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.

TRPV1-positive sensory nerves and neuropeptides are involved in epidermal barrier repair after tape stripping in mice.

BACKGROUND: The integumentary system of the skin serves as an exceptional protective barrier, with the stratum corneum situated at the forefront. This outermost layer is composed of keratinocytes that biosynthesize filaggrin (encoded by the gene Flg), a pivotal constituent in maintaining skin health. Nevertheless, the precise role of sensory nerves in restoration of the skin barrier after tape stripping-induced epidermal disruption, in contrast to the wound-healing process, remains a tantalizing enigma. OBJECTIVE: This study aimed to elucidate the cryptic role of sensory nerves in repair of the epidermal barrier following tape stripping-induced disruption. METHODS: Through the implementation of resiniferatoxin (RTX)-treated denervation mouse model, we investigated the kinetics of barrier repair after tape stripping and performed immunophenotyping and gene expression analysis in the skin or dorsal root ganglia (DRG) to identify potential neuropeptides. Furthermore, we assessed the functional impact of candidates on the recovery of murine keratinocytes and RTX-treated mice. RESULTS: Ablation of TRPV1-positive sensory nerve attenuated skin barrier recovery and sustained subcutaneous inflammation, coupled with elevated IL-6 level in ear homogenates after tape stripping. Expression of the keratinocyte differentiation marker Flg in the ear skin of RTX-treated mice was decreased compared with that in control mice. Through neuropeptide screening, we found that the downregulation of Flg by IL-6 was counteracted by somatostatin or octreotide (a chemically stable somatostatin analog). Furthermore, RTX-treated mice given octreotide exhibited a partial improvement in barrier recovery after tape stripping. CONCLUSION: Sensory neurons expressing TRPV1 play an indispensable role in restoring barrier function following epidermal injury. Our findings suggest the potential involvement of somatostatin in restoring epidermal repair after skin injury.

Cutaneous manifestations of COVID-19 and COVID-19 vaccination.

In December 2019, a new infectious pathogen named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified in Wuhan, China. Transmitted through respiratory droplets, SARS-CoV-2 is the causative pathogen of coronavirus disease 2019 (COVID-19). Although this new COVID-19 infection is known to cause primarily interstitial pneumonia and respiratory failure, it is often associated with cutaneous manifestations as well. These manifestations with COVID-19 can be classified into seven categories: (i) chilblain-like skin eruption (e.g., COVID toes), (ii) urticaria-like skin eruption, (iii) maculopapular lesions, (iv) vesicular eruptions, (v) purpura, (vi) livedo reticularis and necrotic lesions, (vii) urticarial vasculitis, and others such as alopecia and herpes zoster. The pathogenesis of skin eruptions can be broadly divided into vasculitic and inflammatory skin eruptions. Various cutaneous adverse reactions have also been observed after COVID-19 mRNA vaccination. The major cutaneous adverse reactions are type I hypersensitivity (urticaria and anaphylaxis) and type IV hypersensitivity (COVID arm and erythema multiform). Autoimmune-mediated reactions including bullous pemphigus, vasculitis, vitiligo, and alopecia areata have also been reported. Several cases with chilblain-like lesions and herpes zoster after COVID-19 mRNA vaccination have been published. Various skin diseases associated with COVID-19 and COVID-19 vaccination have been reported, and the mechanism has been partly elucidated. In the process, for example, some papers have reported that it is not related to COVID-19 infection, although it was initially called COVID-toe and considered a COVID-19-associated cutaneous eruption. In fact, some COVID-19-associated skin reactions are indistinguishable from drug eruptions. In the future, the mechanisms of COVID-19- or COVID-19 vaccine-associated skin reactions need to be elucidated and verification of causal relationships is required.

Decreased peripheral basophil counts in urticaria and mouse model of oxazolone-induced hypersensitivity, the latter suggesting basopenia reflecting migration to skin.

A decrease in the number of basophils in the peripheral blood, or basopenia, has been noted, reflecting the activity of chronic spontaneous urticaria (CSU). Infiltration of basophils into the skin has also been reported, but the mechanism of basopenia in CSU has not been clarified. The phenomenon of basopenia during the active phase of urticaria was confirmed, and basophil numbers increased following symptom improvement in 15 out of 17 patients treated with omalizumab and in 13 of 15 patients treated with antihistamines. Our examination by immunostaining also revealed basophil infiltration of the CSU lesions, as in previous reports, but since most of our patients were already taking oral steroids, it was not considered appropriate to examine the relationship between basophil numbers in tissue and peripheral blood. Then, we used mouse model of contact hypersensitivity with a single application of oxazolone, which is known to stimulate basophil infiltration, and investigated basophil counts in the skin, peripheral blood, and bone marrow. In this model, a decrease in peripheral blood basophil numbers was observed one day after challenge, but not after 2 days, reflecting supplementation from the bone marrow. Indeed, when cultured basophils expressing GFP were transplanted into the peripheral blood, GFP-positive basophil numbers in the peripheral blood remained low even after 2 days of challenge. Despite differences among species and models, these results suggest that one reason for the decrease of basophils in the peripheral blood in CSU may involve migration of circulating basophils into the skin.

Innovation in the treatment of atopic dermatitis: Emerging topical and oral Janus kinase inhibitors.

Atopic dermatitis (AD) is characterized by chronic, eczematous, severe pruritic skin lesions. The knowledge on the pathogenesis of AD is driving the development of new drugs. From the research results, it has been revealed that Th2 cell-mediated immunity, skin barrier dysfunction, and pruritus cause a vicious cycle of AD. On the other hand, the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway are one of the essential signaling pathways in various inflammatory diseases including AD. In particular, TSLP, IL-4, IL-13 and IL-22 occupy an important position for Th2 cell-mediated immune reaction. Moreover, experimentally pan-JAK inhibitor suppress the STAT3 activation and improved the skin barrier function. Furthermore TSLP, IL-4, IL-13 and IL-31 contribute a lot to chronic pruritus of AD, and transmitted via JAK-STAT pathway. Therefore, JAK inhibitors are promising candidates for the treatment of severe AD. Here we review clinical trials of topical dergocitinib; a pan-JAK inhibitor, ruxolitinib; a JAK1 and JAK2 inhibitor, and tofacitinib; a JAK1, JAK2, and JAK3 inhibitor and oral baricitinib; a JAK1 and JAK2 inhibitor, abrocitinib and upadacitinib; JAK1 inhibitor. Significant improvements in the symptoms were obtained by each drug with low frequency of adverse events. In particular, oral JAK inhibitors have the ability to improve the pruritus and skin symptoms quickly. Therefore, the emergence of these topical and oral JAK inhibitors would be regarded as an innovation in the treatment of atopic dermatitis.

Pituitary adenylate cyclase-activating polypeptide promotes cutaneous dendritic cell functions in contact hypersensitivity.

BACKGROUND: Sensory nerves regulate cutaneous local inflammation indirectly through induction of pruritus and directly by acting on local immune cells. The underlying mechanisms for how sensory nerves influence cutaneous acquired immune responses remain to be clarified. OBJECTIVE: This study aimed to explore the effect of peripheral nerves on cutaneous immune cells in cutaneous acquired immune responses. METHODS: We analyzed contact hypersensitivity (CHS) responses as a murine model of delayed-type hypersensitivity in absence or presence of resiniferatoxin-induced sensory nerve denervation. We conducted ear thickness measurements, flow cytometric analyses, and mRNA expression analyses in CHS. RESULTS: CHS responses were attenuated in mice that were denervated during the sensitization phase of CHS. By screening neuropeptides, we found that pituitary adenylate cyclase-activating polypeptide (PACAP) mRNA expression was decreased in the dorsal root ganglia after denervation. Administration of PACAP restored attenuated CHS response in resiniferatoxin-treated mice, and pharmacological inhibition of PACAP suppressed CHS. Flow cytometric analysis of skin-draining lymph nodes showed that cutaneous dendritic cell migration and maturation were reduced in both denervated mice and PACAP antagonist-treated mice. The expression of chemokine receptors CCR7 and CXCR4 of dendritic cell s was enhanced by addition of PACAP in vitro. CONCLUSION: These findings indicate that a neuropeptide PACAP promotes the development of CHS responses by inducing cutaneous dendritic cell functions during the sensitization phase.

Variable indoleamine 2,3-dioxygenase expression in acral/mucosal melanoma and its possible link to immunotherapy.

Immune checkpoint inhibitors have improved the prognosis of advanced melanoma. Although anti-programmed death ligand-1 (PD-L1) is a well-studied biomarker for response to anti-programmed death-1 PD-1 therapy in melanoma, its clinical relevance remains unclear. It has been established that the high expression of indoleamine 2,3-dioxygenase (IDO) is correlated to a response to anti-CTLA-4 treatment in melanoma. However, it is still unknown whether the IDO expression is associated with response to anti-PD-1 therapy in advanced melanoma. In addition, acral and mucosal melanomas, which comprise a great proportion of all melanomas in Asians, are genetically different subtypes from cutaneous melanomas; however, they have not been independently analyzed due to their low frequency in Western countries. To evaluate the association of IDO and PD-L1 expression with response to anti-PD-1 antibody in acral and mucosal melanoma patients, we analyzed 32 Japanese patients with acral and mucosal melanomas treated with anti-PD-1 antibody from the perspective of IDO and PD-L1 expression levels by immunohistochemistry (IHC). Multivariate Cox regression models showed that the low expression of IDO in tumors was associated with poor progression-free survival (HR = 0.33, 95% CI = 0.13-0.81, P = 0.016), whereas PD-L1 expression on tumors was not associated with progression-free survival. Significantly lower expression of IDO in tumors was found in non-responders compared to responders. Assessment of the IDO expression could be useful for the identification of suitable candidates for anti-PD-1 therapy among acral and mucosal melanomas patients. Further validation study is needed to estimate the clinical utility of our findings.

Interaction of peripheral nerves and mast cells, eosinophils, and basophils in the development of pruritus.

Mast cells, eosinophils and basophils are central effector immune cells in allergic skin inflammation including atopic dermatitis (AD). Recent studies revealed that the bidirectional interaction between these three immune cell types (mast cells, eosinophils and basophils) and the nervous system is involved in the pathogenesis of neurogenic inflammation, pain and pruritus. Emerging evidence shows that these cells are the main source of pruritogens such as histamine, neuropeptides and cytokines, which are potential new therapeutic targets for drug development in chronic pruritus. For instance, many Th2 cytokines including interleukin (IL)-4, 13 and 31 have been recognized as some of the most promising targets for the treatment of chronic pruritus in AD. In this review, we highlight the link between these three immune cell subsets and peripheral nerves, with emphasis on the development of chronic pruritus such as AD. We present cytokines and receptors of these three immune cells and peripheral nerves, and discuss the therapeutic potential of targeting these neuro-immunological processes.

Accumulation of exhausted CD8+ T cells in extramammary Paget's disease.

Cancer immunotherapy has highlighted the clinical relevance of enhancing anti-tumor response of CD8+ T cells in several cancer types. Little is known, however, about the involvement of the immune system in extramammary Paget's disease (EMPD). We examined the cytotoxicity and the effector functions of CD8+ T cells using paired samples of peripheral blood and tumors by flow cytometry. Expression levels of perforin, granzyme B, IFN-g, TNF-a, and IL-2 in CD8+ tumor-infiltrating lymphocytes (TILs) were significantly lower than those in CD8+ T cells of peripheral blood. Significantly higher expression of PD-1 was found in CD8+TILs than in CD8+ T cells of peripheral blood. A high number of CD8+ cells was significantly associated with poor overall survival (OS) adjusted with age, sex, and clinical stage (hazard ratio [HR] = 5.03, P = 0.045, 95% confidence interval [CI] 1.03-24.4). On the other hand, the number of PD-1+ cells was not associated with OS or disease-free survival (DFS). Moreover, we found that tumor cells produced immunosuppressive molecule indoleamine 2,3-dyoxygenae (IDO). In conclusion, CD8+ TILs displayed an exhausted phenotype in EMPD. IDO expression seemed more relevant in inducing CD8 exhaustion than PD-1 upregulation or PD-L1 expression by immune cells. Restoring the effector functions of CD8+ TILs could be an effective treatment strategy for advanced EMPD.

Killer immunoglobulin-like receptor genotype did not correlate with response to anti-PD-1 antibody treatment in a Japanese cohort.

Immune checkpoint blockade (ICB) induces a remarkable response in patients with certain cancers. However, the response rate is not yet satisfactory. Biomarkers that help physicians identify patients who would benefit from ICB need to be developed. Killer immunoglobulin-like receptors (KIRs) are a class of receptors that are mainly expressed by natural killer cells. KIR genotypes have been shown to influence the outcomes of patients with neuroblastoma and hematopoietic malignancies. KIRs may thus influence the clinical outcomes of melanoma patients receiving nivolumab. We aimed to identify the KIR genotype, or KIR/KIR-ligand combinations, which influence the outcomes of melanoma patients receiving nivolumab. We genotyped 112 melanoma patients who were treated with nivolumab for KIR and human leukocyte antigen. The clinical records of the patients were analyzed to determine if they showed a response to nivolumab, and whether or not they experienced adverse events. Our analysis showed that no KIR gene was associated with a response to nivolumab. The KIR/KIR-ligand combination did not correlate with a response to nivolumab. KIR genes were not predictive of experiencing adverse events of grade 2 or greater. We conclude that the KIR genotype or KIR/KIR-ligand genotype do not show predictive value in melanoma patients receiving nivolumab.

Recent advancement in the mechanism of basophil activation.

Basophils have been recognized as crucial players in allergic inflammation. Basophils have the potential to initiate and expand inflammation through the production of specific cytokines and proteases, and are associated with T helper 2 (Th2) immune responses. In addition, recent studies revealed the heterogeneity in basophil populations. Basophils have been clarified important roles in not only IgE-mediated allergic inflammation but also TSLP-mediated and IgE-independent inflammation. Moreover, basophils infiltrate in many human cutaneous diseases. Basophils are responsible for recruiting other inflammatory cells such as macrophages, eosinophils, and fibroblasts. In this review, we discuss recent advances in our understanding of basophil activation and migration in allergic inflammation.

Interleukin-31 and interleukin-31 receptor: New therapeutic targets for atopic dermatitis.

Atopic dermatitis (AD) is characterized by chronic, eczematous, severe pruritic skin lesions caused by skin barrier dysfunction and T helper (Th)2 cell-mediated immunity. Interleukin (IL)-31 is a potent pruritogenic cytokine primarily produced by Th2 cells. Both IL-31 transgenic mice and wild-type mice treated with IL-31 exhibit AD-like skin lesions and scratching behaviour. IL-31 receptor α-chain (IL-31RA) is also expressed in peripheral nerves and epidermal keratinocytes, and the roles of IL-31 on pruritus and skin barrier have been investigated. Recently, an anti-IL-31 receptor antibody was shown to significantly improve pruritus in AD patients. This review focuses on IL-31 and IL-31RA in AD.

Biomarkers for evaluation of mast cell and basophil activation.

Mast cells and basophils play a pathogenetic role in allergic, inflammatory, and autoimmune disorders. These cells have different development, anatomical location and life span but share many similarities in mechanisms of activation and type of mediators. Mediators secreted by mast cells and basophils correlate with clinical severity in asthma, chronic urticaria, anaphylaxis, and other diseases. Therefore, effective biomarkers to measure mast cell and basophil activation in vivo could potentially have high diagnostic and prognostic values. An ideal biomarker should be specific for mast cells or basophils, easily and reproducibly detectable in blood or biological fluids and should be metabolically stable. Markers of mast cell and basophil include molecules secreted by stimulated cells and surface molecules expressed upon activation. Some markers, such as histamine and lipid mediators are common to mast cells and basophils whereas others, such as tryptase and other proteases, are relatively specific for mast cells. The best surface markers of activation expressed on mast cells and basophils are CD63 and CD203. While these mediators and surface molecules have been associated to a variety of diseases, none of them fulfills requirements for an optimal biomarker and search for better indicators of mast cell/basophil activation in vivo is ongoing.

Decrease of superficial serine and lactate in the stratum corneum due to repetitive frictional trauma.

BACKGROUND: Repetitive frictional trauma can be induced in daily and occupational activities, such as daily ablutions with washcloths. The influence of frictional trauma on the skin barrier function, especially in the perspective of the components of stratum corneum (SC), has not yet been studied in detail. Raman spectroscopy is a noninvasive optical technique based on inelastic light scattering that is capable of measuring several components in the skin. In this study, we used Raman spectroscopy to investigate the change in natural moisturizing factor (NMF) components in the SC following repetitive physical friction. METHODS: Six healthy volunteers, who were included in the study after obtaining an informed consent, performed repetitive washing with soap using nylon towels on the forearm twice a day for 2 weeks and used Raman spectroscopy to investigate the change in NMF components in the SC. RESULTS: Compared with the control, which was washed with soap at the same frequency on the opposite forearm, a significant increase in the transepidermal water loss (TEWL) and a decrease in NMF, serine, and total lactate, responsible for maintenance the SC hydration and structuring and maintaining the epidermal barrier function, in the SC were found. CONCLUSIONS: Increased TEWL and decreased NMF are considered as an etiology of atopic dermatitis (AD); therefore, our findings provide evidence that daily activities with repetitive frictional trauma may be related to the predisposition of AD.