The epithelial cell-derived atopic dermatitis cytokine TSLP activates neurons to induce itch

Deficiency of inducible nitric oxide synthase (iNOS) enhances MC903-induced atopic dermatitis-like inflammation in mice

The production and secretion of inflammatory mediators contribute to the development of atopic dermatitis (AD). The production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) is essential for inflammation. Because of the association of iNOS with type 2 inflammation, upregulated iNOS expression in patients with AD suggests a potential pathogenic role of iNOS in AD. In addition, NO regulates keratinocyte and immune cell functions in various inflammatory dermatoses, contributing to the triggering and amplification of inflammation. To ascertain the role of iNOS in inflammation, we utilized a calcipotriol (CPT, MC903)-induced AD-like inflammation in C57BL/6J wildtype mice and iNOS knockout (iNOS KO) mice to investigate the role of iNOS in inflammation. The results showed that iNOS deficiency aggravated dermatitis in MC903-induced inflammation. The expression levels of pro-inflammatory cytokines and chemokines were dramatically elevated, accompanied by the activation of several pro-inflammatory signaling pathways. Moreover, immunofluorescence staining showed that iNOS was mainly expressed in the epidermis and iNOS deficiency significantly promoted the expression of inflammatory factors in keratinocytes. Additionally, topical application of NO donors ameliorated dermatitis symptoms in the iNOS KO mice. These results indicated that epidermal iNOS is important for the occurrence and development of AD. Our results also underscore the therapeutic potential of NO donors in the treatment of AD.

SYSTEMIC INFLAMMATORY MARKERS CORRELATE WITH CHRONIC KIDNEY DISEASE-ASSOCIATED PRURITUS AND RESPONSE TO TREATMENT

Chronic kidney disease-associated pruritus (CKD-aP) is a distressing condition with a poorly understood pathogenesis. We investigated the relationship between itch intensity and serum levels of 20 pruritic and inflammatory markers in patients with moderate-to-severe CKD-aP. This was a retrospective analysis of data from 851 patients enrolled in two randomized phase 3 trials of difelikefalin, a selective kappa-opioid receptor agonist approved for treating moderate-to-severe CKD-aP. Itch intensity was assessed using the patient-reported Worst Itching Intensity Numerical Rating Scale (WI-NRS). Samples for marker measurement were collected at baseline (pre-treatment) and at Week 12. Multiple regression analysis revealed that baseline itch intensity correlated with a group of chemokines and other markers (CCL2, CCL17, CCL22, CCL27, CXCL10, CXCL11, IFNγ, IL-2, IL-31, NGF). At Week 12, levels of 10 markers (CCL2, CCL22, CXCL2, CXCL10, IFNγ, IL 2RA, IL-31, NGF, TNFα, TSLP) were significantly decreased from baseline in responders to difelikefalin treatment (defined as ≥30% WI-NRS score reduction), but not in non-responders. Levels did not differ between placebo-treated responders and non-responders. The difelikefalin-associated reductions in the 10-marker group levels examined together also revealed a significant difference between the entire difelikefalin- and placebo-treated populations. These findings indicate that CKD-aP intensity is linked to systemic inflammation, potentially via a neuroimmune crosstalk mechanism. They also suggest an anti-inflammatory mechanism of action provides a significant contribution to difelikefalin's efficacy.

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.

Drosophila epidermal cells are intrinsically mechanosensitive and modulate nociceptive behavioral outputs

Somatosensory neurons (SSNs) that detect and transduce mechanical, thermal, and chemical stimuli densely innervate an animal's skin. However, although epidermal cells provide the first point of contact for sensory stimuli, our understanding of roles that epidermal cells play in SSN function, particularly nociception, remains limited. Here, we show that stimulating Drosophila epidermal cells elicits activation of SSNs including nociceptors and triggers a variety of behavior outputs, including avoidance and escape. Further, we find that epidermal cells are intrinsically mechanosensitive and that epidermal mechanically evoked calcium responses require the store-operated calcium channel Orai. Epidermal cell stimulation augments larval responses to acute nociceptive stimuli and promotes prolonged hypersensitivity to subsequent mechanical stimuli. Hence, epidermal cells are key determinants of nociceptive sensitivity and sensitization, acting as primary sensors of noxious stimuli that tune nociceptor output and drive protective behaviors.

Costunolide nanosuspension loaded in dissolvable microneedle arrays for atopic dermatitis treatment

Transdermal drug delivery systems (TDDS) have garnered increasing attention due to their potential to overcome the limitations of the traditional oral route. This study developed a novel transdermal delivery system integrating costunolide nanosuspension (COS-NS) with dissolvable microneedles (DMN) to address the poor aqueous solubility and bioavailability of COS for atopic dermatitis (AD) treatment. COS-NS was prepared via antisolvent precipitation, stabilized with PVP K30 and SDS, and freeze-dried with mannitol (COS NS-M), yielding nanoparticles (203.42 ± 1.99 nm) with enhanced solubility (388.61 ± 9.35 μg/mL) and cumulative release (93.00 ± 2.92 % over 24 h). COS NS-M was incorporated into hyaluronic acid-based DMN (COS-DMN), demonstrating robust mechanical strength (0.12 N/needle) and efficient epidermal penetration (630 µm depth, 95 % success rate in mice skin). Pharmacokinetic studies in rats revealed superior transdermal performance for COS-DMN, achieving a Cmax of 26.30 ± 3.49 ng/mL and AUC0-24h of 210.80 ± 8.15 h·ng/mL, outperforming oral administration. In the 2,4-Dinitrochlorobenzene (DNCB)-induced AD mice model, COS-DMN (less than 10 % of the oral dose) significantly reduced skin thickness, pruritus scores, and inflammatory cytokines (IgE, TNF-α, IL-13) Histological and molecular analyses confirmed attenuated epidermal hyperplasia and inflammatory infiltration. These findings highlight COS-DMN as a minimally invasive, high-efficacy platform for transdermal delivery of hydrophobic therapeutics, offering a promising strategy for AD management.

Long-term application of MC903 in mice prolongs the characteristic symptoms of atopic dermatitis, such as inflammation, skin barrier dysfunction, and itching

Atopic dermatitis (AD) is a chronic skin disease that causes itching and is characterized by recurrent flares and remissions. The interactions among type 2 inflammation, skin barrier dysfunction, and pruritus play important roles in the pathogenesis of AD. AD symptoms persist for a long period; thus, it is desirable to have disease models that reproduce a prolonged AD-like phenotype. Although MC903-induced AD model mice reportedly exhibit type 2 inflammation, skin barrier dysfunction, and pruritus, the effects of long-term application of MC903 on the changes in these symptoms over time are not fully understood. To clarify this point, we conducted a long-term time course analysis of these symptoms by applying MC903 to the ears of mice every other day for four weeks. Increased ear thickness, transepidermal water loss, number of scratching events, and serum IgE levels were observed in the MC903 model. Histological analysis revealed the infiltration of granulocytes and CD3-positive T cells and an increase in mast cells in the dermis. Furthermore, analyses of mRNA and protein expression in ear tissue revealed increased expression of thymic stromal lymphopoietin, IL-4, IL-13, and IL-33, which are involved in type 2 inflammation. All these changes were observed within two weeks after the initial application of MC903 and thereafter persisted throughout the experimental period. In conclusion, our data indicate that the long-term application of MC903 prolongs the duration of the three major symptoms of AD.

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.

Triclosan exacerbates atopic dermatitis in mouse models via thymic stromal lymphopoietin

BACKGROUND

Triclosan, a common antimicrobial agent, is widely used in personal-care products and as a topical antiseptic in atopic dermatitis (AD).

OBJECTIVE

This study aimed to evaluate the topical and systemic effect of triclosan on AD in murine models, with a specific focus on the role of thymic stromal lymphopoietin (TSLP).

METHODS

AD-like skin disease was induced by topical application of MC903 and house dust mites in female wildtype BALB/c, C57BL/6 J, and TSLP receptor (TSLPR)-knockout mouse strains. Mice were treated with triclosan both topically and systemically. Skin inflammation was assessed by measuring ear thickness. Infiltration of immune cells was analyzed by flow cytometry and immunohistochemistry (IHC). Cytokine expression was determined by quantitative real-time PCR.

RESULTS

Triclosan application induced skin inflammation in a dose-dependent manner. Topical triclosan treatment increased ear inflammation and immune cell infiltration in AD-like mouse models. Systemic administration of triclosan also enhanced local AD-like skin reactions. Triclosan-induced skin inflammation was reduced in TSLP-receptor-knockout mice or by blocking TSLP, thus indicating the pivotal role of TSLP in mediating the immunological effects of triclosan.

CONCLUSIONS

Topical and systemic administration of triclosan exacerbates AD-like skin inflammation in murine models, with TSLP being a central mediator of this process. The translational relevance of these findings to human disease remains uncertain, as no direct human data are available.

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.

Type 2 cytokine-JAK1 signaling is involved in the development of dry skin-induced mechanical alloknesis

BACKGROUND

Mechanical alloknesis (m-alloknesis) is itch hypersensitivity induced by normally innocuous stimuli. It is sometimes observed in dry skin based itch-related diseases such as atopic dermatitis (AD), and often triggers the vicious itch-scratch cycle. The acetone-ether and water (AEW) mouse model mimics dry skin-induced m-alloknesis, yet its underlying mechanism remains unclear. Janus kinase (JAK) inhibitors are used to treat AD, but their effects on m-alloknesis are not fully known.

OBJECTIVE

To reveal the effects of various oral JAK inhibitors on m-alloknesis and their action points, using AEW model.

METHODS

AEW model was prepared by treatment with a mixture of acetone-ether, and they were orally administrated a JAK1/2 inhibitor baricitinib, a selective JAK1 inhibitor abrocitinib, or a JAK2 selective inhibitor AZ960, and evaluated m-alloknesis score as the total number of scratching responses in 30 mechanical stimulations. To further elucidate the mechanism of action, IL-4, IL-13 or thymic stromal lymphopoietin (TSLP) or their neutralizing antibodies were also applied to mice. In addition, the levels of these cytokines in mouse skin were measured using multiple immunoassays.

RESULTS

All of JAK inhibitors effectively reduced m-alloknesis, with abrocitinib demonstrating the most significant inhibition. The neutralizing antibodies against IL-4, IL-13, and TSLP inhibited m-alloknesis in AEW mice. Intradermal administration of IL-4, IL-13, or TSLP induced m-alloknesis, and abrocitinib effectively mitigated each cytokine-induced response. Highly sensitive assays detected IL-4, IL-13, IL-31 and TSLP in AEW-treated skin, with TSLP levels significantly increased.

CONCLUSION

Type 2 cytokine-JAK1 signaling is involved in the development of m-alloknesis in dry skin.

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.

The future of topical JAK inhibitors in the treatment of atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) is a chronic inflammatory skin condition, rising in prevalence and significantly impacting quality of life. Janus kinase (JAK) inhibitors are small molecules targeting the JAK-STAT signaling pathway, responsible for immune response and cell proliferation. Therapy with topical JAK inhibitors (JAKinibs) improves AD itch and skin lesions and is well tolerated with no major side effects, making it an interesting novel therapy for AD.

AREAS COVERED

This review provides a comprehensive look at the available research on topical JAK inhibitors, primarily for atopic dermatitis, based on clinical trial outcomes.

EXPERT OPINION

In this review, we summarize research on topical JAKinibs, including ruxolitinib, tofacitinib, delgocitinib, cerdulatinib, and bredocitinib, which target multiple cytokine pathways and have been shown to reduce the itch and inflammation. Their low bioavailability contributes to infrequent and mild side effects. The main limitation of predominantly short-term studies is that the long-term effects of JAK inhibitor therapy are not yet fully known. The body of research is growing, and more information about their effectiveness and safety is being added each year.

S1P/S1PRs-TRPV4 axis is a novel therapeutic target for persistent pain and itch in chronic dermatitis

BACKGROUND AND PURPOSE

While pain and itch are both commonly associated with chronic dermatitis (CD), the molecular mechanisms underlying these debilitating symptoms is not well understood. This study aims to identify novel, endogenous compounds that mediate CD-associated pain and itch.

EXPERIMENTAL APPROACH

Lesional skin of CD model mice was examined using unbiased metabolomic analysis to identify candidate pain or itch inducing compounds in CD. Sphingosine-1-phosphate (S1P) concentration in CD model skin was analysed using UPLC/MS/MS. Behaviour, calcium imaging and immunofluorescence staining were used to determine the pain and itch effects and mechanisms of the identified CD-related compounds.

KEY RESULTS

In the lesional skin of CD model mice, 136 compounds were significantly changed. These compounds are predominately associated with the sphingolipids metabolism pathway. S1P is significantly increased in the lesional skin . The TRPV4 channel was critical for S1P induced itch and pain. Sphingosine kinase 2 (SPHK2), the key enzyme controlling S1P synthesis, was significantly increased in lesional skin. ABC294640, a SPHK2 inhibitor, significantly decreased S1P concentration in lesional CD model skin, as well as in model associated epidermal hyperplasia and chronic pain and itch. In CD patients, SPHK2 expression and S1P concentration were significantly elevated compared to healthy control skin.

CONCLUSION AND IMPLICATIONS

Our results indicate that, in CD, increased S1P induces chronic pain and itch partly through TRPV4. Inhibition of S1P synthesis or the S1P/S1P receptor-TRPV4 pathway are promising treatment strategies for CD-associated pain and itch.

Therapeutic potential of a systemically applied humanized monoclonal antibody targeting Toll‑like receptor 2 in atopic‑dermatitis‑like skin lesions in a mouse model

Atopic dermatitis (AD) is a prevalent, persistent inflammatory skin disorder distinguished by pruritic and irritated skin. Toll-like receptors (TLRs) are specialized receptors that recognize specific patterns associated with pathogens and tissue damage, triggering an innate immune response that protects the host from invading pathogens. Previously, it was demonstrated that intradermal injection of the humanized anti-TLR2 monoclonal antibody (Ab) Tomaralimab effectively relieved AD-like skin inflammation in BALB/c mouse models exposed to house dust mite extracts. However, it remains unclear whether allergenic hapten-induced AD can be effectively treated with systemically administered TLR2-targeting Abs. In the present study, it was observed that administrating Tomaralimab through intravenous injection alleviated AD-like skin lesions in BALB/c mice challenged with topical application of 2,4-dinitrochlorobenzene by reducing the infiltration of inflammatory cells into skin lesions and preventing the creation of various inflammatory cytokines, including thymic stromal lymphopoietin, interleukin (IL)-4, IL-13, IL-17 and IL-31, which are associated with the pathogenesis of AD. These findings support the feasibility of using a humanized anti-TLR2 monoclonal Ab as systemic therapy for AD.

Skin-Protective Performance of Alternative Stratum Corneum Formed by a Pseudo-Ceramide-Containing Steroid Lamellar Cream

Ceramides in the stratum corneum (SC) are important for epidermal barrier function. We previously developed a synthetic pseudo-ceramide for medical (SPCM)-containing steroid cream [SPCM (+)]. This cream forms films on the skin surface and exerts anti-inflammatory effects through steroids. However, the preventive effects of this cream on the disruption of the skin barrier remained unclear. Therefore, in this study, we aimed to evaluate the protective role of SPCM (+) cream against atopic dermatitis (AD)-associated protease allergens on the skin in recovery from barrier-broken skin. We used three-dimensional (3D) skin and mouse models of disrupted skin barriers to evaluate the protective effect of SPCM (+) cream against V8 protease produced by Staphylococcus aureus. In NC/Nga mice with itching caused by living mites, SPCM (+) cream was repeatedly applied once a day for 2 weeks, and scratching behaviour was assessed every week using the MicroAct system. In the 3D skin model, the SPCM (+) cream directly blocked SC degradation by V8 protease of S. aureus and suppressed the expression of interleukin-36 gamma. The application of SPCM (+) cream to mite-parasitised mice suppressed scratching, reduced elevated activity of skin proteases, and inhibited upregulation of thymic stromal lymphopoietin. These beneficial effects of SPCM (+) cream were not observed with steroid creams without SPCM. These results suggest that the SPCM (+) cream is effective in relieving inflammation and itching by protecting the skin from proteases and allergens through its lamellar structure. This cream may be a promising treatment option for skin barrier disorders including AD and xerosis.

The Skin Acid Mantle: An Update on Skin pH

The acid mantle concept refers to the buffer system located in the upper stratum corneum of the skin. By sustaining an acidic environment, the acid mantle contributes to the regulation of the microbiome, structural stability, and inflammation. Skin pH is pivotal in maintaining the integrity of the epidermal barrier. Shifts in pH can disrupt barrier properties, and recent studies have emphasized its impact on dermatologic disease processes. This review explores the complex relationship of mechanisms through which skin pH impacts dermatologic pathologies. Furthermore, we highlight the promising potential of pH-targeted therapies for advancing the management of skin conditions.

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.

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.

Reductive Adjuvant Nanosystem for Alleviated Atopic Dermatitis Syndromes

Atopic dermatitis (AD) is a recurrent and chronic inflammatory skin condition characterized by a high lifetime prevalence and significant impairment of patients' quality of life, primarily due to intense itching and discomfort. However, current pharmacological interventions provide only moderate efficacy and are frequently accompanied by adverse side effects. The immune-pathogenesis of AD involves dysregulation of the Th2 immune response and exacerbation of inflammation related to excessive reactive oxygen species (ROS). Therefore, to address these issues, in this study, we targeted the upstream pathogenesis by designing a pro-Th1 adjuvant nanoemulsion loaded with poly(I:C) and encapsulated with the ROS-scavenger vitamin E, termed PV-NE. PV-NE effectively rebalanced the Th1/Th2 immune response and reduced ROS levels both in vivo and ex vivo, leading to the restoration of immune balance in AD-affected skin and alleviation of symptoms such as lichenification and erythematous patches. In conclusion, our development of the reductive adjuvant nanosystem PV-NE demonstrates its biocompatibility and efficacy in combating AD progression without the use of immunosuppressant glucocorticoids. This has the potential to significantly impact the design and enhancement of pharmacotherapy in future clinical research aimed at curing AD.

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.

Maternal supplementation with α-tocopherol inhibits the development of offspring food allergy, H1R signaling and ultimately anaphylaxis early in life

Food allergy has had a rapid rise in prevalence, and thus it is important to identify approaches to limit the development of food allergy early in life. Because maternal dietary supplementation with α-tocopherol (α-T), an isoform of vitamin E, during pregnancy and nursing increases neonate plasma levels of α-T and can limit neonate development of other allergies, we hypothesized that α-T can limit development of food allergy. To assess this, male mice with mutations in their skin barrier genes (FT-/- mice) were mated with wild-type females that received a diet supplemented with α-tocopherol or a control diet. Starting at postnatal day 3, these FT+/- pups were sensitized 4 to 5 times over 2.5 weeks by skin co-exposure to the food allergen peanut extract (PNE) and the environmental allergen Alternaria alternata (Alt). Control pups were exposed to saline, PNE only or Alt only. Supplementation with α-T blocked Alt+PNE sensitization (anti-PNE-specific IgE), without blocking Alt+PNE-stimulated skin IL33, Areg, OSM, CCL11, TSLP or plasma MCPT1. However, supplementation with α-T blocked mast cell activation, the increase in plasma histamine in Alt+PNE sensitized pups, histamine receptor stimulation of endothelial PKCα signaling, and ultimately oral PNE-induced anaphylaxis in Alt+PNE sensitized mice. Thus, maternal supplementation with α-tocopherol reduced development of food allergy and anaphylaxis in neonates. These results have implications for supplementation of mothers with α-tocopherol to limit development of food allergy in neonates with skin barrier mutations.

Scratching promotes allergic inflammation and host defense via neurogenic mast cell activation

Itch is a dominant symptom in dermatitis, and scratching promotes cutaneous inflammation, thereby worsening disease. However, the mechanisms through which scratching exacerbates inflammation and whether scratching provides benefit to the host are largely unknown. We found that scratching was required for skin inflammation in mouse models dependent on FcεRI-mediated mast cell activation. Scratching-induced inflammation required pain-sensing nociceptors, the neuropeptide substance P, and the mast cell receptor MrgprB2. Scratching also increased cutaneous inflammation and augmented host defense to superficial Staphylococcus aureus infection. Thus, through the activation of nociceptor-driven neuroinflammation, scratching both exacerbated allergic skin disease and provided protection from S. aureus, reconciling the seemingly paradoxical role of scratching as a pathological process and evolutionary adaptation.

Itch

A camping trip will quickly become unpleasant if a horde of mosquitoes descends while you pitch your tent, or you find yourself in a patch of poison oak. Whether due to an insect bite, a poisonous plant, or a chronic skin disease, everyone has experienced the urgent sensation of itch and the sweet relief of scratching. The itch-scratch cycle is so powerful that just reading about itch or seeing someone scratching elicits a strong desire to scratch. Itch is a unique sensation that is mediated by specialized neurons that innervate the skin. In this primer, we will discuss recent advancements that define the molecules and cells that mediate acute itch and that promote chronic itch associated with inflammatory diseases.

Asthma Biologics Across the T2 Spectrum of Inflammation in Severe Asthma: Biomarkers and Mechanism of Action

Airway inflammation, a hallmark feature of asthma, drives many canonical features of the disease, including airflow limitation, mucus plugging, airway remodeling, and hyperresponsiveness. The T2 inflammatory paradigm is firmly established as the dominant mechanism of asthma pathogenesis, largely due to the success of inhaled corticosteroids and biologic therapies targeting components of the T2 pathway, including IL-4, IL-5, IL-13, and thymic stromal lymphopoietin (TSLP). However, up to 30% of patients may lack signatures of meaningful T2 inflammation (ie, T2 low). In T2-low asthma patients, T2 inflammation may be masked due to anti-inflammatory treatments or may be highly variable depending on exposure to common asthma triggers such as allergens, respiratory infections, and smoke or pollution. The epithelium and epithelial cytokines (TSLP, IL-33) are increasingly recognized as upstream drivers of canonical T2 pathways and as modulators of various effector cells, including mast cells, eosinophils, and neutrophils, which impact the pathological manifestations of airway smooth muscle hypertrophy, hypercontractility, and airway hyperresponsiveness. Approved biologics for severe asthma target several distinct mechanisms of action, leading to differential effects on the spectrum of T2 inflammation, inflammatory biomarkers, and treatment efficacy (reducing asthma exacerbations, improving lung function, and diminishing symptoms). The approved anti-asthma biologics primarily target T2 immune pathways, with little evidence suggesting a benefit of targeting non-T2 asthma-associated mediators. Indeed, many negative results challenge current assumptions about the etiology of non-T2 asthma and raise doubts about the viability of targeting popular alternative inflammatory pathways, such as T17. Novel data have emerged from the use of biologics to treat various inflammatory mediators and have furthered our understanding of pathogenic mechanisms that drive asthma. This review discusses inflammatory pathways that contribute to asthma, quantitatively outlines effects of available biologics on biomarkers, and summarizes data and challenges from clinical trials that address non-T2 mechanisms of asthma.

NLRP3 deficiency aggravated DNFB-induced chronic itch by enhancing type 2 immunity IL-4/TSLP-TRPA1 axis in mice

Background

The nod-like receptor family pyrin domain-containing 3 (NLRP3) has been implicated in various skin diseases. However, its role in mediating 2, 4-dinitrofluorobenzene (DNFB)-induced chronic itch remains unclear.

Methods

Widetype (WT) and Nlrp3 deletion (Nlrp3-/- )mice, the expression of transient receptor potential (TRP) ankyrin 1 (TRPA1) inhibitor or recombinant mice interleukin-18 (IL-18) were used to establish and evaluate the severity of DNFB-mediated chronic itch. Quantitative real-time PCR, western blotting, immunohistochemistry staining, immunofluorescence staining and enzyme-linked immunosorbent assay (ELISA) was used to examine the expression of NLRP3 inflammasome, type 2 immunity and receptors in dorsal root ganglion (DRG) neurons related with chronic itch. Flow cytometry was performed to quantify the frequency of type 2 immune cells.

Results

This study revealed that the NLRP3 inflammasome was activated in the skin of DNFB-induced chronic itch mice. Surprisingly, the absence of Nlrp3 exacerbated itch behavior. In Nlrp3-/- mice, IL-18 expression was downregulated, whereas markers of type 2 immunity, such as IL-4 and thymic stromal lymphopoietin (TSLP), were significantly upregulated in the skin. Furthermore, TRPA1 and its colocalization with the IL-4 receptor were increased in the DRG. Inhibition of TRPA1 or administration of recombinant IL-18 significantly reduced DNFB-induced itch behavior in Nlrp3-/- mice. Recombinant IL-18 also decreased the expression of TRPA1, IL-4, and TSLP.

Discussion

These findings suggested that the absence of Nlrp3 aggravated DNFB-induced chronic itch by exacerbating type 2 immunity in the skin and enhancing the IL-4/TSLP-TRPA1 axis, potentially driven by reduced IL-18 levels.

[Mechanism of transduction of itch and strategy of treatment for itch]

Itch is an unpleasant sense to evoke desire to scratch skin. Itch not only disturbs daily lives, but also exacerbates inflammation in case of atopic dermatitis (AD). It had been thought that both itch and pain are transduced by the same neurons; however, it is now known that neutrons transducing either itch or pain are distinct. Moreover, TRP channels, a family of calcium channels, play an important role for transducing itch as well as pain, temperature, and pressure. Development of neuroscience and molecular biology has dramatically advanced our understanding of how itch is transduced in recent years. On the other hand, development of immunology has revealed that there exist several immune types in our host defense mechanism and that type 2 immune reaction is dominant in the pathogenesis of allergic diseases including AD. Although it had been already known that type 2 cytokines contribute to the pathogenesis of AD by binding to their receptors on both immune cells and tissue resident cells, it has been recently found that several type 2 cytokines directly transduce the itch signals by binding to peripheral nerves. Due to this discovery, we can understand more deeply the itch mechanism of AD and can develop molecularly targeted drugs for AD targeting type 2 cytokines, which has dramatically changed the treatment of AD. In this review article, we describe the progress of our recent understanding of the itch mechanism and the strategy of treatment against it.

Cytokines reprogram airway sensory neurons in asthma

Nociceptor neurons play a crucial role in maintaining the body's homeostasis by detecting and responding to potential environmental dangers. However, this function can be detrimental during allergic reactions, as vagal nociceptors contribute to immune cell infiltration, bronchial hypersensitivity, and mucus imbalance in addition to causing pain and coughing. Despite this, the specific mechanisms by which nociceptors acquire pro-inflammatory characteristics during allergic reactions are not yet fully understood. In this study, we investigate the changes in the molecular profile of airway nociceptor neurons during allergic airway inflammation and identify the signals driving such reprogramming. Using retrograde tracing and lineage reporting, we identify a specific class of inflammatory vagal nociceptor neurons that exclusively innervate the airways. In the ovalbumin mouse model of allergic airway inflammation, these neurons undergo significant reprogramming characterized by the upregulation of the neuropeptide Y (NPY) receptor Npy1r. A screening of cytokines and neurotrophins reveals that interleukin 1β (IL-1β), IL-13, and brain-derived neurotrophic factor (BDNF) drive part of this reprogramming. IL-13 triggers Npy1r overexpression in nociceptors via the JAK/STAT6 pathway. In parallel, NPY is released into the bronchoalveolar fluid of asthmatic mice, which limits the excitability of nociceptor neurons. Single-cell RNA sequencing of lung immune cells reveals that a cell-specific knockout of NPY1R in nociceptor neurons in asthmatic mice altered T cell infiltration. Opposite findings are observed in asthmatic mice in which nociceptor neurons are chemically ablated. In summary, allergic airway inflammation reprograms airway nociceptor neurons to acquire a pro-inflammatory phenotype, while a compensatory mechanism involving NPY1R limits the activity of nociceptor neurons.

IL-27 as a novel biomarker for pruritus in nodular prurigo and bullous pemphigoid

Introduction

Bullous pemphigoid (BP) and prurigo nodularis (PN) are chronic pruritic skin diseases that severely impact patients' quality of life. Despite the widespread attention these two diseases have garnered within the dermatological field, the specific pathogenesis, particularly the molecular mechanisms underlying the pruritus, remains largely unclear. Limited clinical sequencing studies focusing on BP and PN have hindered the identification of pathological mechanisms and the exploration of effective treatment strategies.

Methods

To address this gap, we collected a total of 23 peripheral blood mononuclear cell samples from BP and PN patients, as well as healthy controls, and performed RNA sequencing analysis. By integrating bioinformatics and machine learning techniques, we aimed to uncover the shared immune regulatory networks and pruritus-related mechanisms between BP and PN.

Results

Our study identified 161 differentially expressed genes shared between BP and PN, which were primarily enriched in immune activation and neural pathways, providing crucial molecular insights into the pruritus-related mechanisms of both diseases. Furthermore, using the machine learning algorithms of support vector machines and random forest, we pinpoint 7 crucial genes shared between the BP and PN databases. Among these, IL-27 emerged as a potential pivotal gene, as its mRNA expression levels strongly correlated with clinical parameters including pruritus scores, immunoglobulin E levels, and eosinophil counts. Validation experiments conducted on clinical samples from an additional 22 participants confirmed the upregulation of IL-27 expression in both BP and PN lesions.

Discussion

This study is the first to unveil the shared inflammatory and immune pathways common to BP and PN, highlighting the critical role of IL-27 in the pathogenesis of these conditions. Our findings not only enhance the understanding of the intricate relationship between BP and PN, but also provide a foundation for the development of novel therapeutic strategies targeting these two dermatological conditions.

From the bench to the clinic: basophils and type 2 epithelial cytokines of thymic stromal lymphopoietin and IL-33

Type 2 epithelial cytokines, including thymic stromal lymphopoietin and IL-33, play central roles in modulation of type 2 immune cells, such as basophils. Basophils are a small subset of granulocytes within the leukocyte population that predominantly exist in the blood. They have non-redundant roles in allergic inflammation in peripheral tissues such as the lung, skin and gut, where they increase and accumulate at inflammatory lesions and exclusively produce large amounts of IL-4, a type 2 cytokine. These inflammatory reactions are known to be, to some extent, phenocopies of infectious diseases of ticks and helminths. Recently, biologics related to both type 2 epithelial cytokines and basophils have been approved by the US Food and Drug Administration for treatment of allergic diseases. We summarised the roles of Type 2 epithelial cytokines and basophils in basic science to translational medicine, including recent findings.

Alarmins in Chronic Spontaneous Urticaria: Immunological Insights and Therapeutic Perspectives

Background: In the world, approximately 1% of the population suffers from chronic spontaneous urticaria (CSU), burdening patients' quality of life and challenging clinicians in terms of treatment. Recent scientific evidence has unveiled the potential role of a family of molecules known as "alarmins" in the pathogenesis of CSU. Methods: Papers focusing on the potential pathogenetic role of alarmins in CSU with diagnostic (as biomarkers) and therapeutic implications, in English and published in PubMed, Scopus, Web of Science, as well as clinical studies registered in ClinicalTrials.gov and the EudraCT Public website, were reviewed. Results: The epithelial-derived alarmins thymic stromal lymphopoietin and IL-33 could be suitable diagnostic and prognostic biomarkers and possible therapeutic targets in CSU. The evidence on the role of non-epithelial-derived alarmins (heat shock proteins, S-100 proteins, eosinophil-derived neurotoxin, β-defensins, and acid uric to high-density lipoproteins ratio) is more heterogeneous and complex. Conclusions: More homogeneous studies on large cohorts, preferably supported by data from international registries, will be able to elucidate the intriguing and complex pathogenetic world of CSU.

Decoding the neuroimmune axis in the atopic march: mechanisms and implications

The immune and nervous systems have co-evolved complex mechanisms to sense environmental dangers and orchestrate a concerted response to safeguard tissue and mobilize host defenses. This sophisticated interplay, marked by a shared repertoire of receptors and ligands, influences disease pathogenesis. Neuro-immune interactions in allergic diseases are pivotal for symptom development, from anaphylaxis to chronic conditions like asthma and atopic dermatitis. This review explores the neuro-immune interplay within the atopic march, emphasizing its role in host defense, inflammation resolution, and tissue repair. We delve into the multifaceted functions of nociceptors in orchestrating type 2 immune responses and the progression of allergic disorders, focusing on key regulators such as CGRP-RAMP1 and SP-MRGPRB2/A2. Additionally, we discuss the potential of nociceptor neuron-blocking drugs to target neuro-immunity, offering the possibility of reversing the progression of the atopic march. Altogether, we underscore the need for targeted interventions to disrupt the pathological processes and enhance therapeutic outcomes at various stages of the atopic march.

Atopic dermatitis: pathogenesis and therapeutic intervention

The skin serves as the first protective barrier for nonspecific immunity and encompasses a vast network of skin-associated immune cells. Atopic dermatitis (AD) is a prevalent inflammatory skin disease that affects individuals of all ages and races, with a complex pathogenesis intricately linked to genetic, environmental factors, skin barrier dysfunction as well as immune dysfunction. Individuals diagnosed with AD frequently exhibit genetic predispositions, characterized by mutations that impact the structural integrity of the skin barrier. This barrier dysfunction leads to the release of alarmins, activating the type 2 immune pathway and recruiting various immune cells to the skin, where they coordinate cutaneous immune responses. In this review, we summarize experimental models of AD and provide an overview of its pathogenesis and the therapeutic interventions. We focus on elucidating the intricate interplay between the immune system of the skin and the complex regulatory mechanisms, as well as commonly used treatments for AD, aiming to systematically understand the cellular and molecular crosstalk in AD-affected skin. Our overarching objective is to provide novel insights and inform potential clinical interventions to reduce the incidence and impact of AD.

TRPV4-β-catenin axis is a novel therapeutic target for dry skin-induced chronic itch

Dry skin induced chronic pruritus is an increasingly common and debilitating problem, especially in the elderly. Although keratinocytes play important roles in innate and adaptive immunity and keratinocyte proliferation is a key feature of dry skin induced chronic pruritus, the exact contribution of keratinocytes to the pathogenesis of dry skin induced chronic pruritus is poorly understood. In this study, we generated the acetone-ether-water induced dry skin model in mice and found that epidermal hyperplasia induced by this model is partly dependent on the β-catenin signaling pathway. XAV939, an antagonist of β-catenin signaling pathway, inhibited epidermal hyperplasia in dry skin model mice. Importantly, dry skin induced chronic pruritus also dramatically reduced in XAV939 treated mice. Moreover, acetone-ether-water treatment-induced epidermal hyperplasia and chronic itch were decreased in Trpv4-/- mice. In vitro, XAV939 inhibited hypo-osmotic stress induced proliferation of HaCaT cells, and hypo-osmotic stress induced proliferation of in HaCaT cells and primary cultured keratinocytes were also significantly reduced by blocking TRPV4 function. Finally, thymic stromal lymphopoietin release was examined both in vivo and in vitro, which was significantly inhibited by XAV939 treatment and Trpv4 deficiency, and anti-TSLP antibody treatment significantly decreased AEW-induced scratching behavior. Overall, our study revealed a unique ability of TRPV4 expressing keratinocytes in the skin, which critically mediated dry skin induced epidermal hyperplasia and chronic pruritus, thus provided novel insights into the development of therapies for chronic pruritus in the elderly.

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.

Rosmarinic Acid Ameliorates Dermatophagoides farinae Extract-Induced Atopic Dermatitis-like Skin Inflammation by Activating the Nrf2/HO-1 Signaling Pathway

Atopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases. AD pathogenesis is associated with increased oxidative stress, impairment of the skin barrier, and activation of the immune response. Rosmarinic acid (RA), a caffeic acid ester, is known for its anti-inflammatory and antioxidant properties. However, the effects of RA on Dermatophagoides farinae extract (DfE)-induced AD-like skin inflammation, as well as its ability to regulate oxidative stress through the Nrf2/HO-1 pathway in TNF-α/IFN-γ-treated keratinocytes, remain unclear. We investigated RA activity in a DfE-induced AD-like skin inflammation mouse model and IFN-γ/TNF-α-stimulated keratinocytes. We found that RA attenuates DfE-induced inflammation by decreasing dermatitis scores and serum inflammatory marker levels and mast cell infiltration. Additionally, RA significantly suppressed IFN-γ/TNF-α-induced chemokine production in keratinocytes and reduced Th cytokine levels in concanavalin A-stimulated splenocytes. Importantly, RA also increased Nrf2/HO-1 expression in TNF-α/IFN-γ-treated keratinocytes. In conclusion, this study demonstrated that RA effectively alleviates DfE-induced AD-like skin lesions by reducing the levels of inflammatory cytokines and chemokines. Furthermore, RA promotes Nrf2/HO-1 signaling in keratinocytes, which may help mitigate DfE-induced oxidative stress, thereby alleviating AD-like skin inflammation. These findings highlight the potential of RA as a therapeutic agent for treating AD and other skin inflammation.

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.

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

The Pathogenesis of CKD-Associated Pruritus: A Theoretical Model and Relevance for Treatment

Our understanding of the pathogenesis of uremic pruritus (also known as CKD-associated pruritus [CKD-aP]) remains elusive. Although multiple discrete changes in the immunochemical milieu of the skin of patients with CKD-aP have been described, a coherent theory of mechanism is absent. This article proposes a theoretical model of mechanism. It concentrates on the initiation phase of CKD-aP and its three parts: ( 1 ) genesis, triggered by first precipitants; ( 2 ) cascade of cytokine release that follows and the cross-talking of multiple skin cells with each other and afferent nerve fibers; and ( 3 ) enhancement. The limitation of the model will be described and ideas for future research proposed. Implications for management shall be examined.

Antipruritic effect of ursolic acid through MRGPRX2/MrgprB2-dependent inhibition of mast cell degranulation and reduced TSLP production

Ursolic acid (UA), a pentacyclic triterpene, exhibits diverse pharmacological effects, including potential treatment for allergic diseases. It downregulates thymic stromal lymphopoietin (TSLP) and disrupts mast cell signaling pathways. However, the exact molecular mechanism by which UA interferes with mast cell action remains unclear. Therefore, the current study aimed to uncover molecular entities underlying the effect of UA on mast cells and its potential antipruritic effect, specifically investigating its modulation of key molecules such as TRPV4, PAR2, and MRGPRX2, which are involved in TSLP regulation and sensation. Calcium imaging experiments revealed that UA pretreatment significantly suppressed MRGPRX2 activation (and its mouse orthologue MrgprB2), a G protein-coupled receptor predominantly expressed in mast cells. Molecular docking predictions suggested potential interactions between UA and MRGPRX2/MrgprB2. UA pretreatment also reduced mast cell degranulation through MRGPRX2 and MrgprB2-dependent mechanisms. In a dry skin mouse model, UA administration decreased tryptase and TSLP production in the skin, and diminished TSLP response in the sensory neurons. While PAR2 and TRPV4 activation enhances TSLP production, UA did not inhibit their activity. Notably, UA attenuated compound 48/80-induced scratching behaviors in mice and suppressed spontaneous scratching in a dry skin model. The present study confirms the effective inhibition of UA on MRGPRX2/MrgprB2, leading to reduced mast cell degranulation and suppressed scratching behaviors. These findings highlight the potential of UA as an antipruritic agent for managing various allergy- or itch-related conditions.

The Role of Neuro-Immune Interactions in the Pathology and Pathogenesis of Allergic Rhinitis

BACKGROUND

Allergic rhinitis (AR) is a non-infectious inflammatory disease of the nasal mucosa mediated by IgE and involving a variety of immune cells such as mast cells. In previous studies, AR was considered as an isolated disease of the immune system. However, recent studies have found that the nervous system is closely related to the development of AR. Bidirectional communication between the nervous and immune systems plays an important role in AR.

SUMMARY

The nervous system and immune system depend on the anatomical relationship between nerve fibers and immune cells, as well as various neurotransmitters, cytokines, inflammatory mediators, etc. to produce bidirectional connections, which affect the development of AR.

KEY MESSAGES

This article reviews the impact of neuro-immune interactions in AR on the development of AR, including neuro-immune cell units.

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.

Navigating the evolving landscape of atopic dermatitis: Challenges and future opportunities: The 4th Davos declaration

The 4th Davos Declaration was developed during the Global Allergy Forum in Davos which aimed to elevate the care of patients with atopic dermatitis (AD) by uniting experts and stakeholders. The forum addressed the high prevalence of AD, with a strategic focus on advancing research, treatment, and management to meet the evolving challenges in the field. This multidisciplinary forum brought together top leaders from research, clinical practice, policy, and patient advocacy to discuss the critical aspects of AD, including neuroimmunology, environmental factors, comorbidities, and breakthroughs in prevention, diagnosis, and treatment. The discussions were geared towards fostering a collaborative approach to integrate these advancements into practical, patient-centric care. The forum underlined the mounting burden of AD, attributing it to significant environmental and lifestyle changes. It acknowledged the progress in understanding AD and in developing targeted therapies but recognized a gap in translating these innovations into clinical practice. Emphasis was placed on the need for enhanced awareness, education, and stakeholder engagement to address this gap effectively and to consider environmental and lifestyle factors in a comprehensive disease management strategy. The 4th Davos Declaration marks a significant milestone in the journey to improve care for people with AD. By promoting a holistic approach that combines research, education, and clinical application, the Forum sets a roadmap for stakeholders to collaborate to improve patient outcomes in AD, reflecting a commitment to adapt and respond to the dynamic challenges of AD in a changing world.

Cytokines reprogram airway sensory neurons in asthma

Nociceptor neurons play a crucial role in maintaining the body's homeostasis by detecting and responding to potential dangers in the environment. However, this function can be detrimental during allergic reactions, since vagal nociceptors can contribute to immune cell infiltration, bronchial hypersensitivity, and mucus imbalance, in addition to causing pain and coughing. Despite this, the specific mechanisms by which nociceptors acquire pro-inflammatory characteristics during allergic reactions are not yet fully understood. In this study, we aimed to investigate the molecular profile of airway nociceptor neurons during allergic airway inflammation and identify the signals driving such reprogramming. Using retrograde tracing and lineage reporting, we identified a unique class of inflammatory vagal nociceptor neurons that exclusively innervate the airways. In the ovalbumin mouse model of airway inflammation, these neurons undergo significant reprogramming characterized by the upregulation of the NPY receptor Npy1r. A screening of cytokines and neurotrophins revealed that IL-1β, IL-13 and BDNF drive part of this reprogramming. IL-13 triggered Npy1r overexpression in nociceptors via the JAK/STAT6 pathway. In parallel, sympathetic neurons and macrophages release NPY in the bronchoalveolar fluid of asthmatic mice, which limits the excitability of nociceptor neurons. Single-cell RNA sequencing of lung immune cells has revealed that a cell-specific knockout of Npy1r in nociceptor neurons in asthmatic mice leads to an increase in airway inflammation mediated by T cells. Opposite findings were observed in asthmatic mice in which nociceptor neurons were chemically ablated. In summary, allergic airway inflammation reprograms airway nociceptor neurons to acquire a pro-inflammatory phenotype, while a compensatory mechanism involving NPY1R limits nociceptor neurons' activity.

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.

NOCICEPTOR NEURONS CONTROL POLLUTION-MEDIATED NEUTROPHILIC ASTHMA

The immune and sensory nervous systems, having evolved together, use a shared language of receptors and transmitters to maintain homeostasis by responding to external and internal disruptions. Although beneficial in many cases, neurons can exacerbate inflammation during allergic reactions, such as asthma. Our research modeled asthma aggravated by pollution, exposing mice to ambient PM2.5 particles and ovalbumin. This exposure significantly increased bronchoalveolar lavage fluid neutrophils and γδ T cells compared to exposure to ovalbumin alone. We normalized airway inflammation and lung neutrophil levels by silencing nociceptor neurons at inflammation's peak using intranasal QX-314 or ablating TRPV1-expressing neurons. Additionally, we observed heightened sensitivity in chemical-sensing TRPA1 channels in neurons from pollution-exacerbated asthmatic mice. Elevated levels of artemin were detected in the bronchoalveolar lavage fluid from pollution-exposed mice, with artemin levels normalizing in mice with ablated nociceptor neurons. Upon exposure PM2.5 particles, alveolar macrophages expressing pollution-sensing aryl hydrocarbon receptors, were identified as the source of artemin. This molecule enhanced TRPA1 responsiveness and increased neutrophil influx, providing a novel mechanism by which lung-innervating neurons respond to air pollution and suggesting a potential therapeutic target for controlling neutrophilic airway inflammation in asthma, a clinically intractable condition.

Agrimonia coreana Extract Exerts Its Therapeutic Effect through CRAC Channel Inhibition for Atopic Dermatitis Treatment

Atopic dermatitis (AD) is a common allergic inflammatory skin condition marked by severe itching, skin lichenification, and chronic inflammation. AD results from a complex immune response, primarily driven by T lymphocytes and environmental triggers, leading to a disrupted epidermal barrier function. Traditional treatments, such as topical corticosteroids, have limitations due to long-term side effects, highlighting the need for safer alternatives. Here, we aimed to show that Agrimonia coreana extract (ACext) can be used in treating AD-related dermatologic symptoms. ACext could inhibit CRAC (Calcium Release-Activated Calcium) channel activity, reducing Orai1/CRAC currents and decreasing intracellular calcium signaling. This inhibition was further confirmed by the reduced IL-2 levels and T cell proliferation upon ACext treatment. In a mouse model of AD, ACext significantly ameliorates symptoms, improves histological parameters, and enhances skin barrier function, demonstrating its potential for treating AD.