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

ΔNp63 regulates IL-33 and IL-31 signaling in atopic dermatitis

Atopic dermatitis (AD) is the most common inflammatory skin disease with no well-delineated cause or effective cure. Here we show that the p53 family member p63, specifically the ΔNp63, isoform has a key role in driving keratinocyte activation in AD. We find that overexpression of ΔNp63 in transgenic mouse epidermis results in a severe skin phenotype that shares many of the key clinical, histological and molecular features associated with human AD. This includes pruritus, epidermal hyperplasia, aberrant keratinocyte differentiation, enhanced expression of selected cytokines and chemokines and the infiltration of large numbers of inflammatory cells including type 2  T-helper cells – features that are highly representative of AD dermatopathology. We further demonstrate several of these mediators to be direct transcriptional targets of ΔNp63 in keratinocytes. Of particular significance are two p63 target genes, IL-31 and IL-33, both of which are key players in the signaling pathways implicated in AD. Importantly, we find these observations to be in good agreement with elevated levels of ΔNp63 in skin lesions of human patients with AD. Our studies reveal an important role for ΔNp63 in the pathogenesis of AD and offer new insights into its etiology and possible therapeutic targets.

Ultraviolet light-emitting-diode irradiation inhibits TNF-α and IFN-γ-induced expression of ICAM-1 and STAT1 phosphorylation in human keratinocytes

BACKGROUND AND OBJECTIVES

Ultraviolet light-emitting diodes (UV-LEDs) are a novel light source for phototherapy. This research investigated the in vitro safety and efficacy of UV-LEDs as a phototherapeutic device for atopic dermatitis (AD).

STUDY DESIGN/MATERIALS AND METHODS

Human keratinocytes and fibroblasts were irradiated by UV-LEDs with a center wavelength of 310 and 340 nm. We examined the effects of UV-LED irradiation on the suppression of TNF-α/IFN-γ-induced activation of STAT1 and ICAM-1 and on NF-κB expression; we used the following methods: cell viability assay, reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, Western blotting, and immunocytochemistry.

RESULTS

We observed anti-inflammatory responses through the suppression of TNF-α/IFN-γ-induced expression of TARC and MCP-1/CCL2, IL-1beta, IL-6, and sICAM-1 via blockage of ICAM-1 activation and subsequent activation of STAT1 and NF-κB. The results suggested that UV-LED irradiation inhibited ICAM expression by suppressing TNF-α/IFN-γ-induced NF-κB activation in vitro.

CONCLUSION

We concluded that novel UV-LED (310 and 340 nm) modalities were effective for the treatment of AD and may be promising for the treatment of inflammatory skin diseases.

Morphological and inflammatory changes in the skin of autopsied fetuses according to the type of stress

INTRODUCTION

The fetal skin acts on the development and activation of the immune response via immune-neuroendocrine communication coordinated by corticotropin-releasing hormone.

OBJECTIVE

This study aimed to evaluate the morphological and inflammatory changes in the skin due to acute stress and chronic stress, associated with perinatal asphyxia, ascending infection and congenital malformation.

METHODS

We measured dermal and epidermal thickness, the diameter of keratinocytes, and the percentage of collagen and elastic fibers. Immunohistochemistry was used to evaluate both Langerhans cell and mast cell density, and corticotropin-releasing hormone expression in the epidermis, sebaceous gland, sebaceous duct, sudoriparous gland and in the hair follicle.

RESULTS

The epidermis was thinner in the cases with perinatal asphyxia, ascending infection and chronic stress. The diameter of keratinocytes was smaller in ascending infection and chronic stress. Mast cell density showed an indirect correlation with gestational age. Corticotropin-releasing hormone expression was significantly higher in ascending infection and chronic stress.

CONCLUSIONS

Chronic stress is associated with immunological and morphological changes in the skin of fetuses with perinatal asphyxia and ascending infection. Thus, corticotropin-releasing hormone seems to play a vital role in the differentiation and activation of innate and adaptive immune cells of the skin of fetuses.

Reduced filaggrin expression is accompanied by increased Staphylococcus aureus colonization of epidermal skin models

BACKGROUND

Atopic dermatitis is an inflammatory skin disease that is characterized by a reduced skin barrier function, reduced filaggrin (FLG) expression as well as increased colonization by Staphylococcus aureus.

OBJECTIVE

This study focused on the possible involvement of FLG in epidermal colonization by S. aureus and/or whether it affects the epidermal defence mechanisms, including the expression of antimicrobial peptides (AMPs) and enzymes involved in stratum corneum barrier lipid synthesis. Furthermore, IL-31 has been shown to reduce FLG expression, but its effects on bacterial colonization and on the expression of AMPs and enzymes involved in the barrier lipid synthesis are not known.

MATERIAL AND METHODS

We established N/TERT-based epidermal models (NEMs), after FLG knockdown (FLG-KD) and/or cultured with IL-31, that were colonized with S. aureus for 24 h.

RESULTS

Both FLG-KD and IL-31 supplementation resulted in significantly increased epidermal S. aureus colonization, as well as in an up-regulation of S. aureus-induced IL-8 expression. IL-31, but not FLG-KD, prevented S. aureus-induced up-regulation of mRNA expression for the AMPs human β-defensin 2 and -3 and RNAse7, whereas psoriasin expression remained unchanged. Furthermore, the S. aureus colonization induced changes in mRNA expression of ELOVL4 was not affected by FLG-KD, but was blocked by IL-31. Expression of SCD-1 and Gcase mRNA was reduced by IL-31, but not by FLG-KD.

CONCLUSION

This study shows that NEMs, with FLG-KD and/or cultured in the presence of IL-31, mimic the skin of patients with atopic dermatitis in several aspects, including enhanced bacterial colonization, increased inflammatory and reduced protective responses.

Advances in the diagnosis and therapeutic management of atopic dermatitis

Atopic dermatitis is a very prevalent disease that affects children as well as adults. The disease has a severe impact on quality of life for the patients and their families. The skin in atopic dermatitis patients is a site of both a severe inflammatory reaction dominated by lymphocytes and decreased skin barrier function. The treatment of the disease is mainly aimed at reducing the inflammation in the skin and/or restoring the skin barrier function. However, most of the treatments used today singularly aim at reducing the inflammation in the skin. Depending on the severity of the disease, the anti-inflammatory treatment may be topical or systemic, but basic treatment, no matter the severity, should always be emollients. In addition, new studies have shown good effects of psychosocial interventions, such as eczema schools, for patients and their families. This review covers the latest trends in the treatment of atopic dermatitis.

The role of neuropeptides in the control of regional immunity

Neuropeptides (NPs) and neurotransmitters are a heterogeneous group of soluble factors that make connections within the neuroendocrine and immune systems. NPs, including substance P (SP), vasoactive intestinal peptide (VIP), α melanocyte-stimulating hormone (α-MSH), and calcitonin gene-related peptide (CGRP), released by nerves that innervate the skin, can modulate the action of innate and adaptive skin immunity as well as the skin cells functions. Their role in several inflammatory skin diseases, such as atopic dermatitis, psoriasis, and vitiligo, and in the isotopic response has been reported. Further progress in understanding the various processes that modulate the interactions of the nervous and the skin immune system is essential to develop effective treatment for inflammatory skin conditions with neurogenic components and for understanding signs and symptoms in the isotopic response and, in general, in the control of global and regional immunity.

The translational revolution and use of biologics in patients with inflammatory skin diseases

Psoriasis and atopic dermatitis (AD) are common inflammatory skin diseases characterized by immune-mediated inflammation and abnormal keratinocyte differentiation. Although T-cell infiltration characterizes both diseases, T-cell polarization differs. Psoriasis is currently the best model for translational medicine because many targeted therapeutics have been developed and testing of targeted therapeutics has cemented psoriasis as IL-23/TH17 polarized. In patients with AD, although therapeutic development is approximately a decade behind that in patients with psoriasis, there is now active development and testing of targeted therapeutics against various immune axes (TH2, TH22, and IL-23/TH17). These clinical trials and subsequent molecular analyses using human samples will be able to clarify the relative roles of polar cytokines in patients with AD.

Molecular biology of atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with specific genetic and immunological mechanisms. The rapid development of new techniques in molecular biology had ushered in new discoveries on the role of cytokines, chemokines, and immune cells in the pathogenesis of AD. New polymorphisms of AD are continually being reported in different populations. The physical and immunological barrier of normal intact skin is an important part of the innate immune system that protects the host against microbials and allergens that are associated with AD. Defects in the filaggrin gene FLG may play a role in facilitating exposure to allergens and microbial pathogens, which may induce Th2 polarization. Meanwhile, Th22 cells also play roles in skin barrier impairment through IL-22, and AD is often considered to be a Th2/Th22-dominant allergic disease. Mast cells and eosinophils are also involved in the inflammation via Th2 cytokines. Release of pruritogenic substances by mast cells induces scratching that further disrupts the skin barrier. Th1 and Th17 cells are mainly involved in chronic phase of AD. Keratinocytes also produce proinflammatory cytokines such as thymic stromal lymphopoietin (TSLP), which can further affect Th cells balance. The immunological characteristics of AD may differ for various endotypes and phenotypes. Due to the heterogeneity of the disease, and the redundancies of these mechanisms, our knowledge of the pathophysiology of the disease is still incomplete, which is reflected by the absence of a cure for the disease.

Deciphering the complexities of atopic dermatitis: shifting paradigms in treatment approaches

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease. It often precedes the development of food allergy and asthma. Recent insights into AD reveal abnormalities in terminal differentiation of the epidermal epithelium leading to a defective stratum corneum, which allows enhanced allergen penetration and systemic IgE sensitization. Atopic skin is also predisposed to colonization or infection by pathogenic microbes, most notably Staphylococcus aureus and herpes simplex virus. Causes of this abnormal skin barrier are complex and driven by a combination of genetic, environmental, and immunologic factors. These factors likely account for the heterogeneity of AD onset and the severity and natural history of this skin disease. Recent studies suggest prevention of AD can be achieved through early interventions to protect the skin barrier. Onset of lesional AD requires effective control of local and systemic immune activation for optimal management. Early intervention might improve long-term outcomes for AD and reduce the systemic allergen sensitization that leads to associated allergic diseases in the gastrointestinal and respiratory tract.

Anti-IL-31 receptor antibody is shown to be a potential therapeutic option for treating itch and dermatitis in mice

BACKGROUND AND PURPOSE

IL-31, which is described as a pruritogenic cytokine, is linked to the itching that is associated with allergic and non-allergic eczema, but the precise pruritogenic mechanism of IL-31 and its potential as a therapeutic target for atopic dermatitis (AD) have not been determined.

EXPERIMENTAL APPROACH

We investigated the effects of existing drugs on the scratching behaviour induced by an i.v. injection of IL-31 to clarify whether IL-31 induced pruritus indirectly. In addition, we studied the effects of an anti-IL-31 receptor α subunit (anti-IL-31 receptor α) neutralizing antibody on chronic pruritus-inducing dermatitis in an AD-like model to determine whether IL-31 not only induces scratching behaviour, but is also the causative factor in an AD phenotype.

KEY RESULTS

The scratching behaviour induced by an i.v. injection of IL-31 was inhibited by pretreatment with an anti-IL-31 receptor α-neutralizing antibody. In contrast, it was not inhibited significantly by a non-sedative antihistamine (terfenadine), immunosuppressants (dexamethasone and tacrolimus), or a μ-opioid receptor antagonist (naloxone). The anti-IL-31 receptor α-neutralizing antibody reduced the ear swelling and dermatitis score in a chronic pruritus-inducing AD-like model. Moreover, treatment with the anti-IL-31 receptor α-neutralizing antibody showed therapeutic effects on the dermatitis even if it was injected after the disease had developed.

CONCLUSIONS AND IMPLICATIONS

Anti-IL-31 receptor α is a potential novel therapeutic approach for escaping from the itch-scratch cycle and also a treatment for dermatitis in AD.

Causes of epidermal filaggrin reduction and their role in the pathogenesis of atopic dermatitis

The epidermis protects human subjects from exogenous stressors and helps to maintain internal fluid and electrolyte homeostasis. Filaggrin is a crucial epidermal protein that is important for the formation of the corneocyte, as well as the generation of its intracellular metabolites, which contribute to stratum corneum hydration and pH. The levels of filaggrin and its degradation products are influenced not only by the filaggrin genotype but also by inflammation and exogenous stressors. Pertinently, filaggrin deficiency is observed in patients with atopic dermatitis regardless of filaggrin mutation status, suggesting that the absence of filaggrin is a key factor in the pathogenesis of this skin condition. In this article we review the various causes of low filaggrin levels, centralizing the functional and morphologic role of a deficiency in filaggrin, its metabolites, or both in the etiopathogenesis of atopic dermatitis.

Knock-down of filaggrin does not affect lipid organization and composition in stratum corneum of reconstructed human skin equivalents

Human skin mainly functions as an effective barrier against unwanted environmental influences. The barrier function strongly relies on the outermost layer of the skin, the stratum corneum (SC), which is composed of corneocytes embedded in an extracellular lipid matrix. The importance of a proper barrier function is shown in various skin disorders such as atopic dermatitis (AD), a complex human skin disorder strongly associated with filaggrin (FLG) null mutations, but their role in barrier function is yet unclear. To study the role of FLG in SC barrier properties in terms of SC lipid organization and lipid composition, we generated an N/TERT-based 3D-skin equivalent (NSE) after knock-down of FLG with shRNA. In these NSEs, we examined epidermal morphogenesis by evaluating the expression of differentiation markers keratin 10, FLG, loricrin and the proliferation marker ki67. Furthermore, the SC was extensively analysed for lipid organization, lipid composition and SC permeability. Our results demonstrate that FLG knock-down (FLG-KD) did not affect epidermal morphogenesis, SC lipid organization, lipid composition and SC permeability for a lipophilic compound in NSEs. Therefore, our findings indicate that FLG-KD alone does not necessarily affect the functionality of a proper barrier function.

Skin barrier defects in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin condition with complex etiology that is dependent upon interactions between the host and the environment. Acute skin lesions exhibit the features of a Th2-driven inflammatory disorder, and many patients are highly atopic. The skin barrier plays key roles in immune surveillance and homeostasis, and in preventing penetration of microbial products and allergens. Defects that compromise the structural integrity or else the immune function of the skin barrier play a pivotal role in the pathogenesis of AD. This article provides an overview of the array of molecular building blocks that are essential to maintaining healthy skin. The basis for structural defects in the skin is discussed in relation to AD, with an emphasis on filaggrin and its genetic underpinnings. Aspects of innate immunity, including the role of antimicrobial peptides and proteases, are also discussed.

Interleukin-31: a novel diagnostic marker of allergic diseases

Interleukin-31 (IL-31) is a newly discovered cytokine associated with chronic skin inflammation and pruritus. Patients with atopic dermatitis, chronic spontaneous urticaria, allergic contact dermatitis, prurigo nodularis, primary cutaneous lymphoma and mastocytosis exhibit increased serum levels of IL-31 protein and elevated IL-31 mRNA in the skin. Interestingly, in some of these diseases, IL-31 serum levels correlate with disease activity. In the present review, we particularly focus on studies investigating IL-31 as a novel diagnostic biomarker indicating the severity of allergic diseases. We highlight a recent study on IL-31 in mastocytosis, which reports on elevated serum levels of IL-31 in adults correlating with the severity of disease categories, tryptase levels and percentage of bone marrow infiltration. We conclude that growing knowledge about IL-31, its receptors and signaling pathways serves to better understand the pathogenesis of allergic diseases and may lead to the development of novel treatment approaches.

TNF-α and Th2 cytokines induce atopic dermatitis-like features on epidermal differentiation proteins and stratum corneum lipids in human skin equivalents

Atopic dermatitis (AD) is a chronic inflammatory skin disease in which the skin barrier function is disrupted. In this inflammatory AD environment, cytokines are upregulated, but the cytokine effect on the AD skin barrier is not fully understood. We aimed to investigate the influence of Th2 (IL-4, IL-13, IL-31) and pro-inflammatory (tumor necrosis factor alpha (TNF-α)) cytokines on epidermal morphogenesis, proliferation, differentiation, and stratum corneum lipid properties. For this purpose, we used the Leiden epidermal model (LEM) in which the medium was supplemented with these cytokines. Our results show that IL-4, IL-13, IL-31, and TNF-α induce spongiosis, augment TSLP secretion by keratinocytes, and alter early and terminal differentiation-protein expression in LEMs. TNF-α alone or in combination with Th2 cytokines decreases the level of long chain free fatty acids (FFAs) and ester linked ω-hydroxy (EO) ceramides, consequently affecting the lipid organization. IL-31 increases long chain FFAs in LEMs but decreases relative abundance of EO ceramides. These findings clearly show that supplementation with TNF-α and Th2 cytokines influence epidermal morphogenesis and barrier function. As a result, these LEMs show similar characteristics as found in AD skin and can be used as an excellent tool for screening formulations and drugs for the treatment of AD.

Reactive eccrine syringofibroadenomatosis secondary to primary cutaneous amyloidosis: a novel association

We report the unprecedented case of reactive eccrine syringofibroadenoma (ESFA) secondary to primary cutaneous amyloidosis. A 62-year-old woman of Asian ethnicity presented with a pruritic rash on the back of long-standing duration. Physical examination revealed diffuse hyperpigmentation localized to the interscapular region; there were a multitude of hyperpigmented macules merged in a rippled pattern intermixed with scattered papules and cobblestone-like areas. A punch biopsy from a papule was taken. Histopathological examination revealed a network of epithelial strands and cords hanging from the epidermis and harboring foci of ductal differentiation. Eosinophilic collections of amorphous material were found between the epithelial strands, obscuring the superficial dermis. The microscopic picture was consistent with primary cutaneous amyloidosis associated with reactive ESFA. Results of histochemical and immunohistochemical staining confirmed the diagnosis. We speculate that pathogenetic mechanisms intrinsic to primary cutaneous amyloidosis, in addition to unknown genetic factors, resulted in clinical changes of lichen amyloidosus associated with an abnormal hyperplastic epithelial response with histopathological features of ESFA rather than the common epidermal change of acanthosis and hyperkeratosis.

Staphylococcal and streptococcal superantigen exotoxins

SUMMARY This review begins with a discussion of the large family of Staphylococcus aureus and beta-hemolytic streptococcal pyrogenic toxin T lymphocyte superantigens from structural and immunobiological perspectives. With this as background, the review then discusses the major known and possible human disease associations with superantigens, including associations with toxic shock syndromes, atopic dermatitis, pneumonia, infective endocarditis, and autoimmune sequelae to streptococcal illnesses. Finally, the review addresses current and possible novel strategies to prevent superantigen production and passive and active immunization strategies.

Interleukin-31 does not induce immediate itch in atopic dermatitis patients and healthy controls after skin challenge

BACKGROUND

The most intriguing function attributed to interleukin-31 (IL-31) is its ability to induce pruritus in pathologic conditions, such as atopic dermatitis (AD). As of today, this feature of IL-31 was tested in vivo only in animal models.

METHODS

Ten patients with AD and 10 healthy controls were challenged with IL-31 and NaCl (negative control) by skin prick testing. Twenty additional healthy controls were subjected to skin prick testing with histamine. Itch and local inflammatory responses of the skin were assessed for up to 72 h.

RESULTS

All of the histamine-challenged subjects developed immediate pruritus (i.e. within the first 5 min). In contrast, only one IL-31- and two of the NaCl-challenged subjects reported immediate itch at the provocation site (short lasting, for 2-6 min). Nine subjects (five patients with AD) reported late itch responses to IL-31 challenges with a mean delay of 143 min. No subject reported late itch responses to histamine or NaCl testing. There was no significant difference in IL-31-induced itch start time, duration and intensity between patients with AD and healthy volunteers.

CONCLUSION

IL-31 does not induce immediate itch responses in humans. The late onset of IL-31-induced itch supports the notion that IL-31 exerts its pruritic effect indirectly via keratinocytes and secondary mediators, rather than through its receptors on cutaneous nerves.

Eccrine sweat contains IL-1α, IL-1β and IL-31 and activates epidermal keratinocytes as a danger signal

Eccrine sweat is secreted onto the skin's surface and is not harmful to normal skin, but can exacerbate eczematous lesions in atopic dermatitis. Although eccrine sweat contains a number of minerals, proteins, and proteolytic enzymes, how it causes skin inflammation is not clear. We hypothesized that it stimulates keratinocytes directly, as a danger signal. Eccrine sweat was collected from the arms of healthy volunteers after exercise, and levels of proinflammatory cytokines in the sweat were quantified by ELISA. We detected the presence of IL-1α, IL-1β, and high levels of IL-31 in sweat samples. To investigate whether sweat activates keratinocytes, normal human keratinocytes were stimulated with concentrated sweat. Western blot analysis demonstrated the activation of NF-κB, ERK, and JNK signaling in sweat-stimulated keratinocytes. Real-time PCR using total RNA and ELISA analysis of supernatants showed the upregulation of IL-8 and IL-1β by sweat. Furthermore, pretreatment with IL-1R antagonist blocked sweat-stimulated cytokine production and signal activation, indicating that bioactive IL-1 is a major factor in the activation of keratinocytes by sweat. Moreover, IL-31 seems to be another sweat stimulator that activates keratinocytes to produce inflammatory cytokine, CCL2. Sweat is secreted onto the skin's surface and does not come into contact with keratinocytes in normal skin. However, in skin with a defective cutaneous barrier, such as atopic dermatitis-affected skin, sweat cytokines can directly act on epidermal keratinocytes, resulting in their activation. In conclusion, eccrine sweat contains proinflammatory cytokines, IL-1 and IL-31, and activates epidermal keratinocytes as a danger signal.

The cutaneous innate immune response in patients with atopic dermatitis

Orchestrating when and how the cutaneous innate immune system should respond to commensal or pathogenic microbes is a critical function of the epithelium. The cutaneous innate immune system is a key determinant of the physical, chemical, microbial, and immunologic barrier functions of the epidermis. A malfunction in this system can lead to an inadequate host response to a pathogen or a persistent inflammatory state. Atopic dermatitis is the most common inflammatory skin disorder and characterized by abnormalities in both skin barrier structures (stratum corneum and tight junctions), a robust T(H)2 response to environmental antigens, defects in innate immunity, and an altered microbiome. Many of these abnormalities may occur as the consequence of epidermal dysfunction. The epidermis directly interfaces with the environment and, not surprisingly, expresses many pattern recognition receptors that make it a key player in cutaneous innate immune responses to skin infections and injury. This review will discuss the role epidermal innate receptors play in regulation of skin barriers and, where possible, discuss the relevance of these findings for patients with atopic dermatitis.

Intrinsic atopic dermatitis shows similar TH2 and higher TH17 immune activation compared with extrinsic atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is classified as extrinsic and intrinsic, representing approximately 80% and 20% of patients with the disease, respectively. Although sharing a similar clinical phenotype, only extrinsic AD is characterized by high serum IgE levels. Because most patients with AD exhibit high IgE levels, an "allergic"/IgE-mediated disease pathogenesis was hypothesized. However, current models associate AD with T-cell activation, particularly TH2/TH22 polarization, and epidermal barrier defects.

OBJECTIVE

We sought to define whether both variants share a common pathogenesis.

METHODS

We stratified 51 patients with severe AD into extrinsic AD (n = 42) and intrinsic AD (n = 9) groups (with similar mean disease activity/SCORAD scores) and analyzed the molecular and cellular skin pathology of lesional and nonlesional intrinsic AD and extrinsic AD by using gene expression (real-time PCR) and immunohistochemistry.

RESULTS

A significant correlation between IgE levels and SCORAD scores (r = 0.76, P < 10(-5)) was found only in patients with extrinsic AD. Marked infiltrates of T cells and dendritic cells and corresponding epidermal alterations (keratin 16, Mki67, and S100A7/A8/A9) defined lesional skin of patients with both variants. However, higher activation of all inflammatory axes (including TH2) was detected in patients with intrinsic AD, particularly TH17 and TH22 cytokines. Positive correlations between TH17-related molecules and SCORAD scores were only found in patients with intrinsic AD, whereas only patients with extrinsic AD showed positive correlations between SCORAD scores and TH2 cytokine (IL-4 and IL-5) levels and negative correlations with differentiation products (loricrin and periplakin).

CONCLUSIONS

Although differences in TH17 and TH22 activation exist between patients with intrinsic AD and those with extrinsic AD, we identified common disease-defining features of T-cell activation, production of polarized cytokines, and keratinocyte responses to immune products. Our data indicate that a TH2 bias is not the sole cause of high IgE levels in patients with extrinsic AD, with important implications for similar therapeutic interventions.

New insights into atopic dermatitis: role of skin barrier and immune dysregulation

Atopic dermatitis (AD) is a chronic inflammatory skin disease that is often associated with the development of food allergy and asthma. New insights into AD reveals an important role for structural abnormalities in the epidermis resulting in a leaky epithelial barrier as well as chronic immune activation that contribute to the pathophysiology of this common skin disease. Patients with AD have a predisposition to colonization or infection by microbial organisms, most notably Staphylococcus aureus and herpes simplex virus (HSV). Measures directed at healing and protecting the skin barrier and controlling the immune activation are needed for effective management of AD. Early intervention may improve outcomes for AD as well as reduce the systemic allergen sensitization that may lead to associated allergic diseases in other organs.

Human IL-31 is induced by IL-4 and promotes TH2-driven inflammation

BACKGROUND

The pruritic cytokine IL-31 has been shown to be expressed by murine activated effector T Lymphocytes of a TH2 phenotype. Like IL-17 and IL-22, IL-31 is a tissue-signaling cytokine the receptor of which is mainly found on nonimmune cells. An overabundance of IL-31 has been shown in patients with atopic disorders, including dermatitis, as well as asthma, and therefore represents a promising drug target, although its regulation in the context of the human TH2 clusters is not yet known.

OBJECTIVE

We sought to address the gene regulation of human IL-31 and to test whether IL-31 possesses a similar proallergic function as members of the human TH2 cytokine family, such as IL-4, IL-5, and IL-13.

METHODS

Polyclonal and purified protein derivative of tuburculin-specific T-cell clones were generated. TH phenotype was determined, and IL-31 was measured by means of ELISA. Gene expression of primary bronchial epithelial cells treated with IL-31 was also measured.

RESULTS

IL-31 was expressed by all of the TH2 clones and not by TH1, TH17, or TH22. This expression was dependent on autocrine IL-4 expression from these clones because it could be reduced if blocking antibodies to IL-4 were present. Interestingly, TH1 clones were able to express IL-31 if IL-4 was added to culture. This IL-31 expression was transient and did not affect the phenotype of the TH1 clones. IL-31 was able to induce proinflammatory genes, such as CCL2 and granulocyte colony-stimulating factor.

CONCLUSION

IL-31 is not a TH2 cytokine in the classical sense but is likely to be expressed by a number of cells in an allergic situation in which IL-4 is present and possibly contribute to the allergic reaction.

Role of fibroblasts in the pathogenesis of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a common dermatosis that highly impairs a patient's quality of life. The recent discovery that epidermal barrier defects caused by an aberrant differentiation process of keratinocytes are comparably important to the well-characterized changes in immune response patterns attributed a crucial role to the keratinocytes. Fibroblasts are able to alter proliferation and differentiation of keratinocytes, but their role in AD is not yet fully understood.

OBJECTIVE

We sought to determine the role of fibroblasts in skin proliferation and differentiation in patients with AD.

METHODS

We used human 3-dimensional organotypic skin cultures consisting of atopic fibroblasts and healthy keratinocytes, as well as healthy fibroblasts and atopic keratinocytes, and compared them with their controls. The expression of differentiation markers in these organotypic cultures were analyzed by using immunohistology and quantitative RT-PCR. Furthermore, the fundamental role of fibroblast-secreted leukemia inhibitory factor was assessed by using small interfering RNA-mediated knockdown cultures.

RESULTS

We observed that atopic fibroblasts influence the proliferation of keratinocytes and the terminal differentiation process, resulting in an in vivo-like morphology of AD. Subsequently, healthy fibroblasts were able to restore the structural deficits of the epidermis consisting of atopic keratinocytes. Partially, these effects were due to a reduced expression of the differentiation-associated cytokine leukemia inhibitory factor by atopic fibroblasts.

CONCLUSION

These data demonstrate that fibroblasts and the modulation of fibroblast-derived factors might be new therapeutic targets for the alleviation of AD.

New era of biologic therapeutics in atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) is a common inflammatory skin disease regulated by genetic and environmental factors. Both skin barrier defects and aberrant immune responses are believed to drive cutaneous inflammation in AD. Existing therapies rely largely on allergen avoidance, emollients and topical and systemic immune-suppressants, some with significant toxicity and transient efficacy; no specific targeted therapies are in clinical use today. As our specific understanding of the immune and molecular pathways that cause different subsets of AD increases, a variety of experimental agents, particularly biologic agents that target pathogenic molecules bring the promise of safe and effective therapeutics for long-term use.

AREAS COVERED

This paper discusses the molecular pathways characterizing AD, the contributions of barrier and immune abnormalities to its pathogenesis, and development of new treatments that target key molecules in these pathways. In this review, we will discuss a variety of biologic therapies that are in development or in clinical trials for AD, perhaps revolutionizing treatment of this disease.

EXPERT OPINION

Biologic agents in moderate to severe AD offer promise for controlling a disease that currently lacks good and safe therapeutics posing a large unmet need. Unfortunately, existing treatments for AD aim to decrease cutaneous inflammation, but are not specific for the pathways driving this disease. An increasing understanding of the immune mechanisms underlying AD brings the promise of narrow targeted therapies as has occurred for psoriasis, another inflammatory skin disease, for which specific biologic agents have been demonstrated to both control the disease and prevent occurrence of new skin lesions. Although no biologic is yet approved for AD, these are exciting times for active therapeutic development in AD that might lead to revolutionary therapeutics for this disease.

Cytokines and the skin barrier

The skin is the largest organ of the human body and builds a barrier to protect us from the harmful environment and also from unregulated loss of water. Keratinocytes form the skin barrier by undergoing a highly complex differentiation process that involves changing their morphology and structural integrity, a process referred to as cornification. Alterations in the epidermal cornification process affect the formation of the skin barrier. Typically, this results in a disturbed barrier, which allows the entry of substances into the skin that are immunologically reactive. This contributes to and promotes inflammatory processes in the skin but also affects other organs. In many common skin diseases, including atopic dermatitis and psoriasis, a defect in the formation of the skin barrier is observed. In these diseases the cytokine composition within the skin is different compared to normal human skin. This is the result of resident skin cells that produce cytokines, but also because additional immune cells are recruited. Many of the cytokines found in defective skin are able to influence various processes of differentiation and cornification. Here we summarize the current knowledge on cytokines and their functions in healthy skin and their contributions to inflammatory skin diseases.

Investigation of the effect of probiotic exposure on filaggrin expression in an experimental model of canine atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) results from complex interactions between an impaired skin barrier and immunological stimulation. Filaggrin is a key protein for the skin barrier, and its expression is decreased in subsets of atopic dogs and can be modified by inflammation; thus, immunomodulatory approaches may alter its expression. Probiotics have been explored for the prevention and treatment of allergies, owing to their immunomodulatory properties; however, it is currently unknown whether they can modulate filaggrin expression.

OBJECTIVE

The purpose of this study was to evaluate whether probiotics can modulate filaggrin expression in an experimental model of canine AD.

ANIMALS AND METHODS

Eighteen atopic (11 probiotic exposed and seven control) and five normal beagles were challenged for three consecutive days with Dermatophagoides farinae. Skin biopsies were taken before (day 0), at the peak (day 3) and after the end of the allergen challenge (day 10). Immunohistochemistry for filaggrin was done using a polyclonal antibody specific for canine filaggrin, and staining was scored both subjectively (for intensity, granularity and continuity) and objectively, by tracing the stratum granulosum and calculating the percentage of filaggrin per unit traced area.

RESULTS

Analysis of variance of the percentage of filaggrin in the stratum granulosum showed a significant effect of group (P = 0.0414, AD < normal), time (P = 0.0066, days 3 and 10 > day 0) and marginal group × time interaction (P = 0.0606). Within the atopic group, exposure to probiotics did not change filaggrin expression. No significant differences were found in the subjective scores among groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

It is concluded that probiotic exposure early in life does not alter filaggrin expression in this AD model.

Epidermal nerve fibers modulate keratinocyte growth via neuropeptide signaling in an innervated skin model

Atopic eczema is a chronic inflammatory skin disease characterized by cutaneous nerve fiber sprouting and epidermal hyperplasia, pointing to an involvement of the peripheral nervous system in cutaneous homeostasis. However, the interaction of sensory neurons and skin cells is poorly understood. Using an innervated skin model, we investigated the influence of sensory neurons on epidermal morphogenesis. Neurons induced the proliferation of keratinocytes, resulting in an increase in the epidermal thickness. Inhibition of calcitonin gene-related peptide (CGRP), but not substance P (SP) signaling, reversed this effect. Human CGRP enhanced keratinocyte proliferation and epidermal thickness in skin models, demonstrating a key role of CGRP in modulating epidermal morphogenesis, whereas SP had only a moderate effect. Innervated skin models composed of atopic skin cells showed increased neurite outgrowth, accompanied by elevated CGRP release. As atopic keratinocytes were sensitized to CGRP owing to higher expression levels of the CGRP receptor components, receptor activity-modifying protein 1 (RAMP1) and receptor component protein (RCP), atopic innervated skin models displayed a thicker epidermis than did healthy controls. We conclude that neural CGRP controls local keratinocyte growth. Our results show that the crosstalk of the cutaneous peripheral nervous system and skin cells significantly influences epidermal morphogenesis and homeostasis in healthy and atopic skin.

Histamine suppresses epidermal keratinocyte differentiation and impairs skin barrier function in a human skin model

Background

Defects in keratinocyte differentiation and skin barrier are important features of inflammatory skin diseases like atopic dermatitis. Mast cells and their main mediator histamine are abundant in inflamed skin and thus may contribute to disease pathogenesis.

Methods

Human primary keratinocytes were cultured under differentiation-promoting conditions in the presence and absence of histamine, histamine receptor agonists and antagonists. The expression of differentiation-associated genes and epidermal junction proteins was quantified by real-time PCR, Western blot, and immunofluorescence labeling. The barrier function of human skin models was tested by the application of biotin as tracer molecule.

Results

The addition of histamine to human keratinocyte cultures and organotypic skin models reduced the expression of the differentiation-associated proteins keratin 1/10, filaggrin, and loricrin by 80–95%. Moreover, the addition of histamine to skin models resulted in the loss of the granular layer and thinning of the epidermis and stratum corneum by 50%. The histamine receptor H1R agonist, 2-pyridylethylamine, suppressed keratinocyte differentiation to the same extent as did histamine. Correspondingly, cetirizine, an antagonist of H1R, virtually abrogated the effect of histamine. The expression of tight junction proteins zona occludens-1, occludin, claudin-1, and claudin-4, as well as that of desmosomal junction proteins corneodesmosin and desmoglein-1, was down-regulated by histamine. The tracer molecule biotin readily penetrated the tight junction barrier of skin cultures grown in the presence of histamine, while their diffusion was completely blocked in nontreated controls.

Conclusions

Our findings suggest a new mechanism by which mast cell activation and histamine release contribute to skin barrier defects in inflammatory skin diseases.

Progressive activation of T(H)2/T(H)22 cytokines and selective epidermal proteins characterizes acute and chronic atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a common disease with an increasing prevalence. The primary pathogenesis of the disease is still elusive, resulting in the lack of specific treatments. AD is currently considered a biphasic disease, with T(H)2 predominating in acute disease and a switch to T(H)1 characterizing chronic disease. Elucidation of the molecular factors that participate in the onset of new lesions and maintenance of chronic disease is critical for the development of targeted therapeutics.

OBJECTIVES

We sought to characterize the mechanisms underlying the onset and maintenance of AD.

METHODS

We investigated intrapersonal sets of transcriptomes from nonlesional skin and acute and chronic lesions of 10 patients with AD through genomic, molecular, and cellular profiling.

RESULTS

Our study associated the onset of acute lesions with a striking increase in a subset of terminal differentiation proteins, specifically the cytokine-modulated S100A7, S100A8, and S100A9. Acute disease was also associated with significant increases in gene expression levels of major T(H)22 and T(H)2 cytokines and smaller increases in IL-17 levels. A lesser induction of T(H)1-associated genes was detected in acute disease, although some were significantly upregulated in chronic disease. Further significant intensification of major T(H)22 and T(H)2 cytokines was observed between acute and chronic lesions.

CONCLUSIONS

Our data identified increased S100A7, S100A8, and S100A9 gene expression with AD initiation and concomitant activation of T(H)2 and T(H)22 cytokines. Our findings support a model of progressive activation of T(H)2 and T(H)22 immune axes from the acute to chronic phases, expanding the prevailing view of pathogenesis with important therapeutic implications.

Advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insects in 2012

This review highlights some of the research advances in anaphylaxis; hypersensitivity reactions to foods, drugs, and insects; and allergic skin diseases that were reported in the Journal in 2012. Studies support an increase in peanut allergy prevalence in children and exposure to the antibacterial agent triclosan and having filaggrin (FLG) loss-of-function mutations as risk factors for food sensitization. The role of specific foods in causing eosinophilic esophagitis is elucidated by several studies, and microRNA analysis is identified as a possible noninvasive disease biomarker. Studies on food allergy diagnosis emphasize the utility of component testing and the possibility of improved diagnosis through stepped approaches, epitope-binding analysis, and bioinformatics. Treatment studies of food allergy show promise for oral immunotherapy, but tolerance induction remains elusive, and additional therapies are under study. Studies on anaphylaxis suggest an important role for platelet-activating factor and its relationship to the need for prompt treatment with epinephrine. Insights on the pathophysiology and diagnosis of non-IgE-mediated drug allergy are offered, with novel data regarding the interaction of drugs with HLA molecules. Numerous studies support influenza vaccination of persons with egg allergy using modest precautions. Evidence continues to mount that there is cross-talk between skin barrier defects and immune responses in patients with atopic dermatitis. Augmentation of the skin barrier with reduction in skin inflammatory responses will likely lead to the most effective intervention in patients with this common skin disease.

Increased frequencies of IL-31-producing T cells are found in chronic atopic dermatitis skin

Interleukin (IL)-31 has been associated with pruritus, a characteristic feature of atopic dermatitis (AD). Local T cell responses may be responsible for the increased level of IL-31 mRNA observed in AD. We investigated the frequency of IL-31-producing T cells in AD lesions, as well as their cytokine profile. T cells were isolated from chronic AD lesions, autologous blood and healthy donor skin. Intracellular expression of IL-31, IFN-γ, IL-13, IL-17 and IL-22 was measured using flow cytometry. T cells from AD lesions contained significantly higher percentages of IL-31-producing T cells compared to autologous blood and donor skin. Many IL-31-producing T cells co-produced IL-13 and to lesser extent IL-22, but rarely IFN-γ or IL-17. A substantial part of the IL-31-producing T cells did not co-produce any of the other cytokines and could therefore not be linked to any of the known functionally different T cell subsets. The T cell infiltrates were also relatively enriched for Th2/Tc2 and Th22/Tc22 cells, while frequencies of Th1/Tc1 and Th17 cells were decreased. This is the first report describing the detection of IL-31 at protein level in skin-infiltrating T cells. We show here that T cells in chronic AD skin produce IL-31 and that AD lesions contain increased levels of these IL-31-producing T cells. This suggests that a substantial part of previously reported increased IL-31 mRNA levels in AD skin is T cell derived and that these cells may be involved in the pathogenesis of AD.

Atopic dermatitis results in intrinsic barrier and immune abnormalities: implications for contact dermatitis

Atopic dermatitis (AD), as well as irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD), are common skin diseases. These diseases are characterized by skin inflammation mediated by activated innate immunity or acquired immune mechanisms. Although AD, ICD, and ACD can be encountered in pure forms by allergists and dermatologists, patients with AD often present with increased frequency of ICD and ACD. Although a disturbed barrier alone could potentiate immune reactivity in patients with AD through increased antigen penetration, additional immune mechanisms might explain the increased susceptibility of atopic patients to ICD and ACD. This review discusses cellular pathways associated with increased skin inflammation in all 3 conditions and presents mechanisms that might contribute to the increased rate of ICD and ACD in patients with AD.