FLG mutations in ichthyosis vulgaris and atopic eczema: spectrum of mutations and population genetics

Targeted next-generation sequencing analysis in Italian patients with keratoconus

OBJECTIVE

To report variants in 26 candidate genes and describe the clinical features of Italian patients with keratoconus (KC).

SUBJECTS/METHODS

Sixty-four patients with a confirmed diagnosis of KC were enrolled in this genetic association study. Patients were classified into two study groups according to whether they had a confirmed diagnosis of progressive or stable KC. A purpose-developed Next Generation Sequencing (NGS) panel was used to identify and analyse the coding exons and flanking exon/intron boundaries of 26 genes known to be associated with KC and corneal dystrophies. Interpretation of the pathogenic significance of variants was performed using in silico predictive algorithms.

RESULT

The targeted NGS research identified a total of 167 allelic variants of 22 genes in the study population; twenty-four patients had stable keratoconus (n. 54 variants) and forty patients had progressive disease (n. 113 variants). We identified genetic variants of certain pathogenic significance in five patients with progressive KC; in addition, eight novel genetic variants were found in eight patients with progressive KC. Mutations of FLG, LOXHD1, ZNF469, and DOCK9 genes were twice more frequently identified in patients with progressive than stable disease. Filaggrin gene variants were found in 49 patients (76% of total), of whom 32 patients (80% of progressive KC group) had progressive disease.

CONCLUSIONS

Targeted NGS research provided new insights into the causative effect of candidate genes in the clinical phenotype of keratoconus. Filaggrin mutations were found to represent a genetic risk factor for development of progressive disease in Italy.

Genome-wide Association Study of Susceptibility Loci for Self-Reported Atopic Dermatitis and Allergic Rhinitis in the Korean Population

BACKGROUND

Allergic diseases include atopic dermatitis (AD) and allergic rhinitis (AR), which are chronic, relapsing inflammatory disorders of the skin or mucosa that usually accompany immunoglobulin E-mediated immune responses. They are complex, multifactorial diseases with an etiology involving interactions between genetic and environmental factors.

OBJECTIVE

We performed a genome-wide association study (GWAS) to identify single nucleotide polymorphisms (SNPs) associated with allergic diseases in the Korean population.

METHODS

A total of 8,840 samples were obtained from the Korean Association Resource Consortium dataset of the Korean Genome and Epidemiology Study Ansan-Anseong cohort. The allergic disease phenotype was determined based on self-reported physician diagnoses. After quality control, 8,823 subjects with 877,242 variants remained for the final analysis. The GWAS was performed using logistic regression analysis in an additive model adjusted for age and sex.

RESULTS

A total of 636 patients with allergic disease and 8,176 controls were analyzed. Three SNPs were associated with allergic disease at a level of genome-wide suggestive significance (p<1.0×10-5) in the Korean population: rs7275360, located in neural cell adhesion molecule 2; rs698195; and rs3750552, located in family with sequence similarity 189, member A2. These polymorphisms were on chromosomes 21q21.1, 7q31.1, and 9q21.12, respectively.

CONCLUSION

We identified 3 novel SNPs significantly associated with allergic diseases in the Korean population. Further research is required to confirm the association between these novel SNPs and allergic disease in the Korean population and in other ethnicities.

Association between filaggrin gene mutations and the clinical features of molluscum contagiosum: The Yamanashi Adjunct Study of the Japan Environment and Children's Study

Previous studies have reported swimming, atopic dermatitis, and filaggrin (FLG) gene mutations as risk factors for molluscum contagiosum (MC) infection. FLG gene mutations impair skin barrier function. The aim of this study was to determine the impact of FLG mutations on the incidence and clinical features of MC. We used data from 2036 children who participated in the Yamanashi Adjunct Study of the Japan Environment and Children's Study, a prospective, birth cohort study. A questionnaire for caregivers (when children were 4 and 8 years of age) asked about clinical features including previous MC incidence and treatment, number of MC lesions at first visit, and time to resolution. Participants underwent genotyping to detect six FLG mutations that are common in the Japanese population. A logistic regression model was used to analyze the association between MC incidence and FLG mutations, adjusted for potential confounders. The cumulative incidence of MC at age 8 years was 47.1%. Among participants with a history of MC, 67.6% had undergone curettage. FLG mutation was a significant risk factor for MC incidence (adjusted odds ratio [aOR] 1.69, 95% confidence interval [CI] 1.18-2.42). Swimming and atopic dermatitis were also significant risk factors for MC. There was no significant association between FLG mutation and the number of MC lesions at the first visit or the time to resolution of lesions. FLG mutation is a risk factor for MC incidence; however, FLG mutations do not affect the number of MC lesions at presentation or the time to resolution.

Particulate matter and inflammatory skin diseases: From epidemiological and mechanistic studies

Epidemiological and toxicological studies have confirmed that exposure to atmospheric particulate matter (PM) could affect our cardiovascular and respiratory systems. Recent studies have shown that PM can penetrate the skin and cause skin inflammation, but the evidence is limited and contradictory. As the largest outermost surface of the human body, the skin is constantly exposed to the environment. The aim of this study was to assess the relationship between PM and inflammatory skin diseases. Most epidemiological studies have provided positive evidence for outdoor, indoor, and wildfire PM and inflammatory skin diseases. The effects of PM exposure during pregnancy and inflammatory skin diseases in offspring are heterogeneous. Skin barrier dysfunction, Oxidative stress, and inflammation may play a critical role in the underlying mechanisms. Finally, we summarize some interventions to alleviate PM-induced inflammatory skin diseases, which may contribute to public health welfare. Overall, PM is related to inflammatory skin diseases via skin barrier dysfunction, oxidative stress, and inflammation. Appropriate government interventions are beneficial.

Advanced In Vitro Three-Dimensional Skin Models of Atopic Dermatitis

Atopic dermatitis (AD) is one of the most prevalent inflammatory skin diseases that is characterized by eczematous rashes, intense itching, dry skin, and sensitive skin. Although AD significantly impacts the quality of life and the number of patients keeps increasing, its pathological mechanism is still unknown because of its complexity. The importance of developing new in vitro three-dimensional (3D) models has been underlined in order to understand the mechanisms for the development of therapeutics since the limitations of 2D models or animal models have been repeatedly reported. Thus, the new in vitro AD models should not only be created in 3D structure, but also reflect the pathological characteristics of AD, which are known to be associated with Th2-mediated inflammatory responses, epidermal barrier disruption, increased dermal T-cell infiltration, filaggrin down-regulation, or microbial imbalance. In this review, we introduce various types of in vitro skin models including 3D culture methods, skin-on-a-chips, and skin organoids, as well as their applications to AD modeling for drug screening and mechanistic studies.

The PI3K-Akt-mTOR and Associated Signaling Pathways as Molecular Drivers of Immune-Mediated Inflammatory Skin Diseases: Update on Therapeutic Strategy Using Natural and Synthetic Compounds

The dysregulated phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway has been implicated in various immune-mediated inflammatory and hyperproliferative dermatoses such as acne, atopic dermatitis, alopecia, psoriasis, wounds, and vitiligo, and is associated with poor treatment outcomes. Improved comprehension of the consequences of the dysregulated PI3K/Akt/mTOR pathway in patients with inflammatory dermatoses has resulted in the development of novel therapeutic approaches. Nonetheless, more studies are necessary to validate the regulatory role of this pathway and to create more effective preventive and treatment methods for a wide range of inflammatory skin diseases. Several studies have revealed that certain natural products and synthetic compounds can obstruct the expression/activity of PI3K/Akt/mTOR, underscoring their potential in managing common and persistent skin inflammatory disorders. This review summarizes recent advances in understanding the role of the activated PI3K/Akt/mTOR pathway and associated components in immune-mediated inflammatory dermatoses and discusses the potential of bioactive natural products, synthetic scaffolds, and biologic agents in their prevention and treatment. However, further research is necessary to validate the regulatory role of this pathway and develop more effective therapies for inflammatory skin disorders.

Large-scale analysis of de novo mutations identifies risk genes for female infertility characterized by oocyte and early embryo defects

BACKGROUND

Oocyte maturation arrest and early embryonic arrest are important reproductive phenotypes resulting in female infertility and cause the recurrent failure of assisted reproductive technology (ART). However, the genetic etiologies of these female infertility-related phenotypes are poorly understood. Previous studies have mainly focused on inherited mutations based on large pedigrees or consanguineous patients. However, the role of de novo mutations (DNMs) in these phenotypes remains to be elucidated.

RESULTS

To decipher the role of DNMs in ART failure and female infertility with oocyte and embryo defects, we explore the landscape of DNMs in 473 infertile parent-child trios and identify a set of 481 confident DNMs distributed in 474 genes. Gene ontology analysis reveals that the identified genes with DNMs are enriched in signaling pathways associated with female reproductive processes such as meiosis, embryonic development, and reproductive structure development. We perform functional assays on the effects of DNMs in a representative gene Tubulin Alpha 4a (TUBA4A), which shows the most significant enrichment of DNMs in the infertile parent-child trios. DNMs in TUBA4A disrupt the normal assembly of the microtubule network in HeLa cells, and microinjection of DNM TUBA4A cRNAs causes abnormalities in mouse oocyte maturation or embryo development, suggesting the pathogenic role of these DNMs in TUBA4A.

CONCLUSIONS

Our findings suggest novel genetic insights that DNMs contribute to female infertility with oocyte and embryo defects. This study also provides potential genetic markers and facilitates the genetic diagnosis of recurrent ART failure and female infertility.

Prognostic analysis of smoldering ATLL with skin eruptions based on genomic aberrations

BACKGROUND

Patients with smoldering ATLL often present with a skin eruption due to skin infiltration of ATLL cells. Although skin eruption type is known to be associated with prognosis based on its pattern, it is unknown why different types of skin eruptions are associated with different prognoses.

OBJECTIVE

Genomic analysis of patients with skin eruptions of smoldering ATLL will be performed to determine the mechanism of ATLL development and its association with prognosis.

METHODS

DNA from skin biopsy specimens was used for targeted sequencing of 280 genes to examine the association between genomic variation and prognosis.

RESULTS

Due to the small number of smoldering ATLL patients (27 cases), we could not find a clear relationship between skin eruption and prognosis in this study. Genomic analysis identified 247 genomic variants (108 genes), with an average of 9.2 variants and 3.2 variants as driver genes. Pathway analysis of the driver genes showed activation of the pathway associated with HTLV-1 infection, as well as activation of the signaling pathway observed throughout ATLL. Furthermore, multivariate analysis identified age>70 years and STAT3 mutation as prognostic risk factors and TBL1XR1 mutation as a risk factor for progression-free survival.

CONCLUSION

Although the small number of patient samples did not allow us to determine a prognostic association with skin eruption, STAT3 mutation was identified as a prognostic risk factor for smoldering ATLL with skin eruption. Further studies are needed to increase the number of patients with this disease.

Genetic polymorphism (rs6587666) in FLG protects from eczema in admixed Brazilian children population with high African ancestry

Genetic variants in filaggrin (FLG) are key in eczema and are less common in Africans than in Europeans and Asians. Here we examined the association between FLG Single Nucleotide Polymorphisms (SNPs) and eczema in a population of admixed Brazilian children and whether African ancestry modifies this association. We included 1010 controls and 137 cases and ran logistic regressions between SNPs in FLG and eczema in the studied population and also stratified the analyses according to the degree of African ancestry. In addition, we tested the replication of the findings on an independent set of individuals, as well as, we verified the impact on FLG expression according to each SNP genotype. The T allele of SNP rs6587666 was negatively associated with eczema in additive model (OR: 0.66, 95% CI: 0.47-0.93, P: 0.017). Moreover, African ancestry modifies the association between rs6587666 and eczema. The effect of the T allele was higher among individuals with higher African ancestry and the association with eczema was lost in individuals with lower African ancestry. In our analyses the expression of FLG in skin was slightly downregulated by the presence of the T allele of rs6587666. In our population, the T allele of rs6587666 in FLG was associated with protection to eczema and the degree of African ancestry was able to modify the observed association.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

Stratum Corneum Ceramide Profiles Provide Reliable Indicators of Remission and Potential Flares in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease. Prevention of exacerbation of AD is a crucial issue for all physicians. However, exacerbation of AD often is seen during reduction of AD treatment, even with appropriate follow-up by tapered topical corticosteroids and daily topical moisturizers, indicating the need for good indicators of AD remission. We hypothesized that the presence of mutations in FLG or the stratum corneum ceramide profile on AD remission phase may predict the ease of AD exacerbation. This study examined the differences in the frequency of FLG mutations or stratum corneum ceramide profiles (stratum corneum levels and carbon chain length for 11 ceramide classes [ceramides containing nonhydroxy fatty acids and dihydrosphingosines; nonhydroxy fatty acids and sphingosines; nonhydroxy fatty acids and 6-hydroxysphingosines; nonhydroxy fatty acids and phytosphingosines; a-hydroxy fatty acids and dihydrosphingosines; a-hydroxy fatty acids and sphingosines; a-hydroxy fatty acids and 6-hydroxysphingosines; a-hydroxy fatty acids and phytosphingosines; ester-linked fatty acids, o-hydroxy fatty acids, and sphingosines; ester-linked fatty acids, o-hydroxy fatty acids, and 6-hydroxysphingosines; and ester-linked fatty acids, o-hydroxy fatty acids, and phytosphingosines]) at AD remission phase between the two AD study groups: subsequent exacerbation (‒) and (+) of AD. The frequency of FLG mutations did not differ between the study groups. On the other hand, the carbon chain lengths of ceramides containing nonhydroxy fatty acids and dihydrosphingosines, nonhydroxy fatty acids and sphingosines, and nonhydroxy fatty acids and 6-hydroxysphingosines were shorter in the exacerbated AD group than in the maintained-AD group. Thus, the stratum corneum ceramide profile at the remission phase of AD is a potential biomarker, predicting the likelihood of substantial AD remission or subsequent AD exacerbation.

Genetic Etiology of Ichthyosis in Turkish Patients: Nextgeneration Sequencing Identified Seven Novel Mutations

Objective:

Ichthyosis is a clinically heterogeneous group of genodermatoses characterized by widespread drying and scaling of the skin. It is also a genetically heterogeneous disorder, and 67 genes associated with the disease have been identified to date. However, there are still undiscovered genes causing the disease.

Methods:

We investigated 19 Turkish patients from 17 unrelated families using clinical exome sequencing or multigene panel screening.

Results:

Sixteen likely pathogenic or pathogenic variants were detected in 13 unrelated patients. We identified “variant of unknown significance” alteration in only one patient. Seven novel variants were identified in ABCA12, ALOX12B, and ALOXE3. The most commonly mutated gene was TGM1, followed by ABCA12 and ALOX12B.

Conclusions:

Because of the wide genetic variability of ichthyosis, it is difficult to diagnose the disease quickly and definitively. The clinical use of next-generation sequencing (NGS) methodologies is beneficial in the diagnostic approach to ichthyosis and genetic counseling. This study highlights the underlying molecular cause of ichthyosis by determining the mutational spectrum in a cohort of 19 patients. This study is the first and largest research from Turkey using NGS that highlights all ichthyosis subtypes.

Incomplete Penetrance and Variable Expressivity: From Clinical Studies to Population Cohorts

The same genetic variant found in different individuals can cause a range of diverse phenotypes, from no discernible clinical phenotype to severe disease, even among related individuals. Such variants can be said to display incomplete penetrance, a binary phenomenon where the genotype either causes the expected clinical phenotype or it does not, or they can be said to display variable expressivity, in which the same genotype can cause a wide range of clinical symptoms across a spectrum. Both incomplete penetrance and variable expressivity are thought to be caused by a range of factors, including common variants, variants in regulatory regions, epigenetics, environmental factors, and lifestyle. Many thousands of genetic variants have been identified as the cause of monogenic disorders, mostly determined through small clinical studies, and thus, the penetrance and expressivity of these variants may be overestimated when compared to their effect on the general population. With the wealth of population cohort data currently available, the penetrance and expressivity of such genetic variants can be investigated across a much wider contingent, potentially helping to reclassify variants that were previously thought to be completely penetrant. Research into the penetrance and expressivity of such genetic variants is important for clinical classification, both for determining causative mechanisms of disease in the affected population and for providing accurate risk information through genetic counseling. A genotype-based definition of the causes of rare diseases incorporating information from population cohorts and clinical studies is critical for our understanding of incomplete penetrance and variable expressivity. This review examines our current knowledge of the penetrance and expressivity of genetic variants in rare disease and across populations, as well as looking into the potential causes of the variation seen, including genetic modifiers, mosaicism, and polygenic factors, among others. We also considered the challenges that come with investigating penetrance and expressivity.

Skin barrier defects in atopic dermatitis: From old idea to new opportunity

Atopic dermatitis (AD) is the most common chronic skin inflammatory disease, with a profound impact on patients’ quality of life. AD varies considerably in clinical course, age of onset and degree to which it is accompanied by allergic and non-allergic comorbidities. Skin barrier impairment in both lesional and nonlesional skin is now recognized as a critical and often early feature of AD. This may be explained by a number of abnormalities identified within both the stratum corneum and stratum granulosum layers of the epidermis. The goal of this review is to provide an overview of key barrier defects in AD, starting with a historical perspective. We will also highlight some of the commonly used methods to characterize and quantify skin barrier function. There is ample opportunity for further investigative work which we call out throughout this review. These include: quantifying the relative impact of individual epidermal abnormalities and putting this in a more holistic view with physiological measures of barrier function, as well as determining whether these barrier-specific endotypes predict clinical phenotypes (e.g. age of onset, natural history, comorbidities, response to therapies, etc). Mechanistic studies with new (and in development) AD therapies that specifically target immune pathways, Staphylococcus aureus abundance and/or skin barrier will help us understand the dynamic crosstalk between these compartments and their relative importance in AD.

Ichthyosis and hereditary cornification disorders in dogs

The stratum corneum (SC), the outermost layer of the epidermis, serves a crucial role in maintaining body hydration and protection from environmental insults. When the stratum corneum is injured or when the genetic blueprints are flawed, the body is at risk of dehydration, secondary infections and allergen sensitization. Advancements in veterinary dermatology have revealed a wide gamut of disease from relatively benign to lethal that specifically arise from flawed structural proteins, enzymes or lipids needed to create the corneocytes and lipid bilayers of the SC. Some conditions closely mimic their human counterparts while others are unique to the dog. This review will focus on forms of ichthyosis in the dog.

The Pathogenesis of Eosinophilic Asthma: A Positive Feedback Mechanism That Promotes Th2 Immune Response via Filaggrin Deficiency

Eosinophilic asthma (EA) is a common subtype of asthma and often progresses to severe disease. In order to understand its pathogenesis, targeted next-generation gene sequencing was performed on 77 Chinese EA patients and 431 Chinese healthy controls to obtain differential genomic variations. Among the 41 Single Nucleotide Polymorphisms (SNPs) screened for mutation sites in more than 3 patients, filaggrin gene FLG rs192116923 T>G and FLG rs75235053 C>G were newly found to be associated with EA patients with atopic dermatitis (AD) (P <0.001) and severe EA (P=0.032), respectively. Filaggrin has been shown to be mainly expressed in epithelial cells and plays an important role in formation of an effective skin barrier. Bioinformatic analysis indicated FLG rs192116923 T>G may increase the binding of Smad3 to transmit TGF-β1 signaling, and thereby inhibit filaggrin expression, and FLG rs75235053 C>G may add new splicing sites to reduce filaggrin monomers. It has been known that the level of Th2 cytokine IL-4 is increased in EA patients, and IL-4 increases airway epithelial permeability and enhances inflammatory response through some unclear mechanisms. To figure out whether filaggrin is involved in immune responses in asthma, we have treated human respiratory epithelial cell line BEAS-2B cells with IL-4 and found that the expression levels of filaggrin and E-cadherin decreased significantly in a time and dose-dependent manner, suggesting that IL-4 increased airway epithelial permeability by reducing filaggrin and adhesion molecule. In addition, in our study, IL-4 increased the expression of epithel-derived inflammatory cytokines IL-33 and TSLP which further enhanced the Th2 inflammatory response. To investigate the role of filaggrin in development of EA, knockdown filaggrin with siRNA revealed a decrease in E-cadherin levels, which were further down-regulated by IL-4 stimulation. Knockdown of filaggrin alone did not affect the levels of IL-33 and TSLP, but further exacerbated the decrease of IL-33/TSLP caused by IL-4, suggesting that filaggrin may involve in IL-4R signaling pathway to regulate the level of IL-33/TSLP. In conclusion, in the Th2 cytokine milieu of asthma, FLG deficient mutation in airway epithelial cells may increase the epithelial permeability and the expression of IL-33/TSLP which positively feedback the Th2 inflammation response.

Comprehensive Molecular Analyses of a Novel Mutational Signature Classification System with Regard to Prognosis, Genomic Alterations, and Immune Landscape in Glioma

Background: Glioma is the most common malignant brain tumor with complex carcinogenic process and poor prognosis. The current molecular classification cannot fully elucidate the molecular diversity of glioma.

Methods: Using broad public datasets, we performed cluster analysis based on the mutational signatures and further investigated the multidimensional heterogeneity of the novel glioma molecular subtypes. The clinical significance and immune landscape of four clusters also investigated. The nomogram was developed using the mutational clusters and clinical characteristics.

Results: Four heterogenous clusters were identified, termed C1, C2, C3, and C4, respectively. These clusters presented distinct molecular features: C1 was characterized by signature 1, PTEN mutation, chromosome seven amplification and chromosome 10 deletion; C2 was characterized by signature 8 and FLG mutation; C3 was characterized by signature 3 and 13, ATRX and TP53 mutations, and 11p15.1, 11p15.5, and 13q14.2 deletions; and C4 was characterized by signature 16, IDH1 mutation and chromosome 1p and 19q deletions. These clusters also varied in biological functions and immune status. We underlined the potential immune escape mechanisms: abundant stromal and immunosuppressive cells infiltration and immune checkpoints (ICPs) blockade in C1; lack of immune cells, low immunogenicity and antigen presentation defect in C2 and C4; and ICPs blockade in C3. Moreover, C4 possessed a better prognosis, and C1 and C3 were more likely to benefit from immunotherapy. A nomogram with excellent performance was also developed for assessing the prognosis of patients with glioma.

Conclusion: Our results can enhance the mastery of molecular features and facilitate the precise treatment and clinical management of glioma.

Polygenic prediction of atopic dermatitis improves with atopic training and filaggrin factors

BACKGROUND

While numerous genetic loci associated with atopic dermatitis (AD) have been discovered, to date, work leveraging the combined burden of AD risk variants across the genome to predict disease risk has been limited.

OBJECTIVES

This study aims to determine whether polygenic risk scores (PRSs) relying on genetic determinants for AD provide useful predictions for disease occurrence and severity. It also explicitly tests the value of including genome-wide association studies of related allergic phenotypes and known FLG loss-of-function (LOF) variants.

METHODS

AD PRSs were constructed for 1619 European American individuals from the Atopic Dermatitis Research Network using an AD training dataset and an atopic training dataset including AD, childhood onset asthma, and general allergy. Additionally, whole genome sequencing data were used to explore genetic scoring specific to FLG LOF mutations.

RESULTS

Genetic scores derived from the AD-only genome-wide association studies were predictive of AD cases (PRS_AD: odds ratio [OR], 1.70; 95% CI, 1.49-1.93). Accuracy was first improved when PRSs were built off the larger atopy genome-wide association studies (PRS_AD+: OR, 2.16; 95% CI, 1.89-2.47) and further improved when including FLG LOF mutations (PRS_AD++: OR, 3.23; 95% CI, 2.57-4.07). Importantly, while all 3 PRSs correlated with AD severity, the best prediction was from PRS_AD++, which distinguished individuals with severe AD from control subjects with OR of 3.86 (95% CI, 2.77-5.36).

CONCLUSIONS

This study demonstrates how PRSs for AD that include genetic determinants across atopic phenotypes and FLG LOF variants may be a promising tool for identifying individuals at high risk for developing disease and specifically severe disease.

Targeting immunoglobulin E in atopic dermatitis: A review of the existing evidence

Immunoglobulin E (IgE) plays an essential role in many allergic diseases. This review highlights the role of IgE in atopic dermatitis (AD), a common, chronic, and complex skin inflammation, and the available therapeutic approaches that target IgE in AD. We examine the existing data showing the use of omalizumab, the only biologic anti-IgE therapy available in clinical use, plasma apheresis, and a combination of both therapeutic approaches for the treatment of AD. Existing data on the efficacy of omalizumab in AD are inconclusive. A limited number of randomised controlled studies, few uncontrolled prospective and retrospective reports, as well as multiple case series and case reports observed varying degrees of the efficacy of omalizumab in AD. Omalizumab displays a trend of higher efficacy in AD patients with low IgE levels compared with those with very high-to-extremely high serum IgE concentrations. Plasma apheresis and its combination with omalizumab show good efficacy, even in patients with unusually high serum IgE concentrations. Combining apheresis and anti-IgE treatment may serve as a comprehensive therapeutic approach for patients with elevated levels of IgE. Dedicated clinical studies with robust study designs are needed to establish the therapeutic efficacy of omalizumab in AD.

Structural properties of target binding by profilaggrin A and B domains and other S100 fused-type calcium-binding proteins

BACKGROUND

Profilaggrin belongs to the S100 fused-type protein family expressed in keratinocytes and is important for skin barrier integrity. Its N-terminus contains an S100 ("A") domain and a unique "B" domain with a nuclear localization sequence.

OBJECTIVE

To determine whether profilaggrin B domain cooperates with the S100 domain to bind macromolecules. To characterize the biochemical and structural properties of the profilaggrin N-terminal "AB" domain and compare it to other S100 fused-type proteins.

METHODS

We used biochemical (protease protection, light scattering, fluorescence spectroscopy, pull-down assays) and computational techniques (sequence analysis, molecular modeling with crystallographic structures) to examine human profilaggrin and S100 fused-type proteins.

RESULTS

Comparing profilaggrin S100 crystal structure with models of the other S100 fused-type proteins demonstrated each has a unique chemical composition of solvent accessible surface around the hydrophobic binding pocket. S100 fused-type proteins exhibit higher pocket hydrophobicity than soluble S100 proteins. The inter-EF-hand linker in S100 fused-type proteins contains conserved hydrophobic residues involved in binding substrates. Profilaggrin B domain cooperates with the S100 domain to bind annexin II and keratin intermediate filaments in a calcium-dependent manner using exposed cationic surface. Using molecular modeling we demonstrate profilaggrin B domain likely interacts with annexin II domains I and II. Steric clash analysis shows annexin II N-terminal peptide is favored to bind profilaggrin among S100 fused-type proteins.

CONCLUSION

The N-terminal S100 and B domains of profilaggrin cooperate to bind substrate molecules in granular layer keratinocytes to provide epidermal barrier functions.

Prevalence of Filaggrin Gene R501X Mutation in Indian Children with Allergic Diseases

OBJECTIVE

To determine the prevalence of R501X mutation of Filaggrin gene in children with allergic diseases.

METHODS

Ninety patients recruited from Allergy and Asthma clinic of Advanced Pediatric Centre, PGIMER, Chandigarh and 81 healthy controls from local schools matched for age, gender and BMI were enroled in the present study. The R501X mutation analysis was done by PCR-RFLP method.

RESULTS

Out of the 90 enroled allergic children, 5 (5.5%) were mutant (AA) for R501X genotype, 44 (43.3%) had (AA+Aa) genotype and 46 (51.1%) had (aa) genotype. However, in the control group there were no mutant (AA) for R501X, 36 (44.4%) had (AA+Aa) genotype and 45 had wild type homozygous (aa) genotype. There were 3.3% and 2.2% children with asthma and asthma concomitantly with eczema having mutant R501X genotype.

CONCLUSIONS

In the present study, the prevalence of Filaggrin mutant genotype (R501X) was detected in approximately 5.5% of children with allergic diseases.

Egg Allergy: Diagnosis and Immunotherapy

Hypersensitivity or an allergy to chicken egg proteins is a predominant symptomatic condition affecting 1 in 20 children in Australia; however, an effective form of therapy has not yet been found. This occurs as the immune system of the allergic individual overreacts when in contact with egg allergens (egg proteins), triggering a complex immune response. The subsequent instantaneous inflammatory immune response is characterized by the excessive production of immunoglobulin E (IgE) antibody against the allergen, T-cell mediators and inflammation. Current allergen-specific approaches to egg allergy diagnosis and treatment lack consistency and therefore pose safety concerns among anaphylactic patients. Immunotherapy has thus far been found to be the most efficient way to treat and relieve symptoms, this includes oral immunotherapy (OIT) and sublingual immunotherapy (SLIT). A major limitation in immunotherapy, however, is the difficulty in preparing effective and safe extracts from natural allergen sources. Advances in molecular techniques allow for the production of safe and standardized recombinant and hypoallergenic egg variants by targeting the IgE-binding epitopes responsible for clinical allergic symptoms. Site-directed mutagenesis can be performed to create such safe hypoallergens for their potential use in future methods of immunotherapy, providing a feasible standardized therapeutic approach to target egg allergies safely.

Host-microbial dialogues in atopic dermatitis

Recent advances in sequencing technologies have revealed the diversity of microbes that reside on the skin surface which has enhanced our understanding on skin as an ecosystem, wherein the epidermis, immune cells and the microbiota engage in active dialogues that maintain barrier integrity and functional immunity. This mutual dialogue is altered in atopic dermatitis (AD), in which an impaired epidermal barrier, the skin microbial flora and aberrant immunity can form a vicious cycle that leads to clinical manifestations as eczematous dermatitis. Microbiome studies have revealed an altered microbial landscape in AD and genetic studies have identified genes that underlie barrier impairment and immune dysregulation. Shifting from the long-standing notion that AD was mediated by conventional allergic responses, emerging data suggest that it is a disorder of an altered host-microbial relationship with sophisticated pathophysiology. In this review, we will discuss recent advancements that suggest the roles of the skin microbiota in AD pathophysiology, genetic factors that mediate barrier impairment, dysbiosis and inflammation. Studies in mice, classic AD and monogenic disorders that manifest as AD collectively facilitate our understanding of AD pathophysiology and provide a foundation for novel therapeutic strategies.

CD8+ T cells regulated by CD4+CD25+ regulatory T cells in the early stage exacerbate the development of Dermatophagoides farinae-induced skin lesions via increasing mast cell infiltration in mice

Atopic dermatitis is a chronic inflammatory skin disease associated with CD4⁺ Th2 cell-shifted immune responses. Although the infiltration of skin lesions by CD8⁺ T cells has been recognized, their roles have not been fully defined. In this study, we examined the relationship between CD4⁺ and CD8⁺ cells in antigen-induced skin lesions of mice. BALB/c mice were repeatedly challenged with Dermatophagoides farinae (Der f) applied to the right ear nine times. Pre-treatment with anti-CD4 monoclonal antibody (mAb) during the third to sixth challenges, but not the post-treatment during the sixth to ninth challenges, exacerbated the development of Der f-induced ear swelling; pre-treatment with anti-CD25 mAb, which depletes regulatory T cells (Tregs), also exacerbated the lesions. Furthermore, the number of CD8⁺ T cells in lymph nodes was augmented by these pre-treatments. These findings prompted us to examine the effect of anti-CD8 mAb. Pre-treatment with anti-CD8 mAb, but not post-treatment, strongly inhibited the development of Der f-induced ear swelling; additionally, the epidermal hyperplasia and infiltration of mast cells were inhibited by the pre-treatment. Collectively, we revealed that CD8⁺ T cells regulated by CD4⁺CD25⁺ Tregs in the early stage are key contributors to the development of Der f-induced skin lesions via increasing mast cell infiltration, indicating that CD8⁺ T and Tregs could be potential therapeutic targets for atopic dermatitis.

The Human Microbiota and Its Relationship with Allergies

Allergic diseases have been increasing to epidemic proportions during the past century, especially in high-income countries. Recent evidence suggests there might be a link between the allergy epidemic and reduced microbial exposures, resulting from a rapidly evolved modern lifestyle, including changed diets, health and hygiene standards, and daily habits. Recently it has become clear that the microbial communities in our respiratory system and our gut, as well as on our skin, may play a key role in shaping our physiology, and influencing our health. We are only beginning to understand the mechanisms by which the human microbiota may be regulating the immune system, and sudden changes in the composition of the microbiota may have profound effects, linked with an increased risk of developing chronic inflammatory disorders, including allergies.

Palmar hyperlinearity in early childhood atopic dermatitis is associated with filaggrin mutation and sensitization to egg

BACKGROUND/OBJECTIVES

Palmar hyperlinearity is a typical clinical feature of Filaggrin gene (FLG) null mutations. There are reports of FLG mutations and allergic sensitization; however, reports on the relationship between palmar hyperlinearity to sensitization are limited. This study aimed to examine the association between palmar hyperlinearity and sensitization in atopic dermatitis (AD) children.

METHODS

This cross-sectional, case-control study included children ˂ 6 years old with moderate-severe AD whose parents consented for mutation analysis and photographic documentation. Each child underwent genotyping to detect the eight most prevalent FLG mutations in the Japanese population: R501X, 3321delA, S1695X, Q1701X, S2554X, S2889X, S3296X, and K4022X. Clinical features and parameters including egg-specific IgE were examined, and palm photographs were evaluated by 12 trained dermatologists blinded to genotyping results.

RESULTS

Of the 57 patients (age range, 2 months to 5 years; median, 22 months), 16 were heterozygotes and three were compound heterozygotes. Palmar hyperlinearity, as recognized by more than two-thirds of dermatologists, was significantly associated with FLG mutation (P = 0.002, OR = 6.98, 95% CI = 2.1-23.7), and this association was observed especially in children over 2 years. Cross-shaped crease of the thenar eminence, as known in previous reports, also demonstrated significant correlation with FLG mutation. When the children were divided according to the presence or absence of palmar hyperlinearity, the egg white-specific IgE was significantly higher in the hyperlinearity group (55.9 vs 18.3 IU/mL, P < 0.05).

CONCLUSIONS

Palmar hyperlinearity indicates possible inherited barrier abnormalities of the skin in early childhood. Its identification may help to predict a more accurate prognosis, such as sensitization.

Activography reveals aberrant proteolysis in desquamating diseases of differing backgrounds

The role of epidermal proteolysis in overdesquamation was revealed in Netherton syndrome, a rare ichthyosis due to genetic deficiency of the LEKTI inhibitor of serine proteases. Recently, we developed activography, a new histochemical method, to spatially localize and semiquantitatively assess proteolytic activities using activity-based probes. Activography provides specificity and versatility compared to in situ zymography, the only available method to determine enzymatic activities in tissue biopsies. Here, activography was validated in skin biopsies obtained from an array of distinct disorders and compared with in situ zymography. Activography provides a methodological advancement due to its simplicity and specificity and can be readily adapted as a routine diagnostic assay. Interestingly, the levels of epidermal proteolysis correlated with the degree of desquamation independent of skin pathology. Thus, deregulated epidermal proteolysis likely represents a universal mechanism underlying aberrant desquamation.

Heparinoid suppresses Der p-induced IL-1β production by inhibiting ERK and p38 MAPK pathways in keratinocytes

Epidermal keratinocytes initiate skin inflammation by activating immune cells. The skin barrier is disrupted in atopic dermatitis (AD) and epidermal keratinocytes can be exposed to environmental stimuli, such as house dust mite (HDM) allergens. We showed previously that HDM allergens activate the NLRP3 inflammasome of keratinocytes, thereby releasing pro-inflammatory cytokines. Heparinoid is an effective moisturizer for atopic dry skin. However, a recent report showed that heparinoid treatment can improve inflammation of lichen planus. Therefore, we hypothesized that it acts on epidermal keratinocytes not only as a moisturizer, but also as a suppressant of the triggers of skin inflammation. We found that HDM allergen-induced interleukin (IL)-1β release from keratinocytes was inhibited significantly by heparinoid pretreatment without affecting cell viability. However, heparinoid did not affect caspase-1 release, suggesting that heparinoid did not affect HDM allergen-induced inflammasome activation. Heparinoid treatment not only decreased intracellular levels of pro-IL-1β, but also suppressed IL-1β messenger RNA (mRNA) expression in keratinocytes. Among the intracellular signalling pathways, the activation of extracellular signal-regulated kinase and p38 pathways, which are required for IL-1β expression in keratinocytes, was inhibited by heparinoid treatment. The inhibitory effect of heparinoid on IL-1β mRNA expression was also confirmed with living skin equivalents. Our results demonstrated that heparinoid suppresses the initiation of keratinocyte-mediated skin inflammation.

Uncommon Filaggrin Variants Are Associated with Persistent Atopic Dermatitis in African Americans

Atopic dermatitis (AD) is a common illness that has been associated with filaggrin gene (FLG) loss of function (LoF) variation. In African Americans, a group that commonly has AD and has not been well studied, FLG LoF variation is rarely found. Our objective was to use massively parallel sequencing to evaluate FLG LoF variation in children of African ancestry to evaluate the association between FLG LoF variation and AD and AD persistence. We studied 262 African American children with AD. Nine unique FLG exon 3 LoF variants were identified for an overall minor variant frequency of 6.30% (95% confidence interval [CI] = 4.37-8.73). The most common variants were p.R501X (1.72%, 95% CI = 0.79-3.24), p.S3316X (1.34%, 95% CI = 0.54-2.73), and p.R826X (0.95%, 95% CI = 0.31-2.2). Over an average follow-up period of 96.4 (95% CI = 92.0-100.8) months, African American children with FLG LoF were less likely to be symptom free (odds ratio = 0.36, 95% CI = 0.14-0.89, P = 0.027) compared with a FLG wild-type child. In contrast to previous reports, uncommon FLG LoF variants in African American children exist and are associated with AD and more persistent AD. In contrast to Europeans, no FLG LoF variants predominate in African American children. Properly determining FLG LoF status requires advanced sequencing techniques.

Sensitive skin is highly frequent in extrinsic atopic dermatitis and correlates with disease severity markers but not necessarily with skin barrier impairment

BACKGROUND

Sensitive skin is a condition of cutaneous hypersensitivity to environmental factors. Lactic acid stinging test (LAST) is commonly used to assess sensitive skin and composed of four distinct sensations (pain, burning sensation, itch, and crawly feeling). A link between sensitive skin and barrier dysfunction has been proposed in atopic dermatitis (AD) patients. However, clinical and laboratory factors that are associated with sensitive skin remain unelucidated.

OBJECTIVE

To investigate relationship between sensitive skin and AD-associated markers.

METHODS

Forty-two Japanese AD patients and 10 healthy subjects (HS) were enrolled. AD patients were divided into extrinsic (EAD; high IgE levels) and intrinsic (IAD; normal IgE levels) types. We conducted 1% LAST by assessing the four distinct sensations and calculated the frequencies of sensitive skin in EAD, IAD, and HS. We also performed clinical AD-related tests, including transepidermal water loss (TEWL), visual analogue scale (VAS) of pruritus, and quality of life, and measured laboratory markers, including blood levels of IgE, CCL17/TARC, lactate dehydrogenase (LDH) and eosinophil counts, and concentration levels of serum Th1/Th2 cytokines. Filaggrin (FLG) mutations were examined in 21 patients. These values were subjected to correlation analyses with each of the four sensation elements.

RESULTS

According to the standard criteria for LAST positivity, the frequencies of LAST-positive subjects were 54.8% and 10.0% in AD and HS, respectively (P=0.014). EAD patients showed a significantly (P=0.026) higher frequency of positive LAST (65.6%) than did IAD patients (20.0%). Among the four LAST sensation elements, the crawly feeling and pain scores positively correlated with VAS of pruritus, total serum IgE, mite-specific IgE, CCL17/TARC, and/or LDH. There was no association of the LAST scores with serum Th1/Th2 cytokine levels. Notably, neither TEWL nor FLG mutations correlated with LAST positivity or any sensation scores.

CONCLUSIONS

The frequency of sensitive skin is higher in EAD than in IAD. Sensitive skin is associated with AD severity, but not necessarily with barrier condition.

Peeling skin syndrome associated with novel variant in FLG2 gene

Peeling skin syndrome is a rare genodermatosis characterized by variably pruritic superficial generalized peeling of the skin with several genes involved until now little is known about the association between FLG2 and peeling skin syndrome. We describe multiple family members from a consanguineous Saudi family with peeling skin syndrome. Next Generation Sequencing identifies a cosegregating novel variant in FLG2 c.632C>G (p.Ser211*) as a likely etiology in this family. Here, we reported on the clinical manifestation of homozygous loss of function variant in FLG2 as a disease-causing gene for peeling skin syndrome and expand the dermatology findings.

Atopic Dermatitis Studies through In Vitro Models

Atopic dermatitis (AD) is a complex inflammatory skin condition that is not fully understood. Epidermal barrier defects and Th2 immune response dysregulations are thought to play crucial roles in the pathogenesis of the disease. A vicious circle takes place between these alterations, and it can further be complicated by additional genetic and environmental factors. Studies investigating in more depth the etiology of the disease are thus needed in order to develop functional treatments. In recent years, there have been significant advances regarding in vitro models reproducing important features of AD. However, since a lot of models have been developed, finding the appropriate experimental setting can be difficult. Therefore, herein, we review the different types of in vitro models mimicking features of AD. The simplest models are two-dimensional culture systems composed of immune cells or keratinocytes, whereas three-dimensional skin or epidermal equivalents reconstitute more complex stratified tissues exhibiting barrier properties. In those models, hallmarks of AD are obtained, either by challenging tissues with interleukin cocktails overexpressed in AD epidermis or by silencing expression of pivotal genes encoding epidermal barrier proteins. Tissue equivalents cocultured with lymphocytes or containing AD patient cells are also described. Furthermore, each model is placed in its study context with a brief summary of the main results obtained. In conclusion, the described in vitro models are useful tools to better understand AD pathogenesis, but also to screen new compounds in the field of AD, which probably will open the way to new preventive or therapeutic strategies.

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.

Genetic and epigenetic studies of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory disease caused by the complex interaction of genetic, immune and environmental factors. There have many recent discoveries involving the genetic and epigenetic studies of AD.

METHODS

A retrospective PubMed search was carried out from June 2009 to June 2016 using the terms "atopic dermatitis", "association", "eczema", "gene", "polymorphism", "mutation", "variant", "genome wide association study", "microarray" "gene profiling", "RNA sequencing", "epigenetics" and "microRNA". A total of 132 publications in English were identified.

RESULTS

To elucidate the genetic factors for AD pathogenesis, candidate gene association studies, genome-wide association studies (GWAS) and transcriptomic profiling assays have been performed in this period. Epigenetic mechanisms for AD development, including genomic DNA modification and microRNA posttranscriptional regulation, have been explored. To date, candidate gene association studies indicate that filaggrin (FLG) null gene mutations are the most significant known risk factor for AD, and genes in the type 2 T helper lymphocyte (Th2) signaling pathways are the second replicated genetic risk factor for AD. GWAS studies identified 34 risk loci for AD, these loci also suggest that genes in immune responses and epidermal skin barrier functions are associated with AD. Additionally, gene profiling assays demonstrated AD is associated with decreased gene expression of epidermal differentiation complex genes and elevated Th2 and Th17 genes. Hypomethylation of TSLP and FCER1G in AD were reported; and miR-155, which target the immune suppressor CTLA-4, was found to be significantly over-expressed in infiltrating T cells in AD skin lesions.

CONCLUSIONS

The results suggest that two major biologic pathways are responsible for AD etiology: skin epithelial function and innate/adaptive immune responses. The dysfunctional epidermal barrier and immune responses reciprocally affect each other, and thereby drive development of AD.

An Analysis of the Filaggrin Gene Polymorphism in Korean Atopic Dermatitis Patients

Research of the FLG mutation in various ethnic groups revealed non-overlapping mutation patterns. In addition, Japanese and Chinese atopic patients showed somewhat different mutations. These ethnic differences make the research on Korean patients mandatory; however, no systematic research on Korean atopic dermatitis (AD) patients has been performed. This study aims to investigate the genetic polymorphism of FLG in Korean atopic dermatitis patients. The study was made up of three groups including 9 Ichthyosis vulgaris (IV) patients, 50 AD patients and 55 normal controls: the ichthyosis group was incorporated due to the reported association between the FLG mutation and IV. In comparison to other sequencing methods, the overlapping long-range PCR was used. We revealed the genetic polymorphism of filaggrin in Koreans, and at the same time, we discovered nonsense mutations in p.Y1767X and p.K4022X in Korean AD patients. By using FLG sequencing techniques confirmed in this study, new mutations or genetic polymorphisms with ethnic characteristics would be detected and further larger studies of repeat number polymorphisms could be performed.

The study of filaggrin gene mutations and copy number variation in atopic dermatitis patients from Volga-Ural region of Russia

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by age-specific localization, dryness, itch and hypersensitivity to allergens. In our study, we investigated FLG gene mutations and CNVs in AD patients and control subjects of different ethnic origin from Volga-Ural region. AD group included 303 patients (177 Russians, 126 Tatars). Control group consisted of 261 healthy individuals (152 Russians, 109 Tatars). The study revealed 66 FLG mutation carriers and demonstrated an association between c.2282del4 deletion and AD development in Russians and Tatars of Volga-Ural region of Russia. In the analysis of the FLG gene CNVs, the most common was 10-repeat allele in both Russian and Tatar patients and controls. We were unable to find any significant difference in CNV repeats count between AD patients and control individuals.

The course and treatment of atopic erythroderma Hill (case study)

Relevance. Atopic erythroderma Hill (AEH) is a severe variant of the disease. Its occurrence depends on the examined patients and between 1.9% (young men of military age) to 42% (persons admitted to hospital). The treatment procedure is directly related to the presence of trigger factors, aggravating the disease. The purpose of this publication. To analyze the errors of physicians in the choice of Treatment for patients with AEH. Materials and methods. Use material during the examination and treatment of two patients with AEH aged 5 and 17 years in the allergological center of professor Ado A.D. The detailed analysis of the characteristics of AEH and reasons for the ineffectiveness of traditional treatment methods. Main results. Clinical, immunological, bacteriological methods have made it possible to identify trigger factors contributing to the transformation of the classical course of atopic dermatitis in AEH. Limiting their influence helped improve efficiency. Conclusion. The drug of choice for topical therapy AEH is the methylprednisolone aceponate + ceramides (Komfoderm K), which has a pronounced anti-inflammatory and moisturizing effect with the ability to handle up to 60% of the skin within 12 weeks.

Control of the Physical and Antimicrobial Skin Barrier by an IL-31-IL-1 Signaling Network

Atopic dermatitis, a chronic inflammatory skin disease with increasing prevalence, is closely associated with skin barrier defects. A cytokine related to disease severity and inhibition of keratinocyte differentiation is IL-31. To identify its molecular targets, IL-31-dependent gene expression was determined in three-dimensional organotypic skin models. IL-31-regulated genes are involved in the formation of an intact physical skin barrier. Many of these genes were poorly induced during differentiation as a consequence of IL-31 treatment, resulting in increased penetrability to allergens and irritants. Furthermore, studies employing cell-sorted skin equivalents in SCID/NOD mice demonstrated enhanced transepidermal water loss following s.c. administration of IL-31. We identified the IL-1 cytokine network as a downstream effector of IL-31 signaling. Anakinra, an IL-1R antagonist, blocked the IL-31 effects on skin differentiation. In addition to the effects on the physical barrier, IL-31 stimulated the expression of antimicrobial peptides, thereby inhibiting bacterial growth on the three-dimensional organotypic skin models. This was evident already at low doses of IL-31, insufficient to interfere with the physical barrier. Together, these findings demonstrate that IL-31 affects keratinocyte differentiation in multiple ways and that the IL-1 cytokine network is a major downstream effector of IL-31 signaling in deregulating the physical skin barrier. Moreover, by interfering with IL-31, a currently evaluated drug target, we will have to consider that low doses of IL-31 promote the antimicrobial barrier, and thus a complete inhibition of IL-31 signaling may be undesirable.