Mutual upregulation of endothelin-1 and IL-25 in atopic dermatitis

The involvement of keratinocytes in pruritus of chronic inflammatory dermatosis

Frequent itching and incessant scratching are commonly observed in various chronic inflammatory skin conditions, including atopic dermatitis and psoriasis. The persistent and prolonged nature of pruritus can worsen one's quality of life. Keratinocytes (KCs), the predominant cells of the epidermis, have been confirmed to interact with sensory neurons and immune cells and be involved in chronic skin inflammatory diseases associated with pruritus. Initially, KCs and sensory neurons form a unique synapse-like connection within the epidermis, serving as the structural foundation for their interaction. Additionally, several receptors, including toll-like receptors and protease-activated receptor 2, expressed on KCs, become activated in an inflammatory milieu. On the one hand, activated KCs are sources of pro-inflammatory cytokines and neurotrophic factors, such as adenosine triphosphate, thymic stromal lymphopoietin, and nerve growth factor, which directly or indirectly participate in stimulating sensory neurons, thereby contributing to the itch sensations. On the other hand, KCs also function as primary transducers alongside intraepidermal nerve endings, directly initiating pruritic responses. This review summarizes the current literature and highlights the critical role of KCs in the development and persistence of chronic itch in inflammatory skin disorders.

Interplay of cytokines in the pathophysiology of atopic dermatitis: insights from Murin models and human

The pathogenesis of atopic dermatitis (AD) is understood to be crucially influenced by three main factors: dysregulation of the immune response, barrier dysfunction, and pruritus. In the lesional skin of AD, various innate immune cells, including Th2 cells, type 2 innate lymphoid cells (ILC2s), and basophils, produce Th2 cytokines [interleukin (IL)-4, IL-5, IL-13, IL-31]. Alarmins such as TSLP, IL-25, and IL-33 are also produced by epidermal keratinocytes, amplifying type 2 inflammation. In the chronic phase, not only Th2 cells but also Th22 and Th17 cells increase in number, leading to suppression of filaggrin expression by IL-4, IL-13, and IL-22, which further deteriorates the epidermal barrier function. Dupilumab, which targets IL-4 and IL-13, has shown efficacy in treating moderate to severe AD. Nemolizumab, targeting IL-31RA, effectively reduces pruritus in AD patients. In addition, clinical trials with fezakinumab, targeting IL-22, have demonstrated promising results, particularly in severe AD cases. Conversely, in murine models of AD, several cytokines, initially regarded as promising therapeutic targets, have not demonstrated sufficient efficacy in clinical trials. IL-33 has been identified as a potent activator of immune cells, exacerbating AD in murine models and correlating with disease severity in human patients. However, treatments targeting IL-33 have not shown sufficient efficacy in clinical trials. Similarly, thymic stromal lymphopoietin (TSLP), integral to type 2 immune responses, induces dermatitis in animal models and is elevated in human AD, yet clinical treatments like tezepelumab exhibit limited efficacy. Therapies targeting IL-1α, IL-5, and IL-17 also failed to achieve sufficient efficacy in clinical trials. It has become clear that for treating AD, IL-4, IL-13, and IL-31 are relevant therapeutic targets during the acute phase, while IL-22 emerges as a target in more severe cases. This delineation underscores the necessity of considering distinct pathophysiological aspects and therapeutic targets in AD between mouse models and humans. Consequently, this review delineates the distinct roles of cytokines in the pathogenesis of AD, juxtaposing their significance in human AD from clinical trials against insights gleaned from AD mouse models. This approach will improve our understanding of interspecies variation and facilitate a deeper insight into the pathogenesis of AD in humans.

Fluoxetine exerts anti-inflammatory effects on human epidermal keratinocytes and suppresses their endothelin release

Fluoxetine is a safe antidepressant with remarkable anti-inflammatory actions; therefore, we aimed to investigate its effects on immortalized (HaCaT) as well as primary human epidermal keratinocytes in a polyinosinic-polycytidylic acid (p(I:C))-induced inflammatory model. We found that a non-cytotoxic concentration (MTT-assay, CyQUANT-assay) of fluoxetine significantly suppressed p(I:C)-induced expression and release of several pro-inflammatory cytokines (Q-PCR, cytokine array, ELISA), and it decreased the release of the itch mediator endothelins (ELISA). These effects were not mediated by the inhibition of the NF-κB or p38 MAPK pathways (western blot), or by the suppression of the p(I:C)-induced elevation of mitochondrial ROS production (MitoSOX Red labeling). Instead, unbiased activity profiling revealed that they were most likely mediated via the inhibition of the phosphoinositide 3-kinase (PI3K) pathway. Importantly, the PI3K-inhibitor GDC0941 fully mimicked the effects of fluoxetine (Q-PCR, ELISA). Although fluoxetine was able to occupy the binding site of GDC0941 (in silico molecular docking), and exerted direct inhibitory effect on PI3K (cell-free PI3K activity assay), it exhibited much lower potency and efficacy as compared to GDC0941. Finally, RNA-Seq analysis revealed that fluoxetine deeply influenced the transcriptional alterations induced by p(I:C)-treatment, and exerted an overall anti-inflammatory activity. Collectively, our findings demonstrate that fluoxetine exerts potent anti-inflammatory effects, and suppresses the release of the endogenous itch mediator endothelins in human keratinocytes, most likely via interfering with the PI3K pathway. Thus, clinical studies are encouraged to explore whether the currently reported beneficial effects translate in vivo following its topical administration in inflammatory and pruritic dermatoses.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

Interleukin-33, endothelin-1, and inflammatory parameters in chronic spontaneous urticaria

Background: Endothelin-1 (ET-1) and interleukin-33 (IL-33) can modulate the activation of mast cells and basophils in the pathophysiology of allergic diseases, interplaying with other mediators of "low-grade inflammation." Objective: To compare ET-1, IL-33, the neutrophil-lymphocyte ratio (NLR), eosinophil-lymphocyte ratio (ELR), platelet-lymphocyte ratio (PLR), eosinophil-basophil ratio (EBR), systemic immune inflammation index (SII), and system inflammation response index (SIRI) in patients with chronic spontaneous urticaria (CSU) and are antihistamine sensitive (AHS), antihistamine resistant (AHR), omalizumab sensitive (OmS), and omalizumab resistant (OmR). Methods: A prospective observational study enrolled 68 consecutive patients with CSU diagnosed and managed according to the dermatology section of the European Academy of Allergology and Clinical Immunology (EAACI), the European Union funded network of excellence, the Global Allergy and Asthma European Network (GA2LEN), the European Dermatology Forum (EDF), and the World Allergy Organization guidelines. Patients with a urticaria control test score of >12 are considered treatment sensitive, and ≤ 12 are considered resistant. The control group consisted of 20 sex-matched subjects without urticarial diseases. Total immunoglobulin E (IgE), antinuclear antibodies (ANA), thyroid stimulating hormone, antithyroid peroxidase, mean platelet volume (MPV), NLR, ELR, PLR, EBR, SII, SIRI, ET-1, and IL-33 were measured at the study entry and compared between the study groups. Results: Thirty AHS group, 38 AHR group, and 20 control group patients were included. The AHS, AHR, and control groups did not differ in demographic parameters, but the CSU groups were characterized by higher indicators of inflammation. In comparison with the AHS group, the AHR group was characterized by higher levels of IL-33 (p = 0.007), ET-1 (p = 0.032), C-reactive protein (p = 0.016), MPV (p = 0.002), and higher rates of positive ANA (p = 0.019). Of the 38 patients from the AHR group, 30 (79%) were included in the OmS group and 8 (21%) were included in the OmR group. The OmR group was characterized by higher levels of C-reactive protein (p = 0.022), EBR (p < 0.001), higher rates of ANA (p = 0.004), and lower levels of ET-1 (p = 0.025) than the OmS group. Conclusion: Our study did not confirm NRL, PRL, SII, and SIRI, PLR as the biomarkers of treatment response to antihistamines and/or omalizumab in CSU. Higher blood levels of IL-33 and ET-1 characterize AHR CSU.

Basic mechanisms of itch

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

New insights into the function of Interleukin-25 in disease pathogenesis

Interleukin-25 (IL-25), also known as IL-17E, is a cytokine belonging to the IL-17 family. IL-25 is abundantly expressed by Th2 cells and various kinds of epithelial cells. IL-25 is an alarm signal generated upon cell injury or tissue damage to activate immune cells through the interaction with IL-17RA and IL-17RB receptors. The binding of IL-25 to IL-17RA/IL-17RB complex not only initiates and maintains type 2 immunity but also regulates other immune cells (e.g., macrophages and mast cells) via various signaling pathways. It has been well-documented that IL-25 is critically involved in the development of allergic disorders (e.g., asthma). However, the roles of IL-25 in the pathogenesis of other diseases and the underlying mechanisms are still unclear. This review presents current evidence on the roles of IL-25 in cancers, allergic disorders, and autoimmune diseases. Moreover, we discuss the unanswered key questions underlying IL-25-mediated disease pathology, which will provide new insights into the targeted therapy of this cytokine in clinical treatment.

Pruritogenic Mediators and New Antipruritic Drugs in Atopic Dermatitis

Atopic dermatitis (AD) is a common highly pruritic chronic inflammatory skin disorder affecting 5-20% of children worldwide, while the prevalence in adults varies from 7 to 10%. Patients with AD experience intense pruritus that could lead to sleep disturbance and impaired quality of life. Here, we analyze the pathophysiology of itchiness in AD. We extensively review the histamine-dependent and histamine-independent pruritogens. Several receptors, substance P, secreted molecules, chemokines, and cytokines are involved as mediators in chronic itch. We also, summarize the new emerging antipruritic drugs in atopic dermatitis.

The Interplay of Type 1, Type 2, and Type 3 Lymphocytes and Cytokines in Atopic Dermatitis

Atopic dermatitis (AD) is classified as a type 2 disease owing to the majority of type 2 lymphocytes that constitute the skin-infiltrating leukocytes. However, all of the type 1-3 lymphocytes intermingle in inflamed skin lesions. Here, using an AD mouse model where caspase-1 was specifically amplified under keratin-14 induction, we analyzed the sequential changes in type 1-3 inflammatory cytokines in lymphocytes purified from the cervical lymph nodes. Cells were cultured and stained for CD4, CD8, and γδTCR, followed by intracellular cytokines. Cytokine production in innate lymphocyte cells (ILCs) and the protein expression of type 2 cytokine IL-17E (IL-25) were investigated. We observed that, as inflammation progresses, the cytokine-producing T cells increased and abundant IL-13 but low levels of IL-4 are produced in CD4-positive T cells and ILCs. TNF-α and IFN-γ levels increased continuously. The total number of T cells and ILCs peaked at 4 months and decreased in the chronic phase. In addition, IL-25 may be simultaneously produced by IL-17F-producing cells. IL-25-producing cells increased in a time-dependent manner during the chronic phase and may work specifically for the prolongation of type 2 inflammation. Altogether, these findings suggest that inhibition of IL-25 may be a potential target in the treatment of inflammation.

Ufl1 deficiency causes skin pigmentation by up-regulation of Endothelin-1

Ufmylation (UFM1 modification) is a newly identified ubiquitin-like modification system involved in numerous cellular processes. However, the regulatory mechanisms and biological functions of this modification remain mostly unknown. We have recently reported that Ufmylation family genes have frequent somatic copy number alterations in human cancer including melanoma, suggesting involvement of Ufmylation in skin function and disease. UFL1 is the only known Ufmylation E3-like ligase. In this study, we generated the skin-specific Ufl1 knockout mice and show that ablation of Ufl1 caused epidermal thickening, pigmentation and shortened life span. RNA-Seq analysis indicated that Ufl1 deletion resulted in upregulation of the genes involved in melanin biosynthesis. Mechanistically, we found that Endothelin-1 (ET-1) is a novel substrate of Ufmylation and this modification regulates ET-1 stability, and thereby deletion of Ufl1 upregulates the expression and secretion of ET-1, which in turn results in up-regulation of genes in melanin biosynthesis and skin pigmentation. Our findings establish the role of Ufl1 in skin pigmentation through Ufmylation modification of ET-1 and provide opportunities for therapeutic intervention of skin diseases.

Potential Natural Biomolecules Targeting JAK/STAT/SOCS Signaling in the Management of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease caused by the dysregulation of cytokines and other immune mediators. JAK/STAT is a classical signal transduction pathway involved in various biological processes, and its dysregulation contributes to the key aspects of AD pathogenesis. Suppressor of cytokine signaling (SOCS) proteins negatively regulate the immune-related inflammatory responses mediated by the JAK/STAT pathway. JAK/STAT-mediated production of cytokines including IL-4, IL-13, IL-31, and TSLP inhibits the expression of important skin barrier proteins and triggers pruritus in AD. The expression of SOCS proteins regulates the JAK-mediated cytokines and facilitates maintaining the skin barrier disruptions seen in AD. STATs are crucial in dendritic-cell-activated Th2 cell differentiation in the skin, releasing inflammatory cytokines, indicating that AD is a Th2-mediated skin disorder. SOCS proteins aid in balancing Th1/Th2 cells and, moreover, regulate the onset and maintenance of Th2-mediated allergic responses by reducing the Th2 cell activation and differentiation. SOCS proteins play a pivotal role in inflammatory cytokine-signaling events that act via the JAK/STAT pathway. Therapies relying on natural products and derived biomolecules have proven beneficial in AD when compared with the synthetic regimen. In this review, we focused on the available literature on the potential natural-product-derived biomolecules targeting JAK/STAT/SOCS signaling, mainly emphasizing the SOCS family of proteins (SOCS1, SOCS3, and SOCS5) acting as negative regulators in modulating JAK/STAT-mediated responses in AD pathogenesis and other inflammatory disorders.

Peripheral itch sensitization in atopic dermatitis

Atopic dermatitis is a skin disorder caused by skin dryness and barrier dysfunction, resulting in skin inflammation and chronic itch (or pruritus). The pathogenesis of atopic dermatitis is thought to be initiated by a lowering of the itch threshold due to dry skin. This lowering of the itch threshold is at least partially due to the increase in intraepidermal nerve fibers and sensitization of sensory nerves by interleukin (IL)-33 produced and secreted by keratinocytes. Such skin is easily prone to itch due to mechanical stimuli, such as rubbing of clothing and chemical stimuli from itch mediators. In patients with atopic dermatitis, once itch occurs, further itch is induced by scratching, and the associated scratching breaks down the skin barrier. Disruption of the skin barrier allows entry into the epidermis of external foreign substances, such as allergens derived from house dust mites, leading to an increased induction of type 2 inflammatory responses. As a result, type 2 cytokines IL-4, IL-13, and IL-31 are mainly secreted by Th2 cells, and their action on sensory nerve fibers causes further itch sensitization. These sequences of events are thought to occur simultaneously in patients with atopic dermatitis, leading to a vicious itch-scratch cycle. This vicious cycle becomes a negative spiral that leads to disease burden. Therefore, controlling itch is essential for the treatment of atopic dermatitis. In this review, we summarize and discuss advances in the mechanisms of peripheral itch sensitization in atopic dermatitis, focusing on skin barrier-neuro-immune triadic connectivity.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

Role of ERK Pathway in the Pathogenesis of Atopic Dermatitis and Its Potential as a Therapeutic Target

Atopic dermatitis (AD) is an eczematous skin disorder characterized by type 2 inflammation, barrier disruption, and intense itch. In addition to type 2 cytokines, many other cytokines, such as interferon gamma (IFN-γ), interleukin 17 (IL-17), and interleukin 22 (IL-22), play roles in the pathogenesis of AD. It has been reported that the extracellular signal-regulated kinase (ERK) is downstream of such cytokines. However, the involvement of the ERK pathway in the pathogenesis of AD has not yet been investigated. We examined the expression of p-ERK in mouse and human AD skin. We also investigated the effects of the topical application of an ERK inhibitor on the dermatitis score, transepidermal water loss (TEWL), histological change, and expression of filaggrin, using an AD-like NC/Nga murine model. The effects of an ERK inhibitor on filaggrin expression in normal human epidermal keratinocytes (NHEKs) and on chemokine production from bone marrow-derived dendritic cells (BMDCs) were also evaluated. p-ERK was highly expressed in mouse and human AD skin. Topical application of an ERK inhibitor alleviated the clinical symptoms, histological changes, TEWL, and decrease in expression of filaggrin in the AD-like NC/Nga murine model. The ERK inhibitor also restored the IL-4 induced reduction in the expression of filaggrin in NHEK, and inhibited chemokine production from BMDC induced by IL-4. These results indicate that the ERK pathway is involved in the pathogenesis of AD, and suggest that the ERK pathway has potential as a therapeutic target for AD in the future.

Neuro-immune communication regulating pruritus in atopic dermatitis

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

IL-25 participates in keratinocyte-driven dermal matrix turnover and is reduced in Systemic Sclerosis epidermis

OBJECTIVES

Evidence shows that dysfunctional SSc keratinocytes contribute to fibrosis by altering dermal homeostasis. Whether interleukin-25 (IL-25), an IL-17 family member regulating many epidermal functions, takes part in skin fibrosis is unknown. Here we address the role of IL-25 in skin fibrosis.

METHODS

The expression of IL-25 was evaluated by immunofluorescence and in situ hybridization in 10 SSc and 7 healthy donors (HD) skin biopsies. Epidermal equivalents (EE) reconstituted by primary HD keratinocytes were used as a model to study transcriptomic changes induced by IL-25 in the epidermis. RNA expression profile in EE was characterized by RNAseq. The conditioned medium (CM) from primary SSc and HD keratinocytes primed with IL-25 was used to stimulate fibroblasts. IL-6, IL-8, MMP-1, type-I collagen (col-I), and fibronectin production by fibroblasts was assessed by ELISA.

RESULTS

SSc epidermis expressed lower levels of IL-25 compared with HD. In EE, IL-25 regulated several molecular pathways related to wound healing and ECM remodeling. Compared with control CM, the CM from IL-25-primed keratinocytes enhanced the fibroblast production of MMP-1, IL-6, IL-8, but not of Col-I nor fibronectin. However, IL-25 significantly reduced the production of Col-I when applied directly to fibroblasts. The activation of keratinocytes by IL-25 was receptor-dependent and evident after a very short incubation time (10 min), largely mediated by IL-1, suggesting enhanced and specific release of preformed mediators.

CONCLUSIONS

These results show that IL-25 participates to skin homeostasis and its decreased expression in SSc may contribute to skin fibrosis by favoring ECM deposition over degradation.

Evaluation of the effect of the interleukin-25 serum concentration on the intensity of the symptoms of atopic dermatitis and epidermal barrier

Introduction

Interleukin 25 (IL-25) is a cytokine with proinflammatory and anti-inflammatory effects, and its biological function of reciprocal epidermal hyperplasia and of inhibiting the filaggrin synthesis points to an essential role connecting the inflammatory process with damage to the epidermal barrier in the course of atopic dermatitis (AD).

Aim

To assess the IL-25 in serum concentration in AD patients and to analyse its possible correlation with the disease intensity and selected epidermal barrier parameters such as transepidermal water loss (TEWL).

Material and methods

The study involved 43 patients with AD and 22 healthy volunteers. The IL-25 concentration was measured using the ELISA method. The intensity of disease symptoms was investigated using W-AZS and EASI indicators. The epidermal barrier was evaluated using a Tewameter TM300 and Corneometer CM825.

Results

The concentration of IL-25 in serum was higher in the study group than in the control group. IL-25 serum concentration correlates with W-AZS/EASI in patients with a severe and moderate course of AD. The concentration of IL-25 affects the TEWL within the affected, evaluated skin surface.

Conclusions

An elevated IL-25 concentration in serum is characteristic for patients with moderate and severe AD intensity. The IL-25 concentration in serum correlates with TEWL and with the moisture level in the affected area. However, further studies are necessary to determine the role played by IL-25 in the course of the disease and how it affects the functional parameters of the epidermal barrier.

Novel pathogenesis of atopic dermatitis from the view of cytokines in mice and humans

Type 2 immunity and inflammation underlie allergic skin disorders, such as atopic dermatitis (AD). In type 2 inflammation, IL-4, IL-13, and IL-5, which are signature type 2 cytokines, are mainly produced by type 2 helper T (Th2) cells and form the characteristic features of AD. Epithelial cell-derived cytokines such as IL-25, IL-33, and TSLP initiate type 2 inflammation by modulating various cells, including group 2 innate lymphoid cells. Moreover, IL-31, a newly identified type 2 cytokine produced mainly by Th2 cells, induces pruritus by acting on sensory neurons in the skin. Based on both basic and clinical findings, several biologics targeting Th2 cytokines have been developed and exhibited significant efficacy as therapeutic reagents for AD. We have summarized the roles of each cytokine (IL-4, 5, 13, 25, 31, and 33, and TSLP) in the development of type 2 inflammation, especially AD, from the view of basic studies in mice and clinical trials/observation in humans.

The Implications of Pruritogens in the Pathogenesis of Atopic Dermatitis

Atopic dermatitis (AD) is a prototypic inflammatory disease that presents with intense itching. The pathophysiology of AD is multifactorial, involving environmental factors, genetic susceptibility, skin barrier function, and immune responses. A recent understanding of pruritus transmission provides more information about the role of pruritogens in the pathogenesis of AD. There is evidence that pruritogens are not only responsible for eliciting pruritus, but also interact with immune cells and act as inflammatory mediators, which exacerbate the severity of AD. In this review, we discuss the interaction between pruritogens and inflammatory molecules and summarize the targeted therapies for AD.

The Nax (SCN7A) channel: an atypical regulator of tissue homeostasis and disease

Within an articulately characterized family of ion channels, the voltage-gated sodium channels, exists a black sheep, SCN7A (Nax). Nax, in contrast to members of its molecular family, has lost its voltage-gated character and instead rapidly evolved a new function as a concentration-dependent sensor of extracellular sodium ions and subsequent signal transducer. As it deviates fundamentally in function from the rest of its family, and since the bulk of the impressive body of literature elucidating the pathology and biochemistry of voltage-gated sodium channels has been performed in nervous tissue, reports of Nax expression and function have been sparse. Here, we investigate available reports surrounding expression and potential roles for Nax activity outside of nervous tissue. With these studies as justification, we propose that Nax likely acts as an early sensor that detects loss of tissue homeostasis through the pathological accumulation of extracellular sodium and/or through endothelin signaling. Sensation of homeostatic aberration via Nax then proceeds to induce pathological tissue phenotypes via promotion of pro-inflammatory and pro-fibrotic responses, induced through direct regulation of gene expression or through the generation of secondary signaling molecules, such as lactate, that can operate in an autocrine or paracrine fashion. We hope that our synthesis of much of the literature investigating this understudied protein will inspire more research into Nax not simply as a biochemical oddity, but also as a potential pathophysiological regulator and therapeutic target.

Th2 Modulation of Transient Receptor Potential Channels: An Unmet Therapeutic Intervention for Atopic Dermatitis

Atopic dermatitis (AD) is a multifaceted, chronic relapsing inflammatory skin disease that affects people of all ages. It is characterized by chronic eczema, constant pruritus, and severe discomfort. AD often progresses from mild annoyance to intractable pruritic inflammatory lesions associated with exacerbated skin sensitivity. The T helper-2 (Th2) response is mainly linked to the acute and subacute phase, whereas Th1 response has been associated in addition with the chronic phase. IL-17, IL-22, TSLP, and IL-31 also play a role in AD. Transient receptor potential (TRP) cation channels play a significant role in neuroinflammation, itch and pain, indicating neuroimmune circuits in AD. However, the Th2-driven cutaneous sensitization of TRP channels is underappreciated. Emerging findings suggest that critical Th2-related cytokines cause potentiation of TRP channels, thereby exaggerating inflammation and itch sensation. Evidence involves the following: (i) IL-13 enhances TRPV1 and TRPA1 transcription levels; (ii) IL-31 sensitizes TRPV1 via transcriptional and channel modulation, and indirectly modulates TRPV3 in keratinocytes; (iii) The Th2-cytokine TSLP increases TRPA1 synthesis in sensory neurons. These changes could be further enhanced by other Th2 cytokines, including IL-4, IL-25, and IL-33, which are inducers for IL-13, IL-31, or TSLP in skin. Taken together, this review highlights that Th2 cytokines potentiate TRP channels through diverse mechanisms under different inflammatory and pruritic conditions, and link this effect to distinct signaling cascades in AD. This review strengthens the notion that interrupting Th2-driven modulation of TRP channels will inhibit transition from acute to chronic AD, thereby aiding the development of effective therapeutics and treatment optimization.

OX40L-OX40 Signaling in Atopic Dermatitis

OX40 is one of the co-stimulatory molecules expressed on T cells, and it is engaged by OX40L, primarily expressed on professional antigen-presenting cells such as dendritic cells. The OX40L-OX40 axis is involved in the sustained activation and expansion of effector T and effector memory T cells, but it is not active in naïve and resting memory T cells. Ligation of OX40 by OX40L accelerates both T helper 1 (Th1) and T helper 2 (Th2) effector cell differentiation. Recent therapeutic success in clinical trials highlights the importance of the OX40L-OX40 axis as a promising target for the treatment of atopic dermatitis.

Current views on neuropeptides in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease involving skin barrier dysfunction and immune imbalance. However, the mechanism of AD is not clear completely and may be related to heredity and environment. Neuropeptides are a class of peptides secreted by nerve endings, they may play roles in promoting vasodilation, plasma extravasation, chemotaxis of inflammatory cells and mediating pruritus. Since itching and immune cell infiltration are the main manifestations of atopic dermatitis, to further investigate the impact of neuropeptides on AD, our review summarized the mechanisms of several common neuropeptides in AD and hypothesized that neuropeptides may be the novel potential targets in AD treatment.

The role of endothelin-1 and its autoantibodies in the pathogenesisof atopic dermatitis: a case-control study

Background. Atopic dermatitis is a chronic multifactorial dermatosis with a complex pathophysiological basis. One of the poorly studied links in the pathogenesis of the disease is endothelin-1. Its main biological effects include pronounced vasoconstriction of blood vessels. Aim. To study the role of endothelin-1 and its autoantibodies in the pathogenesis of atopic dermatitis. Materials and methods. The study included 40 patients with common and limited forms of atopic dermatitis in the period of exacerbation and remission. The concentration of endothelin-1 and autoantibodies to it in the blood serum was determined by the ELISA method. Statistical processing of the obtained data was performed using Statistica 6.0. Statistical significance was determined at p 0.05. Results. High concentrations of endothelin-1 and autoantibodies to it were determined during the exacerbation of the disease. When the clinical picture was resolved; the concentration of endothelin-1 and autoantibodies to it significantly decreased; but remained higher than the control group. Based on the data obtained; it can be assumed that an increase in the concentration of endothelin-1 may be a marker of white dermographism and a regulator of the microcirculation process in the skin. Conclusions. A high level of endothelin-1 contributes to the development of inflammatory reactions in the skin; white dermographism and itching. Endothelin-1 receptors may be potential aim for targeted therapy of atopic dermatitis.

IL-25 (IL-17E) in epithelial immunology and pathophysiology

IL-25, also known as IL-17E, is a unique cytokine of the IL-17 family. Indeed, IL-25 exclusively was shown to strongly induce expression of the cytokines associated with type 2 immunity. Although produced by several types of immune cells, such as T cells, dendritic cells, or group 2 innate lymphoid cells, a vast amount of IL-25 derives from epithelial cells. The functions of IL-25 have been actively studied in the context of physiology and pathology of various organs including skin, airways and lungs, gastrointestinal tract, and thymus. Accumulating evidence suggests that IL-25 is a "barrier surface" cytokine whose expression depends on extrinsic environmental factors and when upregulated may lead to inflammatory disorders such as atopic dermatitis, psoriasis, or asthma. This review summarizes the progress of the recent years regarding the effects of IL-25 on the regulation of immune response and the balance between its homeostatic and pathogenic role in various epithelia. We revisit IL-25's general and tissue-specific mechanisms of action, mediated signaling pathways, and transcription factors activated in immune and resident cells. Finally, we discuss perspectives of the IL-25-based therapies for inflammatory disorders and compare them with the mainstream ones that target IL-17A.

Inhibition of mite-induced dermatitis, pruritus, and nerve sprouting in mice by the endothelin receptor antagonist bosentan

BACKGROUND

Endothelin-1 (EDN1) can evoke histamine-independent pruritus in mammals and is upregulated in the lesional epidermis of atopic dermatitis (AD). EDN1 increases the production of interleukin 25 (IL-25) from keratinocytes to accelerate T helper type 2 immune deviation. Plasma EDN1 levels are positively correlated with the clinical severity and itch intensity of AD. Therefore, we hypothesized that the inhibition of EDN1 might be useful for treating atopic inflammation and itch and investigated the effects of the topical application of the EDN1 receptor antagonist bosentan on the skin inflammation and itch in a murine AD model.

METHODS

We analyzed the mite-induced AD-like NC/Nga murine model, which was topically applied with bosentan or ethanol control every day for 3 weeks. We also subjected in vitro primary sensory neuron culture systems to nerve elongation and branching assays after EDN1 stimulation.

RESULTS

Topical application of bosentan significantly attenuated the development of mite-induced AD-like skin inflammation, dermatitis scores, ear thickness, scratching bouts, and serum level of thymus and activation-regulated chemokine in NC/Nga mice. Bosentan application also significantly reduced the gene expression of Il13, Il17, and Ifng in the treated lesions. Histologically, the number of infiltrated dermal cells, the epidermal EDN1 expression, and the number of intraepidermal nerve fibers were significantly inhibited upon bosentan application. While EDN1 significantly elongated the neurites of dorsal root ganglion cells in a dose- and time-dependent manner, bosentan treatment attenuated this.

CONCLUSIONS

EDN1 plays a significant role in mite-induced inflammation and itch. Topical bosentan is a potential protective candidate for AD.

Regulation of Skin Barrier Function via Competition between AHR Axis versus IL-13/IL-4‒JAK‒STAT6/STAT3 Axis: Pathogenic and Therapeutic Implications in Atopic Dermatitis

Atopic dermatitis (AD) is characterized by skin inflammation, barrier dysfunction, and chronic pruritus. As the anti-interleukin-4 (IL-4) receptor α antibody dupilumab improves all three cardinal features of AD, the type 2 cytokines IL-4 and especially IL-13 have been indicated to have pathogenic significance in AD. Accumulating evidence has shown that the skin barrier function is regulated via competition between the aryl hydrocarbon receptor (AHR) axis (up-regulation of barrier) and the IL-13/IL-4‒JAK‒STAT6/STAT3 axis (down-regulation of barrier). This latter axis also induces oxidative stress, which exacerbates inflammation. Conventional and recently developed agents for treating AD such as steroid, calcineurin inhibitors, cyclosporine, dupilumab, and JAK inhibitors inhibit the IL-13/IL-4‒JAK‒STAT6/STAT3 axis, while older remedies such as coal tar and glyteer are antioxidative AHR agonists. In this article, I summarize the pathogenic and therapeutic implications of the IL-13/IL-4‒JAK‒STAT6/STAT3 axis and the AHR axis in AD.

The IL-23/IL-17 Pathway in Inflammatory Skin Diseases: From Bench to Bedside

Interleukin-17 (IL-17) is an essential proinflammatory cytokine, which is mainly secreted by the CD4⁺ helper T cells (Th17 cells) and subsets of innate lymphoid cells. IL-17A is associated with the pathogenesis of inflammatory diseases, including psoriasis, atopic dermatitis, hidradenitis suppurativa, alopecia areata, pityriasis rubra pilaris, pemphigus, and systemic sclerosis. Interleukin-23 (IL-23) plays a pivotal role in stimulating the production of IL-17 by activating the Th17 cells. The IL-23/IL-17 axis is an important pathway for targeted therapy for inflammatory diseases. Emerging evidence from clinical trials has shown that monoclonal antibodies against IL-23, IL-17, and tumor necrosis factor are effective in the treatment of patients with psoriasis, atopic dermatitis, hidradenitis suppurativa, pityriasis rubra pilaris, pemphigus, and systemic sclerosis. Here, we summarize the latest knowledge about the biology, signaling, and pathophysiological functions of the IL-23/IL-17 axis in inflammatory skin diseases. The currently available biologics targeting the axis is also discussed.

Exploration of biomarkers to predict clinical improvement of atopic dermatitis in patients treated with dupilumab: A study protocol

BACKGROUND

Atopic dermatitis (AD) is a common eczematous skin disorder that profoundly reduces the quality of life due to intractable pruritus. Excellent therapeutic success of the anti-interleukin 4 receptor-α antibody dupilumab in clinical trials and a real-world clinical context indicates the crucial roles of interleukin (IL)-4 and IL-13 in the pathogenesis of AD. Along with the clinical improvement in skin scores and pruritus, dupilumab significantly and progressively reduces and normalizes the upregulated expression of T helper type 2 signatures such as Chemokine (C-C motif) ligand (CCL)17, CCL18, CCL22, and CCL26 in the lesional skin of AD. However, no blood/serum biomarkers are known to predict good or poor outcome in patients with AD treated with dupilumab.

METHODS

Patients are at least 18 years of age and have moderate-to-severe AD with Eczema Area and Severity Index (EASI) ≥16, Investigator's Global Assessment ≥3, and body surface area ≥10%. We are going to enroll more than 130 subjects from 18 medical facilities. Clinical objective findings will be evaluated by EASI. Subjective symptoms will be assessed by Patient-Oriented Eczema Measure, Numerical Rating Scale for Pruritus (Pruritus-NRS), Skin Comfort-NRS, and Treatment Satisfaction-NRS. We will measure 18 blood/serum biomarkers including % eosinophils in blood cell count, lactate dehydrogenase, total IgE, soluble interleukin 2 receptor, CCL17, CCL18, CCL22, CCL26, CCL27, IL-13, IL-22, IL-24, IL-25, IL-31, IL-33, thymic stromal lymphopoietin, periostin, and squamous cell carcinoma antigen-2. The clinical evaluation and biomarker sampling will be performed at 0, 2, 4, 8, and 16 weeks of dupilumab treatment. We will also perform proteomic analysis (of roughly 300 proteins) of the patients' sera obtained at 0 and 2 weeks of treatment. The primary endpoint is the association between "baseline levels of 18 biomarkers" and "% change from baseline of EASI at 16 weeks of dupilumab treatment."

DISCUSSION

This is the first clinical trial to explore the biomarkers, including potential proteomic markers, most strongly associated with improvement in EASI in patients with moderate-to-severe AD treated with dupilumab for 16 weeks (B-PAD study). A limitation is that we will only enroll Japanese patients.

Topical application of endothelin receptor a antagonist attenuates imiquimod-induced psoriasiform skin inflammation

Endothelin-1 (ET-1) is well known as the most potent vasoconstrictor, and can evoke histamine-independent pruritus. Recently, its involvement in cutaneous inflammation has begun to draw attention. The upregulation of ET-1 expression in the epidermis of human psoriasis patients has been reported. It was also demonstrated that ET-1 can stimulate dendritic cells to induce Th17/1 immune responses. However, the role of the interaction between ET-1 and ET-1 receptors in the pathogenesis of psoriasis remains elusive. Here, we investigated the effects of ET-1 receptor antagonist on imiquimod (IMQ) -induced psoriasiform dermatitis in mouse. Psoriasis-related cytokines such as IL-17A and TNF-α induced ET-1 expression in human keratinocytes. Topical application of selective endothelin A receptor (ETAR) antagonist ambrisentan significantly attenuated the development of IMQ-induced psoriasiform dermatitis and also significantly inhibited the histological inflammation and cytokine expression (TNF-α, IL-12p40, IL-12 p19, and IL-17) in the lesional skin of the mouse model. Furthermore, topical application of ambrisentan suppressed phenotypic and functional activation of dendritic cells in lymph nodes. Our findings indicate that the ET-1 and ETAR axis plays an important role in the pathogenesis of psoriasis and is a potential therapeutic target for treating psoriasis.

Interleukin-17A and Keratinocytes in Psoriasis

The excellent clinical efficacy of anti-interleukin 17A (IL-17A) biologics on psoriasis indicates a crucial pathogenic role of IL-17A in this autoinflammatory skin disease. IL-17A accelerates the proliferation of epidermal keratinocytes. Keratinocytes produce a myriad of antimicrobial peptides and chemokines, such as CXCL1, CXCL2, CXCL8, and CCL20. Antimicrobial peptides enhance skin inflammation. IL-17A is capable of upregulating the production of these chemokines and antimicrobial peptides in keratinocytes. CXCL1, CXCL2, and CXCL8 recruit neutrophils and CCL20 chemoattracts IL-17A-producing CCR6⁺ immune cells, which further contributes to forming an IL-17A-rich milieu. This feed-forward pathogenic process results in characteristic histopathological features, such as epidermal hyperproliferation, intraepidermal neutrophilic microabscess, and dermal CCR6⁺ cell infiltration. In this review, we focus on IL-17A and keratinocyte interaction regarding psoriasis pathogenesis.

Novel Neuropathic Pain Mechanisms Associated With Allergic Inflammation

Allergic diseases are associated with central and peripheral nervous system diseases such as autism spectrum disorders and eosinophilic granulomatosis with polyangiitis, which frequently causes mononeuritis multiplex. Thus, it is possible that patients with an atopic constitution might develop multifocal inflammation in central and peripheral nervous system tissues. In a previous study in Japan, we reported a rare form of myelitis with persistent neuropathic pain (NeP) in patients with allergic disorders. However, the underlying mechanism of allergic inflammation-related NeP remains to be elucidated. First, we analyzed the effect of allergic inflammation on the nociceptive system in the spinal cord. Mice with atopy showed microglial and astroglial activation in the spinal cord and tactile allodynia. In a microarray analysis of isolated microglia from the spinal cord, endothelin receptor type B (EDNRB) was the most upregulated cell surface receptor in mice with atopy. Immunohistochemical analysis demonstrated EDNRB expression was upregulated in microglia and astroglia. The EDNRB antagonist BQ788 abolished glial activation and allodynia. These findings indicated that allergic inflammation induced widespread glial activation through the EDNRB pathway and NeP. Second, we investigated whether autoantibody-mediated pathogenesis underlies allergic inflammation-related NeP. We detected specific autoantibodies to small dorsal root ganglion (DRG) neurons and their nerve terminals in the dorsal horns of NeP patients with allergic disorders. An analysis of IgG subclasses revealed a predominance of IgG2. These autoantibodies were mostly colocalized with isolectin B4- and P2X3-positive unmyelinated C-fiber type small DRG neurons. By contrast, immunostaining for S100β, a myelinated DRG neuron marker, showed no colocalization with patient IgG. Immunoprecipitation and liquid chromatography-tandem mass spectrometry identified plexin D1 as a target autoantigen. Patients with anti-plexin D1 antibodies often present with burning pain and thermal hyperalgesia. Immunotherapies, including plasma exchange, are effective for NeP management. Therefore, anti-plexin D1 antibodies may be pathogenic for immune-mediated NeP, especially under allergic inflammation conditions. Thus, allergic inflammation may induce NeP through glial inflammation in the spinal cord and the anti-plexin D1 antibody-mediated impairment of small DRG neurons.

IL-17 and its role in inflammatory, autoimmune, and oncological skin diseases: state of art

Recent data support the theory of the involvement of IL‐17 in the pathogenesis of several chronic inflammatory skin diseases (psoriasis, atopic dermatitis, acne, hidradenitis suppurativa) and autoimmune skin diseases (alopecia areata, vitiligo, bullous diseases). Even if the role of IL‐17 in inflammatory and autoimmune diseases has been reported extensively, its role in tumor is still controversial. Some reports show that Th17 cells eradicate tumors, while others reveal that they promote the initiation and early growth of tumors. Herein, we review the role of IL‐17 in the involvement of some common dermatologic diseases: psoriasis, atopic dermatitis, hidradenitis suppurativa, acne, vitiligo, melanoma, and nonmelanoma skin cancers.

Psoriasis and the TNF/IL23/IL17 axis

The excellent response of psoriasis to anti-TNF-α(TNF)/IL23/IL17A biologics implies a crucial role for the TNF/IL23/IL17 axis in developing psoriasis. In addition to the TNF/IL23/IL17 axis provided by immune cells, current evidence points to an important contribution of TNF, IL23 and IL17C produced from non-hematopoietic keratinocytes. Therefore, crosstalk between immune cells and keratinocytes forms a multilayered feed-forward loop to accelerate the TNF/IL23/IL17A axis. Many biologics have already been licensed or are under clinical trials. Given that the IL-17 signature is more upregulated in the skin than in synovium in psoriatic arthritis, anti-IL-23/IL-17 agents seem to be superior to anti-TNF-α remedies in the treatment of skin lesions. In this review, we summarize recent topics in psoriasis and the TNF/IL23/IL17 axis.

Leveraging Multilayered "Omics" Data for Atopic Dermatitis: A Road Map to Precision Medicine

Atopic dermatitis (AD) is a complex multifactorial inflammatory skin disease that affects ~280 million people worldwide. About 85% of AD cases begin in childhood, a significant portion of which can persist into adulthood. Moreover, a typical progression of children with AD to food allergy, asthma or allergic rhinitis has been reported (“allergic march” or “atopic march”). AD comprises highly heterogeneous sub-phenotypes/endotypes resulting from complex interplay between intrinsic and extrinsic factors, such as environmental stimuli, and genetic factors regulating cutaneous functions (impaired barrier function, epidermal lipid, and protease abnormalities), immune functions and the microbiome. Though the roles of high-throughput “omics” integrations in defining endotypes are recognized, current analyses are primarily based on individual omics data and using binary clinical outcomes. Although individual omics analysis, such as genome-wide association studies (GWAS), can effectively map variants correlated with AD, the majority of the heritability and the functional relevance of discovered variants are not explained or known by the identified variants. The limited success of singular approaches underscores the need for holistic and integrated approaches to investigate complex phenotypes using trans-omics data integration strategies. Integrating omics layers (e.g., genome, epigenome, transcriptome, proteome, metabolome, lipidome, exposome, microbiome), which often have complementary and synergistic effects, might provide the opportunity to capture the flow of information underlying AD disease manifestation. Overlapping genes/candidates derived from multiple omics types include FLG, SPINK5, S100A8, and SERPINB3 in AD pathogenesis. Overlapping pathways include macrophage, endothelial cell and fibroblast activation pathways, in addition to well-known Th1/Th2 and NFkB activation pathways. Interestingly, there was more multi-omics overlap at the pathway level than gene level. Further analysis of multi-omics overlap at the tissue level showed that among 30 tissue types from the GTEx database, skin and esophagus were significantly enriched, indicating the biological interconnection between AD and food allergy. The present work explores multi-omics integration and provides new biological insights to better define the biological basis of AD etiology and confirm previously reported AD genes/pathways. In this context, we also discuss opportunities and challenges introduced by “big omics data” and their integration.

The IL-17 Family of Cytokines in Psoriasis: IL-17A and Beyond

Psoriasis is a frequent chronic inflammatory skin disease, nowadays considered a major global health problem. Several new drugs, targeting the IL-23/IL-17A pathway, have been recently licensed or are in clinical development. These therapies represent a major improvement of the way in which psoriasis is managed, since they show an unprecedented efficacy on skin symptoms of psoriasis. This has been made possible, thanks to an increasingly more accurate pathogenic view of psoriasis. Today, the belief that Th17 cells mediate psoriasis is moving to the concept of psoriasis as an IL-17A-driven disease. New questions arise at the horizon, given that IL-17A is part of a newly described family of cytokines, which has five distinct homologous: IL-17B, IL-17C, IL-17D, IL-17E, also known as IL-25 and IL-17F. IL-17 family cytokines elicit similar effects in target cells, but simultaneously trigger different and sometimes opposite functions in a tissue-specific manner. This is complicated by the fact that IL-17 cytokines show a high capacity of synergisms with other inflammatory stimuli. In this review, we will summarize the current knowledge around the cytokines belonging to the IL-17 family in relation to skin inflammation in general and psoriasis in particular, and discuss possible clinical implications. A comprehensive understanding of the different roles played by the IL-17 cytokines is crucial to appreciate current and developing therapies and to allow an effective pathogenesis- and mechanisms-driven drug design.

Leptin Promotes Allergic Airway Inflammation through Targeting the Unfolded Protein Response Pathway

Allergic asthma and obesity are major public health problems in the world. Recent Meta-analysis studies implicated a positive relationship between serum leptin, which is elevated in obese individuals, and the risk of asthma. However, it is not well understood how obesity-associated elevation of leptin increases the risk of asthma. In the current study, we have found that leptin induces the unfolded protein response factor XBP1s in an mTOR- and MAPK-dependent manner in pro-allergic TH2 cells; in vivo, mice fed with high fat diet had increased serum leptin as observed in human obese population and exacerbated asthmatic symptoms, associated with increased XBP1s expression in splenic CD4+ T cells. XBP1s is required for leptin-mediated pro-allergic TH2 cell survival and cytokine production. Our results reveal a previously unappreciated insight that obesity-associated hyperleptinemia contributes to enhanced pro-allergic lymphocyte responses through induction of XBP1s, leading to exacerbation of allergic asthma.

Mechanistic insights into topical tacrolimus for the treatment of atopic dermatitis

More than 15 years have passed since the clinical launch of topical tacrolimus for the treatment of atopic dermatitis. Its efficacy and safety have been clearly demonstrated in many global and domestic short-term and long-term clinical trials. Although the prolonged external application of steroids causes many adverse reactions including cutaneous atrophy, no such reactions occur with the use of topical tacrolimus. Therefore, the therapeutic guidelines recommend a combined topical treatment with tacrolimus and steroids. Tacrolimus is a potent immunosuppressant. However, recent studies have revealed its diverse action on the cardinal pathomechanisms of atopic dermatitis. In this review, we summarize the mechanistic role of tacrolimus in various aspects of allergic inflammation including mast cell activation, innate allergic response, pruritus, sensory nerve activation, and skin barrier dysfunction.

Interleukin 17 Family Cytokines: Signaling Mechanisms, Biological Activities, and Therapeutic Implications

The cytokines of the interleukin 17 (IL-17) family play a central role in the control of infections, especially extracellular fungi. Conversely, if unrestrained, these inflammatory cytokines contribute to the pathology of numerous autoimmune and chronic inflammatory conditions. Recent advances have led to the approval of IL-17A-blocking biologics for the treatment of moderate to severe plaque psoriasis, but much remains to be understood about the biological functions, regulation, and signaling pathways downstream of these factors. In this review, we outline the current knowledge of signal transduction and known physiological activities of IL-17 family cytokines. We will highlight in particular the current understanding of these cytokines in the context of skin manifestations of disease.

Interleukin-25 is involved in cutaneous T-cell lymphoma progression by establishing a T helper 2-dominant microenvironment

BACKGROUND

Interleukin (IL)-25 is a member of the IL-17 family, which can promote and augment T-helper (Th) type 2 responses. The expression of IL-25 and its cognate receptor, IL-25 receptor (IL-25R), is upregulated and correlated with disease activity in Th2-associated diseases.

OBJECTIVES

To examine the expression and function of IL-25 in cutaneous T-cell lymphoma (CTCL).

METHODS

Expression and location of IL-25 in lesional skin was investigated with immunohistochemistry. The effect of various cytokines on IL-25 production from normal human epidermal keratinocytes was assessed by quantitative reverse-transcription real-time polymerase chain reaction. Serum IL-25 levels were measured by enzyme-linked immunosorbent assay. The direct effect of IL-25 on tumour cells was also examined using CTCL cell lines and peripheral blood mononuclear cells in patients with Sézary syndrome.

RESULTS

IL-25 expression was increased in epidermal keratinocytes in lesional skin of CTCL. Th2 cytokines, IL-4 and IL-13, and periostin induced IL-25 expression by normal human epidermal keratinocytes. Serum IL-25 levels were increased in patients with advanced CTCL and correlated with serum lactate dehydrogenase levels. MyLa cells expressed IL-25R and its expression was augmented by stimulation with IL-25. IL-25 enhanced IL-13 production from MyLa cells via phosphorylation of signal transducer and activator of transcription 6. Peripheral blood mononuclear cells from one patient with Sézary syndrome expressed IL-25R and showed increase of IL-13 production by IL-25.

CONCLUSIONS

Th2 cytokines highly expressed in CTCL lesional skin induce IL-25 production by epidermal keratinocytes, which may, in turn, lead to formation of a Th2-dominant microenvironment through the direct induction of IL-13 by tumour cells.