IL-23 induced in keratinocytes by endogenous TLR4 ligands polarizes dendritic cells to drive IL-22 responses to skin immunization

Experimental verification of Myriocin molecular bioactivity in revoking rheumatoid arthritis: New emphasis on S100A1 repression and PPAR-γ activation via non-canonical pathways in the flare-up of cytokines

Myriocin (MYR), the immunosuppressive agent isolated from Mycelia sterilia is recently nominated as a potential therapy for various inflammatory disorders. This work is a primary insight on the mechanistic pathways for its potential anti-arthritic effect against complete Freund's adjuvant-induced arthritis in mice. First day double injection of 0.1 ml adjuvant, followed by a single booster dose in the second day provoked arthritis after 5 weeks. Initiation of treatment with MYR (0.4 mg/kg, i.p.) and the anti-arthritic drug; methotrexate (MT, 0.75 mg/kg, i.p., 3 times/week) was commenced from day 10 to the end of the study. MYR, similar to MT, mitigate arthritis progression through distinct lowering in serum rheumatoid factor, arthritis index, paw thickness, and lessen joint inflammation and destruction in limb architecture. MYR inhibited S100A1/TLR4 signaling, thus, reduced IL-23 generation and subsequent IL-17 production. MYR exerted additional anti-inflammatory effects via marked reduction in NF-κBp65, TNF-α, IL-1β, IL-6, and COX-2 tissue levels. These effects are linked with myriocin-induced PPAR-γ stimulatory actions, thus explaining the transrepression between PPAR-γ, S100A1/TLR4/NF-κB and IL-23/IL-17 signaling, with emphasizing the central role of PPAR-γ activation in the connection between multiple pathways. In view of these results, myriocin could be a possible innovative cure for immune/inflammatory disorders as rheumatoid arthritis.

Investigation of Clostridium butyricum on atopic dermatitis based on gut microbiota and TLR4/MyD88/ NF-κB signaling pathway

BackgroundProbiotics, as common regulators of the gut microbiota, have been used in research to alleviate clinical symptoms of atopic dermatitis (AD).ObjectiveOur research team has previously identified a potential relieving effect of Clostridium butyricum on the treatment of AD, but the specific mechanism of how Clostridium butyricum alleviates AD has not yet been confirmed.MethodsIn this study, we explored the relieving effect of Clostridium butyricum on AD through in vivo and in vitro experiments. AD mice induced by 2,4-dinitrofluorobenzene (DNFB) were orally administered with 1 × 108 CFU of Clostridium butyricum for three consecutive weeks.ResultsOral administration of Clostridium butyricum reduced ear swelling, alleviated back skin lesions, decreased mast cell and inflammatory cell infiltration, and regulated the levels of inflammation-related cytokines. Clostridium butyricum activated the intestinal immune system through the TLR4/MyD88/NF-κB signaling pathway, suppressed the expression of inflammatory factors IL-10 and IL-13, and protected the damaged intestinal mucosa.ConclusionClostridium butyricum administration improved the diversity and abundance of the gut microbiota, enhanced the functionality of the immune system, and protected the epidermal barrier.

Possibility and Potenzial Intervention Targets of Saffron Extract in the Treatment of Atopic Dermatitis: A Review

Atopic dermatitis (AD) is a chronic, recurrent inflammatory skin disorder characterized by dry skin, eczema-like lesions, and severe itching. The multifaceted etiology of AD, which is not yet fully understood, includes genetic predispositions, immune dysfunctions(such as an impaired skin barrier and abnormal immune regulation), imbalances in the skin microbiota, and environmental factors, among others. In the field of AD treatment, the combination of traditional Chinese medicine and modern medicine is becoming an emerging trend. Given the potenzial side effects and reduced efficacy of conventional therapeutic drugs, Chinese herbal medicines offer patients new treatment options because of their unique efficacy and low toxicity. Some saffron extracts derived from saffron and gardenia, such as crocin, crocetin, and safranal, have shown promising potenzial in the treatment of AD. These natural ingredients not only possess anti-inflammatory and immunomodulatory properties similar to those of traditional Chinese medicines but also demonstrate excellent effects in promoting the repair of damaged skin barriers. Therefore, this article reviews the therapeutic potenzial of saffron extract in the treatment of AD, with a special focus on its mechanisms and potenzial interventions, while emphasizing the importance of herbal medicines as alternatives to traditional treatments, providing AD patients with safer and more effective treatment options.

Toll-like receptors in atopic dermatitis: pathogenesis and therapeutic implications

Toll-like receptors (TLR), the key players of the innate immune system, contribute to the pathogenesis of atopic dermatitis (AD) through multiple pathways. TLRs play a crucial role in delaying barrier repair, promoting Th2-mediated dermatitis, shifting the response toward Th1 in the chronic phase, and contributing to the establishment of the itch-scratch cycle, as well as mediating the effects of UV radiation. The dysregulation of proinflammatory and immunomodulatory effects of TLRs can be attributed to their ligand structures, receptor heterodimerization, the relative frequency of each TLR, interactions with other receptors/signalling pathways, cytokine milieu, and genetic polymorphisms. Current AD treatments like vitamin-D analogs, tacrolimus, and cyclosporine partially work through TLR modulation. Direct TLR stimulation using different compounds has shown therapeutic benefits in preclinical studies. However, significant challenges exist, including off-target effects due to ubiquitous TLR expression and complex roles in immune responses. Future directions include CRISPR-based gene editing to understand TLR functions, development of specific TLR modulators for targeted therapy, and machine learning applications to predict drug responses and identify novel ligands. Patient heterogeneity, including the presence or absence of polymorphisms, variations in TLR expression levels, and differences in immune responses, underscores the need for personalized therapeutic approaches.

IL-4 acts on skin-derived dendritic cells to promote the TH2 response to cutaneous sensitization and the development of allergic skin inflammation

BACKGROUND

Atopic dermatitis is characterized by scratching and a TH2-dominated local and systemic response to cutaneously encountered antigens. Dendritic cells (DCs) capture antigens in the skin and rapidly migrate to draining lymph nodes (dLNs) where they drive the differentiation of antigen-specific naive T cells.

OBJECTIVE

We sought to determine whether non-T-cell-derived IL-4 acts on skin-derived DCs to promote the TH2 response to cutaneously encountered antigen and allergic skin inflammation.

METHODS

DCs from dLNs of ovalbumin (OVA)-exposed skin were analyzed by flow cytometry and for their ability to polarize OVA-specific naive CD4+ T cells. Skin inflammation following epicutaneous sensitization of tape-stripped skin was assessed by flow cytometry of skin cells and real-time quantitative PCR of cytokines. Cytokine secretion and antibody levels were evaluated by ELISA.

RESULTS

Scratching upregulated IL4 expression in human skin. Similarly, tape stripping caused rapid basophil-dependent upregulation of cutaneous Il4 expression in mouse skin. In vitro treatment of DCs from skin dLNs with IL-4 promoted their capacity to drive TH2 differentiation. DCs from dLNs of OVA-sensitized skin of Il4-/- mice and CD11c-CreIl4rflox/- mice, which lack IL-4Rα expression in DCs (DCΔ/Δll4ra mice), were impaired in their capacity to drive TH2 polarization compared with DCs from controls. Importantly, OVA-sensitized DCΔ/Δll4ra mice demonstrated impaired allergic skin inflammation and OVA-specific systemic TH2 response evidenced by reduced TH2 cytokine secretion by OVA-stimulated splenocytes and lower levels of OVA-specific IgE and IgG1 antibodies, compared with controls.

CONCLUSIONS

Mechanical skin injury causes basophil-dependent upregulation of cutaneous IL-4. IL-4 acts on skin DCs that capture antigen and migrate to dLNs to promote their capacity for TH2 polarization and drive allergic skin inflammation.

Topical Application of Nano-Sized Graphene Oxide Cream Ameliorates Acute Skin Inflammation in Mice

We have previously shown that nano-sized graphene oxide (NGO) displays anti-inflammatory activities against NKT cell-mediated sepsis. To address whether NGO could be applied to treat acute skin inflammation, we developed a conventional skin Cetaphil cream containing NGO (denoted as NGO cream) for topical application to skin lesions and investigated its therapeutic efficacy by employing the tape-stripping-induced acute skin inflammation model. Topical application of NGO cream to the wounded area significantly reduced skin lesions compared with application of the control cream. Moreover, NGO cream treatment prevented the tape-stripping-elicited infiltration of, and IL-1β production by, skin neutrophils and dendritic cells. Furthermore, such anti-inflammatory effects of NGO cream were attributed to decreased infiltration of IL-12-producing dendritic cells and IFNγ-producing cells (eg, CD4+ T, CD8+ T, γδ T, NK, and NKT cells) into the skin. In addition, topical NGO cream administration enhanced the expression of suppressive molecules such as FR4 on skin regulatory T cells. Through RNA-sequencing analysis, we found that the preventive effect of NGO cream on acute skin inflammation may be correlated with the activation of keratinocytes located in the epidermis. Our results support NGO cream as a therapeutic option to control acute skin inflammation.

Molecular mechanisms of obesity predisposes to atopic dermatitis

Obesity is a prevalent metabolic disease that reduces bacterial diversity, colonizes the epidermis with lipophilic bacteria, and increases intestinal pro-inflammatory species, all of which lead to impaired epithelial barriers. Adipose tissue secretes immunomodulatory molecules, such as adipokines, leptin, and adiponectin, which alters the morphology of adipocytes and macrophages as well as modulates T cell differentiation and peripheral Th2-dominated immune responses. Atopic dermatitis (AD) and obesity have similar pathological manifestations, including inflammation as well as insulin and leptin resistance. This review examines the major mechanisms between obesity and AD, which focus on the effect on skin and gut microbiota, immune responses mediated by the toll like receptor (TLR) signaling pathway, and changes in cytokine levels (TNF-a, IL-6, IL-4, and IL13). Moreover, we describe the potential effects of adipokines on AD and finally mechanisms by which PPAR-γ suppresses and regulates type 2 immunity.

A comprehensive immunobiology review of IBD: With a specific glance to Th22 lymphocytes development, biology, function, and role in IBD

The two primary forms of inflammatory disorders of the small intestine andcolon that make up inflammatory bowel disease (IBD) are ulcerative colitis (UC) and Crohn's disease (CD). While ulcerative colitis primarily affects the colon and the rectum, CD affects the small and large intestines, as well as the esophagus,mouth, anus, andstomach. Although the etiology of IBD is not completely clear, and there are many unknowns about it, the development, progression, and recurrence of IBD are significantly influenced by the activity of immune system cells, particularly lymphocytes, given that the disease is primarily caused by the immune system stimulation and activation against gastrointestinal (GI) tract components due to the inflammation caused by environmental factors such as viral or bacterial infections, etc. in genetically predisposed individuals. Maintaining homeostasis and the integrity of the mucosal barrier are critical in stopping the development of IBD. Specific immune system cells and the quantity of secretory mucus and microbiome are vital in maintaining this stability. Th22 cells are helper T lymphocyte subtypes that are particularly important for maintaining the integrity and equilibrium of the mucosal barrier. This review discusses the most recent research on these cells' biology, function, and evolution and their involvement in IBD.

Basophils Play a Protective Role in the Recovery of Skin Barrier Function from Mechanical Injury in Mice

Physical trauma disrupts skin barrier function. How the skin barrier recovers is not fully understood. We evaluated in mice the mechanism of skin barrier recovery after mechanical injury inflicted by tape stripping. Tape stripping disrupted skin barrier function as evidenced by increased transepidermal water loss. We show that tape stripping induces IL-1-, IL-23-, and TCRγδ+-dependent upregulation of cutaneous Il17a and Il22 expression. We demonstrate that IL-17A and IL-22 induce epidermal hyperplasia, promote neutrophil recruitment, and delay skin barrier function recovery. Neutrophil depletion improved the recovery of skin barrier function and decreased epidermal hyperplasia. Single-cell RNA sequencing and flow cytometry analysis of skin cells revealed basophil infiltration into tape-stripped skin. Basophil depletion upregulated Il17a expression, increased neutrophil infiltration, and delayed skin barrier recovery. Comparative analysis of genes differentially expressed in tape-stripped skin of basophil-depleted mice and Il17a-/- mice indicated that basophils counteract the effects of IL-17A on the expression of epidermal and lipid metabolism genes important for skin barrier integrity. Our results demonstrate that basophils play a protective role by downregulating Il17a expression after mechanical skin injury, thereby counteracting the adverse effect of IL-17A on skin barrier function recovery, and suggest interventions to accelerate this recovery.

Exogenous drug-induced mouse models of atopic dermatitis

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

Basophils are important for development of allergic skin inflammation

BACKGROUND

Atopic dermatitis skin lesions exhibit increased infiltration by basophils. Basophils produce IL-4, which plays an important role in the pathogenesis of atopic dermatitis.

OBJECTIVE

We sought to determine the role of basophils in a mouse model of antigen-driven allergic skin inflammation.

METHODS

Wild-type mice, mice with selective and inducible depletion of basophils, and mice expressing Il4-driven enhanced green fluorescent protein were subjected to epicutaneous sensitization with ovalbumin or saline. Sensitized skin was examined by histology for epidermal thickening. Cells were analyzed for surface markers and intracellular expression of enhanced green fluorescent protein by flow cytometry. Gene expression was evaluated by real-time reverse transcription-quantitative PCR.

RESULTS

Basophils were important for epidermal hyperplasia, dermal infiltration by CD4+ T cells, mast cells, and eosinophils in ovalbumin-sensitized mouse skin and for the local and systemic TH2 response to epicutaneous sensitization. Moreover, basophils were the major source of IL-4 in epicutaneous-sensitized mouse skin and promote the ability of dendritic cells to drive TH2 polarization of naive T cells.

CONCLUSION

Basophils play an important role in the development of allergic skin inflammation induced by cutaneous exposure to antigen in mice.

Considerations for managing elderly patients with atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) diagnosis in elderly is challenging, due to its clinical polymorphism and the lack of diagnostic biomarkers. Moreover, the chronicity of the disease and the complex pathogenetic mechanism, make elderly AD management challenging.

AREAS COVERED

A narrative review of the current literature was performed using the PubMed, Medline, Embase, and Cochrane Skin databases, by researching the following terms: 'atopic dermatitis,' 'clinical phenotypes,' 'eczema,' 'elderly patients,' 'elderly type atopic dermatitis,' 'eczema clinical presentation.' The aim was to report the current knowledge on pathogenesis, clinical presentation, and treatment options of elderly AD.

EXPERT OPINION

Elderly type AD has recently been identified as a separate entity, with an increasing prevalence. With aging, both immunosenescence and barrier alterations can cause or modify AD presentation. Moreover, a chronic proinflammatory state (so-called 'inflammaging') is often present in elderly subjects. Older patients with AD may present with peculiar immunophenotypic profile, making AD diagnosis challenging. Similarly, the chronicity of the disease and the complex pathogenetic mechanism, make AD management a challenge. Indeed, systemic therapies for AD are often contraindicated or not tolerated and the management of elderly type AD is often burdened with numerous difficulties, leading to undertreated disease. Even if dupilumab and tralokinumab represent a valuable therapeutic weapon, more data on safety of JAK inhibitors are required.

Sex Dimorphism in Pain Threshold and Neuroinflammatory Response: The Protective Effect of Female Sexual Hormones on Behavior and Seizures in an Allergic Rhinitis Model

Our previous research demonstrated that allergic rhinitis could impact behavior and seizure threshold in male mice. However, due to the complex hormonal cycles and hormonal influences on behavior in female mice, male mice are more commonly used for behavioral tests. In this study, we aimed to determine whether these findings were replicable in female mice and to explore the potential involvement of sexual hormones in regulating neuroinflammation in an allergic model. Our results indicate that pain threshold was decreased in female mice with allergic rhinitis and the levels of IL-23/IL-17A/IL-17R were increased in their Dorsal root ganglia. However, unlike males, female mice with AR did not display neuropsychological symptoms such as learning and memory deficits, depression, and anxiety-like behavior. This was along with decreased levels of DNA methyl transferase 1 (DNMT1) and inflammatory cytokines in their hippocampus. Ovariectomized mice were used to mitigate hormonal effects, and the results showed that they had behavioral changes and neuroinflammation in their hippocampus similar to male mice, as well as increased levels of DNMT1. These findings demonstrate sex differences in how allergic rhinitis affects behavior, pain sensitivity, and seizure thresholds. Furthermore, our data suggest that DNMT1 may be influenced by sexual hormones, which could play a role in modulating inflammation in allergic conditions.

Epithelial-derived interleukin-23 promotes oral mucosal immunopathology

At mucosal surfaces, epithelial cells provide a structural barrier and an immune defense system. However, dysregulated epithelial responses can contribute to disease states. Here, we demonstrated that epithelial cell-intrinsic production of interleukin-23 (IL-23) triggers an inflammatory loop in the prevalent oral disease periodontitis. Epithelial IL-23 expression localized to areas proximal to the disease-associated microbiome and was evident in experimental models and patients with common and genetic forms of disease. Mechanistically, flagellated microbial species of the periodontitis microbiome triggered epithelial IL-23 induction in a TLR5 receptor-dependent manner. Therefore, unlike other Th17-driven diseases, non-hematopoietic-cell-derived IL-23 served as an initiator of pathogenic inflammation in periodontitis. Beyond periodontitis, analysis of publicly available datasets revealed the expression of epithelial IL-23 in settings of infection, malignancy, and autoimmunity, suggesting a broader role for epithelial-intrinsic IL-23 in human disease. Collectively, this work highlights an important role for the barrier epithelium in the induction of IL-23-mediated inflammation.

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.

IL-23 stabilizes an effector Treg cell program in the tumor microenvironment

Interleukin-23 (IL-23) is a proinflammatory cytokine mainly produced by myeloid cells that promotes tumor growth in various preclinical cancer models and correlates with adverse outcomes. However, as to how IL-23 fuels tumor growth is unclear. Here, we found tumor-associated macrophages to be the main source of IL-23 in mouse and human tumor microenvironments. Among IL-23-sensing cells, we identified a subset of tumor-infiltrating regulatory T (Treg) cells that display a highly suppressive phenotype across mouse and human tumors. The use of three preclinical models of solid cancer in combination with genetic ablation of Il23r in Treg cells revealed that they are responsible for the tumor-promoting effect of IL-23. Mechanistically, we found that IL-23 sensing represents a crucial signal driving the maintenance and stabilization of effector Treg cells involving the transcription factor Foxp3. Our data support that targeting the IL-23/IL-23R axis in cancer may represent a means of eliciting antitumor immunity.

An AhR-Ovol1-Id1 regulatory axis in keratinocytes promotes skin homeostasis against atopic dermatitis

Skin is our outer permeability and immune defense barrier against myriad external assaults. Aryl hydrocarbon receptor (AhR) senses environmental factors and regulates barrier robustness and immune homeostasis. AhR agonist is in clinical trial for atopic dermatitis (AD) treatment, but the underlying mechanism of action remains ill-defined. Here we report OVOL1/Ovol1 as a conserved and direct transcriptional target of AhR in epidermal keratinocytes. We show that OVOL1/Ovol1 impacts AhR regulation of keratinocyte gene expression, and Ovol1 deletion in keratinocytes hampers AhR's barrier promotion function and worsens AD-like inflammation. Mechanistically, we identify Ovol1's direct downstream targets genome-wide, and provide in vivo evidence for Id1's critical role in barrier maintenance and disease suppression. Furthermore, our findings reveal an IL-1/dermal γδT cell axis exacerbating both type 2 and type 3 immune responses downstream of barrier perturbation in Ovol1 -deficient AD skin. Finally, we present data suggesting the clinical relevance of OVOL1 and ID1 function in human AD. Our study highlights a keratinocyte-intrinsic AhR-Ovol1-Id1 regulatory axis that promotes both epidermal and immune homeostasis against AD-like inflammation, implicating new therapeutic targets for AD.

Immune cells in the epithelial immune microenvironment of psoriasis: emerging therapeutic targets

Psoriasis is a chronic autoimmune inflammatory disease characterized by erroneous metabolism of keratinocytes. The development of psoriasis is closely related to abnormal activation and disorders of the immune system. Dysregulated skin protective mechanisms can activate inflammatory pathways within the epithelial immune microenvironment (EIME), leading to the development of autoimmune-related and inflammatory skin diseases. In this review, we initially emphasized the pathogenesis of psoriasis, paying particular attention to the interactions between the abnormal activation of immune cells and the production of cytokines in psoriasis. Subsequently, we delved into the significance of the interactions between EIME and immune cells in the emergence of psoriasis. A thorough understanding of these immune processes is crucial to the development of targeted therapies for psoriasis. Finally, we discussed the potential novel targeted therapies aimed at modulating the EIME in psoriasis. This comprehensive examination sheds light on the intricate underlying immune mechanisms and provides insights into potential therapeutic avenues of immune-mediated inflammatory diseases.

γδ T cells respond directly and selectively to the skin commensal yeast Malassezia for IL-17-dependent fungal control

Stable microbial colonization of the skin depends on tight control by the host immune system. The lipid-dependent yeast Malassezia typically colonizes skin as a harmless commensal and is subject to host type 17 immunosurveillance, but this fungus has also been associated with diverse skin pathologies in both humans and animals. Using a murine model of Malassezia exposure, we show that Vγ4+ dermal γδ T cells expand rapidly and are the major source of IL-17A mediating fungal control in colonized skin. A pool of memory-like Malassezia-responsive Vγ4+ T cells persisted in the skin, were enriched in draining lymph nodes even after fungal clearance, and were protective upon fungal re-exposure up to several weeks later. Induction of γδT17 immunity depended on IL-23 and IL-1 family cytokine signalling, whereas Toll-like and C-type lectin receptors were dispensable. Furthermore, Vγ4+ T cells from Malassezia-exposed hosts were able to respond directly and selectively to Malassezia-derived ligands, independently of antigen-presenting host cells. The fungal moieties detected were shared across diverse species of the Malassezia genus, but not conserved in other Basidiomycota or Ascomycota. These data provide novel mechanistic insight into the induction and maintenance of type 17 immunosurveillance of skin commensal colonization that has significant implications for cutaneous health.

Gut microbiota-mediated IL-22 alleviates metabolic inflammation

Low-grade chronic inflammation, also known as metabolic inflammation, promotes the development of metabolic diseases. Increasing evidence suggests that changes in gut microbes and metabolites disrupt the integrity of the gut barrier and exert significant effects on the metabolism of various tissues, including the liver and adipose tissue, thereby contributing to metabolic inflammation. We observed that IL-22 is a key signaling molecule that serves as a bridge between intestinal microbes and the host, effectively alleviating metabolic inflammation by modulating the host immunomodulatory network. Here, we focused on elucidating the underlying mechanisms by which the gut microbiota and their metabolites reduce inflammation via IL-22, highlighting the favorable impact of IL-22 on metabolic inflammation. Furthermore, we discuss the potential of IL-22 as a therapeutic target for the management of metabolic inflammation and related diseases.

IL-4 receptor alpha blockade dampens allergic inflammation and upregulates IL-17A expression to promote Saureus clearance in antigen sensitized mouse skin

BACKGROUND

Skin colonization with Staphylococcus aureus aggravates atopic dermatitis and exaggerates allergic skin inflammation in mice. IL-4 receptor α (IL-4Rα) blockade is beneficial in atopic dermatitis and reduces Saureus skin colonization through unknown mechanisms. The cytokine IL-17A restrains Saureus growth.

OBJECTIVES

This study sought to examine the effect of IL-4Rα blockade on Saureus colonization at sites of allergic skin inflammation in mice and determine the mechanism involved.

METHODS

BALB/c mice were epicutaneously sensitized with ovalbumin (OVA). Immediately after, PSVue 794-labeled S aureus strain SF8300 or saline was applied and a single dose of anti-IL-4Rα blocking antibody, a mixture of anti-IL-4Rα and anti-IL-17A blocking antibodies, or IgG isotype controls were administered intradermally. Saureus load was assessed 2 days later by in vivo imaging and enumeration of colony forming units. Skin cellular infiltration was examined by flow cytometry and gene expression by quantitative PCR and transcriptome analysis.

RESULTS

IL-4Rα blockade decreased allergic skin inflammation in OVA-sensitized skin, as well as in OVA-sensitized and Saureus-exposed skin, evidenced by significantly decreased epidermal thickening and reduced dermal infiltration by eosinophils and mast cells. This was accompanied by increased cutaneous expression of Il17a and IL-17A-driven antimicrobial genes with no change in Il4 and Il13 expression. IL-4Rα blockade significantly decreased Saureus load in OVA-sensitized and S aureus-exposed skin. IL-17A blockade reversed the beneficial effect of IL-4Rα blockade on Saureus clearance and reduced the cutaneous expression of IL-17A-driven antimicrobial genes.

CONCLUSIONS

IL-4Rα blockade promotes Saureus clearance from sites of allergic skin inflammation in part by enhancing IL-17A expression.

Toll-like receptors: their roles in pathomechanisms of atopic dermatitis

The skin functions as a physical barrier and represents the first line of the innate immune system. There is increasing evidence that toll-like receptors (TLRs) are involved in the pathomechanisms of not only infectious diseases, but also non-infectious inflammatory diseases. Interestingly, it has been demonstrated that TLRs recognize both exogenous threats, e.g. bacteria and viruses, and endogenous danger signals related to inflammation, cell necrosis, or tissue damage. Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disease, which is associated with impaired skin barrier function, increased skin irritability to non-specific stimuli, and percutaneous sensitization. The impairment of skin barrier function in AD allows various stimuli, such as potential allergens and pathogens, to penetrate the skin and activate the innate immune system, including TLR signaling, which can lead to the development of adaptive immune reactions. In this review, I summarize the current understanding of the roles of TLR signaling in the pathogenesis of AD, with special emphasis on skin barrier function and inflammation.

Complex interactions of cellular players in chronic Graft-versus-Host Disease

Chronic Graft-versus-Host Disease is a life-threatening inflammatory condition that affects many patients after allogeneic hematopoietic stem cell transplantation. Although we have made substantial progress in understanding disease pathogenesis and the role of specific immune cell subsets, treatment options are still limited. To date, we lack a global understanding of the interplay between the different cellular players involved, in the affected tissues and at different stages of disease development and progression. In this review we summarize our current knowledge on pathogenic and protective mechanisms elicited by the major involved immune subsets, being T cells, B cells, NK cells and antigen presenting cells, as well as the microbiome, with a special focus on intercellular communication of these cell types via extracellular vesicles as up-and-coming fields in chronic Graft-versus-Host Disease research. Lastly, we discuss the importance of understanding systemic and local aberrant cell communication during disease for defining better biomarkers and therapeutic targets, eventually enabling the design of personalized treatment schemes.

The IL-4Rα Q576R polymorphism is associated with increased severity of atopic dermatitis and exaggerates allergic skin inflammation in mice

BACKGROUND

Atopic dermatitis (AD) is characterized by TH2-dominated skin inflammation and systemic response to cutaneously encountered antigens. The TH2 cytokines IL-4 and IL-13 play a critical role in the pathogenesis of AD. The Q576->R576 polymorphism in the IL-4 receptor alpha (IL-4Rα) chain common to IL-4 and IL-13 receptors alters IL-4 signaling and is associated with asthma severity.

OBJECTIVE

We sought to investigate whether the IL-4Rα R576 polymorphism is associated with AD severity and exaggerates allergic skin inflammation in mice.

METHODS

Nighttime itching interfering with sleep, Rajka-Langeland, and Eczema Area and Severity Index scores were used to assess AD severity. Allergic skin inflammation following epicutaneous sensitization of mice 1 or 2 IL-4Rα R576 alleles (QR and RR) and IL-4Rα Q576 (QQ) controls was assessed by flow cytometric analysis of cells and quantitative RT-PCR analysis of cytokines in skin.

RESULTS

The frequency of nighttime itching in 190 asthmatic inner-city children with AD, as well as Rajka-Langeland and Eczema Area and Severity Index scores in 1116 White patients with AD enrolled in the Atopic Dermatitis Research Network, was higher in subjects with the IL-4Rα R576 polymorphism compared with those without, with statistical significance for the Rajka-Langeland score. Following epicutaneous sensitization of mice with ovalbumin or house dust mite, skin infiltration by CD4+ cells and eosinophils, cutaneous expression of Il4 and Il13, transepidermal water loss, antigen-specific IgE antibody levels, and IL-13 secretion by antigen-stimulated splenocytes were significantly higher in RR and QR mice compared with QQ controls. Bone marrow radiation chimeras demonstrated that both hematopoietic cells and stromal cells contribute to the mutants' exaggerated allergic skin inflammation.

CONCLUSIONS

The IL-4Rα R576 polymorphism predisposes to more severe AD and increases allergic skin inflammation in mice.

Immunosenescence and Skin: A State of Art of Its Etiopathogenetic Role and Crucial Watershed for Systemic Implications

Immunosenescence is a complex multifactorial phenomenon consisting of wide-ranging remodeling of the immune system during the life span, resulting in an age-related qualitative-quantitative decline of immune cells and cytokines. A growing body of evidence in the international literature is highlighting the etiopathogenetic role of skin immunosenescence in the onset of various dermatologic conditions. Skin immunosenescence also serves as an interesting watershed for the onset of system-wide conditions in the context of allergic inflammation. Moreover, in recent years, an increasingly emerging and fascinating etiopathogenetic parallelism has been observed between some mechanisms of immunosenescence, both at cutaneous and systemic sites. This would help to explain the occurrence of apparently unconnected comorbidities. Throughout our review, we aim to shed light on emerging immunosenescent mechanisms shared between dermatologic disorders and other organ-specific diseases in the context of a more extensive discussion on the etiopathogenetic role of skin immunosenescence. A promising future perspective would be to focus on better understanding the mutual influence between skin and host immunity, as well as the influence of high inter-individual variability on immunosenescence/inflammaging. This can lead to a more comprehensive "immunobiographic" definition of each individual.

Resveratrol Protects against Skin Inflammation through Inhibition of Mast Cell, Sphingosine Kinase-1, Stat3 and NF-κB p65 Signaling Activation in Mice

Inflammation is pathogenic to skin diseases, including atopic dermatitis (AD) and eczema. Treatment for AD remains mostly symptomatic with newer but costly options, tainted with adverse side effects. There is an unmet need for safe therapeutic and preventative strategies for AD. Resveratrol (R) is a natural compound known for its anti-inflammatory properties. However, animal and human R studies have yielded contrasting results. Mast cells (MCs) are innate immune skin-resident cells that initiate the development of inflammation and progression to overt disease. R's effects on MCs are also controversial. Using a human-like mouse model of AD development consisting of a single topical application of antigen ovalbumin (O) for 7 days, we previously established that the activation of MCs by a bioactive sphingolipid metabolite sphingosine-1-phosphate (S1P) initiated substantial skin remodeling compared to controls. Here, we show that daily R application normalized O-mediated epidermal thickening, ameliorated cell infiltration, and inhibited skin MC activation and chemokine expression. We unraveled R's multiple mechanisms of action, including decreased activation of the S1P-producing enzyme, sphingosine kinase 1 (SphK1), and of transcription factors Signal Transducer and Activator of Transcription 3 (Stat3) and NF-κBp65, involved in chemokine production. Thus, R may be poised for protection against MC-driven pathogenic skin inflammation.

Risankizumab in Patients with Moderate-to-Severe Atopic Dermatitis: A Phase 2, Randomized, Double-Blind, Placebo-Controlled Study

INTRODUCTION

Atopic dermatitis (AD) is a heterogeneous disease, with involvement of the T-helper cell (Th) 2, Th22, and potentially Th17 pathways, supporting the use of interleukin (IL)-23 and IL-22 blockade in AD.

METHODS

This phase 2, multicenter, randomized, double-blind, placebo-controlled trial (NCT03706040) evaluated the efficacy and safety of risankizumab, an IL-23 inhibitor, in patients (≥ 12 years old) with moderate-to-severe AD, defined by an Eczema Area and Severity Index (EASI) ≥ 16, affected body surface area ≥ 10%, and a Validated Investigator Global Assessment for AD (vIGA-AD) score ≥ 3. Patients were randomized 2:2:1 to 16-week treatment with risankizumab 150 mg, risankizumab 300 mg, or placebo in period A; patients receiving placebo were re-randomized 1:1 to risankizumab 150 mg or 300 mg and patients receiving risankizumab continued on their randomized dose in 36-week period B. Study drug was administered at baseline and weeks 4, 16, 28, and 40. The primary endpoint was the proportion of patients achieving a ≥ 75% reduction from baseline in EASI (EASI 75) at week 16. Safety was analyzed in all randomized patients who received study medication.

RESULTS

Neither the risankizumab 150 mg (n = 69) nor the 300 mg dose group (n = 69) demonstrated a significantly higher proportion of patients achieving EASI 75 at week 16 compared with the placebo group (n = 34; treatment difference [95% CI] 13.0% [-1.7 to 27.7%; P = 0.084] and 10.0% [-4.6 to 24.6%; P = 0.179], respectively). Most adverse events were mild to moderate in severity; five patients receiving risankizumab reported serious adverse events, including two patients who reported cellulitis.

CONCLUSIONS

Risankizumab was generally well tolerated, with no new safety concerns identified. The study's primary endpoint was not met, with no significant difference in the proportion of patients achieving an EASI 75 response at week 16 with risankizumab 150 mg or 300 mg versus placebo.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03706040.

Immunization with a Pneumococcal pep27 Mutant Strain Alleviates Atopic Dermatitis through the Upregulation of Regulatory T-Cell Activity and Epithelial Barrier Function and Suppressing TSLP Expression

Atopic dermatitis (AD) is an inflammatory disease driven in part by type 2 helper T (Th2) cytokines and skin barrier disruption alleviating the entry of allergens. Thymic stromal lymphopoietin (TSLP), an epithelial cell‒derived cytokine, is known to aggravate AD symptoms by activating Th2. In addition, regulatory T cells (Tregs) inhibit inflammatory cells such as Th2. However, the relationship between TSLP and Tregs in AD is unclear. A murine dermatitis model was induced by applying oxazolone to the ear skin of mice. Prophylactic and therapeutic responses were analyzed by immunizing mice intranasally with a pneumococcal pep27 mutant (Δpep27 mutant), attenuated strain by reducing the virulence of a pathogen. Intranasal immunization with a pneumococcal pep27 mutant could elicit anti-inflammatory Treg-relevant factors and epithelial barrier genes (loricrin, involucrin, filaggrin, and small proline-rich repeat proteins). Thus, pneumococcal pep27-mutant immunization suppressed epidermal collapse, IgE, TSLP, and upregulation of Th2 expression by upregulating Treg activity. In contrast, Treg inhibition aggravated AD symptoms through the upregulation of TSLP and Th2 and the repression of epithelial barrier function compared with that of the noninhibited pneumococcal Δpep27-mutant group. Taken together, immunization with pneumococcal Δpep27 mutant upregulated Treg and epithelial barrier function and inhibited TSLP and Th2 to relieve AD symptoms.

An updated review of the immunological mechanisms of keloid scars

Keloid is a type of disfiguring pathological scarring unique to human skin. The disorder is characterized by excessive collagen deposition. Immune cell infiltration is a hallmark of both normal and pathological tissue repair. However, the immunopathological mechanisms of keloid remain unclear. Recent studies have uncovered the pivotal role of both innate and adaptive immunity in modulating the aberrant behavior of keloid fibroblasts. Several novel therapeutics attempting to restore regulation of the immune microenvironment have shown variable efficacy. We review the current understanding of keloid immunopathogenesis and highlight the potential roles of immune pathway-specific therapeutics.

Single-cell transcriptome profile of mouse skin undergoing antigen-driven allergic inflammation recapitulates findings in atopic dermatitis skin lesions

BACKGROUND

Allergic skin inflammation elicited in mice by epicutaneous (EC) sensitization with antigen shares characteristics with human atopic dermatitis (AD).

OBJECTIVE

We characterized gene expression by single cells in mouse skin undergoing antigen-driven allergic inflammation and compared the results with findings in AD skin lesions.

METHODS

Mice were EC sensitized by application of ovalbumin (OVA) or saline to tape-stripped skin. Single-cell RNA sequencing was performed on skin cells 12 days later. Flow cytometry analysis was performed to validate results.

RESULTS

Sequencing identified 7 nonhematopoietic and 6 hematopoietic cell subsets in EC-sensitized mouse skin. OVA sensitization resulted in the expansion in the skin of T cells, dendritic cells, macrophages, mast cells/basophils, fibroblasts, and myocytes cell clusters, and in upregulation of T_H2 cytokine gene expression in CD4⁺ T cells and mast cells/basophils. Genes differentially expressed in OVA-sensitized skin included genes important for inflammation in dendritic cells and macrophages, collagen deposition, and leukocyte migration in fibroblasts, chemotaxis in endothelial cells and skin barrier integrity, and differentiation in KCs-findings that recapitulate those in AD skin lesions. Unexpectedly, mast cells/basophils, rather than T cells, were the major source of Il4 and ll13 in OVA-sensitized mouse skin. In addition, our results suggest novel pathways in fibroblast and endothelial cells that may contribute to allergic skin inflammation.

CONCLUSION

The gene expression profile of single cells in mouse skin undergoing antigen-driven shares many features with that in AD skin lesions and unveils novel pathways that may be involved in allergic skin inflammation.

The Role of T Helper 22 Cells in Dermatological Disorders

T helper 22 (Th22) cells are a newly identified subset of CD4+ T cells that secrete the effector cytokine interleukin 22 (IL-22) upon specific antigen stimulation, barely with IFN-γ or IL-17. Increasing studies have demonstrated that Th22 cells and IL-22 play essential roles in skin barrier defense and skin disease pathogenesis since the IL-22 receptor is widely expressed in the skin, especially in keratinocytes. Herein, we reviewed the characterization, differentiation, and biological activities of Th22 cells and elucidated their roles in skin health and disease. We mainly focused on the intricate crosstalk between Th22 cells and keratinocytes and provided potential therapeutic strategies targeting the Th22/IL-22 signaling pathway.

Molecular and cellular regulation of psoriatic inflammation

This review highlights the molecular and cellular mechanisms underlying psoriatic inflammation with an emphasis on recent developments which may impact on treatment approaches for this chronic disease. We consider both the skin and the musculoskeletal compartment and how different manifestations of psoriatic inflammation are linked. This review brings a focus to the importance of inflammatory feedback loops that exist in the initiation and chronic stages of the condition, and how close interaction between the epidermis and both innate and adaptive immune compartments drives psoriatic inflammation. Furthermore, we highlight work done on biomarkers to predict the outcome of therapy as well as the transition from psoriasis to psoriatic arthritis.

Comparative Analysis of Single-Cell Transcriptome Data Reveals a Novel Role of Keratinocyte-Derived IL-23 in Psoriasis

Psoriasis, a common inflammatory skin disease, is critically dependent on the IL-23/IL-17 cytokine axis. Although immune cell-derived IL-23 is generally associated with the disease pathogenesis, there have been reports of IL-23 production in keratinocytes. To determine the presence and potential role of keratinocyte-derived IL-23 in psoriasis, we investigated its expression levels using publicly available single-cell RNA sequencing data from human samples. We discovered that the expression of IL23A was detectable in keratinocytes as well as dendritic cells. Furthermore, we examined the IL-23p19 expression in an imiquimod-induced mouse model of psoriasis and found a close relationship between keratinocyte-produced IL-23 and IL-36, another key cytokine in psoriasis pathogenesis. The blockade of IL-23 signaling resulted in the reduced expression of IL-36 in the keratinocytes. Our findings reveal the novel association between keratinocyte-derived IL-23 and IL-36 in psoriasis progression.

Multiple Roles for Cytokines in Atopic Dermatitis: From Pathogenic Mediators to Endotype-Specific Biomarkers to Therapeutic Targets

Atopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases, which generally presents with intense itching and recurrent eczematous lesions. AD affects up to 20% of children and 10% of adults in high-income countries. The prevalence and incidence of AD have increased in recent years. The onset of AD mostly occurs in childhood, although in some cases AD may persist in adult life or even manifest in middle age (adult-onset AD). AD pathophysiology is made of a complex net, in which genetic background, skin barrier dysfunction, innate and adaptive immune responses, as well as itch contribute to disease development, progression, and chronicization. One of the most important features of AD is skin dehydration, which is mainly caused by filaggrin mutations that determine trans-epidermal water loss, pH alterations, and antigen penetration. In accordance with the “outside-inside” theory of AD pathogenesis, in a context of an altered epidermal barrier, antigens encounter epidermal antigen presentation cells (APCs), such as epidermal Langerhans cells and inflammatory epidermal dendritic cells, leading to their maturation and Th-2 cell-mediated inflammation. APCs also bear trimeric high-affinity receptors for immunoglobulin E (IgE), which induce IgE-mediated sensitizations as part of pathogenic mechanisms leading to AD. In this review, we discuss the role of cytokines in the pathogenesis of AD, considering patients with various clinical AD phenotypes. Moreover, we describe the cytokine patterns in patients with AD at different phases of the disease evolution, as well as in relation to different phenotypes/endotypes, including age, race, and intrinsic/extrinsic subtypes. We also discuss the outcomes of current biologics for AD, which corroborate the presence of multiple cytokine axes involved in the background of AD. A deep insight into the correlation between cytokine patterns and the related clinical forms of AD is a crucial step towards increasingly personalized, and therefore more efficient therapy.

A role for neutrophils in early enthesitis in spondyloarthritis

Background

Neutrophils are present in the early phases of spondyloarthritis-related uveitis, skin and intestinal disease, but their role in enthesitis, a cardinal musculoskeletal lesion in spondyloarthritis, remains unknown. We considered the role of neutrophils in the experimental SKG mouse model of SpA and in human axial entheses.

Methods

Early inflammatory infiltrates in the axial and peripheral entheseal sites in SKG mice were evaluated using immunohistochemistry and laser capture microdissection of entheseal tissue. Whole transcriptome analysis was carried out using Affymetrix gene array MTA 1.0, and data was analyzed via IPA. We further isolated neutrophils from human peri-entheseal bone and fibroblasts from entheseal soft tissue obtained from the axial skeleton of healthy patients and determined the response of these cells to fungal adjuvant.

Results

Following fungal adjuvant administration, early axial and peripheral inflammation in SKG mice was characterized by prominent neutrophilic entheseal inflammation. Expression of transcripts arising from neutrophils include abundant mRNA for the alarmins S100A8 and S100A9. In normal human axial entheses, neutrophils were present in the peri-entheseal bone. Upon fungal stimulation in vitro, human neutrophils produced IL-23 protein, while isolated human entheseal fibroblasts produced chemokines, including IL-8, important in the recruitment of neutrophils.

Conclusion

Neutrophils with inducible IL-23 production are present in uninflamed human entheseal sites, and neutrophils are prominent in early murine spondyloarthritis-related enthesitis. We propose a role for neutrophils in the early development of enthesitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02693-7.

IFN-κ Is a Rheostat for Development of Psoriasiform Inflammation

Psoriasis is a common, inflammatory autoimmune skin disease. Early detection of an IFN-1 signature occurs in many psoriasis lesions, but the source of IFN production remains debated. IFN-κ is an important source of IFN-1 production in the epidermis. We identified a correlation between IFN-regulated and psoriasis-associated genes in human lesional skin. We thus wanted to explore the effects of IFN-κ in psoriasis using the well-characterized imiquimod psoriasis model. Three mouse strains aged 10 weeks were used: wild-type C57Bl/6, C57Bl/6 that overexpress Ifnk in the epidermis (i.e., transgenic), and total body Ifnk^-/- (i.e., knockout) strain. Psoriasis was induced by topical application of imiquimod on both ears for 8 consecutive days. Notably, the severity of skin lesions and inflammatory cell infiltration was more significantly increased in transgenic than in wild-type than in knockout mice. Gene expression analysis identified greater upregulation of Mxa, Il1b, Tnfa, Il6, Il12, Il23, Il17, and Ifng in transgenic compared to wild-type compared to knockout mice after imiquimod treatment. Furthermore, imiquimod increased CD8⁺ and CD4⁺ T-cell infiltration more in transgenic than in wild-type than in knockout mice. In summary, we identified IFN-κ as a rheostat for initiation of psoriasiform inflammation. This suggests that targeting IFN-1s early in the disease may be an effective way of controlling psoriatic inflammation.

Basophil-derived IL-4 promotes cutaneous Staphylococcus aureus infection

Superficial cutaneous Staphylococcus aureus (S. aureus) infection in humans can lead to soft tissue infection, an important cause of morbidity and mortality. IL-17A production by skin TCRγδ+ cells in response to IL-1 and IL-23 produced by epithelial and immune cells is important for restraining S. aureus skin infection. How S. aureus evades this cutaneous innate immune response to establish infection is not clear. Here we show that mechanical injury of mouse skin by tape stripping predisposed mice to superficial skin infection with S. aureus. Topical application of S. aureus to tape-stripped skin caused cutaneous influx of basophils and increased Il4 expression. This basophil-derived IL-4 inhibited cutaneous IL-17A production by TCRγδ+ cells and promoted S. aureus infection of tape-stripped skin. We demonstrate that IL-4 acted on multiple checkpoints that suppress the cutaneous IL-17A response. It reduced Il1 and Il23 expression by keratinocytes, inhibited IL-1+IL-23-driven IL-17A production by TCRγδ+ cells, and impaired IL-17A-driven induction of neutrophil-attracting chemokines by keratinocytes. IL-4 receptor blockade is shown to promote Il17a expression and enhance bacterial clearance in tape-stripped mouse skin exposed to S. aureus, suggesting that it could serve as a therapeutic approach to prevent skin and soft tissue infection.

The Keratinocyte as a Crucial Cell in the Predisposition, Onset, Progression, Therapy and Study of the Atopic Dermatitis

The keratinocyte (KC) is the main functional and structural component of the epidermis, the most external layer of the skin that is highly specialized in defense against external agents, prevention of leakage of body fluids and retention of internal water within the cells. Altered epidermal barrier and aberrant KC differentiation are involved in the pathophysiology of several skin diseases, such as atopic dermatitis (AD). AD is a chronic inflammatory disease characterized by cutaneous and systemic immune dysregulation and skin microbiota dysbiosis. Nevertheless, the pathological mechanisms of this complex disease remain largely unknown. In this review, we summarize current knowledge about the participation of the KC in different aspects of the AD. We provide an overview of the genetic predisposing and environmental factors, inflammatory molecules and signaling pathways of the KC that participate in the physiopathology of the AD. We also analyze the link among the KC, the microbiota and the inflammatory response underlying acute and chronic skin AD lesions.

Role of Th22 Cells in Human Viral Diseases

Naive CD4⁺ T cells can differentiate into different cell subsets after receiving antigen stimulation, which secrete corresponding characteristic cytokines and thereby exert biological effects in various diseases. Th22 cells, a novel subset of CD4⁺ T cells, are different from Th1, Th2, Th17, and Treg cell subsets, which have been discovered in recent years. They can express CCR4, CCR6, and CCR10 molecules and secrete IL-22, IL-13, and TNF-α. They are not able to secrete IL-17, IL-4, and interferon-γ (IFN-γ). IL-22 is considered as a major effector molecule of Th22 cells whose functions and mechanisms of regulating cell differentiation have been constantly improved. In this review, we provide an overview of the origin, differentiation of Th22 cells. Moreover, we also describe the interrelationships between Th22 cells and Th17, Th1, and Th2 cells. Additionally, the role of Th22 cells were discussed in human diseases with virus infection, which will provide novel insight for the prevention and treatment of viral infection in human.

Molecular Pathogenesis of Psoriasis and Biomarkers Reflecting Disease Activity

Psoriasis is a chronic inflammatory skin disease induced by multifactorial causes and is characterized by bothersome, scaly reddish plaques, especially on frequently chafed body parts, such as extensor sites of the extremities. The latest advances in molecular-targeted therapies using biologics or small-molecule inhibitors help to sufficiently treat even the most severe psoriatic symptoms and the extra cutaneous comorbidities of psoriatic arthritis. The excellent clinical effects of these therapies provide a deeper understanding of the impaired quality of life caused by this disease and the detailed molecular mechanism in which the interleukin (IL)-23/IL-17 axis plays an essential role. To establish standardized therapeutic strategies, biomarkers that define deep remission are indispensable. Several molecules, such as cytokines, chemokines, antimicrobial peptides, and proteinase inhibitors, have been recognized as potent biomarker candidates. In particular, blood protein markers that are repeatedly measurable can be extremely useful in daily clinical practice. Herein, we summarize the molecular mechanism of psoriasis, and we describe the functions and induction mechanisms of these biomarker candidates.

Gut Microbiota, Probiotics, and Their Interactions in Prevention and Treatment of Atopic Dermatitis: A Review

Atopic dermatitis (AD) is a public health concern and is increasing in prevalence in urban areas. Recent advances in sequencing technology have demonstrated that the development of AD not only associate with the skin microbiome but gut microbiota. Gut microbiota plays an important role in allergic diseases including AD. The hypothesis of the “gut-skin” axis has been proposed and the cross-talk mechanism between them has been gradually demonstrated in the research. Probiotics contribute to the improvement of the intestinal environment, the balance of immune responses, regulation of metabolic activity. Most studies suggest that probiotic supplements may be an alternative for the prevention and treatment of AD. This study aimed to discuss the effects of probiotics on the clinical manifestation of AD based on gut microbial alterations. Here we reviewed the gut microbial alteration in patients with AD, the association between gut microbiota, epidermal barrier, and toll-like receptors, and the interaction of probiotics and gut microbiota. The potential mechanisms of probiotics on alleviating AD via upregulation of epidermal barrier and regulation of immune signaling had been discussed, and their possible effective substances on AD had been explored. This provides the supports for targeting gut microbiota to attenuate AD.

Role of Th22 Cells in the Pathogenesis of Autoimmune Diseases

Upon antigenic stimulation, naïve CD4+T cells differentiate into different subsets and secrete various cytokines to exert biological effects. Th22 cells, a newly identified CD4+T cell subset,are distinct from the Th1, Th2 and Th17 subsets. Th22 cells secrete certain cytokines such as IL-22, IL-13 and TNF-α, but not others, such as IL-17, IL-4, or interferon-γ (IFN-γ), and they express chemokine receptors CCR4, CCR6 and CCR10. Th22 cells were initially found to play a role in skin inflammatory diseases, but recent studies have demonstrated their involvement in the development of various autoimmune diseases. Here, we review research advances in the origin, characteristics and effector mechanisms of Th22 cells, with an emphasis on the role of Th22 cells and their main effector cytokine IL-22 in the pathogenesis of autoimmune diseases. The findings presented here may facilitate the development of new therapeutic strategies for targeting these diseases.

Immunological Aspects of Skin Aging in Atopic Dermatitis

The cutaneous immune response is important for the regulation of skin aging well as for the development of immune-mediated skin diseases. Aging of the human skin undergoes immunosenescence with immunological alterations and can be affected by environmental stressors and internal factors, thus leading to various epidermal barrier abnormalities. The dysfunctional epidermal barrier, immune dysregulation, and skin dysbiosis in the advanced age, together with the genetic factors, facilitate the late onset of atopic dermatitis (AD) in the elderly, whose cases have recently been on the rise. Controversial to the healthy aged skin, where overproduction of many cytokines is found, the levels of Th2/Th22 related cytokines inversely correlated with age in the skin of older AD patients. As opposed to an endogenously aged skin, the expression of the terminal differentiation markers significantly increases with age in AD. Despite the atenuated barrier disturbances in older AD patients, the aged skin carries an impairment associated with the aging process, which reflects the persistence of AD. The chronicity of AD in older patients might not directly affect skin aging but does not allow spontaneous remission. Thus, adult- and elderly subtypes of AD are considered as a lifelong disease.

Keratinocytes: innate immune cells in atopic dermatitis

The skin is a unique immune organ that constitutes a complex network of physical, chemical and microbiological barriers against external insults. Keratinocytes are the most abundant cell type in the epidermis. These cells form the physical skin barrier and represent the first line of the host defense system by sensing pathogens via innate immune receptors, initiating anti-microbial responses and producing various cytokines, chemokines and anti-microbial peptides, which are important events in immunity. A damaged epidermal barrier in atopic dermatitis allows the penetration of potential allergens and pathogens to activate keratinocytes. Among the dysregulation of immune responses in atopic dermatitis, activated keratinocytes play a role in several biological processes that contribute to the pathogenesis of atopic dermatitis. In this review, we summarize the current understanding of the innate immune functions of keratinocytes in the pathogenesis of atopic dermatitis, with a special emphasis on skin-derived anti-microbial peptides and atopic dermatitis-related cytokines and chemokines in keratinocytes. An improved understanding of the innate immunity mediated by keratinocytes can provide helpful insight into the pathophysiological processes of atopic dermatitis and support new therapeutic efforts.

Interleukin 22 mitigates endothelial glycocalyx shedding after lipopolysaccharide injury

BACKGROUND

The endothelial glycocalyx (EG) on the luminal surface of endothelial cells contributes to the permeability barrier of vessels and prevents activation of the coagulation cascade. Endothelial glycocalyx damage, which occurs in the shock state, results in endotheliopathy. Interleukin (IL)-22 is a cytokine with both proinflammatory and anti-inflammatory properties, and how IL-22 affects the EG has not been studied. We hypothesized that IL-22:Fc, a recombinant fusion protein with human IL-22 and the Fc portion of human immunoglobulin G1 (which extends the protein half-life), would not affect EG shedding in endothelium after injury.

METHODS

Human umbilical vein endothelial cells (HUVECs) were exposed to 1 μg/mL lipopolysaccharide (LPS). Lipopolysaccharide-injured cells (n = 284) were compared with HUVECs with LPS injury plus 0.375 μg/mL of IL-22:Fc treatment (n = 293) for 12 hours. These two cohorts were compared with control HUVECs (n = 286) and HUVECs exposed to IL-22:Fc alone (n = 269). Cells were fixed and stained with fluorescein isothiocyanate-labeled wheat germ agglutinin to quantify EG. Total RNA was collected, and select messenger RNAs were quantified by real time - quantitative polymerase chain reaction (RT-qPCR) using SYBR green fluorescence.

RESULTS

Exposure of HUVECs to LPS resulted in degradation of the EG compared with control (5.86 vs. 6.09 arbitrary unit [AU], p = 0.01). Interleukin-22:Fc alone also resulted in degradation of EG (5.08 vs. 6.09 AU, p = 0.01). Treatment with IL-22:Fc after LPS injury resulted in less degradation of EG compared with LPS injury alone (5.86 vs. 5.08 AU, p = 0.002). Expression of the IL-22Ra1 receptor was not different for IL-22:Fc treated compared with LPS injury only (0.69 vs. 0.86 relative expression, p = 0.10). Treatment with IL-22:Fc after LPS injury resulted in less matrix metalloproteinase 2 (0.79 vs. 1.70 relative expression, p = 0.005) and matrix metalloproteinase 14 (0.94 vs. 2.04 relative expression, p = 0.02).

CONCLUSIONS

Interleukin-22:Fc alone induces EG degradation. However, IL-22:Fc treatment after LPS injury appears to mitigate EG degradation. This protective effect appears to be mediated via reduced expression of metalloproteinases.

Enhanced IL-36R signaling promotes barrier impairment and inflammation in skin and intestine

Deficiency in interleukin-36R (IL-36R) antagonist caused by loss-of-function mutations in IL-36RN leads to DITRA (deficiency of IL-36 receptor antagonist), a rare inflammatory human disease that belongs to a subgroup of generalized pustular psoriasis (GPP). We report a functional genetic mouse model of DITRA with enhanced IL-36R signaling analogous to that observed in patients with DITRA, which provides new insight into our understanding of the IL-36 family of molecules in regulating barrier integrity across multiple tissues. Humanized DITRA-like mice displayed increased skin inflammation in a preclinical model of psoriasis, and in vivo blockade of IL-36R pathway using anti-human IL-36R antibody ameliorated imiquimod-induced skin pathology as both prophylactic and therapeutic treatments. Deeper characterization of the humanized DITRA-like mice revealed that deregulated IL-36R signaling promoted tissue pathology during intestinal injury and led to impairment in mucosal restoration in the repair phase of chronic dextran sulfate sodium (DSS)-induced colitis. Blockade of IL-36R pathway significantly ameliorated DSS-induced intestinal inflammation and rescued the inability of DITRA-like mice to recover from mucosal damage in vivo. Our results indicate a central role for IL-36 in regulating proinflammatory responses in the skin and epithelial barrier function in the intestine, suggesting a new therapeutic potential for targeting the IL-36R axis in psoriasis and at the later stages of intestinal pathology in inflammatory bowel disease.