Serum IL-33 levels are increased in patients with psoriasis

Skin damage signals mediate allergic sensitization to spatially unlinked antigen

Our current understanding of immunity to pathogens suggests that anatomic coupling of antigens with danger signals is a required feature for the formation of immune memory. However, in the context of pathogen-independent inflammation, the stringency of this anatomical coupling is unclear. Here, we demonstrate that multiple modes of skin injury were sufficient to induce a humoral response to antigens introduced in the gut. Skin damage induced a narrow subset of endocrine cytokines that were necessary and sufficient for the priming of antigens introduced at various distal tissues. Thus, in addition to "local priming" of antigen entering through damaged skin, there also exists another paradigm of "remote priming" where anatomical coupling is not essential because of the dissemination of damage-associated intermediaries. Our findings have implications for understanding the fundamental mechanisms of the formation of humoral memory with wide implications for diseases such as food allergy and in vaccinology.

Safe and effective management of psoriasis through Ayurveda: A case report

Ayurveda, an ancient system, offers in-depth insights into various skin disorders. It provides detailed understanding of causative factors and pathomechanisms, along with time-tested traditional treatments based on its principles. We report a 16-year chronic case of psoriasis (36-year-old male patient) with plaques and peeling erythrodermic skin rashes over the back and front of the trunk area and both legs. The scalp area and nail beds were also affected. The early involvement of joints was also noted. A two-year multimodal Ayurveda treatment has shown notable efficacy in managing chronic plaque and erythrodermic psoriasis, with no reported adverse events or side effects. The progressive events were documented in the form of photographs with the proper consent of the patient. The Ayurveda medicines, strict dietary regimen, and regular follow-ups together resulted in promising outcomes, revalidating the potential of Ayurveda in controlling psoriasis and its complications.

Limonin alleviates imiquimod-induced psoriasis-like skin inflammation in mice model by downregulating inflammatory responses

Psoriasis is a chronic inflammatory condition affecting 1-2% of the global population. Phytomedicine, which uses plant-based compounds, is emerging as a promising approach to managing such inflammatory diseases. Limonin, a phytochemical found in citrus fruits and known for its bitter taste, possesses significant pharmacological properties. In this study, we evaluated the anti-psoriatic effects of limonin using a psoriasis-induced mice model. BALB/c mice were treated with imiquimod to induce psoriasis and then administered limonin at doses of 20 and 40 mg/kg/day for 6 days. Tacrolimus ointment served as a positive control. We assessed the hematological profile to determine limonin's impact on leukocytes in the psoriasis model. Additionally, histomorphometric analysis of ear and skin tissues was conducted to evaluate the therapeutic effects of limonin. We further investigated the antioxidant properties of limonin by measuring levels of antioxidants and oxidative stress markers. The anti-inflammatory effects were evaluated by quantifying inflammatory cytokines and signaling proteins. In vitro, the cytotoxicity and anti-inflammatory potential of limonin were assessed using murine macrophage RAW264.7 cells. Our findings showed that limonin significantly reduced leukocyte counts, decreased inflammatory cell infiltration, and improved skin histoarchitecture in psoriasis-induced mice. Limonin also effectively scavenged free radicals and reduced levels of inflammatory cytokines and proteins without causing cytotoxicity in RAW264.7 cells. Overall, our in vivo and in vitro results confirm that limonin is a potent anti-inflammatory agent that effectively ameliorates imiquimod-induced psoriasis.

Cytokines in psoriasis: From pathogenesis to targeted therapy

Psoriasis is a multifactorial disease that affects 0.84% of the global population and it can be associated with disabling comorbidities. As patients present with thick scaly lesions, psoriasis was long believed to be a disorder of keratinocytes. Psoriasis is now understood to be the outcome of the interaction between immunological and environmental factors in individuals with genetic predisposition. While it was initially thought to be solely mediated by cytokines of type-1 immunity, namely interferon-γ, interleukin-2, and interleukin-12 because it responds very well to cyclosporine, a reversible IL-2 inhibitor; the discovery of Th-17 cells advanced the understanding of the disease and helped the development of biological therapy. This article aims to provide a comprehensive review of the role of cytokines in psoriasis, highlighting areas of controversy and identifying the connection between cytokine imbalance and disease manifestations. It also presents the approved targeted treatments for psoriasis and those currently under investigation.

Interleukin-1 family cytokines at the crossroads of microbiome regulation in barrier health and disease

Recent advances in understanding how the microbiome can influence both the physiology and the pathogenesis of disease in humans have highlighted the importance of gaining a deeper insight into the complexities of the host-microbial dialogue. In tandem with this progress, has been a greater understanding of the biological pathways which regulate both homeostasis and inflammation at barrier tissue sites, such as the skin and the gut. In this regard, the Interleukin-1 family of cytokines, which can be segregated into IL-1, IL-18 and IL-36 subfamilies, have emerged as important custodians of barrier health and immunity. With established roles as orchestrators of various inflammatory diseases in both the skin and intestine, it is now becoming clear that IL-1 family cytokine activity is not only directly influenced by external microbes, but can also play important roles in shaping the composition of the microbiome at barrier sites. This review explores the current knowledge surrounding the evidence that places these cytokines as key mediators at the interface between the microbiome and human health and disease at the skin and intestinal barrier tissues.

Etiopathogenesis of Psoriasis: Integration of Proposed Theories

Psoriasis is a chronic inflammatory disease characterized by squamous and erythematous plaques on the skin and the involvement of the immune system. Global prevalence for psoriasis has been reported around 1-3% with a higher incidence in adults and similar proportions between men and women. The risk factors associated with psoriasis are both extrinsic and intrinsic, out of which a polygenic predisposition is a highlight out of the latter. Psoriasis etiology is not yet fully described, but several hypothesis have been proposed: 1) the autoimmunity hypothesis is based on the over-expression of antimicrobial peptides such as LL-37, the proteins ADAMTSL5, K17, and hsp27, or lipids synthesized by the PLA2G4D enzyme, all of which may serve as autoantigens to promote the differentiation of autoreactive lymphocytes T and unleash a chronic inflammatory response; 2) dysbiosis of skin microbiota hypothesis in psoriasis has gained relevance due to the observations of a loss of diversity and the participation of pathogenic bacteria such as Streptococcus spp. or Staphylococcus spp. the fungi Malassezia spp. or Candida spp. and the virus HPV, HCV, or HIV in psoriatic plaques; 3) the oxidative stress hypothesis, the most recent one, describes that the cell injury and the release of proinflammatory mediators and antimicrobial peptides that leads to activate of the Th1/Th17 axis observed in psoriasis is caused by a higher release of reactive oxygen species and the imbalance between oxidant and antioxidant mechanisms. This review aims to describe the mechanisms involved in the three hypotheses on the etiopathogeneses of psoriasis.

Regulatory Mechanism of the IL-33-IL-37 Axis via Aryl Hydrocarbon Receptor in Atopic Dermatitis and Psoriasis

Interleukin (IL)-33 and IL-37 have been identified as novel cytokines involved in various inflammatory diseases. However, their specific roles remain largely unknown. Recent studies have shown that IL-33, which triggers inflammation, and IL-37, which suppresses it, cooperatively regulate the balance between inflammation and anti-inflammation. IL-33 and IL-37 are also deeply involved in the pathogenesis of inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis. Furthermore, a signaling pathway by which aryl hydrocarbon receptor (AHR), a receptor for dioxins, regulates the expression of IL-33 and IL-37 has been revealed. Here, we outline recent findings on the mechanisms regulating IL-33 and IL-37 expression in AD and psoriasis. IL-33 expression is partially dependent on mitogen-activated protein kinase (MAPK) activation, and IL-37 has a role in suppressing MAPK in human keratinocytes. Furthermore, IL-33 downregulates skin barrier function proteins including filaggrin and loricrin, thereby downregulating the expression of IL-37, which colocalizes with these proteins. This leads to an imbalance of the IL-33-IL-37 axis, involving increased IL-33 and decreased IL-37, which may be associated with the pathogenesis of AD and psoriasis. Therefore, AHR-mediated regulation of the IL-33-IL-37 axis may lead to new therapeutic strategies for the treatment of AD and psoriasis.

Clinical application of serum biomarkers for detecting and monitoring of chronic plaque psoriasis

Psoriasis, a chronic, multisystemic inflammatory disease affecting millions of people globally, manifests as erythematous, thick, scaly plaques on the skin. Clinical evaluation remains to be the benchmark for diagnosis and monitoring of this debilitating disease. With current advancements in targeted molecular therapy for psoriasis such as biologics, molecular detection methods may also help guide clinical decisions and therapeutic strategies through quantification of circulating biomarkers, which could reflect the underlying pathogenic events happening at a certain point of the disease course. In this review, we will discuss how biomarkers are detected in serum samples using enzyme-linked immunosorbent assay (ELISA). This review will feature candidate biomarkers supported by clinical data for psoriasis including, but not limited to, cytokines, chemokines, adipokines, and antimicrobial peptides. A better understanding of the common method used for biomarker detection would enable physicians to interpret and correlate laboratory results with the disease pathogenesis and clinical outcomes, e.g., severity assessment and/or therapeutic response. With better health outcomes as the main goal, the utility of such information to evaluate and even predict treatment response would be a major step closer towards patient-tailored management.

Microbiota and IL-33/31 Axis Linkage: Implications and Therapeutic Perspectives in Atopic Dermatitis and Psoriasis

Microbiome dysbiosis and cytokine alternations are key features of atopic dermatitis (AD) and psoriasis (PsO), two of the most prevalent and burdensome pruritic skin conditions worldwide. Interleukin (IL)-33 and IL-31 have been recognized to be major players who act synergistically in the pathogenesis and maintenance of different chronic inflammatory conditions and pruritic skin disorders, including AD and PsO, and their potential role as therapeutic targets is being thoroughly investigated. The bidirectional interplay between dysbiosis and immunological changes has been extensively studied, but there is still debate regarding which of these two factors is the actual causative culprit behind the aetiopathological process that ultimately leads to AD and PsO. We conducted a literature review on the Pubmed database assessing articles of immunology, dermatology, microbiology and allergology with the aim to strengthen the hypothesis that dysbiosis is at the origin of the IL-33/IL-31 dysregulation that contributes to the pathogenesis of AD and PsO. Finally, we discussed the therapeutic options currently in development for the treatment of these skin conditions targeting IL-31, IL-33 and/or the microbiome.

Anti-interleukin 33 treatment alleviates psoriatic dermatitis in mice induced imiquimod

Interleukin-33（IL-33), is constitutively expressed in the epithelial cells of the skin. It has been reported that IL-33 contributed to the severity of the disease in psoriasis-like mouse models. In the current study, we evaluated the effect of anti-IL-33 antibody (Ab) in imiquimod-induced psoriatic dermatitis in mice. Our observations showed that anti-IL-33 Ab ameliorated the erythema, scaling, epidermal thickness and spleen index. Additionally, we found anti-IL-33 Ab significantly decreased the expression of psoriasis-related cytokines. Moreover, anti-IL-33 Ab significantly reduced Ki-67 positive cells, CD3⁺CD4⁺T cells, and CD3⁺CD8⁺T cells in the skin lesions. Furthermore, anti-IL-33 Ab treatment down-regulated the expression of phosphorylation of STAT3 and IL-33 in model mouse. These results indicated that the anti-IL-33 Ab alleviated the seriousness of skin lesions, inhibited the activation of the STAT3, lymphocyte infiltration and the secretion of pro-inflammatory cytokines in imiquimod-induced psoriatic dermatitis in mice, suggesting IL-33 may be a therapeutic target for the treatment of psoriasis.

Skin Barrier Function and Its Relationship With IL-17, IL-33, and Filaggrin in Malar Melasma

BACKGROUND

The pathogenesis of melasma remains unclear. Interleukin (IL)-17, a proinflammatory mediator, disturbs barrier function. Filaggrin (FLG) is a protein involved in epidermal barrier homeostasis and may be affected by IL-17 and IL-33.

OBJECTIVE

To evaluate epidermal barrier function in malar melasma and its association with the expression of FLG, IL-17, and IL-33.

METHODS

Twenty patients with malar melasma were included in this study. Colorimetric and transepidermal water loss (TEWL) was measured in lesional and adjacent unaffected skin at baseline and 30 minutes after barrier disruption using the tape-stripping test. Biopsies from melasma and perilesional skin were performed to evaluate the presence of FLG by immunohistochemistry, and profilaggrin, IL-17, and IL-33 expression were analyzed by reverse transcription-qualitative polymerase chain reaction.

RESULTS

After the stripping test, the erythema and TEWL values were higher in the melasma than in the unaffected skin ( P = 0.01). Thirty minutes later, TEWL diminished, but it remained higher than in the perilesional skin. Profilaggrin increased as TEWL gradually decreased (R = -0.68, P = 0.04). FLG and IL-17 were higher in the melasma than in the perilesional skin ( P = 0.003). IL-17 and profilaggrin expression were positively associated (R = 0.60, P = 0.04). IL-33 expression was higher in the adjacent normal skin than in the melasma ( P = 0.01).

CONCLUSION

This study found subclinical inflammation in the skin adjacent to the melasma, dysfunction of the epidermal barrier in lesions associated with chronic inflammation, and an abnormal differentiation process promoting an increase in FLG. These findings highlight the need to preserve the integrity of the facial stratum corneum in these patients.

IL-33-mediated activation of mast cells is involved in the progression of imiquimod-induced psoriasis-like dermatitis

BACKGROUND

Psoriasis is a chronic inflammatory dermatosis with an unclear pathogenesis. Mast cells (MCs) can serve as a bridge between innate and adaptive immunity and are involved in the regulation of the inflammatory state and immune homeostasis in diseases. MCs constitutively express interleukin-33 receptor T1/ST2 (IL-33R). IL-33 is a potent MCs activator that is actively secreted by keratinocytes in psoriasis. However, the regulatory role of MCs in psoriasis remains uncertain. Therefore, we hypothesised that IL-33 could promote MC activation to regulate psoriasis development.

METHODS

We performed experiments on wild-type (WT) and MC-deficient (Kit Wsh/Wsh) mice, established psoriasis-like mouse models using imiquimod (IMQ), and performed RNA sequencing and transcriptomic analysis of skin lesions. Exogenous administration was performed using recombinant IL-33. Validation and evaluation were performed using PSI scoring, immunofluorescence, immunohistochemistry, and qPCR.

RESULTS

We observed an upregulation in the number and activation of MCs in patients with psoriasis and in IMQ-induced psoriasis-like dermatitis. Deficiency of MCs ameliorates IMQ-induced psoriatic dermatitis at an early stage. IL-33 is increased and co-localized with MCs in the dermis of psoriasis-like lesions using immunofluorescence. Compared to WT mice, IMQ-induced Kit^Wsh/Wsh mice demonstrated a delayed response to exogenous IL-33.

CONCLUSIONS

MCs are activated by IL-33 in the early stages of psoriasis and exacerbate psoriasis-associated skin inflammation. The regulation of MC homeostasis may be a potential therapeutic strategy for psoriasis. Video Abstract.

IL-33 induces histidine decarboxylase, especially in c-kit+ cells and mast cells, and roles of histamine include negative regulation of IL-33-induced eosinophilia

OBJECTIVE AND METHODS

IL-33 is present in endothelial, epithelial, and fibroblast-like cells and released upon cell injury. IL-33 reportedly induces mast-cell degranulation and is involved in various diseases, including allergic diseases. So, IL-33-related diseases seem to overlap with histamine-related diseases. In addition to the release from mast cells, histamine is newly formed by the induction of histidine decarboxylase (HDC). Some inflammatory and/or hematopoietic cytokines (IL-1, IL-3, etc.) are known to induce HDC, and the histamine produced by HDC induction is released without storage. We examined the involvement of HDC and histamine in the effects of IL-33.

RESULTS

A single intraperitoneal injection of IL-33 into mice induced HDC directly and/or via other cytokines (including IL-5) within a few hours in various tissues, particularly strongly in hematopoietic organs. The major cells exhibiting HDC-induction were mast cells and c-kit⁺ cells in the bone marrow. HDC was also induced in non-mast cells in non-hematopoietic organs. HDC, histamine, and histamine H4 receptors (H4Rs) contributed to the suppression of IL-33-induced eosinophilia.

CONCLUSION

IL-33 directly and indirectly (via IL-5) induces HDC in various cells, particularly potently in c-kit⁺ cells and mature mast cells, and the newly formed histamine contributes to the negative regulation of IL-33-induced eosinophilia via H4Rs.

Neuroblast Differentiation-Associated Protein Derived Polypeptides: AHNAK(5758-5775) Induces Inflammation by Activating Mast Cells via ST2

Psoriasis is a chronic inflammatory skin disease. Mast cells are significantly increased and activated in psoriatic lesions and are involved in psoriatic inflammation. Some endogenous substances can interact with the surface receptors of mast cells and initiate the release of downstream cytokines that participate in inflammatory reactions. Neuroblast differentiation-associated protein (AHNAK) is mainly expressed in the skin, esophagus, kidney, and other organs and participates in various biological processes in the human body. AHNAK and its derived peptides have been reported to be involved in the activation of mast cells and other immune processes. This study aimed to investigate whether AHNAK (5758-5775), a neuroblast differentiation-associated protein-derived polypeptide, could be considered a new endogenous substance in psoriasis patients, which activates mast cells and induces the skin inflammatory response contributing to psoriasis. Wild-type mice were treated with AHNAK(5758-5775) to observe the infiltration of inflammatory cells in the skin and cytokine release in vivo. The release of inflammatory mediators by mouse primary mast cells and the laboratory of allergic disease 2 (LAD2) human mast cells was measured in vitro. Molecular docking analysis, molecular dynamics simulation, and siRNA transfection were used to identify the receptor of AHNAK(5758-5775). AHNAK(5758-5775) could cause skin inflammation and cytokine release in wild-type mice and activated mast cells in vitro. Moreover, suppression of tumorigenicity 2 (ST2) might be a key receptor mediating AHNAK(5758-5775)'s effect on mast cells and cytokine release. We propose a novel polypeptide, AHNAK(5758-5775), which induces an inflammatory reaction and participates in the occurrence and development of psoriasis by activating mast cells.

IL-33/ST2 axis in autoimmune disease

Interleukin-33 (IL-33) is a member of the IL-1 family and plays an ambivalent role in autoimmune diseases. IL-33 signals via the ST2 receptor and drives cytokine production in mast cells, basophils, eosinophils, NK cells, and T lymphocyte cells. The vital role of IL-33 as an active component gives rise to aberrant local and systemic damage which has been demonstrated in numerous inflammatory disorders and immune-mediated pathological conditions including multiple sclerosis (MS), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), psoriasis, Sjogren's syndrome, inflammatory bowel disease (IBD), etc. IL-33/ST2 axis can up-regulate pro-inflammatory cytokine release in autoimmune disease, however, in some metabolic diseases like diabetes mellitus type 1 IL-33 can be considered an anti-inflammatory cytokine. The purpose of this review is to discuss selected studies on IL-33/ST2 axis in autoimmune diseases and its potential role as a pathogenic or protective cytokine.

IL-1 Family Cytokines in Inflammatory Dermatoses: Pathogenetic Role and Potential Therapeutic Implications

The interleukin-1 (IL-1) family is involved in the correct functioning and regulation of the innate immune system, linking innate and adaptative immune responses. This complex family is composed by several cytokines, receptors, and co-receptors, all working in a balanced way to maintain homeostasis. Dysregulation of these processes results in tissue inflammation and is involved in the pathogenesis of common inflammatory dermatoses such as psoriasis, hidradenitis suppurativa, and atopic dermatitis. Therefore, therapeutic targeting of IL-1 pathways has been studied, and several monoclonal antibodies are currently being assessed in clinical trials. So far, promising results have been obtained with anti-IL-36R spesolimab and imsidolimab in pustular psoriasis, and their efficacy is being tested in other conditions.

IL-33/ST2 Activation Is involved in Ro60-Regulated Photosensitivity in Cutaneous Lupus Erythematosus

Interleukin- (IL-) 33 contributes to various inflammatory processes. IL-33/ST2 activation participates in systemic lupus erythematous via binding to the receptor of Suppression of Tumorigenicity 2 protein (ST2). However, whether IL-33/ST2 interferes with the nosogenesis of cutaneous lupus erythematosus (CLE) has not been reported so far. Herein, we proposed to disclose the impacts on IL-33/ST2 activation and Ro60 on CLE and their potential implications in the photosensitization of CLE cells. IL-33, ST2, and Ro60 in CLE patients' skin lesions were detected. Murine keratinocytes stimulated with or without IL-33 were irradiated by ultraviolet B (UVB), and the levels of Ro60 and inflammation markers were determined. Keratinocytes were cocultured with J774.2 macrophages and stimulated with IL-33 for analysis of chemostasis. The results identified that IL-33, ST2, and downstream inflammation markers were significantly upregulated in CLE lesions with Ro60 overexpression. Additionally, IL-33 treatment promoted the upregulation of Ro60 induced by UVB treatment in murine keratinocytes. Moreover, IL-33 stimulates keratinocytes to induce macrophage migration via enhancing the generation of the chemokine (C–C motif) ligands 17 and 22. Meanwhile, the silencing of ST2 or nuclear factor-kappa B (NF-κB) suppression abolished IL-33-induced upregulation of Ro60 in keratinocytes. Similarly, the inhibition of SOX17 expression was followed by downregulation of Ro60 in keratinocytes following IL-33 stimulation. In addition, UVB irradiation upregulated SOX17 in keratinocytes. Conclusively, the IL-33/ST2 axis interferes with Ro60-regulated photosensitization via activating the NF-κB- and PI3K/Akt- and SOX17-related pathways.

Alarmins in autoimmune diseases

Alarmins are endogenous, constitutively expressed, chemotacting and immune activating proteins or peptides released because of non-programmed cell death (i.e. infections, trauma, etc). They are considered endogenous damage-associated molecular patterns (DAMPs), able to induce a sterile inflammation. In the last years, several studies highlighted a possible role of different alarmins in the pathogenesis of various autoimmune and immune-mediated diseases. We reviewed the relevant literature about this topic, for about 160 articles. Particularly, we focused on systemic autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, idiopathic inflammatory myopathies, ANCA-associated vasculitides, Behçet's disease) and cutaneous organ-specific autoimmune diseases (vitiligo, psoriasis, alopecia, pemphigo). Finally, we discussed about future perspectives and potential therapeutic implications of alarmins in autoimmune diseases. In fact, identification of receptors and downstream signal transducers of alarmins may lead to the identification of antagonistic inhibitors and agonists, with the capacity to modulate alarmins-related pathways and potential therapeutic applicability.

Targeting the Epithelium-Derived Innate Cytokines: From Bench to Bedside

When epithelial cells are exposed to potentially threatening external stimuli such as allergens, bacteria, viruses, and helminths, they instantly produce "alarmin" cytokines, namely, IL-33, IL-25, and TSLP. These alarmins alert the immune system about these threats, thereby mobilizing host immune defense mechanisms. Specifically, the alarmins strongly stimulate type-2 immune cells, including eosinophils, mast cells, dendritic cells, type-2 helper T cells, and type-2 innate lymphoid cells. Given that the alarm-raising role of IL-33, IL-25, and TSLP was first detected in allergic and infectious diseases, most studies on alarmins focus on their role in these diseases. However, recent studies suggest that alarmins also have a broad range of effector functions in other pathological conditions, including psoriasis, multiple sclerosis, and cancer. Therefore, this review provides an update on the epithelium-derived cytokines in both allergic and non-allergic diseases. We also review the progress of clinical trials on biological agents that target the alarmins and discuss the therapeutic potential of these agents in non-allergic diseases.

Therapeutic potential of targeting IL-1 family cytokines in chronic inflammatory skin diseases

The interleukin-1 (IL-1) family of cytokines is a central regulator of a myriad of immunological responses. It comprises several cytokines, including those belonging to the IL-1, IL-36 and IL-18 subfamilies, as well as IL-33. The IL-1 family primarily plays a role in orchestrating innate immune responses but also in adaptive immunity. Increased interest in the IL-1 family occurred following the discovery that dysregulation of IL-1 signalling underlies the pathogenesis of several monogenic auto-inflammatory diseases, characterized by sterile inflammation involving the skin and other organs. This also provided increased understanding of the role of innate immunity and the IL-1 family in polygenic auto-inflammatory skin conditions, such as neutrophilic dermatoses, as well as in some of the most common chronic inflammatory skin diseases, such as psoriasis or hidradenitis suppurativa. Several therapeutic agents have been developed to inhibit the IL-1 family members and their signalling pathways. These have shown therapeutic efficacy in several chronic inflammatory skin disorders. The aim of this review is to thoroughly describe the consequences of pathological dysregulation of IL-1, IL-33, IL-36, IL-18 pathways in dermatological conditions and to provide a forward-looking update on therapeutic strategies targeting signalling by IL-1 family cytokines.

The Role of Interleukins in the Pathogenesis of Dermatological Immune-Mediated Diseases

Autoimmune inflammatory diseases are primarily characterized by deregulated expression of cytokines, which drive pathogenesis of these diseases. A number of approved and experimental therapies utilize monoclonal antibodies against cytokine proteins. Cytokines can be classified into different families including the interleukins, which are secreted and act on leukocytes, the tumor necrosis factor (TNF) family, as well as chemokine proteins. In this review article, we focus on the interleukin family of cytokines, of which 39 members have been identified to this date. We outline the role of each of these interleukins in the immune system, and various dermatological inflammatory diseases with a focused discussion on the pathogenesis of psoriasis and atopic dermatitis. In addition, we describe the roles of various interleukins in psychiatric, cardiovascular, and gastrointestinal comorbidities. Finally, we review clinical efficacy and safety data from emerging late-phase anti-interleukin therapies under development for psoriasis and atopic dermatitis. Collectively, additional fundamental and clinical research remains necessary to fully elucidate the roles of various interleukin proteins in the pathogenesis of inflammatory dermatologic diseases, and treatment outcomes in patients.

Cytokine alterations in psoriasis: an updated review

INTRODUCTION

Psoriasis is a chronic immune-mediated disease affecting 125 million people globally. It is characterized by erythematous plaques in the skin, covered by silvery scales. However, non-cutaneous manifestations (e.g., joint symptoms in psoriatic arthritis) and a high prevalence of other immune-mediated diseases such as inflammatory bowel diseases reflect its systemic nature. So far, research on psoriasis pathogenesis has improved our knowledge of the roles of the immune system, and cytokines play significant roles in immune responses.

AREAS COVERED

Herein, we review cytokine changes in psoriasis patients. Moreover, we will investigate the possible relationships between disease severity and cytokines alongside describing cytokine alterations in psoriasis patients with other comorbidities. Lastly, we will discuss the biologics and their effects on cytokines in psoriasis patients.

EXPERT OPINION

Psoriasis could develop various clinical types and clinical manifestations in people. It is an immune-mediated disease, and these manifestations are associated with different impaired cytokines. Imbalanced cytokines could lead to abnormal keratinocytes, neovascularization, and inflammation in psoriasis patients. So, a better understanding of the cytokine roles can help one choose a specific cytokine-targeting biologic to treat psoriasis. Moreover, these cytokines may be used as a severity marker for following up with these patients.

Early Origins of Psoriatic Arthritis: Clinical, Genetic and Molecular Biomarkers of Progression From Psoriasis to Psoriatic Arthritis

Greater than 90% of patients with psoriatic arthritis (PsA) first develop their arthritis on a background of known psoriasis (Pso). Thus, having skin/nail Pso certainly is an important risk factor for PsA but as PsA develops in <30% of those affected with Pso, the presence of Pso alone is insufficient as a means of identifying which patients with Pso will develop PsA. It is hoped that with further molecular assessment of Pso patients who do not have any evidence of inflammatory musculoskeletal disease compared to those with early PsA features, that the “at risk” profile of Pso patients destined to develop PsA can be refined such that disease prevention studies can be designed and a new era of treatment for PsA can emerge. In this article, the early stages in the development of PsA are outlined and what is currently known about clinical features, genetic factors and soluble or tissue biomarkers associated with the development of PsA in patients with Pso is reviewed in detail. Finally, proposals are outlined regarding the approaches required in order to address this important research area.

Immune responses and therapeutic options in psoriasis

Psoriasis is a chronic inflammatory disease of the skin that affects about 2-3% of the population and greatly impairs the quality of life of affected individuals. Psoriatic skin is characterized by excessive proliferation and aberrant differentiation of keratinocytes, as well as redness caused by increased dilation of the dermal blood vessels and infiltration of immune cells. Although the pathogenesis of psoriasis has not yet been completely elucidated, it is generally believed to arise from a complex interplay between hyperproliferating keratinocytes and infiltrating, activated immune cells. So far, the exact triggers that elicit this disease are still enigmatic, yet, it is clear that genetic predisposition significantly contributes to the development of psoriasis. In this review, we summarize current knowledge of important cellular and molecular mechanisms driving the initiation and amplification stages of psoriasis development, with a particular focus on cytokines and emerging evidence illustrating keratinocyte-intrinsic defects as key drivers of inflammation. We also discuss mouse models that have contributed to a better understanding of psoriasis pathogenesis and the preclinical development of novel therapeutics, including monoclonal antibodies against specific cytokines or cytokine receptors that have revolutionized the treatment of psoriasis. Future perspectives that may have the potential to push basic research and open up new avenues for therapeutic intervention are provided.

The interleukin-1 family cytokines in psoriasis: pathogenetic role and therapeutic perspectives

Introduction: IL-1 family cytokines play an important role in the innate immune system and their uncontrolled activation and expression can initiate a pathologic inflammatory response. Their role in psoriasis, pustular psoriasis, and psoriatic arthritis has been studied, and they offer potential interest as therapeutic targets.Areas covered: This review focuses on the role that interleukin (IL)-1 family cytokines play in psoriasis pathogenesis, with a special focus on pustular psoriasis, and how these cytokines can be used as therapeutic targets. Using PubMed, we review the literature for articles related to IL-1 family cytokines and psoriasis, focusing on pustular psoriasis, and including pathogenesis, genetics and therapeutic targets.Expert opinion: IL-1 and IL-36 cytokines act as critical drivers of the autoinflammatory responses involved in pustular psoriasis. Studies on the specific role of each IL-1 cytokine are needed, as well as of their regulatory pathways. Targeting of IL-1 family cytokines has been used in pustular psoriasis, with IL-1 and IL-36 R blockade showing promising results.

The Role of the IL-33/ST2 Immune Pathway in Autoimmunity: New Insights and Perspectives

Interleukin (IL)-33, a member of IL-1 cytokine family, is produced by various immune cells and acts as an alarm to alert the immune system after epithelial or endothelial cell damage during cell necrosis, infection, stress, and trauma. The biological functions of IL-33 largely depend on its ligation to the corresponding receptor, suppression of tumorigenicity 2 (ST2). The pathogenic roles of this cytokine have been implicated in several disorders, including allergic disease, cardiovascular disease, autoimmune disease, infectious disease, and cancers. However, alerted levels of IL-33 may result in either disease amelioration or progression. Genetic variations of IL33 gene may confer protective or susceptibility risk in the onset of autoimmune diseases. The purpose of this review is to discuss the involvement of IL-33 and ST2 in the pathogenesis of a variety of autoimmune disorders, such as autoimmune rheumatic, neurodegenerative, and endocrine diseases.

Broad proteomic screen reveals shared serum proteomic signature in patients with psoriatic arthritis and psoriasis without arthritis

OBJECTIVE

To identify novel serum proteins involved in the pathogenesis of PsA as compared with healthy controls, psoriasis (Pso) and AS, and to explore which proteins best correlated to major clinical features of the disease.

METHODS

A high-throughput serum biomarker platform (Olink) was used to assess the level of 951 unique proteins in serum of patients with PsA (n = 20), Pso (n = 18) and AS (n = 19), as well as healthy controls (HC, n = 20). Pso and PsA were matched for Psoriasis Area and Severity Index (PASI) and other clinical parameters.

RESULTS

We found 68 differentially expressed proteins (DEPs) in PsA as compared with HC. Of those DEPs, 48 proteins (71%) were also dysregulated in Pso and/or AS. Strikingly, there were no DEPs when comparing PsA with Pso directly. On the contrary, hierarchical cluster analysis and multidimensional scaling revealed that HC clustered distinctly from all patients, and that PsA and Pso grouped together. The number of swollen joints had the strongest positive correlation to ICAM-1 (r = 0.81, P < 0.001) and CCL18 (0.76, P < 0.001). PASI score was best correlated to PI3 (r = 0.54, P < 0.001) and IL-17 receptor A (r = -0.51, P < 0.01). There were more proteins correlated to PASI score when analysing Pso and PsA patients separately, as compared with analysing Pso and PsA patients pooled together.

CONCLUSION

PsA and Pso patients share a serum proteomic signature, which supports the concept of a single psoriatic spectrum of disease. Future studies should target skin and synovial tissues to uncover differences in local factors driving arthritis development in Pso.

IL-33/Vitamin D Crosstalk in Psoriasis-Associated Osteoporosis

Patients with psoriasis (Pso) and, in particular, psoriatic arthritis (PsoA) have an increased risk of developing osteoporosis (OP). It has been shown that OP is among the more common pathologies associated with Pso, mainly due to the well-known osteopenizing conditions coexisting in these patients. Pso and OP share common risk factors, such as vitamin D deficiency and chronic inflammation. Interestingly, the interleukin (IL)-33/ST2 axis, together with vitamin D, is closely related to both Pso and OP. Vitamin D and the IL-33/ST2 signaling pathways are closely involved in bone remodeling, as well as in skin barrier pathophysiology. The production of anti-osteoclastogenic cytokines, e.g., IL-4 and IL-10, is promoted by IL-33 and vitamin D, which are stimulators of both regulatory and Th2 cells. IL-33, together with other Th2 cytokines, shifts osteoclast precursor differentiation towards macrophage and dendritic cells and inhibits receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis by regulating the expression of anti-osteoclastic genes. However, while the vitamin D protective functions in OP and Pso have been definitively ascertained, the overall effect of IL-33 on bone and skin homeostasis, because of its pleiotropic action, is still controversial. Emerging evidence suggests a functional link between vitamin D and the IL-33/ST2 axis, which acts through hormonal influences and immune-mediated effects, as well as cellular and metabolic functions. Based on the actions of vitamin D and IL-33 in Pso and OP, here, we hypothesize the role of their crosstalk in the pathogenesis of both these pathologies.

Goeckerman Regimen Reduces Alarmin Levels and PASI Score in Paediatric Patients with Psoriasis

BACKGROUND

Psoriasis is a chronic systemic inflammatory disease with (extra-)cutaneous manifestations. Inflammation is associated with cellular stress and tissue damage which lead to the release of alarmins (signals of danger). Goeckerman regimen (GR) is a highly efficacious treatment consisting of the application of pharmaceutical crude tar and UVB light exposure. The reduction of inflammatory processes in the skin is accompanied by changes in the levels of inflammatory markers - alarmins (HMBG-1, S100A7, S1000A8, S100A9, S100A12, IL-17, IL-22, and IL-33).

METHODS

The alarmin levels in sera of 19 paediatric patients with psoriasis were determined before and after GR using commercial ELISA kits. The Psoriasis area severity index (PASI) was used to determine the disease severity.

RESULTS

GR reduced both PASI and the levels of all measured alarmins. The levels of S100A7, S100A9, IL-22, IL-33, and HMGB-1 were significantly decreased. Positive correlations between IL-22 and PASI, between S100A9 and IL-17, S100A9 and IL-22, and a negative correlation between S100A8 and IL-33 were found.

CONCLUSIONS

Goeckerman regimen is a very effective, safe and low-cost therapy. We confirmed, it modulates the immune system reactivity, ameliorates the severity of the disease and reduces the levels of alarmins reflecting the presence and intensity of inflammation.

Does interleukin-33 level correlate with the activity of Pemphigus vulgaris?: A case-control study

Pemphigus is a group of immune-mediated blistering diseases of skin and mucus membrane caused by destruction of the intercellular junction (desmosomes) by autoantibodies. Pemphigus vulgaris (PV) is considered the most common type of all pemphigus family. Various cytokines play a major role in pemphigus pathogenesis. Interleukin-33 (IL-33) role has been studied in various autoimmune diseases as; psoriasis and rheumatoid arthritis, yet it has not been studied in Egyptian patients with PV. The study aimed to evaluate the possible role of IL-33 in PV by assessing its level in the serum using ELISA and to detect its correlation with activity score using Pemphigus Disease Area Index (PDAI). Forty-four patients with PV and 36 age and sex-matched healthy controls were enrolled in the study. After full history taking and complete dermatological examination, the severity score was calculated using PDAI, then serum samples were taken from each patient and control subjects and subjected to quantitative measurement of serum IL-33 using ELISA. Serum level of IL-33 is significantly raised in PV patients compared to control subjects (P-value = .007). The level of IL-33 was found to be strongly correlated with the activity of the disease measured by PDAI. IL-33 might have a role in PV pathogenesis as shown by its rising level in PV patients. In addition, serum level of IL-33 is strongly correlated with the activity of PV. Thus, we suspect that IL-33 can be used as marker for monitoring PV severity and measuring treatment efficacy.

Very low-calorie ketogenic diet (VLCKD) in patients with psoriasis and obesity: an update for dermatologists and nutritionists

Psoriasis is a chronic skin immune-mediated disease with systemic pro-inflammatory activation; both genetic and lifestyles factors contribute to its pathogenesis and severity. In this context, nutrition plays a significant role, per se, in psoriasis' pathogenesis. Obesity is another important risk factor for psoriasis, and weight reduction may improve psoriasis' clinical severity. The excess body weight, particularly visceral fat mass, can affect both drug's pharmacokinetics and pharmacodynamics. Therefore, psoriasis and obesity share a certain degree of synergy, and the chronic inflammatory state represents the basis of this vicious cycle. Evidence reported that nutrition has different impact on the clinical severity of psoriasis, though some specific diets have been more investigated in clinical studies compared to others. Diets with systemic anti-inflammatory properties seem to have a higher effect on improving the clinical severity of psoriasis. Of interest, very-low-calorie ketogenic diet (VLCKD), through the production of ketone bodies, has been associated with both a significant reduction of body weight and inflammatory state. VLCKD leading to both weight loss and reduction of systemic inflammation may decrease the exacerbation of the clinical manifestations or even it may block the trigger of psoriatic disease. This dietary pattern could represent a potential first-line treatment in psoriatic patients with obesity. The review aims to summarize the current evidence regarding VLCKD and psoriasis with specific reference to antioxidant and anti-inflammatory effects of this dietary pattern.

Cancer stem cells and their niche in the progression of squamous cell carcinoma

Most cancers harbor a small population of highly tumorigenic cells known as cancer stem cells (CSCs). Because of their stem cell-like properties and resistance to conventional therapies, CSCs are considered to be a rational target for curable cancer treatment. However, despite recent advances in CSC research, CSC-targeted therapies are not as successful as was initially hoped. The proliferative, invasive, and drug-resistant properties of CSCs are regulated by the tumor microenvironment associated with them, the so-called CSC niche. Thus, targeting tumor-promoting cellular crosstalk between CSCs and their niches is an attractive avenue for developing durable therapies. Using mouse models of squamous cell carcinoma (SCC), we have demonstrated that tumor cells responding to transforming growth factor β (TGF-β) function as drug-resistant CSCs. The gene expression signature of TGF-β-responding tumor cells has accelerated the identification of novel pathways that drive invasive tumor progression. Moreover, by focusing on the cytokine milieu and macrophages in the proximity of TGF-β-responding tumor cells, we recently uncovered the molecular basis of a CSC-niche interaction that emerges during early tumor development. This review article summarizes the specialized tumor microenvironment associated with CSCs and discusses mechanisms by which malignant properties of CSCs are maintained and promoted.

An Autocrine Circuit of IL-33 in Keratinocytes Is Involved in the Progression of Psoriasis

IL-33 is constitutively expressed in the skin. Psoriasis is a common skin inflammatory disease. The roles of IL-33 in psoriasis have not been well-elucidated. We identified that keratinocytes (KCs) are the predominant cells expressing IL-33 and its receptor, suppression of tumorigenicity 2, in the skin. KCs actively released IL-33 on psoriasis inflammatory stimuli and induced psoriasis-related cytokine, chemokine, and inflammatory molecules genes transcription in KCs in an autocrine manner. IL-33‒specific deficiency in KCs ameliorated imiquimod-induced psoriatic dermatitis. In addition, intradermal injection of recombinant IL-33 alone induced psoriasis-like dermatitis, which is attributed to the transcriptional upregulation of genes enriched in IL-17, TNF, and chemokine signaling pathway in KCs on recombinant IL-33 stimulation. Our data demonstrate that the autocrine circuit of IL-33 in KCs promotes the progression of psoriatic skin inflammation, and IL-33 is a potential therapeutic target for psoriasis.

Tumor-initiating cells establish an IL-33-TGF-β niche signaling loop to promote cancer progression

Targeting the cross-talk between tumor-initiating cells (TICs) and the niche microenvironment is an attractive avenue for cancer therapy. We show here, using a mouse model of squamous cell carcinoma, that TICs play a crucial role in creating a niche microenvironment that is required for tumor progression and drug resistance. Antioxidant activity in TICs, mediated by the transcription factor NRF2, facilitates the release of a nuclear cytokine, interleukin-33 (IL-33). This cytokine promotes differentiation of macrophages that express the high-affinity immunoglobulin E receptor FcεRIα and are in close proximity to TICs. In turn, these IL-33-responding FcεRIα+ macrophages send paracrine transforming growth factor β (TGF-β) signals to TICs, inducing invasive and drug-resistant properties and further upregulating IL-33 expression. This TIC-driven, IL-33-TGF-β feedforward loop could potentially be exploited for cancer treatment.

IL-33/13 Axis and IL-4/31 Axis Play Distinct Roles in Inflammatory Process and Itch in Psoriasis and Atopic Dermatitis

BACKGROUND

Pruritus is the most common symptom in patients with skin disease. Psoriasis and atopic dermatitis are clinically distinct inflammatory diseases. Interleukins are cytokines which play key roles in inflammatory signaling pathways.

MATERIALS AND METHODS

Cross-sectional study was conducted among patients with psoriasis and atopic dermatitis: 59 psoriatic patients, 56 AD patients, and 49 matched healthy controls. Interleukins 4, 13, 31, 33 serum levels were assayed by ELISA and results were compared using SPSS. Itch severity and disease severity were measured and correlation with interleukin levels was determined using SPSS.

RESULTS

The serum levels of IL-4, -13, -31, -33 were elevated in atopic dermatitis patients compared to controls. Itch and disease severity were not correlated with elevated serum levels of these interleukins. In psoriasis, the levels of IL-4 and -31 were elevated compared to controls, whereas the levels of IL-13 and -33 were lower than controls. The levels of measured interleukins in psoriasis did not correlate with itch and disease severity.

CONCLUSION

IL-31 is the key mediator for pruritus in both AD and Ps patients. IL-4/31 axis and IL-33/13 axis play distinct roles in the pathogenesis of Atopic dermatitis and Psoriasis. Interleukin serum levels were not correlated with itch and disease severity in both conditions.

Interleukin-33 alleviates psoriatic inflammation by suppressing the T helper type 17 immune response

Psoriasis is a chronic inflammatory skin disease with unclear pathogenesis. Interleukin-33 (IL-33) is highly expressed in patients with psoriasis, but its role in psoriasis is unknown. The aim of this study was to investigate the possible role of IL-33 in the pathogenesis and treatment of psoriasis. IL-33 expression was determined using enzyme-linked immunosorbent assay, real-time fluorescent quantitative polymerase chain reaction and immunohistochemical staining. CD4⁺ T cells were sorted using magnetic beads and treated with or without IL-33. Imiquimod (IMQ) was used to induce psoriatic inflammation in mice. The frequency of immune cells was determined using flow cytometry. The cytokine level in mouse skin was measured using cytometric bead array. Our results showed that IL-33 was highly expressed in the lesional skin and serum of patients with moderate-to-severe plaque psoriasis. IL-33 inhibited the expression of IL-17 in CD4⁺ T cells of psoriasis patients. Subcutaneous injection of IL-33 alleviated the IMQ-induced psoriatic inflammation in mice, reduced tumor necrosis factor-α and IL-23 expression, and decreased the proportion of T helper type 17 (Th17) cells in the skin-draining lymph nodes in the mice. Our results suggest that IL-33 plays a protective role in the pathogenesis of psoriasis by suppressing Th17 cell differentiation and function. The potential therapeutic effect of IL-33 in treating psoriasis warrants further investigation.

Alarmins HMGB1, IL-33, S100A7, and S100A12 in Psoriasis Vulgaris

Background

Psoriasis vulgaris is a chronic autoimmune disease associated with systemic inflammation. Increased levels of numerous cytokines, chemokines, growth factors, and other molecules were found in the skin and in the circulation of psoriatic patients. Alarmins, also known as danger signals, are intracellular proteins, which are released to an extracellular space after infection or damage. They are the markers of cell destructive processes.

Objective

The aim of the present study was to evaluate the suitability of selected alarmins (HMGB1, IL-33, S100A7, and S100A12) as potential biomarkers of severity of psoriasis and to explore possible relationships between these proteins for the purpose of better understanding their roles in the immunopathology of psoriasis.

Methods

The serum levels of selected alarmins were measured in 63 psoriatic patients and 95 control individuals. The levels were assessed by the ELISA technique using commercial kits. The data were statistically processed with MedCalc version 19.0.5.

Results

In psoriatic patients, we found significantly increased levels of HMGB1 (p < 0.05), IL-33 (p < 0.01), S100A7 (p < 0.0001), and S100A12 (p < 0.0001). In addition, we found a significant relationship between HMGB1 and S100A7 (Spearman's rho = 0.276, p < 0.05) in the patients and significant relationship between HMGB1 and IL-33 in the controls (Spearman's rho = 0.416, p < 0.05). We did not find any relationship between observed alarmins and the disease severity.

Conclusions

The alarmins HMGB1, IL-33, S100A7, and S100A12 were significantly elevated in the serum of patients, which states the hypothesis that they play specific roles in the immunopathology of psoriasis. However, we have not yet found a relationship between observed alarmins and the disease severity. The discovery of the relationship between HMGB1 and S100A7 is a novelty that should be studied in the future to further clarify its role and importance.

Possible Roles of IL-33 in the Innate-Adaptive Immune Crosstalk of Psoriasis Pathogenesis

Background

IL-33 belongs to the IL-1 family, playing a role in several biologic processes as well as in the pathogenesis of different diseases, including skin pathologies. It acts as an alarmin, released by damaged cells. Binding to a ST2 receptor, it stimulates many immune cells such as ILC2 and Th2 cells. IL-33/ST2 axis seems to be involved in Th17 response. According to this, a review was performed to analyze if IL-33 even interplay in the onset of psoriasis, a Th1/Th17 inflammatory disease.

Methods

Data obtained from the included articles are study author name, publication date, group studied, clinical and biological variables, laboratory tests, and outcome of interest of the study.

Results

Data are obtained from the 19 studies identified, which assessed the association between IL-33 and psoriasis.

Discussion

It seems to promote the innate-adaptive immune crosstalk: it could induce mast cells and neutrophil response after being released by injured keratinocytes and after stimulation by some cytokines, in particular TNFα, INFγ, and IL-17A. In addition, it seems to be involved from the onset of disease to the development of comorbidities, as psoriatic arthritis.

Conclusion

The core of the future research on psoriasis could be to fully understand the role of this complex cytokine, in order also to find a new therapeutic approach.

IL-33 contributes to disease severity in Psoriasis-like models of mouse

Immune cells infiltrating the psoriatic skin secrete high amounts of pro-inflammatory cytokines IL-17, TNF-α, IL-21 and IL-36 resulting in chronic inflammation. However, the exact cellular and molecular mechanisms have not been fully understood. We report here elevation of IL-33 expression in psoriatic lesions. Studies in imiquimod (IMQ)-induced mice with psoriatic inflammation confirmed a critical role for IL-33 in driving the disease. IL-33 reduces the CD4⁺ and CD8⁺ cells, inhibits autophagy in IMQ-treated mouse skin, and promoted tyrosyl phosphorylation of STAT3. Thus, IL-33 appears to be a major risk factor for severity of psoriasis-like skin inflammation. Our findings may open new perspectives for understanding the mechanisms and developing a therapeutic strategy for psoriasis.

Interleukin (IL)-33 and the IL-1 Family of Cytokines-Regulators of Inflammation and Tissue Homeostasis

Cytokines play an integral role in shaping innate and adaptive immune responses. Members of the interleukin (IL)-1 family regulate a plethora of immune-cell-mediated processes, which include pathogen defense and tissue homeostasis. Notably, the IL-1 family cytokine IL-33 promotes adaptive and innate type 2 immune responses, confers viral protection and facilitates glucose metabolism and tissue repair. At the cellular level, IL-33 stimulates differentiation, maintenance, and function of various immune cell types, including regulatory T cells, effector CD4⁺ and CD8⁺ T cells, macrophages, and type 2 innate lymphoid cells (ILC2s). Other IL-1 family members, such as IL-1β and IL-18 promote type 1 responses, while IL-37 limits immune activation. Although IL-1 cytokines play critical roles in immunity and tissue repair, their deregulated expression is often linked to autoimmune and inflammatory diseases. Therefore, IL-1 cytokines are regulated tightly by posttranscriptional mechanisms and decoy receptors. In this review, we discuss the biology and function of IL-1 family cytokines, with a specific focus on regulation and function of IL-33 in immune and tissue homeostasis.

Increased expression of IL-33 in rosacea skin and UVB-irradiated and LL-37-treated HaCaT cells

Rosacea is one of the most common dermatoses of adults. Although the detailed pathophysiology remains unknown, it is thought that rosacea is caused by a consistently aberrant, innate immune response, and that LL-37 plays an important role. However, involvement of the inflammatory cytokine IL-33 has not yet been studied. We explored the role played by IL-33 in the pathophysiology of rosacea. First, we immunohistochemically evaluated the expression of IL-33 and its receptor (ST2) in rosacea skin. Second, we exposed HaCaT cells to ultraviolet B (UVB) irradiation in the presence or absence of LL-37 and measured the expression of proinflammatory cytokines including IL-33. We also analysed VEGF (vascular endothelial growth factor) mRNA expression and protein release after costimulation of HaCaT cells by LL-37 and IL-33. Immunohistochemically, IL-33 expression was enhanced in the skin of rosacea patients, especially with erythematotelangiectatic subtype. In vitro, UVB and LL-37 synergistically increased mRNAs expression of proinflammatory cytokines, especially IL-33 and IL-1β. IL-33 protein release was also synergistically increased by LL-37 and UVB treatment. LL-37 and IL-33 stimulated VEGF mRNA expression and VEGF release from HaCaT cells. Our findings suggest that rosacea skin with abundant LL-37 may robustly produce and release IL-33 when exposed to UV radiation. IL-33 may participate in the angiogenesis and vasodilation of rosacea skin by enhancing VEGF release.

TNF stimulates IL-6, CXCL8 and VEGF secretion from human keratinocytes via activation of mTOR, inhibited by tetramethoxyluteolin

Psoriasis is an autoimmune skin disease characterized by keratinocyte hyperproliferation and chronic inflammation. The pathogenesis of psoriasis involves proinflammatory cytokines, such as tumor necrosis factor (TNF), but the mechanism of keratinocyte activation is not well understood. Here, we show that TNF (10 or 50 ng/mL) stimulates a significant (P < .0001) gene expression and secretion of proinflammatory IL-6, CXCL8 and VEGF from both cultured human HaCaT and normal epidermal human keratinocytes (NHEKs). This effect occurs via activation of the mammalian target of rapamycin (mTOR) signalling complex as shown by Western blot analysis and phospho-ELISAs. Pretreatment with the novel natural flavonoid tetramethoxyluteolin (10-100 μmol L^-1 ) significantly (P < .0001) inhibits gene expression and secretion (P < .0001) of all 3 mediators in a concentration-dependent manner. Moreover, tetramethoxyluteolin (50 μmol L^-1 ) appears to be a potent inhibitor of the phosphorylated mTOR substrates (pmTOR^Ser2448 , pp70S6K^Thr389 and p4EBP1^Thr37/46 ) as compared to known mTOR inhibitors in keratinocytes. The present findings indicate that TNF stimulates skin inflammation via mTOR signalling. Inhibition by tetramethoxyluteolin may be used in the treatment for psoriasis.

IL-33 promotes the egress of group 2 innate lymphoid cells from the bone marrow

ILC2s are potent mucosal effector cells that participate in type 2 inflammatory responses. Stier et al. demonstrate that IL-33 negatively regulates CXCR4, mediating the egress of ILC2 lineage cells from the bone marrow for potential hematogenous trafficking.

Group 2 innate lymphoid cells (ILC2s) are effector cells within the mucosa and key participants in type 2 immune responses in the context of allergic inflammation and infection. ILC2s develop in the bone marrow from common lymphoid progenitor cells, but little is known about how ILC2s egress from the bone marrow for hematogenous trafficking. In this study, we identified a critical role for IL-33, a hallmark peripheral ILC2-activating cytokine, in promoting the egress of ILC2 lineage cells from the bone marrow. Mice lacking IL-33 signaling had normal development of ILC2s but retained significantly more ILC2 progenitors in the bone marrow via augmented expression of CXCR4. Intravenous injection of IL-33 or pulmonary fungal allergen challenge mobilized ILC2 progenitors to exit the bone marrow. Finally, IL-33 enhanced ILC2 trafficking to the lungs in a parabiosis mouse model of tissue disruption and repopulation. Collectively, these data demonstrate that IL-33 plays a critical role in promoting ILC2 egress from the bone marrow.

Anti-interleukin and interleukin therapies for psoriasis: current evidence and clinical usefulness

Anti-interleukin (IL) therapies have emerged as a major treatment for patients with moderate-to-severe psoriasis. This article reviews the up-to-date results of pivotal clinical trials targeting the interleukins used for the treatment of psoriasis, including IL-1, IL-2, IL-6, IL-8, IL-10, IL-12, IL-17, IL-20, IL-22, IL-23, IL-36 and bispecific biologics IL-17A/tumor necrosis factor alpha (TNF-α). Cytokines involved in the circuits of psoriasis inflammation without ongoing clinical trials are also mentioned (IL-9, IL-13, IL-15, IL-16, IL-18, IL-19, IL-21, IL-24, IL-27, IL-33, IL-35, IL-37, and IL-38).