR) and reside in murine epidermis from birth. We asked if dermal γδ cells freely re-circulated out of skin, or behaved more like dermal resident memory T cells (TRM) in mice. We found that, unlike epidermal γδ T cells (DETC), dermal γδ cells are not homogeneous with regard to TCR, express the tissue resident T cell markers CD69 and CD103, bear skin homing receptors, and produce IL-17 and IL-22. We created GFP+: GFP- parabiotic mice and found that dermal γδ T cells re-circulate very slowly-more rapidly than authentic αβ TCR TRM, but more slowly than the recently described dermal αβ TCR T migratory memory cells (TMM). Mice lacking the TCR δ gene (δ-/-) had a significant reduction of 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity (CHS). We created mice deficient in dermal γδ T cells but not DETC, and these mice also showed a markedly reduced CHS response after DNFB challenge. The infiltration of effector T cells during CHS was not reduced in dermal γδ T cell-deficient mice; however, infiltration of Gr-1+CD11b+ neutrophils, as well as ear swelling, was reduced significantly. We next depleted Gr-1+ neutrophils in vivo, and demonstrated that neutrophils are required for ear swelling, the accepted metric for a CHS response. Depletion of IL-17-producing dermal Vγ4+ cells and neutralization of IL-17 in vivo, respectively, also led to a significantly reduced CHS response and diminished neutrophil infiltration. Our findings here suggest that dermal γδ T cells have an intermediate phenotype of T cell residence, and play an important role in primary CHS through producing IL-17 to promote neutrophil infiltration.

Hapten-Specific T Cell-Mediated Skin Inflammation: Flow Cytometry Analysis of Mouse Skin Inflammatory Infiltrate

Hapten-specific T cell-mediated skin inflammation also known as contact hypersensitivity (CHS) is characterized by a strong influx of CD8⁺ cytotoxic T cells within the skin upon reexposure of sensitized individuals to the same hapten. As many other leukocytes are also recruited during this elicitation phase, we attempted to revisit the skin infiltrate and characterize the inflammatory pattern. Recent improvement in the isolation in conventional as well as inflammatory dendritic cell and macrophage subsets from tissues and in the use of appropriate surface markers unraveling their heterogeneity should allow to determinate their specific functions in the CHS model. Here, we describe procedures to extract those cells from the skin and to analyze them by flow cytometry using a combination of appropriate surface markers allowing further transcriptomic analysis and functional assays.

Monocyte/Macrophage: NK Cell Cooperation-Old Tools for New Functions

Monocyte/macrophage and natural killer (NK) cells are partners from a phylogenetic standpoint of innate immune system development and its evolutionary progressive interaction with adaptive immunity. The equally conservative ways of development and differentiation of both invertebrate hemocytes and vertebrate macrophages are reviewed. Evolutionary conserved molecules occurring in macrophage receptors and effectors have been inherited by vertebrates after their common ancestor with invertebrates. Cytolytic functions of mammalian NK cells, which are rooted in immune cells of invertebrates, although certain NK cell receptors (NKRs) are mammalian new events, are characterized. Broad heterogeneity of macrophage and NK cell phenotypes that depends on surrounding microenvironment conditions and expression profiles of specific receptors and activation mechanisms of both cell types are discussed. The particular tissue specificity of macrophages and NK cells, as well as their plasticity and mechanisms of their polarization to different functional subtypes have been underlined. The chapter summarized studies revealing the specific molecular mechanisms and regulation of NK cells and macrophages that enable their highly specific cross-cooperation. Attention is given to the evolving role of human monocyte/macrophage and NK cell interaction in pathogenesis of hypersensitivity reaction-based disorders, including autoimmunity, as well as in cancer surveillance and progression.

An in vitro skin sensitization assay termed EpiSensA for broad sets of chemicals including lipophilic chemicals and pre/pro-haptens

To evaluate chemicals (e.g. lipophilic chemicals, pre/pro-haptens) that are difficult to correctly evaluate using in vitro skin sensitization tests (e.g. DPRA, KeratinoSens or h-CLAT), we developed a novel in vitro test termed "Epidermal Sensitization Assay: EpiSensA" that uses reconstructed human epidermis. This assay is based on the induction of multiple marker genes (ATF3, IL-8, DNAJB4 and GCLM) related to two keratinocyte responses (inflammatory or cytoprotective) in the induction of skin sensitization. Here, we first confirmed the mechanistic relevance of these marker genes by focusing on key molecules that regulate keratinocyte responses in vivo (P2X₇ for inflammatory and Nrf2 for cytoprotective responses). The up-regulation of ATF3 and IL-8, or DNAJB4 and GCLM induced by the representative sensitizer 2,4-dinitrochlorobenzene in human keratinocytes was significantly suppressed by a P2X₇ specific antagonist KN-62, or by Nrf2 siRNA, respectively, which supported mechanistic relevance of marker genes. Moreover, the EpiSensA had sensitivity, specificity and accuracy of 93%, 100% and 93% for 29 lipophilic chemicals (logKow≥3.5), and of 96%, 75% and 88% for 43 hydrophilic chemicals including 11 pre/pro-haptens, compared with the LLNA. These results suggested that the EpiSensA could be a mechanism-based test applicable to broad sets of chemicals including lipophilic chemicals and pre/pro-haptens.

1-Fluoro-2,4-dinitrobenzene and its derivatives act as secretagogues on rodent mast cells

Accumulating evidence suggests that activated mast cells are involved in contact hypersensitivity, although the precise mechanisms of their activation are still not completely understood. We investigated the potential of common experimental allergens to induce mast cell activation using murine bone marrow-derived cultured mast cells and rat peritoneal mast cells. Among these allergens, 1-chloro-2,4-dinitrobenzene and 1-fluoro-2,4-dinirobenzene (DNFB) were found to induce degranulation of rat peritoneal mast cells. DNFB-induced degranulation is accompanied by cytosolic Ca²⁺ mobilization and is significantly inhibited by pertussis toxin, U73122 (a phospholipase C inhibitor), and BAPTA (a Ca²⁺ chelator), raising the possibility that DNFB acts on the G protein-coupled receptors and activates G_i , which induces activation of phospholipase C, as well as known mast cell secretagogues, such as compound 48/80. DNFB could induce mast cell degranulation in the absence of serum proteins and IgE. Structure-activity relationship analyses revealed an inverse correlation between the degree of degranulation and the electron density of the C1 carbon of the DNFB derivatives. These findings raise a possibility that DNFB functions as a potent contact allergen through induction of cutaneous mast cell degranulation.

Adenosine diphosphate involvement in THP-1 maturation triggered by the contact allergen 1-fluoro-2,4-dinitrobenzene

Dendritic cells' (DC) activation is considered a key event in the adverse outcome pathway for skin sensitization elicited by covalent binding of chemicals to proteins. The mechanisms underlying DC activation by contact sensitizers are not completely understood. However, several "danger signals" are pointed as relevant effectors. Among these extra-cellular early danger signals, purines may be crucial for the development of xenoinflammation and several reports indicate their involvement in contact allergic reactions. In the present work we used the DC-surrogate monocytic cell line THP-1, cultured alone or co-cultured with the human keratinocyte cell line HaCaT, to explore the contribution of extracellular adenine nucleotides to THP-1 maturation triggered by the extreme contact sensitizer, 1-fluoro-2,4-dinitrobenzene (DNFB). We found that THP-1 maturation induced by DNFB is impaired after purinergic signaling inhibition, and that the transcription of the purinergic metabotropic receptors P2Y2 and P2Y11 is modulated by the sensitizer. We also detected that THP-1 cells only partially hydrolyse extracellular adenosine triphosphate, leading to accumulation of the mono-phosphate derivative, AMP. We detected different and non-overlapping activation patterns of mitogen activated protein kinases by DNFB and extracellular nucleotides. Overall, our results indicate that THP-1 maturation induced by DNFB is strongly modulated by extracellular adenine nucleotides through metabotropic purinergic receptors. This knowledge unveils a molecular toxicity pathway evoked by sensitizers and involved in THP-1 maturation, a DC-surrogate cell line thoroughly used in in vitro tests for the identification of skin allergens.

Understanding chemical allergen potency: role of NLRP12 and Blimp-1 in the induction of IL-18 in human keratinocytes

Keratinocytes (KCs) play a key role in all phases of skin sensitization. We recently identified interleukin-18 (IL-18) production as useful end point for determination of contact sensitization potential of low molecular weight chemicals. The aim of this study was to identify genes involved in skin sensitizer-induced inflammasome activation and to establish their role in IL-18 production. For gene expression analysis, cells were treated for 6 h with p-phenylenediamine (PPD) as reference contact allergen; total RNA was extracted and examined with a commercially available Inflammasome Polymerase Chain Reaction (PCR) array. Among genes induced, NLRP12 (Nod-like receptor P12) was selected for further investigation. NLRP12 promoter region contains Blimp-1 (B-lymphocyte-induced maturation protein-1)/PRDM1 binding site, and from the literature, it is reported that Blimp-1 reduces NLRP12 activity and expression in monocytes/macrophages. Their expression and role in KCs are currently unknown. To confirm NLRP12 expression and to investigate its relationship with Blimp-1, cells were exposed for different times (3, 6 and 24 h) to the extreme sensitizer 2,4-dinitrochlorobenzene (DNCB) and the strong sensitizer PPD. Allergens were able to induce both genes, however, with different kinetic, with DNCB more rapidly upregulating Blimp-1 and inducing IL-18 production, compared to PPD. NLRP12 and Blimp-1 expression appeared to be inversely correlated: Blimp-1 silencing resulted in increased NLRP12 expression and reduced contact allergen-induced IL-18 production. Overall results indicate that contact allergens of different potency differently modulate Blimp-1/NLRP12 expression, with strong allergen more rapidly downregulating NLRP12, thus more rapidly inducing IL-18 production. Data confirm that also in KCs, NLRP12 has an inhibitory effect on inflammasome activation assessed by IL-18 maturation.

In Vivo Expansion of Endogenous Regulatory T Cell Populations Induces Long-Term Suppression of Contact Hypersensitivity

Contact hypersensitivity (CHS) of murine skin serves as a model of allergic contact dermatitis. Hapten-specific CD8 T cells and neutrophils represent the major effector cells driving this inflammatory reaction whereas Foxp3(+) regulatory T cells (Tregs) control the severity of inflammation. However, whether in vivo expansion of endogenous Tregs can downregulate CHS-mediated inflammation remains to be elucidated. In this study, we addressed this issue by using injection of an IL-2/anti-IL-2 mAb JES6-1 complex (IL-2/JES6-1) as a means of Treg induction in 2,4,6-trinitrochlorobenzene-induced CHS. IL-2/JES6-1 injection before or after hapten sensitization led to a considerable reduction of skin inflammation, even when rechallenged up to 3 wk after the last treatment. Conversely, Treg depletion re-established the CHS response in IL-2/JES6-1-treated mice. IL-2/JES6-1 injection resulted in increased frequencies of natural and peripheral Tregs in spleen and draining lymph nodes (LNs), elevated IL-10 and TGF-β production by CD4 T cells, reduced CD86 expression by dendritic cells, and led to lower numbers of hapten-specific IFN-γ-producing CD8 T effector cells in LNs. Neutrophil and CD8 T cell infiltration was reduced in inflamed ear tissue, whereas CTLA-4(+)Foxp3(+) Treg frequencies were augmented. Adoptive transfer of LN cells of sensitized mice into recipients treated with IL-2/JES6-1 showed impaired CHS. Our results show that in vivo Treg expansion results in a prolonged CHS suppression, a sustained reduction of hapten-specific CD8 T cells, and a decrease in effector cell influx in inflamed tissue.

Novel insights into cutaneous immune systems revealed by in vivo imaging

In vivo imaging is a novel experimental approach for biological research. Multiphoton microscopy (MPM), a type of fluorescence microscopy, is a new tool for in vivo imaging analysis. MPM allows observation of both tissue structures and cell behaviors or cell-cell interactions in living animals in real time. Skin is an ideal tissue for MPM analysis as it is directly accessible to the microscope. In the skin, immune cells cooperate to maintain skin homeostasis or to exert immune responses against foreign antigens. In vivo imaging by MPM analysis provides precise information on cell dynamics in the skin, and has significantly expanded our knowledge of the cutaneous immune system. In this review, we will discuss recent insights related to the mechanisms of allergic skin inflammation that have been revealed by MPM analysis.

In Situ Metabolism of Cinnamyl Alcohol in Reconstructed Human Epidermis: New Insights into the Activation of This Fragrance Skin Sensitizer

Chemical modification of epidermal proteins by skin sensitizers is the molecular event which initiates the induction of contact allergy. However, not all chemical skin allergens react directly as haptens with epidermal proteins but need either a chemical (prehaptens) or metabolic (prohaptens) activation step to become reactive. Cinnamyl alcohol has been considered a model prohapten, as this skin sensitizer has no intrinsic reactivity. Therefore, the prevailing theory is that cinnamyl alcohol is enzymatically oxidized into the protein-reactive cinnamaldehyde, which is the sensitizing agent. Knowing that reconstructed human epidermis (RHE) models have been demonstrated to be quite similar to the normal human epidermis in terms of metabolic enzymes, use of RHE may be useful to investigate the in situ metabolism/activation of cinnamyl alcohol, particularly when coupled with high-resolution magic angle spinning nuclear magnetic resonance. Incubation of carbon-13 substituted cinnamyl derivatives with RHE did not result in the formation of cinnamaldehyde. The metabolites formed suggest the formation of an epoxy-alcohol and an allylic sulfate as potential electrophiles. These data suggest that cinnamyl alcohol is inducing skin sensitization through a route independent of the one involving cinnamaldehyde and should therefore be considered as a skin sensitizer on its own.

Paeoniflorin suppresses IL-6/Stat3 pathway via upregulation of Socs3 in dendritic cells in response to 1-chloro-2,4-dinitrobenze

Mounting evidence has suggested that inflammation is associated with IL-6/Stat3 pathway in dendritic cells (DCs) and Th17 cells, which are critical for development of allergic contact dermatitis (ACD). Paeoniflorin (PF) has been clinically proved to be effective in the treatment of inflammatory skin diseases such as ACD. We have previously demonstrated the effect of PF on DCs stimulated with 1-chloro-2,4-dinitrobenze (DNCB) and naïve CD4(+)CD45RA(+) T cells for Th17 cell differentiation. However, whether PF down-regulates IL-6/Stat3 in DCs and Th17 cells remains to be explored. In this study, we show clearly that PF markedly decreases IL-6/Stat3 in DCs stimulated with DNCB at both gene and protein levels compared with control DCs in vitro. Meanwhile, PF up-regulates suppressor of cytokine signaling 3 (Socs3). Such decreased expression of IL-6/Stat3 is abolished in DCs that were transfected with Socs3 short interfering RNA (siRNA). When mice CD4(+)CD45 RA(+) T cells were co-cultured with PF-treated DCs stimulated with/without DNCB, the gene expression of the Th17 cell markers such as retinoic acid-related orphan nuclear hormone receptor γt (RORγt), IL-17A, and IL-23R decreased, in accordance with the less secretions of IL-17 and IL-23 in vitro and in vivo. Finally, the suppressed Th17 differentiation induced by PF can be abolished by additional recombinant mouse IL-6. Our results suggest that the anti-inflammatory mechanisms introduced by depletion of Socs3 expression or inactivation of the negative regulator such as Socs3 may represent a promising strategy for the prevention of ACD.

Contact dermatitis: in pursuit of sensitizer's molecular targets through proteomics

Protein haptenation, i.e., the modification of proteins by small reactive chemicals, is the key step in the sensitization phase of allergic contact dermatitis (ACD). Despite the research effort in past decades, the identification of immunogenic hapten-protein complexes that trigger a relevant pathogenic immune response in ACD, as well as the haptenation reaction molecular site, and the elements of a potentially conditioning environment during each of these stages, remain poorly understood. These questions led us to employ a proteomics-based approach to identify modified proteins in the dendritic-like cell line THP-1 sensitized with fluorescein isothiocyanate (FITC), through a combination of 2D-gel electrophoresis, nano-LC and mass spectrometry. A specific set of 39 targeted proteins was identified and comprised proteins from various cellular locations and biological functions. One of FITC targets was identified as MLK, a member of the mixed-lineage kinase family known to act as a mitogen-activated protein kinase kinase kinase and to control the activity of specific mitogen-activated protein kinase pathways, namely p38 and JNK pathways. Haptenated in the vicinity of its active site, our results point to MLK being a relevant target due to a consistent non-activation at early time points of these pathways upon FITC sensitization in THP-1 cells. Moreover, FITC pre-treatment significantly decrease phospho-p38 and phospho-JNK levels induced upon exposure to a classical activator such as lipopolysaccharide or to the sensitizer 2,4-dinitrofluorobenzene. Overall, our data point to specific amino acid residues haptenation within critical proteins as the key step in the subsequent signaling pathways modulation responsible for DC activation and maturation events.

Evaluation of a High-Throughput Peptide Reactivity Format Assay for Assessment of the Skin Sensitization Potential of Chemicals

The direct peptide reactivity assay (DPRA) is a validated method for in vitro assessment of the skin sensitization potential of chemicals. In the present work, we describe a peptide reactivity assay using 96-well plate format and systematically identified the optimal assay conditions for accurate and reproducible classification of chemicals with known sensitizing capacity. The aim of the research is to ensure that the analytical component of the peptide reactivity assay is robust, accurate, and reproducible in accordance with criteria that are used for the validation of bioanalytical methods. Analytical performance was evaluated using quality control samples (QCs; heptapeptides at low, medium, and high concentrations) and incubation of control chemicals (chemicals with known sensitization capacity, weak, moderate, strong, extreme, and non-sensitizers) with each of three synthetic heptapeptides, viz Cor1-C420 (Ac-NKKCDLF), cysteine- (Ac-RFAACAA), and lysine- (Ac-RFAAKAA) containing heptapeptides. The optimal incubation temperature for all three heptapeptides was 25°C. Apparent heptapeptide depletion was affected by vial material composition. Incubation of test chemicals with Cor1-C420, showed that peptide depletion was unchanged in polypropylene vials over 3-days storage in an autosampler but this was not the case for borosilicate glass vials. For cysteine-containing heptapeptide, the concentration was not stable by day 3 post-incubation in borosilicate glass vials. Although the lysine-containing heptapeptide concentration was unchanged in both polypropylene and borosilicate glass vials, the apparent extent of lysine-containing heptapeptide depletion by ethyl acrylate, differed between polypropylene (24.7%) and glass (47.3%) vials. Additionally, the peptide-chemical complexes for Cor1-C420-cinnamaldehyde and cysteine-containing heptapeptide-2, 4-dinitrochlorobenzene were partially reversible during 3-days of autosampler storage. These observations further highlight the difficulty in adapting in vitro methods to high-throughput format for screening the skin sensitization potential of large numbers of chemicals whilst ensuring that the data produced are both accurate and reproducible.

Molecular Mechanisms of Nickel Allergy

Allergic contact hypersensitivity to metals is a delayed-type allergy. Although various metals are known to produce an allergic reaction, nickel is the most frequent cause of metal allergy. Researchers have attempted to elucidate the mechanisms of metal allergy using animal models and human patients. Here, the immunological and molecular mechanisms of metal allergy are described based on the findings of previous studies, including those that were recently published. In addition, the adsorption and excretion of various metals, in particular nickel, is discussed to further understand the pathogenesis of metal allergy.

Novel concept of iSALT (inducible skin-associated lymphoid tissue) in the elicitation of allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most common inflammatory skin diseases, which is classified as a delayed-type hypersensitivity immune response. The development of ACD is divided into two phases: sensitization and elicitation. In the sensitization phase, antigen-specific effector T cells are induced in the draining lymph nodes by antigen-captured cutaneous dendritic cells (DCs) that migrate from the skin. In the elicitation phase, the effector T cells are activated in the skin by antigen-captured cutaneous DCs and produce various chemical mediators, which create antigen-specific inflammation. In this review, we discuss the recent advancements in the immunological mechanisms of ACD, focusing on the mechanisms in the elicitation phase. The observations of elicitation of CHS lead to the emerging novel concept of iSALT (inducible skin-associated lymphoid tissue).

Oral Administration of Achyranthis radix Extract Prevents TMA-induced Allergic Contact Dermatitis by Regulating Th2 Cytokine and Chemokine Production in Vivo

Allergic contact dermatitis (ACD) remains a major skin disease in many countries, necessitating the discovery of novel and effective anti-ACD agents. In this study, we investigated the preventive effects of Achyranthis radix extract (AcRE) on trimellitic anhydride (TMA)-induced dermatitis and the potential mechanism of action involved. Oral administration of AcRE and prednisolone (PS) significantly suppressed TMA-induced increases in ear and epidermal thickness, and IgE expression. In addition, abnormal expression of IL-1β and TNF-α protein and mRNA was also significantly attenuated by oral administration of AcRE. Treatment with AcRE also significantly suppressed TMA-induced IL-4 and IL-13 cytokines and mRNA expression in vivo. Moreover, AcRE strongly suppressed TMA-induced IL-4 and IL-5 production in draining lymph nodes, as well as OVA-induced IL-4 and IL-5 expression in primary cultured splenocytes. Interestingly, AcRE suppressed IL-4-induced STAT6 phosphorylation in both primary cultured splenocytes and HaCaT cells, and TMA-induced GATA3 mRNA expression ex vivo. AcRE also suppressed TMA-mediated CCL11 and IL-4-induced CCL26 mRNA expression and infiltration of CCR3 positive cells. The major compounds from AcRE were identified as gentisic acid (0.64 ± 0.2 μg/g dry weight of AcRE), protocatechuic acid (2.69 ± 0.1 μg/g dry weight of AcRE), 4-hydroxybenzoic acid (5.59 ± 0.3 μg/g dry weight of AcRE), caffeic acid (4.21 ± 0.1 μg/g dry weight of AcRE), and ferulic acid (14.78 ± 0.4 ± 0.3 μg/g dry weight of AcRE). Taken together, these results suggest that AcRE has potential for development as an agent to prevent and treat allergic contact dermatitis.

Analysis of odour compounds from scented consumer products using gas chromatography-mass spectrometry and gas chromatography-olfactometry

Scented consumer products are being bought in increasing amounts and gaining more popularity. There is, however, relatively little information available about their ingredients, emissions and allergenic potential. Frequently, a mixture of different fragrance substances and not solely an individual substance contributes to the overall desired smell. The aim of this study was to investigate the odorous volatile organic compounds (OVOCs) in consumer products containing fragrances. Over 44 products were selected: various scented candles, printing products with different scent types and other products types particularly meant to be used indoors. Measurements were carried out in a desiccator. Air samples were collected on thermal desorption tubes to determine the released fragrance substances by means of gas chromatography-mass spectrometry (GC-MS). Moreover, gas chromatography-olfactometry (GC-O) was used to obtain sensory data and to ensure no important odorant was overlooked. Using both methods it was possible to distinguish between odour active and inactive compounds and subsequently to identify almost 300 different odorants across all scented products. Besides the advantage of differentiation, as the human nose is a very sensitive detector, GC-O was found to be a useful tool for detecting traces and chosen target compounds. One focus in this study lay on the 26 EU-regulated fragrance allergens to prove their relevance in scented consumer goods. In total, 18 of them were identified, with at least one substance being present in almost every product. Benzyl alcohol, cinnamaldehyde, citronellol, eugenol, linalool and limonene were the prevalently detected allergens. Particularly linalool and limonene were observed in over 50% of the products. In addition, eugenol appeared to be one of the most frequently detected compounds in trace-level concentrations in the candle emissions.

Nickel Allergy Is a Risk Factor for Endometriosis: An 11-Year Population-Based Nested Case-Control Study

BACKGROUND

A cross-sectional study has reported that nickel allergy is associated with endometriosis. However, causal studies of this association are limited.

OBJECTIVE

The objective of this study was to compare the prevalence of nickel allergy in women with and without endometriosis.

METHODS

We used a National Health Insurance Service (NHIS) sample cohort dataset that included approximately 1 million individuals from South Korea; the data were obtained between January 01, 2002, and December 31, 2013. We selected the endometriosis group according to diagnosis code (N80.X), surgery codes, and drug codes during the years 2009~2013. The controls were randomly matched to the endometriosis patients at a ratio of 4:1 by age and socioeconomic status. Patients with nickel allergy were defined in the cohort dataset as those with a simultaneous diagnosis code (L23.0) and patch test code during 2002~2008.

RESULTS

In total, 4,985 women were selected from the NHIS cohort database and divided into an endometriosis group (997 women) and a control group (3,988 women). The number of patients with nickel allergy in the endometriosis group was eight (0.8%), and that in the control group was thirteen (0.3%). After adjustment for age and socioeconomic status, the rate of nickel allergy in was higher in the endometriosis group than in the control group [odds ratio: 2.474; 95% confidence interval: 1.023~5.988; p = 0.044].

CONCLUSIONS

We found that nickel allergy is a risk factor for endometriosis.

Probabilistic hazard assessment for skin sensitization potency by dose-response modeling using feature elimination instead of quantitative structure-activity relationships

Supervised learning methods promise to improve integrated testing strategies (ITS), but must be adjusted to handle high dimensionality and dose-response data. ITS approaches are currently fueled by the increasing mechanistic understanding of adverse outcome pathways (AOP) and the development of tests reflecting these mechanisms. Simple approaches to combine skin sensitization data sets, such as weight of evidence, fail due to problems in information redundancy and high dimensionality. The problem is further amplified when potency information (dose/response) of hazards would be estimated. Skin sensitization currently serves as the foster child for AOP and ITS development, as legislative pressures combined with a very good mechanistic understanding of contact dermatitis have led to test development and relatively large high-quality data sets. We curated such a data set and combined a recursive variable selection algorithm to evaluate the information available through in silico, in chemico and in vitro assays. Chemical similarity alone could not cluster chemicals' potency, and in vitro models consistently ranked high in recursive feature elimination. This allows reducing the number of tests included in an ITS. Next, we analyzed with a hidden Markov model that takes advantage of an intrinsic inter-relationship among the local lymph node assay classes, i.e. the monotonous connection between local lymph node assay and dose. The dose-informed random forest/hidden Markov model was superior to the dose-naive random forest model on all data sets. Although balanced accuracy improvement may seem small, this obscures the actual improvement in misclassifications as the dose-informed hidden Markov model strongly reduced " false-negatives" (i.e. extreme sensitizers as non-sensitizer) on all data sets.

Histopathology and immune histochemistry of red tattoo reactions. Interface dermatitis is the lead pathology, with increase in T-lymphocytes and Langerhans cells suggesting an allergic pathomechanism

BACKGROUND

The majority of tattoo reactions are affiliated to red pigmented areas and often suspected to be allergic in nature. A sizeable series of biopsies of such reactions has not previously been performed. The aim of this study was to type and grade epidermal and dermal changes in tattoo reactions to red/red nuances by microscopy and immunochemistry relevant for the assessment of a possible allergic pathomechanism.

METHODS

Skin biopsies were taken from red tattoo reactions, graded by conventional microscopy and stained for T and B-lymphocytes, Langerhans cells, macrophages and tumour necrosis factor (TNF)-α.

RESULTS

The study included 19 biopsies from 19 patients. The culprit colours were red/pink (n = 15) and purple/bordeaux (n = 4). Interface dermatitis was clearly the lead pathology found in 78% of samples, overlapped with granulomatous (in 32%) and pseudolymphomatous reaction patterns (in 32%). Epidermal hyperkeratosis (in 89%) was common as was leakage of red pigment across the dermo-epidermal junction, with transepidermal elimination (in 28%). The dermal cellular infiltration was dominated by T-lymphocytes (in 100%), Langerhans cells (in 95%) and macrophages (in 100%). TNF-α was common.

CONCLUSION

The predominant histological pattern of chronic tattoo reactions in red/red nuances is interface dermatitis. T-lymphocytes and Langerhans cells are increased suggesting an allergic pathomechanism. TNF-α may contribute to reactions. In many cases, overlapping reactive patterns were identified.

Review of allergic contact dermatitis: Scratching the surface

Contact dermatitis-including allergic contact dermatitis (ACD)-n and results in over four million lost work days per year in the United States alone. ACD is a classic example of a type IV delayed hypersensitivity reaction, and represents a significant burden on the health system, economy, and patient quality of life. Thorough history taking, clinical examination, histologic evaluation, and patch testing are keys to diagnosing contact dermatitis. Patch testing, especially with comprehensive and customized panels based on the patient’s exposure history, is particularly useful in identifying potential allergens in the case of allergic contact dermatitis. ACD management requires a combination of direct medical intervention, patient education, and appropriate environmental modification to prevent exposure to offending allergens in the home or workplace. Continuing advances in the study of ACD has led to an increased understanding of the disease processes, new methods for diagnosis, and improved management. This article reviews ACD-aiming to connect recent investigational data with the current clinical understanding of disease pathophysiology, diagnostic techniques, and management strategies.

Phenolic composition and effects on allergic contact dermatitis of phenolic extracts Sapium sebiferum (L.) Roxb. leaves

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Sapium sebiferum (L.) Roxb. have long been used in Traditional Chinese Medicine (TCM) for the treatment of eczema, shingles, edema, swelling, ascites, scabs, and snakebites, among other maladies. The present study was an outreach research behind our previous study and aimed to analyze the chemical composition of phenolic extracts of Sapium sebiferum leaves and evaluate their effects on allergic contact dermatitis (ACD).

MATERIALS AND METHODS

The main compounds of Sapium sebiferum leaves were identified using UPLC-PDA method by comparing retention times and UV-vis spectra with those of reference standards. Their effects on ACD were examined using a dinitrofluorobenzene (DNFB) induced mice ACD model. Chemical parameters including reactive oxygen species (ROS), MDA and GSH/T-GSH ratio of ear tissue were also determined.

RESULTS

Seven compounds including gallic acid, ellagic acid, hyperin, isoquercitrin, astragalin, quercetin and kaempferol were identified from Sapium sebiferum leaves, and their contents were also determined; ellagic acid, isoquercitrin and astragalin were in the majority. Phenolic extracts of Sapium sebiferum leaves exhibited dose-dependent inhibitory effects on edema induced by ACD at doses of 0.03, 0.1 and 0.3 mg/ear. The application of extracts also decreased ROS and MDA levels and increased GSH/T-GSH ratio of ear tissue.

CONCLUSION

The present study demonstrated that the bioactivity of Sapium sebiferum leaves may be due to the existence of the identified phenolic components, and several high polarity compounds were also active. The beneficial effect of Sapium sebiferum leaves on skin diseases is based on its antioxidant activity or effects on antioxidant defense system.

Encapsulation of hydrophobic allergens into nanoparticles improves the in vitro immunological diagnosis of allergic contact dermatitis

The diagnosis of allergic contact dermatitis (ACD) relies on in vivo patch testing. In vitro immunological assays based on the characterization of circulating allergen-specific memory T cells represent a promising alternative to patch testing. However, their development is hampered by the technical challenge of assessing hydrophobic allergens in serum-based assays. In this study, we show that the encapsulation of fragrance mix 1 (FMI, a mixture of 8 hydrophobic allergens) into poly-ε-caprolactone nanoparticle (NP) vectors: (1) dramatically increases the solubilization of allergens in conventional cell culture media and (2) allows for a robust in vitro reactivation of allergen-specific T cells in large numbers of fragrance allergic patients. Therefore, the encapsulation of hydrophobic allergens into NP vectors opens new avenues to improve the in vitro immunobiological diagnosis of ACD.

FROM THE CLINICAL EDITOR

Allergic Contact Dermatitis (ACD) is a delayed-type hypersensivity reaction prevalent in many individuals. Currently, skin patch testing has been the mainstay for diagnosis clinically. In this study, the authors described an improvement to in vitro immunological assays measuring circulating allergen-specific memory T cells, using nanoparticle vectors. The positive data might provide an exciting alternative to current practice of patch-testing.

Stat5 gene dosage in T cells modulates CD8+ T-cell homeostasis and attenuates contact hypersensitivity response in mice

BACKGROUND

Contact hypersensitivity assay (CHS) faithfully models human allergies. The Stat5 transcription factors are essential for both lymphocyte development and acute immune responses. Although consequences of Stat5 ablation and transgenic overexpression for the lymphocyte development and functions have been extensively studied, the role of Stat5 gene dosage in contact allergies has not been addressed.

OBJECTIVE

We investigated the effect of Stat5 gene dosage modulation in contact allergies using CHS in mice.

METHODS

Transgenic animals heterozygous for the germline Stat5 null allele were subjected to CHS. To dissect cell type sensitive to Stat5 gene dosage, animals with Stat5 haplo-insufficiency in T cells, where one Stat5 allele was removed by Lck-Cre-mediated deletion (Stat5(ΔT/+)), were tested by CHS. Frequency of T cells, B cells, and monocytes were analyzed in Stat5(ΔT/+) and wild-type animals by flow cytometry. Proliferation of Stat5(ΔT/+) CD8(+) T cells was studied in vitro by stimulation with IL-4 and IL-2 cytokines, and changes in the expression of Stat5 target genes were assayed by quantitative real-time PCR assay.

RESULT

Haplo-insufficiency of Stat5 in T cells leads to the reduction in CD8(+) T cells in all lymphoid organs and attenuates CHS response. Stat5(ΔT/+) CD8(+) T cells failed to fully activate Stat5-dependent expression of cell cycle/survival target genes, such as Bcl2 and Pim1, and to proliferate efficiently in response to IL-2 and IL-4 cytokine.

CONCLUSION

Our data identify Stat5 as a dose-dependent regulator of CD8(+) T-cell functions in contact allergies and suggest that modulation of Stat5 dosage could be used to target contact allergies in humans.

Total glucosides of paeony inhibit the inflammatory responses of mice with allergic contact dermatitis by restoring the balanced secretion of pro-/anti-inflammatory cytokines

The present study aimed to investigate the regulation exerted by the total glucosides of paeony (TGP) on the production of interleukin-2 (IL-2), IL-4, IL-10 and IL-17 in the serum and lymphocytes of mice with allergic contact dermatitis (ACD). ACD in mice was induced by the repeated application of 2,4-dinitrochlorobenzene (DNCB) to their skins. The mice were orally administered TGP (35, 70, and 140mg/kg/d) and prednisone (Pre, 5mg/kg/d) from day 1 to day 7 after immunization. The inflammatory responses were evaluated by ear swelling and histological examination. Thymocyte proliferation was assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide assay. The cytokine production in the serum and lymphocytes supernatant was measured by enzyme-linked immunosorbent assay. The results indicated that the topical application of DNCB to the skin provoked obvious inflammatory responses. The oral administration of TGP (70 and 140mg/kg/d) and Pre (5mg/kg/d) significantly inhibited skin inflammation, decreased the thymus and spleen indices, and inhibited thymocyte proliferation in mice treated with DNCB. Further study indicated that TGP increased IL-4 and IL-10 production but decreased the production of IL-2 and IL-17 in the serum and lymphocyte supernatant. The correlation analysis suggested significantly positive correlations between IL-2 and IL-17 production and the severity of skin inflammation, whereas negative correlations were obtained for IL-4 and IL-10 production and skin inflammation. In summary, these results suggest that the therapeutic effects of TGP on ACD may result from its regulation of the imbalanced secretion of IL-2/IL-4 and IL-10/IL-17.

Oxidative stress-dependent activation of the eIF2α–ATF4 unfolded protein response branch by skin sensitizer 1-fluoro-2,4-dinitrobenzene modulates dendritic-like cell maturation and inflammatory status in a biphasic manner [corrected]

The pathogenesis of allergic contact dermatitis, the most common manifestation of immunotoxicity in humans, is intimately connected to hapten-induced maturation of dendritic cells (DC). The molecular mechanisms driving this maturational program are not completely known; however, initial danger signals such as the generation of reactive oxygen species (ROS) were shown to play a critical role. Recent evidence linking ROS production, endoplasmic reticulum (ER) stress, and the pathogenesis of several inflammatory diseases led us to analyze, in the present work, the ability of the skin sensitizer 1-fluoro-2,4-dinitrobenzene (DNFB) to evoke ER stress in DC-like THP-1 cells and the concomitant consequences to their immunobiology. We found that DNFB triggers a ROS-dependent activation of the PERK-eIFα-ATF4 unfolded protein response (UPR) branch conferring cytoprotection and modulating the maturation/proinflammatory cell status in a biphasic manner. Early DNFB induction of ATF4 positively modulates autophagy-related genes MAP1LC3B and ATG3 and stabilizes the transcription factor Nrf2, causing a strong induction of the HMOX1-detoxifying gene. Moreover, we observed that in a first phase, DNFB-induced ATF4 upregulates IL8 mRNA levels while blocking CD86, IL1B, IL12B, and CXL10 transcription. Later, following ATF4 decay, HMOX1 and IL8 transcription drastically decrease and CD86, IL1B, and Il12B are upregulated. Overall, our results evidence a connection between sensitizer-induced redox imbalance and the establishment of ER stress in DC-like cells and provide new insights into the role of UPR effectors such as ATF4 to the complex DC maturational program.

Adaptation in the innate immune system and heterologous innate immunity

The innate immune system recognizes deviation from homeostasis caused by infectious or non-infectious assaults. The threshold for its activation seems to be established by a calibration process that includes sensing of microbial molecular patterns from commensal bacteria and of endogenous signals. It is becoming increasingly clear that adaptive features, a hallmark of the adaptive immune system, can also be identified in the innate immune system. Such adaptations can result in the manifestation of a primed state of immune and tissue cells with a decreased activation threshold. This keeps the system poised to react quickly. Moreover, the fact that the innate immune system recognizes a wide variety of danger signals via pattern recognition receptors that often activate the same signaling pathways allows for heterologous innate immune stimulation. This implies that, for example, the innate immune response to an infection can be modified by co-infections or other innate stimuli. This "design feature" of the innate immune system has many implications for our understanding of individual susceptibility to diseases or responsiveness to therapies and vaccinations. In this article, adaptive features of the innate immune system as well as heterologous innate immunity and their implications are discussed.

Hyaluronan regulates chemical allergen-induced IL-18 production in human keratinocytes

Interleukin-18 (IL-18) has been shown to play a key proximal role in the induction of allergic contact dermatitis. Low molecular weight hyaluronan (LMWHA), an endogenous molecule and a member of the so-called damage associated molecular patterns (DAMPs), has been suggested to elicit immune-stimulatory effects. The purpose of this study was to examine the role of hyaluronan (HA) degradation in IL-18 production in human keratinocytes following stimulation with the contact sensitizers 2,4-dinitrochlorobenzene (DNCB) and PPD. IL-18 production in the human keratinocyte cell line NCTC2544 was measured by ELISA, whereas changes in HA metabolism were determined by Real-time PCR and immunofluorescence. Both contact allergens were able to enhance hyaluronidase (HYAL) 1 and 2 expression inducing HA degradation. Modulation of HA production, by HYAL or aristolochic acid pre-treatment, resulted in a significant reduction of contact allergen-induced IL-18 production. Oxidative stress appears to be the initial step in KC activation, as all the sequels of events can be blocked using antioxidants. This is the first indication that LMWHA can act as a DAMP in keratinocytes. In conclusion LMWHA fragments are important mediators in the process of contact sensitisation leading to IL-18 dependent responses.

Pathogenesis and diagnosis of contact dermatitis: Applications of reflectance confocal microscopy

Contact dermatitis (CD) is the most common professional skin disease, with frequencies ranging from 24 to 170 every 100000 individuals. Approximately 20% of the United States population suffers from CD. CD can be classified according to its origin and severity. ICD stands for irritant CD, whereas ACD means allergic CD. Their clinical presentation includes acute, sub-acute and chronic eczema. Despite their different origin, ICD and ACD often present similar clinical and histologic findings. The current gold standard for diagnosis is patch-testing. However, patch-testing is being questioned in terms of validity and reproducibility, as it relies heavily on the skill of the observer. Real-time reflectance confocal microscopy is a non-invasive imaging technique that bears strong promise for the study of CD, and it enables the evaluation of cellular and subcellular changes over time with similar resolution compared to that of conventional histology.

The balance between pro- and anti-inflammatory cytokines is crucial in human allergic contact dermatitis pathogenesis: the role of IL-1 family members

The interleukin (IL)-1 family includes 11 members that are important in inflammatory processes. It includes various agonists and two antagonists, IL-1Ra and IL-36Ra. Our aim was to investigate whether the IL-1 family is involved in allergic contact dermatitis (ACD). The expression of IL-1 family members was evaluated by PCR and immunohistochemistry in the positive patch test reaction site (involved skin) and in the uninvolved skin of ACD patients. We also examined these cytokines in an ex vivo model of ACD. The antagonistic activity of IL-36Ra was evaluated by injecting recombinant IL-36Ra in uninvolved skin biopsies of ACD patients. IL-1Ra and IL-36Ra expression was quantified in mononuclear cells of nickel-sensitized patients challenged in vitro with nickel. IL-33 involvement in ACD was investigated by intra-dermal injection of anti-IL-33 in the uninvolved skin of patients ex vivo. Results showed that IL-1β, IL-1Ra, IL-36α, IL-36β, IL-36γ and IL-33 expression, but not IL-36Ra expression, was enhanced in ACD-involved skin. Immunohistochemical analysis and ex vivo skin cultures confirmed these results. Injection of anti-IL-33 in ACD-uninvolved skin inhibited IL-8 expression, whereas IL-36Ra inhibited IL-36α, IL-36β, IL-36γ and IL-8 expression. Nickel induced IL-1Ra expression in lymphocytes of nickel-sensitized patients. Hence, various IL-1 agonists and antagonists may be involved in ACD pathogenesis.