IL-31 regulates differentiation and filaggrin expression in human organotypic skin models

Skin microbiome influences the progression of cutaneous squamous cell carcinoma through the immune system

Cutaneous squamous cell carcinoma (cSCC) is a type of skin tumor that develops in the epithelial cells. This disease has the second highest incidence of human skin cancers, with a high metastatic rate. While ultraviolet radiation significantly contributes to the genomic changes that support cSCC development, the dysbiosis of the skin microbiome and influence of the immune system also play important roles in this process. In this review, we discuss the effects of skin microbes and their metabolites on the immune system, including innate immune cells, T cells, and cytokines. We also discuss how Staphylococcus aureus and human papillomavirus can affect cSCC by impacting the immune system. Furthermore, we explore the antagonism of symbiotic microorganisms with cSCC-associated pathogens and their potential as novel therapeutic modalities.

Osthole ameliorates chronic pruritus in 2,4-dichloronitrobenzene-induced atopic dermatitis by inhibiting IL-31 production

Objective

This study aims to elucidate the therapeutic potential of osthole for the treatment of atopic dermatitis (AD), focusing on its ability to alleviate chronic pruritus (CP) and the underlying molecular mechanisms.

Methods

In this study, we investigated the anti-inflammatory effects of osthole in both a 2,4-dichloronitrobenzene (DNCB)-induced AD mouse model and tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) stimulated huma immortalized epidermal (HaCaT) cells. The anti-itch effect of osthole was specifically assessed in the AD mouse model. Using methods such as hematoxylin and eosin (HE) staining, enzyme-linked immunosorbent assay (ELISA), western blot (WB), quantitative real-time PCR (qRT-PCR), and immunofluorescence staining.

Results

Osthole improved skin damage and clinical dermatitis scores, reduced scratching bouts, and decreased epidermal thickness AD-like mice. It also reduced the levels of interleukin (IL)-31 and IL-31 receptor A (IL-31 RA) in both skin tissues and HaCaT cells. Furthermore, Osthole suppressed the protein expression levels of phosphor-p65 (p-p65) and phosphor-inhibitor of nuclear factor kappa-Bα (p-IκBα). Meanwhile, it increased the protein expression levels of peroxisome proliferator-activated receptor α (PPARα) and PPARγ in HaCaT cells.

Conclusion

These findings indicated that osthole effectively inhibited CP in AD by activating PPARα, PPARγ, repressing the NF-κB signaling pathway, as well as the expression of IL-31 and IL-31 RA.

Reconstructed Epidermis Produced with Atopic Dog Keratinocytes Only Exhibit Skin Barrier Defects after the Addition of Proinflammatory and Allergic Cytokines

Our objectives were to explore epidermal barrier defects in dogs with atopic dermatitis and to determine whether the defects are genetically determined or secondary to skin inflammation. First, the expression of filaggrin, corneodesmosin, and claudin1, analyzed using indirect immunofluorescence in skin biopsies collected from 32 healthy and 32 dogs with atopic dermatitis, was weaker in the atopic skin (P = .003). Second, primary keratinocytes of atopic dogs and healthy dogs were used to produce 3-dimensional reconstructed canine epidermis. The expression of the same proteins was analyzed using indirect immunofluorescence, immunoblotting, and RT-qPCR, whereas reconstructed canine epidermis morphology was investigated by transmission electron microscopy, and the barrier was investigated by functional assays. Next, inflammatory cytokines (IL-4, IL-13, IL-31, and TNFα) were added to the culture medium. The morphology, protein expression, and barrier function of the reconstructed canine epidermis were similar whether produced with keratinocytes from healthy dogs or dogs with atopy. Addition of inflammatory cytokines impaired the protein expression and epidermal barrier of the 2 types of reconstructed canine epidermis equally. To conclude, the reduced expression of epidermal barrier proteins observed in vivo was not reproduced in vitro unless cytokines were used, suggesting that it is induced by the inflammatory milieu.

Cannabinol modulates the endocannabinoid system and shows TRPV1-mediated anti-inflammatory properties in human keratinocytes

Cannabinol (CBN) is a secondary metabolite of cannabis whose beneficial activity on inflammatory diseases of human skin has attracted increasing attention. Here, we sought to investigate the possible modulation by CBN of the major elements of the endocannabinoid system (ECS), in both normal and lipopolysaccharide-inflamed human keratinocytes (HaCaT cells). CBN was found to increase the expression of cannabinoid receptor 1 (CB1) at gene level and that of vanilloid receptor 1 (TRPV1) at protein level, as well as their functional activity. In addition, CBN modulated the metabolism of anandamide (AEA) and 2-arachidonoylglicerol (2-AG), by increasing the activities of N-acyl phosphatidylethanolamines-specific phospholipase D (NAPE-PLD) and fatty acid amide hydrolase (FAAH)-the biosynthetic and degradative enzyme of AEA-and that of monoacylglycerol lipase (MAGL), the hydrolytic enzyme of 2-AG. CBN also affected keratinocyte inflammation by reducing the release of pro-inflammatory interleukin (IL)-8, IL-12, and IL-31 and increasing the release of anti-inflammatory IL-10. Of note, the release of IL-31 was mediated by TRPV1. Finally, the mitogen-activated protein kinases (MAPK) signaling pathway was investigated in inflamed keratinocytes, demonstrating a specific modulation of glycogen synthase kinase 3β (GSK3β) upon treatment with CBN, in the presence or not of distinct ECS-directed drugs. Overall, these results demonstrate that CBN modulates distinct ECS elements and exerts anti-inflammatory effects-remarkably via TRPV1-in human keratinocytes, thus holding potential for both therapeutic and cosmetic purposes.

ARCADIA trials: Can nemolizumab be a valid alternative to the therapies currently available?

ARCADIA 1 and ARCADIA 2 were two randomized, placebo-controlled phase 3 trials showing the effectiveness of nemolizumab with concomitant use of low-to-medium potency topical corticosteroids, and/or with or without topical calcineurin inhibitors, in adults and adolescents with moderate-to-severe atopic dermatitis. Coprimary endpoints were met in the nemolizumab plus background therapy groups in both trials, with significant differences versus placebo.

Skin barrier: new therapeutic targets for chronic kidney disease-associated pruritus - a narrative review

The current incidence of chronic kidney disease-associated pruritus (CKD-aP) in patients with end-stage renal disease (ESRD) is approximately 70%, especially in those receiving dialysis, which negatively affects their work and private lives. The CKD-aP pathogenesis remains unclear, but uremic toxin accumulation, histamine release, and opioid imbalance have been suggested to lead to CKD-aP. Current therapeutic approaches, such as opioid receptor modulators, antihistamines, and ultraviolet B irradiation, are associated with some limitations and adverse effects. The skin barrier is the first defense in preventing external injury to the body. Patients with chronic kidney disease often experience itch due to the damaged skin barrier and reduced secretion of sweat and secretion from sebaceous glands. Surprisingly, skin barrier-repairing agents repair the skin barrier and inhibit the release of inflammatory cytokines, maintain skin immunity, and ameliorate the micro-inflammatory status of afferent nerve fibers. Here, we summarize the epidemiology, pathogenesis, and treatment status of CKD-aP and explore the possibility of skin barrier repair in CKD-aP treatment.

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

The Role of Interleukin-24 and Downstream Pathways in Inflammatory and Autoimmune Diseases

Inflammatory and autoimmune diseases are pathological immune disorders and pose significant public health challenges due to their impact on individuals and society. Cytokine dysregulation plays a critical role in the development of these disorders. Interleukin (IL)-24, a member of the IL-10 cytokine family, can be secreted by various cell types, including immune and non-immune cells. The downstream effects of IL-24 upon binding to its receptors can occur in dependence on, or independently of, the Janus kinase (JAK)/signal transducer and the activator of transcription (STAT) signaling pathway. IL-24 and its downstream pathways influence crucial processes such as cell differentiation, proliferation, apoptosis, and inflammation, with its role varying across different diseases. On the one hand, IL-24 can inhibit the activation of pathogenic cells and autoimmune responses in autoimmune ocular diseases; on the other hand, IL-24 has been also implicated in promoting tissue damage by fostering immune cell activation and infiltration in psoriasis and allergic diseases. It suggests that IL-24, as a multifunctional cytokine, has complex regulatory functions in immune cells and related diseases. In this paper, we summarize the current knowledge on IL-24's immunomodulatory actions and its involvement in inflammatory and autoimmune disorders. Such insights may pave the way for novel therapeutic strategies for these diseases.

Enhancement of keratinocyte survival and migration elicited by interleukin 24 upregulation in dermal microvascular endothelium upon welding-fume exposure

Occupational exposure to welding fumes constitutes a serious health concern. Although the effects of fumes on the respiratory tract have been investigated, few apparent reports were published on their effects on the skin. The purpose of this study was to investigate the effects of exposure to welding fumes on skin cells, focusing on interleukin-24 (IL-24), a cytokine involved in the pathophysiology of skin conditions, such as atopic dermatitis and psoriasis. Treatment with welding fumes increased IL-24 expression and production levels in human dermal microvascular endothelial cells (HDMEC) which were higher than that in normal human epidermal keratinocytes. IL-24 levels in Trolox and deferoxamine markedly suppressed welding fume-induced IL-24 expression in HDMEC, indicating that oxidative stress may be involved in this cytokine expression. IL-24 released from HDMEC protected keratinocytes from welding fume-induced damage and enhanced keratinocyte migration. Serum IL-24 was higher in welding workers than in general subjects and was positively correlated with elevated serum levels of 8-hydroxy-2'-deoxyguanosine, an oxidative stress marker. In summary, welding fumes enhanced IL-24 expression in HDMEC, stimulating keratinocyte survival and migration. IL-24 expression in endothelial cells may act as an adaptive response to welding-fume exposure in the skin.

Novel insight into MDA-7/IL-24: A potent therapeutic target for autoimmune and inflammatory diseases

Melanoma differentiation-associated gene-7 (MDA-7)/interleukin-24 (IL-24) is a pleiotropic member of the IL-10 family of cytokines, and is involved in multiple biological processes, including cell proliferation, cell differentiation, tissue fibrosis, the inflammatory response, and antitumor activity. MDA-7/IL-24 can regulate epithelial integrity, homeostasis, mucosal immunity and host resistance to various pathogens by enhancing immune and inflammatory responses. Our recent study revealed the mechanism of MDA-7/IL-24 in promoting airway inflammation and airway remodeling through activating the JAK/STAT3 and ERK signaling pathways in bronchial epithelial cells. Herein, we summarize the cellular sources, inducers, target cells, signaling pathways, and biological effects of MDA-7/IL-24 in several allergic and autoimmune diseases. This review also synopsizes recent advances in clinical research targeting MDA-7/IL-24 or its receptors. Based on these advancements, we emphasize its potential as a target for immunotherapy and discuss the challenges of developing immunotherapeutic drugs targeting MDA-7/IL-24 or its receptors in autoimmune and inflammatory disorders.

A Comprehensive Review of Biologics in Phase III and IV Clinical Trials for Atopic Dermatitis

Atopic dermatitis (AD) is a skin condition characterized by significant challenges and a substantial deterioration in the life quality for affected patients. The therapeutic landscape for AD has witnessed a transformative shift with the emergence of biologic therapies. Our focus centers on biologics currently undergoing phase III and IV clinical trials, deeming them to hold the highest potential for significant clinical relevance. To identify biologic drugs under development in phase III and IV clinical trials, we searched ClinicalTrials.gov. Additional relevant trials were identified through JapicCTI/ Japan Registry of Clinical Trials (jRCT) with a citation search. A search in MEDLINE and EMBASE was performed. There have been 76 clinical trials identified concerning biologic drugs: dupilumab (34 trials), lebrikizumab (14 trials), tralokinumab (10 trials), rocatinlimab (7 trials), amlitelimab (2 trials), nemolizumab (6 trials), MG-K10 (1 trial), CM310 (1 trial), 611 (1 trial). A search in MEDLINE revealed 132 articles concerning phase III and IV clinical trials for AD treatment. A total of 39 articles concerned biologic drugs covering 23 clinical trials. A search in EMBASE revealed 268 relevant articles, allowing us to identify results of an additional six clinical trials. The safety and efficacy of these biologics are comprehensively addressed in this review. This comprehensive review aims to explore the current landscape of biologic therapies for AD, delving into the latest research findings, clinical trial outcomes, and the diverse mechanisms of action employed by these novel interventions.

Serum level of interleukin-24 and its polymorphism in eczematic Iraqi patients

Eczema is a common skin disease associated with inflammation. Interleukin (IL)-24 is crucial in the pathogenesis of inflammatory diseases like eczema. The study objective was the assessment of IL-24 serum levels and its gene polymorphisms in eczematic Iraqi patients. This retrospective case-control study involved 145 participants, divided into 82 patients with eczema and 63 healthy controls. An enzyme-linked immunosorbent assay measured serum IL-24, while polymerase chain reaction and Sanger DNA sequencing were used for genotype analysis. Serum IL-24 level was significantly higher (P value < .001) in patients compared to controls (41.6 [interquartile range (IQR): 28.9-53.6] vs 9.8 [IQR: 0.8-19.6] pg/mL, respectively). DNA sequence illustrated 2 SNPs with polymorphic frequencies (rs1150256 G/A and rs3093425 del/ins). The first SNP (rs1150256 G/A) showed 3 genotypes (GG, AA, and G/A), while the second SNP (rs3093425) showed 3 genotypes (-/G del/Ins, G Ins/Ins, and - del/del). The subsequent investigation revealed the presence of the following findings within the DNA sequence of the PCR amplified region (329bp). In the control group, all participants had GG/G (wild type) genotype/allele for the rs1150256 SNP, while in eczematic patients, 24.4% GG, 50% GA, and 25.6% AA. For the second SNP genotype (rs3093425 del/ins), the genotype frequencies in patients vs control were (24.4% vs 84.1%, 50.0% vs 11.1%, and 25.6% vs 4.8; Del/Del, Del/Ins, and Ins/Ins, respectively). The presence of Ins compared to Del increased the risk of eczema by 8.91 (4.66-17.03); OR (95% CI). In conclusion, IL-24 is a good predictor of eczema and A-allele carrier for rs1150256 SNP, and insertion-allele carrier for rs3093425 SNP is associated with elevated serum IL-24 and higher risk of eczema.

Monoclonal antibodies for moderate-to-severe atopic dermatitis: a look at phase III and beyond

INTRODUCTION

The understanding of atopic dermatitis (AD) pathogenesis has rapidly expanded in recent years, catalyzing the development of new targeted monoclonal antibody treatments for AD.

AREAS COVERED

This review aims to summarize the latest clinical and molecular data about monoclonal antibodies that are in later stages of development for AD, either in Phase 3 trials or in the pharmacopoeia for up to 5 years, highlighting the biologic underpinning of each drug's mechanism of action and the potential modulation of the AD immune profile.

EXPERT OPINION

The therapeutic pipeline of AD treatments is speedily progressing, introducing the potential for a personalized medical approach in the near future. Understanding how targeting pathogenic players in AD modifies disease progression and symptomatology is key in improving therapeutic choices for patients and identifying ideal patient candidates.

Potential Aspects of the Use of Cytokines in Atopic Dermatitis

Atopic dermatitis (AD) is an abnormal inflammatory response in the skin to food, environmental IgE, or non-IgE allergens. This disease belongs to a group of inflammatory diseases that affect both children and adults. In highly developed countries, AD is diagnosed twice as often in children than in adults, which may possibly be connected to increased urbanization. The immune system's pathomechanisms of AD involve humoral mechanisms with IgE, cellular T lymphocytes, dendritic cells occurring in the dermis, Langerhans cells occurring in the epidermis, and other cells infiltrating the site of inflammation (eosinophils, macrophages, mast cells, neutrophils, and basophils). Cytokines are small proteins that affect the interaction and communication between cells. This review characterizes cytokines and potential aspects of the treatment of atopic dermatitis, as well as new strategies that are currently being developed, including targeting cytokines and their receptors.

PNAd-expressing vessels characterize the dermis of CD3+ T-cell-mediated cutaneous diseases

T-cell recruitment to skin tissues is essential for inflammation in different cutaneous diseases; however, the mechanisms by which these T cells access the skin remain unclear. High endothelial venules expressing peripheral node address in (PNAd), an L-selectin ligand, are located in secondary lymphoid organs and are responsible for increasing T-cell influx into the lymphoid tissues. They are also found in non-lymphoid tissues during inflammation. However, their presence in different common inflammatory cutaneous diseases and their correlation with T-cell infiltration remain unclear. Herein, we explored the mechanisms underlying the access of T cells to the skin by investigating the presence of PNAd-expressing vessels in different cutaneous diseases, and its correlation with T cells' presence. Skin sections of 43 patients with different diseases were subjected to immunohistochemical and immunofluorescence staining to examine the presence of PNAd-expressing vessels in the dermis. The correlation of the percentage of these vessels in the dermis of these patients with the severity/grade of CD3+ T-cell infiltration was assessed. PNAd-expressing vessels were commonly found in the skin of patients with different inflammatory diseases. A high percentage of these vessels in the dermis was associated with increased severity of CD3+ T-cell infiltration (P < 0.05). Additionally, CD3+ T cells were found both around the PNAd-expressing vessels and within the vessel lumen. PNAd-expressing vessels in cutaneous inflammatory diseases, characterized by CD3+ T-cell infiltration, could be a crucial entry point for T cells into the skin. Thus, selective targeting of these vessels could be beneficial in cutaneous inflammatory disease treatment.

Update on the role of cytokines and chemokines in canine atopic dermatitis

BACKGROUND

Cytokines and chemokines play central roles in the pathogenesis of canine atopic dermatitis (cAD). Numerous studies have been published and provide new insights into their roles in cAD.

OBJECTIVES

To summarise the research updates on the role of cytokines and chemokines in the pathogenesis of cAD since the last review by the International Committee on Allergic Diseases of Animals in 2015.

MATERIAL AND METHODS

Online citation databases, abstracts and proceedings from international meetings on cytokines and chemokines relevant to cAD that had been published between 2015 and 2022 were reviewed.

RESULTS

Advances in technologies have allowed the simultaneous analysis of a broader range of cytokines and chemokines, which revealed an upregulation of a multipolar immunological axis (Th1, Th2, Th17 and Th22) in cAD. Most studies focused on specific cytokines, which were proposed as potential novel biomarkers and/or therapeutic targets for cAD, such as interleukin-31. Most other cytokines and chemokines had inconsistent results, perhaps as a consequence of their varied involvement in the pathogenesis of different endotypes of cAD.

CONCLUSIONS AND CLINICAL RELEVANCE

Inconsistent results for many cytokines and chemokines illustrate the difficulty of studying the complex cytokine and chemokine networks in cAD, and highlight the need for more comprehensive and structured studies in the future.

Dysregulation of the Skin-Liver Axis in Prurigo Nodularis: An Integrated Genomic, Transcriptomic, and Population-Based Analysis

Pruritus has long been linked to hepatic dysfunction; however, there are limited data characterizing the association between liver disease and prurigo nodularis (PN), a chronic inflammatory skin disease featuring severe pruritis. We thus conducted a cross-sectional analysis of hepatic comorbidities in PN patients using TriNetX, a large global health research network. This analysis revealed that PN patients had a higher risk (p < 0.001) of developing liver cirrhosis, acute and subacute hepatic failure, inflammatory liver disease, chronic hepatitis, nonalcoholic steatohepatitis, portal hypertension, fatty liver, chronic passive congestion of the liver, and hepatocellular carcinoma compared with healthy controls. The cumulative incidence of liver disease was about three times higher in PN patients compared with healthy controls. These findings provided the basis for translational studies to investigate a genetic mechanism for this association. Cutaneous transcriptomic analysis performed on PN patients revealed the dysregulation of genes related to hepatic failure in lesional PN compared with both nonlesional PN and control skin. Similarly, gene set variation analysis (GSVA) revealed a significantly increased (p < 0.05) activation of liver metabolism, chronic hepatic failure, acute hepatic failure, cholestatic liver disease, polycystic liver disease, and hepatocellular carcinoma pathways in lesional PN compared with control skin. A subsequent genome-wide association study (GWAS) identified shared single-nucleotide polymorphisms (SNPs) in the genes AR, EDIL3, MACROD2, PCSK5, RUNX1T1, TENM4, and ZEB2 between PN and liver disease from the FinnGen cohort. Significant dysregulation of the skin-liver axis in PN patients may explain the increased incidence and severity of hepatic comorbidities and help identify future therapeutic targets for PN.

Temporal relationships between Staphylococcus aureus colonization, filaggrin expression, and pediatric atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is characterized by Staphylococcus aureus (S. aureus) colonization. Longitudinal early life data delineating relationships of S. aureus colonization, barrier function, and AD outcomes are lacking. We define longitudinal S. aureus endotypes and AD pathogenesis in early life.

METHODS

We defined longitudinal S. aureus skin colonization phenotypes across two annual visits (non-colonized: V1- V2- , early transient: V1+ V2- , late-onset: V1- V2+ , persistent: V1+ V2+ ) in the Mechanisms of Progression of Atopic Dermatitis to Asthma in Children cohort. We analyzed AD severity, sensitization, and skin barrier function across phenotypes, and performed mediation analyses between colonization and FLG expression.

RESULTS

Persistent S. aureus colonization was associated with increased SCORAD at V1 (33.5 vs. 19.0, p = .004) and V2 (40.1 vs.16.9, p < .001), and lower non-lesional (NL) FLG at V2 (1.77 vs. 4.09, p = .029) compared to the non-colonized phenotype, with early transient and late-onset colonization as intermediate phenotypes. Children colonized at V2 demonstrated a decrease in NL-FLG expression from V1 to V2 compared to those non-colonized at V2 (p = .0012), who maintained expression. This effect remained significant even after adjusting for V1 colonization and SCORAD (p = .011).

CONCLUSIONS

Our findings are the first to present longitudinal quantitative FLG expression and S. aureus skin colonization in early life and suggest that a decrease in NL-FLG drives later colonization. Hence, therapies to maintain NL-FLG expression may prevent S. aureus colonization. Further, a longitudinal AD endotype of persistent colonization is characterized by increased AD severity, sensitization, and decreasing NL-FLG.

Biological effect of laser-assisted scar healing (LASH) on standardized human three-dimensional wound healing skin models using fractional non-ablative 1540 nm Er:Glass or 1550 nm diode lasers

PURPOSE

In postoperative wound healing after surgical operations or ablative laser treatments, recent studies suggest the timely use of non-ablative fractional laser treatments with the aim to improve wound healing and prevent pathological scar formation. However, the underlying molecular mechanisms are poorly understood. The aim of this study was to investigate the effects of laser-assisted scar healing (LASH) at the molecular level and to combine it with already established wound healing-promoting local treatments.

METHODS

We irradiated full-thickness 3D skin models with a fractional ablative Er:YAG laser to set standardized lesions to the epidermal and upper dermal layer. Subsequently, LASH was induced by irradiating the models with either a fractional non-ablative 1540 nm Er:Glass or 1550 nm diode laser. In addition, we tested the combination of non-ablative fractional laser treatment and topical aftercare with a dexpanthenol-containing ointment (DCO).

RESULTS

Histological analysis revealed that models irradiated with the 1540 nm Er:Glass or 1550 nm diode laser exhibited accelerated but not complete wound closure after 16 h. In contrast, additional topical posttreatment with DCO resulted in complete wound closure. At gene expression level, both non-ablative laser systems showed similar effects on epidermal differentiation and mild anti-inflammatory properties. The additional posttreatment with DCO enhanced the wound-healing effects of LASH, especially the upregulation of epidermal differentiation markers and anti-inflammatory cytokines at the gene expression level.

CONCLUSION

This in vitro study deciphers the biological effects of LASH with a fractional non-ablative 1540 nm Er:Glass or a 1550 nm diode laser in 3D skin models. These data help to better understand the biological properties of the LASH technique and is important to optimize its application.

Cytokines and Epidermal Lipid Abnormalities in Atopic Dermatitis: A Systematic Review

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease and presents a major public health problem worldwide. It is characterized by a recurrent and/or chronic course of inflammatory skin lesions with intense pruritus. Its pathophysiologic features include barrier dysfunction, aberrant immune cell infiltration, and alterations in the microbiome that are associated with genetic and environmental factors. There is a complex crosstalk between these components, which is primarily mediated by cytokines. Epidermal barrier dysfunction is the hallmark of AD and is caused by the disruption of proteins and lipids responsible for establishing the skin barrier. To better define the role of cytokines in stratum corneum lipid abnormalities related to AD, we conducted a systematic review of biomedical literature in PubMed from its inception to 5 September 2023. Consistent with the dominant TH2 skewness seen in AD, type 2 cytokines were featured prominently as possessing a central role in epidermal lipid alterations in AD skin. The cytokines associated with TH1 and TH17 were also identified to affect barrier lipids. Considering the broad cytokine dysregulation observed in AD pathophysiology, understanding the role of each of these in lipid abnormalities and barrier dysfunction will help in developing therapeutics to best achieve barrier homeostasis in AD patients.

"Input/output cytokines" in epidermal keratinocytes and the involvement in inflammatory skin diseases

Considering the role of epidermal keratinocytes, they occupy more than 90% of the epidermis, form a physical barrier, and also function as innate immune barrier. For example, epidermal keratinocytes are capable of recognizing various cytokines and pathogen-associated molecular pattern, and producing a wide variety of inflammatory cytokines, chemokines, and antimicrobial peptides. Previous basic studies have shown that the immune response of epidermal keratinocytes has a significant impact on inflammatory skin diseases. The purpose of this review is to provide foundation of knowledge on the cytokines which are recognized or produced by epidermal keratinocytes. Since a number of biologics for skin diseases have appeared, it is necessary to fully understand the relationship between epidermal keratinocytes and the cytokines. In this review, the cytokines recognized by epidermal keratinocytes are specifically introduced as "input cytokines", and the produced cytokines as "output cytokines". Furthermore, we also refer to the existence of biologics against those input and output cytokines, and the target skin diseases. These use results demonstrate how important targeted cytokines are in real skin diseases, and enhance our understanding of the cytokines.

New insight into the role of fibroblasts in the epithelial immune microenvironment in the single-cell era

The skin is exposed to environmental challenges and contains heterogeneous cell populations such as epithelial cells, stromal cells, and skin-resident immune cells. As the most abundant type of stromal cells, fibroblasts have been historically considered silent observers in the immune responses of the cutaneous epithelial immune microenvironment (EIME), with little research conducted on their heterogeneity and immune-related functions. Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) have overcome the limitations of bulk RNA sequencing and help recognize the functional and spatial heterogeneity of fibroblasts, as well as their crosstalk with other types of cells in the cutaneous EIME. Recently, emerging single-cell sequencing data have demonstrated that fibroblasts notably participate in the immune responses of the EIME and impact the initiation and progression of inflammatory skin diseases. Here, we summarize the latest advances in the role of fibroblasts in the cutaneous EIME of inflammatory skin diseases and discuss the distinct functions and molecular mechanisms of activated fibroblasts in fibrotic skin diseases and non-fibrotic inflammatory skin diseases. This review help unveil the multiple roles of fibroblasts in the cutaneous EIME and offer new promising therapeutic strategies for the management of inflammatory skin diseases by targeting fibroblasts or the fibroblast-centered EIME.

Critical role of epigenetic modification in the pathogenesis of atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin disease characterised by recurrent eczema-like lesions and severe pruritus, along with drying and decrustation of skin. Current research relates the pathogenesis of atopic dermatitis mainly to genetic susceptibility, abnormal skin barrier function, immune disorders, Staphylococcus aureus colonisation, microbiological dysfunction and vitamin D insufficiency. Epigenetic modifications are distinct genetic phenotypes resulting from environment-driven changes in chromosome functions in the absence of nuclear DNA sequence variation. Classic epigenetic events include DNA methylation, histone protein modifications and non-coding RNA regulation. Increasing evidence has indicated that epigenetic events are involved in the pathogenesis of atopic dermatitis by their effects on multiple signalling pathways which in turn influence the above factors. This review primarily analyses the function of epigenetic regulation in the pathogenesis of atopic dermatitis. In addition, it tries to make recommendations for personalised epigenetic treatment strategies for atopic dermatitis in the future.

Mast cell-mediated immune regulation in health and disease

Mast cells are important components of the immune system, and they perform pro-inflammatory as well as anti-inflammatory roles in the complex process of immune regulation in health and disease. Because of their strategic perivascular localization, sensitivity and adaptability to the microenvironment, and ability to release a variety of preformed and newly synthesized effector molecules, mast cells perform unique functions in almost all organs. Additionally, Mast cells express a wide range of surface and cytoplasmic receptors which enable them to respond to a variety of cytokines, chemicals, and pathogens. The mast cell's role as a cellular interface between external and internal environments as well as between vasculature and tissues is critical for protection and repair. Mast cell interactions with different immune and nonimmune cells through secreted inflammatory mediators may also turn in favor of disease promoting agents. First and forefront, mast cells are well recognized for their multifaceted functions in allergic diseases. Reciprocal communication between mast cells and endothelial cells in the presence of bacterial toxins in chronic/sub-clinical infections induce persistent vascular inflammation. We have shown that mast cell proteases and histamine induce endothelial inflammatory responses that are synergistically amplified by bacterial toxins. Mast cells have been shown to exacerbate vascular changes in normal states as well as in chronic or subclinical infections, particularly among cigarette smokers. Furthermore, a potential role of mast cells in SARS-CoV-2-induced dysfunction of the capillary-alveolar interface adds to the growing understanding of mast cells in viral infections. The interaction between mast cells and microglial cells in the brain further highlights their significance in neuroinflammation. This review highlights the significant role of mast cells as the interface that acts as sensor and early responder through interactions with cells in systemic organs and the nervous system.

"Outside-to-inside," "inside-to-outside," and "intrinsic" endogenous pathogenic mechanisms in atopic dermatitis: keratinocytes as the key functional cells involved in both permeability barrier dysfunction and immunological alterations

Permeability barrier disruption has been shown to induce immunological alterations (i.e., an "outside-to-inside" pathogenic mechanism). Conversely, several inflammatory and immunological mechanisms reportedly interrupt permeability barrier homeostasis (i.e., an "inside-to-outside" pathogenic mechanism). It is now widely recognized that alterations of even a single molecule in keratinocytes can lead to not only permeability barrier dysfunction but also to immunological alterations. Such a simultaneous, bidirectional functional change by keratinocytes is herein named an "intrinsic" pathogenic mechanism. Molecules and/or pathways involved in this mechanism could be important not only as factors in disease pathogenesis but also as potential therapeutic targets for inflammatory cutaneous diseases, such as atopic dermatitis, psoriasis, and prurigo nodularis. Elevation of skin surface pH following permeability barrier abrogation comprises one of the key pathogenic phenomena of the "outside-to-inside" mechanism. Not only type 2 cytokines (e.g., IL-4, IL-13, IL-31) but also type 1 (e.g. IFN-γ), and type 3 (e.g., IL-17, IL-22) as well as several other inflammatory factors (e.g. histamine) can disrupt permeability barrier homeostasis and are all considered part of the "inside-to-outside" mechanism. Finally, examples of molecules relevant to the "intrinsic" pathogenic mechanism include keratin 1, filaggrin, and peroxisome proliferator-activated receptor-α (PPARα).

Basic mechanisms of itch

Pruritus (or itch) is an unpleasant sensation leading to a desire to scratch. In the epidermis, there are selective C or Aδ epidermal nerve endings that are pruriceptors. At their other ends, peripheral neurons form synapses with spinal neurons and interneurons. Many areas in the central nervous system are involved in itch processing. Although itch does not occur solely because of parasitic, allergic, or immunologic diseases, it is usually the consequence of neuroimmune interactions. Histamine is involved in a minority of itchy conditions, and many other mediators play a role: cytokines (eg, IL-4, IL-13, IL-31, IL-33, and thymic stromal lymphopoietin), neurotransmitters (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, neuropeptide Y, NBNP, endothelin 1, and gastrin-releasing peptide), and neurotrophins (eg, nerve growth factor and brain-derived neurotrophic factor). Moreover, ion channels such as voltage-gated sodium channels, transient receptor potential vanilloid 1, transient receptor ankyrin, and transient receptor potential cation channel subfamily M (melastatin) member 8 play a crucial role. The main markers of nonhistaminergic pruriceptors are PAR-2 and MrgprX2. A notable phenomenon is the sensitization to pruritus, in which regardless of the initial cause of pruritus, there is an increased responsiveness of peripheral and central pruriceptive neurons to their normal or subthreshold afferent input in the context of chronic itch.

Post-Treatment of Micro-Needling with a Dexpanthenol-Containing Ointment Accelerates Epidermal Wound Healing in Human 3D Skin Models

Purpose

In vitro study on the molecular effects of post-treatment after micro-needling applications with a dexpanthenol-containing ointment (DCO) using 3D skin models.

Patients and Methods

In this in vitro study, full-thickness human 3D skin models were treated with a micro-needling device according to its clinical application. For post-treatment, some of the models were additionally treated with a dexpanthenol-containing ointment (DCO). Histological samples were taken at 0, 24 and 48 hours. Gene expression analysis was performed after 24 hours.

Results

Histological examination showed that DCO post-treated 3D skin models revealed a completed wound closure 24 hours after the micro-needling procedure. In contrast, DCO-untreated models still clearly exhibited the micro-needling lesions after the same period of time. After 48 hours, all models revealed a completed wound healing. In skin models that received micro-needling but no post-treatment with DCO, microarray analysis identified an upregulation of proinflammatory cytokines and chemokines and a downregulation of skin barrier and differentiation markers. In contrast, post-treatment with DCO leads to accelerated wound healing without affecting the initial inflammatory response caused by micro-needling, which leads to the subsequent collagen expression. This data was supported by qRT-PCR analyses.

Conclusion

Post-treatment with DCO accelerates epidermal wound healing after micro-needling of 3D skin models without impairing the immunostimulatory properties of micro-needling. These findings can help to optimise the aftercare routine after micro-needling procedures and to shorten the downtime for the patient after treatment.

Allergen sensitization stratifies IL-31 production by memory T cells in atopic dermatitis patients

Background

The role of allergen sensitization in IL-31 production by T cells and specifically in the clinical context of atopic dermatitis (AD) has not been characterized.

Methods

The response to house dust mite (HDM) in purified memory T cells cocultured with epidermal cells from AD patients (n=58) and control subjects (n=11) was evaluated. AD-associated cytokines from culture supernatants, plasma proteins and mRNA expression from cutaneous lesions were assessed and related with the clinical features of the patients.

Results

HDM-induced IL-31 production by memory T cells defined two subsets of AD patients according to the presence or absence of IL-31 response. Patients in the IL-31 producing group showed a more inflammatory profile, and increased HDM-specific (sp) and total IgE levels compared to the IL-31 non-producing group. A correlation between IL-31 production and patient’s pruritus intensity, plasma CCL27 and periostin was detected. When the same patients were analyzed based on sp IgE and total IgE levels, an increased IL-31 in vitro response, as well as type 2 markers in plasma and cutaneous lesions, was found in patients with sp IgE levels &gt; 100 kUA/L and total IgE levels &gt; 1000 kU/L. The IL-31 response by memory T cells was restricted to the cutaneous lymphocyte-associated antigen (CLA)+ T-cell subset.

Conclusion

IgE sensitization to HDM allows stratifying IL-31 production by memory T cells in AD patients and relating it to particular clinical phenotypes of the disease.

Clinically meaningful improvements in cutaneous lesions and quality of life measures in patients with atopic dermatitis with greater pruritus reductions after treatment with 60 mg nemolizumab subcutaneously every 4 weeks: Subgroup analysis from a phase 3, randomized, controlled trial

BACKGROUND

Data from the Japanese phase 3 Nemolizumab-JP01 study (JapicCTI-173740) found that nemolizumab in combination with topical treatments reduced pruritus associated with atopic dermatitis inadequately controlled with current therapies.

METHODS

This post-hoc analysis examined associations between improvements in pruritus (visual analog scale [VAS]) and eczema (Eczema Area and Severity Index [EASI]), and achievement of other clinically relevant endpoints including the Insomnia Severity Index (ISI), Dermatology Life Quality Index (DLQI), and Patient-Oriented Eczema Measure (POEM).

RESULTS

Pruritus VAS responders (≥50% improvement from baseline to week 16) showed greater improvements from baseline in these additional endpoints as early as week 1, compared with non-responders. Responders also had EASI improvement, and more than 80% achieved an ISI score ≤7, or had improvement in the DLQI or POEM. The percent change from baseline in VAS and EASI scores at week 16 was in favor of nemolizumab in all subgroups based on baseline characteristics. No specific factor affecting treatment response to nemolizumab was identified.

CONCLUSIONS

In this post-hoc analysis, nemolizumab-treated patients who had greater pruritus reductions also showed improvements in other eczema symptoms; pruritus alleviation appeared to be responsible for the improvements in eczema, sleep and daily life.

The evolving landscape of biologic therapies for atopic dermatitis: Present and future perspective

Atopic dermatitis (AD) is one of the most common, chronic inflammatory skin diseases with a significant physical, emotional and socioeconomic burden. In recent years the understanding of AD pathogenesis has expanded from the Th2-centred perspective, with the recognition of the involvement of other immune axes. In different AD endotypes, influenced by environment, genetics and race, transcriptomic profiles have identified differing contributions of multiple immune axes such as, Th17, Th22 and Th1. The enriched pathogenic model of AD has catalysed the development of numerous biologic therapies targeting a range of key molecules implicated in disease progression. Currently, dupilumab and tralokinumab, which both target the Th2 pathway, are the only approved biologic therapies for AD in the United States and Europe. New biologic therapies in development, however, target different Th2-pathway molecules along with cytokines in other immune axes, including Th17 and Th22, offering promise for varied treatments for this heterogeneous disease. As the biologic pipeline advances, the integration into clinical practice and approval of these experimental biologics may provide more effective, tailored therapeutic solutions and illuminate on the pathologic processes of AD across a broader, more diverse patient population.

Apigenin: A Therapeutic Agent for Treatment of Skin Inflammatory Diseases and Cancer

The skin is the main barrier between the body and the environment, protecting it from external oxidative stress induced by ultraviolet rays. It also prevents the entrance of infectious agents such as viruses, external antigens, allergens, and bacteria into our bodies. An overreaction to these agents causes severe skin diseases, including atopic dermatitis, pruritus, psoriasis, skin cancer, and vitiligo. Members of the flavonoid family include apigenin, quercetin, luteolin, and kaempferol. Of these, apigenin has been used as a dietary supplement due to its various biological activities and has been shown to reduce skin inflammation by downregulating various inflammatory markers and molecular targets. In this review, we deal with current knowledge about inflammatory reactions in the skin and the molecular mechanisms by which apigenin reduces skin inflammation.

Genetic/Environmental Contributions and Immune Dysregulation in Children with Atopic Dermatitis

Atopic dermatitis (AD) is one of the most common skin conditions in humans. AD affects up to 20% of children worldwide and results in morbidity for both patients and their caregivers. The basis of AD is an interplay between genetics and the environment characterized by immune dysregulation. A myriad of mutations that compromise the skin barrier and/or immune function have been linked to AD. Of these, filaggrin gene (FLG) mutations are the most evidenced. Many other mutations have been implicated in isolated studies that are often unreplicated, creating an archive of genes with potential but unconfirmed relevance to AD. Harnessing big data, polygenic risk scores (PRSs) and genome-wide association studies (GWAS) may provide a more practical strategy for identifying the genetic signatures of AD. Epigenetics may also play a role. Staphylococcus aureus is the most evidenced microbial contributor to AD. Cutaneous dysbiosis may result in over-colonization by pathogenic strains and aberrant skin immunity and inflammation. Aeroallergens, air pollution, and climate are other key environmental contributors to AD. The right climate and/or commensals may improve AD for some patients.

Treating allergies via skin - Recent advances in cutaneous allergen immunotherapy

Subcutaneous allergen immunotherapy has been practiced clinically for decades to treat airborne allergies. Recently, the cutaneous route, which exploits the immunocompetence of the skin has received attention, which is evident from attempts to use it to treat peanut allergy. Delivery of allergens into the skin is inherently impeded by the barrier imposed by stratum corneum, the top layer of the skin. While the stratum corneum barrier must be overcome for efficient allergen delivery, excessive disruption of this layer can predispose to development of allergic inflammation. Thus, the most desirable allergen delivery approach must provide a balance between the level of skin disruption and the amount of allergen delivered. Such an approach should aim to achieve high allergen delivery efficiency across various skin types independent of age and ethnicity, and optimize variables such as safety profile, allergen dosage, treatment frequency, application time and patient compliance. The ability to precisely quantify the amount of allergen being delivered into the skin is crucial since it can allow for allergen dose optimization and can promote consistency and reproducibility in treatment response. In this work we review prominent cutaneous delivery approaches, and offer a perspective on further improvisation in cutaneous allergen-specific immunotherapy.

IL-37 protects against airway remodeling by reversing bronchial epithelial-mesenchymal transition via IL-24 signaling pathway in chronic asthma

BACKGROUND

Epithelial-mesenchymal transition (EMT) is one of the mechanisms of airway remodeling in chronic asthma. Interleukin (IL)-24 has been implicated in the promotion of tissue fibrosis, and increased IL-24 levels have been observed in the nasal secretions and sputum of asthmatic patients. However, the role of IL-24 in asthmatic airway remodeling, especially in EMT, remains largely unknown. We aimed to explore the effect and mechanism of IL-24 on EMT and to verify whether IL-37 could alleviate IL-24-induced EMT in chronic asthma.

METHODS

BEAS-2B cells were exposed to IL-24, and cell migration was assessed by wound healing and Transwell assays. The expression of EMT-related biomarkers (E-cadherin, vimentin, and α-SMA) was evaluated after the cells were stimulated with IL-24 with or without IL-37. A murine asthma model was established by intranasal administration of house dust mite (HDM) extracts for 5 weeks, and the effects of IL-24 and IL-37 on EMT and airway remodeling were investigated by intranasal administration of si-IL-24 and rhIL-37.

RESULTS

We observed that IL-24 significantly enhanced the migration of BEAS-2B cells in vitro. IL-24 promoted the expression of the EMT biomarkers vimentin and α-SMA via the STAT3 and ERK1/2 pathways. In addition, we found that IL-37 partially reversed IL-24-induced EMT in BEAS-2B cells by blocking the ERK1/2 and STAT3 pathways. Similarly, the in vivo results showed that IL-24 was overexpressed in the airway epithelium of an HDM-induced chronic asthma model, and IL-24 silencing or IL-37 treatment could reverse EMT biomarker expression.

CONCLUSIONS

Overall, these findings indicated that IL-37 mitigated HDM-induced airway remodeling by inhibiting IL-24-mediated EMT via the ERK1/2 and STAT3 pathways, thereby providing experimental evidence for IL-24 as a novel therapeutic target and IL-37 as a promising agent for treating severe asthma.

European guideline (EuroGuiDerm) on atopic eczema - part II: non-systemic treatments and treatment recommendations for special AE patient populations

The evidence- and consensus-based guideline on atopic eczema was developed in accordance with the EuroGuiDerm Guideline and Consensus Statement Development Manual. Four consensus conferences were held between December 2020 and July 2021. Twenty-nine experts (including clinicians and patient representatives) from 12 European countries participated. This second part of the guideline includes recommendations and detailed information on basic therapy with emollients and moisturizers, topical anti-inflammatory treatment, antimicrobial and antipruritic treatment and UV phototherapy. Furthermore, this part of the guideline covers techniques for avoiding provocation factors, as well as dietary interventions, immunotherapy, complementary medicine and educational interventions for patients with atopic eczema and deals with occupational and psychodermatological aspects of the disease. It also contains guidance on treatment for paediatric and adolescent patients and pregnant or breastfeeding women, as well as considerations for patients who want to have a child. A chapter on the patient perspective is also provided. The first part of the guideline, published separately, contains recommendations and guidance on systemic treatment with conventional immunosuppressive drugs, biologics and janus kinase (JAK) inhibitors, as well as information on the scope and purpose of the guideline, and a section on guideline methodology.

Equine keratinocytes in the pathogenesis of insect bite hypersensitivity: Just another brick in the wall?

Equine insect bite hypersensitivity (IBH) is the most common skin disease affecting horses. It is described as an IgE-mediated, Type I hypersensitivity reaction to salivary gland proteins of Culicoides insects. Together with Th2 cells, epithelial barrier cells play an important role in development of Type I hypersensitivities. In order to elucidate the role of equine keratinocytes in development of IBH, we stimulated keratinocytes derived from IBH-affected (IBH-KER) (n = 9) and healthy horses (H-KER) (n = 9) with Culicoides recombinant allergens and extract, allergic cytokine milieu (ACM) and a Toll like receptor ligand 1/2 (TLR-1/2-L) and investigated their transcriptomes. Stimulation of keratinocytes with Culicoides allergens did not induce transcriptional changes. However, when stimulated with allergic cytokine milieu, their gene expression significantly changed. We found upregulation of genes encoding for CCL5, -11, -20, -27 and interleukins such as IL31. We also found a strong downregulation of genes such as SCEL and KRT16 involved in the formation of epithelial barrier. Following stimulation with TLR-1/2-L, keratinocytes significantly upregulated expression of genes affecting Toll like receptor and NOD-receptor signaling pathway as well as NF-kappa B signaling pathway, among others. The transcriptomes of IBH-KER and H-KER were very similar: without stimulations they only differed in one gene (CTSL); following stimulation with allergic cytokine milieu we found only 23 differentially expressed genes (e.g. CXCL10 and 11) and following stimulation with TLR-1/2-L they only differed by expression of seven genes. Our data suggests that keratinocytes contribute to the innate immune response and are able to elicit responses to different stimuli, possibly playing a role in the pathogenesis of IBH.

Distribution of Cannabinoid Receptors in Keratinocytes of Healthy Dogs and Dogs With Atopic Dermatitis

It is commonly accepted that some form of skin barrier dysfunction is present in canine atopic dermatitis (AD), one of the most common cutaneous pruritic inflammatory diseases of dogs. The impaired skin barrier function facilitates the penetration of allergens and subsequently stronger sensitization responses. The role of the endocannabinoid system (ECS) in the physiology and pathology of the skin is becoming increasingly established. It has been demonstrated that cannabinoid receptors are expressed in healthy and diseased skin and, based on current knowledge, it could be stated that cannabinoids are important mediators in the skin. The present study has been designed to immunohistochemically investigate the expression of the cannabinoid receptors type 1 (CB1R) and 2 (CB2R) and the cannabinoid-related receptors G protein-coupled receptor 55 (GPR55), transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1), peroxisome proliferator-activated receptors alpha (PPARα), and serotoninergic receptor 1a (5-HT1aR) in keratinocytes of healthy dogs and of dogs with AD. Samples of skin tissues were collected from 7 healthy controls (CTRL-dogs) and from 8 dogs with AD (AD-dogs). The tissue samples were processed using an immunofluorescence assay with commercially available antibodies, and the immunolabelling of the receptors studied was quantitatively evaluated. The keratinocytes of the CTRL- and the AD-dogs showed immunoreactivity for all the receptors investigated with a significant upregulation of CB2R, TRPA1, and 5-HT1aR in the epidermis of the AD-dogs. The presence of cannabinoid and cannabinoid-related receptors in healthy keratinocytes suggested the possible role of the ECS in canine epidermal homeostasis while their overexpression in the inflamed tissues of the AD-dogs suggested the involvement of the ECS in the pathogenesis of this disease, having a possible role in the related skin inflammation and itching. Based on the present findings, the ECS could be considered a potential therapeutic target for dogs with AD.

Beneficial Effect of Heat-Killed Lactiplantibacillus plantarum L-137 on Skin Functions in Healthy Participants: A Randomized, Placebo-Controlled, Double-Blind Study

To determine whether consuming heat-killed Lactiplantibacillus plantarum L-137 (HK L-137) influences skin functions, we performed a randomized, placebo-controlled, double-blind study in healthy participants who were conscious of dry skin. A total of 80 healthy participants (20 men, 60 women; mean age, 47.3 years) were assigned to receive a tablet containing HK L-137 or a placebo tablet daily for 12 weeks. Every 4 weeks, the skin water content and transepidermal water loss (TEWL) were measured at the forearm and face, and participants completed two skin-related questionnaires, the Dermatology Life Quality Index and a self-evaluation. The HK L-137 group tended to show greater increases from baseline of water content at the forearm and larger decreases of TEWL at the face. The total scores of both questionnaires improved significantly more in the HK L-137 group. Water content and TEWL improved significantly in participants in the HK L-137 group who were above the median age of study participants or had relatively dry skin. These findings suggest that daily HK L-137 intake can improve dry skin, thereby contributing to skin satisfaction.

Current and Emerging Strategies to Inhibit Type 2 Inflammation in Atopic Dermatitis

Type 2 immunity evolved to combat helminth infections by orchestrating a combined protective response of innate and adaptive immune cells and promotion of parasitic worm destruction or expulsion, wound repair, and barrier function. Aberrant type 2 immune responses are associated with allergic conditions characterized by chronic tissue inflammation, including atopic dermatitis (AD) and asthma. Signature cytokines of type 2 immunity include interleukin (IL)-4, IL-5, IL-9, IL-13, and IL-31, mainly secreted from immune cells, as well as IL-25, IL-33, and thymic stromal lymphopoietin, mainly secreted from tissue cells, particularly epithelial cells. IL-4 and IL-13 are key players mediating the prototypical type 2 response; IL-4 initiates and promotes differentiation and proliferation of naïve T-helper (Th) cells toward a Th2 cell phenotype, whereas IL-13 has a pleiotropic effect on type 2 inflammation, including, together with IL-4, decreased barrier function. Both cytokines are implicated in B-cell isotype class switching to generate immunoglobulin E, tissue fibrosis, and pruritus. IL-5, a key regulator of eosinophils, is responsible for eosinophil growth, differentiation, survival, and mobilization. In AD, IL-4, IL-13, and IL-31 are associated with sensory nerve sensitization and itch, leading to scratching that further exacerbates inflammation and barrier dysfunction. Various strategies have emerged to suppress type 2 inflammation, including biologics targeting cytokines or their receptors, and Janus kinase inhibitors that block intracellular cytokine signaling pathways. Here we review type 2 inflammation, its role in inflammatory diseases, and current and future therapies targeting type 2 pathways, with a focus on AD. INFOGRAPHIC.

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

IL-20 promotes cutaneous inflammation and peripheral itch sensation in atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease, which is associated with intense itch, skin barrier dysfunction and eczematous lesions. Aberrant IL‐20 expression has been implicated in numerous inflammatory diseases, including psoriasis. However, the role of IL‐20 in AD remains unknown. Here, RNA‐seq, Q‐PCR, and immunocytochemistry were utilized to examine disease‐driven changes of IL‐20 and its cognate receptor subunits in skin from healthy human subjects, AD patients and murine AD‐models. Calcium imaging, knockdown and cytokine array were used to investigate IL‐20‐evoked responses in keratinocytes and sensory neurons. The murine cheek model and behavioral scoring were employed to evaluate IL‐20‐elicited sensations in vivo. We found that transcripts and protein of IL‐20 were upregulated in skin from human AD and murine AD‐like models. Topical MC903 treatment in mice ear enhanced IL‐20R1 expression in the trigeminal sensory ganglia, suggesting a lesion‐associated and epidermal‐driven mechanism for sensitization of sensory IL‐20 signaling. IL‐20 triggered calcium influx in both keratinocytes and sensory neurons, and promoted their AD‐related molecule release and transcription of itch‐related genes. In sensory neurons, IL‐20 application increased TLR2 transcripts, implicating a link between innate immune response and IL‐20. In a murine cheek model of acute itch, intradermal injection IL‐20 and IL‐13 elicited significant itch‐like behavior, though only when co‐injected. Our findings provide novel insights into IL‐20 function in peripheral (skin‐derived) itch and clinically relevant intercellular neuron‐epidermal communication, highlighting a role of IL‐20 signaling in the pathophysiology of AD, thus forming a new basis for the development of a novel antipruritic strategy via interrupting IL‐20 epidermal pathways.

Cytokine-Mediated Crosstalk Between Keratinocytes and T Cells in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction, dysregulated immune response, and dysbiosis with increased Staphylococcus aureus colonization. Infiltration of various T helper cell subsets into lesional skin and subsequent cytokine release are a hallmark of AD. Release of cytokines by both T cells and keratinocytes plays a key role in skin inflammation and drives many AD features. This review aims to discuss cytokine-mediated crosstalk between T cells and keratinocytes in AD pathogenesis and the potential impact of virulence factors produced by Staphylococcus aureus on these interactions.

Granzyme B in Epithelial Barrier Dysfunction and Related Skin Diseases

The predominant function of the skin is to serve as a barrier - to protect against external insults and to prevent water loss. Junctional and structural proteins in the stratum corneum, the outermost layer of the epidermis, are critical to the integrity of the epidermal barrier as it balances ongoing outward migration, differentiation, and desquamation of keratinocytes in the epidermis. As such, epidermal barrier function is highly susceptible to upsurges of proteolytic activity in the stratum corneum and epidermis. Granzyme B is a serine protease scarce in healthy tissues but present at high levels in tissues encumbered by chronic inflammation. Discovered in the 1980s, Granzyme B is currently recognized for its intracellular roles in immune cell-mediated targeted apoptosis as well as extracellular roles in inflammation, chronic injuries, tissue remodeling, and processing of cytokines, matrix proteins, and autoantigens. Increasing evidence has emerged in recent years supporting a role for Granzyme B in promoting barrier dysfunction in the epidermis by direct cleavage of barrier proteins and eliciting immunoreactivity. Likewise, Granzyme B contributes to impaired epithelial function of the airways, retina, gut and vessels. In the present review, the role of Granzyme B in cutaneous epithelial dysfunction is discussed in the context of specific conditions with an overview of underlying mechanisms as well as utility of current experimental and therapeutic inhibitors.

Atopic dermatitis: molecular, cellular, and clinical aspects

Atopic dermatitis (AD) is a complicated, inflammatory skin disease, which numerous genetic and environmental factors play roles in its development. AD is categorized into different phenotypes and stages, although they are mostly similar in their pathophysiological aspects. Immune response alterations and structural distortions of the skin-barrier layer are evident in AD patients. Genetic makeup, lifestyle, and environment are also significantly involved in contextual factors. Genes involved in AD-susceptibility, including filaggrin and natural moisturizing, cause considerable structural modifications in the skin's lipid bilayer and cornified envelope. Additionally, the skin's decreased integrity and altered structure are accompanied by biochemical changes in the normal skin microflora's dysbiosis. The dynamic immunological responses, genetic susceptibilities, and structural modifications associated with AD's pathophysiology will be extensively discussed in this review, each according to the latest achievements and findings.

Neuro-immune communication regulating pruritus in atopic dermatitis

Atopic dermatitis (AD) is a common, chronic-relapsing inflammatory skin disease with significant disease burden. Genetic and environmental trigger factors contribute to AD, activating two of our largest organs, the nervous and immune system. Dysregulation of neuro-immune circuits plays a key role in the pathophysiology of AD causing inflammation, pruritus, pain, and barrier dysfunction. Sensory nerves can be activated by environmental or endogenous trigger factors transmitting itch stimuli to the brain. Upon stimulation, sensory nerve endings also release neuromediators into the skin contributing again to inflammation, barrier dysfunction and itch. Additionally, dysfunctional peripheral and central neuronal structures contribute to neuroinflammation, sensitization, nerve elongation, neuropathic itch, thus chronification and therapy-resistance. Consequently, neuro-immune circuits in skin and central nervous system may be targets to treat pruritus in AD. Cytokines, chemokines, proteases, lipids, opioids, ions excite/sensitize sensory nerve endings not only induce itch but further aggravate/perpetuate inflammation, skin barrier disruption, and pruritus. Thus, targeted therapies for neuro-immune circuits as well as pathway inhibitors (e.g., kinase inhibitors) may be beneficial to control pruritus in AD either in systemic and/or topical form. Understanding neuro-immune circuits and neuronal signaling will optimize our approach to control all pathological mechanisms in AD, inflammation, barrier dysfunction and pruritus.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

Multiple Roles for Cytokines in Atopic Dermatitis: From Pathogenic Mediators to Endotype-Specific Biomarkers to Therapeutic Targets

Atopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases, which generally presents with intense itching and recurrent eczematous lesions. AD affects up to 20% of children and 10% of adults in high-income countries. The prevalence and incidence of AD have increased in recent years. The onset of AD mostly occurs in childhood, although in some cases AD may persist in adult life or even manifest in middle age (adult-onset AD). AD pathophysiology is made of a complex net, in which genetic background, skin barrier dysfunction, innate and adaptive immune responses, as well as itch contribute to disease development, progression, and chronicization. One of the most important features of AD is skin dehydration, which is mainly caused by filaggrin mutations that determine trans-epidermal water loss, pH alterations, and antigen penetration. In accordance with the “outside-inside” theory of AD pathogenesis, in a context of an altered epidermal barrier, antigens encounter epidermal antigen presentation cells (APCs), such as epidermal Langerhans cells and inflammatory epidermal dendritic cells, leading to their maturation and Th-2 cell-mediated inflammation. APCs also bear trimeric high-affinity receptors for immunoglobulin E (IgE), which induce IgE-mediated sensitizations as part of pathogenic mechanisms leading to AD. In this review, we discuss the role of cytokines in the pathogenesis of AD, considering patients with various clinical AD phenotypes. Moreover, we describe the cytokine patterns in patients with AD at different phases of the disease evolution, as well as in relation to different phenotypes/endotypes, including age, race, and intrinsic/extrinsic subtypes. We also discuss the outcomes of current biologics for AD, which corroborate the presence of multiple cytokine axes involved in the background of AD. A deep insight into the correlation between cytokine patterns and the related clinical forms of AD is a crucial step towards increasingly personalized, and therefore more efficient therapy.

The interaction between the immune system and the peripheral sensory nerves in pruritus

Pruritus is a skin-specific sensation that is observed in various skin diseases, especially in inflammatory skin diseases such as atopic dermatitis, and is deeply involved in their pathogenesis. Pruritus also adversely affects patients' sleep and mental health, placing a heavy burden on daily life. As such, pruritus control is important to the maintenance of health. The mechanism of pruritus has recently been clarified and the discovery of various pruritus mediators, the identification of specific nerves that transmit pruritus and the accumulation of knowledge on pruritus perception have led to a better understanding of all aspects of pruritus generation, transmission and recognition. In the case of pruritus caused by dermatitis, immune cells infiltrating the skin secrete inflammatory cytokines, which also act on peripheral nerves as pruritus mediators and induce an inflammatory response. Interestingly, there has been accumulating evidence that peripheral nerves are also involved in the inflammation via neuropeptides. In this article, we summarize the findings on pruritus mediators secreted by immune cells and the roles of peripheral nerves in pruritus in terms of their interactions with immunity.