Staphylococcus aureus-specific skin resident memory T cells protect against bacteria colonization but exacerbate atopic dermatitis-like flares in mice.

BACKGROUND: The contribution of Staphylococcus aureus to the exacerbation of atopic dermatitis (AD) is widely documented, but its role as a primary trigger of AD skin symptoms remains poorly explored. OBJECTIVES: This study sought to reappraise the main bacterial factors and underlying immune mechanisms by which S aureus triggers AD-like inflammation. METHODS: This study capitalized on a preclinical model, in which different clinical isolates were applied in the absence of any prior experimental skin injury. RESULTS: The development of S aureus-induced dermatitis depended on the nature of the S aureus strain, its viability, the concentration of the applied bacterial suspension, the production of secreted and nonsecreted factors, as well as the activation of accessory gene regulatory quorum sensing system. In addition, the rising dermatitis, which exhibited the well-documented AD cytokine signature, was significantly inhibited in inflammasome adaptor apoptosis-associated speck-like protein containing a CARD domain- and monocyte/macrophage-deficient animals, but not in T- and B-cell-deficient mice, suggesting a major role for the innate response in the induction of skin inflammation. However, bacterial exposure generated a robust adaptive immune response against S aureus, and an accumulation of S aureus-specific γδ and CD4+ tissue resident memory T cells at the site of previous dermatitis. The latter both contributed to worsen the flares of AD-like dermatitis on new bacteria exposures, but also, protected the mice from persistent bacterial colonization. CONCLUSIONS: These data highlight the induction of unique AD-like inflammation, with the generation of proinflammatory but protective tissue resident memory T cells in a context of natural exposure to pathogenic S aureus strains.

Topical corticosteroids inhibit allergic skin inflammation but are ineffective in impeding the formation and expansion of resident memory T cells.

BACKGROUND: Tissue-resident memory T (TRM ) cells are detrimental in allergic contact dermatitis (ACD), in which they contribute to the chronicity and severity of the disease. METHODS: We assessed the impact of a standard topical corticosteroid (TCS) treatment, triamcinolone acetonide (TA), on the formation, maintenance and reactivation of epidermal TRM cells in a preclinical model of ACD to 2,4-dinitrofluorobenzene. TA 0.01% was applied at different time points of ACD response and we monitored skin inflammation and tracked CD8+ CD69+ CD103+ TRM by flow cytometry and RNA sequencing. RESULTS: The impact of TA on TRM formation depended on treatment regimen: (i) in a preventive mode, that is, in sensitized mice before challenge, TA transiently inhibited the infiltration of effector T cells and the accumulation of TRM upon hapten challenge. In contrast, (ii) in a curative mode, that is, at the peak of the ACD response, TA blocked skin inflammation but failed to prevent the formation of TRM . Finally, (iii) in a proactive mode, that is, on previous eczema lesions, TA had no effect on the survival of skin TRM , but transiently inhibited their reactivation program upon allergen reexposure. Indeed, specific TRM progressively regained proliferative functions upon TA discontinuation and expanded in the tissue, leading to exaggerated iterative responses. Interestingly, TRM re-expansion correlated with the decreased clearance of hapten moieties from the skin induced by repeated TA applications. CONCLUSIONS: Our results demonstrate that TCS successfully treat ACD inflammation, but are mostly ineffective in impeding the formation and expansion of allergen-specific TRM , which certainly restricts the induction of lasting tolerance in patients with chronic dermatitis.

Gene profiling in active dermatitis lesions strengthens the diagnosis of allergic contact dermatitis.

BACKGROUND: Distinguishing between allergic and nonallergic forms of Contact Dermatitis (CD) is challenging and requires investigations based on patch-testing. Early detection of allergy biomarkers in active CD lesions could refine and simplify the management of CD patients. OBJECTIVE: To characterize the molecular signatures of active CD lesions. METHODS: We studied the expression of 12 allergy biomarkers by qRT-PCR in active lesions of 38 CD patients. Allergic CD (ACD) was diagnosed based on patch test (PT) results and exposure assessment. Molecular signatures of active lesions, as well as positive PT reactions, were compared with those of reference chemical allergens and irritants. RESULTS: Nineteen of the 38 CD patients reacted positively upon patch-testing and exposure assessment confirmed ACD diagnosis for 17 of them. Gene profiling of active CD lesions revealed 2 distinct molecular patterns: patients harboring signatures similar to reference allergens (n = 23) or irritants (n = 15). Among the 23 patients with an "allergy signature," we found the 17 patients with confirmed ACD, while no culprit allergen was identified for the 6 other patients. Interestingly, the 15 patients without biomarker induction had negative PT, suggesting that they developed nonallergic CD reactions. CONCLUSION: Molecular signatures from active skin lesions may help to stratify CD patients and predict those suffering from ACD.

Role of miR-24-3p and miR-146a-5p in dendritic cells' maturation process induced by contact sensitizers.

MiRNAs are non-coding RNA molecules that regulate gene expression at the post-transcriptional level. Although allergic contact dermatitis has been studied extensively, few studies addressed miRNA expression and their role in dendritic cell activation. The main aim of this work was to investigate the role of miRNAs in the underlying mechanism of dendritic cell maturation induced by contact sensitizers of different potency. Experiments were conducted using THP-1-derived immature DCs (iDCs). Contact allergens of different potency were used: p-benzoquinone, Bandrowski's base, and 2,4-dinitrochlorobenzene as extreme; nickel sulfate hexahydrate, diethyl maleate and 2-mercaptobenzothiazole as moderate; and α-hexyl cinnamaldehyde, eugenol, and imidazolidinyl urea as weak. Selective inhibitor and mimic miRNAs were then used and several cell surface markers was evaluated as targets. Also, patients patch tested with nickel were analyzed to determine miRNAs expression. Results indicate an important role of miR-24-3p and miR-146a-5p in DCs activation. miR-24-3p was up-regulated by extreme and weak contact allergens, while miR-146a-5p was up-regulated by weak and moderate contact allergens and down-regulated only by the extreme ones. Also, the involvement of PKCß in contact allergen-induced miR-24-3p and miR-146a-5p expression was demonstrated. Furthermore, the expression of the two miRNAs maintains the same trend of expression in both in vitro and in human conditions after nickel exposure. Results obtained suggest the involvement of miR-24 and miR-146a in DCs maturation process in the proposed in vitro model, supported also by human evidences.

Epicutaneous allergen immunotherapy induces a profound and selective modulation in skin dendritic-cell subsets.

BACKGROUND: Epicutaneous immunotherapy (EPIT) protocols have recently been developed to restore tolerance in patients with food allergy. The mechanisms by which EPIT protocols promote desensitization rely on a profound immune deviation of pathogenic T- and B-cell responses. OBJECTIVE: To date, little is known about the contribution of skin dendritic cells (skDCs) to T-cell remodeling and EPIT efficacy. METHODS: We capitalized on a preclinical model of food allergy to ovalbumin (OVA) to characterize the phenotype and functions of OVA+ skDCs throughout the course of EPIT. RESULTS: Our results showed that both Langerhans cells and dermal conventional cDC1 and cDC2 subsets retained their ability to capture OVA in the skin and to migrate toward the skin-draining lymph nodes during EPIT. However, their activation/maturation status was significantly impaired, as evidenced by the gradual and selective reduction of CD86, CD40, and OVA protein expression in respective subsets. Phenotypic changes during EPIT were also characterized by a progressive diversification of single-cell gene signatures within each DC subset. Interestingly, we observed that OVA+ Langerhans cells progressively lost their capacity to prime CD4+ TEFF cells, but gained regulatory T-cell stimulatory properties. In contrast, cDC1 were inefficient in priming CD4+ TEFF cells or in reactivating TMEM cells in vitro, whereas cDC2 retained moderate stimulatory properties, and progressively biased type 2 immunity toward type 1 and type 17 responses. CONCLUSIONS: Our results therefore emphasize that the acquisition of distinct phenotypic and functional specializations by skDCs during EPIT is at the cornerstone of the desensitization process.

Gene profiling reveals a contact allergy signature in most positive Amerchol L-101 patch test reactions.

BACKGROUND: Diagnosis of contact allergy (CA) to Amerchol L-101 (AL-101), a marker for lanolin allergy, is problematic. Positive patch test reactions are frequently doubtful or weakly positive and difficult to associate with clinical relevance. OBJECTIVE: To gain further insight on the allergic or irritant nature of skin reactions induced by AL-101 patch test. METHODS: We re-tested in a dose-response fashion, 10 subjects with AL-101 CA and performed comprehensive transcriptomic analysis (gene arrays, quantitative real-time polymerase chain reaction [qRT-PCR]) of samples of their skin reactions. RESULTS: Eight of the 10 CA subjects reacted positively upon re-test, whereas two did not react. Most of AL-101 positive patch tests expressed an allergy signature with strong activation of gene modules associated with adaptive immunity and downregulation of cornification pathway genes. In addition, the breadth of gene modulation correlated with the magnitude of patch test reactions and the concentration of AL-101 applied. However, we observed that some of the positive patch test reactions to AL-101 expressed no/few allergy biomarkers, suggesting the induction of an irritant skin inflammation in these samples. CONCLUSIONS: This study confirms that AL-101 is an allergen that can cause both contact allergy and contact irritation. Our results also highlight that molecular profiling might help to strengthen clinical diagnosis.

CD8+ T cells mediate ultraviolet A-induced immunomodulation in a model of extracorporeal photochemotherapy.

Extracorporeal photochemotherapy (ECP) that takes advantage of the immunomodulatory effects of UV light has been extensively used for many years for the treatment of several T cell-mediated diseases, including graft-versus-host disease (GvHD) and systemic scleroderma. Immune mechanisms that lead to the establishment of T cell tolerance in ECP-treated patients remain poorly known. In this study, we have tested the effect of UV/psoralen-treated BM-derived dendritic cells, referred to as ECP-BMDCs on the outcome of an antigen-specific T cell-mediated reaction, that is, contact hypersensitivity (CHS), which is mediated by CD8+ effector T cells (CD8+ Teff ). The intravenous (i.v.) injection of antigen-pulsed ECP-BMDCs in recipient C57BL/6 mice induced specific CD8+ T cells endowed with immunomodulatory properties (referred to as CD8+ TECP ), which prevented the priming of CD8+ Teff and the development of CHS, independently of conventional CD4+ regulatory T cells. CD8+ TECP mediated tolerance by inhibiting the migration and functions of skin DC and subsequently the priming of CD8+ Teff . CD8+ TECP displayed none of the phenotypes of the usual CD8+ T regulatory cells described so far. Our results reveal an underestimated participation of CD8+ T cells to ECP-induced immunomodulation that could explain the therapeutic effects of ECP in T cell-mediated diseases.

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.

Inhibitory checkpoint receptors control CD8+ resident memory T cells to prevent skin allergy.

BACKGROUND: Tissue-resident memory T (Trm) cells are detrimental in patients with numerous chronic inflammatory diseases, including allergic contact dermatitis (ACD). OBJECTIVES: We sought to analyze the contribution of Trm cells to the chronicity and severity of ACD and to define the local parameters regulating their development and functions. METHODS: We used an experimental model of ACD (ie, contact hypersensitivity to 2,4-dinitrofluorobenzene) that is mediated by CD8+ T cells. RESULTS: Our data show that early effector T cells accumulated in the skin during the acute contact hypersensitivity reaction and gave rise to epidermal CD8+ Trm cells expressing a specific set of inhibitory checkpoint receptors (ICRs), such as programmed cell death protein 1 (PD-1) and T cell immunoglobulin and mucin domain 3 (TIM-3). Those Trm cells remained in the epidermis for several weeks and mediated the eczema exacerbations, which developed on allergen re-exposure without the contribution of circulating specific T cells. Furthermore, allergen-induced Trm cell reactivation was constrained because treatment with ICR antagonists dramatically enhanced the magnitude and severity of eczema exacerbations. Finally, we show that the persistence of the allergen in the epidermis for long periods of time was responsible for both the development and maintenance of epidermal Trm cells, as well as the sustained expression of ICRs. CONCLUSION: Although CD8+ Trm cells are key for the pathophysiology of ACD, intrinsic mechanisms control their reactivation to prevent damaging immunopathology. Developing strategies targeting the reactivation of skin Trm cells in situ through their ICRs should open new perspectives for the treatment of ACD.

IL-1ß induces thymic stromal lymphopoietin and an atopic dermatitis-like phenotype in reconstructed healthy human epidermis.

Atopic dermatitis (AD) is a common skin inflammatory disease characterized by the production of thymic stromal lymphopoietin (TSLP) and marked TH 2 polarization. Recent studies suggest that IL-1ß contributes to the development of AD skin inflammation. Here, we have investigated the impact of IL-1ß signalling on the epidermal homeostasis of both healthy subjects and AD patients [with functional filaggrin (FLG) alleles], with particular attention to TSLP production and keratinocyte differentiation. In healthy reconstructed human epidermis (RHE), IL-1ß promoted (i) robust secretion of TSLP in an NF-κB-dependent manner and (ii) a significant decrease in the expression of filaggrin and other proteins of the epidermal differentiation complex. These effects were prevented by treatment of RHE with the anti-IL-1ß mAb canakinumab and by the IL-1 receptor antagonist anakinra. Interestingly, RHE generated from AD donors behaved like that of healthy individuals and showed comparable responses to IL-1ß signals. Collectively, our results suggest that IL-1ß may be an early key mediator for the acquisition of an AD phenotype through induction of TSLP and alteration of the epidermal homeostasis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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.

Microbial derived antimicrobial peptides as potential therapeutics in atopic dermatitis.

Atopic dermatitis (AD) is a common chronic inflammatory skin disease that significantly affects the patient's quality of life. A disrupted skin barrier, type 2 cytokine-dominated inflammation, and microbial dysbiosis with increased Staphylococcus aureus colonization are critical components of AD pathogenesis. Patients with AD exhibit decreased expression of antimicrobial peptides (AMPs) which is linked to increased colonization by Staphylococcus aureus. The skin microbiome itself is a source of several AMPs. These host- and microbiome-derived AMPs define the microbial landscape of the skin based on their differential antimicrobial activity against a range of skin microbes or their quorum sensing inhibitory properties. These are particularly important in preventing and limiting dysbiotic colonization with Staphylococcus aureus. In addition, AMPs are critical for immune homeostasis. In this article, we share our perspectives about the implications of microbial derived AMPs in AD patients and their potential effects on overlapping factors involved in AD. We argue and discuss the potential of bacterial AMPs as therapeutics in AD.

Deciphering Differential Behavior of Immune Responses as the Foundation for Precision Dosing in Allergen Immunotherapy.

Like in many fields of medicine, the concept of precision dosing has re-emerged in routine practice in allergology. Only one retrospective study on French physicians' practice has addressed this topic so far and generated preliminary data supporting dose adaptation, mainly based on experience, patient profile understanding and response to treatment. Both intrinsic and extrinsic factors shape the individual immune system response to allergen immunotherapy (AIT). Herein, we focus on key immune cells (i.e., dendritic cells, innate lymphoid cells, B and T cells, basophils and mast cells) involved in allergic disease and its resolution to further understand the effect of AIT on the phenotype, frequency or polarization of these cells. We strive to discriminate differences in immune responses between responders and non-responders to AIT, and discuss the eligibility of a non/low-responder subset for dose adaptation. A differential behavior in immune cells is clearly observed in responders, highlighting the importance of conducting clinical trials with large cohorts of well-characterized subjects to decipher the immune mechanism of AIT. We conclude that there is a need for designing new clinical and mechanistic studies to support the scientific rationale of dose adaptation in the interest of patients who do not properly respond to AIT.

Ultraviolet exposure regulates skin metabolome based on the microbiome.

Skin metabolites (< 1500 Da) play a critical role in barrier function, hydration, immune response, microbial invasion, and allergen penetration. We aimed to understand the global metabolic profile changes of the skin in relation to the microbiome and UV exposure and exposed germ-free (devoid of microbiome), disinfected mice (partially devoid of skin microbiome) and control mice with intact microbiome to immunosuppressive doses of UVB radiation. Targeted and untargeted lipidome and metabolome profiling was performed with skin tissue by high-resolution mass spectrometry. UV differentially regulated various metabolites such as alanine, choline, glycine, glutamine, and histidine in germ-free mice compared to control mice. Membrane lipid species such as phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin were also affected by UV in a microbiome-dependent manner. These results shed light on the dynamics and interactions between the skin metabolome, microbiome, and UV exposure and open new avenues for the development of metabolite- or lipid-based applications to maintain skin health.

Hyperactivation of the JAK2/STAT5 Signaling Pathway and Evaluation of Baricitinib Treatment Among Patients With Eosinophilic Cellulitis.

Importance: The pathogenesis of eosinophilic cellulitis (EC) is poorly understood, limiting available treatment options. The current treatment paradigm focuses on delayed type 2 hypersensitivity reaction to various triggers. Objective: To gain further insight into the nature of EC inflammation and into the cellular signal transduction pathways that are activated in the context of EC. Design, Setting, and Participants: This case series was conducted in Lyon, France, from January 2018 to December 2021. Analysis of archival skin biopsy samples from patients with EC and from healthy control participants was performed using histology, Janus kinase (JAK)-signal transducer and activator of transcription (STAT) immunohistochemistry, and gene profiling. Data analysis was conducted between January 2020 and January 2022. Main Outcomes and Measures: Pruritus (visual analog score), percentage of body surface area with lesional skin, and RNA transcripts of inflammatory biomarkers from the skin (threshold cycle) were assessed in 1 index patient with refractory EC who received oral JAK1/JAK2 inhibitor baricitinib (4 mg/d). Results: This study included samples from 14 patients with EC (7 men and 7 women) and 8 healthy control participants (4 men and 4 women). The mean (SD) age of patients was 52 (20) years. Marked type 2 inflammation (chemokines CCL17, CCL18, and CCL26 and interleukin 13) with preferential activation of the JAK1/JAK2-STAT5 pathways in EC lesions was observed. In the 1 index patient with refractory EC, complete clinical remission of skin lesions was observed after 1 month of treatment with baricitinib. Conclusions and Relevance: These findings suggest that EC is a type 2 inflammatory disease with preferential activation of the JAK1/JAK2-STAT5 pathways. In addition, these results suggest the potential of treatment approaches targeting JAK1/JAK2 for patients with EC.

Histamine receptor H1 signaling on dendritic cells plays a key role in the IFN-γ/IL-17 balance in T cell-mediated skin inflammation.

BACKGROUND: The diverse effects of histamine on immune regulation are a result of the differential expression and regulation of 4 histamine receptors. Many of the immediate allergic and inflammatory actions of histamine are mediated via the type 1 receptor (H1R). OBJECTIVES: We hypothesized that H1R was involved in the fine-tuning of the initiation of T cell-mediated skin pathology-that is, dermatitis. METHODS: The impact of the H1R invalidation on the development of skin inflammation was analyzed in a mouse model of atopic dermatitis. RESULTS: We show that H1r(-)/(-) mice developed reduced allergen-specific skin lesions. Lack of H1R expression on dendritic cells (DCs) led to diminished IL-12, upregulated IL-23, and IL-6 production upon allergen stimulation. H1R engagement on dendritic cells was necessary for DC activation and subsequent priming of effector IFN-γ(+)CD8(+) T cells. We demonstrate here that H1R blockade on DCs promotes generation of noneffector IL-17(+)CD8(+) T cells that are unable to initiate the skin inflammation. CONCLUSION: Our data identify that histamine signaling through the H1R on DCs is an important early event conditioning the quality of the skin effector immune response.