Epidermal barrier dysfunction and cutaneous sensitization in atopic diseases

Adherens Junctions and Desmosomes Coordinate Mechanics and Signaling to Orchestrate Tissue Morphogenesis and Function: An Evolutionary Perspective

Cadherin-based adherens junctions (AJs) and desmosomes are crucial to couple intercellular adhesion to the actin or intermediate filament cytoskeletons, respectively. As such, these intercellular junctions are essential to provide not only integrity to epithelia and other tissues but also the mechanical machinery necessary to execute complex morphogenetic and homeostatic intercellular rearrangements. Moreover, these spatially defined junctions serve as signaling hubs that integrate mechanical and chemical pathways to coordinate tissue architecture with behavior. This review takes an evolutionary perspective on how the emergence of these two essential intercellular junctions at key points during the evolution of multicellular animals afforded metazoans with new opportunities to integrate adhesion, cytoskeletal dynamics, and signaling. We discuss known literature on cross-talk between the two junctions and, using the skin epidermis as an example, provide a model for how these two junctions function in concert to orchestrate tissue organization and function.

Pathophysiology of Eosinophilic Esophagitis

Eosinophilic esophagitis (EoE) is a chronic inflammatory disease of the esophagus associated with an atopic predisposition which appears to be increasing in prevalence over the last few decades. Symptoms stem from fibrosis, swelling, and smooth muscle dysfunction. In the past two decades, the etiology of EoE has been and is continuing to be revealed. This review provides an overview of the effects of genetics, environment, and immune function including discussions that touch on microbiome, the role of diet, food allergy, and aeroallergy. The review further concentrates on the pathophysiology of the disease with particular focus on the important concepts of the molecular etiology of EoE including barrier dysfunction and allergic hypersensitivity.

Atopic dermatitis: the skin barrier and beyond

BACKGROUND

Atopic dermatitis is the most common chronic inflammatory skin disorder, affecting up to 20% of children and 10% of adults in industrialized countries. This highly debilitating condition poses a considerable burden to both the individual and society at large. The pathophysiology of atopic dermatitis is complex, encompassing both genetic and environmental risk factors.

METHODS

This is a narrative review based on a systematic literature search.

CONCLUSIONS

Dysregulation of innate and adaptive immunity plays a key role; however, recent epidemiological, genetic and molecular research has focused interest on skin barrier dysfunction as a common precursor and pathological feature. Current understanding of the aetiology of atopic dermatitis highlights disruption of the epidermal barrier leading to increased permeability of the epidermis, pathological inflammation in the skin, and percutaneous sensitization to allergens. Thus, most novel treatment strategies seek to target specific aspects of the skin barrier or cutaneous inflammation. Several studies have also shown promise in preventing atopic dermatitis, such as the early use of emollients in high-risk infants. This may have broader implications in terms of halting the progression to atopic comorbidities including food allergy, hay fever and asthma.

Evaluation of immunoresponses and cytotoxicity from skin exposure to metallic nanoparticles

Nanotechnology is an interdisciplinary science that has developed rapidly in recent years. Metallic nanoparticles (NPs) are increasingly utilized in dermatology and cosmetology, because of their unique properties. However, skin exposure to NPs raises concerns regarding their transdermal toxicity. The tight junctions of epithelial cells form the skin barrier, which protects the host against external substances. Recent studies have found that NPs can pass through the skin barrier into deeper layers, indicating that skin exposure is a means for NPs to enter the body. The distribution and interaction of NPs with skin cells may cause toxic side effects. In this review, possible penetration pathways and related toxicity mechanisms are discussed. The limitations of current experimental methods on the penetration and toxic effects of metallic NPs are also described. This review contributes to a better understanding of the risks of topically applied metallic NPs and provides a foundation for future studies.

Epithelial barrier dysfunctions in atopic dermatitis: a skin-gut-lung model linking microbiome alteration and immune dysregulation

BACKGROUND

Atopic dermatitis is a systemic disorder characterized by abnormal barrier function across multiple organ sites. Causes of epidermal barrier breakdown are complex and driven by a combination of structural, genetic, environmental and immunological factors. In addition, alteration in microflora diversity can influence disease severity, duration, and response to treatment. Clinically, atopic dermatitis can progress from skin disease to food allergy, allergic rhinitis, and later asthma, a phenomenon commonly known as the atopic march. The mechanism by which atopic dermatitis progresses towards gastrointestinal or airway disease remains to be elucidated.

OBJECTIVES

This review addresses how epithelial dysfunction linking microbiome alteration and immune dysregulation can predispose to the development of the atopic march.

METHODS

A literature search was conducted using the PubMed database for relevant articles with the keywords 'atopic dermatitis', 'epithelial barrier', 'skin', 'gut', 'lung', 'microbiome' and 'immune dysregulation'.

RESULTS

Initial disruption in the skin epidermal barrier permits allergen sensitization and colonization by pathogens. This induces a T helper 2 inflammatory response and a thymic stromal lymphopoietin-mediated pathway that further promotes barrier breakdown at distant sites, including the intestinal and respiratory tract.

CONCLUSIONS

As there are no immediate cures for food allergy or asthma, early intervention aimed at protecting the skin barrier and effective control of local and systemic inflammation may improve long-term outcomes and reduce allergen sensitization in the airway and gut.

Taking the lead - how keratinocytes orchestrate skin T cell immunity

The skin comprises a complex coordinated system of epithelial tissue cells and immune cells that ensure adequate immune reactions against trauma, toxins and pathogens, while maintaining tissue homeostasis. Keratinocytes form the outermost barrier of the skin, and sense changes in barrier integrity, intrusion of microbial components and stress molecules. Thus, they act as sentinels that continuously communicate the status of the organ to the cutaneous immune system. Upon damage the keratinocytes initiate a pro-inflammatory signaling cascade that leads to the activation of resident immune cells. Simultaneously, the tissue mediates and supports immune-suppressive functions to contain inflammation locally. After resolution of inflammation, the skin provides a niche for regulatory and effector memory T cells that can quickly respond to reoccurring antigens. In this review we discuss the central role of keratinocyte-derived signals in controlling cutaneous T cell immunity.

The atopic march: current insights into skin barrier dysfunction and epithelial cell-derived cytokines

Atopic dermatitis often precedes the development of other atopic diseases. The atopic march describes this temporal relationship in the natural history of atopic diseases. Although the pathophysiological mechanisms that underlie this relationship are poorly understood, epidemiological and genetic data have suggested that the skin might be an important route of sensitization to allergens. Animal models have begun to elucidate how skin barrier defects can lead to systemic allergen sensitization. Emerging data now suggest that epithelial cell-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 may drive the progression from atopic dermatitis to asthma and food allergy. This review focuses on current concepts of the role of skin barrier defects and epithelial cell-derived cytokines in the initiation and maintenance of allergic inflammation and the atopic march.

Improvement of skin barrier dysfunction by Scutellaria baicalensis GEOGI extracts through lactic acid fermentation

BACKGROUND

The development of an alternative medicine to treat atopic dermatitis (AD) from natural sources is necessary.

AIMS

To improve skin barrier dysfunction by enhancing the differentiation of human keratinocytes with the fermented Scutellaria baicalensis.

METHODS

Scutellaria baicalensis was fermented with Lactobacillus plantarum and extracted with 70% ethanol (FE). Antioxidant activities and the regulation of the gene expression related to keratinocyte differentiation were measured as well as its proliferation.

RESULT

This work first proved that the FE had multiple activities, both increasing keratinocyte differentiation and proliferation: The FE greatly up-regulated expression of the genes of keratinocyte differentiation such as involucrin, keratin 10, and transglutaminase-1 (TG-1) up to 4.06-fold, which was 3 times higher than the 2 other extracts. The effect of baicalein on keratinocyte differentiation was also first found; however, its efficacy was lower than that of the fermented extract. The FE proved to effectively accelerate keratinocyte differentiation, rather than to initiate the differentiation, and also showed an ability of stimulating keratinocyte proliferation up to 2.8 × 10⁶ viable cells/mL as well as 70.24 ng/mL of collagen production in fibroblasts. High efficacy of the FE was confirmed by synergistic effects of large amounts of various bioactive substances in the extracts as baicalein alone did not show remarkable effects and even positive controls had not much better activities than the FE.

CONCLUSION

The fermented extract was able to improve skin barrier dysfunction, and the ointment with 1%-5% (v/v) of the extract be directly used for skin clinical trials to treat AD.

Anti-IL-12/IL-23p40 antibody ameliorates dermatitis and skin barrier dysfunction in mice with imiquimod-induced psoriasis-like dermatitis

Psoriasis is a chronic inflammatory skin disease characterized by erythema, skin hyperplasia, scales, and keratinocyte hyperproliferation. While the cause of psoriasis is not clearly understood, a dysregulated immune system, especially activation of IL-23/IL-17 axis, has been strongly implicated in the pathogenesis of psoriasis. For example, anti-IL-23 therapy is effective in psoriasis patients, and thus IL-23 is considered as a potential therapeutic target for the treatment of psoriasis. The skin barrier provides protection of the human body against infection from external pathogens. Dysfunction of the skin barrier is also one of the characteristics in psoriasis and is correlated with disease severity. However, there have been no reports regarding the effectiveness of antipsoriatic agents on the skin barrier dysfunction of psoriasis. In this study, we examined the effect of anti-IL-12/IL-23p40 monoclonal antibody (p40 mAb) on dermatitis symptoms and skin barrier dysfunction in mice with imiquimod-induced psoriasis-like dermatitis. We found that p40 mAb suppressed epidermal thickness and increased transepidermal water loss (TEWL) as indicator for skin barrier function with accompanying suppression of IL-23p19, IL-17A, IL-22, and keratin 16 gene expression. These results suggest that p40 mAb is not only effective against dermatitis symptoms but also skin barrier dysfunction in mice with imiquimod-induced psoriasis-like dermatitis. This is the first report on the effect of p40 mAb on skin barrier dysfunction related to psoriasis. Taken together, our results indicate the possibility of new insights as well as the therapeutic potential of anti-IL-23 for the treatment of psoriasis.

Skin barrier in the neonate

The purpose of this review is to focus on determinants of skin barrier function in neonates at molecular and cellular levels. The skin barrier is critical in terms of water and gas exchanges during fetal life and undergoes rapid changes at birth, followed by a progressive maturation. Consequences of skin barrier disruption can be extremely detrimental or lethal, as shown in severe genetic epidermal defects. In this context, the fine-tuned rapid adaptation from a liquid to a gaseous milieu is not fully understood. The stratum corneum provides an air-liquid barrier, tight junctions in the granular layer provide a liquid-liquid barrier, aquaporins represent a plumbing system for water-glycerol as well as gas exchanges, and Langerhans cells are central to the immunological barrier. Acid mantle formation is essential for appropriate interaction between the skin and microbial symbionts. Temperature and pH regulate the key enzyme activities responsible for the integrity of the stratum corneum. Skin barrier permeability can be assessed noninvasively and simply with miniaturized devices measuring transepidermal water loss, where water flow is faster in cases of a damaged or functionally premature barrier. New avenues for therapeutic skin barrier research in neonates include a better delineation of the maturation of aquaporins in water balance and gas exchanges from fetal to neonatal life and a better understanding of the role of vernix caseosa, in particular, for the implantation of a healthy microbiote. Practical applications should be derived for caring for infant skin, particularly in fragile zones, such as the diaper area.

Epistasis between FLG and IL4R Genes on the Risk of Allergic Sensitization: Results from Two Population-Based Birth Cohort Studies

Immune-specific genes as well as genes responsible for the formation and integrity of the epidermal barrier have been implicated in the pathogeneses of allergic sensitization. This study sought to determine whether an epistatic effect (gene-gene interaction) between genetic variants within interleukin 4 receptor (IL4R) and filaggrin (FLG) genes predispose to the development of allergic sensitization. Data from two birth cohort studies were analyzed, namely the Isle of Wight (IOW; n = 1,456) and the Manchester Asthma and Allergy Study (MAAS; n = 1,058). In the IOW study, one interaction term (IL4R rs3024676 × FLG variants) showed statistical significance (interaction term: P = 0.003). To illustrate the observed epistasis, stratified analyses were performed, which showed that FLG variants were associated with allergic sensitization only among IL4R rs3024676 homozygotes (OR, 1.97; 95% CI, 1.27–3.05; P = 0.003). In contrast, FLG variants effect was masked among IL4R rs3024676 heterozygotes (OR, 0.53; 95% CI, 0.22–1.32; P = 0.175). Similar results were demonstrated in the MAAS study. Epistasis between immune (IL4R) and skin (FLG) regulatory genes exist in the pathogenesis of allergic sensitization. Hence, genetic susceptibility towards defective epidermal barrier and deviated immune responses could work together in the development of allergic sensitization.

Efficacy and safety of topical JTE-052, a Janus kinase inhibitor, in Japanese adult patients with moderate-to-severe atopic dermatitis: a phase II, multicentre, randomized, vehicle-controlled clinical study

BACKGROUND

JTE-052 is a novel Janus kinase inhibitor presently under clinical development for the topical treatment of atopic dermatitis (AD).

OBJECTIVES

To evaluate the efficacy and safety of JTE-052 ointment in Japanese adult patients with AD.

METHODS

Patients with moderate-to-severe AD were randomized (2: 2: 2: 2: 1: 1) to receive JTE-052 ointment at 0·25%, 0·5%, 1% or 3%, the vehicle ointment or tacrolimus 0·1% ointment (reference) twice daily for 4 weeks. The primary efficacy end point was the percentage change in modified Eczema Area Severity Index (mEASI) score from baseline at the end of treatment (EOT). Secondary efficacy end points included change from baseline in the pruritus numerical rating scale (NRS) score.

RESULTS

In total, 327 patients were enrolled. At EOT, the least-squares mean percentage changes from baseline in mEASI score for JTE-052 at 0·25%, 0·5%, 1% and 3% and the vehicle ointment were -41·7%, -57·1%, -54·9%, -72·9% and -12·2%, respectively. All JTE-052 groups showed significant reductions of mEASI score vs. the vehicle group (P < 0·001 for all). In the tacrolimus group, the mean percentage change in mEASI score was -62·0%. The JTE-052 groups also showed significant improvement in other parameters; notably, the pruritus NRS score was reduced as early as day 1 night-time. JTE-052 ointment at doses up to 3% was safe and well tolerated.

CONCLUSIONS

Topical JTE-052 markedly and rapidly improved clinical signs and symptoms in Japanese adult patients with moderate-to-severe AD, with a favourable safety profile. The study results indicate that topical JTE-052 is a promising therapeutic option for AD. The trial registration number is JapicCTI-152887.

Evidence of an abnormal epithelial barrier in active, untreated and corticosteroid-treated eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EoE) is a chronic, immune/antigen-mediated disease characterized by symptoms related to esophageal dysfunction and an eosinophil-predominant inflammation. This study has aimed to investigate whether the recently observed sensitization to Candida albicans in patients with EoE is owing to pre-existing disease and its underlying abnormal epithelial barrier or, alternatively, is linked to corticosteroid (CS) therapy.

METHODS

Medical histories, as well as serum and tissue samples of 60 patients with EoE (15 CS naive, 45 with current or previous CS therapy) and 20 controls, stored in the Swiss Eosinophilic Esophagitis Database (SEED) and Biobank, were analyzed. We applied ImmunoCAP to measure IgE levels and immunofluorescence techniques to examine epithelial barrier components.

RESULTS

Patients with EoE had higher total IgE levels and were more frequently sensitized to C. albicans than controls. In EoE tissue specimens, increased numbers of eosinophils and mast cells, a higher expression levels of thymic stromal lymphopoietin (TSLP), cathelicidin, proteases, that is, the kallikreins (KLK)-5 and KLK-7, were observed as compared with controls, while reduced expression of lympho-epithelial Kazal-type-related inhibitor (LEKTI), filaggrin, E-cadherin, claudin, occludin, desmoglein-1 was found, independent of CS therapy. In CS-treated EoE, significantly lower numbers of CD1a+ cells and cathelicidin expression were noted as compared to CS-naive EoE.

CONCLUSION

This study provides further evidence that EoE is associated with an abnormal epithelial barrier and postulates that CS therapy, by reducing innate immune mechanisms, may promote C. albicans colonization and likely subsequent sensitization.

Simple Markers for Systemic Inflammation in Pediatric Atopic Dermatitis Patients

Background:

Atopic dermatitis is a dermatological disease characterized by chronic inflammation. In recent years, systemic inflammation is also mentioned along with local inflammation for its pathogenesis. Neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), and mean platelet volume (MPV) are nonspecific indicators of systemic inflammation, and they were shown to be associated with the disease and its prognosis in allergic or nonallergic diseases.

Aims and Objectives:

The aim of this study was to evaluate the values of NLR, PLR, and MPV in atopic dermatitis patients and also to investigate the associations of them with the atopic dermatitis disease severity and duration.

Materials and Methods:

Two hundred and fifty-two atopic dermatitis patients and 75 control group individuals were included in the study. Mean/median values of NLR, PLR, and MPV were compared among patients and controls, severity groups classified according to SCORing Atopic Dermatitis (SCORAD) and intrinsic and extrinsic groups. Correlation of disease duration and SCORAD with NLR, PLR, and MPV values were examined. Disease duration and its association with NLR were evaluated by correlation and linear regression analysis.

Results:

Mean NLR and median PLR values of atopic dermatitis patients were higher than those of controls (0.97 ± 0.69 and 80.86 [59.86–108.23], respectively). NLR and PLR values were found to be positively correlated with disease duration and NLR was positively associated with disease duration after adjustment. NLR value was also higher in the extrinsic group than the intrinsic group.

Conclusion:

Presence of systemic inflammation in the pathogenesis of atopic dermatitis was considered to be associated with increased NLR and PLR values. These parameters were also associated with disease duration and might vary between subtypes of atopic dermatitis. NLR and PLR were cheaper and easily accessible alternatives to the systemic inflammation biomarkers that were expensive and not accessible for all laboratories, particularly in economically disadvantaged countries.

The Origin of Skin Dendritic Cell Network and Its Role in Psoriasis

Dendritic cells (DCs) are heterogeneous groups of innate immune cells, which orchestrate immune responses by presenting antigens to cognate T cells and stimulating other types of immune cells. Although the term ‘DCs’ generally represent highly mixed subsets with functional heterogeneity, the classical definition of DCs usually denotes conventional DCs (cDCs). Skin contains a unique DC network mainly composed of embryo precursor-derived epidermal Langerhans cells (LCs) and bone marrow-derived dermal cDCs, which can be further classified into type 1 (cDC1) and type 2 (cDC2) subsets. Psoriasis is a chronic inflammatory skin disease, which is principally mediated by IL-23/IL-17 cytokine axis. In the psoriatic skins, DCs are prominent cellular sources for TNF-α and IL-23, and the use of blocking antibodies against TNF-α and IL-23 leads to a significant clinical improvement in psoriatic patients. Recent elegant human and mouse studies have shown that inflammation-induced inflammatory DCs, LCs, dermal cDC2, and monocyte-derived DCs are pivotal DC subsets in psoriatic inflammation. Thus, targeting specific pathogenic DC subsets would be a potential strategy for alleviating and preventing DC-derived IL-23-dependent psoriatic inflammation and other inflammatory dermatoses in the future.

Skin-Specific CD301b+ Dermal Dendritic Cells Drive IL-17-Mediated Psoriasis-Like Immune Response in Mice

Conventional dendritic cells (cDCs) are composed of heterogeneous subsets commonly arising from dendritic cell (DC)-committed progenitors. A population of CD301b-expressing DCs has recently been identified in non-lymphoid barrier tissues such as skin. However, whether CD301b⁺ DCs in the skin represent an ontogenetically unique subpopulation of migratory cDCs has not been fully addressed. Here, we demonstrated that CD301b⁺ dermal DCs were distinct subpopulation of FMS-like tyrosine kinase 3 ligand (FLT3L)-dependent CD11b⁺ cDC2 lineage, which required an additional GM-CSF cue for the adequate development. Although the majority of lymphoid-resident cDC2 lacked CD301b expression, dermal migratory cDC2 contained a substantial fraction of CD301b⁺ subset. Similar to CD301b^- population, CD301b⁺ dermal DC development was closely regulated by FLT3 signaling, suggesting their common origin from FLT3L-responsive cDC progenitors. However, FLT3L-driven cDC progenitor culture was not sufficient, but additional GM-CSF treatment was required to produce CD301b⁺ cDC2. In vivo development of CD301b⁺ cDC2 was significantly augmented by exogenous GM-CSF, while the repopulation of CD301b⁺ dermal cDC2 was abrogated by GM-CSF neutralization. Functionally, CD301b⁺ cDC2 was capable of producing a high level of IL-23, and the depletion of CD301b⁺ cDC2 effectively prevented IL-17-mediated psoriasiform dermatitis. Therefore, our findings highlight the differentiation program of a distinct CD301b⁺ dermal cDC2 subset in the skin and its involvement in psoriatic inflammation.

E-cadherin integrates mechanotransduction and EGFR signaling to control junctional tissue polarization and tight junction positioning

Generation of a barrier in multi-layered epithelia like the epidermis requires restricted positioning of functional tight junctions (TJ) to the most suprabasal viable layer. This positioning necessitates tissue-level polarization of junctions and the cytoskeleton through unknown mechanisms. Using quantitative whole-mount imaging, genetic ablation, and traction force microscopy and atomic force microscopy, we find that ubiquitously localized E-cadherin coordinates tissue polarization of tension-bearing adherens junction (AJ) and F-actin organization to allow formation of an apical TJ network only in the uppermost viable layer. Molecularly, E-cadherin localizes and tunes EGFR activity and junctional tension to inhibit premature TJ complex formation in lower layers while promoting increased tension and TJ stability in the granular layer 2. In conclusion, our data identify an E-cadherin-dependent mechanical circuit that integrates adhesion, contractile forces and biochemical signaling to drive the polarized organization of junctional tension necessary to build an in vivo epithelial barrier.

Antioxidant Artemisia princeps Extract Enhances the Expression of Filaggrin and Loricrin via the AHR/OVOL1 Pathway

The Japanese mugwort, Artemisia princeps (yomogi in Japanese), has anti-inflammatory and antioxidant effects. Skin care products containing Artemisia princeps extract (APE) are known to improve dry skin symptoms in atopic dermatitis. Atopic dry skin is associated with a marked reduction of skin barrier proteins, such as filaggrin (FLG) and loricrin (LOR). Recently, aryl hydrocarbon receptor (AHR), and its downstream transcription factor OVO-like 1 (OVOL1), have been shown to regulate the gene expression of FLG and LOR. The focus of this paper is to evaluate the effects of APE on the AHR/OVOL1/FLG or LOR pathway since they have remained unknown to this point. We first demonstrated that non-cytotoxic concentrations of APE significantly upregulated antioxidant enzymes, NAD(P)H dehydrogenase quinone 1 and heme oxygenase 1, in human keratinocytes. Even at these low concentrations, APE induced nuclear translocation of AHR and significantly upregulated CYP1A1 (a specific target gene for AHR activation), FLG, and LOR expression. AHR knockdown downregulated OVOL1 expression. The APE-induced upregulation of FLG and LOR was canceled in keratinocytes with AHR or OVOL1 knockdown. In conclusion, antioxidant APE is a potent phytoextract that upregulates FLG and LOR expression in an AHR/OVOL1-dependent manner and this may underpin the barrier-repairing effects of APE in treating atopic dry skin.

Evaluation of the relation between lipid coat, transepidermal water loss, and skin pH

OBJECTIVE

The epidermis is an epidermal barrier which accumulates lipid substances and participates in skin moisturizing. An evaluation of the epidermal barrier efficiency can be made, among others, by the measurement of the following values: the lipid coat, the transepidermal water loss (TEWL) index, and pH.

MATERIALS

The study involved 50 Caucasian, healthy women aged 19-35 years (mean 20.56).

METHODS

Measurements were made using Courage & Khazaka Multi Probe Adapter MPA 580: Tewameter TM 300, pH-Meter PH 905, Sebumeter SM 815. The areas of measurements included forehead, nose, left cheek, right cheek, chin, and thigh.

RESULTS

In the T-zone, the lipid coat was in the range between 0 and 270 μg/cm² (mean 128 μg/cm² ), TEWL between 1 and 55 g/m² /h (mean 11.1 g/m² /h), and pH 4.0-5.6 (mean 5.39). Lower values of the lipid coat up to 100 μg/cm² were accompanied by TEWL greater than 30 g/m² /h and less acidic pH of 5.6-9.0. In the U-zone the range of lipid coat was up to 200 μg/cm² (mean 65.2 μg/cm² ), the skin pH remained 4.0-5.6 (mean 5.47), and TEWL was in the range between 1 and 20 g/m² /h (mean 8.7 g/m² /h). Lower values of the lipid coat up to 100 μg/cm² were accompanied by TEWL between 1 and 20 g/m² /h and less acidic pH of 5.6-9.0. High values of the lipid coat between 180 and 200 μg/cm² were connected with TEWL of 1-15 g/m² /h. On the skin of the thigh, we observed a very thin lipid coat - 35 μg/cm² (mean 5.6 μg/cm² ), pH (mean 5.37), and TEWL (mean 8.5 g/m² /h) were considered by us to be within regular limits.

CONCLUSIONS

In the T-zone, a thinner lipid coat resulted in relatively high TEWL and pH levels changing toward alkaline. In the U-zone, thinner lipid coat was accompanied by lower TEWL and pH changing toward alkaline. We also observed that lower values of lipid coat up to 100 μg/cm² were associated with higher pH values ranging toward the basic character pH 5.6-9.0).

Anaphylaxis after disinfection with 2% chlorhexidine wand applicator

A 54-year-old man with end-stage renal failure attended for dialysis. Within seconds of applying 2% w/v chlorhexidine (ChloraPrep 3 mL Wand Applicator) to the skin surrounding the insertion point of his dialysis catheter (Tesio catheter), he developed pruritus, urticaria, shortness of breath, hypotension and reduced responsiveness. Treatment for anaphylaxis was initiated with rapid improvement of his symptoms, and he made a full recovery. Allergy to chlorhexidine was confirmed with skin testing, and the patient was warned against all future exposure to chlorhexidine. Subsequent dialysis without chlorhexidine was uneventful.

Topical application of Dermatophagoides farinae or oxazolone induces symptoms of atopic dermatitis in the rabbit ear

Atopic dermatitis (AD) is a chronically relapsing inflammatory skin disease characterized by hyperproliferation and abnormal differentiation of the epidermis, and dermal infiltration of inflammatory cells. Appropriate animal models that recapitulate human AD and allow the analysis of disease processes in a reliable manner are essential to the study of AD. In this study, we established two AD models in rabbits by applying an allergen, Dermatophagoides farinae (Der f), or a hapten, oxazolone (OXZ). Application of the allergen or hapten induced a rapid onset and a chronically sustained AD-like skin lesion. The clinical symptoms, which include skin erythema, scaling, papula and edema, of AD-like rabbit skin were similar to those in human AD. Histological analysis showed that allergen- or hapten-treated rabbit skin showed increased epidermal thickening and inflammatory cell infiltration. Furthermore, PCNA and keratin 10 (K10) staining revealed excessive proliferation and insufficient differentiation of the epidermis in the rabbit AD-like skin. Western blot analysis showed decreased expression of thymic stromal lymphopoietin (TSLP), an AD cytokine, in the rabbit AD-like skin. Our results suggest that the allergen- or hapten-induced rabbit AD models have pathological features of human AD-like symptoms and will be useful for evaluating both pathogenic mechanisms and potential therapeutic agents for human AD.

Cimifugin suppresses allergic inflammation by reducing epithelial derived initiative key factors via regulating tight junctions

Cimifugin is a bioactive component of Saposhnikovia divaricata, a Chinese herb for treating allergy. Our previous studies demonstrated that cimifugin inhibited allergic inflammation efficiently. This study aims to determine the mechanism of cimifugin on epithelial cells in allergic inflammation. Mice were sensitized and challenged with FITC to establish type 2 atopic dermatitis (AD) model. The initial stage of AD model, in which mice were just sensitized with FITC, was established in vivo and immortalized human epidermal (HaCaT) cells were utilized in vitro. Initiative key cytokines, TSLP and IL-33, were measured by ELISA, the junctions in ECs were observed by electron microscopy and TJs (CLDN-1, occludin and CLDND1) were assessed by Western blot, immunohistochemistry and immunofluorescence. The results showed that TSLP and IL-33 were inhibited significantly by cimifugin in the initial stage of AD model. Simultaneously, cimifugin reduced the separated gap among the epithelial cells and increased the expression of TJs. Similar effects on TSLP/IL-33 and TJs were obtained in vitro. The effect of cimifugin on TSLP decreased significantly when expression of CLDN1 was interfered with siRNA and this implied cimifugin inhibits initiative cytokines through restoring TJs. Furthermore, cimifugin administered only in the initial stage obviously attenuated the ultimate allergic inflammation, which indicate that impacts of cimifugin in the initial stage on TSLP/IL-33 and TJs are sufficient for suppressing allergic inflammation. This study not only revealed the mechanisms of cimifugin, but also indicated the possibility of initiative key cytokines and TJs as therapeutic targets.

Therapeutic vaccines for allergic disease

Allergic diseases are highly prevalent worldwide and affect all age groups, contributing to a high personal and socioeconomic burden. Treatment with an “allergy vaccine” or allergen immunotherapy aims to provide long-lasting benefits by inducing unresponsiveness to the relevant antigen. The consequences of the therapy are considered disease modifying and range from dampening of the immediate immune responses to the reduction of secondary tissue remodeling. Furthermore, allergen immunotherapy interventions have a potential to slow or cease the development of additional allergic manifestations with a long-term overall effect on morbidity and quality of life. Here, we review proposed mechanisms underlying the therapeutic effects of immunotherapy for allergic diseases. Further, we discuss both standard and novel approaches and possible future directions in the development of allergen immunotherapy.

Atopic Eczema: Genetic Associations and Potential Links to Developmental Exposures

Atopic eczema (AE), or atopic dermatitis (AD), is a common inflammatory skin disease with a disrupted epidermal barrier and an allergic immune response. AD/AE is prominently characterized by a symptomatic itch and transient skin lesions. Infants compose a significant percentage affected. Two models have been proposed to explain AD/AE skin pathology: the gut microbiome-focused inside-outside model and the outside-inside model concentrating on the disrupted skin barrier/skin microbiome. Gene disruptions contributing to epidermal structure, as well as those in immune system genes, are implicated. Over 30 genes have been linked to AD/AE with Flg and Tmem79/Matt alterations being common. Other linked disruptions are in the interleukin-1 family of cytokines/receptors and the TH2 gene family of cytokines. Inheritable epigenetic modifications of the genes or associated proteins may also be involved. Skin barrier disruption and the allergic immune response have been the main foci in mechanistic studies of AD/AE, but the role of the environment is becoming more apparent. Thus, an examination of in utero exposures could be very helpful in understanding the heterogeneity of AD/AE. Although research is limited, there is evidence that developmental exposure to environmental tobacco smoke or phthalates may impact disease. Management for AD/AE includes topical corticosteroids and calcineurin inhibitors, which safely facilitate improvements in select individuals. Disease heterogeneity warrants continued research not only into elucidating disease mechanism(s), via identification of contributing genetic alterations, but also research to understand how/when these genetic alterations occur. This may lead to the cure that those affected by AD/AE eagerly await.

Filaggrin Mutation in Korean Patients with Atopic Dermatitis

PURPOSE

Atopic dermatitis (AD) is a chronic, relapsing eczematous inflammatory skin disease. Mutations in the filaggrin gene (FLG) are major predisposing factors for AD. Ethnic differences exist between Asian and European populations in the frequency and spectrum of FLG mutations. Moreover, a distinct set of FLG mutations has been reported in Asian populations. The aim of this study was to examine the spectrum of FLG mutations in Koreans with AD. We also investigated the association of FLG mutations and clinical features of AD and compared the Korean FLG landscape with that of other East Asian countries.

MATERIALS AND METHODS

Seventy Korean patients with AD were enrolled in this study. Fourteen FLG mutations previously detected in Korean, Japanese, and Chinese patients were screened by genotyping.

RESULTS

Four FLG null mutations (3321delA, K4022X, S3296X, and S2889X) were identified in eleven patients (15.7%). The most commonly detected mutations in Korean patients with AD were 3321delA (n=6, 9.1%) and K4022X (n=3, 4.5%). FLG mutations were significantly associated with elevated IgE (≥200 KIU/L and/or MAST-CLA >3+, p=0.005), palmar hyperlinearity (p<0.001), and a family history of allergic disease (p=0.021).

CONCLUSION

This study expanded our understanding of the landscape of FLG mutations in Koreans and revealed an association between FLG mutations and AD phenotype.

Epicutaneous sensitization to house dust mite allergen requires interferon regulatory factor 4-dependent dermal dendritic cells

BACKGROUND

Exposure to allergens, such as house dust mite (HDM), through the skin often precedes allergic inflammation in the lung. It was proposed that T_H2 sensitization through the skin occurs when skin barrier function is disrupted by, for example, genetic predisposition, mechanical damage, or the enzymatic activity of allergens.

OBJECTIVE

We sought to study how HDM applied to unmanipulated skin leads to T_H2 sensitization and to study which antigen-presenting cells mediate this process.

METHODS

HDM was applied epicutaneously by painting HDM on unmanipulated ear skin or under an occlusive tape. HDM challenge was through the nose. Mouse strains lacking different dendritic cell (DC) populations were used, and 1-DER T cells carrying a transgenic T-cell receptor reactive to Der p 1 allergen were used as a readout for antigen presentation. The T_H2-inducing capacity of sorted skin-derived DC subsets was determined by means of adoptive transfer to naive mice.

RESULTS

Epicutaneous HDM application led to T_H2 sensitization and eosinophilic airway inflammation upon intranasal HDM challenge. Skin sensitization did not require prior skin damage or enzymatic activity within HDM extract, yet was facilitated by applying the allergen under an occlusive tape. Primary proliferation of 1-DER T cells occurred only in the regional skin-draining lymph nodes. Epicutaneous sensitization was found to be driven by 2 variants of interferon regulatory factor 4-dependent dermal type 2 conventional DC subsets and not by epidermal Langerhans cells.

CONCLUSION

These findings identify skin type 2 conventional DCs as crucial players in T_H2 sensitization to common inhaled allergens that enter the body through the skin and can provoke features of allergic asthma.

Evaluation of the concentration of allergens from mites in fur and households dust of dogs with atopic dermatitis

ABSTRACT: This study evaluated the concentration of Der p 1, Der f 1 and Blo t 5 in the fur and households of 20 dogs with atopic dermatitis (AD) and 20 healthy dogs. The diagnosis of AD was clinical based on Favrot’s criteria. Dust samples were collected with a domestic vacuum cleaner. For each site, 1m2 was vacuumed for 2 min. The samples were collected in separate filters, transferred into plastic containers, sealed and kept frozen until ELISA analysis. In the fur of atopic dogs the average concentration of Der p 1 was 0.25μg/g compared to 0.03μg/g in healthy dogs. In households with atopic dogs the highest concentrations of Der p 1 were found in carpets (2.18μg/g), followed by couches (1.53μg/g), beds (1.14μg/g), dogs’ bed linen (0.64μg/g) and floors (0.14μg/g). The concentrations of Der p 1 on carpets, couches and beds were significantly higher than in atopic dogs’ fur (p<0.05). There was no statistical difference when comparing the concentrations of Der f 1 and Blo t 5 in different environments of atopic dogs (p>0.05). The concentrations of Der p 1, Der f 1 and Blo t 5 were equivalent in atopic and non-atopic dog’s households. Among the allergens studied, Der p 1 was the most commonly found, predominantly in carpets and couches.

Exploring the active site binding specificity of kallikrein-related peptidase 5 (KLK5) guides the design of new peptide substrates and inhibitors

Kallikrein-related peptidase 5 (KLK5) is a promising therapeutic target in several skin diseases, including Netherton syndrome, and is emerging as a potential target in various cancers. In this study, we used a sparse matrix library of 125 individually synthesized peptide substrates to characterize the binding specificity of KLK5. The sequences most favored by KLK5 were GRSR, YRSR and GRNR, and we identified sequence-specific interactions involving the peptide N-terminus by analyzing kinetic constants (kcat and KM) and performing molecular dynamics simulations. KLK5 inhibitors were subsequently engineered by substituting substrate sequences into the binding loop (P1, P2 and P4 residues) of sunflower trypsin inhibitor-1 (SFTI-1). These inhibitors were effective against KLK5 but showed limited selectivity, and performing a further substitution at P2′ led to the design of a new variant that displayed improved activity against KLK5 (Ki=4.2±0.2 nm), weak activity against KLK7 and 12-fold selectivity over KLK14. Collectively, these findings provide new insight into the design of highly favored binding sequences for KLK5 and reveal several opportunities for modulating inhibitor selectivity over closely related proteases that will be useful for future studies aiming to develop therapeutic molecules targeting KLK5.

Epidermal cell turnover across tight junctions based on Kelvin's tetrakaidecahedron cell shape

In multicellular organisms, cells adopt various shapes, from flattened sheets of endothelium to dendritic neurons, that allow the cells to function effectively. Here, we elucidated the unique shape of cells in the cornified stratified epithelia of the mammalian epidermis that allows them to achieve homeostasis of the tight junction (TJ) barrier. Using intimate in vivo 3D imaging, we found that the basic shape of TJ-bearing cells is a flattened Kelvin's tetrakaidecahedron (f-TKD), an optimal shape for filling space. In vivo live imaging further elucidated the dynamic replacement of TJs on the edges of f-TKD cells that enables the TJ-bearing cells to translocate across the TJ barrier. We propose a spatiotemporal orchestration model of f-TKD cell turnover, where in the classic context of 'form follows function', cell shape provides a fundamental basis for the barrier homeostasis and physical strength of cornified stratified epithelia.

DOI:http://dx.doi.org/10.7554/eLife.19593.001

The skin surface – known as the epidermis – is made up of sheets of cells that are stacked up in layers. One of the roles of the skin is to provide a protective barrier that limits what leaks into or out of the body. A particular layer of the epidermis – referred to as the stratum granulosum – is primarily responsible for forming this barrier. The cells in this layer are sealed together in a zipper-like fashion by structures known as tight junctions.

New skin cells are continuously produced in the lowest cell layers of the epidermis, and move upwards to integrate into the stratum granulosum layer to replace old cells (which also move upwards to leave the layer). How stratum granulosum cells are replaced without disrupting the tight junction barrier was not well understood.

Yokouchi et al. used a technique called confocal microscopy to examine the stratum granulosum cells in the ears of mice, and found that the shape of these cells forms the basis of the barrier that they form. These cells resemble a flattened version of a shape called Kelvin’s tetrakaidecahedron: a 14-sided solid with six rectangular and eight hexagonal sides. This structure was proposed by Lord Kelvin in 1887 to be the best shape for filling space. Tight junctions are present on the edges of the flattened Kelvin’s tetrakaidecahedron.

Further experiments revealed that the tight junctions move from cell to cell in a spatiotemporally-coordinated manner in order to maintain a continuous barrier throughout the stratum granulosum as cells are replaced. A newly formed stratum granulosum cell appears beneath the cell that it will replace. The shape of these cells enables a new barrier of three-way tight junction contacts to form between them and the neighboring cells in the stratum granulosum. After this barrier has formed, the upper cell leaves the stratum granulosum.

Future research could address how cells adopt the flattened Kelvin’s tetrakaidecahedron shape, and discover why tight junctions only form in one layer of the epidermis.

DOI:http://dx.doi.org/10.7554/eLife.19593.002

Hyperglycemia Induces Skin Barrier Dysfunctions with Impairment of Epidermal Integrity in Non-Wounded Skin of Type 1 Diabetic Mice

Diabetes causes skin complications, including xerosis and foot ulcers. Ulcers complicated by infections exacerbate skin conditions, and in severe cases, limb/toe amputations are required to prevent the development of sepsis. Here, we hypothesize that hyperglycemia induces skin barrier dysfunction with alterations of epidermal integrity. The effects of hyperglycemia on the epidermis were examined in streptozotocin-induced diabetic mice with/without insulin therapy. The results showed that dye leakages were prominent, and transepidermal water loss after tape stripping was exacerbated in diabetic mice. These data indicate that hyperglycemia impaired skin barrier functions. Additionally, the distribution of the protein associated with the tight junction structure, tight junction protein-1 (ZO-1), was characterized by diffuse and significantly wider expression in the diabetic mice compared to that in the control mice. In turn, epidermal cell number was significantly reduced and basal cells were irregularly aligned with ultrastructural alterations in diabetic mice. In contrast, the number of corneocytes, namely, denucleated and terminally differentiated keratinocytes significantly increased, while their sensitivity to mechanical stress was enhanced in the diabetic mice. We found that cell proliferation was significantly decreased, while apoptotic cells were comparable in the skin of diabetic mice, compared to those in the control mice. In the epidermis, Keratin 5 and keratin 14 expressions were reduced, while keratin 10 and loricrin were ectopically induced in diabetic mice. These data suggest that hyperglycemia altered keratinocyte proliferation/differentiation. Finally, these phenotypes observed in diabetic mice were mitigated by insulin treatment. Reduction in basal cell number and perturbation of the proliferation/differentiation process could be the underlying mechanisms for impaired skin barrier functions in diabetic mice.

Guanine nucleotide exchange factor RABGEF1 regulates keratinocyte-intrinsic signaling to maintain skin homeostasis

Epidermal keratinocytes form a structural and immune barrier that is essential for skin homeostasis. However, the mechanisms that regulate epidermal barrier function are incompletely understood. Here we have found that keratinocyte-specific deletion of the gene encoding RAB guanine nucleotide exchange factor 1 (RABGEF1, also known as RABEX-5) severely impairs epidermal barrier function in mice and induces an allergic cutaneous and systemic phenotype. RABGEF1-deficient keratinocytes exhibited aberrant activation of the intrinsic IL-1R/MYD88/NF-κB signaling pathway and MYD88-dependent abnormalities in expression of structural proteins that contribute to skin barrier function. Moreover, ablation of MYD88 signaling in RABGEF1-deficient keratinocytes or deletion of Il1r1 restored skin homeostasis and prevented development of skin inflammation. We further demonstrated that epidermal RABGEF1 expression is reduced in skin lesions of humans diagnosed with either atopic dermatitis or allergic contact dermatitis as well as in an inducible mouse model of allergic dermatitis. Our findings reveal a key role for RABGEF1 in dampening keratinocyte-intrinsic MYD88 signaling and sustaining epidermal barrier function in mice, and suggest that dysregulation of RABGEF1 expression may contribute to epidermal barrier dysfunction in allergic skin disorders in mice and humans. Thus, RABGEF1-mediated regulation of IL-1R/MYD88 signaling might represent a potential therapeutic target.

Increasing Comorbidities Suggest that Atopic Dermatitis Is a Systemic Disorder

Atopic dermatitis comorbidities extend well beyond the march to allergic conditions (food allergy, asthma, allergic rhinitis, allergic conjunctivitis, and eosinophilic esophagitis), suggesting both cutaneous and systemic immune activation. In reviewing atopic dermatitis comorbidities, Councilors of the International Eczema Council found a strong pattern of immune activation in peripheral blood and the propensity to both skin and systemic infections. Associations with cardiovascular, neuropsychiatric, and malignant diseases were increasingly reported, but confirmation of their link with atopic dermatitis requires longitudinal studies. Given the possibility of atopic dermatitis-related systemic immune activation, future investigations of new interventions should concurrently examine the impact on these comorbidities.

IL-23 induced in keratinocytes by endogenous TLR4 ligands polarizes dendritic cells to drive IL-22 responses to skin immunization

Atopic dermatitis (AD) is a Th2-dominated inflammatory skin disease characterized by epidermal thickening. Serum levels of IL-22, a cytokine known to induce keratinocyte proliferation, are elevated in AD, and Th22 cells infiltrate AD skin lesions. We show that application of antigen to mouse skin subjected to tape stripping, a surrogate for scratching, induces an IL-22 response that drives epidermal hyperplasia and keratinocyte proliferation in a mouse model of skin inflammation that shares many features of AD. DC-derived IL-23 is known to act on CD4(+) T cells to induce IL-22 production. However, the mechanisms that drive IL-23 production by skin DCs in response to cutaneous sensitization are not well understood. We demonstrate that IL-23 released by keratinocytes in response to endogenous TLR4 ligands causes skin DCs, which selectively express IL-23R, to up-regulate their endogenous IL-23 production and drive an IL-22 response in naive CD4(+) T cells that mediates epidermal thickening. We also show that IL-23 is released in human skin after scratching and polarizes human skin DCs to drive an IL-22 response, supporting the utility of IL-23 and IL-22 blockade in AD.

Importance of Water Content of the Stratum Corneum in Mouse Models for Contact Hypersensitivity

Although a marked rise in the prevalence of allergic diseases over the past few decades may be related to environmental factors in industrialized countries, evidence for the protective effect of humidity on the barrier function of the skin is still awaited. We asked whether an increase in the water content of stratum corneum at the site of hapten application had a strong impact on the magnitude of contact hypersensitivity (CHS). The magnitude of CHS, induced by either lipid-soluble or water-soluble hapten, was inversely correlated with the water content of stratum corneum at the hapten application site in the elicitation phase. An increase in the water content induced by exposure to high humidity for 6 hours was sufficient to ameliorate the magnitude of CHS even in mice with the genetic defect in attenuating the CHS responses, such as flaky tail mice. The reduced CHS was associated with downregulation of IL-1α, IL-4, and IFN-γ mRNA expression. Epicutaneously applied hapten can penetrate more readily through the stratum corneum with lower water content than that with higher water content, even after tape-stripping. These findings indicate that increased levels of water in the stratum corneum serve to ameliorate the CHS beyond the genetic effects.

Epidermal barrier in hereditary ichthyoses, atopic dermatitis, and psoriasis

Several skin disorders are associated with impaired skin barrier function. Primary dysfunction is caused by monogenic defects in key components of the epidermis (for example ichthyoses). Secondary barrier impairment occurs in inflammatory dermatoses marked by disturbed epidermal homeostasis (eczema, psoriasis, etc.). In these disorders, inflammation impedes the synthesis or maintenance of skin barrier components. Recent evidence suggests a combination of primary and secondary barrier dysfunction in atopic dermatitis and, to a lesser extent, also in psoriasis. In the future, subtypes of atopic dermatitis may likely be defined, in which one or the other is prevalent.