Pathomechanisms of Contact Sensitization

Neuropeptide FF prevented histamine- or chloroquine-induced acute itch behavior through non-NPFF receptors mechanism in male mice

The neuropeptide FF (NPFF) system regulates various physiological and pharmacological functions, particularly pain modulation. However, the modulatory effect of NPFF system on itch remains unclear. To investigate the modulatory effect and functional mechanism induced by NPFF system on acute itch, we examined the effects of supraspinal administration of NPFF and related peptides on acute itch induced by intradermal (i.d.) injection of histamine or chloroquine in male mice. Our results indicated that intracerebroventricular (i.c.v.) administration of NPFF dose-dependently prevented histamine- or chloroquine-induced acute itch behaviors. In addition, the modulatory effect of NPFF was not affected by the selective NPFF receptor antagonist RF9. Furthermore, we investigated the effects of NPVF and dNPA, the selective agonists of NPFF1 and NPFF2 receptors respectively, on the acute itch. The results demonstrated that both NPFF agonists effectively prevented acute itch induced by histamine or chloroquine in a manner similar to NPFF, and their effects were also not modified by RF9. To further investigate the possible mechanism of the NPFF receptors agonists, the NPFF-derived analogues [Phg8]-NPFF and NPFF(1-7)-NH2 that could not activate NPFF receptors in cAMP assays were subsequently tested in the acute itch model. Interestingly, [Phg8]-NPFF, but not NPFF(1-7)-NH2, prevented acute itch behavior after i.c.v. administration. In conclusion, our findings reveal that NPFF and related peptides prevent histamine- and chloroquine-induced acute itch through a NPFF receptor-independent mechanism. And it was revealed that the C-terminal phenyl structure of NPFF may play a crucial role in these modulatory effects on acute itch.

Comorbid Scenarios in Contact Dermatitis: Atopic Dermatitis, Irritant Dermatitis, and Extremes of Age

Contact dermatitis (allergic and irritant) occurs when the skin encounters haptens that elicit a T cell-mediated hypersensitivity reaction (allergic) or a nonimmunologic, toxic reaction (irritant). Patch testing is the reference standard for diagnosing allergic contact dermatitis (ACD), although positive results are not always relevant. Therefore, the definitive diagnosis of ACD requires an astute clinician able to connect the results of patch testing appropriately with the clinical history and the cutaneous examination findings. Comorbid conditions such as atopic dermatitis can confound the accurate diagnosis of ACD because of the similarities in clinical presentation. Furthermore, both extremes of age can further challenge the diagnostic specificity of ACD owing to the maturing immune system and the space limitations present when the very young are patch tested. The goal of this Continuing Medical Education article is to discuss the challenges of diagnosing ACD in patients with unique comorbidities such as atopic dermatitis, given the morphologic similarities, and when to patch test these patients. Diagnosis of ACD will also be discussed in very young patients with a focus on patch test allergen selection despite the limited geographic space. The most common allergens reported in very young and old patients will also be discussed.

In Vitro Prediction of Skin-Sensitizing Potency Using the GARDskin Dose-Response Assay: A Simple Regression Approach

Toxicological assessments of skin sensitizers have progressed towards a higher reliance on non-animal methods. Current technological trends aim to extend the utility of non-animal methods to accurately characterize skin-sensitizing potency. The GARDskin Dose-Response assay has previously been described; it was shown that its main readout, cDV0 concentration, is associated with skin-sensitizing potency. The ability to predict potency from cDV0 in the form of NESILs derived from LLNAs or human NOELs was evaluated. The assessment of a dataset of 30 chemicals showed that the cDV0 values still correlated strongly and significantly with both LLNA EC3 and human NOEL values (ρ = 0.645-0.787 [p < 1 × 10-3]). A composite potency value that combined LLNA and human potency data was defined, which aided the performance of the proposed model for the prediction of NESILs. The potency model accurately predicted sensitizing potency, with cross-validation errors of 2.75 and 3.22 fold changes compared with NESILs from LLNAs and humans, respectively. In conclusion, the results suggest that the GARDskin Dose-Response assay may be used to derive an accurate quantitative continuous potency estimate of skin sensitizers.

Application of Luteolin in Neoplasms and Nonneoplastic Diseases

Researchers are amazed at the multitude of biological effects of 3',4',5,7-tetrahydroxyflavone, more commonly known as luteolin, as it simultaneously has antioxidant and pro-oxidant, as well as antimicrobial, anti-inflammatory, and cancer-preventive, properties. The anticancer properties of luteolin constitute a mosaic of pathways due to which this flavonoid influences cancer cells. Not only is it able to induce apoptosis and inhibit cancer cell proliferation, but it also suppresses angiogenesis and metastasis. Moreover, luteolin succeeds in cancer cell sensitization to therapeutically induced cytotoxicity. Nevertheless, apart from its promising role in chemoprevention, luteolin exhibits numerous potential utilizations in patients with conditions other than neoplasms, which include inflammatory skin diseases, diabetes mellitus, and COVID-19. This review aims to present the multidimensionality of the luteolin's impact on both neoplastic and nonneoplastic diseases. When it comes to neoplasms, we intend to describe the complexity of the molecular mechanisms that underlay luteolin's anticancer effectiveness, as well as to prove the usefulness of integrating this flavonoid in cancer therapy via the analysis of recent research on breast, colon, and lung cancer. Regarding nonneoplastic diseases, this review aims to emphasize the importance of researching the potential of luteolin in areas such as diabetology, virology, and dermatology as it summarizes the most important discoveries in those fields regarding its application.

N-Methyl-(2S,4R)-trans-4-hydroxy-L-proline isolated Sideroxylon obtusifolium attenuates TPA-induced irritant contact dermatitis in mice

Dermatitis is defined as a set of inflammatory diseases that affect the skin, with varied causes. Among the different types of dermatitis, contact dermatitis is the most prevalent. Although the current therapy is often effective, it is associated with adverse effects and the possibility of drug tolerance. N-Methyl-(2S, 4R)-trans-4-hydroxy-L-proline is a L-proline amino acid derivative found in the leaves of Sideroxylon obtusifolium, a species traditionally used to treat inflammatory diseases. The aim of this study was to investigate the topical anti-inflammatory effect of N-methyl-(2S, 4R)-trans-4-hydroxy-L-proline (NMP) in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced irritant contact dermatitis in mice. Topically administered NMP, at doses of 0.03 - 0.50 mg/ear, reduced TPA-induced ear edema and neutrophil migration, as evidenced by low tissue myeloperoxidase activity and verified by histological examination. In addition, NMP (0.06 mg/ear) reduced tissue levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, INF-γ and MCP-1) and of the anti-inflammatory cytokine IL-10, and reduced gene expression of TNF-α, IL-6 and IL-1β increased by TPA. The data suggest that N-methyl-(2S, 4R)-trans-4-hydroxy-L-proline acts as a topical anti-inflammatory agent that decreases the expression of inflammatory cytokines, making it useful for the treatment of skin inflammation. Further investigations are necessary for its development as a therapeutic agent.

Endoplasmic reticulum stress and the inflammatory response in allergic contact dermatitis

Maintaining homeostasis is central to organismal health. Deviation is detected by a variety of sensors that react to alarm signals arising from injury, infection, and other inflammatory triggers. One important element of this alarm system is the innate immune system, which recognizes pathogen-/microbe- or damage-associated molecular patterns via pattern recognition receptors localized in the cytosol or in membranes of innate immune cells such as macrophages, dendritic cells, and mast cells but also of T cells, B cells, and epithelial cells. Activation of the innate immune system results in inflammation and is a pre-requisite for activation of the adaptive immune system. Another important element is represented by the unfolded protein response (UPR), a stress response of the endoplasmic reticulum. The UPR regulates proteostasis and also contributes to the course of inflammatory diseases such as cancer, diabetes, obesity, and neurodegenerative diseases. In addition, the UPR is instrumental in allergic contact dermatitis. This inflammatory skin disease, affecting 5-10% of the population, is caused by T cells recognizing low-molecular weight organic chemicals and metal ions. In this mini-review, we discuss the orchestration of inflammatory responses by the interplay of the innate immune system with cellular stress responses in allergic contact dermatitis, with a focus on the UPR.

Tolerance to 2,4-Dinitrofluorobenzene‒Induced Contact Hypersensitivity Is Mediated by CD73-Expressing Tissue-homing Regulatory T Cells

Regulatory T cells (Tregs) express CD73, an ectonucleotidase that converts adenosine (Ado) monophosphate to Ado, which has been shown to suppress immune reactions. To investigate the role(s) of CD73⁺ Tregs during the induction of tolerance, we used a 2,4-dinitrofluorobenzene‒driven contact hypersensitivity model, in which tolerance can be induced by pretreating wild type mice with 2,4-dinitrothiocyanobenzene. CD73-deficient mice were unable to acquire tolerance. Likewise, transfer of CD73^‒/‒ Tregs failed to suppress 2,4-dinitrofluorobenzene‒induced ear swelling in wild type mice, whereas transfer of wild type‒derived Tregs into CD73^‒/‒ mice re-established tolerance. This indicates a crucial role of CD73⁺ Tregs for skin-induced tolerance. Furthermore, we found that 2,4-dinitrothiocyanobenzene induces more activated CD73⁺ tissue-homing Tregs (marked by Ki-67, CTLA4, CCR4, CD103, CCR6, and CD49b expression) in draining lymph nodes and blood, eventually accumulating in the skin. The application of anti-CD73 antibodies that block CD73-derived Ado production as well as the injection of Ado deaminase, which degrades Ado in tissues, abrogated tolerance induction. Thus, our data indicate that CD73⁺ Ado-producing Tregs are crucial for the regulation of contact hypersensitivity reactions and tolerance induction in the skin and that manipulating the function(s) of CD73 in tissues may offer a tool to influence autoimmunity and inflammation in vivo.

Mechanisms of unconventional CD8 Tc2 lymphocyte induction in allergic contact dermatitis: Role of H3/H4 histamine receptors

Histamine (HA) is a potent mediator that plays a central role in inflammation and allergy, acting through four G-protein-coupled receptors (i.e. H₁–H₄). HA is an accepted promoter of type 2 immunity in CD4⁺ T cells during hypersensitivity. Previously, we demonstrated that HA can promote antigen cross-presentation, inducing the activation of antigen-specific CD8⁺ T cells in an asthmatic murine model. Non-classical CD8+ T-cell profiles, such as Tc2 or Tc17, are associated with allergic disease persistence and chronicity. In this paper, we focus on the role of the H₃ receptor (H₃R) and the H₄ receptor (H₄R) in the development of allergic contact dermatitis. We were able to show that induction of the type 2 profiles associated with interleukin 13 production, both by CD4 and CD8 lymphocytes, depend on the interaction of HA with H₃R and H₄R. Blocking both receptors using the selective H₃/H₄ receptor antagonist thioperamide or the selective H₄R ligand JNJ777120 reduces the inflammatory response, inducing an immunosuppressive profile associated with the increased proportion of FOXp3⁺ regulatory T lymphocytes and CD11b⁺Gr-1⁺ myeloid suppressor cells. Interestingly, in dendritic cells, only H₄R blockade, and not H₃R blockade, is capable of modulating most of the inflammatory effects observed in our model.

Consensus on the Key Characteristics of Immunotoxic Agents as a Basis for Hazard Identification

BACKGROUND

Key characteristics (KCs), properties of agents or exposures that confer potential hazard, have been developed for carcinogens and other toxicant classes. KCs have been used in the systematic assessment of hazards and to identify assay and data gaps that limit screening and risk assessment. Many of the mechanisms through which pharmaceuticals and occupational or environmental agents modulate immune function are well recognized. Thus KCs could be identified for immunoactive substances and applied to improve hazard assessment of immunodulatory agents.

OBJECTIVES

The goal was to generate a consensus-based synthesis of scientific evidence describing the KCs of agents known to cause immunotoxicity and potential applications, such as assays to measure the KCs.

METHODS

A committee of 18 experts with diverse specialties identified 10 KCs of immunotoxic agents, namely, 1) covalently binds to proteins to form novel antigens, 2) affects antigen processing and presentation, 3) alters immune cell signaling, 4) alters immune cell proliferation, 5) modifies cellular differentiation, 6) alters immune cell-cell communication, 7) alters effector function of specific cell types, 8) alters immune cell trafficking, 9) alters cell death processes, and 10) breaks down immune tolerance. The group considered how these KCs could influence immune processes and contribute to hypersensitivity, inappropriate enhancement, immunosuppression, or autoimmunity.

DISCUSSION

KCs can be used to improve efforts to identify agents that cause immunotoxicity via one or more mechanisms, to develop better testing and biomarker approaches to evaluate immunotoxicity, and to enable a more comprehensive and mechanistic understanding of adverse effects of exposures on the immune system. https://doi.org/10.1289/EHP10800.

Synchrotron-based characterization of arthroprosthetic CoCrMo particles in human bone marrow

Particles released from cobalt-chromium-molybdenum (CoCrMo) alloys are considered common elicitors of chronic inflammatory adverse effects. There is a lack of data demonstrating particle numbers, size distribution and elemental composition of bone marrow resident particles which would allow for implementation of clinically relevant test strategies in bone marrow models at different degrees of exposure. The aim of this study was to investigate metal particle exposure in human periprosthetic bone marrow of three types of arthroplasty implants. Periprosthetic bone marrow sections from eight patients exposed to CoCrMo particles were analyzed via spatially resolved and synchrotron-based nanoscopic X-ray fluorescence imaging. These analyses revealed lognormal particle size distribution patterns predominantly towards the nanoscale. Analyses of particle numbers and normalization to bone marrow volume and bone marrow cell number indicated particle concentrations of up to 1 × 10¹¹ particles/ml bone marrow or 2 × 10⁴ particles/bone marrow cell, respectively. Analyses of elemental ratios of CoCrMo particles showed that particularly the particles' Co content depends on particle size. The obtained data point towards Co release from arthroprosthetic particles in the course of dealloying and degradation processes of larger particles within periprosthetic bone marrow. This is the first study providing data based on metal particle analyses to be used for future in vitro and in vivo studies of possible toxic effects in human bone marrow following exposure to arthroprosthetic CoCrMo particles of different concentration, size, and elemental composition. Graphical abstract.

Transient injection site reaction to alirocumab during immune system activation: a case series

Background

Injection site reactions (ISRs) are known side effects of the proprotein convertase subtilisin kexin 9 (PCSK9) inhibitor alirocumab. Transient ISR to alirocumab after a long phase of good tolerability have not been reported previously.

Case summary

A 55-year-old woman (Patient 1) and a 77-year-old man (Patient 2) were treated with alirocumab for the management of dyslipidaemia. Both patients tolerated the treatment without side effects for 7 and 2 months, respectively. After an upper respiratory tract infection in Patient 1 and a first COVID-19 vaccination in Patient 2, both patients suddenly developed ISR with erythema, calor, and itching upon 2 (Patient 1) and 1 (Patient 2) subsequent injection(s), respectively. Symptoms resolved with local steroids, oral antihistamines, and cooling. After termination of the presumed immune system activated state, alirocumab was well tolerated again in both patients without recurrence of any ISR upon repeated applications.

Discussion

These are the first cases to report transient ISR to a PCSK9 inhibitor, possibly triggered by activation of the immune system, after prolonged good tolerability. Based on the transient and benign nature of the reaction, such patients should be encouraged to continue supervised treatment, as tolerability may return after resolution of the pro-inflammatory state.

IRE1 and PERK signaling regulates inflammatory responses in a murine model of contact hypersensitivity

BACKGROUND

Contact sensitizers may interfere with correct protein folding. Generation of un-/misfolded proteins can activate the IRE-1 or PERK signaling pathways initiating the unfolded protein response (UPR) and thereby determine inflammatory immune responses. We have analyzed the effect of sensitizers with different potencies on the induction of UPR activation/inhibition and the subsequent generation of a pro-inflammatory micromilieu in vitro as well as the effect of UPR modulation on the inflammatory response in the murine contact hypersensitivity (CHS) in vivo.

METHODS

Semi-quantitative and quantitative PCR, fluorescence microscopy, ELISA, NF-κB activation and translocation assays, DC/keratinocyte co-culture assay, FACS, and in vivo CHS experiments were performed.

RESULTS

Sensitizers and irritants activate IRE-1 and PERK in murine and human keratinocytes. Synergistic effects occur after combination of different weak sensitizers / addition of irritants. Moreover, tolerogenic dinitrothiocyanobenzene can be converted into a strong sensitizer by pre-activation of the UPR. Blocking UPR signaling results in decreased NF-κB activation and cytokine production in keratinocytes and in activation marker downregulation in a HaCaT/THP-1 co-culture. Interestingly, not only systemic but also topical application of UPR inhibitors abrogates CHS responses in vivo.

CONCLUSION

These observations highlight an important role of the UPR in determination of the inflammatory response in vitro and in vivo further underlining the importance of tissue stress and damage responses in the development of ACD and provide mechanistically based concepts as a basis for the development of new therapeutic approaches to treat allergic contact dermatitis.

Frequencies and TCR Repertoires of Human 2,4,6-Trinitrobenzenesulfonic Acid-specific T Cells

Allergic contact dermatitis is a widespread T cell-mediated inflammatory skin disease, but in vitro monitoring of chemical-specific T cells remains challenging. We here introduce short-term CD154/CD137 upregulation to monitor human T cell responses to the experimental sensitizer 2,4,6-trinitrobenzenesulfonic acid (TNBS). Peripheral blood mononuclear cells (PBMC) from healthy donor buffy coats were TNBS-modified and incubated with unmodified PBMC. After 5 and 16 h, we detected TNBS-specific activated CD154+CD4+ and CD137+CD8+ T cells by multi-parameter flow cytometry, respectively. Activated cells were sorted for restimulation and bulk T cell receptor (TCR) high-throughput sequencing (HTS). Stimulation with TNBS-modified cells (3 mM) induced CD154 expression on 0.04% of CD4+ and CD137 expression on 0.60% of CD8+ memory T cells, respectively (means, n = 11-17 donors). CD69 co-expression argued for TCR-mediated activation, which was further supported by TNBS-specific restimulation of 10/13 CD154+CD4+ and 11/15 CD137+CD8+ T cell clones and lines. Major histocompatibility complex (MHC) blocking antibodies prevented activation, illustrating MHC restriction. The high frequencies of TNBS-specific T cells were associated with distinct common changes in the TCR β-chain repertoire. We observed an overrepresentation of tryptophan and lysine in the complementarity determining regions 3 (CDR3) (n = 3-5 donors), indicating a preferential interaction of these amino acids with the TNBS-induced epitopes. In summary, the detection of TNBS-specific T cells by CD154/CD137 upregulation is a fast, comprehensive and quantitative method. Combined with TCR HTS, the mechanisms of chemical allergen recognition that underlie unusually frequent T cell activation can be assessed. In the future, this approach may be adapted to detect T cells activated by additional chemical sensitizers.

In Vitro Monitoring of Human T Cell Responses to Skin Sensitizing Chemicals-A Systematic Review

Background: Chemical allergies are T cell-mediated diseases that often manifest in the skin as allergic contact dermatitis (ACD). To prevent ACD on a public health scale and avoid elicitation reactions at the individual patient level, predictive and diagnostic tests, respectively, are indispensable. Currently, there is no validated in vitro T cell assay available. The main bottlenecks concern the inefficient generation of T cell epitopes and the detection of rare antigen-specific T cells. Methods: Here, we systematically review original experimental research papers describing T cell activation to chemical skin sensitizers. We focus our search on studies published in the PubMed and Scopus databases on non-metallic allergens in the last 20 years. Results: We identified 37 papers, among them 32 (86%) describing antigen-specific human T cell activation to 31 different chemical allergens. The remaining studies measured the general effects of chemical allergens on T cell function (five studies, 14%). Most antigen-specific studies used peripheral blood mononuclear cells (PBMC) as antigen-presenting cells (APC, 75%) and interrogated the blood T cell pool (91%). Depending on the individual chemical properties, T cell epitopes were generated either by direct administration into the culture medium (72%), separate modification of autologous APC (29%) or by use of hapten-modified model proteins (13%). Read-outs were mainly based on proliferation (91%), often combined with cytokine secretion (53%). The analysis of T cell clones offers additional opportunities to elucidate the mechanisms of epitope formation and cross-reactivity (13%). The best researched allergen was p-phenylenediamine (PPD, 12 studies, 38%). For this and some other allergens, stronger immune responses were observed in some allergic patients (15/31 chemicals, 48%), illustrating the in vivo relevance of the identified T cells while detection limits remain challenging in many cases. Interpretation: Our results illustrate current hardships and possible solutions to monitoring T cell responses to individual chemical skin sensitizers. The provided data can guide the further development of T cell assays to unfold their full predictive and diagnostic potential, including cross-reactivity assessments.

Unique molecular signatures typify skin inflammation induced by chemical allergens and irritants

BACKGROUND

Skin exposure to chemicals may induce an inflammatory disease known as contact dermatitis (CD). Distinguishing the allergic and irritant forms of CD often proves challenging in the clinic.

METHODS

To characterize the molecular signatures of chemical-induced skin inflammation, we conducted a comprehensive transcriptomic analysis on the skin lesions of 47 patients with positive patch tests to reference contact allergens and nonallergenic irritants.

RESULTS

A clear segregation was observed between allergen- and irritant-induced gene profiles. Distinct modules pertaining to the epidermal compartment, metabolism, and proliferation were induced by both contact allergens and irritants; whereas only contact allergens prompted strong activation of adaptive immunity, notably of cytotoxic T-cell responses. Our results also confirmed that: (a) unique pathways characterize allergen- and irritant-induced dermatitis; (b) the intensity of the clinical reaction correlates with the magnitude of immune activation. Finally, using a machine-learning approach, we identified and validated several minimal combinations of biomarkers to distinguish contact allergy from irritation.

CONCLUSION

These results highlight the value of molecular profiling of chemical-induced skin inflammation for improving the diagnosis of allergic versus irritant contact dermatitis.

Evaluation of skin sensitization based on interleukin-2 promoter activation in Jurkat cells

Skin sensitization is an allergic reaction caused by certain chemical substances, and is an important factor to be taken into consideration when evaluating the safety of numerous types of products. Although animal testing has long been used to evaluate skin sensitization, the recent trend to regulate such testing has led to the development and use of alternative methods. Skin sensitization reactions are summarized in the form of an adverse outcome pathway consisting of four key events (KE), including covalent binding to skin proteins (KE1), keratinocyte activation (KE2), and dendritic cell activation (KE3). Equivalent alternative methods have been developed for KE1 to KE3, but no valid alternative has yet been developed for the evaluation of KE4 and T-cell activation. Current alternative methods rely on data from KE1 to KE3 to predict the effect of chemicals on skin sensitization. The addition of KE4 data is expected to improve the accuracy and reproducibility of such predictions. The aim of this study was to establish an assay to evaluate KE4 T-cell activation to supplement data on skin sensitization related to KE4. To evaluate T-cell activation, the Jurkat T-cell line stably expressing luciferase downstream of the pro-inflammatory cytokine interleukin-2 promoter was used. After exposure to known skin sensitizing agents and control substances, luciferase activity measurements revealed that this assay was valid for evaluating skin sensitization. However, two skin sensitizers known to have immunosuppressive effects on T-cells reacted negatively in this assay. The results revealed that this assay simultaneously allows for monitoring of the skin sensitization and immuno-suppressiveness of chemical substances and supplements KE4 T-cell activation data, and may thus contribute to reducing the use of animal experiments.

Analytical aspects of meet-in-metabolite analysis for molecular pathway reconstitution from exposure to adverse outcome

To explore the etiology of diseases is one of the major goals in epidemiological study. Meet-in-metabolite analysis reconstitutes biomonitoring-based adverse outcome (AO) pathways from environmental exposure to a disease, in which the chemical exposome-related metabolism responses are transmitted to incur the AO-related metabolism phenotypes. However, the ongoing data-dependent acquisition of non-targeted biomonitoring by high-resolution mass spectrometry (HRMS) is biased against the low abundance molecules, which forms the major of molecular internal exposome, i.e., the totality of trace levels of environmental pollutants and/or their metabolites in human samples. The recent development of data-independent acquisition protocols for HRMS screening has opened new opportunities to enhance unbiased measurement of the extremely low abundance molecules, which can encompass a wide range of analytes and has been applied in metabolomics, DNA, and protein adductomics. In addition, computational MS for small molecules is urgently required for the top-down exposome databases. Although a holistic analysis of the exposome and endogenous metabolites is plausible, multiple and flexible strategies, instead of "putting one thing above all" are proposed.

Skin Sodium Accumulates in Psoriasis and Reflects Disease Severity

Sodium can accumulate in the skin at concentrations exceeding serum levels. A high sodium environment can lead to pathogenic T helper 17 cell expansion. Psoriasis is a chronic inflammatory skin disease in which IL-17‒producing T helper 17 cells play a crucial role. In an observational study, we measured skin sodium content in patients with psoriasis and in age-matched healthy controls by Sodium-23 magnetic resonance imaging. Patients with PASI > 5 showed significantly higher sodium and water content in the skin but not in other tissues than those with lower PASI or healthy controls. Skin sodium concentrations measured by Sodium-23 spectroscopy or by atomic absorption spectrometry in ashed-skin biopsies verified the findings with Sodium-23 magnetic resonance imaging. In vitro T helper 17 cell differentiation of naive CD4⁺ cells from patients with psoriasis markedly induced IL-17A expression under increased sodium chloride concentrations. The imiquimod-induced psoriasis mouse model replicated the human findings. Extracellular tracer Chromium-51-EDTA measurements in imiquimod- and sham-treated skin showed similar extracellular volumes, rendering excessive water of intracellular origin. Chronic genetic IL-17A‒driven psoriasis mouse models underlined the role of IL-17A in dermal sodium accumulation and inflammation. Our data describe skin sodium as a pathophysiological feature of psoriasis, which could open new avenues for its treatment.

Eosinophils in skin diseases

Eosinophil infiltration is a common finding in a broad spectrum of skin diseases, despite the fact that the skin is devoid of eosinophils under physiologic conditions. Although cutaneous eosinophilia is reactive, cytokine-mediated in most cases, diseases with an intrinsic mutation-mediated clonal expansion of eosinophils can also manifest on the skin. As eosinophils are involved in host defense, regulate immune responses, generate pruritus, induce remodeling and fibrosis, and can cause tissue damage, they have the capacity to actively contribute to the pathogenesis of diseases. Recent research provided deeper insights in the mechanisms, e.g., bacterial and viral clearance, blister formation, recruitment of cytotoxic T cells, and generation of pruritus, by which eosinophils might come into action. This review aims at providing an overview on the clinical presentations of eosinophil-associated dermatoses and the current understanding of their pathogenic role in these diseases. Further, we discuss the effects of therapies targeting eosinophils.

Contact dermatitis

Contact dermatitis (CD) is among the most common inflammatory dermatological conditions and includes allergic CD, photoallergic CD, irritant CD, photoirritant CD (also called phototoxic CD) and protein CD. Occupational CD can be of any type and is the most prevalent occupational skin disease. Each CD type is characterized by different immunological mechanisms and/or requisite exposures. Clinical manifestations of CD vary widely and multiple subtypes may occur simultaneously. The diagnosis relies on clinical presentation, thorough exposure assessment and evaluation with techniques such as patch testing and skin-prick testing. Management is based on patient education, avoidance strategies of specific substances, and topical treatments; in severe or recalcitrant cases, which can negatively affect the quality of life of patients, systemic medications may be needed.

Occupational Contact Dermatitis: An Update

Occupation contact dermatitis (CD) is a common inflammatory skin condition impacting every professional industry in the United States. It is associated with significant personal and professional distress, loss of revenue, and decreased productivity. Occupational CD is further subdivided into irritant CD and allergic CD. Frequently, workers may suffer from a combination of both types. Numerous workplace exposures are implicated, but there are several themes across professions, such as CD related to frequent handwashing and wet work. A detailed occupational history, physical examination, and patch testing can help to make the diagnosis. Treatment includes identification of the substance and avoidance, which often is quite challenging.

In-Vitro Approaches to Predict and Study T-Cell Mediated Hypersensitivity to Drugs

Mitigating the risk of drug hypersensitivity reactions is an important facet of a given pharmaceutical, with poor performance in this area of safety often leading to warnings, restrictions and withdrawals. In the last 50 years, efforts to diagnose, manage, and circumvent these obscure, iatrogenic diseases have resulted in the development of assays at all stages of a drugs lifespan. Indeed, this begins with intelligent lead compound selection/design to minimize the existence of deleterious chemical reactivity through exclusion of ominous structural moieties. Preclinical studies then investigate how compounds interact with biological systems, with emphasis placed on modeling immunological/toxicological liabilities. During clinical use, competent and accurate diagnoses are sought to effectively manage patients with such ailments, and pharmacovigilance datasets can be used for stratification of patient populations in order to optimise safety profiles. Herein, an overview of some of the in-vitro approaches to predict intrinsic immunogenicity of drugs and diagnose culprit drugs in allergic patients after exposure is detailed, with current perspectives and opportunities provided.

Structured diagnostic assessment of hand eczema in cleaning workers

Hand dermatitis is a widespread problem among cleaners. In most cases, it is caused by a combination of wet work and contact with irritants, which can result in irritant (toxic) contact dermatitis. In some cases, the irritant contact eczema then evolves into allergic contact dermatitis, although not all cases of allergic contact dermatitis are preceded by irritant contact dermatitis. This mini-review proposes a two-step diagnostic algorithm based on patch testing, which can be used if allergic contact dermatitis is suspected in cleaning workers. As a first step, we recommend performing the DKG standard series (German Contact allergy research group, DKG), the DKG rubber series, both DKG "further fragrances" series as well as the DKG preservative and disinfectant series. If there are clear hints of an occupational contact dermatitis, the first step can also involve testing patients' own products alongside the standardized tests. In a second step (at the latest), if standardized tests do not suffice to identify the culprit allergen and there is well-founded suspicion, we recommend testing the patients' own products. If necessary, the second step can also include testing the individual contact allergens contained in the screening mixes that are part of the standard series.

Luteolin as a modulator of skin aging and inflammation

Luteolin belongs to the group of flavonoids and can be found in flowers, herbs, vegetables and spices. It plays an important role in defending plants, for example against UV radiation by partially absorbing UVA and UVB radiation. Thus, luteolin can also decrease adverse photobiological effects in the skin by acting as a first line of defense. Furthermore, anti-oxidative and anti-inflammatory activities of luteolin were described on keratinocytes and fibroblasts as well as on several immune cells (e.g., macrophages, mast cell, neutrophils, dendritic cells and T cells). Luteolin can suppress proinflammatory mediators (e.g., IL-1β, IL-6, IL-8, IL-17, IL-22, TNF-α and COX-2) and regulate various signaling pathway (e.g., the NF-κB, JAK-STAT as well as TLR signaling pathway). In this way, luteolin modulates many inflammatory processes of the skin. The present review summarizes the recent in vitro and in vivo research on luteolin in the field of skin aging and skin cancer, wound healing as well as inflammatory skin diseases, including psoriasis, contact dermatitis and atopic dermatitis. In conclusion, luteolin might be a promising molecule for the development of topic formulations and systemic agents against inflammatory skin diseases.

Stratum corneum levels of inflammatory mediators and natural moisturizing factor in patch test reactions to thiurams and fragrances and their possible role in discrimination between irritant and allergic reactions to hapten mixtures

BACKGROUND

Patch test (PT) reactions to thiuram mix (TM) and fragrance mix (FM) I or II without concomitant reactions to their single constituents are potentially caused by the irritant properties of the mixes.

OBJECTIVE

Comparing inflammatory profiles of PT reactions to TM, FM I, FM II, and their constituents and assessing their potential in discrimination of irritant and allergic reactions.

PATIENTS AND METHODS

Levels of 14 cytokines and natural moisturizing factor (NMF) were determined in stratum corneum samples collected from PT reactions to TM, FM I or II, their constituents, and petrolatum (pet.) control sites in 36 individuals.

RESULTS

Levels of interleukin (IL)-16, chemokine (CXC motif) ligand (CXCL) 8, CXCL10, chemokine (CC motif) ligand (CCL) 17, and CCL22 were significantly increased in reactions (+, ++) to thiurams and fragrances compared to their petrolatum. controls, except for PT reactions to FM I/II with negative breakdown testing in which, however, decreased levels of NMF were observed. In doubtful reactions to FM I/II with negative breakdown testing, NMF was significantly lower than in petrolatum controls.

CONCLUSIONS

PT reactions to thiurams and fragrances indicate a Th2-skewed inflammation. The inflammatory profiles suggest that weak or doubtful FM I/II reactions without accompanying reaction to a constituent were irritant. IL-16 might be suitable to distinguish irritant from allergic reaction.

Intricate Relationship Between Adaptive and Innate Immune System in Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a complex immunological allergic disease characterized by the interplay between the innate and adaptive immune system. Initially, the role of the innate immune system was believed to be confined to the initial sensitization phase, while adaptive immune reactions were linked with the advanced elicitation phase. However, recent data predicted a comparatively mixed and interdependent role of both immune systems throughout the disease progression. Therefore, the actual mechanisms of disease progression are more complex and interlinked. The aim of this review is to combine such findings that enhanced our understanding of the pathomechanisms of ACD. Here, we focused on the main cell types from both immune domains, which are involved in ACD, such as CD4+ and CD8+ T cells, B cells, neutrophils, and innate lymphoid cells (ILCs). Such insights can be useful for devising future therapeutic interventions for ACD.

Allergic contact dermatitis: From pathophysiology to development of new preventive strategies

As the body's first line of defense, the skin is the organ most frequently exposed to chemicals present in personal hygiene products, household products, or materials used in the work environment. In this context, skin disorders account for more than 40 % of all occupational and work-related diseases, constituting a significant public health burden. Among skin disorders, allergic contact dermatitis (ACD) is the most prevalent occupational disease and the most common form of immunotoxicity in humans. ACD is a T-cell-mediated skin inflammation resulting from the priming and expansion of allergen-specific CD4⁺ and CD8⁺ T cells. The clinical condition is characterized by local skin rash, itchiness, redness, swelling, and lesions, being mainly diagnosed by the patch test. Upon ACD diagnosis, avoiding the exposure to the triggering allergen is the mainstay of treatment to prevent future flares. In cases where avoidance is not possible, the use of a standard of care interim treatments such as steroid creams or ointments, barrier creams, and moisturizers are strongly recommended to alleviate symptoms. In this review, we sought to provide the reader with an overview of the pathophysiology of ACD as well as the currently available pharmacological treatment options. Furthermore, a comprehensive outline of several preventive strategies is also provided.

TCRs with segment TRAV9-2 or a CDR3 histidine are overrepresented among nickel-specific CD4+ T cells

BACKGROUND

Nickel is the most frequent cause of T cell-mediated allergic contact dermatitis worldwide. In vitro, CD4+ T cells from all donors respond to nickel but the involved αβ T cell receptor (TCR) repertoire has not been comprehensively analyzed.

METHODS

We introduce CD154 (CD40L) upregulation as a fast, unbiased, and quantitative method to detect nickel-specific CD4+ T cells ex vivo in blood of clinically characterized allergic and non allergic donors. Naïve (CCR7+ CD45RA+) and memory (not naïve) CD154+ CD4+ T cells were analyzed by flow cytometry after 5 hours of stimulation with 200 µmol/L NiSO₄ ., TCR α- and β-chains of sorted nickel-specific and control cells were studied by high-throughput sequencing.

RESULTS

Stimulation of PBMCs with NiSO₄ induced CD154 expression on ~0.1% (mean) of naïve and memory CD4+ T cells. In allergic donors with recent positive patch test, memory frequencies further increased ~13-fold and were associated with markers of in vivo activation. CD154 expression was TCR-mediated since single clones could be specifically restimulated. Among nickel-specific CD4+ T cells of allergic and non allergic donors, TCRs expressing the α-chain segment TRAV9-2 or a histidine in their α- or β-chain complementarity determining region 3 (CDR3) were highly overrepresented.

CONCLUSIONS

Induced CD154 expression represents a reliable method to study nickel-specific CD4+ T cells. TCRs with particular features respond in all donors, while strongly increased blood frequencies indicate nickel allergy for some donors. Our approach may be extended to other contact allergens for the further development of diagnostic and predictive in vitro tests.

NLRP3 Inflammasome and Allergic Contact Dermatitis: A Connection to Demystify

Allergic contact dermatitis is a common occupational disease that manifests as a cell-mediated hypersensitivity reaction following skin exposure to small reactive chemicals termed haptens. Haptens penetrate the stratum corneum and covalently modify proteins in the epidermis, inducing intracellular stress, which further leads to the release of damage-associated molecular patterns (DAMPs), such as uric acid, reactive oxygen species, hyaluronic acid fragments and extracellular adenosine triphosphate (ATP). These DAMPs are recognized by pattern recognition receptors (PRRs) in innate immune cells, namely dendritic cells (DCs), leading to their maturation and migration to the draining lymph nodes where they activate naïve T lymphocytes. Among all PRRs, several studies emphasize the role of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome on the allergic contact dermatitis (ACD) sensitization phase. However, skin allergens-danger signals-NLRP3 inflammasome axis is yet to be completely elucidated. Therefore, in this review, we sought to discuss the molecular mechanisms underlying DAMPs release and NLRP3 inflammasome activation triggered by skin allergens. The elucidation of these key events might help to identify novel therapeutic strategies for ACD, as well as the development of nonanimal alternative methods for the identification and potency categorization of skin sensitizers.

Microfluidic skin chip with vasculature for recapitulating the immune response of the skin tissue

There is a considerable need for cell-based in vitro skin models for studying dermatological diseases and testing cosmetic products, but current in vitro skin models lack physiological relevance compared to human skin tissue. For example, many dermatological disorders involve complex immune responses, but current skin models are not capable of recapitulating the phenomena. Previously, we reported development of a microfluidic skin chip with a vessel structure and vascular endothelial cells. In this study, we cocultured dermal fibroblasts and keratinocytes with vascular endothelial cells, human umbilical vascular endothelial cells. We verified the formation of a vascular endothelium in the presence of the dermis and epidermis layers by examining the expression of tissue-specific markers. As the vascular endothelium plays a critical role in the migration of leukocytes to inflammation sites, we incorporated leukocytes in the circulating media and attempted to mimic the migration of neutrophils in response to external stimuli. Increased secretion of cytokines and migration of neutrophils was observed when the skin chip was exposed to ultraviolet irradiation, showing that the microfluidic skin chip may be useful for studying the immune response of the human tissue.

Differences in itch and pain behaviors accompanying the irritant and allergic contact dermatitis produced by a contact allergen in mice

Supplemental Digital Content is Available in the Text.

Introduction:

Irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD) are inflammatory skin diseases accompanied by itch and pain. Irritant contact dermatitis is caused by chemical irritants eliciting an innate immune response, whereas ACD is induced by haptens additionally activating an adaptive immune response: After initial exposure (sensitization) to the hapten, a subsequent challenge can lead to a delayed-type hypersensitivity reaction. But, the sensory and inflammatory effects of sensitization (ICD) vs challenge of ACD are insufficiently studied. Therefore, we compared itch- and pain-like behaviors and inflammatory reactions evoked in mice during the sensitization (ICD) vs challenge phase (ACD) of application of the hapten, squaric acid dibutylester (SADBE).

Objectives:

Our aim was to compare itch- and pain-like behaviors and inflammatory reactions evoked in mice during the sensitization (ICD) vs challenge phase (ACD) of application of the hapten, squaric acid dibutylester (SADBE).

Methods:

Mice were sensitized on the abdomen with 1% SADBE (ACD) or vehicle treated (ICD, control). Spontaneous and stimulus-evoked itch- and pain-like behaviors were recorded in mice before and after 3 daily challenges of the cheek with 1% SADBE (ACD, ICD). Cutaneous inflammation was evaluated with clinical scoring, ultrasound imaging, skin thickness, histology, and analyses of selected biomarkers for contact dermatitis, IL-1β, TNF-α, CXCL10, and CXCR3.

Results:

Allergic contact dermatitis vs ICD mice exhibited more spontaneous site-directed scratching (itch) and wiping (pain). Allergic contact dermatitis—but not ICD—mice exhibited allodynia and hyperalgesia to mechanical and heat stimuli. Inflammatory mediators IL-1β and TNF-α were upregulated in both groups as well as the chemokine receptor, CXCR3. CXCL10, a CXCR3 ligand, was upregulated only for ACD. Inflammatory responses were more pronounced in ACD than ICD.

Conclusion:

These findings provide new information for differentiating the behavioral and inflammatory reactions to hapten-induced ICD and ACD.

Angioedema Masqueraders

Angioedema is a common reason for referral to immunology and allergy specialists. Not all cases are in fact angioedema. There are many conditions that may mimic its appearance, resulting in misdiagnosis. This may happen when a clinician is unfamiliar with conditions resembling angioedema or when there is a low index of clinical suspicion. In this article, we explore a list of differential diagnoses based on body parts, including the lips, the limbs, periorbital tissues, the face, epiglottis and uvula, as well as the genitalia, that may pose as a masquerader even to an experienced eye.

Case report of recalcitrant allergic contact eczema successfully treated with teriflunomide

Allergic contact dermatitis (ACD) is a type IV, delayed-type reaction caused by skin contact with low-molecular-weight organic chemicals and metal ions that activate antigen-specific T cells, primarily T-helper 1 (Th1), in a sensitized individual, leading to skin eczema.First-line treatments are based on avoidance of causal agents and topical corticosteroids/immunomodulators. In recalcitrant cases, chronic oral immunosuppressive agents may be used, but they may have serious adverse effects and do not address the immunological disfunction. We report a case of severe ACD, unresponsive to topical or oral immunosuppressive therapy, which resolved itself after treatment with teriflunomide (TF) 14 mg/daily used for multiple sclerosis. TF is a once-daily, oral selective and reversible dihydroorotate dehydrogenase inhibitor, revealing a new treatment option for ACD.

Salicylic acid amplifies Carbachol-induced bronchoconstriction in human precision-cut lung slices

BACKGROUND

Asthma exacerbations evoke emergency room visits, progressive loss of lung function and increased mortality. Environmental and industrial toxicants exacerbate asthma, although the underlying mechanisms are unknown. We assessed whether 3 distinct toxicants, salicylic acid (SA), toluene diisocyanate (TDI), and 1-chloro-2,4-dinitrobenzene (DNCB) induced airway hyperresponsiveness (AHR) through modulating excitation-contraction coupling in human airway smooth muscle (HASM) cells. The toxicants include a non-sensitizing irritant (SA), respiratory sensitizer (TDI) and dermal sensitizer (DNCB), respectively. We hypothesized that these toxicants induce AHR by modulating excitation-contraction (EC) coupling in airway smooth muscle (ASM) cells.

METHODS

Carbachol-induced bronchoconstriction was measured in precision-cut human lung slices (hPCLS) following exposure to SA, TDI, DNCB or vehicle. Culture supernatants of hPCLS were screened for mediator release. In HASM cells treated with the toxicants, surrogate readouts of EC coupling were measured by phosphorylated myosin light chain (pMLC) and agonist-induced Ca²⁺ mobilization ([Ca²⁺]_i). In addition, Nrf-2-dependent antioxidant response was determined by NAD(P) H quinone oxidoreductase 1 (NQO1) expression in HASM cells.

RESULTS

In hPCLS, SA, but not TDI or DNCB, potentiated carbachol-induced bronchoconstriction. The toxicants had little effect on release of inflammatory mediators, including IL-6, IL-8 and eotaxin from hPCLS. In HASM cells, TDI amplified carbachol-induced MLC phosphorylation. The toxicants also had little effect on agonist-induced [Ca²⁺]_i. CONCLUSION: SA, a non-sensitizing irritant, amplifies agonist-induced bronchoconstriction in hPCLS via mechanisms independent of inflammation and Ca²⁺ homeostasis in HASM cells. The sensitizers TDI and DNCB, had little effect on bronchoconstriction or inflammatory mediator release in hPCLS.

IMPLICATIONS

Our findings suggest that non-sensitizing irritant salicylic acid may evoke AHR and exacerbate symptoms in susceptible individuals or in those with underlying lung disease.

IL-24 contributes to skin inflammation in Para-Phenylenediamine-induced contact hypersensitivity

Para-Phenylenediamine (PPD) is an aromatic amine used in hair dyes and in temporary black henna tattoos, which is a frequent cause of allergic contact dermatitis (ACD). ACD is a skin inflammatory reaction characterized by modifications such as spongiosis, exocytosis and acanthosis. The aim of this study is to characterize the expression and the role of IL-20-related cytokines, including IL-19, IL-20, IL-22 and IL-24, in ACD. The expression of IL19, IL20, IL22 and IL24 is increased in affected skin from PPD allergic patients compared with uninvolved skin. In addition, the expression of these cytokines positively correlates with clinical symptoms. To assess their role in ACD, we set up a mouse model of PPD-induced allergic contact dermatitis and we showed that, in contrast to Il22-deficient mice, Il22ra1-, Il20rb- and Il24-deficient mice are partially protected against development of PPD-induced contact hypersensitivity. These mice have decreased ear thickening and less acanthosis compared with WT mice after PPD treatment. In addition, the absence of IL-22R, IL-20R2 or IL-24 affects the recruitment of neutrophils into the skin but not the total IgE production. Taken together, these results demonstrate the implication of IL-24 via the IL-20R type II receptor in the inflammatory process of ACD.

Neutrophil Cathepsin G Regulates Dendritic Cell Production of IL-12 during Development of CD4 T Cell Responses to Antigens in the Skin

Contact hypersensitivity (CHS) is a CD8 T cell-mediated response to hapten skin sensitization and challenge. Sensitization of wild-type (WT) mice induces hapten-reactive effector CD8 T cells producing IFN-γ and IL-17- and IL-4-producing CD4 T cells that cannot mediate CHS. Although CXCR2-dependent Ly6G⁺ (neutrophil) cell recruitment into hapten-challenged skin is required to direct effector CD8 T cell infiltration into the challenge site to elicit CHS, 2,4-dinitrofluorobenezene (DNFB) sensitization of CXCR2^-/- mice and neutrophil-depleted WT mice induced both hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17. CD4 T cell-mediated CHS responses were not generated during DNFB sensitization of neutrophil-depleted WT mice treated with anti-IL-12 mAb or neutrophil-depleted IL-12^-/- mice. Neutrophil depletion during DNFB sensitization of WT mice markedly increased IL-12-producing hapten-primed dendritic cell numbers in the skin-draining lymph nodes. Sensitization of mice lacking the neutrophil serine protease cathepsin G (CG)-induced hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17 with elevated and elongated CHS responses to DNFB challenge. Induction of CHS effector CD4 T cells producing IFN-γ in neutrophil-depleted WT mice was eliminated by s.c. injection of active, but not inactivated, CG during sensitization. Thus, hapten skin sensitization induces neutrophil release of CG that systemically inhibits hapten-presenting dendritic cell production of IL-12 and the development of hapten-reactive CD4 T cells to IFN-γ-producing CHS effector cells.

IL-27 Production and Regulation in Human Dendritic Cells Treated with the Chemical Sensitizer NiSO4

Allergic contact dermatitis (ACD) is a major cause of occupational skin disease, and nickel is among the most prevalent contact allergens. Dendritic cells (DC) play an important role in ACD and in the type of the ensuing immune response through differential phenotypes and cytokine production. The interleukin (IL)-12 cytokine family is composed of heterodimeric cytokines sharing homology at the subunit, receptors and signaling levels. We previously showed that nickel can upregulate the production of IL-12p40 and IL-23, both known to be pro-inflammatory. In this work, we aimed to extend our knowledge on nickel regulation of the IL-12 cytokine family by focusing on IL-27, a recently identified immunomodulatory cytokine from this family. We showed that nickel induced the production of IL-27 in human monocyte-derived DC (MoDC), regulating IL-22 production by human CD4+ T cells. We also showed that nickel was able to induce the expression of the two subunits of IL-27: il-27p28 and ebi3. Furthermore, we demonstrated that the production of IL-27 was dependent on the TLR4, p38 MAPK, NF-κB, and Jak-STAT signaling. However, IL-27 subunits were differentially regulated by these pathways. Indeed, both subunits were positively regulated by the TLR4 and NF-κB pathways, but only il-27p28 was also dependent on p38 MAPK and Jak-STAT pathways. Our results contribute to a better understanding of nickel-induced ACD by focusing on the IL-12 cytokine family and elucidating the mechanism of IL-27 regulation in human dendritic cells.