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

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.

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.

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.

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.

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.

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.

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.

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.

Anti-atopic dermatitis effect of fraxinellone via inhibiting IL-31 in vivo and in vitro

Chronic recurrent itch and skin inflammation are prominent features of atopic dermatitis (AD), which is closely related to the immune response driven by T-helper type 2 (Th2) cells. The expression of interleukin 31 (IL-31) is positively correlated with the severity of dermatitis. Anti-IL-31 receptor α (IL-31RA) targeted drugs have been used to treat AD, however, they are expensive and have side effects. Fraxinellone (FRA) is one of the main limonoid components in the dried root bark of Dictamnus dasycarpus Turcz.; however, its anti-inflammatory and antipruritic effects on atopic dermatitis (AD) have not been previously reported. In this study, we investigated the anti-dermatitis effect of FRA and its potential mechanism of action using a 2,4-dinitrofluorobenzene (DNFB)-induced AD-like mouse model and lipopolysaccharide (LPS)-stimulated HaCaT cells. FRA significantly inhibited chronic pruritus, epidermal thickening, and inflammatory infiltration in AD mice. FRA not only inhibited the levels of IL-31 in the serum and lesioned skin of AD mice but also significantly downregulated the mRNA expression and protein levels of IL-31, IL-31RA, transient receptor potential (TRP) V1, and TRPA1 in the lesioned skin and dorsal root ganglion (DRG) of AD mice. In LPS-stimulated HaCaT cells, FRA inhibited the production of iNOS and COX2, as well as the protein levels of IL-31, IL-31RA, TRPV1 and TRPA1, showing significant anti-inflammatory effects. In summary, our findings suggest that FRA exerts antipruritic and anti-inflammatory effects in AD by regulating the IL-31 pathway, and may hold promise for the clinical treatment of AD.

Commensal microbe regulation of skin cells in disease

Human skin is the host to various commensal microbes that constitute a substantial microbial community. The reciprocal communication between these microbial inhabitants and host cells upholds both the morphological and functional attributes of the skin layers, contributing indispensably to microenvironmental and tissue homeostasis. Thus, disruption of the skin barrier or imbalances in the microbial communities can exert profound effects on the behavior of host cells. This influence, mediated by the microbes themselves or their metabolites, manifests in diverse outcomes. In this review, we examine existing knowledge to provide insight into the nuanced behavior exhibited by the microbiota on skin cells in health and disease states. These interactions provide insight into potential cellular targets for future microbiota-based therapies to prevent and treat skin disease.

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.

A Narrative Review of the IL-18 and IL-37 Implications in the Pathogenesis of Atopic Dermatitis and Psoriasis: Prospective Treatment Targets

Atopic dermatitis and psoriasis are prevalent inflammatory skin conditions that significantly impact the quality of life of patients, with diverse treatment options available. Despite advances in understanding their underlying mechanisms, recent research highlights the significance of interleukins IL-18 and IL-37, in Th1, Th2, and Th17 inflammatory responses, closely associated with the pathogenesis of psoriasis and atopic dermatitis. Hence, IL-18 and IL-37 could potentially become therapeutic targets. This narrative review synthesizes knowledge on these interleukins, their roles in atopic dermatitis and psoriasis, and emerging treatment strategies. Findings of a literature search up to 30 May 2024, underscore a research gap in IL-37-targeted therapies. Conversely, IL-18-focused treatments have demonstrated promise in adult-onset Still's Disease, warranting further exploration for their potential efficacy in psoriasis and atopic dermatitis.

Neuronal BST2: A Pruritic Mediator alongside Protease-Activated Receptor 2 in the IL-27-Driven Itch Pathway

Chronic itch is a common and complex symptom often associated with skin diseases such as atopic dermatitis (AD). Although IL-27 is linked to AD, its role and clinical significance in itch remain undefined. We sought to investigate IL-27 function in itch using tissue-specific transgenic mice, various itch models, behavior scoring, RNA sequencing, and cytokine/kinase array. Our findings show that IL-27 receptors were overexpressed in human AD skin. Intradermal IL-27 injection failed to directly induce itch in mice but upregulated skin protease-activated receptor 2 (PAR2) transcripts, a key factor in itch and AD. IL-27 activated human keratinocytes, increasing PAR2 transcription and activity. Coinjection of SLIGRL (PAR2 agonist) and IL-27 in mice heightened PAR2-mediated itch. In addition, IL-27 boosted BST2 transcription in sensory neurons and keratinocytes. BST2 was upregulated in AD skin, and its injection in mice induced itch-like response. BST2 colocalized with sensory nerve branches in AD skin from both human and murine models. Sensory neurons released BST2, and mice with sensory neuron-specific BST2 knockout displayed reduced itch responses. Overall, this study provides evidence that skin IL-27/PAR2 and neuronal IL-27/BST2 axes are implicated in cutaneous inflammation and pruritus. The discovery of neuronal BST2 in pruritus shed light on BST2 in the itch cascade.

Transcriptional profiling identifies IL-33-expressing intestinal stromal cells as a signaling hub poised to interact with enteric neurons

Recent advancements in mucosal immunology have unveiled a complex network of intercellular connections within diverse tissues, shedding light on the unique properties of different cell types. Central to this intricate network is the cytokine IL-33, which has gained significant attention for its critical role in various diseases, from allergy to cancer, triggering type 2 immune responses, among others. Recent research has challenged the prior assumptions attributing IL-33 expression to epithelial cells, highlighting stromal cells as the predominant source in adipose tissue and the lungs. However, in the complex landscape of the intestine, where IL-33 plays a crucial role in mediating immune surveillance and tolerance and is implicated in many gut-related disorders, its primary source, regulation, and main characteristics need more exploration. This study identifies stromal cells as the primary IL-33-expressing cell type in the small intestine. By investigating their transcriptome and intrinsic signaling pathways, we have uncovered a possible role of IL-33+ stromal cells in maintaining the stem cell niche and their potential crosstalk with neurons relevant to the regulation of axonogenesis. Importantly, our experiments have demonstrated that vasoactive intestinal peptide stimulation of a primary intestinal stromal cell culture significantly amplifies IL-33 expression on mRNA and protein level. Therefore, our study represents a significant leap forward in understanding the plethora of interactions IL-33+ intestinal stromal cells maintain in the intestine, paving the way for future investigations into stromal-neuro crosstalk in the gut. These findings hold great promise for developing targeted therapeutic strategies aimed at harnessing the potential of IL-33 across a spectrum of diseases.

IL-4 and IL-13 are not involved in IL-31-induced itch-associated scratching behaviour in mice

Itchy skin or pruritus is a common cutaneous symptom that causes an urge to scratch, and the role of interleukins (IL) in itchy skin has been widely studied. IL-4 and IL-13 are known to induce chronic itch. Similarly, the direct role of IL-31 in inducing itch has been demonstrated in clinical situations such as atopic dermatitis and prurigo nodularis. Moreover, IL-4 receptor α antibodies (dupilumab) and IL-31 receptor A antibodies (nemolizumab) inhibit pruritus. However, the interplay between these ILs in pruritus remains unclear. Therefore, we investigated the reciprocal effects of these cytokines on pruritus in mice. The intradermal administration of IL-31 induced itch-associated scratching behaviour in a dose-dependent manner. Interestingly, the amount of IL-31 and IL-4/IL-13, co-administration or 30 min pre-administration of IL-4/IL-13 and intradermal or intravenous pre-administration of IL-4 did not affect IL-31-induced itch-associated scratching behaviour when it was observed for 30 min, 2 h, 24 h or 48 h. Pre-administration of neutralising antibodies against IL-4 and IL-13 also did not affect IL-31-induced itch-associated scratching behaviour. These results suggest that IL-31 can induce itching independently of IL-4 and IL-13 in vivo.

Characterisation of the pruritus responses and pruritic behaviours in an interleukin 31-induced canine model of pruritus

BACKGROUND

Intravenous administration of interleukin (IL)-31 in healthy dogs has been used as a model to assess antipruritic drugs. However, there is no known in-depth characterisation of pruritic behaviours, and the repeatability of the IL-31-induced pruritus in the individual dogs is currently unknown.

OBJECTIVES

To evaluate the immediate/delayed pruritus responses and the pruritic behaviours observed in the IL-31-induced pruritic model in healthy dogs after repeated IL-31 injections.

ANIMALS

Fifteen healthy laboratory beagles.

METHODS

All dogs were video-recorded for 270 min after two intravenous recombinant IL-31 injections (1.75 μg/kg) and vehicle (phosphate-buffered saline, control) injections, respectively; interventions were randomised and performed with a 2 week wash-out period. Two blinded investigators reviewed the pruritic behaviours of all video recordings.

RESULTS

Both canine IL-31 (IL-31_01, IL-31_02) injections significantly increased pruritic seconds and categorical minutes ('YES'/'NO' behaviour per discrete 1 min interval) in healthy dogs compared with both vehicle groups (Vehicle_01, Vehicle_02). The second intravenous canine IL-31 (IL-31_02) administered 14 days after the first IL-31 injection induced a significant increase in pruritic seconds (p = 0.021) and not pruritic categorical minutes (p = 0.231). An increase in pruritic seconds was observed in both IL-31 groups in the first 30 min post-administration, while there was no significant difference between IL-31 and vehicle groups.

CONCLUSIONS AND CLINICAL RELEVANCE

In conclusion, intravenous IL-31 reproducibly induces itch responses in dogs. Future evaluations of the canine IL-31 pruritic model should assess total pruritic behaviours in seconds rather than using a biased 'YES/NO' behaviour per 1 min scoring system.

Exogenous drug-induced mouse models of atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disease characterized by intense pruritus. AD is harmful to both children and adults, but its pathogenic mechanism has yet to be fully elucidated. The development of mouse models for AD has greatly contributed to its study and treatment. Among these models, the exogenous drug-induced mouse model has shown promising results and significant advantages. Until now, a large amount of AD-related research has utilized exogenous drug-induced mouse models, leading to notable advancements in research. This indicates the crucial significance of applying such models in AD research. These models exhibit diverse characteristics and are highly complex. They involve the use of various strains of mice, diverse types of inducers, and different modeling effects. However, there is currently a lack of comprehensive comparative studies on exogenous drug-induced AD mouse models, which hinders researchers' ability to choose among these models. This paper provides a comprehensive review of the features and mechanisms associated with various exogenous drug-induced mouse models, including the important role of each cytokine in AD development. It aims to assist researchers in quickly understanding models and selecting the most suitable one for further investigation.

Monoclonal antibodies for moderate-to-severe atopic dermatitis: a look at phase III and beyond

INTRODUCTION

The understanding of atopic dermatitis (AD) pathogenesis has rapidly expanded in recent years, catalyzing the development of new targeted monoclonal antibody treatments for AD.

AREAS COVERED

This review aims to summarize the latest clinical and molecular data about monoclonal antibodies that are in later stages of development for AD, either in Phase 3 trials or in the pharmacopoeia for up to 5 years, highlighting the biologic underpinning of each drug's mechanism of action and the potential modulation of the AD immune profile.

EXPERT OPINION

The therapeutic pipeline of AD treatments is speedily progressing, introducing the potential for a personalized medical approach in the near future. Understanding how targeting pathogenic players in AD modifies disease progression and symptomatology is key in improving therapeutic choices for patients and identifying ideal patient candidates.

Knowledge mapping of links between dendritic cells and allergic diseases: A bibliometric analysis (2004-2023)

In this study, bibliometric analysis was carried out to comprehend the global research trends, hotspots, scientific frontiers, and output characteristics of the links between dendritic cells (DCs) and allergic diseases from 2004 to 2023. Publications and their recorded information were retrieved from the Web of Science Core Collection (WoSCC). VOSviewer and Citespace were used to visualize the hotspots and trends of research area. ChemBio 3D, Autodock tools, and Discovery Studio were used to visualize the molecular docking results of hotspots. A total of 4861 articles were retrieved. The number of publications (Np) was in a high and stable state. Years 2011 and 2017 were two peaks in Np. The largest contributor in terms of publications, scholars, and affiliations was the USA. The paper published in NATURE MEDICINE (IF: 82.9) and written by Trompette, A in 2006 had the highest global citation score (GCS). Keywords, such as "asthma," "t-cells," "inflammation," "expression," "atopic dermatitis," "food allergy," "gut microbiota," "murine model," and "cytokines related to immunity" appeared the most frequently. Most of the binding free energy of the key active components of Saposhnikovia divaricata docked with toll-like receptor proteins well. This bibliometric study aimed to help better comprehend the present state and make decisions from a macro viewpoint.

Genetic analyses unravel the causal association of cytokine levels on lichen simplex chronicus risk: insights from a mendelian randomization study

Lichen simplex chronicus (LSC) presents a challenge in dermatology due to its elusive pathogenic mechanisms. While associations between circulating inflammatory cytokines and LSC were observed, the definitive causal dynamics remain to be elucidated. Our study used a two-sample Mendelian randomization (MR) approach to investigate causal relationships. We applied a suite of MR methodologies, including IVW, Weighted Median, MR-Egger, Weighted Mode, Simple Mode, MR-PRESSO, and the Steiger test, to ensure robust causal inference. Our analysis confirmed the causal impact of genetically determined cytokine levels on LSC risk, particularly MMP-10 (OR = 0.493, P = 0.004) and DNER (OR = 0.651, P = 0.043) in risk attenuation. We also found a positive causal correlation between GDNF levels (OR = 1.871, P = 0.007) and LSC prevalence. Notably, bidirectional causality was observed between DNER and LSC. Consistency across various MR analyses and sensitivity analyses confirmed the absence of horizontal pleiotropy, validating the causal estimates. This pioneering MR investigation unveils a novel genetically anchored causal relationship between the circulating levels of MMP-10, DNER, and GDNF and LSC risk. Although further validation is requisite, our findings augment the understanding of cytokine mediation in LSC and underscore prospective avenues for research.

Design, synthesis, and biological evaluation of 2-(2-oxoindolin-3-ylidene)hydrazinecarbothioamides as a potential EGR-1 inhibitor for targeted therapy of atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin disease characterized by intense itching and frequent skin barrier dysfunctions. EGR-1 is a transcription factor that aggravates the pathogenesis of atopic dermatitis by promoting the production of various inflammatory cytokines. Three 2-(2-oxoindolin-3-ylidene)hydrazinecarbothioamides (IT21, IT23, and IT25) were identified as novel inhibitors of EGR-1 DNA-binding activity. In silico docking experiments were performed to elucidate the binding conditions of the EGR-1 zinc-finger (ZnF) DNA-binding domain. Electrophoretic mobility shift assays confirmed the targeted binding effect on the EGR-1 ZnF DNA-binding domain, leading to dose-dependent dissociation of the EGR-1-DNA complex. At the functional cellular level, IT21, IT23, and IT25 effectively reduced mRNA expression of TNFα-induced EGR-1-regulated inflammatory genes, particularly in HaCaT keratinocytes inflamed by TNFα. In the in vivo efficacy study, IT21, IT23, and IT25 demonstrated the potential to alleviate atopic dermatitis-like skin lesions in the ear skin of BALB/c mice. These findings suggest that targeting the EGR-1 ZnF DNA-binding domain with 2-(2-oxoindolin-3-ylidene)hydrazinecarbothioamide derivatives (IT21, IT23, and IT25) could serve as lead compounds for the development of potential therapeutic agents against inflammatory skin disorders, including atopic dermatitis.

Prurigo Nodularis: Pathogenesis and the Horizon of Potential Therapeutics

Chronic pruritus that lasts for over 6 weeks can present in various forms, like papules, nodules, and plaque types, with prurigo nodularis (PN) being the most prevalent. The pathogenesis of PN involves the dysregulation of immune cell-neural circuits and is associated with peripheral neuropathies, possibly due to chronic scratching. PN is a persistent and challenging condition, involving complex interactions among the skin, immune system, and nervous system. Lesional skin in PN exhibits the infiltration of diverse immune cells like T cells, eosinophils, macrophages, and mast cells, leading to the release of inflammatory cytokines and itch-inducing substances. Activated sensory nerve fibers aggravate pruritus by releasing neurotransmitters, perpetuating a vicious cycle of itching and scratching. Traditional treatments often fail, but recent advancements in understanding the inflammatory and itch transmission mechanisms of PN have paved the way for innovative therapeutic approaches, which are explored in this review.

Staphylococcus aureus: The Bug Behind the Itch in Atopic Dermatitis

Pruritus or itch is a defining symptom of atopic dermatitis (AD). The origins of itch are complex, and it is considered both a defense mechanism and a cause of disease that leads to inflammation and psychological stress. Considerable progress has been made in understanding the processes that trigger itch, particularly the pruritoceptive origins that are generated in the skin. This perspective review discusses the implications of a recent observation that the V8 protease expressed by Staphylococcus aureus can directly trigger sensory neurons in the skin through activation of protease-activated receptor 1. This may be a key to understanding why itch is so common in AD because S. aureus commonly overgrows in this disease owing to deficient antimicrobial defense from both the epidermis and the cutaneous microbiome. Increased understanding of the role of microbes in AD provides increased opportunities for safely improving the treatment of this disorder.

Genetic and Immunological Pathogenesis of Atopic Dermatitis

Type 2 immune-mediated diseases give a clear answer to the issue of nature (genetics) versus nurture (environment). Both genetics and environment play vital complementary roles in the development of atopic dermatitis (AD). As a key component of the atopic march, AD demonstrates the interactive nature of genetic and environmental contributions to atopy. From sequence variants in the epithelial barrier gene encoding FLG to the hygiene hypothesis, AD combines a broad array of contributions into a single syndrome. This review will focus on the genetic contribution to AD and where genetics facilitates the elicitation or enhancement of AD pathogenesis.

Atopic Dermatitis Itch: Scratching for an Explanation

Chronic pruritus is a cardinal symptom of atopic dermatitis (AD). The mechanisms underlying atopic itch involve intricate crosstalk among skin, immune components, and neural components. In this review, we explore these mechanisms, focusing on key players and interactions that induce and exacerbate itch. We discuss the similarities and differences between pruritus and pain in patients with AD as well as the relationship between pruritus and factors such as sweat and the skin microbiome. Furthermore, we explore novel targets that could provide significant itch relief in these patients as well as exciting future research directions to better understand atopic pruritus in darker skin types.

Sensory neuronal control of skin barrier immunity

Peripheral sensory neurons recognize diverse noxious stimuli, including microbial products and allergens traditionally thought to be targets of the mammalian immune system. Activation of sensory neurons by these stimuli leads to pain and itch responses as well as the release of neuropeptides that interact with their cognate receptors expressed on immune cells, such as dendritic cells (DCs). Neuronal control of immune cell function through neuropeptide release not only affects local inflammatory responses but can impact adaptive immune responses through downstream effects on T cell priming. Numerous neuropeptide receptors are expressed by DCs but only a few have been characterized, presenting opportunities for further investigation of the pathways by which cutaneous neuroimmune interactions modulate host immunity.

The relationship and clinical significance of serum cytokine expression level and skin pruritus in patients with Hodgkin lymphoma and angioimmunoblastic T-cell lymphoma

Pruritus of lymphoma is commonly associated with both Hodgkin lymphoma (HL) and angioimmunoblastic T cell lymphoma (AITL) and critically affects the life quality of patient. Recent evidence suggests that the pruritogenic cytokines seem to play a significant role in the genesis of chronic. This study aims to investigate the cytokines associated with itching in lymphoma patients and provide the basis for potential therapeutic targets. Serum samples were collected from 60 lymphoma patients, including 47 with Hodgkin lymphoma (HL) and 13 with angioimmunoblastic T-cell lymphoma (AITL), serving as the observation group (lymphoma group, LP group, n = 60). Additionally, serum samples from 8 healthy donors (HD group, n = 8) were collected for comparison. Within the lymphoma group, patients were stratified into those with pruritus (LWP group, n = 30) and those without pruritus (LWOP group, n = 30) based on the presence of skin pruritus symptoms. Elevated levels of multiple cytokines were significantly observed in the LP group in comparison to the HD group (p < 0.01). Patients in LWP group exhibited higher serum levels of IL-31 (p < 0.001), IL-1β (P = 0.039), and IL-1α (P = 0.037) compared to LWOP group. Notably, serum IL-31 levels were higher in advanced AITL patients (stage IV) than in early AITL patients (stage I-Ⅲ, P < 0.05). In subgroup analysis, patients with pruritus in the AITL group exhibited higher serum levels of MIG and CTACK compared to HL group, whereas PDGF-BB levels were significantly lower (p < 0.05). Elevated serum levels of IL-31, IL-1β, and IL-1α are linked to lymphoma-associated pruritus. Differences in serum cytokine profiles between HL and AITL subgroups are also highlighted. These findings offer valuable insights for clinical intervention in managing lymphoma-related pruritus.

Similarities and differences in peripheral itch and pain pathways in atopic dermatitis

Atopic dermatitis (AD) is predominantly characterized by intense itching, but concomitant skin pain is experienced by more than 40% of patients. Patients with AD display considerable somatosensory aberrations, including increased nerve sensitivity to itch stimuli (hyperknesis), perception of itch from innocuous stimuli (alloknesis), or perception of pain from innocuous stimuli (allodynia). This review summarizes the current understanding of the similarities and differences in the peripheral mechanisms underlying itch and pain in AD. These distinct yet reciprocal sensations share many similarities in the peripheral nervous system, including common mediators (such as serotonin, endothelin-1, IL-33, and thymic stromal lymphopoietin), receptors (such as members of the G protein-coupled receptor family and Toll-like receptors), and ion channels for signal transduction (such as certain members of the transient receptor potential [TRP] cation channels). Itch-responding neurons are also sensitive to pain stimuli. However, there are distinct differences between itch and pain signaling. For example, specific immune responses are associated with pain (type 1 and/or type 3 cytokines and certain chemokine C-C [CCL2, CCL5] and C-X-C [CXCL] motif ligands) and itch (type 2 cytokines, including IL-31, and periostin). The TRP melastatin channels TRPM2 and TRPM3 have a role in pain but no known role in itch. Activation of μ-opioid receptors is known to alleviate pain but exacerbate itch. Understanding the connection between itch and pain mechanisms may offer new insights into the treatment of chronic pain and itch in AD.

A systematic review of interleukin-31 inhibitors in the treatment of prurigo nodularis

BACKGROUND

Prurigo nodularis (PN) is a neuroimmunological skin disease. Severe itching is the most challenging symptom which affects patients' quality of life. T helper 2-derived cytokines, such as interleukin-31 and oncostatin M (OSM), play a crucial role in PN pathogenesis. Nemolizumab and vixarelimab are two biologics acting as IL-31 inhibitors. Vixarelimab also suppresses the OSM activity. This systematic review evaluates the efficacy and safety of nemolizumab and vixarelimab in PN management.

METHODS

A systematic search was conducted in PubMed/Medline, Ovid Embase, and Web of Science up to September 17th, 2023. Clinical trials and cohort studies published in English were included.

RESULTS

Among a total of 96 relevant records, five were included. The results of four studies with 452 patients using nemolizumab showed that a significantly higher percentage of patients treated with nemolizumab demonstrated a reduction in peak pruritus numerical rating scale (PP-NRS) and investigator's global assessment along with improved sleep disturbance (SD) and quality of life than the placebo group. Moreover, one study administered vixarelimab to 49 PN patients, and their finding illustrated a higher rate of subjects who received vixarelimab experienced ≥ 4-point diminution in worst itch NRS, visual analog scale, healing of representative lesions, and SD quality compared to the placebo group.

CONCLUSIONS

IL-31 inhibitors suggest distinct advantages in improving pruritus, sleep quality, and overall quality of life in subjects with moderate-to-severe PN. Further clinical studies are recommended to compare the effectiveness of these biologics to other therapeutic choices.

Molecular and cellular pruritus mechanisms in the host skin

Pruritus, also known as itching, is a complex sensation that involves the activation of specific physiological and cellular receptors. The skin is innervated with sensory nerves as well as some receptors for various sensations, and its immune system has prominent neurological connections. Sensory neurons have a considerable impact on the sensation of itching. However, immune cells also play a role in this process, as they release pruritogens. Disruption of the dermal barrier activates an immune response, initiating a series of chemical, physical, and cellular reactions. These reactions involve various cell types, including keratinocytes, as well as immune cells involved in innate and adaptive immunity. Collective activation of these immune responses confers protection against potential pathogens. Thus, understanding the molecular and cellular mechanisms that contribute to pruritus in host skin is crucial for the advancement of effective treatment approaches. This review provides a comprehensive analysis of the present knowledge concerning the molecular and cellular mechanisms underlying itching signaling in the skin. Additionally, this review explored the integration of these mechanisms with the broader context of itch mediators and the expression of their receptors in the skin.

Neuroimmune interplay during type 2 inflammation: Symptoms, mechanisms, and therapeutic targets in atopic diseases

Type 2 inflammation is characterized by overexpression and heightened activity of type 2 cytokines, mediators, and cells that drive neuroimmune activation and sensitization to previously subthreshold stimuli. The consequences of altered neuroimmune activity differ by tissue type and disease; they include skin inflammation, sensitization to pruritogens, and itch amplification in atopic dermatitis and prurigo nodularis; airway inflammation and/or hyperresponsiveness, loss of expiratory volume, airflow obstruction and increased mucus production in asthma; loss of sense of smell in chronic rhinosinusitis with nasal polyps; and dysphagia in eosinophilic esophagitis. We describe the neuroimmune interactions that underlie the various sensory and autonomic pathologies in type 2 inflammatory diseases and present recent advances in targeted treatment approaches to reduce type 2 inflammation and its associated symptoms in these diseases. Further research is needed to better understand the neuroimmune mechanisms that underlie chronic, sustained inflammation and its related sensory pathologies in diseases associated with type 2 inflammation.

Emerging trends and hotspots of the itch research: A bibliometric and visualized analysis

AIMS

Itch, a common uncomfortable sensory experience, occurs frequently in inflammatory or allergic disorders. In recent years, with the discovery of itch-specific pathways in the peripheral and central nervous system, the association between immunology and neural pathways has gradually emerged as the main mechanism of itch. Although many studies have been conducted on itch, no bibliometric analysis study focusing on this topic has been conducted. This study aimed to explore the research hotspots and trends in the itch field from a bibliometric perspective.

METHODS

Publications relevant to itch, published from 2003 to 2022, were retrieved from the Science Citation Index-Expanded of Web of Science Core Collection. Publications were critically reviewed and analyzed with CiteSpace software, Vosviewer, and the bibliometric online analysis platform. Visual maps were conducted in terms of annual production, collaborating countries or institutions, productive authors, core journals, co-cited references, and keyword bursts.

RESULTS

2395 articles on itch that met our criteria were identified and the quantity of publications has been increasing rapidly since 2012. The USA was the most influential country. University Hospital Münster was the institution with the most publications. Gil Yosipovitch was the most prolific author. Atopic dermatitis (AD), intradermal serotonin, chronic pruritus, mechanical itch, gastrin-releasing peptide, substance p, interleukin-31 receptor, histamine-induced itch, bile acid, scratching behavior, and h-4 receptor were the top 11 clusters in co-citation cluster analysis. Keyword burst analysis suggested that treatment, inflammation, and AD are current research hotspots.

CONCLUSION

Global publications on itch research have increased steadily and rapidly over the past 20 years. Inflammation and AD are current research hotspots. The neuroimmunological and neuroinflammatory mechanisms of itch, as well as clinical assessment methods and therapeutic targets, will be novel research directions in the future. This study provides guidance for further itch research.

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.

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.

A Bispecific, Tetravalent Antibody Targeting Inflammatory and Pruritogenic Pathways in Atopic Dermatitis

Inhibition of IL-4/IL-13 signaling has dramatically improved the treatment of atopic dermatitis (AD). However, in many patients, clinical responses are slow to develop and remain modest. Indeed, some symptoms of AD are dependent on IL-31, which is only partially reduced by IL-4/IL-13 inhibition. Thus, there is an unmet need for AD treatments that concomitantly block IL-4/IL-13 and IL-31 pathways. We engineered NM26-2198, a bispecific tetravalent antibody designed to accomplish this task. In reporter cell lines, NM26-2198 concomitantly inhibited IL-4/IL-13 and IL-31 signaling with a potency comparable with that of the combination of an anti-IL-4Rα antibody (dupilumab) and an anti-IL-31 antibody (BMS-981164). In human PBMCs, NM26-2198 inhibited IL-4-induced upregulation of CD23, demonstrating functional binding to FcγRII (CD32). NM26-2198 also inhibited the secretion of the AD biomarker thymus and activation-regulated chemokine (TARC) in blood samples from healthy human donors. In male cynomolgus monkeys, NM26-2198 exhibited favorable pharmacokinetics and significantly inhibited IL-31-induced scratching at a dose of 30 mg/kg. In a repeat-dose, good laboratory practice toxicology study in cynomolgus monkeys, no adverse effects of NM26-2198 were observed at a weekly dose of 125 mg/kg. Together, these results justify the clinical investigation of NM26-2198 as a treatment for moderate-to-severe AD.

TRP Ion Channels in Immune Cells and Their Implications for Inflammation

The transient receptor potential (TRP) ion channels act as cellular sensors and mediate a plethora of physiological processes, including somatosensation, proliferation, apoptosis, and metabolism. Under specific conditions, certain TRP channels are involved in inflammation and immune responses. Thus, focusing on the role of TRPs in immune system cells may contribute to resolving inflammation. In this review, we discuss the distribution of five subfamilies of mammalian TRP ion channels in immune system cells and how these ion channels function in inflammatory mechanisms. This review provides an overview of the current understanding of TRP ion channels in mediating inflammation and may offer potential avenues for therapeutic intervention.

The IL-31/TRPV1 pathway mediates allergic asthma exacerbated by DINP dermal exposure in OVA-sensitized Balb/c mice

BACKGROUND

The potential role of dermal exposure diisononyl phthalate (DINP) as an adjuvant in allergic inflammation and asthma has been suggested. However, the current findings do not provide enough evidence to support this claim.

OBJECTIVES

The purpose of this investigation was to examine the impact and mechanisms of allergic asthma exacerbation through the dermal exposure to DINP.

METHODS

The study was undertaken using OVA-sensitized mice. Lung histopathology and airway hyperreactivity (AHR) were assessed. Expression levels of immunoglobulins (t-IgE, OVA-IgE and OVA-IgG1), cytokines (IL-31, IL-4, IL-5, IL-6, IL-13 and INF-γ), and TRPV1 were measured. To investigate the mechanism by which allergic asthma worsens due to dermal exposure to DINP, the blockade analysis using the IL-31 antagonist SB-431542 and the TRPV1 antagonist capsazepine (CZP) were performed.

RESULTS

The findings of the study revealed that the simultaneous exposure to DINP and OVA resulted in an increase in inspiratory resistance (Ri) and expiratory resistance (Re), a decrease in the minimum value of lung dynamic compliance (Cldyn), and worsened airway remodeling. Additionally, it was found that this exposure led to an increase in the levels of IL-31 and TRPV1, which are biomarkers of Th2 cytokines (IL-4, IL-5, IL-6, and IL-13), as well as immunoglobulins (Total IgE, OVA-lgE, and OVA-IgG1), while decreasing the biomarker of Th1 cytokines (IFN-γ). However, these impairments showed improvement after the administration of SB-431542 or CZP.

CONCLUSION

The findings of this research indicate that the IL-31/TRPV1 pathway plays a moderating function in OVA-induced allergic asthma worsened by dermal exposure to DINP.

The Effect of Osthole on Transient Receptor Potential Channels: A Possible Alternative Therapy for Atopic Dermatitis

Introduction

Chronic recurrent skin inflammation and severe itching in patients with atopic dermatitis (AD) significantly impair their quality of life. The H4 histamine receptor plays a key role in histamine-induced itching. During the skin inflammation associated with AD, pro-inflammatory mediators (interleukins, cytokines) are released from neurons. Ultimately, a cascade of reactions leads to the activation and sensitization of transient receptor potential channels (TRP), which exacerbate the inflammation and itching associated with AD. Osthole (OST) is a natural coumarin with a proven versatile pharmacological effect: anti-cancer, anti-inflammatory and immunomodulatory. However, the molecular mechanism of OST in relieving inflammation in histamine-mediated itching is not yet clear.

Purpose

In the studies presented, the possible effect of the OST action on the inhibition of the gene expression of the histamine H4 receptor and the key genes of the TRP channels as well as on the concentration of proinflammatory interleukins was analyzed.

Methods

Inflammation was induced in a 3D skin model and a keratinocyte cell line Normal Human Epidermal Keratinocytes (NHEK) identical to that of AD, and then OST was administered at various doses. The concentrations of IL-4/-13 were determined by ELISA. RNA was isolated from the 3D skin cells and the NHEK cell line, and the qPCR method was used to determine the expression of: IL-4α, H4R, TRPV1, TRPV4, TRPM8 analyzed.

Results

The study showed that OST significantly reduced the secretion of IL-4/-13 in a keratinocyte cell line and in a 3D skin model. In addition, OST was found to significantly decrease the gene expression of IL-4α, H4R, TRPV1, TRPV4 and increase TRPM8 in both the NHEK cell line and the organotypic 3D skin model.

Conclusion

The data obtained provide the first in vitro evidence of itch relief following the application of OST to atopic skin. Research on the use of OST as an active component of emollients in the treatment of AD should be continued in the future.

TRPV1 Channel in Human Eosinophils: Functional Expression and Inflammatory Modulation

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel expressed on sensory neurons and immune cells. We hypothesize that TRPV1 plays a role in human eosinophil function and is modulated by inflammatory conditions. TRPV1 expression on human eosinophils was examined by qPCR, flow cytometry, and immunohistochemistry, respectively. TRPV1 functionality was analyzed by investigating calcium flux, apoptosis, modulation by cytokines and acidic pH, and CD69 externalization using flow cytometry. Activation of TRPV1 induced calcium influx and prolonged survival. Although eosinophils were not directly activated by TRPV1 agonists, activation by IL-3 or GM-CSF was mainly restricted to TRPV1-positive eosinophils. TRPV1 surface content was increased by acidic pH, IL-3, IL-31, IL-33, TSLP, TNF-α, BDNF, and NGF-β. Interestingly, TRPV1 was also expressed by eosinophils located in proximity to peripheral nerves in atopic dermatitis (AD) skin. In conclusion, eosinophils express functional TRPV1 channels which are increased by extracellular acidification and AD-related cytokines. Since eosinophils also express TRPV1 in AD skin, our results indicate an important role of TRPV1 for neuroimmune interaction mechanisms in itchy, inflammatory skin diseases, like AD.

Serum IL-31 is related to the severity and 3-month prognosis of patients with Intracerebral hemorrhage

Interleukin (IL)-31/IL-33 axis has been proved to play an important role in the regulation of inflammation, and serum IL-33 was found to be a novel serum prognostic marker of intracerebral hemorrhage (ICH), while the value of serum IL-31 levels on prognosis in patients with ICH remains unknown. The present study was designed to study the value of serum IL-31 levels on prognosis in ICH patients. A total of 200 ICH patients and 50 healthy people were included in this study. We collected clinical data such as demographic data, laboratory data, admission disease scores and medical histories of these participants. We measured serum IL-31 levels using enzyme-linked immunosorbent assay, and assessed the prognosis of ICH patients 3 months after onset by mRS scale, and mRS > 2 was defined as a 3-month poor outcome. The level of IL-31 in ICH patients were significantly higher than that in healthy control people (211.91 ± 61.61 vs 167.64 ± 27.45 pg/mL, P < .001), and levels of IL-31 in ICH patients with 3-month good outcome were significantly lower than that in ICH patients with 3-month poor outcome (196.09 ± 50.84 vs 248.05 ± 41.41 pg/mL, P < .001). Results of correlation analysis suggested that the level of serum IL-31 was positively related to admission NIHSS score (r = 0.627, P < .001), hematoma volume (r = 0.352, P < .001), mRS score (r = 0.515, P < .001), high-density lipoprotein-cholesterol (r = 0.177, P = .012), serum C-reactive protein levels (r = 0.483, P < .001), and serum tumor necrosis factor α levels (r = 0.389, P < .001) in ICH patients, while the level of serum IL-31 was negatively related to the admission GCS score (r = -0.518, P < .001) and triglycerides (r = -0.147, P = .038). Results of multivariate regression analysis shows that serum IL-31 levels are an independent risk factor affecting NIHSS scores (OR = 1.023, 95% CI = 1.010-2.036) and 3-month prognosis (OR = 1.023, 95% CI = 0.982-1.747) in ICH patients. The receiver operating characteristic curve analysis showed that the sensitivity and specificity of serum IL-31 level in evaluating the prognosis of ICH were 85.2% and 76.7%, respectively. A cutoff value of serum IL-31 level > 185.30 pg/mL may indicate a poor prognosis for ICH. Serum IL-31 levels on admission in ICH patients are associated with patient prognosis, and higher serum IL-31 levels are associated with a higher risk of poor prognosis in ICH patients.

Establishment of an experimental model of ovalbumin-induced atopic dermatitis in canines

Introduction

A reliable standard model is required to evaluate the efficacy of new drugs for companion animals, especially dogs. Canine atopic dermatitis (cAD), also known as allergic inflammatory skin disease, is a common condition. Currently, the house dust mite animal model is used in the research of cAD; however, this model exhibits significant individual variation and is difficult to standardize. In this study, we used ovalbumin as an antigen to sensitize and stimulate dogs, thereby establishing a stable model mimicking the T-helper 2 (Th2) response seen in cAD. Our objective was to create a cAD model that could be employed to evaluate the efficacy of novel drugs and mimic the Th2 dominant allergic response observed in the pathogenesis of atopic dermatitis of dogs.

Methods

In this study, six beagles were used. Normal saline was applied to two animals, and ovalbumin to four, on their dorsal skin.

Results

The ovalbumin-treated groups exhibited clinical cAD symptoms, such as pruritus and erythema. Moreover, plasma levels of the cAD markers immunoglobulin E and CCL17 chemokine were higher in the ovalbumin-treated group than in the vehicle control group. The skin thickness of the epidermis was significantly increased in the ovalbumin-treated group, with infiltration of inflammatory cells observed in the thickened dermis region. In conclusion, treatment of canine skin with an optimal concentration of ovalbumin induced typical cAD-like symptoms, and histological and molecular analyses confirmed an enhanced Th2-related immune response.

Conclusion

Therefore, we successfully established a suitable Th2-dominant response mimicking cAD, which will facilitate targeted research of atopic dermatitis in dogs.

Site-Specific Transient Receptor Potential Channel Mechanisms and Their Characteristics for Targeted Chronic Itch Treatment

Chronic itch is a debilitating condition with limited treatment options, severely affecting quality of life. The identification of pruriceptors has sparked a growing interest in the therapeutic potential of TRP channels in the context of itch. In this regard, we provided a comprehensive overview of the site-specific expression of TRP channels and their associated functions in response to a range of pruritogens. Although several potent antipruritic compounds that target specific TRP channels have been developed and have demonstrated efficacy in various chronic itch conditions through experimental means, a more thorough understanding of the potential for adverse effects or interactions with other TRP channels or GPCRs is necessary to develop novel and selective therapeutics that target TRP channels for treating chronic itch. This review focuses on the mechanism of itch associated with TRP channels at specific sites, from the skin to the sensory neuron, with the aim of suggesting specific therapeutic targets for treating this condition.