Involvement of IL-31 on scratching behavior in NC/Nga mice with atopic-like dermatitis

Mouse Models of Itch

Murine models are vital preclinical and biological tools for studying itch. In this paper, we explore how these models have enhanced our understanding of the mechanisms underlying itch through both acute and chronic itch models. We provide detailed protocols and recommend experimental setups for specific models to guide researchers in conducting itch research. We distinguish between what constitutes a bona fide pruritogen versus a stimulus that causes pruritogen release, an acute itch model versus a chronic itch model, and how murine models can capture aspects of pruritus in human disease. Finally, we highlight how mouse models of itch have transformed our understanding and development of therapeutics for chronic pruritus in patients.

The Acari Hypothesis, IV: revisiting the role of hygiene in allergy

Allergy and its manifestations were first appreciated in the 1870 s. Today, the mechanism by which specific substances elicit allergic reactions remains poorly understood. This is problematic from a healthcare perspective because the prevalence of allergic disease and its societal costs are substantial. Regarding mechanistic understanding of allergy, a new proposal, The Acari Hypothesis, has been forwarded. The Hypothesis, borne from consideration of alpha-gal syndrome, postulates that acarians, i.e., mites and ticks, are operative agents of allergy. By way of their pathogenic payloads and salivary pattern recognition receptor(s), acarians potentiate in human hosts the generation of IgE against acarian dietary elements. Those elements account for most, if not all, known human allergens. Inasmuch as acarian-human interactions occur on human epithelial surfaces, it is to be expected factors that influence the presence and/or operation of acarians on those surfaces influence the expression of allergic diseases. In this report, it is proposed that two adaptations of catarrhine primates, i.e., Old World monkeys, apes and humans, evolved to deter acarian species: firstly, the expansion of eccrine glands across the entirety of body surface area, and, secondly, the secretion of sweat by those glands. Contemporary hygienic practices that reduce and/or disrupt the operation of eccrine glands are likely responsible for the increase in allergic disease seen today.

Mast cell-sensory neuron crosstalk in allergic diseases

Mast cells (MCs) are tissue-resident immune cells, well-positioned at the host-environment interface for detecting external antigens and playing a critical role in mobilizing innate and adaptive immune responses. Sensory neurons are afferent neurons innervating most areas of the body but especially in the periphery, where they sense external and internal signals and relay information to the brain. The significance of MC-sensory neuron communication is now increasingly becoming recognized, especially because both cell types are in close physical proximity at the host-environment interface and around major organs of the body and produce specific mediators that can activate each other. In this review, we explore the roles of MC-sensory neuron crosstalk in allergic diseases, shedding light on how activated MCs trigger sensory neurons to initiate signaling in pruritus, shock, and potentially abdominal pain in allergy, and how activated sensory neurons regulate MCs in homeostasis and atopic dermatitis associated with contact hypersensitivity and type 2 inflammation. Throughout the review, we also discuss how these 2 sentinel cell types signal each other, potentially resulting in a positive feedback loop that can sustain inflammation. Unraveling the mysteries of MC-sensory neuron crosstalk is likely to unveil their critical roles in various disease conditions and enable the development of new therapeutic approaches to combat these maladies.

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.

Blockade of OSMRβ signaling ameliorates skin lesions in a mouse model of human atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by severe pruritus and eczematous skin lesions. Although IL-31, a type 2 helper T (Th2)-derived cytokine, is important to the development of pruritus and skin lesions in AD, the blockade of IL-31 signaling does not improve the skin lesions in AD. Oncostatin M (OSM), a member of IL-6 family of cytokines, plays important roles in the regulation of various inflammatory responses through OSM receptor β subunit (OSMRβ), a common receptor subunit for OSM and IL-31. However, the effects of OSM on the pathogenesis of AD remain to be elucidated. When AD model mice were treated with OSM, skin lesions were exacerbated and IL-4 production was increased in the lymph nodes. Next, we investigated the effects of the monoclonal antibody (mAb) against OSMRβ on the pathogenesis of AD. Treatment with the anti-OSMRβ mAb (7D2) reduced skin severity score in AD model mice. In addition to skin lesions, scratching behavior was decreased by 7D2 mAb with the reduction in the number of OSMRβ-positive neurons in the dorsal root ganglia of AD model mice. 7D2 mAb also reduced the serum concentration of IL-4, IL-13, and IgE as well as the gene expressions of IL-4 and IL-13 in the lymph nodes of AD model mice. Blockade of both IL-31 and OSM signaling is suggested to suppress both pruritus and Th2 responses, resulting in the improvement of skin lesions in AD. The anti-OSMRβ mAb may be a new therapeutic candidate for the treatment of AD.

IL-31RA and TRPV1 Expression in Atopic Dermatitis Induced with Trinitrochlorobenzene in Nc/Nga Mice

Atopic dermatitis (AD) is a common chronic inflammatory skin disease. Interleukin 31 (IL-31), a novel cytokine in AD, causes pruritus, typically characteristic of AD patients. The transient receptor potential vanilloid type 1 (TRPV1) is a cation channel activated by diverse noxious stimuli that has been studied in a variety of pruritic skin diseases. In this study, the AD animal model was generated by administering the hapten, trinitrochlorobenzene (TNCB), to Nc/Nga mice, and the degree of expression of the IL-31 receptor alpha (IL-31RA) and TRPV1 in the skin of these atopic models was evaluated. The Nc/Nga mice were divided into 3 groups: control, TNCB 2-weeks treated, and TNCB 8-weeks treated. After inducing AD, the skin lesions in each group were scored and compared, and the histology of the skin lesions and the IL-31RA and TRPV1 expression for each group were evaluated by analyzing immunohistochemistry. The results show a significant difference in the skin lesion scores between the groups. The immunohistochemistry evaluation highlighted the remarkable expression of IL-31RA and TRPV1 in the nerve fibers of the TNCB 8-weeks-treated group. We thus confirmed that the long-term application of TNCB induced chronic atopic-like dermatitis and that IL-31RA and TRPV1 were overexpressed in the peripheral nerve fibers in this AD model.

Assessment of Treatment-Relevant Immune Biomarkers in Psoriasis and Atopic Dermatitis: Toward Personalized Medicine in Dermatology

Immunologically targeted therapies have revolutionized the treatment of inflammatory dermatoses, including atopic dermatitis and psoriasis. Although immunologic biomarkers hold great promise for personalized classification of skin disease and tailored therapy selection, there are no approved or widely used approaches for this in dermatology. This review summarizes the translational immunologic approaches to measuring treatment-relevant biomarkers in inflammatory skin conditions. Tape strip profiling, microneedle-based biomarker patches, molecular profiling from epidermal curettage, RNA in situ hybridization tissue staining, and single-cell RNA sequencing have been described. We discuss the advantages and limitations of each and open questions for the future of personalized medicine in inflammatory skin disease.

Interleukin-31 Receptor A Expression in the Dorsal Root Ganglion of Mice with Atopic Dermatitis

Atopic dermatitis (AD) is a common skin disease caused by genetic and environmental factors. However, the mechanisms underlying AD development remain unclear. In this study, we examined the genetic factors contributing to the onset of itch-associated scratching in different strains of mice. Interleukin-31 (IL-31) induces severe scratching and dermatitis in mice. However, the site of action of IL-31 remains unclear. Cutaneous IL-31 and IL-31 receptor A (IL-31RA) mRNAs in the dorsal root ganglion (DRG) are expressed exclusively in the AD model, i.e., NC/Nga mice. Here we evaluated the effects of repeated administration of IL-31 on the scratching behavior in NC/Nga, BALB/c, and C57BL/6 mice. The results showed that repeated administration of IL-31 significantly increased itch-associated scratching (LLS) behavior in the three strains of mice. One hour after an intravenous IL-31 injection, BALB/c mice showed alloknesis-like behavior. Mite infestation and IL-31 administration triggered itchy skin, increased LLS counts and DRG neuronal IL-31RA expression, and eventually caused dermatitis. The dermatitis severity and LLS counts induced by mite infestation and IL-31 administration were in the order NC/Nga > BALB/c > C57BL/6. In conclusion, neuronal IL-31RA expression in the DRG was the most important genetic factor affecting the severity of LLS and dermatitis in mice.

Impact of Chronic Kidney Disease Severity on the Risk of Prurigo Nodularis: A Population-Based Cohort Study

While dialysis is linked with prurigo nodularis, little is known about the impact of non-dialysis chronic kidney disease on prurigo nodularis. The influence of chronic kidney disease on development of prurigo nodularis was measured using the Korean National Health Insurance and National Health Screening Program data, identifying 17,295,576 individuals without prior prurigo nodularis. Chronic kidney disease severity was determined by the estimated glomerular filtration rate (in ml/min/1.73 m²) calculated from serum creatinine, and proteinuria detected with urine dipstick. Prurigo nodularis incidence during follow-up was determined. Over a median follow-up period of 9.72 years, 58,599 individuals developed prurigo nodularis, with an incidence rate of 3.59 per 10,000 person-years. Among different variables, estimated glomerular filtration rate was the strongest risk factor for prurigo nodularis. Compared with estimated glomerular filtration rate ≥ 90, estimated glomerular filtration rate 15–29 (hazard ratio 1.31, 95% confidence interval 1.05–1.62) and end-stage renal disease (hazard ratio 1.46, 95% confidence interval 1.25–1.69) were associated with higher risks. The presence of proteinuria independently increased the risk of prurigo nodularis, increased risks associated with estimated glomerular filtration rate 15–29 and endstage renal disease, and caused risk associated with estimated glomerular filtration rate 30–59 to become significant. With differential impact of chronic kidney disease severity on the risk of prurigo nodularis, preservation of renal function would potentially translate into lower risk of prurigo nodularis.

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.

Selective activation of TRPA1 ion channels by nitrobenzene skin sensitizers DNFB and DNCB

2, 4-dinitrofluorobenzene (DNFB) and 2, 4-dinitrochlorobenzene (DNCB) are well known as skin sensitizers that can cause dermatitis. DNFB has shown to more potently sensitize skin; however, how DNFB and DNCB cause skin inflammation at a molecular level and why this difference in their sensitization ability is observed remains unknown. In this study, we aimed to identify the molecular targets and mechanisms on which DNFB and DNCB act. We used a fluorescent calcium imaging plate reader in an initial screening assay before patch-clamp recordings for validation. Molecular docking in combination with site-directed mutagenesis was then carried out to investigate DNFB and DNCB binding sites in the TRPA1 ion channel that may be selectively activated by these tow sensitizers. We found that DNFB and DNCB selectively activated TRPA1 channel with EC₅₀ values of 2.3 ± 0.7 μM μM and 42.4 ± 20.9 μM, respectively. Single-channel recordings revealed that DNFB and DNCB increase the probability of channel opening and acts on three residues (C621, E625 and Y658) critical for TRPA1 activation. Our findings may not only help explain the molecular mechanism underlying the dermatitis and pruritus caused by chemicals like DNFB and DNCB, but also provide a molecular tool 7.5-fold more potent than the current TRPA1 activator allyl isothiocyanate (AITC) used for investigating TRPA1 channel pharmacology and pathology.

Suppressive effect of 1,4-anhydro-4-seleno-D-talitol (SeTal) on atopic dermatitis-like skin lesions in mice through regulation of inflammatory mediators

BACKGROUND

Atopic dermatitis (AD) is a multifactorial chronic inflammatory disease that affects ∼20 % of children and 3% of adults globally and is generally treated by the topical application of steroidal drugs that have undesirable side-effects. The development of alternative therapies is therefore an important objective. The present study investigated the effects of topical treatment with a novel water-soluble selenium-containing carbohydrate derivative (4-anhydro-4-seleno-D-tatitol, SeTal) on the symptoms and inflammatory parameters in an AD mouse model.

METHODS

Mice were sensitized by applying 2,4-dinitrochlorobenzene (DNCB) to their dorsal skin on days 1-3, then further challenged on their ears and dorsal skin on days 14, 17, 20, 23, 26, and 29. SeTal (1 and 2%) or hydrocortisone (1%) was applied topically to the backs of the mice from days 14-29, and skin severity scores and scratching behavior determined on day 30. The mice were euthanized, and their ears and dorsal skin removed to quantify inflammatory parameters, edema, myeloperoxidase (MPO) activity, and AD-associated cytokines (tumor necrosis factor alpha (TNF-α), interleukins (IL)-18, and IL-33).

RESULTS

DNCB treatment induced skin lesions and increased the scratching behavior, ear edema, MPO activity (ear and dorsal skin), and cytokine levels in dorsal skin. Topical application of SeTal improved inflammatory markers (cytokine levels and MPO activity), cutaneous severity scores, and scratching behavior.

CONCLUSION

The efficacy of SeTal was satisfactory in the analyzed parameters, showing similar or better results than hydrocortisone. SeTal appears to be therapeutically advantageous for the treatment and control of AD.

Effects of Josamycin on Scratching Behavior in NC/Nga Mice with Atopic Dermatitis-Like Skin Lesions

Our previous study showed that chronic skin colonization by Staphylococcus aureus exacerbated atopic dermatitis (AD) and that control of such skin colonization using antibiotic ointment might relieve AD-related skin inflammation. However, the role of S. aureus colonization in the pruritus accompanying AD was not elucidated. The aim of the present study was to evaluate the effect of topically applied josamycin, a macrolide antibiotic, on the scratching behavior of NC/Nga mice with AD-like skin lesions. Josamycin (0.1%) was topically administered to NC/Nga mice with AD-like skin lesions induced by a mite antigen, Dermatophagoides farinae extract, and the therapeutic effects of josamycin were assessed by measurement of the skin severity score, S. aureus colonization, scratching count, and interleukin (IL)-31 mRNA expression in the skin lesions. Topical treatment with josamycin ointment significantly suppressed the increase of the skin severity score in NC/Nga mice. This suppressive effect was associated with decreases in the S. aureus count on the lesioned skin, scratching behavior of mice and IL-31 mRNA expression in the lesions. The present results show that the severity of AD-like skin inflammation in NC/Nga mice is correlated with the level of S. aureus colonization and subsequent IL-31 production in the skin. Therefore, topical application of josamycin to AD lesions colonized by S. aureus would be beneficial for control of AD by eliminating superficially located S. aureus and by suppressing the IL-31-induced scratching behavior.

Prenylated quinolinecarboxylic acid compound-18 prevents sensory nerve fiber outgrowth through inhibition of the interleukin-31 pathway

Interleukin-31 (IL-31) is involved in excessive development of cutaneous sensory nerves in atopic dermatitis (AD), leading to severe pruritus. We previously reported that PQA-18, a prenylated quinolinecarboxylic acid (PQA) derivative, is an immunosuppressant with inhibition of p21-activated kinase 2 (PAK2) and improves skin lesions in Nc/Nga mice as an AD model. In the present study, we investigate the effect of PQA-18 on sensory nerves in lesional skin. PQA-18 alleviates cutaneous nerve fiber density in the skin of Nc/Nga mice. PQA-18 also inhibits IL-31-induced sensory nerve fiber outgrowth in dorsal root ganglion cultures. Signaling analysis reveals that PQA-18 suppresses phosphorylation of PAK2, Janus kinase 2, and signal transducer and activator of transcription 3 (STAT3), activated by IL-31 receptor (IL-31R), resulting in inhibition of neurite outgrowth in Neuro2A cells. Gene silencing analysis for PAK2 confirms the requirement for STAT3 phosphorylation and neurite outgrowth elicited by IL-31R activation. LC/MS/MS analysis reveals that PQA-18 prevents the formation of PAK2 activation complexes induced by IL-31R activation. These results suggest that PQA-18 inhibits the IL-31 pathway through suppressing PAK2 activity, which suppresses sensory nerve outgrowth. PQA-18 may be a valuable lead for the development of a novel drug for pruritus of AD.

Lactobacillus paracasei KBL382 administration attenuates atopic dermatitis by modulating immune response and gut microbiota

Administration of probiotics has been linked to immune regulation and changes in gut microbiota composition, with effects on atopic dermatitis (AD). In this study, we investigated amelioration of the symptoms of AD using Lactobacillus paracasei KBL382 isolated from the feces of healthy Koreans. Mice with Dermatophagoides farinae extract (DFE)-induced AD were fed 1 × 109 CFU d-1 of L. paracasei KBL382 for 4 weeks. Oral administration of L. paracasei KBL382 significantly reduced AD-associated skin lesions, epidermal thickening, serum levels of immunoglobulin E, and immune cell infiltration. L. paracasei KBL382-treated mice showed decreased production of T helper (Th)1-, Th2-, and Th17-type cytokines, including thymic stromal lymphopoietin, thymus, and activation-regulated chemokine, and macrophage-derived chemokine, and increased production of the anti-inflammatory cytokine IL-10 and transforming growth factor-β in skin tissue. Intake of L. paracasei KBL382 also increased the proportion of CD4+ CD25+ Foxp3+ regulatory T cells in mesenteric lymph nodes. In addition, administration of L. paracasei KBL382 dramatically changed the composition of gut microbiota in AD mice. Administration of KBL382 significantly ameliorates AD-like symptoms by regulating the immune response and altering the composition of gut microbiota.

Lactobacillus paracasei KBL382 administration attenuates atopic dermatitis by modulating immune response and gut microbiota

Administration of probiotics has been linked to immune regulation and changes in gut microbiota composition, with effects on atopic dermatitis (AD). In this study, we investigated amelioration of the symptoms of AD using Lactobacillus paracasei KBL382 isolated from the feces of healthy Koreans. Mice with Dermatophagoides farinae extract (DFE)-induced AD were fed 1 × 10⁹ CFU d^-1 of L. paracasei KBL382 for 4 weeks. Oral administration of L. paracasei KBL382 significantly reduced AD-associated skin lesions, epidermal thickening, serum levels of immunoglobulin E, and immune cell infiltration. L. paracasei KBL382-treated mice showed decreased production of T helper (Th)1-, Th2-, and Th17-type cytokines, including thymic stromal lymphopoietin, thymus, and activation-regulated chemokine, and macrophage-derived chemokine, and increased production of the anti-inflammatory cytokine IL-10 and transforming growth factor-β in skin tissue. Intake of L. paracasei KBL382 also increased the proportion of CD4+ CD25+ Foxp3+ regulatory T cells in mesenteric lymph nodes. In addition, administration of L. paracasei KBL382 dramatically changed the composition of gut microbiota in AD mice. Administration of KBL382 significantly ameliorates AD-like symptoms by regulating the immune response and altering the composition of gut microbiota.

Comparison of the presentation of atopic dermatitis induced by trinitrochlorobenzene and house dust mite in NC/Nga mice

Background

Atopic dermatitis (AD) is a common chronic inflammatory skin disease. To understand AD, there have been many trials establishing AD animal models. Although various trials to establish AD animal models have been existed, even the mechanisms of AD in animal models are not enough clarified.

Objectives

This study assessed AD characteristics induced in Nishiki-nezumi Cinnamon/Nagoya (Nc/Nga) mice following trinitrochlorobenzene (TNCB) treatment for different periods and house dust mite (HDM) treatment to compare each model's immunological patterns, especially with cytokine antibody array tool.

Methods

In this study, we exposed Nc/Nga mice to TNCB or HDM extract to induce AD. Nc/Nga mice were divided into 4 groups: control, TNCB 2 weeks-treated, TNCB 8 weeks-treated, and HDM-treated groups. After AD induction, all mice were evaluated by serum immunoglobulin E (IgE) concentration and serum cytokine antibody assays, scoring of skin lesions, scoring of scratching frequency, and histological analysis.

Results

The results showed significant differences between groups in serum IgE concentration, skin lesion scores, and scratching frequency. The analysis results for serum cytokine antibody arrays showed that in the TNCB 8 weeks- and HDM-treated groups, but not in the TNCB 2 weeks-treated group, expressions of genes related to the immune response were enriched. Among the histological results, the skin lesions in the HDM-treated group were most similar to those of AD.

Conclusions

We confirmed that immunological pattern of AD mice was markedly different between HDM and TNCB treated groups. In addition, the immunological pattern was quietly different dependent on TNCB treated duration.

Advances in Understanding the Initial Steps of Pruritoceptive Itch: How the Itch Hits the Switch

Pruritoceptive (dermal) itch was long considered an accompanying symptom of diseases, a side effect of drug applications, or a temporary sensation induced by invading pruritogens, as produced by the stinging nettle. Due to extensive research in recent years, it was possible to provide detailed insights into the mechanism of itch mediation and modulation. Hence, it became apparent that pruritus is a complex symptom or disease in itself, which requires particular attention to improve patients’ health. Here, we summarize recent findings in pruritoceptive itch, including how this sensation is triggered and modulated by diverse endogenous and exogenous pruritogens and their receptors. A differentiation between mediating pruritogen and modulating pruritogen seems to be of great advantage to understand and decipher the molecular mechanism of itch perception. Only a comprehensive view on itch sensation will provide a solid basis for targeting this long-neglected adverse sensation accompanying numerous diseases and many drug side effects. Finally, we identify critical aspects of itch perception that require future investigation.

Feline Interleukin-31 Shares Overlapping Epitopes with the Oncostatin M Receptor and IL-31RA

Interleukin-31 (IL-31) is a major protein involved in severe inflammatory skin disorders. Its signaling pathway is mediated through two type I cytokine receptors, IL-31RA (also known as the gp130-like receptor) and the oncostatin M receptor (OSMR). Understanding molecular details in these interactions would be helpful for developing antagonist anti-IL-31 monoclonal antibodies (mAbs) as potential therapies. Previous studies suggest that human IL-31 binds to IL-31RA and then recruits OSMR to form a ternary complex. In this model, OSMR cannot interact with IL-31 in the absence of IL-31RA. In this work, we show that feline IL-31 (fIL-31) binds independently with feline OSMR using surface plasmon resonance, an enzyme-linked immunosorbent assay, and yeast surface display. Moreover, competition experiments suggest that OSMR shares a partially overlapping epitope with IL-31RA. We then used deep mutational scanning to map the binding sites of both receptors on fIL-31. In agreement with previous studies of the human homologue, the binding site for IL31-RA contains fIL-31 positions E20 and K82, while the binding site for OSMR comprises the "PADNFERK" motif (P103-K110) and position G38. However, our results also revealed a new overlapping site, composed of positions R69, R72, P73, D76, D81, and E97, between both receptors that we called the "shared site". The conformational epitope of an anti-feline IL-31 mAb that inhibits both OSMR and IL-31RA also mapped to this shared site. Combined, our results show that fIL-31 binds IL-31RA and OSMR independently through a partially shared epitope. These results suggest reexamination of the putative canonical mechanisms for IL-31 signaling in higher animals.

Antipruritic Effects of Kappa Opioid Receptor Agonists: Evidence from Rodents to Humans

Centrally administered bombesin induces scratching and grooming in rats. These behaviors were blocked by early benzomorphan kappa opioid receptor (KOR) agonists as reported by Gmerek and Cowan in 1984. This was the first evidence that KORs may be involved in the sensation of itch-like behaviors. Subsequent development of additional animal models for acute and chronic itch has led to important discoveries since then. For example, it was found that (a) gastrin-releasing peptide (GRP), natriuretic polypeptide b and their cognate receptors are keys for the transmission of itch sensation at the spinal cord level, (b) dynorphins (Dyns), the endogenous KOR agonists, work as inhibitory neuromodulators of itch at the spinal cord level, (c) in a mouse model for acute itch, certain KOR antagonists elicit scratching, (d) in mouse models of acute or chronic itch, KOR agonists (e.g., U50,488, nalfurafine, CR 845, nalbuphine) suppress scratching induced by different pruritogens, and (e) nalfurafine, CR 845, and nalbuphine are in the clinic or in clinical trials for pruritus associated with chronic kidney disease and chronic liver disease, as well as pruritus in chronic skin diseases.

Characteristics of Pruritus according to Morphological Phenotype of Psoriasis and Association with Neuropeptides and Interleukin-31

Background

Pruritus is a common symptom in psoriasis. However, few studies have assessed the characteristics of pruritus according to morphological phenotypes of psoriasis.

Objective

To investigate the characteristics of pruritus according to morphological phenotypes of psoriasis and to assess the association with inflammatory mediators related to pruritus.

Methods

Psoriasis patients were divided into 2 groups according to clinical phenotype: eruptive inflammatory (EI) and chronic stable (CS). Clinical data of pruritus were assessed by an itch questionnaire. Serum neuropeptides and cytokines including substance P, histamine, vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide and interleukin-31 (IL-31) were quantitatively measured.

Results

In total, 50 patients with psoriasis (30 male, 20 female; mean age, 45.7 years) were studied (EI, n=15 and CS, n=35). Pruritus was reported by 80% of EI and CS patients. There were no significant differences in prevalence of pruritus, pruritus intensity, severity of psoriasis, serum neuropeptides, or IL-31 between the 2 groups.

Conclusion

The morphological phenotype does not seem to be an important factor affecting the prevalence and characteristics of pruritus in psoriasis.

Administration of Lactobacillus fermentum KBL375 Causes Taxonomic and Functional Changes in Gut Microbiota Leading to Improvement of Atopic Dermatitis

Gut microbiota play an important role in immune responses and energy metabolism. In this study, we evaluated whether administration of Lactobacillus fermentum (L. fermentum) KBL375 isolated from healthy Korean feces improves the atopic dermatitis using the house dust mite (Dermatophagoides farinae)-induced atopic dermatitis (AD) mouse model. Administration of L. fermentum KBL375 significantly decreased dermatitis score, ear and dorsal thickness, and serum immunoglobulin E level in AD-induced mice. Significant reductions in mast cells and eosinophils were discovered in skin tissues from L. fermentum KBL375-treated mice. T helper 2 cell-related cytokines interleukin (IL)-4, IL-5, IL-13, and IL-31 significantly decreased, and anti-inflammatory cytokine IL-10 or transforming growth factor-β increased in skin tissues from L. fermentum KBL375-treated mice. In addition to phenotypic changes in skin tissues, L. fermentum KBL375 treatment induced an increase in the CD4+CD25+Foxp3+ cell population in mesenteric lymph nodes. Taxonomic and functional analyses of gut microbiota showed significantly higher cecum bacterial diversities and abundances including genus Bilophila, Dorea, and Dehalobacterium in L. fermentum KBL375-treated mice. Metabolic analysis of the cecum also showed significant changes in the levels of various amino acids including methionine, phenylalanine, serine, and tyrosine, as well as short chain fatty acids such as acetate, butyrate, and propionate in AD-induced mice due to L. fermentum KBL375 treatment. These altered metabolites in AD-induced mice returned to the levels similar to those in control mice when treated with L. fermentum KBL375. Therefore, L. fermentum KBL375 could be useful for AD treatment by modulating the immune system and inducing various metabolites.

Disease-specific primed human adult stem cells effectively ameliorate experimental atopic dermatitis in mice

Although human mesenchymal stem cells (hMSCs) hold considerable promise as an alternative therapeutic reagent for allergic disorders including atopic dermatitis (AD), the strategy for enhancing hMSC-based therapy remains challenging. We sought to investigate whether preconditioning with mast cell (MC) granules could enhance the therapeutic efficiency of human umbilical cord blood-derived MSCs (hUCB-MSCs) against AD.

Methods: AD was experimentally induced in NC/Nga mice by repeated applications of 4% sodium dodecyl sulfate (SDS) and dermatophagoides farinae (Df) extract, and preconditioned hUCB-MSCs were subcutaneously injected. The therapeutic effect was determined by gross examination and additional ex vivo experiments performed using blood and skin samples to determine the resolution of allergic inflammation. To explore the underlying mechanisms, several co-culture assays with primary isolated immune cells and wound closure assays were conducted.

Results: Pretreatment of MC granules enhanced the therapeutic effects of hUCB-MSCs by attenuating the symptoms of AD in an experimental animal model. MC granule-primed cells suppressed the activation of major disease-inducing cells, MCs and B lymphocytes more efficiently than naïve cells both in vitro and in vivo. Histamine-mediated upregulation of the COX-2 signaling pathway was shown to play a crucial role in suppression of the allergic immune response by MC-pretreated hUCB-MSCs. Moreover, MC pretreatment improved the wound healing ability of hUCB-MSCs.

Conclusions: Our findings indicate that pre-exposure to MC granules improved the therapeutic effect of hUCB-MSCs on experimental AD by resolving the allergic immune reaction and accelerating the tissue regeneration process more efficiently than naïve cells, suggesting a potential enhancement strategy for stem cell-based therapy.

Biological Therapeutic Treatment of Atopic Dermatitis

Atopic dermatitis is a chronic recurrent inflammatory disease caused, inter alia, by violations of the barrier function of the skin and pathological immune response in the form of an imbalance of Th1 and Th2 lymphocytes with increased production of IL-4, IL-5, IL-13, IL-31. Treatment of severe forms of atopic dermatitis is not an easy task due to the variability of the individual response to treatment, the short duration of the therapeutic effect and the frequent development of undesirable phenomena associated with the use of existing methods of systemic immunosuppressive therapy. The study of the pathogenesis of atopic dermatitis made it possible to identify the spectrum of molecular targets, providing the basis for researching alternative variants to the previously used systemic therapy methods – genetic engineering biological preparations. Contemporary data on the pathogenesis of atopic dermatitis as well as potential molecular targets for innovative biological preparations, the efficacy of which has been evaluated through clinical trials, are presented in the review. 

Therapeutic Effects of Korean Red Ginseng Extract in a Murine Model of Atopic Dermatitis: Anti-pruritic and Anti-inflammatory Mechanism

Korean red ginseng (KRG) and ginsenosides exhibit diverse biological effects, including anti-inflammatory and anti-allergic. We aimed to investigate the therapeutic effect of KRG in a murine model of atopic dermatitis (AD) is mediated whether by diminishing the pruritus or by suppressing the inflammation. Thirty NC/Nga mice were randomly divided to 5 groups. AD-like skin lesions were induced by percutaneous challenge with 2,4,6-trinitro-1-chrolobenzene (TNCB) on the ears and backs of NC/Nga mice. KRG extract, evening primrose oil, cyclosporine, and phosphate-buffered saline were administered orally by a gastric tube. Each study group was also divided into scratching-permitted and scratching-restricted subgroups to evaluate the impact of scratching behavior on AD. The effects of KRG and the other agents were assessed by measuring the clinical severity score, ear thickness, extent of transepidermal water loss (TEWL), number of scratching movements, total systemic immunoglobulin E (IgE) and interleukin (IL)-31 levels, histologic changes of cutaneous lesions, and mRNA expression levels of tumor necrosis factor (TNF)-α, interferon (IFN)-γ, thymic stromal lymphopoietin (TSLP), and IL-31. KRG exerts therapeutic effects against AD by inhibiting the T helper 2 (Th2) mediated inflammation as well as by diminishing the itching sensation. Moreover, restricting scratching behavior suppresses the vicious cycle of itching and scratching, thus reducing clinical and systemic inflammation in our murine model of AD.

Interleukin-31 pathway and its role in atopic dermatitis: a systematic review

BACKGROUND

Atopic dermatitis, a chronic inflammatory disease, has a lifetime prevalence of 10-20%. Atopic dermatitis reduces quality of life, primarily due to pruritus. Interleukin-31 and its target receptor are newly discovered entities that are involved in pruritus.

PURPOSE

To summarize the current understanding of interleukin-31 and its role in atopic dermatitis, potential therapeutic interventions and future prospects.

METHODS

A systematic review was designed to identify articles related to interleukin-31 and its role in pruritus. Predefined queries containing interleukin-31 and related key terms were searched with no past date restriction, through 31 August 2016, using MEDLINE, Cochrane Controlled Trials Register, ClinicalTrials.gov and the International Clinical Trials Registry Platform Search Portal database.

RESULTS

Of 151 identified articles, 61 met eligibility criteria. Interleukin-31 receptors are expressed constitutively on the surface of keratinocytes, eosinophils and small diameter neurons. Overexpression of interleukin-31, independent of mast cells and lymphocytes, induces clinical and histological features consistent with atopic dermatitis. In addition, overexpression of interleukin-31 causes reversible alopecia. Human monoclonal interleukin-31 antagonist, CIM331, decreased pruritus in phase-I and phase-II clinical trials.

CONCLUSIONS

Interleukin-31 plays an important role in atopic dermatitis and alopecia. Inhibiting this pathway may provide an alternative to antihistamines for the pruritus of atopic dermatitis.

Genetic and epigenetic studies of atopic dermatitis

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Atopic dermatitis: allergic dermatitis or neuroimmune dermatitis?

Advances in knowledge of neurocellulars relations have provided new directions in the understanding and treatment of numerous conditions, including atopic dermatitis. It is known that emotional, physical, chemical or biological stimuli can generate more accentuated responses in atopic patients than in non-atopic individuals; however, the complex network of control covered by these influences, especially by neuropeptides and neurotrophins, and their genetic relations, still keep secrets to be revealed. Itching and airway hyperresponsiveness, the main aspects of atopy, are associated with disruption of the neurosensory network activity. Increased epidermal innervation and production of neurotrophins, neuropeptides, cytokines and proteases, in addition to their relations with the sensory receptors in an epidermis with poor lipid mantle, are the aspects currently covered for understanding atopic dermatitis.

The first trial of CIM331, a humanized antihuman interleukin-31 receptor A antibody, in healthy volunteers and patients with atopic dermatitis to evaluate safety, tolerability and pharmacokinetics of a single dose in a randomized, double-blind, placebo-controlled study

BACKGROUND

The cytokine interleukin-31 (IL-31) is considered to be responsible for the development of pruritus in humans. At present, no available evidence has been provided on the safety and efficacy of blocking the IL-31 signal in humans for the amelioration of pruritus in atopic dermatitis (AD). CIM331 is a humanized antihuman IL-31 receptor A (IL-31RA) monoclonal antibody, which binds to IL-31RA to inhibit subsequent IL-31 signalling.

OBJECTIVES

To assess the tolerability, safety, pharmacokinetics and preliminary efficacy of CIM331 in healthy Japanese and white volunteers, and Japanese patients with AD.

METHODS

In this randomized, double-blind, placebo-controlled phase I/Ib study, CIM331 was administered in a single subcutaneous dose. The primary outcomes were safety and tolerability; the exploratory analysis was efficacy.

RESULTS

No deaths, serious adverse events (AEs) or discontinuations due to AEs were reported in any part of the study. No dose-dependent increase in the incidence of AEs occurred in any part of the study. In healthy volunteers, all AEs occurred once in the placebo groups, and increased creatine phosphokinase was more common in the CIM331 groups. In patients with AD, CIM331 reduced pruritus visual analogue scale score to about -50% at week 4 with CIM331 compared with -20% with placebo. CIM331 increased sleep efficiency and decreased the use of hydrocortisone butyrate.

CONCLUSIONS

A single subcutaneous administration of CIM331 was well tolerated in healthy volunteers and patients with AD. It decreased pruritus, sleep disturbance and topical use of hydrocortisone. CIM331 may become a novel therapeutic option for AD by inhibiting IL-31.

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.

Th2 Cytokines Augment IL-31/IL-31RA Interactions via STAT6-dependent IL-31RA Expression

Interleukin 31 receptor α (IL-31RA) is a novel Type I cytokine receptor that pairs with oncostatin M receptor to mediate IL-31 signaling. Binding of IL-31 to its receptor results in the phosphorylation and activation of STATs, MAPK, and JNK signaling pathways. IL-31 plays a pathogenic role in tissue inflammation, particularly in allergic diseases. Recent studies demonstrate IL-31RA expression and signaling in non-hematopoietic cells, but this receptor is poorly studied in immune cells. Macrophages are key immune-effector cells that play a critical role in Th2-cytokine-mediated allergic diseases. Here, we demonstrate that Th2 cytokines IL-4 and IL-13 are capable of up-regulating IL-31RA expression on both peritoneal and bone marrow-derived macrophages from mice. Our data also demonstrate that IL-4Rα-driven IL-31RA expression is STAT6 dependent in macrophages. Notably, the inflammation-associated genes Fizz1 and serum amyloid A (SAA) are significantly up-regulated in M2 macrophages stimulated with IL-31, but not in IL-4 receptor-deficient macrophages. Furthermore, the absence of Type II IL-4 receptor signaling is sufficient to attenuate the expression of IL-31RA in vivo during allergic asthma induced by soluble egg antigen, which may suggest a role for IL-31 signaling in Th2 cytokine-driven inflammation and allergic responses. Our study reveals an important counter-regulatory role between Th2 cytokine and IL-31 signaling involved in allergic diseases.

IL-31 is overexpressed in lichen planus but its level does not correlate with pruritus severity

Background. Pruritus is one of the major features of lichen planus (LP); however, its pathogenesis remains largely unknown. Objective. The aim of our study was to analyze the role of IL-31 in the pathogenesis of pruritus in LP. Materials and Methods. The study group included 22 patients with LP. Control group consisted of 14 healthy volunteers. All subjects underwent thorough examination. Pruritus severity was evaluated with the visual analogue scale (VAS) and the 12-item Itch Questionnaire. IL-31 expression in the skin was assessed using semiquantitative immunofluorescence analysis. Results. Pruritus maximal intensity according to VAS was 6.5 ± 2.7 points and according to the 12-item Itch Questionnaire 6.9 ± 2.8 points. Lesional LP skin showed significantly higher IL-31 expression compared to healthy skin (P < 0.001). The most abundant immunofluorescence was observed within granular layer. However, there was no correlation between expression of IL-31 and pruritus intensity assessed according to VAS (VAS_max: ρ = −0.08, P = 0.73), as well as 12-item Itch Questionnaire: ρ = −0.11, P = 0.65. Conclusions. Pruritus is a very common symptom of LP. For the first time we have demonstrated that IL-31 is overexpressed in the lesional skin of LP but its expression does not correlate with intensity of pruritus.

Repeated administration of IL-31 upregulates IL-31 receptor A (IL-31RA) in dorsal root ganglia and causes severe itch-associated scratching behaviour in mice

We investigated the effects of repeated administration of interleukin-31 (IL-31) on itch-associated scratching counts (long-lasting scratching, LLS) and IL-31-related receptor mRNA expression in mice. Intra-dermal (i.d.) injection of IL-31 (100 and 300 ng/site) every 12 h for 3 days significantly increased LLS. Repeated administration of IL-31 also increased the expression of IL-31 receptor A (IL-31RA) and oncostatin M receptor beta (OSMRβ) in dorsal root ganglia (DRG). After the repeated administration of IL-31 was discontinued, IL-31RA expression decreased and reached the baseline level 2 days after the last dose of IL-31. LLS changed along with DRG IL-31RA expression. Moreover, IL-31-induced IL-31RA protein expression was confirmed by Western blotting analysis. These data suggest that IL-31 upregulates IL-31RA expression in DRG neuron cell bodies, and cutaneous-injected IL-31-induced itching is enhanced by DRG IL-31RA expression in mice.

A single dose of interleukin-31 (IL-31) causes continuous itch-associated scratching behaviour in mice

We investigated the effects of a single dose of mouse interleukin-31 (IL-31) on scratching behaviour in comparison with spontaneous skin-lesion- or serotonin (5-HT)- induced scratching behaviour in NC/Nga and BALB/c mice. Intradermal (i.d.) injection of IL-31 caused a gradual increase in long-lasting scratching (LLS, over 1.5 s) about 3 h after administration followed by a gradual decrease for over 24 h after administration. I.d. injection of IL-31 significantly increased the total LLS counts/24 h but not short-lasting scratching (SLS, 0.3-1.5 s). In skin-lesioned NC/Nga mice, the LLS but not SLS counts were significantly higher than those in non-skin-lesioned NC/Nga mice. We also investigated 5-HT-induced scratching in BALB/c mice, SLS but not LLS increased immediately after the injection and then decreased to baseline after at 20 min. These results suggest that IL-31 may participate in the sensation of itching and promote scratching behaviour in skin-lesioned NC/Nga mice, an animal model of atopic dermatitis (AD).

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.

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.

A sensory neuron-expressed IL-31 receptor mediates T helper cell-dependent itch: Involvement of TRPV1 and TRPA1

BACKGROUND

Although the cytokine IL-31 has been implicated in inflammatory and lymphoma-associated itch, the cellular basis for its pruritic action is yet unclear.

OBJECTIVE

We sought to determine whether immune cell-derived IL-31 directly stimulates sensory neurons and to identify the molecular basis of IL-31-induced itch.

METHODS

We used immunohistochemistry and quantitative real-time PCR to determine IL-31 expression levels in mice and human subjects. Immunohistochemistry, immunofluorescence, quantitative real-time PCR, in vivo pharmacology, Western blotting, single-cell calcium imaging, and electrophysiology were used to examine the distribution, functionality, and cellular basis of the neuronal IL-31 receptor α in mice and human subjects.

RESULTS

Among all immune and resident skin cells examined, IL-31 was predominantly produced by TH2 and, to a significantly lesser extent, mature dendritic cells. Cutaneous and intrathecal injections of IL-31 evoked intense itch, and its concentrations increased significantly in murine atopy-like dermatitis skin. Both human and mouse dorsal root ganglia neurons express IL-31RA, largely in neurons that coexpress transient receptor potential cation channel vanilloid subtype 1 (TRPV1). IL-31-induced itch was significantly reduced in TRPV1-deficient and transient receptor channel potential cation channel ankyrin subtype 1 (TRPA1)-deficient mice but not in c-kit or proteinase-activated receptor 2 mice. In cultured primary sensory neurons IL-31 triggered Ca(2+) release and extracellular signal-regulated kinase 1/2 phosphorylation, inhibition of which blocked IL-31 signaling in vitro and reduced IL-31-induced scratching in vivo.

CONCLUSION

IL-31RA is a functional receptor expressed by a small subpopulation of IL-31RA(+)/TRPV1(+)/TRPA1(+) neurons and is a critical neuroimmune link between TH2 cells and sensory nerves for the generation of T cell-mediated itch. Thus targeting neuronal IL-31RA might be effective in the management of TH2-mediated itch, including atopic dermatitis and cutaneous T-cell lymphoma.

Mediators of pruritus in lichen planus

Lichen planus (LP) is an inflammatory mucocutaneous disease, showing a wide variety of clinical subtypes. The classic presentation of LP involves the appearance of polygonal, flat-topped, violaceous papules and plaques with reticulated white lines, termed “Wickham's striae”. Cutaneous lesions tend to be extremely pruritic, and this symptom does not subside after common antipruritic treatment. Moreover, based on our previous pilot study, it could be stated, that itch is the most unpleasant and bothersome symptom of LP for majority of patients suffering from this disease. However, the underlying mechanisms of itch in lichen planus remain still unknown. In addition, there is no study on mediators of this sensation, but taking into account pathogenesis of LP there are some possible mediators implicated to transmit or modulate itch. In pathogenesis of LP important are such mechanisms as apoptosis, autoimmune reaction, and role of stress. With these pathways some, previously described in other diseases, itch mediators such as cytokines, proteases, and opioid system are connected. Whether these mechanisms are involved in pruritus accompanying LP requires further investigation. Limited knowledge of pruritus origin in lichen planus is responsible for the lack of the effective antipruritic treatments. Here, we describe possible mechanisms participating the pathogenesis of pruritus in lichen planus.

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.