Rapid allergen-induced interleukin-17 and interferon-γ secretion by skin-resident memory CD8+T cells

Subclinical immune responses to nickel in sensitized individuals-a dose-response study

BACKGROUND

Nickel is the leading cause of contact allergy in Europe, with 14.5% of the adult population being sensitized. Despite regulations limiting nickel release from consumer items, the incidence and prevalence of nickel allergy remain high.

OBJECTIVE

To investigate the clinical and subclinical immune response to low-dose nickel exposure on nickel pre-exposed skin to assess the adequacy of current regulatory limits.

METHOD

Nickel-allergic and healthy controls were patch tested with nickel twice with a 3-4 weeks interval. The first exposure used the diagnostic concentration of 2000 μg/cm2 nickel sulphate, and the same skin areas were then re-exposed to 0.2, 0.5, 12.8 and 370 μg/cm2 nickel sulphate. After 48 h, the patch reactions were examined for clinical signs of eczema, and skin biopsies were collected. The transcriptomic immune profile was analysed with Nanostring nCounter and quantitative polymerase chain reaction.

RESULTS

Two nickel-allergic participants (15%) had clinical reactions to the regulatory limiting doses for nickel (0.2/0.5 μg/cm2) following re-exposure. There was immune activation in all skin areas following re-exposure to nickel, predominantly mediated by up-regulation of cytokines and chemokines. In all nickel re-exposed skin areas, 81 genes were up-regulated independent from the clinical response. In skin areas exposed to 0.2 μg/cm2, 101 immune-related genes were differentially expressed, even when no clinical response was observed. Healthy controls showed up-regulation of three genes in response to nickel re-exposures without any clinical reactions.

CONCLUSION

Immune activation can be induced in skin with local memory to nickel upon challenge with nickel doses within the regulatory limits. Our findings suggest that the regulatory limits in the European nickel regulation may not provide sufficient protection for consumers against low-dose exposures.

Fragrances as a trigger of immune responses in different environments

Fragrances can cause allergic skin reactions, expressed as allergic contact dermatitis and reactions in the respiratory tract that range from acute temporary upper airway irritation to obstructive lung disease. These adverse health effects may result from the stimulation of a specific (adaptive) immune response. Th1 cells, which essentially produce interleukin-2 (IL-2) and interferon-γ (IFN-γ), play a key role in allergic contact dermatitis and also on allergic sensitization to common allergens (e.g., nickel and fragrance). It has been shown that fragrance allergy leads to Th2/Th22 production of IL-4, IL-5 and IL-13, controlling the development of IgE and mediating hypersensitivity reactions in the lung, such as asthma. Cytokines released during immune response modulate the expression of cytochrome P450 (CYPs) proteins, which can result in alterations of the pharmacological effects of substances in inflammatory diseases. The mechanisms linking environment and immunity are still not completely understood but it is known that aryl hydrocarbon receptor (AhR) is a sensor with conserved ligand-activated transcription factor, highly expressed in cells that controls complex transcriptional programs which are ligand and cell type specific, with CYPs as targeted genes. This review focuses on these important aspects of immune responses of the skin and respiratory tract cells, describing some in vitro models applied to evaluate the mechanisms involved in fragrance-induced allergy.

Neutrophil infiltration in allergic contact dermatitis to nickel

Allergic contact dermatitis (ACD) is traditionally recognized as a T-cell-mediated delayed-type hypersensitivity reaction. However, many patients with ACD have been reported to experience rapid-onset ACD reactions within hours of re-exposure on skin areas previously exposed to the contact allergen. In this study, three nickel-allergic patients were patch tested for nickel twice at the same skin site over 21 days. The results demonstrated that neutrophils are rapidly recruited to the skin sites previously exposed to nickel, leading to the rapid onset of ACD. Considering that many patients with ACD are frequently re-exposed to contact allergens on the same skin areas in their daily lives, we propose that mechanisms involved in neutrophil recruitment could be potential targets for future ACD treatment.

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.

CD100 boosts the inflammatory response in the challenge phase of allergic contact dermatitis in mice

BACKGROUND

Allergic contact dermatitis (ACD) is an inflammatory disease with a complex pathophysiology in which epidermal-resident memory CD8+ T (TRM ) cells play a key role. The mechanisms involved in the activation of CD8+ TRM cells during allergic flare-up responses are not understood.

METHODS

The expression of CD100 and its ligand Plexin B2 on CD8+ TRM cells and keratinocytes before and after allergen exposure was determined by flow cytometry and RT-qPCR. The role of CD100 in the inflammatory response during the challenge phase of ACD was determined in a model of ACD in CD100 knockout and wild-type mice.

RESULTS

We show that CD8+ TRM cells express CD100 during homeostatic conditions and up-regulate it following re-exposure of allergen-experienced skin to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene (DNFB). Furthermore, Plexin B2 is up-regulated on keratinocytes following exposure to some contact allergens. We show that loss of CD100 results in a reduced inflammatory response to DNFB with impaired production of IFNγ, IL-17A, CXCL1, CXCL2, CXCL5, and IL-1β and decreased recruitment of neutrophils to the epidermis.

CONCLUSION

Our study demonstrates that CD100 is expressed on CD8+ TRM cells and is required for full activation of CD8+ TRM cells and the flare-up response of ACD.

Resident cutaneous memory T cells: a clinical review of their role in chronic inflammatory dermatoses and potential as therapeutic targets

Resident memory T cells (T-RMs) remain in epithelial barrier tissues after antigen exposure and the initial effector phase. These T-RMs provide effective antimicrobial and anticancer immunity; however, pathogenic T-RMs have been shown to mediate various chronic inflammatory disorders in a variety of tissue types. In the skin, T-RMs are referred to as resident cutaneous memory T cells (cT-RMs). Understanding the mechanisms leading to the development and establishment of these cT-RMs populations may allow for targeted treatments that provide durable responses in chronic immune-mediated skin diseases, even after cessation. In this review, we summarize the evidence on cT-RMs as drivers of chronic inflammatory dermatoses, including psoriasis, vitiligo, atopic dermatitis, cutaneous lupus erythematosus and alopecia areata, among others. Data from in vitro, animal model and ex vivo human studies are presented, with a focus on the potential for cT-RMs to trigger acute disease flares, as well as recurrent disease, by establishing an immune 'memory' in the skin. Furthermore, the available data on the potential for existing and novel treatments to affect the development or survival of cT-RMs in the skin are synthesized. The data suggest a dynamic and rapidly growing area in the field of dermatology; however, we also discuss areas in need of greater research to allow for optimal treatment selection for long-term disease control.

Neutrophil recruitment by CD4 tissue-resident memory T cells induces chronic recurrent inflammation in atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease that continues to impose significant physical, mental, and economic burdens on patients. Recent research has suggested the significant role of tissue-resident memory (TRM) cells in AD. However, the precise role and mechanisms of action of TRM cells in AD remain unclear. A deeper understanding of the involvement of TRM cells in AD will unveil promising pathways for future innovative therapeutic strategies.

METHODS

To investigate the involvement of TRM cells in AD, we used diverse mouse models and employed experimental techniques to manipulate cell formation and depletion. We assessed the inflammatory response by analyzing mouse ear phenotype, measuring ear thickness, and performing hematoxylin and eosin staining. Flow cytometry and immunofluorescence staining were used to identify different cell types and evaluate changes in cell quantity. Additionally, we used qPCR to analyze gene expression of relevant chemokines and cytokines.

RESULTS

Our study revealed the presence of TRM cells in the skin after exposure to calcipotriol. After a 24-h re-challenge, we observed substantial neutrophil infiltration into the previously irritated skin. Neutrophil depletion prior to re-challenge effectively prevented early flare-up responses during AD recurrence. Furthermore, we demonstrate that CD4+TRM cells upregulate expression of cytokines INF-γ and TNF-α, which may induce the expression of CXCL1, thereby recruiting neutrophils and contributing to the chronic recurrent inflammation observed in AD.

CONCLUSIONS

We have established a novel, chronic recurrent mouse model for investigating TRM cells in AD. Our findings demonstrate that CD4+TRM cells in the skin mediate early flare-up response during AD recurrence and influence the chronic recurrent inflammation of AD by recruiting neutrophils. Targeting CD4+TRM cells may represent a promising approach for the treatment of chronic recurrent inflammation in AD.

The junctional adhesion molecule-like protein (JAML) is important for the inflammatory response during contact hypersensitivity

BACKGROUND

The junctional adhesion molecule-like protein (JAML) plays important roles in wound healing and activation of epidermal γδ T cells in mice. Whether JAML plays a role in contact hypersensitivity (CHS), the animal model of allergic contact dermatitis (ACD), is not known.

METHODS

To examine the role of JAML in CHS, we used various mouse models of CHS in JAML knockout (KO) and wild-type (WT) mice. Furthermore, the expression of the JAML ligand coxsackievirus and adenovirus receptor (CXADR) on keratinocytes was accessed in vitro and in vivo.

RESULTS

JAML KO mice had a diminished inflammatory response during both the sensitization and elicitation phase of CHS and had reduced numbers of CD8+ and CD4+ T cells in the epidermis. Furthermore, interferon γ (IFNγ), interleukin 1β (IL-1β) and CXCL10 production were significantly reduced in JAML KO mice during the elicitation phase. We found that CD8+ T cells express JAML and that JAML is essential for rapid flare-up responses to contact allergens. Finally, we show that keratinocytes up-regulate the JAML ligand CXADR following exposure to contact allergens.

CONCLUSION

Our study is the first to show a central role of JAML in CHS and reveals a potential new target for the treatment of ACD in humans.

Allergic Contact Cell-Mediated Hypersensitivity in Psoriasis: A Narrative Minireview

The dysfunctionality of the protective skin barrier in psoriasis allows easier cutaneous penetration of various contact haptens; thus, such patients can develop allergic contact hypersensitivity as a comorbidity. Both skin conditions involve T-cell-mediated mechanisms. Dermatologists and allergists should consider assessing allergic contact cell-mediated hypersensitivity in selected psoriasis patients, especially those with palmoplantar psoriasis and who are refractory to topical treatments, and in patients with psoriasis, with or without arthritis, treated with biologics that present skin lesions clinically suggestive of contact dermatitis.

Preclinical Efficacy of a Capsid Virus-like Particle-Based Vaccine Targeting IL-1β for Treatment of Allergic Contact Dermatitis

Hypersensitivity to a contact allergen is one of the most abundant forms of inflammatory skin disease. Today, more than 20% of the general population are sensitized to one or more contact allergens, making this disease an important healthcare issue, as re-exposure to the allergen can initiate the clinical disease termed allergic contact dermatitis (ACD). The current standard treatment using corticosteroids is effective, but it has side effects when used for longer periods. Therefore, there is a need for new alternative therapies for severe ACD. In this study, we used the versatile Tag/Catcher AP205 capsid virus-like particle (cVLP) vaccine platform to develop an IL-1β-targeted vaccine and to assess the immunogenicity and in vivo efficacy of the vaccine in a translational mouse model of ACD. We show that vaccination with cVLPs displaying full-length murine IL-1β elicits high titers of neutralizing antibodies, leading to a significant reduction in local IL-1β levels as well as clinical symptoms induced by treatment with 1-Fluoro-2,4-dinitrobenzene (DNFB). Moreover, we show that a single amino acid mutation in muIL-1β reduces the biological activity while maintaining the ability to induce neutralizing antibodies. Collectively, the data suggest that a cVLP-based vaccine displaying full-length IL-1β represents a promising vaccine candidate for use as an alternative treatment modality against severe ACD.

Novel insights into contact dermatitis

Contact dermatitis is a common disease, caused by repeated skin contact to contact allergens or irritants, resulting in allergic contact dermatitis (ACD) and/or irritant contact dermatitis. Attempts have been made to identify biomarkers to distinguish irritant and allergic patch test reactions, which could aid diagnosis. Some promising candidates have recently been identified, but verification and validation in clinical cases still need to be done. New causes of ACD are constantly recognized. In this review, 10 new contact allergens from recent years, were identified, several relating to anti-age products. Frequent allergens causing considerable morbidity in the population such as the preservative methylisothiazolinone (MI) have been regulated in EU. A significant drop in cases has been seen, while high rates are still occurring in other areas such as North America. Other frequent causes are fragrance allergens especially widely used terpenes and acrylates used in medical devises for control of diabetes. These represent unsolved problems. Recent advances in immunology have opened for a better understanding of the complexity of contact dermatitis, especially ACD. The disease may be more heterogenous that previous understood with several subtypes. With the rapidly evolving molecular understanding of the disease, the potential for development of new drugs for personalized treatment of contact dermatitis is considerable.

CD8+ tissue-resident memory T cells recruit neutrophils that are essential for flare-ups in contact dermatitis

BACKGROUND

Allergic contact dermatitis (ACD) is classically described as a delayed-type hypersensitivity reaction. However, patients often experience flare-ups characterized by itching erythema, edema, and often vesicles occurring within hours after re-exposure of previously sensitized skin to the specific contact allergen. Recent studies have indicated that skin-resident memory T (T_RM ) cells play a central role in ACD. However, the pathogenic role of T_RM cells in allergen-induced flare-ups is not known.

METHODS

By the use of various mouse models and cell depletion protocols, we investigated the role of epidermal T_RM cells in flare-up reactions to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene. The inflammatory response was measured by changes in ear thickness, and the cellular composition in epidermis was determined by flow cytometry and confocal microscopy. Finally, adaptive transfer and inhibitors were used to determine the role of T_RM cells, neutrophils, and CXCL1/CXCL2 in the response.

RESULTS

We show that CD8⁺ T_RM cells initiate massive infiltration of neutrophils in the epidermis within 12 h after re-exposure to the contact allergen. Depletion of neutrophils before re-exposure to the allergen abrogated the flare-up reactions. Furthermore, we demonstrate that CD8⁺ T_RM cells mediate neutrophil recruitment by inducing CXCL1 and CXCL2 production in the skin, and that blockage of the C-X-C chemokine receptor type 1 and 2 inhibits flare-up reactions and neutrophil infiltration.

CONCLUSION

As the first, we show that epidermal CD8⁺ T_RM cells cause ACD flare-ups by rapid recruitment of neutrophils to the epidermis.

Low-dose intralesional injection of 5-fluorouracil and triamcinolone reduces tissue resident memory T cells in chronic eczema

BACKGROUND

Tissue resident memory T (T_RM) cells have been reported to play a significant role in the pathogenesis and relapse of chronic eczema.

AIM

To compare the efficacy and safety of the intralesional injection of 5-fluorouracil (5-FU) and triamcinolone (TA) with those associated with TA alone for the treatment of chronic eczema.

METHODS

A total of 168 patients were randomized to 5-FU+TA or TA groups and received a one-time intralesional injection of 5-FU+TA or TA only. Biopsies were collected before and 2 wk after treatment for evaluation of histopathological changes. All patients were followed up monthly for up to 1 year.

RESULTS

No serious adverse event was observed in either group. Although the mean atopic dermatitis severity index scores and effective rates were comparable between the two groups after 2 wk of treatment, the relapse rate was significantly lower in the 5-FU+TA group than in the TA group. Histological examination showed significantly fewer CD8⁺ and CD103⁺ T cells but not CD4⁺ T cells in the 5-FU+TA group.

CONCLUSION

One-time intralesional injection of 5-FU+TA is effective and safe for chronic eczema treatment and can further reduce the retention of T_RM cells in the lesional skin and the relapse rate of chronic eczema.

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.

Immunological Mechanisms of Metal Allergies and the Nickel-Specific TCR-pMHC Interface

Besides having physiological functions and general toxic effects, many metal ions can cause allergic reactions in humans. We here review the immune events involved in the mediation of metal allergies. We focus on nickel (Ni), cobalt (Co) and palladium (Pd), because these allergens are among the most prevalent sensitizers (Ni, Co) and immediate neighbors in the periodic table of the chemical elements. Co-sensitization between Ni and the other two metals is frequent while the knowledge on a possible immunological cross-reactivity using in vivo and in vitro approaches remains limited. At the center of an allergic reaction lies the capability of a metal allergen to form T cell epitopes that are recognized by specific T cell receptors (TCR). Technological advances such as activation-induced marker assays and TCR high-throughput sequencing recently provided new insights into the interaction of Ni2+ with the αβ TCR-peptide-major histocompatibility complex (pMHC) interface. Ni2+ functionally binds to the TCR gene segment TRAV9-2 or a histidine in the complementarity determining region 3 (CDR3), the main antigen binding region. Thus, we overview known, newly identified and hypothesized mechanisms of metal-specific T cell activation and discuss current knowledge on cross-reactivity.

Feeding of a fat-enriched diet causes the loss of resistance to contact hypersensitivity

BACKGROUND

Low-molecular weight chemicals or metal ions can cause allergic contact dermatitis, an inflammatory skin disease. Mice lacking Toll-like receptors 2 and 4 (TLR2/4 mice) are resistant to contact hypersensitivity (CHS). In the Western population obesity is increasing, which is known to have a proinflammatory impact.

OBJECTIVES

The aim of this study was to investigate the impact of a high-fat diet (HFD) on the sensitization and elicitation of CHS. We hypothesized that a proinflammatory micromilieu can be caused by an increase in adipose tissue, which might be sufficient to break the resistance of TLR2/4 mice.

METHODS

Four weeks prior to sensitization, wild-type (wt) or TLR2/4 mice were fed normal chow (NC), control diet (CD), or HFD. The effects on CHS and inflammation were analysed by measuring the ear swelling response, using flow cytometry and enzyme-linked immunosorbent assay.

RESULTS

The reaction of wt mice to 2,4,6-trinitro-1-chlorobenzene (TNCB) was increased by HFD. While NC-fed TLR2/4 mice were still resistant to CHS, HFD and, unexpectedly, CD feeding broke the resistance of TLR2/4 mice to TNCB.

CONCLUSIONS

These experiments suggest that the increased fat content or the different fatty acid composition of the diets increases inflammation and, therefore, the likelihood of developing CHS.

Tissue-Resident Memory T Cells in Skin Diseases: A Systematic Review

In health, the non-recirculating nature and long-term persistence of tissue-resident memory T cells (TRMs) in tissues protects against invading pathogens. In disease, pathogenic TRMs contribute to the recurring traits of many skin diseases. We aimed to conduct a systematic literature review on the current understanding of the role of TRMs in skin diseases and identify gaps as well as future research paths. EMBASE, PubMed, SCOPUS, Web of Science, Clinicaltrials.gov and WHO Trials Registry were searched systematically for relevant studies from their inception to October 2020. Included studies were reviewed independently by two authors. This study was conducted in accordance with the PRISMA-S guidelines. This protocol was registered with the PROSPERO database (ref: CRD42020206416). We identified 96 studies meeting the inclusion criteria. TRMs have mostly been investigated in murine skin and in relation to infectious skin diseases. Pathogenic TRMs have been characterized in various skin diseases including psoriasis, vitiligo and cutaneous T-cell lymphoma. Studies are needed to discover biomarkers that may delineate TRMs poised for pathogenic activity in skin diseases and establish to which extent TRMs are contingent on the local skin microenvironment. Additionally, future studies may investigate the effects of current treatments on the persistence of pathogenic TRMs in human skin.

Role of tissue-resident memory T cells in the pathophysiology of allergic contact dermatitis

PURPOSE OF REVIEW

We bring updated knowledge on tissue-resident memory T cells (TRM), underlining their major role in the recurrence and the severity of allergic contact dermatitis (ACD).

RECENT FINDINGS

ACD is a frequently encountered skin disease. It is defined as a delayed-type hypersensitivity reaction initiated by the recruitment of antigen-specific T cells into the skin of sensitized patients. ACD lesions tend to develop on already-exposed areas and worsen over time. That clinical observation has raised questions on the contribution of TRM to ACD recurrence and severity. TRM are memory T cells that persist in peripheral tissues, such as the skin, without recirculating through the blood. These cells provide effective immune memory against pathogens, but they may also participate in the development or exacerbation of numerous inflammatory diseases, including skin allergies. Recent works have demonstrated a major role for TRM in ACD pathophysiology.

SUMMARY

In ACD, TRM accumulate preferentially at the allergen contact site during the sensitization phase. Thereafter, these cells cause a rapid and intense response to any new allergen exposure. They also play a key role in flare-ups of ACD and the chronicity and severity of the disease. These aspects suggest that TRM may have an interest as therapeutic targets.

The role of interleukin-1β in the immune response to contact allergens

Interleukin-1β (IL-1β) is an important pro-inflammatory cytokine that has an effect on almost every cell lineage in the body. By blocking IL-1β and investigating the IL-1β signaling pathway, several studies have demonstrated a central role of IL-1β in the response to contact allergens. This review summarizes the current literature regarding the basic immunological mechanisms mediated by IL-1β in the different phases of allergic contact dermatitis (ACD) and highlights potential IL-1β-targeted treatment options, which in the future may be relevant in the treatment of patients with ACD. This review is based primarily on studies using various mouse models and human in vitro studies, since clinical studies on the effect of IL-1β in ACD are lacking.

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.

Tattoos - more than just colored skin? Searching for tattoo allergens

During tattooing, a high amount of ink is injected into the skin. Tattoo inks contain numerous substances such as the coloring pigments, impurities, solvents, emulsifiers, and preservatives. Black amorphous carbon particles (carbon black), white titanium dioxide, azo or polycyclic pigments create all varieties of color shades in the visible spectrum. Some ingredients of tattoo inks might be hazardous and allergenic chemicals of unknown potential. In Germany, about 20 % of the general population is tattooed and related adverse reactions are increasingly reported. Since tattoo needles inevitably harm the skin, microorganisms can enter the wound and may cause infections. Non-allergic inflammatory reactions (for example cutaneous granuloma and pseudolymphoma) as well as allergic reactions may emerge during or after wound healing. Especially with allergies occurring after weeks, months or years, it remains difficult to identify the specific ingredient(s) that trigger the reaction. This review summarizes possible adverse effects related to tattooing with a focus on the development of tattoo-mediated allergies. To date, relevant allergens were only identified in rare cases. Here we present established methods and discuss current experimental approaches to identify culprit allergens in tattoo inks - via testing of the patient and in vitro approaches.

Discipline in Stages: Regulating CD8+ Resident Memory T Cells

Resident memory CD8⁺ T (T_RM) cells are a lymphocyte lineage distinct from circulating memory CD8⁺ T cells. T_RM lodge within peripheral tissues and secondary lymphoid organs where they provide rapid, local protection from pathogens and control tumor growth. However, dysregulation of CD8⁺ T_RM formation and/or activation may contribute to the pathogenesis of autoimmune diseases. Intrinsic mechanisms, including transcriptional networks and inhibitory checkpoint receptors control T_RM differentiation and response. Additionally, extrinsic stimuli such as cytokines, cognate antigen, fatty acids, and damage signals regulate T_RM formation, maintenance, and expansion. In this review, we will summarize knowledge of CD8⁺ T_RM generation and highlight mechanisms that regulate the persistence and responses of heterogeneous T_RM populations in different tissues and distinct microenvironments.

Integrative transcriptome analysis deciphers mechanisms of nickel contact dermatitis

Background

Nickel‐induced allergic contact dermatitis (nACD) remains a major occupational skin disorder, significantly impacting the quality of life of suffering patients. Complex cellular compositional changes and associated immunological pathways are partly resolved in humans; thus, the impact of nACD on human skin needs to be further elucidated.

Methods

To decipher involved immunological players and pathways, human skin biopsies were taken at 0, 2, 48, and 96 hours after nickel patch test in six nickel‐allergic patients. Gene expression profiles were analyzed via microarray.

Results

Leukocyte deconvolution of nACD‐affected skin identified major leukocyte compositional changes at 48 and 96 hours, including natural killer (NK) cells, macrophage polarization, and T‐cell immunity. Gene set enrichment analysis mirrored cellular‐linked functional pathways enriched over time. NK cell infiltration and cytotoxic pathways were uniquely found in nACD‐affected skin compared to sodium lauryl sulfate–induced irritant skin reactions.

Conclusion

These results highlight key immunological leukocyte subsets as well as associated pathways in nACD, providing insights into pathophysiology with the potential to unravel novel therapeutic targets.

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.

CD4+ Resident Memory T Cells Mediate Long-Term Local Skin Immune Memory of Contact Hypersensitivity in BALB/c Mice

In allergic contact dermatitis (ACD) and contact hypersensitivity (CHS), the healed skin shows greater swelling than the naïve skin in the same individual upon re-exposure to the same hapten. This “local skin memory” (LSM) in healed skin was maintained for a prolonged period of time and mediated by skin CD8⁺-resident memory T (T_RM) cells in C57BL/6 mice. However, the number of CD4⁺ T cells is elevated in ACD-healed human skin, and the contribution of CD4⁺ T_RM cells to the formation of LSM currently remains unclear. We herein demonstrated that immediately after CHS subsided, the healed skin in BALB/c mice showed an accumulation of hapten-specific CD4⁺ and CD8⁺ T_RM cells, with a predominance of CD4⁺ T_RM cells. The presence of CD4⁺ or CD8⁺ T_RM cells in the healed skin was sufficient for the induction of a flare-up reaction upon a re-challenge. The CD4⁺ and CD8⁺ T_RM cells both produced interferon-γ and tumor necrosis factor early after the re-challenge. Moreover, while CD8⁺ T_RM cells gradually decreased over time and were eventually lost from the healed skin at 40–51 weeks after the resolution of CHS, the CD4⁺ T_RM cell numbers remained elevated during this period. The present results indicate that the long-term maintenance of LSM is mediated by CD4⁺ T_RM cells, and thus CD4⁺ T_RM cells are an important target for the treatment of recurrent human ACD.

Dendritic Epidermal T Cells in Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a common inflammatory skin disease with a prevalence of approximately 20% in the European population. ACD is caused by contact allergens that are reactive chemicals able to modify non-immunogenic self-proteins to become immunogenic proteins. The most frequent contact allergens are metals, fragrances, and preservatives. ACD clinically manifests as pruritic eczematous lesions, erythema, local papules, and oedema. ACD is a T cell-mediated disease, involving both CD4⁺ and CD8⁺ T cells. In addition, γδ T cells appear to play an important role in the immune response to contact allergens. However, it is debated whether γδ T cells act in a pro- or anti-inflammatory manner. A special subset of γδ T cells, named dendritic epidermal T cells (DETC), is found in the epidermis of mice and it plays an important role in immunosurveillance of the skin. DETC are essential in sensing the contact allergen-induced stressed environment. Thus, allergen-induced activation of DETC is partly mediated by numerous allergen-induced stress proteins expressed on the keratinocytes (KC). Several stress proteins, like mouse UL-16-binding protein-like transcript 1 (Mult-1), histocompatibility 60 (H60) and retinoic acid early inducible-1 (Rae-1) α-ε family in mice and major histocompatibility complex (MHC) class I-chain-related A (MICA) in humans, are upregulated on allergen-exposed KC. Allergen-induced stress proteins expressed on the KC are consequently recognized by NKG2D receptor on DETC. This review focuses on the role of γδ T cells in ACD, with DETC in the spotlight, and on the role of stress proteins in contact allergen-induced activation of DETC.

[Extended understanding of pathogenesis and treatment of contact allergy]

BACKGROUND

While the pathogenesis of contact allergy in recent years has increasingly focused on the mechanisms of the innate immune response, valid therapeutic options are still lacking.

AIMS

This article intends to shed light on the background of contact allergy development as well as possible risk factors and to highlight potential new therapeutic options.

MATERIALS AND METHODS

Allergic contact dermatitis (ACD) as well as the sensitization and trigger phase, potential risk factors as well as the therapy options including (current) PubMed-listed literature are described.

RESULTS

Inflammation plays a central role in ACD. The innate immune system responds to contact allergens as well as to infection. Elucidation of the mechanisms will enable a targeted therapeutic intervention in the future.

CONCLUSION

Although there is still a need for research, many parts of the contact allergy pathogenesis are now better understood. In particular, the essential role of the innate immune response not only for the sensitization but also for the elicitation phase seems to be established. Implementation of today's knowledge into new therapeutic approaches and their application testing remains important and exciting.

Clinical and histopathological characterization of eczematous eruptions occurring in course of anti IL-17 treatment: a case series and review of the literature

Background: Real-life data often highlight the side effects of certain drugs not previously reported in randomized controlled trials (RCTs).Objective: To describe cutaneous inflammatory eruptions in psoriatic patients treated with an anti IL-17A agent (secukinumab or ixekizumab).Methods: Retrospective analysis of a cohort of patients with chronic plaque psoriasis who started an anti IL-17A agent between September 2016-February 2019 and who developed cutaneous inflammatory eruptions during treatment. A systematic review of similar events reported in the literature was performed.Results: Data of 468 patients were reviewed and 27 cutaneous inflammatory eruptions of 27 (5.8%) patients were collected. The eruptions appeared after a mean of 16.9 ± 17.0 weeks of therapy showing a classical acute eczema in 11 patients (40.7%), an atopic dermatitis-like rash in 11 patients (40.7%) and a psoriasiform eruption in 5 patients (18.5%). Histopathology of 12/27 cases showed epidermal spongiosis in all these variants.Conclusion: We described the clinic-pathologic features of some eczematous eruptions occurring in psoriatic patients, 3-4 months after treatment initiation with an anti IL-17A agent. Further investigations are needed to explain this phenomenon, that might be defined a paradoxical adverse event, based upon the role of IL17 in eczema pathogenesis.

Tissue-resident memory T cells and their biological characteristics in the recurrence of inflammatory skin disorders

The skin is the largest organ of the body. The establishment of immunological memory in the skin is a crucial component of the adaptive immune response. Once naive T cells are activated by antigen-presenting cells, a small fraction of them differentiate into precursor memory T cells. These precursor cells ultimately develop into several subsets of memory T cells, including central memory T (T_CM) cells, effector memory T (T_EM) cells, and tissue resident memory T (T_RM) cells. T_RM cells have a unique transcriptional profile, and their most striking characteristics are their long-term survival (longevity) and low migration in peripheral tissues, including the skin. Under physiological conditions, T_RM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of T_RM cells in the recurrence of chronic inflammatory skin disorders, including psoriasis, vitiligo, and fixed drug eruption, under pathological or uncontrolled conditions. Clarifying and characterizing the mechanisms that are involved in skin T_RM cells will help provide promising strategies for reducing the frequency and magnitude of skin inflammation recurrence. Here, we discuss recent insights into the generation, homing, retention, and survival of T_RM cells and share our perspectives on the biological characteristics of T_RM cells in the recurrence of inflammatory skin disorders.

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.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity

PD-L2 is a ligand for the immune checkpoint receptor PD-1; however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells by topical application of small interfering RNA (siRNA) inhibits the elicitation of contact hypersensitivity (CHS). Here, we investigated the effects of topical application of PD-L2 siRNA on allergic skin disease. PD-L2 was induced in dendritic cells concurrently with the elevation of major histocompatibility complex class II and CD86 expression. Topical application of PD-L2 siRNA inhibited the elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying dendritic cells into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb inhibited CHS to the same extent. PD-L2 siRNA treatment inhibited CHS in PD-1/PD-L1 double knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and T helper type 2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous dendritic cells acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical application of siRNA represents a therapeutic approach for contact allergy.

Evaluation of the profile of inflammatory cytokines, through immunohistochemistry, in the skin of patients with allergic contact dermatitis to nickel in the acute and chronic phases

BACKGROUND

Allergic contact dermatitis to ion nickel (Ni+2) is an inflammatory dermatosis, common in industrialized countries. It involves the activation of nickel-specific T-cells, followed by proliferation and induction of a mixed profile of both proinflammatory and regulatory cytokines, suggesting that several T-cell subtypes (helper - Th and cytotoxic - Tc) are involved. A broader understanding of the cytokine profile may lead to new therapeutic approaches.

OBJECTIVES

This study aimed to analyze the cytokines TNF-α, INF-γ, IL-2, IL-4, IL-10, IL-13, IL-17 and IL-23 using the immunohistochemistry technique in order to try to identify their prevalence in chronic and acute eczema of patients with allergic contact dermatitis to Ni+2.

METHODS

We performed an immunohistochemical study for eight cytokines in 20 patients with Ni+2 allergic contact dermatitis, biopsied at the site of chronic eczema, triggered by the patient's daily contact with Ni+2, and at the site of acute eczema caused by nickel sulfate, 48 hours after applying the contact test.

RESULTS

The stained samples showed positive results for the eight cytokines studied. TNF-α, IFN-γ, IL-4, IL-13 and IL-17 had a higher prevalence in chronic eczema, IL-2 and IL-23 in acute eczema, and IL-10 presented a similar prevalence in both acute and chronic eczema. However, these prevalences were statistically significant only for IL-4 and IL-13.

STUDY LIMITATIONS

Small sample size.

CONCLUSIONS

In chronic and acute eczema, we observed the presence of a mixed cytokine profile of the T cell subtypes (Th/Tc), suggesting that the responses are expressed at the same time.

Tissue-resident lymphocytes: from adaptive to innate immunity

Efficient immune responses against invading pathogens often involve coordination between cells from both the innate and adaptive immune systems. For multiple decades, it has been believed that CD8⁺ memory T cells and natural killer (NK) cells constantly and uniformly recirculate. Only recently was the existence of noncirculating memory T and NK cells that remain resident in the peripheral tissues, termed tissue-resident memory T (T_RM) cells and tissue-resident NK (trNK) cells, observed in various organs owing to improved techniques. T_RM cells populate a wide range of peripheral organs, including the skin, sensory ganglia, gut, lungs, brain, salivary glands, female reproductive tract, and others. Recent findings have demonstrated the existence of T_RM in the secondary lymphoid organs (SLOs) as well, leading to revision of the classic theory that they exist only in peripheral organs. trNK cells have been identified in the uterus, skin, kidney, adipose tissue, and salivary glands. These tissue-resident lymphocytes do not recirculate in the blood or lymphatic system and often adopt a unique phenotype that is distinct from those of circulating immune cells. In this review, we will discuss the recent findings on the tissue residency of both innate and adaptive lymphocytes, with a particular focus on CD8⁺ memory T cells, and describe some advances regarding unconventional T cells (invariant NKT cells, mucosal-associated invariant T cells (MAIT), and γδ T cells) and the emerging family of trNK cells. Specifically, we will focus on the phenotypes and functions of these subsets and discuss their implications in anti-viral and anti-tumor immunity.

Cross-elicitation responses to 2-methoxymethyl-p-phenylenediamine in p-phenylenediamine-allergic individuals: Results from open use testing and diagnostic patch testing

BACKGROUND

Allergic contact dermatitis caused by p-phenylenediamine (PPD) is a health concern for hair dye users. Because of its lower sensitization potency, the PPD derivative 2-methoxymethyl-p-phenylenediamine (ME-PPD) has been developed as an alternative hair dye for primary prevention. However, cross-elicitation responses can occur in PPD-allergic subjects.

OBJECTIVES

To compare cross-elicitation responses to ME-PPD in open use and diagnostic patch testing of PPD-allergic subjects with hair dye-related allergic contact dermatitis.

METHODS

Reactions to ME-PPD were investigated in 25 PPD-allergic subjects by performing (1) 45-minute open use testing with a hair dye containing 2.0% of either ME-PPD or PPD, and (2) patch testing with increasing ME-PPD concentrations (0.1%-2.0% pet.).

RESULTS

Of the 25 PPD-allergic subjects, 21 (84%) reacted to open use testing with a hair dye containing 2.0% PPD, and testing with 2.0% ME-PPD led to cross-elicitation in 12 (48%). When patch tested with increasing ME-PPD concentrations, 13 (52%) cross-reacted at 0.1% (lowest dose) and 21 (84%) at 2.0% (highest dose), indicating decreased reactivity as compared with published PPD dose-response data.

CONCLUSION

In line with the decreased cross-reactivity of ME-PPD in hair dye open use testing, PPD-allergic subjects show an attenuated cross-elicitation dose response to ME-PPD in patch testing.