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

Gut microbes-spinal connection is required for itch sensation

The gut microbiota has been linked to a number of neurological disorders. However, it is unclear whether the gut microbiota is involved in the genesis of chronic itch, a refractory condition that afflicts patients both physically and mentally. Here, we report that depletion of gut microbiota enhances tolerance to itch in mice orally administered with antibiotics (ABX) and mice free of germ. Of note, oral gavage with Bacteroides fragilis (B. fragilis), a prominent species of the genus Bacteroides with most differential change, corrected the ABX-induced itch dysfunction through its driven metabolite acetyl-l-carnitine (ALC). Mechanistically, gut microbiota or B. fragilis depletion caused a decrease in RNA N6-methyladenosine (m6A) demethylase FTO expression in the dorsal horn and a consequent increase in RNA m6A sites in Mas-related G protein-coupled receptor F (MrgprF) mRNA, leading to decreased MRGPRF protein. The downregulation of FTO was triggered by inactivation of ETS proto-oncogene 1 (ETS1), a transcription factor that binds to the Fto promoter. These findings support a gut microbe - spinal connection in modulation of itch sensation in RNA m6A epigenetic-dependent manner and highlight a critical role of ALC in linking the altered B. fragilis and itch dysfunction.

Dupilumab, a Novel Treatment for Peripheral Neuropathy: A Case Series

Peripheral neuropathy is a chronic neurological disorder that can present with a multitude of symptoms. It is observed in association with various disease states and organ systems. In the process of treatment for atopic dermatitis, we have observed that patients reported improvements in their previously diagnosed neuropathies, essentially, relief from neuropathic symptoms such as burning, itching, or tingling. On the basis of these observations, we conducted a single-arm trial to survey the qualitative changes in patients with peripheral neuropathy. Ten patients with atopic dermatitis with previously diagnosed peripheral neuropathies were treated with dupilumab (DP) and observed for symptom changes over 6 months. A paired t-test was used to determine whether DP might potentially be used as an off-label treatment for patients with peripheral neuropathy and dermatological conditions. Our patients showed significant symptom relief, thus suggesting that further investigation of the use of DP for patients with neuropathies is warranted.

Cross-regulation between the nervous system and type 2 immunity

Interactions between the nervous and immune systems are critical to healthy physiology and are altered in many human diseases. Many of the major players in type 2 immune responses, including type 2 lymphocytes and cytokines, mast cells, and immunoglobulin E, have been implicated in neuronal function and behavior. Conversely, neurons in both the central and peripheral nervous systems can affect type 2 immune responses and behaviors relevant to allergy, such as food avoidance. Defining this complex circuitry and its molecular intermediates in physiology may reveal type 2 immunomodulators that can be harnessed for therapeutic benefit in neurologic diseases including Alzheimer's disease, brain injury, and neurodevelopmental disorders. Conversely, modulation of the nervous system may be an important adjunct to treating immunologic disorders including atopic dermatitis, asthma, and food allergy. This Review covers recent work defining how the nervous system can both regulate and be regulated by type 2 immune responses.

The sensory neuroimmune frontier

Sensing and recognition are key properties of both the immune and nervous systems. In the immune system, pattern recognition or antigen-specific receptors represent classic motifs in innate and adaptive immunity, respectively. In the nervous system, there is a major anatomic division between how we sense stimuli from within the body (vagal sensory nervous system) and the outside world (somatosensory nervous system). However, in the last 5 years, there has been an explosion of discoveries revealing interactions between the immune and the sensory nervous systems that govern an array of physiologic and pathologic processes including allergy, infection, autoimmunity, regeneration, cancer, and beyond. Herein, we highlight recent advances that demonstrate how peripheral sensory neuroimmunology has emerged as a powerful field that provides new insights into classic immunologic processes including immune hypersensitivity, inflammation, and tissue homeostasis.

Role of specialized sensory neuron subtypes in modulating peripheral immune responses

The immune and sensory nervous systems detect diverse threats, from tissue damage to infection, and coordinate protective responses to restore homeostasis. Like immune cells, sensory neurons exhibit remarkable heterogeneity, with advanced genetic models revealing that distinct subsets differentially regulate immune responses. Here, we review how various immune signals engage distinct subtypes of sensory neurons to mediate inflammatory pain, itch, relief, protective behavioral adaptations, and autonomic reflexes. We also highlight how specialized sensory neuron populations modulate immune function through the release of neuropeptides, neurokines, or glutamate. This functional specialization enables precise immunomodulation adapted to the kinetics and nature of immune responses, positioning sensory neurons as key regulators of host defense and tissue homeostasis.

Investigation of the participation of the TRPV1 receptor in the irritant effect of dithranol in mice

Dithranol is one of the most effective topical medications for treating plaque psoriasis. However, its clinical use is limited by irritative adverse reactions to the skin, such as oedema, erythema, and pruritus, caused by poorly understood mechanisms. Because TRPV1 activation mediates skin irritation caused by several drugs, we conducted blind and randomised experiments in male and female C57BL/6 mice to elucidate the role of TRPV1 in dithranol-induced irritation. Dithranol (0.01%-0.5%) or vehicle was applied topically to the right ear of the animals. Oedema, erythema, and pruritus were monitored from 2 h to 6 days after application. Treatment with 0.5% dithranol caused oedema and erythema, but not pruritus, starting at 6 h, reaching its highest point at 1 day, and persisting up to 6 days after treatment, mainly in male mice. The 0.1% dose induced erythema but not oedema. Interestingly, topical application of 1% capsaicin was shown to defunctionalise TRPV1-positive fibres and did not influence early irritation caused by dithranol (2 h-2 days). However, it increased the late phase of irritation (5-6 days). Similarly, salicylate did not reduce the early irritation caused by dithranol but also increased the late phase. Antagonism by SB366791 and 4-tert-butylcyclohexanol did not alter skin irritation. Our results suggest that, contrary to our initial hypothesis, TRPV1 appears to act protectively against skin irritation caused by dithranol, particularly in the late stage.

Prevalence and Mechanisms of Itch in Chronic Wounds: A Narrative Review

Itch is a commonly experienced problem by individuals with chronic wounds and greatly compromises their quality of life. Scratching can further hinder the wound healing process. Despite this being a clinically recognized issue, our knowledge of its exact prevalence in chronic wounds of different types and the molecular mechanisms driving it is limited. The multifactorial nature of wound itch makes its characterization particularly challenging. The present review is based on a thorough PubMed search, and it aims to provide an overview of existing evidence on the epidemiology, impact, and pathophysiology of wound itch, along with general recommendations on its management. Importantly, our work highlights the merit of screening chronic wound patients for associated pruritus and incorporating anti-itch measures in mainstream wound care.

Keratinocytes: new perspectives in inflammatory skin diseases

Keratinocytes, the predominant cell type in the epidermis, are indispensable for maintaining skin barrier integrity, mediating host defense, and orchestrating immune responses. Beyond these well-established functions, emerging evidence reveals their dynamic interactions with the nervous system and their capacity to retain inflammatory memory. These discoveries position keratinocytes as key drivers of the onset, progression, and relapse of inflammatory skin diseases. In this review, we delve into the mechanisms underlying keratinocyte crosstalk with immune and neural cells, the metabolic reprogramming, including lactate and other metabolites, that may drive inflammatory memory, and the broader implications for disease pathogenesis and recurrence. Finally, we discuss the challenges to, and therapeutic potential of, targeting keratinocytes for the treatment of chronic inflammatory skin conditions.

Febrile temperature-regulated TRPV1 in CD4+ T cells mediates neuroinflammation in complex febrile seizures

BACKGROUND

Febrile seizures (FS) are the most prevalent convulsive disorder in children characterized by a high recurrence rate. However, the interaction between adaptive and innate immunity in the recurrence of FS remains poorly understood, and the molecular pathways involved are unclear. The objective of this study is to elucidate the role of Th17 cells in seizure susceptibility following complex febrile seizures (CFS), and to explore the regulatory mechanisms underlying Th17 cell differentiation and function under hyperthermic conditions through transient receptor potential vanilloid 1 (TRPV1).

METHODS

RNA sequencing was employed to validate the seizure susceptibility following CFS and to explore the potential mechanisms by which high temperature contributes to Th17 cell differentiation. Neuronal excitability and damage were examined using Multi-electrode array (MEA) analysis and Nissl staining. Flow cytometry, chromatin immunoprecipitation (ChIP) analysis, and immunofluorescence (IF) were applied to examine how TRPV1 facilitates Th17 cell differentiation.

RESULTS

Our study demonstrates that proinflammatory Th17 cells exhibit enhanced differentiation in a CFS mouse model and exacerbate blood-brain barrier (BBB) disruption. After infiltrating the central nervous system (CNS), Th17 cells promote neuroinflammation by activating microglia via IL-17A. Mechanistically, TRPV1 is critical for Th17 cell differentiation and function. Activated by febrile temperature both in vivo and in vitro, TRPV1 facilitates calcium ion influx, leading to the nuclear localization of nuclear factor of activated T cell 2 and 4 (NFAT2/4) and the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Knockdown of TRPV1 attenuates Th17 cell differentiation and CNS infiltration, thereby protecting the BBB and reducing seizure susceptibility following CFS.

CONCLUSION

These results highlight the critical interplay between adaptive and innate immunity in CFS. The TRPV1/NFATs/STAT3 signaling pathway regulates Th17 cell differentiation and function under febrile conditions, revealing a promising therapeutic target for intervention.

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

Objective

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

Methods

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

Results

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

Conclusion

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

Neuroimmune Circuits in Allergic Diseases

Communication between the nervous and immune systems is evolutionarily conserved. From primitive eukaryotes to higher mammals, neuroimmune communication utilizes multiple complex and complementary mechanisms to trigger effective but balanced responses to environmental dangers such as allergens and tissue damage. These responses result from a tight integration of the nervous and immune systems, and accumulating evidence suggests that this bidirectional communication is crucial in modulating the initiation and development of allergic inflammation. In this review, we discuss the basic mechanisms of neuroimmune communication, with a focus on the recent advances underlying the importance of such communication in the allergic immune response. We examine neuronal sensing of allergens, how neuropeptides and neurotransmitters regulate allergic immune cell functions, and how inflammatory factors derived from immune cells coordinate complex peripheral and central nervous system responses. Furthermore, we highlight how fundamental aspects of host biology, from aging to circadian rhythm, might affect these pathways. Appreciating neuroimmune communications as an evolutionarily conserved and functionally integrated system that is fundamentally involved in type 2 immunity will provide new insights into allergic inflammation and reveal exciting opportunities for the management of acute and chronic allergic diseases.

Neuroimmune mechanisms of type 2 inflammation in the skin and lung

Type 2 inflammation has a major role in barrier tissues such as the skin and airways and underlies common conditions including atopic dermatitis (AD) and asthma. Cytokines including interleukin 4 (IL-4), IL-5, and IL-13 are key immune signatures of type 2 inflammation and are the targets of multiple specific therapeutics for allergic diseases. Despite shared core immune mechanisms, the distinct structures and functions of the skin and airways lead to unique therapeutic responses. It is increasingly recognized that the nervous system has a major role in sensing and directing inflammatory processes. Indeed, crosstalk between type 2 immune activation and somatosensory functions mediates tissue-specific signatures such as itching in the skin. However, neuroimmune interactions are shaped by distinct neuronal and immune landscapes, and differ between the skin and airways. In the skin, dorsal root ganglia-derived neurons mediate pruritus via type 2 cytokines and neurogenic inflammation by mast cell or basophil activation. Conversely, vagal ganglia-derived neurons regulate airway immune responses by releasing neuropeptides/neurotransmitters such as calcitonin gene-related peptides, neuromedin U, acetylcholine, and noradrenaline. Sensory neuron-derived vasoactive intestinal peptide forms a feedback loop with IL-5, amplifying eosinophilic inflammation in the airways, a mechanism that is absent in the skin. These differences influence the efficacy of cytokine-targeted therapies. For instance, IL-4/IL-13-targeted therapies like dupilumab demonstrate efficacy in AD and allergic airway diseases, whereas IL-5-targeted therapies are effective in eosinophilic asthma but not AD. Understanding these neuroimmune interactions underscores the need for tailored therapeutic approaches to address allergic diseases where barrier tissues are involved.

Characterization and targeting of the endosomal signaling of the gastrin releasing peptide receptor in pruritus

Chronic pruritus is a major unmet clinical problem affecting one in four adults. G protein-coupled receptors (GPCRs) are key receptors driving itch signaling and are a therapeutic target for itch relief. The endosomal signaling of GPCRs provides new challenges for understanding how GPCR signaling is regulated, how endosomal signaling of GPCRs contributes to disease states like chronic pruritus and opens new targets for therapeutic development. The Gastrin releasing peptide receptor (GRPR) is a key mediator of pruritus in the spinal cord. Yet, little is known about the molecular mechanisms regulating GRPR signaling in pruritus, if GRPR can signal from endosomes, or the role of endosomal GRPR in the development of pruritus. Here we show the importance of internalization and endosomal signaling of GRPR in pruritus. Agonist induced GRPR internalization and trafficking was quantified using BRET or microscopy while endosomal-mediated ERK signaling was measured using compartmentalized FRET biosensors. Recruitment of G proteins to endosomes was measured with NanoBit BRET. pH sensitive mesoporous silica nanoparticles (MSN) which accumulated in endosomes were used to deliver RC-3095, a GRPR specific antagonist, intracellularly to block endosomal signaling of GRPR. MSN-RC proved more effective than free RC-3095 at inhibiting chloroquine scratching in mice. Our results demonstrate a critical role for GRPR endosomal signaling in itch sensation. These results highlight the ability of endosomally targeted antagonist to inhibit GRPR signaling and provide a new target for developing therapeutics that block GRPR mediated pruritus.

Evolving evidence in the neural sensitization of prurigo nodularis

Prurigo nodularis is a chronic inflammatory skin disorder characterized by relentlessly pruritic, hyperkeratotic nodules. Recent studies have provided compelling evidence for the pivotal role of dysregulated interactions between the nervous and immune systems in its pathogenesis. This article reviews the latest findings on the neurogenic mechanisms contributing to prurigo nodularis, particularly how these processes lead to the sensation of increased itch intensity. Peripheral sensitization is primarily driven by abnormal innervation of histamine-independent, small unmyelinated C fibers, epidermal hypoplasia, and dermal hyperinnervation. This sensitization is further amplified by the cyclic release of neuropeptides such as Substance P, calcitonin gene-related peptide, and nerve growth factor. Although the mechanisms underlying central sensitization in prurigo nodularis remain less understood, it likely involves enhanced itch signaling in the dorsal spinal cord or a lowered threshold for itch perception. Additionally, parallels between pruritus and pain-such as allodynia and alloknesis, as well as hyperalgesia and hyperknesis-along with the association of prurigo nodularis with various comorbid systemic conditions, offer valuable insights into the disorder's pathology. A deeper understanding of the complex neural sensitization mechanisms in prurigo nodularis may lead to the identification of novel therapeutic targets, ultimately alleviating the burden of this debilitating condition.

Pruritus and Neuropsychiatric Symptoms Among Patients with Darier Disease-An Overlooked and Interconnected Challenge

(1) Background: Darier disease (DD) is a rare autosomal dominant disorder caused by mutations in ATP2A2, a gene that encodes the sarco(endo)plasmic reticulum calcium-ATPase 2 enzyme, which disrupts calcium homeostasis in keratinocytes. Pruritus, a frequently overlooked symptom in DD, can lead to physical and emotional complications, especially in patients with DD who are genetically predisposed to psychiatric comorbidities. (2) Methods: This study aimed to analyze pruritus and other related symptoms in patients with DD and explore their correlation with neuropsychiatric conditions, psychological challenges, disease severity, and body surface area (BSA) involvement through a retrospective review of a tertiary center. (3) Results: Data from 76 patients (equal gender distribution, mean age 44 years) revealed a prevalence of pruritus of 90.8%, surpassing symptoms such as pain (34.3%) and malodor (43.4%). Burning sensations due to DD lesions were significantly correlated with the diagnosis of comorbid neuropsychiatric conditions (p = 0.047) and psychiatric medication use (p = 0.019). While pruritus correlated with disease severity and %BSA involvement, the findings were not statistically significant. Patients reporting pruritus had a significantly higher Dermatology Life Quality Index symptom score (2.4 ± 1.0), which is defined as the presence of itch, soreness, pain, or stinging, than those who did not (1.5 ± 0.6), indicating accurate symptom reporting. (4) Conclusions: In conclusion, a striking majority of patients with DD experience pruritus, with higher prevalence among those with neuropsychiatric challenges, severe Darier disease, and greater %BSA skin involvement. Clinicians should recognize pruritus as a key therapeutic target and adopt comprehensive treatment approaches that both address the neuropsychiatric comorbidities and the added psychological burden of pruritus in patients with DD.

Subcutaneous Injection and Brush Application of Ovalbumin-Aluminum Salt Solution Induces Dermatitis-like Changes in Mice

Background: Intraperitoneal sensitization combined with topical and/or epicutaneous treatment using an ovalbumin (OVA)-aluminum salt solution (OVA-AL) represents a model for inducing atopic dermatitis (AD). However, the combination of sensitization with subcutaneous treatment and cutaneous application of OVA-AL via a brush has not been explored as a method for inducing AD. Methods: Adult mice were subcutaneously injected with OVA-AL following sensitization on days 0, 7, and 14 and were treated with OVA-AL via brush application to the dorsal skin fortnightly until days 35 and 49. Concomitant alloknesis and skin changes were assessed. Mice of the Balb/c and ICR-CD1 strains were treated with OVA-AL until day 35, with only the ICR-CD1 strain continuing treatment until day 49. Control animals received saline. At 35 and 49 days, dorsal skin was harvested and processed for histological analysis. Results: Mice treated with OVA-AL developed dry skin, with no scratching or alloknesis. Histological examination of dorsal skin revealed an increase in mast cells and collagen deposition. Conclusions: Dermatitis-like symptoms were observed in mice treated with OVA-AL using this administration method.

Neurogenic inflammation and itch in barrier tissues

Once regarded as distinct systems, the nervous system and the immune system are now recognized for their complex interactions within the barrier tissues. The neuroimmune circuitry comprises a dual-network system that detects external and internal disturbances, providing critical information to tailor a context-specific response to various threats to tissue integrity, such as wounding or exposure to noxious and harmful stimuli like pathogens, toxins, or allergens. Using the skin as an example of a barrier tissue with the polarized sensory neuronal responses of itch and pain, we explore the molecular pathways driving neuronal activation and the effects of this activation on the immune response. We then apply these findings to other barrier tissues, to find common pathways controlling neuroimmune responses in the barriers.

Molecular and cellular mechanisms of itch sensation and the anti-itch drug targets

Itch is an uncomfortable feeling that evokes a desire to scratch. This protective reflex can effectively eliminate parasites that invade the skin. When itchy skin becomes severe or lasts for more than six weeks, it has deleterious effects on both quality of life and productivity. Despite decades of research, the complete molecular and cellular coding of chronic itch remains elusive. This persistent condition often defies treatment, including with antihistamines, and poses a significant societal challenge. Obtaining pathophysiological insights into the generation of chronic itch is essential for understanding its mechanisms and the development of innovative anti-itch medications. In this review we provide a systematic overview of the recent advancement in itch research, alongside the progress made in drug discovery within this field. We have examined the diversity and complexity of the classification and mechanisms underlying the complex sensation of itch. We have also delved into recent advancements in the field of itch mechanism research and how these findings hold potential for the development of new itch treatment medications. But the treatment of clinical itch symptoms still faces significant challenges. Future research needs to continue to delve deeper, not only to discover more itch-related pathways but also to explore how to improve treatment efficacy through multitarget or combination therapy.

Updates on the Pathogenesis of Canine Atopic Dermatitis and Feline Atopic Skin Syndrome: Part 2, the Skin Barrier, the Microbiome, and Immune System Dysfunction

Alterations in the lipid layer and intercellular corneocyte connections can lead to increased allergen penetration through the skin surface. A normal cutaneous microbiome keeps the opportunistic pathogen Staphylococcus pseudintermedius levels low, but allergic inflammation leads to decreased diversity and increase in S pseudintermedius. Keratinocytes sound the initial allergen alarm via cytokine signaling and promote T-helper 2 (Th-2) inflammation. Th-2 cytokine products IL-4, IL-13, and IL-31 are increased in the acute allergic inflammatory response. Altered response in T-helper 1, T-helper 17, and T-regulatory cells play a role in both acute and chronic allergic inflammation.

Type 2 immunity in allergic diseases

Significant advancements have been made in understanding the cellular and molecular mechanisms of type 2 immunity in allergic diseases such as asthma, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis (EoE), food and drug allergies, and atopic dermatitis (AD). Type 2 immunity has evolved to protect against parasitic diseases and toxins, plays a role in the expulsion of parasites and larvae from inner tissues to the lumen and outside the body, maintains microbe-rich skin and mucosal epithelial barriers and counterbalances the type 1 immune response and its destructive effects. During the development of a type 2 immune response, an innate immune response initiates starting from epithelial cells and innate lymphoid cells (ILCs), including dendritic cells and macrophages, and translates to adaptive T and B-cell immunity, particularly IgE antibody production. Eosinophils, mast cells and basophils have effects on effector functions. Cytokines from ILC2s and CD4+ helper type 2 (Th2) cells, CD8 + T cells, and NK-T cells, along with myeloid cells, including IL-4, IL-5, IL-9, and IL-13, initiate and sustain allergic inflammation via T cell cells, eosinophils, and ILC2s; promote IgE class switching; and open the epithelial barrier. Epithelial cell activation, alarmin release and barrier dysfunction are key in the development of not only allergic diseases but also many other systemic diseases. Recent biologics targeting the pathways and effector functions of IL4/IL13, IL-5, and IgE have shown promising results for almost all ages, although some patients with severe allergic diseases do not respond to these therapies, highlighting the unmet need for a more detailed and personalized approach.

Pathophysiology of Prurigo Nodularis: Neuroimmune Dysregulation and the Role of Type 2 Inflammation

Prurigo nodularis (PN) is a chronic, inflammatory skin condition characterized by multiple, intensely pruritic, distinctive nodular lesions. Subsequent scratching can further intensify the pruritus, culminating in a self-reinforcing itch-scratch cycle, which drives lesion development. The latest data indicate dysregulation of the neuroimmune axis in PN pathogenesis, including the involvement of sensory neurons, key effector immune cells, proinflammatory cytokines, dermal fibroblasts, and pruritogens. In this review, we highlight evidence supporting the role of type 2 immune axis dysregulation in driving the clinical presentation of PN and discuss how related signaling pathways may offer effective therapeutic targets to control PN signs and symptoms.

English version of clinical practice guidelines for the management of atopic dermatitis 2024

This is the English version of the 2024 clinical practice guidelines for the management of atopic dermatitis (AD). AD is a disease characterized by relapsing eczema with pruritus as a primary lesion. A crucial aspect of AD treatment is the prompt induction of remission via the suppression of existing skin inflammation and pruritus. To achieve this, topical anti-inflammatory drugs, such as topical corticosteroids, tacrolimus ointment, delgocitinib ointment, and difamilast ointment, have been used. However, the following treatments should be considered in addition to topical therapy for patients with refractory moderate-to-severe AD: oral cyclosporine, subcutaneous injections of biologics (dupilumab, nemolizumab, tralokinumab), oral Janus kinase inhibitors (baricitinib, upadacitinib, abrocitinib), and phototherapy. In these revised guidelines, descriptions of five new drugs, namely, difamilast, nemolizumab, tralokinumab, upadacitinib, and abrocitinib, have been added. The guidelines present recommendations to review clinical research articles, evaluate the balance between the advantages and disadvantages of medical activities, and optimize medical activity-related patient outcomes with respect to several important points requiring decision-making in clinical practice.

Efficacy and Safety of Nemolizumab in Patients With Moderate to Severe Prurigo Nodularis: The OLYMPIA 1 Randomized Clinical Phase 3 Trial

Importance

Prurigo nodularis (PN) is a chronic and debilitating skin condition, characterized by intense itch with multiple nodular lesions. Nemolizumab demonstrated significant improvements in itch and skin nodules in adults with moderate to severe PN in a previous 16-week phase 3 study (OLYMPIA 2).

Objective

To assess the efficacy and occurrence of adverse events in adults with moderate to severe PN treated with nemolizumab vs those receiving placebo.

Design, Setting, and Participants

OLYMPIA 1 was a multicenter, placebo-controlled, phase 3 randomized clinical trial, conducted from August 2020 to March 2023 at 77 centers across 10 countries in adults with moderate to severe PN (at least 20 nodules and an Investigator's Global Assessment [IGA] score ≥3) and Peak Pruritus Numerical Rating Scale (PP-NRS) score of at least 7.0; consisted of screening (up to 4 weeks), 24-week treatment, and 8-week follow-up periods.

Interventions

Patients were randomized (2:1) to nemolizumab monotherapy, 30 mg or 60 mg (depending on baseline weight of less than 90 kg vs 90 kg or greater, respectively), or matching placebo administered every 4 weeks for 24 weeks.

Main Outcomes and Measures

The primary end points were the proportion of patients with itch response (≥4-point improvement from baseline in weekly average PP-NRS) and IGA success (score of 0/1 [clear/almost clear] and 2-grade or more improvement from baseline) at week 16.

Results

Of 286 patients (mean [SD] age, 57.5 [13.0] years; mean [SD] body weight, 85.0 [20.7] kg; 166 [58.0%] female), 190 were randomized to receive nemolizumab, and 96 were randomized to placebo. A significantly greater proportion of patients assigned to nemolizumab vs placebo achieved itch response (111/190 [58.4%] vs 16/96 [16.7%]; Δ, 40.1% [95% CI, 29.4%-50.8%]; P < .001) and IGA success (50/190 [26.3%] vs 7/96 [7.3%]; Δ, 14.6% [95% CI, 6.7%-22.6%]; P = .003) at week 16. At week 24, the proportion of patients with itch response was 58.3% vs 20.4% (Δ, 38.7% [95% CI, 27.5%-49.9%]) in the ad hoc analysis, and IGA success was 58/190 (30.5%) vs 9/96 (9.4%) (Δ, 19.2% [95% CI, 10.3%-28.1%]) in the nemolizumab-treated vs placebo group. During the treatment period, 134 patients (71.7%) receiving nemolizumab vs 62 patients (65.3%) receiving placebo had at least 1 adverse event; most events were of mild to moderate severity.

Conclusions and Relevance

In this randomized clinical trial, nemolizumab monotherapy led to clinically meaningful and statistically significant improvements in core signs and symptoms of PN.

Trial Registration

ClinicalTrials.gov Identifier: NCT04501666.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

Biosynthesis inhibition of miR-142-5p in a N6-methyladenosine-dependent manner induces neuropathic pain through CDK5/TRPV1 signaling

BACKGROUND

Neuropathic pain (NP) represents a debilitating and refractory condition. However, the understanding of NP and the current treatment approaches available for its management are limited. Therefore, there is a significant need to address the dearth of effective therapeutic interventions. This study aims to investigate the regulation of transient receptor potential vanilloid 1 (TRPV1) and cyclin-dependent kinase 5 (CDK5) expression levels by miR-142-5p as a common upstream molecule, and to delve into the mature process of miR-142-5p from the perspective of N6-methyladenosine (m6A) modification.

METHODS

To assess the RNA levels of TRPV1, CDK5, miR-142-5p, pre-miR-142, and pri-miR-142, quantitative PCR with reverse transcription (RT-qPCR) was utilized. Western blot analysis was employed to determine changes in protein expression for TRPV1 and CDK5. For assessing the interaction mechanism and binding site between TRPV1 and CDK5, various techniques were applied, including mass spectrometry, coimmunoprecipitation (co-IP), and glutathione-S-transferase (GST)-pulldown assays. The subcellular localization of TRPV1 on the cell membrane was visualized through immunofluorescence, and the translocation was confirmed by western blot analysis after performing membrane-plasma separation in parallel. Moreover, intracellular calcium transport was monitored using calcium imaging as an indicator of cell excitability. The binding of miRNA-142-5p to the 3'UTR of TRPV1 and CDK5 was investigated using the dual-luciferase reporter assay. The overall level of m6A was first determined by RNA m6A methylation assay, and subsequently the methylation level of pri-miR-142 was assessed using the meRIP assay to detect m6A modification. In addition, an in vivo rat chronic constriction injury (CCI) model was established, and miR-142-5p agomir or antagomir was injected intrathecally. An enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of IL-6 and TNF. Paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were examined.

RESULTS

The expression levels of TRPV1 and CDK5 were found to be upregulated not only in the in vivo CCI model but also in the in vitro lipopolysaccharide (LPS) treatment cell model as well. CDK5 was observed to phosphorylate TRPV1 at T406, prompting the translocation of TRPV1 to the cell membrane and consequent augmentation of cellular excitability. Notably, CDK5 was found to directly bind to TRPV1, and the binding region was localized within the 1-390 amino acid sequence of TRPV1. According to database predictions, miR-142-5p, identified as a shared upstream molecule of TRPV1 and CDK5, exhibited downregulation following induction by NP. MiR-142-5p was shown to simultaneously bind to the mRNA of CDK5 and TRPV1, thereby inhibiting their expression. After LPS treatment, it was observed that pri-miR-142 expression increased, while pre-miR-142 and miR-142-5p expression decreased, suggesting inhibition of the maturation process of pri-miR-142. In addition, the overall level of m6A and in particular the pri-miR-142 m6A modification increased upon LPS treatment. Knockdown of METTL14 led to decreased pri-miR-124 expression, increased pre-miR-124 expression, and enhanced mature miR-142-5p expression, indicating the relief of miR-142-5p maturation repression. The in vivo results indicated that miR-142-5p negatively regulated the expression of CDK5 and TRPV1, suppressed the expression of inflammatory factors IL-6 and TNF, and improved the PWMT and PWTL.

CONCLUSIONS

In this study, we perform a thorough investigation to examine the effects of CDK5 and TRPV1 on NP, elucidating their binding relationship and the impact of CDK5 on the membrane transport of TRPV1. Notably, our findings reveal that miR-142-5p, acting as a crucial upstream molecule, exhibits inhibitory effects on the expression of both CDK5 and TRPV1. Moreover, we observe that METTL14 facilitates the m6A modification of pri-miR-142, thereby impeding the maturation transition of pri-miR-142 and ultimately leading to the downregulation of mature miR-142-5p.

Evaluating duloxetine for pruritus and psychiatric comorbidities in lichen simplex chronicus

The use of antidepressant medications in the treatment of lichen simplex chronicus (LSC) also known as neurodermatitis, is not well-documented in the literature. The primary aim of our study is to evaluate the impact of duloxetine 30 mg on the quality of life in patients with LSC, focusing on both pruritus and psychopathological aspects. The secondary aim is to investigate the relationship between LSC and anxiety and depression. The observational prospective clinical study, conducted from November 2023 to November 2024, included male and female patients aged 18 and older diagnosed with neurodermatitis (lichen simplex chronicus). Inclusion criteria required a confirmed diagnosis by a dermatologist. Exclusion criteria included other skin conditions, polyneuropathies (e.g., diabetic, chemotherapy-induced), malignancy, current use of antidepressants or neuropathic pain medications, and medications known to cause itching (e.g., β-blockers, ACE inhibitors, antacids). Patients with LSC at the dermatology clinic were assessed by a dermatologist using the DLQI and a neurologist using the Beck Depression and Anxiety Inventory before and after three months of treatment. The study included 219 patients with a mean age of 39.6 (12.2) years, 69.5% female and 30.5% male. Post-treatment, the Duloxetine 30 mg + 0.05% alpha clobetasol propionate group showed the most significant improvement in DLQI scores (p < 0.05). This group also had a notable reduction in itchiness scores by the third month, with more change over time. The greatest reduction in scores on the Beck Depression Inventory-II and Beck Anxiety Inventory was observed in the Duloxetine 30 mg + 0.05% alpha-clobetasol propionate group, with this reduction continuing in a decreasing pattern in the Duloxetine 30 mg and 0.05% alpha-clobetasol propionate groups, respectively. Significant changes in the time-group interaction were observed only in the Duloxetine 30 mg + 0.05% alpha-clobetasol propionate and Duloxetine 30 mg groups (p < 0.05). No significant time effect was seen in the 0.05% alpha clobetasol propionate group. In the regression analysis, both BAI and BDI-II showed significant and strong effects on DLQI (p < 0.05). Our study suggests that duloxetine 30 mg may be effective in treating LSC by reducing pruritus and addressing comorbid psychiatric conditions like anxiety and depression. The multidisciplinary approach, involving both dermatological and neuropsychiatric evaluations, is essential for treatment. Long-term, multicenter studies are needed to confirm these findings.

Maladaptive changes in the homeostasis of AEA-TRPV1/CB1R induces pain-related hyperactivity of nociceptors after spinal cord injury

BACKGROUND

Neuropathic pain resulting from spinal cord injury (SCI) is associated with persistent hyperactivity of primary nociceptors. Anandamide (AEA) has been reported to modulate neuronal excitability and synaptic transmission through activation of cannabinoid type-1 receptors (CB1Rs) and transient receptor potential vanilloid 1 (TRPV1). However, the role of AEA and these receptors in the hyperactivity of nociceptors after SCI remains unclear.

RESULTS

In this study, we investigated the effects of AEA and its receptors on the hyperexcitability of mouse dorsal root ganglion (DRG) neurons after SCI. Using a whole-cell patch-clamp technique, we found that the timing of SCI-induced hyperexcitability in nociceptors paralleled an increase in the endocannabinoid AEA content. The expression of TRPV1 and CB1R was also upregulated at different time points after SCI. High-dose extracellular administration of AEA increased the excitability of naive DRG neurons, leading to the transition from a rapidly accommodating (RA) hypoexcitable state to a highly excitable non-accommodating (NA) state. These AEA-induced transitions were facilitated by increased TRPV1 transcription. Pharmacological and Ca2+ imaging experiments revealed that AEA induced hyperexcitability in nociceptors after SCI via the AEA-TRPV1-Ca2+ pathway, whereas activation of CB1Rs reduced SCI-induced hyperexcitability and maintained cytosolic Ca2+ concentration ([Ca2+]cyto) at low levels in the early stages of SCI. As the AEA and TRPV1 levels increased after SCI, adaptive neuroprotection transitioned to a maladaptive hyperactive state, leading to sustained pain.

CONCLUSIONS

Taken together, this study provides new insights into how endocannabinoids regulate nociceptor activity after SCI, offering potential targets for the treatment of neuropathic pain.

Predictive cytokines of omalizumab in the treatment of chronic spontaneous urticaria

BACKGROUND

Omalizumab, an anti-IgE biological agent, is commonly prescribed as a second-line therapy for Chronic Spontaneous Urticaria (CSU). However, there is a lack of biomarkers to predict which CSU patients will respond favorably to omalizumab.

OBJECTIVE

Our study aims to identify cytokine markers associated with the efficacy of omalizumab in treating CSU.

METHODS

We conducted a prospective study, enrolling antihistamine-resistant CSU patients from Tongji Hospital between Feburary and August 2023. All patients received a 16-week course of omalizumab (300 mg, administered every 4 weeks). Following 16 weeks of omalizumab treatment, patients were categorized into responder group and non-responder groups based on their UAS7 scores at the 16th week, using a cut-off value of 7. Serum total IgE (TIgE) and cytokine levels were measured at baseline and at the 16th week.

RESULTS

A total of 59 patients were enrolled in the study, 46 (78.0 %) responded positively to omalizumab. The responder group had lower UAS7 and DLQI scores at 4 and 16 weeks compared to their baseline and the non-responder group. There was no statistical difference in baseline TIgE levels between the two groups, but TIgE significantly increased in both groups after 16 weeks of omalizumab treatment. The responder group had higher baseline levels of IL-2, IL-13, IL-31, and IL-33 than the non-responder group. After 16 weeks of omalizumab treatment, the levels of IL-5, IL-31, and IL-33 were higher in the responder group than in the non-responder group. The AUC of baseline IL-2, IL-13, IL-31, and IL-33 in predicting responses to omalizumab were 0.8250, 0.8125, 0.7938, and 0.7813 (all P < 0.05), and the cut-off value were 154.5 pg/ml, 41.5 pg/ml, 100.8 pg/ml and 3330 pg/ml respectively.

CONCLUSION

CSU patients with high levels of IL-2, IL-13, IL-31, and IL-33 may potentially benefit from omalizumab treatment.

Cough and itch: Common mechanisms of irritation in the throat and skin

Cough and itch are protective mechanisms in the body. Cough occurs as a reflex motor response to foreign body inhalation, while itch is a sensation that similarly evokes a scratch response to remove irritants from the skin. Both cough and itch can last for sustained periods, leading to debilitating chronic disorders that negatively impact quality of life. Understanding the parallels and differences between chronic cough and chronic itch may be paramount to developing novel therapeutic approaches. In this article, we identify connections in the mechanisms contributing to the complex cough and scratch reflexes and summarize potential shared therapeutic targets. An online search was performed using various search engines, including PubMed, Web of Science, Google Scholar, and ClinicalTrials.gov from 1983 to 2024. Articles were assessed for quality, and those relevant to the objective were analyzed and summarized. The literature demonstrated similarities in the triggers, peripheral and central nervous system processing, feedback mechanisms, immunologic mediators, and receptors involved in the cough and itch responses, with the neuronal sensitization processes exhibiting the greatest parallels between cough and itch. Given the substantial impact on quality of life, novel therapies targeting similar neuroimmune pathways may apply to both itch and cough and provide new avenues for enhancing their management.

Skin barrier dysfunction in cutaneous T-cell lymphoma: From pathogenic mechanism of barrier damage to treatment

Cutaneous T-cell lymphoma (CTCL) is a group of non-Hodgkin lymphomas characterized by multiple erythematous patches, plaques, or even nodules on the skin. As the disease progresses, patients develop widespread pruritic skin lesions, leading to skin barrier dysfunction, which significantly impacts their quality of life, appearance, and social adaptation. The pathogenesis of CTCL is not fully understood. Recent studies have recognized the important role of skin barrier dysfunction in the development and progression of CTCL, yet a comprehensive review on this topic is lacking. This review summarizes recent findings on skin barrier dysfunction in CTCL, focusing on physical barrier dysfunction, chronic inflammation, and immune dysregulation. We also discuss current and potential therapies aimed at restoring barrier function in CTCL. By emphasizing the integration of barrier-centric approaches into CTCL management, this review provides valuable insights for improving treatment outcomes.

Efficacy and safety of narrowband ultraviolet B phototherapy for prurigo nodularis: a tertiary center experience

BACKGROUND

Prurigo nodularis is a chronic pruritic dermatosis and narrowband-UVB (NB-UVB) phototherapy is considered an effective and safe treatment option in patients with multiple comorbidities.

OBJECTIVE

In this study, the authors aimed to evaluate the efficacy and safety of NB-UVB phototherapy in the management of prurigo nodularis and to compare response rates according to lesions localization.

METHODS

Thirty prurigo nodularis patients who had been treated with NB-UVB phototherapy were included in this study. The data for this study were retrieved retrospectively from patient follow-up forms in the phototherapy unit.

RESULTS

NB-UVB phototherapy led to a complete response (CR) in 24 (80%) patients while partial response (PR) was achieved in 6 (20%) patients. Regarding prurigo nodularis localization, the CR rate was statistically higher in those with diffuse and central involvement (p < 0.05). Erythema and/or pruritus were observed in 4 (13.3%) patients with prurigo nodularis.

STUDY LIMITATIONS

This study is limited because it is single-centered and has a retrospective design.

CONCLUSIONS

NB-UVB phototherapy is an effective and safe treatment option for prurigo nodularis patients especially those with multiple comorbidities and using several medications. Patients with diffuse and central involvement may respond better to phototherapy than those with peripheral involvement.

Ruxolitinib Cream Monotherapy Improved Symptoms and Quality of Life in Adults and Adolescents with Mild-to-Moderate Atopic Dermatitis: Patient-Reported Outcomes from Two Phase III Studies

BACKGROUND

Atopic dermatitis (AD) is associated with itch, skin pain, sleep disturbances, and diminished quality of life (QoL). Ruxolitinib (Janus kinase [JAK] 1/JAK2 inhibitor) cream demonstrated efficacy and safety in adults and adolescents with mild-to-moderate AD in two phase III studies (TRuE-AD1/TRuE-AD2). In TRuE-AD1/TRuE-AD2, significant improvements in itch were observed as early as 12 h following application of ruxolitinib cream.

OBJECTIVE

The aim of this paper was to assess additional patient-reported outcomes (PROs) in the vehicle-controlled (VC) and long-term safety (LTS) periods of TRuE-AD1/TRuE-AD2.

METHODS

In the TRuE-AD studies, patients aged ≥12 years with AD were randomized 2:2:1 to apply twice-daily 1.5% ruxolitinib cream, 0.75% ruxolitinib cream, or vehicle cream continuously for 8 weeks (VC period). During the LTS period, patients applied the same ruxolitinib cream strength, but on an as-needed basis; patients who initially applied vehicle were re-randomized to apply 0.75% or 1.5% ruxolitinib cream. Pooled data from both study periods were analyzed. PRO assessments included symptoms (itch [Patient-Oriented Eczema Measure, POEM], skin pain [numerical rating scale], and sleep [POEM and Patient-Reported Outcomes Measurement Information System]) and assessments of disease-specific QoL (Dermatology Life Quality Index [DLQI] and the children's version [CDLQI]).

RESULTS

A total of 1208 and 1031 patients from the VC and LTS periods, respectively, were included in the analysis. Significant improvements in skin pain were observed within 12 h among patients who applied ruxolitinib cream versus vehicle; improvements continued throughout the VC period. Improvements in patient-reported symptoms (including sleep) were observed within 2 weeks (first assessment) of ruxolitinib cream application. At Week 2, significant improvements in symptom burden and overall QoL were observed with ruxolitinib cream (0.75%/1.5%) versus vehicle in POEM (-8.9/-9.8 vs -2.2; both p < 0.0001), DLQI (mean changes from baseline, -5.8/-6.1 vs -1.2; both p < 0.0001), and CDLQI (-4.3/-5.3 vs -1.3; both p < 0.0001). Further symptom burden and QoL improvements were reported during the VC period and were maintained through the end of the LTS period (Week 52).

CONCLUSIONS

Consistent with the previously reported itch response data, ruxolitinib cream improved skin pain within 12 h of application. Ruxolitinib cream improved patient-reported AD symptom burden and overall QoL by Week 2. Improvements continued or were maintained for 52 weeks. (Graphical abstract and plain language summary available).

TRIAL REGISTRATION

ClinicalTrials.gov identifiers, NCT03745638 and NCT03745651 (both studies were registered on November 19, 2018).

iPSC-derived human sensory neurons reveal a subset of TRPV1 antagonists as anti-pruritic compounds

Signaling interplay between the histamine 1 receptor (H1R) and transient receptor potential cation channel subfamily V member 1 (TRPV1) in mediating histaminergic itch has been well-established in mammalian models, but whether this is conserved in humans remains to be confirmed due to the difficulties in obtaining human sensory neurons (SNs) for experimentation. Additionally, previously reported species-specific differences in TRPV1 function indicate that use of human SNs is vital for drug candidate screening to have a higher chance of identifying clinically effective TRPV1 antagonists. In this study, we built a histamine-dependent itch model using peripheral SNs derived from human induced pluripotent stem cells (hiPSC-SNs), which provides an accessible source of human SNs for pre-clinical drug screening. We validated channel functionality using immunostaining, calcium imaging, and multielectrode array (MEA) recordings, and confirmed the interdependence of H1R and TRPV1 signalling in human SNs. We further tested the amenability of our model for pre-clinical studies by screening multiple TRPV1 antagonists in parallel, identifying SB366791 as a potent inhibitor of H1R activation and potential candidate for alleviating histaminergic itch. Notably, some of the results using our model corroborated with efficacy and side effect findings from human clinical trials, underscoring the importance of this species-specific platform. Taken together, our results present a robust in vitro human model for histaminergic itch, which can be used to further interrogate the molecular basis of human SN function as well as screen for TRPV1 activity-modifying compounds for a number of clinical indications.

Skin microdialysis detects distinct immunologic patterns in chronic inflammatory skin diseases

BACKGROUND

Insight into the pathophysiology of inflammatory skin diseases, especially at the proteomic level, is severely hampered by the lack of adequate in situ data.

OBJECTIVE

We characterized lesional and nonlesional skin of inflammatory skin diseases using skin microdialysis.

METHODS

Skin microdialysis samples from patients with atopic dermatitis (AD, n = 6), psoriasis vulgaris (PSO, n = 7), or prurigo nodularis (PN, n = 6), as well as healthy controls (n = 7), were subjected to proteomic and multiplex cytokine analysis. Single-cell RNA sequencing of skin biopsy specimens was used to identify the cellular origin of cytokines.

RESULTS

Among the top 20 enriched Gene Ontology (GO; geneontology.org) annotations, nicotinamide adenine dinucleotide metabolic process, regulation of secretion by cell, and pyruvate metabolic process were elevated in microdialysates from lesional AD skin compared with both nonlesional skin and controls. The top 20 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG; genome.jp/kegg) pathways in these 3 groups overlapped almost completely. In contrast, nonlesional skin from patients with PSO or PN and control skin showed no overlap with lesional skin in this KEGG pathway analysis. Lesional skin from patients with PSO, but not AD or PN, showed significantly elevated protein levels of MCP-1 compared with nonlesional skin. IL-8 was elevated in lesional versus nonlesional AD and PSO skin, whereas IL-12p40 and IL-22 were higher only in lesional PSO skin. Integrated single-cell RNA sequencing data revealed identical cellular sources of these cytokines in AD, PSO, and PN.

CONCLUSION

On the basis of microdialysates, the proteomic data of lesional PSO and PN skin, but not lesional AD skin, differed significantly from those of nonlesional skin. IL-8, IL-22, MCP-1, and IL-12p40 might be suitable markers for minimally invasive molecular profiling.

Epithelial-immune interactions govern type 2 immunity at barrier surfaces

Allergic diseases are acute and chronic inflammatory conditions resulting from disproportionate responses to environmental stimuli. Affecting approximately 40% of the global population, these diseases significantly contribute to morbidity and increasing health care costs. Allergic reactions are triggered by pollen, house dust mites, animal dander, mold, food antigens, venoms, toxins, and drugs. This review explores the pivotal role of the epithelium in the skin, lungs, and gastrointestinal tract in regulating the allergic response and delves into the mechanisms of tissue-specific epithelial-immune interactions in this context, with recent advances highlighting their roles in the initiation, elicitation, and resolution phases of allergy. Understanding these intricate interactions at epithelial barriers is essential for developing targeted therapies to manage and treat allergic diseases.

Sensory neuroimmune interactions at the barrier

Epithelial barriers such as the skin, lung, and gut, in addition to having unique physiologic functions, are designed to preserve tissue homeostasis upon challenge with a variety of allergens, irritants, or pathogens. Both the innate and adaptive immune systems play a critical role in responding to epithelial cues triggered by environmental stimuli. However, the mechanisms by which organs sense and coordinate complex epithelial, stromal, and immune responses have remained a mystery. Our increasing understanding of the anatomic and functional characteristics of the sensory nervous system is greatly advancing a new field of peripheral neuroimmunology and subsequently changing our understanding of mucosal immunology. Herein, we detail how sensory biology is informing mucosal neuroimmunology, even beyond neuroimmune interactions seen within the central and autonomic nervous systems.

The peripheral neuroimmune system

Historically, the nervous and immune systems were studied as separate entities. The nervous system relays signals between the body and the brain by processing sensory inputs and executing motor outputs, whereas the immune system provides protection against injury and infection through inflammation. However, recent developments have demonstrated that these systems mount tightly integrated responses. In particular, the peripheral nervous system acts in concert with the immune system to control reflexes that maintain and restore homeostasis. Notwithstanding their homeostatic mechanisms, dysregulation of these neuroimmune interactions may underlie various pathological conditions. Understanding how these two distinct systems communicate is an emerging field of peripheral neuroimmunology that promises to reveal new insights into tissue physiology and identify novel targets to treat disease.

Effects of Huang-Lian-Jie-Du decoction on improving skin barrier function and modulating T helper cell differentiation in 1-chloro-2,4-dinitrobenzene-induced atopic dermatitis mice

Background: Atopic dermatitis (AD) is among the most frequently encountered skin diseases, bothering a considerable number of patients. Today, corticosteroids and antihistamines are among the numerous drugs applied for the therapy of AD. However, lengthy use of them contributes to side effects, such as physiological changes in skin. As an alternative and supplementary therapy, traditional Chinese medicine has become a trend for AD treatment. Huang-Lian-Jie-Du decoction (HLJDD), a renowned herbal formula has been employed to treat inflammatory diseases such as AD. However, its role in regulating immunity in AD remains unclear. The object of this study was to elucidate the efficacy of HLJDD and reveal the implicit mechanism from an immunological perspective in AD-like mice. Methods: In brief, 1-chloro-2,4-dinitrobenzene (DNCB) for the sensitization phase (1% DNCB) and stimulation phase (1.5% DNCB) were applied for BALB/c mice. HLJDD and dexamethasone (DXMS) were administered orally to the mice. Mice skin and spleens were collected to evaluate the efficacy of HLJDD. 16S rRNA sequencing was applied to evaluate the commensal microbiota changes in skin and fecal. In vitro, spleen CD4+ T cells and bone marrow-derived mast cells (BMMCs) were co-cultured to explore the modulation of HLJDD in T helper (Th) cells phenotyping. Results: HLJDD showcased a substantial amelioration in skin through the upregulation of FLG, LOR, AQP3, and reducing scratching behaviors in AD-like mice, Also, the quantity of infiltrated mast cells (MCs), pruritus-related mRNA were decreased. In addition, the expression of OX40/OX40L was decreased by HLJDD, which was critical in Th-cell phenotyping. With the treatment of HLJDD, Th1/Th2 and Th17/Treg ratios in AD-like mice became balanced. The structure of commensal microbiota in AD-like mice was affected by HLJDD. HLJDD could also improve the imbalance of Th17/Treg in vitro. Conclusion: HLJDD could improve the symptoms of AD-like mice by alleviating the scratching behaviors via decreased Th2 and pruritus-related mRNA expression. HLJDD also enhanced the relative diversity of skin microbiota and changed the structure of intestinal microbiota. An in-depth study found that HLJDD could balance the ratio of Th1/Th2, Th17/Treg in AD-like mice, and Th17/Treg in vitro by regulating the OX40/OX40L signaling pathway.

Antibody selection and automated quantification of TRPV1 immunofluorescence on human skin

Assessing localization of the transient receptor potential vanilloid-1 (TRPV1) in skin nerve fibers is crucial for understanding its role in peripheral neuropathy and pain. However, information on the specificity and sensitivity of TRPV1 antibodies used for immunofluorescence (IF) on human skin is currently lacking. To find a reliable TRPV1 antibody and IF protocol, we explored antibody candidates from different manufacturers, used rat DRG sections and human skin samples for screening and human TRPV1-expressing HEK293 cells for further validation. Final specificity assessment was done on human skin samples. Additionally, we developed two automated image analysis methods: a Python-based deep-learning approach and a Fiji-based machine-learning approach. These methods involve training a model or classifier for nerve fibers based on pre-annotations and utilize a nerve fiber mask to filter and count TRPV1 immunoreactive puncta and TRPV1 fluorescence intensity on nerve fibers. Both automated analysis methods effectively distinguished TRPV1 signals on nerve fibers from those in keratinocytes, demonstrating high reliability as evidenced by excellent intraclass correlation coefficient (ICC) values exceeding 0.75. This method holds the potential to uncover alterations in TRPV1 associated with neuropathic pain conditions, using a minimally invasive approach.

Case report: Abrocitinib: a potential therapeutic option for lichen amyloidosis associated with atopic dermatitis

Lichen amyloidosis (LA) is a predominant type of primary cutaneous amyloidosis that is characterized by persistent and intense skin itching. Although multiple therapeutics strategies are available for its treatment, there is no standard treatment so far. Abrocitinib, an oral small-molecule Janus kinase 1 inhibitor, has been authorized for the treatment of severe atopic dermatitis (AD) and can also provide rapid relief from pruritus. Here, we discuss the case of a 32-year-old man who was diagnosed with LA with severe AD based on the presence of multiple, discrete, and hyperpigmented papules and pruritic, erythematous macules with lichenification of the limbs, trunk, and buttocks. Given the inefficacy of conventional therapy, abrocitinib treatment was recommended in this patient. After 1 month of treatment, the patient's Eczema Area And Severity Index score decreased significantly from 48 to 15 points, accompanied by a notable reduction in pruritus symptoms. Furthermore, significant improvements were observed in the thickness and pigmentation of the hyperkeratotic papules. Thus, abrocitinib exhibited excellent effectiveness and safety in the treatment of severe AD with LA and warrants further investigation for its potential therapeutic benefits.

Diospyros lotus leaf extract and its main component myricitrin inhibit itch‑related IL‑6 and IL‑31 by suppressing microglial inflammation and microglial‑mediated astrocyte activation

Diospyros lotus has been traditionally used in Asia for medicinal purposes, exhibiting a broad spectrum of pharmacological effects including antioxidant, neuroprotective and anti‑inflammatory properties. While the anti‑itch effect of D. lotus leaves has been reported, studies on the detailed mechanism of action in microglia and astrocytes, which are members of the central nervous system, have yet to be revealed. The present study aimed to investigate effects of D. lotus leaf extract (DLE) and its main component myricitrin (MC) on itch‑related cytokines and signaling pathways in lipopolysaccharide (LPS)‑stimulated microglia. The effect of DLE and MC on activation of astrocyte stimulated by microglia was also examined. Cytokine production was evaluated through reverse transcription PCR and western blot analysis. Signaling pathway was analyzed by performing western blotting and immunofluorescence staining. The effect of microglia on astrocytes activation was evaluated via western blotting for receptors, signaling molecules and itch mediators and confirmed through gene silencing using short interfering RNA. DLE and MC suppressed the production of itch‑related cytokine IL‑6 and IL‑31 in LPS‑stimulated microglia. These inhibitory effects were mediated through the blockade of NF‑κB, MAPK and JAK/STAT pathways. In astrocytes, stimulation by microglia promoted the expression of itch‑related molecules such as oncostatin M receptor, interleukin 31 receptor a, inositol 1,4,5‑trisphosphate receptor 1, lipocalin‑2 (LCN2), STAT3 and glial fibrillary acidic protein. However, DLE and MC significantly inhibited these receptors. Additionally, astrocytes stimulated by microglia with IL‑6, IL‑31, or both genes silenced did not show activation of LCN2 or STAT3. The findings of the present study demonstrated that DLE and MC could suppress pruritic activity in astrocytes induced by microglia‑derived IL‑6 and IL‑31. This suggested the potential of DLE and MC as functional materials capable of alleviating pruritus.

Cancer Therapy-induced Dermatotoxicity as a Window to Understanding Skin Immunity

Pruritus, rash, and various other forms of dermatotoxicity are the most frequent adverse events among patients with cancer receiving targeted molecular therapy and immunotherapy. Immune checkpoint inhibitors, macrophage-targeting agents, and epidermal growth factor receptor/MEK inhibitors not only exert antitumor effects but also interfere with molecular pathways essential for skin immune homeostasis. Studying cancer therapy-induced dermatotoxicity helps us identify molecular mechanisms governing skin immunity and deepen our understanding of human biology. This review summarizes new mechanistic insights emerging from the analysis of cutaneous adverse events and discusses knowledge gaps that remain to be closed by future research.

A γδ T cell-IL-3 axis controls allergic responses through sensory neurons

In naive individuals, sensory neurons directly detect and respond to allergens, leading to both the sensation of itch and the activation of local innate immune cells, which initiate the allergic immune response1,2. In the setting of chronic allergic inflammation, immune factors prime sensory neurons, causing pathologic itch3-7. Although these bidirectional neuroimmune circuits drive responses to allergens, whether immune cells regulate the set-point for neuronal activation by allergens in the naive state is unknown. Here we describe a γδ T cell-IL-3 signalling axis that controls the allergen responsiveness of cutaneous sensory neurons. We define a poorly characterized epidermal γδ T cell subset8, termed GD3 cells, that produces its hallmark cytokine IL-3 to promote allergic itch and the initiation of the allergic immune response. Mechanistically, IL-3 acts on Il3ra-expressing sensory neurons in a JAK2-dependent manner to lower their threshold for allergen activation without independently eliciting itch. This γδ T cell-IL-3 signalling axis further acts by means of STAT5 to promote neuropeptide production and the initiation of allergic immunity. These results reveal an endogenous immune rheostat that sits upstream of and governs sensory neuronal responses to allergens on first exposure. This pathway may explain individual differences in allergic susceptibility and opens new therapeutic avenues for treating allergic diseases.

TRPV1: The key bridge in neuroimmune interactions

The nervous and immune systems are crucial in fighting infections and inflammation and in maintaining immune homeostasis. The immune and nervous systems are independent, yet tightly integrated and coordinated organizations. Numerous molecules and receptors play key roles in enabling communication between the two systems. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a non-selective cation channel, recently shown to be widely expressed in the neuroimmune axis and implicated in neuropathic pain, autoimmune disorders, and immune cell function. TRPV1 is a key bridge in neuroimmune interactions, allowing for smooth and convenient communication between the two systems. Here, we discuss the coordinated cross-talking between the immune and nervous systems and the functional role and the functioning manner of the TRPV1 involved. We suggest that TRPV1 provides new insights into the collaborative relationship between the nervous and immune systems, highlighting exciting opportunities for advanced therapeutic approaches to treating neurogenic inflammation and immune-mediated diseases.

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.

Tapinarof cream 1% once daily: Significant efficacy in the treatment of moderate to severe atopic dermatitis in adults and children down to 2 years of age in the pivotal phase 3 ADORING trials

BACKGROUND

Tapinarof cream 1% once daily (QD), a topical aryl hydrocarbon receptor agonist, downregulates pro-inflammatory Th2 cytokines, upregulates skin-barrier components, and reduces oxidative stress.

OBJECTIVE

To assess tapinarof efficacy and safety in adults and children down to 2 years of age with atopic dermatitis (AD).

METHODS

Eight hundred and thirteen patients were randomized to tapinarof or vehicle QD in two 8-week phase 3 trials.

RESULTS

The primary efficacy endpoint, Validated Investigator Global Assessment for Atopic Dermatitis score of 0 or 1 and ≥2-grade improvement from baseline at Week 8, was met with statistical significance in both trials: 45.4% versus 13.9% and 46.4% versus 18.0% (tapinarof vs vehicle; both P < .0001). Significantly superior Eczema Area and Severity Index 75 (EASI75) responses were also observed with tapinarof versus vehicle at Week 8: 55.8% versus 22.9% and 59.1% versus 21.2% (both P < .0001). Rapid improvements in patient-reported pruritus were also significant with tapinarof versus vehicle. Common adverse events (≥5%) of folliculitis, headache, and nasopharyngitis were mostly mild or moderate, with lower discontinuations due to adverse events in the tapinarof groups than with vehicle.

LIMITATIONS

Long-term efficacy was not assessed.

CONCLUSION

Tapinarof demonstrated highly significant efficacy and favorable safety and tolerability in a diverse population of patients with AD down to 2 years of age.

Sensory sentinels: Neuroimmune detection and food allergy

Food allergy is classically characterized by an inappropriate type-2 immune response to allergenic food antigens. However, how allergens are detected and how that detection leads to the initiation of allergic immunity is poorly understood. In addition to the gastrointestinal tract, the barrier epithelium of the skin may also act as a site of food allergen sensitization. These barrier epithelia are densely innervated by sensory neurons, which respond to diverse physical environmental stimuli. Recent findings suggest that sensory neurons can directly detect a broad array of immunogens, including allergens, triggering sensory responses and the release of neuropeptides that influence immune cell function. Reciprocally, immune mediators modulate the activation or responsiveness of sensory neurons, forming neuroimmune feedback loops that may impact allergic immune responses. By utilizing cutaneous allergen exposure as a model, this review explores the pivotal role of sensory neurons in allergen detection and their dynamic bidirectional communication with the immune system, which ultimately orchestrates the type-2 immune response. Furthermore, it sheds light on how peripheral signals are integrated within the central nervous system to coordinate hallmark features of allergic reactions. Drawing from this emerging evidence, we propose that atopy arises from a dysregulated neuroimmune circuit.

Integrating multi-omics approaches in deciphering atopic dermatitis pathogenesis and future therapeutic directions

Atopic dermatitis (AD), a complex and heterogeneous chronic inflammatory skin disorder, manifests in a spectrum of clinical subtypes. The application of genomics has elucidated the role of genetic variations in predisposing individuals to AD. Transcriptomics, analyzing gene expression alterations, sheds light on the molecular underpinnings of AD. Proteomics explores the involvement of proteins in AD pathophysiology, while epigenomics examines the impact of environmental factors on gene expression. Lipidomics, which investigates lipid profiles, enhances our understanding of skin barrier functionalities and their perturbations in AD. This review synthesizes insights from these omics approaches, highlighting their collective importance in unraveling the intricate pathogenesis of AD. The review culminates by projecting future trajectories in AD research, particularly the promise of multi-omics in forging personalized medicine and novel therapeutic interventions. Such an integrated multi-omics strategy is poised to transform AD comprehension and management, steering towards more precise and efficacious treatment modalities.

Interleukin-31: The Inflammatory Cytokine Connecting Pruritus and Cancer

Interleukin 31 (IL-31) is a proinflammatory cytokine, mainly secreted by Type II helper T cells. It signals through a heterodimeric receptor complex composed of IL-31 receptor α and oncostatin-M receptor β chain. The hallmark feature of IL-31, in its pathological role, is its ability to induce pruritus in mammals. Pruritus is a common symptom and major reason of morbidity in cancer patients, compromising their quality of life. Although, IL-31 is differentially expressed in different tumor types and could promote or inhibit cancer progression, high expression of IL-31 is a contributing factor to advanced stage tumor and severity of pruritus. The simultaneous existence of pruritus and cancer could either result from the aberrations in common proteins that co-exist in both cancer and pruritus or the therapeutic treatment of cancer could indirectly induce pruritus. Although the biology of IL-31 has predominantly been described in skin diseases such as atopic dermatitis and other inflammatory diseases, the precise role of IL-31 in the tumor biology of different cancer types remains elusive. Herein, we summarize the current understanding on the role of this cytokine in the pathogenesis of different cancers.

Dihydroavenanthramide D Enhances Skin Barrier Function through Upregulation of Epidermal Tight Junction Expression

Skin barrier dysfunction and thin epidermis are hallmarks of sensitive skin and contribute to premature aging. Avenanthramides are the primary bioactive components of colloidal oatmeal, a commonly used treatment to enhance skin barrier function. This study investigated the relationship between skin barrier function and epidermal characteristics and explored the potential of dihydroavenanthramide D (dhAvD), a synthetic avenanthramide, to improve the skin barrier. We observed a significant correlation between impaired skin barrier function and decreased epidermal thickness, suggesting that a weakened barrier contributes to increased sensitivity. Our in vitro results in HaCaT cells demonstrated that dhAvD enhances keratinocyte proliferation, migration, and tight junction protein expression, thereby strengthening the skin barrier. To mimic skin barrier dysfunction, we treated keratinocytes and full-thickness skin equivalents with IL-4 and IL-13, cytokines that are implicated in atopic dermatitis, and confirmed the downregulation of tight junction and differentiation markers. Furthermore, dhAvD treatment restored the barrier function and normalized the expression of key epidermal components, such as tight junction proteins and natural moisturizing factors, in keratinocytes treated with inflammatory cytokines. In the reconstructed human skin model, dhAvD promoted both epidermal and dermal restoration. These findings suggest that dhAvD has the potential to alleviate skin sensitivity and improve skin barrier function.