The balance between pro- and anti-inflammatory cytokines is crucial in human allergic contact dermatitis pathogenesis: the role of IL-1 family members

Subclinical immune responses to nickel in sensitized individuals-a dose-response study

BACKGROUND

Nickel is the leading cause of contact allergy in Europe, with 14.5% of the adult population being sensitized. Despite regulations limiting nickel release from consumer items, the incidence and prevalence of nickel allergy remain high.

OBJECTIVE

To investigate the clinical and subclinical immune response to low-dose nickel exposure on nickel pre-exposed skin to assess the adequacy of current regulatory limits.

METHOD

Nickel-allergic and healthy controls were patch tested with nickel twice with a 3-4 weeks interval. The first exposure used the diagnostic concentration of 2000 μg/cm2 nickel sulphate, and the same skin areas were then re-exposed to 0.2, 0.5, 12.8 and 370 μg/cm2 nickel sulphate. After 48 h, the patch reactions were examined for clinical signs of eczema, and skin biopsies were collected. The transcriptomic immune profile was analysed with Nanostring nCounter and quantitative polymerase chain reaction.

RESULTS

Two nickel-allergic participants (15%) had clinical reactions to the regulatory limiting doses for nickel (0.2/0.5 μg/cm2) following re-exposure. There was immune activation in all skin areas following re-exposure to nickel, predominantly mediated by up-regulation of cytokines and chemokines. In all nickel re-exposed skin areas, 81 genes were up-regulated independent from the clinical response. In skin areas exposed to 0.2 μg/cm2, 101 immune-related genes were differentially expressed, even when no clinical response was observed. Healthy controls showed up-regulation of three genes in response to nickel re-exposures without any clinical reactions.

CONCLUSION

Immune activation can be induced in skin with local memory to nickel upon challenge with nickel doses within the regulatory limits. Our findings suggest that the regulatory limits in the European nickel regulation may not provide sufficient protection for consumers against low-dose exposures.

The skin sensitization adverse outcome pathway: exploring the role of mechanistic understanding for higher tier risk assessment

For over a decade, the skin sensitization Adverse Outcome Pathway (AOP) has served as a useful framework for development of novel in chemico and in vitro assays for use in skin sensitization hazard and risk assessment. Since its establishment, the AOP framework further fueled the existing efforts in new assay development and stimulated a plethora of activities with particular focus on validation, reproducibility and interpretation of individual assays and combination of assay outputs for use in hazard/risk assessment. In parallel, research efforts have also accelerated in pace, providing new molecular and dynamic insight into key events leading to sensitization. In light of novel hypotheses emerging from over a decade of focused research effort, mechanistic evidence relating to the key events in the skin sensitization AOP may complement the tools currently used in risk assessment. We reviewed the recent advances unraveling the complexity of molecular events in sensitization and signpost the most promising avenues for further exploration and development of useful assays.

Emerging Role of the IL-36/IL-36R Axis in Multiple Inflammatory Skin Diseases

IL-36 is a most recent member of the IL-1 cytokine family, primarily expressed at barrier sites of the body such as the skin, lungs, and intestine. It plays a vital role in inflammation and is implicated in the development of various cutaneous; intestinal; and pulmonary disorders, including psoriasis, inflammatory bowel disease, and chronic obstructive pulmonary disease. IL-36 comprises 4 isoforms: the proinflammatory IL-36α, IL-36β, and IL-36γ and the anti-inflammatory IL-36R antagonist. An imbalance between proinflammatory and anti-inflammatory IL-36 isoforms can contribute to the inflammatory fate of cells and tissues. IL-36 cytokines signal through an IL-36R heterodimer mediating their function through canonical signaling cacade, including the NF-B pathway. Prominent for its role in psoriasis, IL-36 has recently been associated with disease mechanisms in atopic dermatitis, hidradenitis suppurativa, neutrophilic dermatoses, autoimmune blistering disease, and Netherton syndrome. The major cutaneous source of IL-36 cytokines is keratinocytes, pointing to its role in the communication between the epidermis, innate (neutrophils, dendritic cells) immune system, and adaptive (T helper [Th]1 cells, Th17) immune system. Thus, cutaneous IL-36 signaling is crucial for the immunopathological outcome of various skin diseases. Consequently, the IL-36/IL-36R axis has recently been recognized as a promising drug target for the treatment of inflammatory disorders beyond psoriasis. This review summarizes the current update on IL-36 cytokines in inflammatory skin diseases.

IL-38 alleviates airway remodeling in chronic asthma via blocking the profibrotic effect of IL-36γ

Airway remodeling is a major feature of asthma. Interleukin (IL)-36γ is significantly upregulated and promotes airway hyper-responsiveness (AHR) in asthma, but its role in airway remodeling is unknown. Here, we aimed to investigate the role of IL-36γ in airway remodeling, and whether IL-38 can alleviate airway remodeling in chronic asthma by blocking the effects of IL-36γ. IL-36γ was quantified in mice inhaled with house dust mite (HDM). Extracellular matrix (ECM) deposition in lung tissues and AHR were assessed following IL-36γ administration to mice. Airway inflammation, AHR, and remodeling were evaluated after IL-38 or blocking IL-36 receptor (IL-36R) treatment in asthmatic mice. The effects of lung fibroblasts stimulated with IL-36γ and IL-38 were quantified in vitro. Increased expression of IL-36γ was detected in lung tissues of HDM-induced asthmatic mice. The intratracheal instillation of IL-36γ to mice significantly enhanced the ECM deposition, AHR, and the number of activated lung fibroblasts around the airways. IL-38 or blocking IL-36R treated asthmatic mice showed a significant alleviation in the airway inflammation, AHR, airway remodeling, and number of activated fibroblasts around airways as compared with the HDM group. In vitro, IL-36γ promoted the activation and migration of human lung fibroblasts (HFL-1). The administration of IL-38 can counteract these biological processes induced by IL-36γ in HFL-1cells. The results indicated that IL-38 can mitigate airway remodeling by blocking the profibrotic effects of IL-36γ in chronic asthma. IL-36γ may be a new therapeutic target, and IL-38 is a potential candidate agent for inhibiting airway remodeling in asthma.

Synergism between IL-33 and MRGPRX2/FcεRI Is Primarily Due to the Complementation of Signaling Modules, and Only Modestly Supplemented by Prolonged Activation of Selected Kinases

Skin mast cells (MCs) express high levels of MRGPRX2, FcεRI, and ST2, and vigorously respond to their ligands when triggered individually. IL-33/ST2 also potently synergizes with other receptors, but the molecular underpinnings are poorly understood. Human skin-derived MCs were stimulated via different receptors individually or jointly in the presence/absence of selective inhibitors. TNF was quantified by ELISA. Signaling cascades were studied by immunoblot. TNF was stimulated by FcεRI ≈ ST2 > MRGPRX2. Surprisingly, neither FcεRI nor MRGPRX2 stimulation elicited NF-κB activation (IκB degradation, p65 phosphorylation) in stark contrast to IL-33. Accordingly, TNF production did not depend on NF-κB in FcεRI- or MRGPRX2-stimulated MCs, but did well so downstream of ST2. Conversely, ERK1/2 and PI3K were the crucial modules upon FcεRI/MRGPRX2 stimulation, while p38 was key to the IL-33-elicited route. The different signaling prerequisites were mirrored by their activation patterns with potent pERK/pAKT after FcεRI/MRGPRX2, but preferential induction of pp38/NF-κB downstream of ST2. FcεRI/MRGPRX2 strongly synergized with IL-33, and some synergy was still observed upon inhibition of each module (ERK1/2, JNK, p38, PI3K, NF-κB). IL-33's contribution to synergism was owed to p38 > JNK > NF-κB, while the partner receptor contributed through ERK > PI3K ≈ JNK. Concurrent IL-33 led to slightly prolonged pERK (downstream of MRGPRX2) or pAKT (activated by FcεRI), while the IL-33-elicited modules (pp38/NF-κB) remained unaffected by co-stimulation of FcεRI/MRGPRX2. Collectively, the strong synergistic activity of IL-33 primarily results from the complementation of highly distinct modules following co-activation of the partner receptor rather than by altered signal strength of the same modules.

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.

Prenatal exposure to nickel and atopic dermatitis at age 3 years: a birth cohort study with cytokine profiles

BACKGROUND

Nickel, the fifth most common element on Earth, is the leading inducer of contact allergies in humans, with potent immunological effects. Nickel-induced contact allergies predominantly affect females. Maternal exposure to nickel has been associated with several developmental abnormalities. However, how a maternal nickel exposure affects the development of atopic diathesis and immune abnormalities in children has never been addressed.

OBJECTIVES

We aimed to determine whether maternal Ni exposure affects the development of atopic dermatitis and immune abnormalities in their children.

METHODS

Using a birth cohort study, we analysed 140 mother-child pairs recruited in 2012-2015 from central Taiwan. Maternal exposure to nickel was estimated using urinary nickel levels measured by inductively coupled plasma mass spectrometry (ICP-MS). The serum levels of 65 analytes and IgE in 3-year-old children were profiled with a multiplex ELISA. The correlation between the maternal urinary nickel concentration and serum analyte levels was assessed using Spearmen's correlation. Multivariant regression analysis was performed to evaluate the association between maternal urinary nickel levels and serum analyte concentrations in their children.

RESULTS

The geometric means of the maternal urinary nickel and the children's serum IgE levels were 2.27 μg/L and 69.71 IU/ml, respectively. The maternal nickel exposure was associated with increased serum levels of IL-1β, IL-2, TNF-α, and leukaemia inhibitory factor (LIF) but with decreased serum levels of matrix metalloproteinase-1 (MMP-1), IL-2R, and eotaxin-1 in the children. In addition, the development of childhood atopic dermatitis at 3 years old was significantly associated with the child's serum levels of IgE and IL-2R, but it was negatively associated with the maternal nickel exposure.

CONCLUSIONS

This is the first study showing the potential immunological effects of maternal nickel exposure in their children at an early developmental stage.

A review of IL-36: an emerging therapeutic target for inflammatory dermatoses

BACKGROUND

IL-36 cytokines are members of the IL-1 superfamily. Increasing evidence in the IL-36 pathway demonstrates their potential as a therapeutic target for treating inflammatory skin diseases, such as generalized pustular psoriasis (GPP).

OBJECTIVE

A narrative review was written to further study preclinical and clinical evidence for the role of IL-36 in psoriasis, atopic dermatitis (AD), hidradenitis suppurativa (HS), acne, autoimmune blistering diseases, and neutrophilic dermatoses.

RESULTS

IL-36 has important downstream effects such as inducing expression of inflammatory cytokines, antimicrobial peptides, and growth factors. Increased expression of IL-36 cytokines has been observed in the lesional skin of patients with psoriasis. Studies of other inflammatory skin diseases have also noted similar findings, albeit to a lesser extent. IL-36 inhibition has been shown to be effective in GPP and is currently being studied for other inflammatory skin diseases.

CONCLUSIONS

The IL-36 pathway contributes to pathogenesis of many inflammatory skin diseases and is a promising therapeutic target.

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.

Immunobiological Properties and Clinical Applications of Interleukin-38 for Immune-Mediated Disorders: A Systematic Review Study

Exponential growth in the usage of "cytokines" (as seroimmunobiomarkers) has facilitated more accurate prognosis, early diagnosis, novel, and efficient immunotherapeutics. Numerous studies have reported immunopathophysiological and immunopathological processes of interleukin-38 (IL-38). Therefore, in this systematic review article, the authors aimed to present an updated comprehensive overview on the immunobiological mechanisms, diagnostic, and immune gene-based therapeutic potentials of IL-38. According to our inclusion and exclusion criteria, a total of 216 articles were collected from several search engines and databases from the January 2012 to July 2021 time interval by using six main keywords. Physiologic or pathologic microenvironments, optimal dosage, and involved receptors affect the functionalities of IL-38. Alterations in serum levels of IL-38 play a major role in the immunopathogenesis of a wide array of immune-mediated disorders. IL-38 shows anti-inflammatory activities by reduction or inhibition of pro-inflammatory cytokines, supporting the therapeutic aspects of IL-38 in inflammatory autoimmune diseases. According to the importance of pre-clinical studies, it seems that manipulation of the immune system by immunomodulatory properties of IL-38 can increase the accuracy of diagnosis, and decipher optimal clinical outcomes. To promote our knowledge, more collaboration is highly recommended among laboratory scientists, internal/infectious diseases specialists, oncologists, immunologists, diseases-specific biomarkers scientists, and basic medical researchers.

Environmental, inflammatory, and anti-inflammatory squad in acne vulgaris pathogenesis: AhR, IL-36, and IL-38

BACKGROUND

Acne vulgaris (AV) is an extraordinarily common skin condition. The high prevalence of AV is linked to the exposure factors, as environmental pollutants and climatic factors, occupational, psychosocial, and lifestyle factors. The AhR plays a critical part in environmental toxic action. The AhR expression and imbalance in the IL-36 & 38 expression may have a role in inflammation and AV pathogenesis.

AIMS

To detect possible links between environmental, inflammatory, and anti-inflammatory factors in AV pathogenesis through measuring AhR, IL-36, and IL-38 mRNA gene expression levels.

PATIENTS AND METHODS

Total of 100 subjects (70 AV patients and 30 apparently healthy control subjects) were tested for AhR, IL-36γ, and IL-38 mRNA levels by quantitative real-time PCR.

RESULTS

The median levels of AhR and IL-36 mRNA gene expression were considerably greater, while that of IL-38 was essentially lower in AV than healthy subjects (p < 0.001, 0.021 and 0.002, respectively). The AhR and IL-36 mRNA gene expression levels increased, while IL-38 decreased significantly with higher grades of severity (p < 0.001, 0.001, and <0.001, respectively). ROC curve showed that AhR mRNA gene expression level had the best AUC for diagnosis of AV, with better sensitivity and specificity than IL-36 and IL-38.

CONCLUSIONS

Higher levels of AhR, IL-36, and lower levels of IL-38 gene expression were significantly associated with AV patients and higher grades of severity. AhR had better diagnostic ability than IL-38 and IL-36.

Immune-Regulatory and Molecular Effects of Antidepressants on the Inflamed Human Keratinocyte HaCaT Cell Line

Allergic contact dermatitis (ACD) is a T cell-mediated type of skin inflammation resulting from contact hypersensitivity (CHS) to antigens. There is strong comorbidity between ACD and major depression. Keratinocytes release immunomodulatory mediators including pro-inflammatory cytokines and chemokines, which modulate skin inflammation and are crucial cell type for the development of CHS. Our previous studies showed that fluoxetine and desipramine were effective in suppressing CHS in different mouse strains. However, the immune and molecular mechanisms underlying this effect remain to be explored. The aim of the current study was to determine the immune and molecular mechanisms of action of antidepressant drugs engaged in the inhibition of CHS response in the stimulated keratinocyte HaCaT cell line. The results show that LPS, TNF-α/IFN-γ, and DNFB stimulate HaCaT cells to produce large amounts of pro-inflammatory factors including IL-1β, IL-6, CCL2, and CXCL8. HaCaT stimulation was associated with increased expression of ICAM-1, a cell adhesion molecule, and decreased expression of E-cadherin. Imipramine, desipramine, and fluoxetine suppress the production of IL-1β, CCL2, as well as the expression of ICAM-1. LPS and TNF-α/IFN-γ activate p-38 kinase, but antidepressants do not regulate this pathway. LPS decreases E-cadherin protein expression and fluoxetine normalizes these effects. In summary, the antidepressant drugs examined in this study attenuate the stimulated secretion of pro-inflammatory cytokines, chemokines, and modulate adhesion molecule expression by the HaCaT cell line. Therefore, antidepressants may have some clinical efficacy in patients with ACD and patients with comorbid depression and contact allergy.

The role of interleukin-1β in the immune response to contact allergens

Interleukin-1β (IL-1β) is an important pro-inflammatory cytokine that has an effect on almost every cell lineage in the body. By blocking IL-1β and investigating the IL-1β signaling pathway, several studies have demonstrated a central role of IL-1β in the response to contact allergens. This review summarizes the current literature regarding the basic immunological mechanisms mediated by IL-1β in the different phases of allergic contact dermatitis (ACD) and highlights potential IL-1β-targeted treatment options, which in the future may be relevant in the treatment of patients with ACD. This review is based primarily on studies using various mouse models and human in vitro studies, since clinical studies on the effect of IL-1β in ACD are lacking.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

Intricate Relationship Between Adaptive and Innate Immune System in Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a complex immunological allergic disease characterized by the interplay between the innate and adaptive immune system. Initially, the role of the innate immune system was believed to be confined to the initial sensitization phase, while adaptive immune reactions were linked with the advanced elicitation phase. However, recent data predicted a comparatively mixed and interdependent role of both immune systems throughout the disease progression. Therefore, the actual mechanisms of disease progression are more complex and interlinked. The aim of this review is to combine such findings that enhanced our understanding of the pathomechanisms of ACD. Here, we focused on the main cell types from both immune domains, which are involved in ACD, such as CD4+ and CD8+ T cells, B cells, neutrophils, and innate lymphoid cells (ILCs). Such insights can be useful for devising future therapeutic interventions for ACD.

The Role of New IL-1 Family Members (IL-36 and IL-38) in Atopic Dermatitis, Allergic Asthma, and Allergic Rhinitis

PURPOSE OF REVIEW

Since the discovery of its very first member in 1974, the IL-1 family has expanded into a group of 11 potent molecules which are essential in both innate and acquired immunity. Pro-inflammatory cytokines IL-36α, IL-36β, and IL-36γ and their receptor antagonists IL-36Ra and IL-38, which belong to the IL-36 subfamily, are some of the most recently identified members. Recent studies show that these members possess pro-inflammatory and anti-inflammatory activities and may take part in the pathogenesis of allergy. In this review, the involvement and importance of these newly described IL-1 family members in the most common allergic diseases, i.e., atopic dermatitis (AD), allergic asthma, and allergic rhinitis, will be discussed.

RECENT FINDINGS

Dysregulation of IL-36 and IL-38 was observed in the skin and respiratory tract of AD, allergic rhinitis, and allergic asthma individuals. Although the upregulation in IL-36α and IL-36γ observed in the lesional skin of AD patients was unexpectedly small, IL-36 may play an important role in AD pathogenesis especially upon Staphylococcus aureus colonization. While IL-36γ regulates eosinophils to induce an inflammatory response in allergic rhinitis, IL-36α was found to regulate Th17 immunity. IL-36 receptor antagonists, IL-36Ra and IL-38, however, both show promising anti-inflammatory activities against allergic asthma. Of note, IL-38 in allergic asthmatic children is significantly lower than their healthy counterparts, while the anti-inflammatory effects of IL-38 in allergic asthma exacerbation upon viral-like infection were demonstrated in in vitro, HDM-induced, and humanized mice models. Dysregulated expression of IL-36 and IL-38 observed in allergic patients and mice models revealed that they may have essential roles in the pathogenesis in AD, allergic rhinitis, and allergic asthma, especially during the host defense against pathogens at inflammatory sites. Their receptor antagonists, IL-36Ra and IL-38, could also be promising biologics in the control of allergy. Since allergic diseases are phenotypically complex, contradictory data obtained in different studies may be explained if further stratification of disease endotypes is explored. Genetically modified mice model and investigation in anti-IL-36 treatment may be useful to characterize the therapeutic potential of these cytokines in the regulation of allergy in the future.

TAK-242 ameliorates contact dermatitis exacerbated by IL-36 receptor antagonist deficiency

Loss-of-function mutations in IL36RN cause generalized pustular psoriasis (GPP), which is characterized by neutrophil-infiltrated lesions. Neutrophils are important during contact hypersensitivity in mice. However, it has never been determined whether interleukin-36 receptor antagonist (IL-36Ra) deficiency is an exacerbating factor in contact dermatitis. We examined whether a loss-of-function IL36RN mutation exacerbates contact dermatitis and evaluated the changes in contact dermatitis-related cytokines. Wild-type and Il36rn^−/− mice were treated with 1-fluoro-2,4-dinitorobenzene (DNFB) and evaluated for ear thickness, histopathological features, numbers of infiltrated neutrophils, and numbers of CD4 + and CD8 + T cells. Furthermore, mRNA levels of contact dermatitis-related cytokines were measured by real-time polymerase chain reaction, and effects of TAK-242, a toll-like receptor 4 (TLR4) inhibitor, on the contact hypersensitivity (CHS) response were evaluated. We found that the ear thickness, cytokine expression, and neutrophil infiltration significantly increased in Il36rn^−/− mice compared with that in wild-type mice. TAK-242 alleviated CHS and prevented neutrophil infiltration, cytokine expression, and ear thickening in Il36rn^−/− mice. These data indicate that Il36rn^−/− mutations are an exacerbating factor for CHS and that TAK-242 can reduce the inflammatory responses that are associated with the CHS response.

Interleukin-36: Structure, Signaling and Function

The IL-36 family belongs to a larger IL-1 superfamily and consists of three agonists (IL-36α/β/γ), one antagonist (IL-36Ra), one cognate receptor (IL-36R) and one accessory protein (IL-1RAcP). The receptor activation follows a two-step mechanism in that the agonist first binds to IL-36R and the resulting binary complex recruits IL-1RAcP. Assembled ternary complex brings together intracellular TIR domains of receptors which activate downstream NF-κB and MAPK signaling. Antagonist IL-36Ra inhibits the signaling by binding to IL-36R and preventing recruitment of IL-1RAcP. Members of IL-36 are normally expressed at low levels. Upon stimulation, they are inducted and act on a variety of cells including epithelial and immune cells. Protease mediated N-terminal processing is needed for cytokine activation. In the skin, the functional role of IL-36 is to contribute to host defense through inflammatory response. However, when dysregulated, IL-36 stimulates keratinocyte and immune cells to enhance the Th17/Th23 axis and induces psoriatic-like skin disorder. Genetic mutations of the antagonist IL-36Ra are associated with occurrence of generalized pustular psoriasis, a rare but life-threatening skin disease. Anti-IL-36 antibodies attenuate IMQ or IL-23 induced skin inflammation in mice, illustrating IL-36's involvement in mouse model of psoriasis. Other organs such as the lungs, the intestine, the joints and the brain also express IL-36 family members upon stimulation. The physiological and pathological roles of IL-36 are less well defined in these organs than in the skin. In this chapter, current progress on IL-36 protein and biology is reviewed with a discussion on investigative tools for this novel target.

The role of IL-37 in skin and connective tissue diseases

IL-37 was discovered as an anti-inflammatory and immunosuppressive cytokine of the IL-1 family. Significant advancements in the understanding of signaling pathways associated with IL-37 have been made in recent years. IL-37 binds to IL-18R and recruits IL-1R8 to form the IL-37/IL-1R8/IL-18Rα complex. Capase-1 plays a key role in the nuclear transduction of IL-37 signal, processing precursor IL-37 into the mature isoform, and interacting with Smad3. IL-37 exerts its role by activating anti-inflammation pathways including AMPK, PTEN, Mer, STAT3 and p62, and promoting tolerogenic dendritic cells and Tregs. In addition, IL-37 inhibits pro-inflammatory cytokines such as IL-1, IL-6, IL-8, IL-17, IL-23, TNF-α, and IFN-γ, and suppresses Fyn, MAPK, TAK1, NFκB, and mTOR signaling. The final effects of IL-37 depend on the interaction among IL-18R, IL-1R8, IL-37 and IL-18BP. Previous studies have deciphered the role of IL-37 in the development and pathogenesis of autoimmune diseases, chronic infections and cancer. In this review, we discuss the role of IL-37 in psoriasis, atopic dermatitis, Behcet's diseases, systemic lupus erythematosus, and other skin and connective tissue diseases.

Transcriptome profiling reveals Th2 bias and identifies endogenous itch mediators in poison ivy contact dermatitis

In the United States, poison ivy is the most common naturally occurring allergen that causes allergic contact dermatitis (ACD). The immune and pruritic mechanisms associated with poison ivy ACD remain largely unexplored. Here, we compared skin whole transcriptomes and itch mediator levels in mouse ACD models induced by the poison ivy allergen, urushiol, and the synthetic allergen, oxazolone. The urushiol model produced a Th2-biased immune response and scratching behavior, resembling findings in poison ivy ACD patients. Urushiol-challenged skin contained elevated levels of the cytokine thymic stromal lymphopoietin (TSLP), a T cell regulator and itch mediator, and pruritogenic serotonin (5-HT) and endothelin (ET-1) but not substance P (SP) or histamine. The oxazolone model generated a mixed Th1/Th2 response associated with increased levels of SP, 5-HT, and ET-1 but not TSLP or histamine. Injections of a TSLP monoclonal neutralizing antibody or serotonergic or endothelin inhibitors, but not SP inhibitors or antihistamines, reduced scratching behaviors in urushiol-challenged mice. Our findings suggest that the mouse urushiol model may serve as a translational model of human poison ivy ACD. Inhibiting signaling by TSLP and other cytokines may represent alternatives to the standard steroid/antihistamine regimen for steroid-resistant or -intolerant patients and in exaggerated systemic responses to poison ivy.

Characterization of the immune and pruritic pathways in a mouse model of poison ivy-induced allergic contact dermatitis.

Interleukin-36 in Infectious and Inflammatory Skin Diseases

Interleukin-36 (IL-36) comprises to a cytokine family consisting of four isoforms IL-36α, IL-36β, IL-36γ, and IL-36 receptor antagonist (IL-36 Ra). These IL-36 cytokines, in turn, belong to the IL-1 superfamily. The IL-36 receptor (IL-1R6) is functional as a heterodimer formed of IL-1R6 and IL-1 receptor accessory protein (IL-1RAcP). IL-36α, IL-36β, and IL-36γ are regarded as pro-inflammatory ligands and IL-36 Ra as well as IL-38 as anti-inflammatory ligands of IL-1R6. IL-36 cytokines are mainly expressed on the barrier sites of the body e.g., bronchial, intestinal, and dermal epithelium. One of their most important biological functions is the bridging of innate and adaptive immune responses. A disturbed balance between pro-inflammatory and anti-inflammatory branches easily leads to inflammation of the corresponding tissue. The most prominent example for an altered IL-36 expression is the spectrum of psoriasis. In addition to inflammatory dermatoses, IL-36 also seems to play a role in infectious dermatoses. Microbial triggers, especially Staphylococcus aureus infection, increase the production of pro-inflammatory IL-36 cytokines and initiate/promote the inflammation of skin lesions. Due to the discovery of IL-36 as an important immune mediator, it has already been possible to develop important diagnostic tools for dermatitis. Not only in the field of inflammatory skin diseases, but also in pulmonary and intestinal inflammation, there is evidence that IL-36 cytokines might have diagnostic and/or therapeutic relevance.

Role and mechanisms of cytokines in the secondary brain injury after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and severe cerebrovascular disease that has high mortality. Few survivors achieve self-care. Currently, patients receive only symptomatic treatment for ICH and benefit poorly from this regimen. Inflammatory cytokines are important participants in secondary injury after ICH. Increases in proinflammatory cytokines may aggravate the tissue injury, whereas increases in anti-inflammatory cytokines might be protective in the ICH brain. Inflammatory cytokines have been studied as therapeutic targets in a variety of acute and chronic brain diseases; however, studies on ICH are limited. This review summarizes the roles and functions of various pro- and anti-inflammatory cytokines in secondary brain injury after ICH and discusses pathogenic mechanisms and emerging therapeutic strategies and directions for treatment of ICH.

IL-36, IL-37, and IL-38 Cytokines in Skin and Joint Inflammation: A Comprehensive Review of Their Therapeutic Potential

The interleukin (IL)-1 family of cytokines is composed of 11 members, including the most recently discovered IL-36α, β, γ, IL-37, and IL-38. Similar to IL-1, IL-36 cytokines are initiators and amplifiers of inflammation, whereas both IL-37 and IL-38 display anti-inflammatory activities. A few studies have outlined the role played by these cytokines in several inflammatory diseases. For instance, IL-36 agonists seem to be relevant for the pathogenesis of skin psoriasis whereas, despite being expressed within the synovial tissue, their silencing or overexpression do not critically influence the course of arthritis in mice. In this review, we will focus on the state of the art of the molecular features and biological roles of IL-36, IL-37, and IL-38 in representative skin- and joint-related inflammatory diseases, namely psoriasis, rheumatoid arthritis, and psoriatic arthritis. We will then offer an overview of the therapeutic potential of targeting the IL-36 axis in these diseases, either by blocking the proinflammatory agonists or enhancing the physiologic inhibitory feedback on the inflammation mediated by the antagonists IL-37 and IL-38.

Polymorphic Light Eruption: What's New in Pathogenesis and Management

Polymorphic light eruption is the commonest photosensitive disorder, characterized by an intermittent eruption of non-scarring erythematous papules, vesicles or plaques that develop within hours of ultraviolet radiation exposure of patient skin. Together with the lesions, a terrible itch starts and increases with the spreading of the disease, sometimes aggravated by a sort of burning sensation. Clinical picture and symptoms can improve during the rest of the summer with further solar exposures. In the last years many advances have been performed in the knowledge of its pathogenesis and some news have been proposed as preventive, as well as therapeutic options. All this has been discussed in the current mini review.

Regulation and function of interleukin-36 cytokines

The interleukin (IL)-36 cytokines include 3 agonists, IL-36α, IL-36β, and IL-36γ that bind to a common receptor composed of IL-36R and IL-1RAcP to stimulate inflammatory responses. IL-36Ra is a natural antagonist that binds to IL-36R, but does not recruit the co-receptor IL-1RAcP and does not stimulate any intracellular responses. The IL-36 cytokines are expressed predominantly by epithelial cells and act on a number of cells including immune cells, epithelial cells, and fibroblasts. Processing of the N-terminus is required for full agonist or antagonist activity for all IL-36 members. The role of IL-36 has been extensively demonstrated in the skin where it can act on keratinocytes and immune cells to induce a robust inflammatory response that has been implicated in psoriatic disorders. Emerging data also suggest a role for this cytokine family in pulmonary and intestinal physiology and pathology.

Polymorphic light eruption and IL-1 family members: any difference with allergic contact dermatitis?

Polymorphic light eruption (PLE) is described as a delayed-type hypersensitivity reaction (DTHR) toward a de novo light-induced antigen, yet to be identified. In effect, the inflammatory pathways of PLE and allergic contact dermatitis (ACD) share common patterns in terms of the mediators involved from the innate and adaptive immune system participating in the DTHR. As we have previously highlighted the role of interleukin (IL)-1 family members in ACD, we hypothesised that the same mediators could have similar functions in PLE. Our research aimed to assess the expression of certain IL-1family members in PLE patients vs. controls, and to compare it with ACD. The study population comprised 17 patients with PLE, 5 affected by ACD and 10 healthy controls in the same age range. Lesional and healthy skin samples were collected respectively from patients and donors. IL-36α, IL-36β, IL-36γ, IL-36 receptor antagonist (Ra), IL-1β, IL-33 gene and protein expressions were evaluated through RT-PCR and immunohistochemistry. Circulating proteins in the PLE patients were analysed by using western blot. The IL-36γ gene expression was significantly increased in PLE lesions compared to that in healthy controls and ACD lesions (***p < 0.001; ##p < 0.01 respectively), whereas the other analyzed ILs were more expressed in ACD. Immunohistochemical analysis revealed that IL-36α and IL-36γ protein levels were increased in PLE lesions compared to those of the healthy samples (***p < 0.001). Furthermore the IL-36γ plasma level was increased in PLE patients vs. controls (*p < 0.05). Our findings indicate that the IL-1 family pro-inflammatory members are increased in PLE with distinct differences from those in ACD, in particular with regard to IL-36γ mRNA regulation. Their role as activators of the local, and perhaps systemic, immune response, or as inhibitors of the immune tolerance machinery, needs further investigation.

Opposing Effects of IL-1Ra and IL-36Ra on Innate Immune Response to Pseudomonas aeruginosa Infection in C57BL/6 Mouse Corneas

Pseudomonas aeruginosa keratitis is characterized by severe corneal ulceration and may lead to blindness if not treated properly in a timely manner. Although the roles of the IL-1 subfamily of cytokines are well established, as a newly discovered subfamily, IL-36 cytokine regulation, immunological relevance, and relation with IL-1 cytokines in host defense remain largely unknown. In this study, we showed that P. aeruginosa infection induces the expression of IL-36α and IL-36γ, as well as IL-1β and secreted IL-1Ra (sIL-1Ra), but not IL-36Ra. Downregulation of IL-1Ra increases, whereas downregulation of IL-36Ra decreases the severity of P. aeruginosa keratitis. IL-1R and IL-36Ra downregulation have opposing effects on the expression of IL-1β, sIL-1Ra, IL-36γ, S100A8, and CXCL10 and on the infiltration of innate immune cells. Administration of recombinant IL-1Ra improved, whereas IL-36Ra worsened the outcome of P. aeruginosa keratitis. Local application of IL-36γ stimulated the expression of innate defense molecules S100A9, mouse β-defensin 3, but suppressed IL-1β expression in B6 mouse corneas. IL-36γ diminished the severity of P. aeruginosa keratitis, and its protective effects were abolished in the presence of S100A9 neutralizing Ab and partially affected by CXCL10 and CXCR3 neutralizations. Thus, our data reveal that IL-1Ra and IL-36Ra have opposing effects on the outcome of P. aeruginosa keratitis and suggest that IL-36 agonists may be used as an alternative therapeutic to IL-1β-neutralizing reagents in controlling microbial keratitis and other mucosal infections.

IL-25 enhances TH17 cell-mediated contact dermatitis by promoting IL-1β production by dermal dendritic cells

BACKGROUND

In addition to thymic stromal lymphopoietin and IL-33, IL-25 is known to induce T_H2 cytokine production by various cell types, including T_H2 cells, T_H9 cells, invariant natural killer T cells, and group 2 innate lymphoid cells, involved in T_H2-type immune responses. Because both T_H2-type and T_H17-type cells/cytokines are crucial for contact hypersensitivity (CHS), IL-25 can contribute to this by enhancing T_H2-type immune responses. However, the precise role of IL-25 in the pathogenesis of fluorescein isothiocyanate-induced CHS is poorly understood.

OBJECTIVE

We investigated the contribution of IL-25 to CHS using Il25^-/- mice.

METHODS

CHS was evaluated by means of measurement of ear skin thickness in mice after fluorescein isothiocyanate painting. Skin dendritic cell (DC) migration, hapten-specific T_H cell differentiation, and detection of IL-1β-producing cells were determined by using flow cytometry, ELISA, and immunohistochemistry, respectively.

RESULTS

In contrast to thymic stromal lymphopoietin, we found that IL-25 was not essential for skin DC migration or hapten-specific T_H cell differentiation in the sensitization phase of CHS. Unexpectedly, mast cell- and non-immune cell-derived IL-25 was important for hapten-specific T_H17 cell-mediated rather than T_H2 cell-mediated inflammation in the elicitation phase of CHS by enhancing T_H17-related, but not T_H2-related, cytokines in the skin. In particular, IL-1β produced by dermal DCs in response to IL-25 was crucial for hapten-specific T_H17 cell activation, contributing to induction of local inflammation in the elicitation phase of CHS.

CONCLUSION

Our results identify a novel IL-25 inflammatory pathway involved in induction of T_H17 cell-mediated, but not T_H2 cell-mediated, CHS. IL-25 neutralization can be a potential approach for treatment of CHS.

Anti‑apoptotic effects of glycosaminoglycans via inhibition of ERK/AP‑1 signaling in TNF‑α‑stimulated human dermal fibroblasts

It has been established that glycosaminoglycans (GAGs) serve an important role in protecting the skin against the effects of aging. A previous clinical trial by our group identified that a cream containing GAGs reduced wrinkles and increased skin elasticity, dermal density and skin tightening. However, the exact molecular mechanism underlying the anti‑aging effect of GAGs has not yet been fully elucidated. The present study assessed the influence of GAGs on cell viability, collagen synthesis and collagen synthesis‑associated signaling pathways in tumor necrosis factor‑α (TNF‑α)‑stimulated human dermal fibroblasts (HDFs); an in vitro model of aging. The results demonstrated that GAGs restored type I collagen synthesis and secretion by inhibiting extracellular signal‑regulated kinase (ERK) signaling in TNF‑α‑stimulated HDFs. However, GAGs did not activate c‑jun N‑terminal kinase or p38. It was determined that GAGs suppressed the phosphorylation of downstream transcription factors of ERK activation, activator protein‑1 (AP‑1; c‑fos and c‑jun), leading to a decrease in matrix metalloproteinase‑1 (MMP‑1) levels and the upregulation of tissue inhibitor of metalloproteinase‑1 in TNF‑α‑stimulated HDFs. In addition, GAGs attenuated the apoptosis of HDFs induced by TNF‑α. The current study revealed a novel mechanism: GAGs serve a crucial role in ameliorating TNF‑α‑induced MMP‑1 expression, which causes type I collagen degeneration via the inactivation of ERK/AP‑1 signaling in HDFs. The results of the present study indicate the potential application of GAGs as effective anti‑aging agents that induce wrinkle reduction.

Shear stress induces human aortic endothelial cell apoptosis via interleukin‑1 receptor‑associated kinase 2‑induced endoplasmic reticulum stress

Atherosclerosis is characterized by localized lesions distributed in the arterial tree due to the shear stress produced by blood flow. Endothelial cells are directly affected by alterations in blood flow. Dysfunction and injury to endothelial cells has been hypothesized to initiate the pathological processes of atherosclerosis. The present study aimed to investigate the mechanism of shear stress-induced endothelial cellular apoptosis. Shear stress was generated using an artificial device to mimic the impact of disturbed blood flow on cultured human aortic endothelial cells (HAECs). Cellular apoptosis was assessed using a terminal deoxynucleotidyl transferase dUTP nick end labeling assay; an ELISA assay was used to detect the produced interleukin (IL)-1β; specific small interfering (si)RNA was used to knockdown the expression of interleukin-1 receptor-associated kinase 2 (IRAK2) in HAECs and the expression levels of 78 kDa glucose-regulated protein, DNA damage-inducible transcript 3 protein (CHOP), IRAK2 and IL-1β were evaluated using western blotting. The results of the present study demonstrated that artificial shear stress induced endoplasmic reticulum (ER) stress, IL-1β production and apoptosis in HAECs in a time-dependent manner. The inhibition of ER stress, and treatment with interleukin-1 receptor antagonist protein and siRNA against IRAK2 attenuated shear stress-induced CHOP signaling-mediated cellular apoptosis. Therefore, overproduction of IL-1β exacerbated shear stress-induced ER stress-mediated apoptosis via the IRAK2/CHOP signaling pathway in endothelial cells.

Increased expression of the interleukin-36 cytokines in lesions of hidradenitis suppurativa

BACKGROUND

Hidradenitis suppurativa (HS) is a recalcitrant chronic skin disease with poorly understood immunopathogenic mechanisms. Previous studies reported that the interleukin-36 (IL-36) cytokines [IL-36α, IL-36β, IL-36γ and IL-36 receptor antagonists (IL-36RA)] are important players in the pathogenesis of psoriasis (PS).

OBJECTIVE

We aim to determine whether the IL-36 cytokines are upregulated in patients with HS. For this purpose, we analysed local expression and systemic levels of the IL-36 cytokines in patients with HS and compared the results to healthy donors and patients with PS.

METHODS

Skin biopsies from healthy donors and HS and PS patients were analysed for expression of the IL-36 cytokines by immunohistochemistry and semiquantitative real-time PCR. The enzyme-linked immunosorbent assay (ELISA) was used to measure systemic levels of the IL-36 cytokines in the serum of the three donor groups.

RESULTS

The agonists IL-36α, IL-36β and IL-36γ were found to be upregulated in HS both systemically and lesionally, while the IL-36RA was not differently regulated in comparison to healthy donors.

CONCLUSION

Our findings suggest that the agonistic IL-36 isoforms are upregulated in HS. The relevance of the enhanced production of IL-36 cytokines in HS pathogenesis remains to be determined.

IL-36 cytokines are increased in acne and hidradenitis suppurativa

Interleukin (IL)-36 cytokines are new members of the IL-1 family, which include pro-inflammatory factors, IL-36α, IL-36β and IL-36γ, and a natural receptor antagonist IL-36Ra. Over recent years, much has been learned on their important functions in the regulation of immune response and, especially, on their role in many inflammatory skin diseases. However, to date, no data have been reported on their possible involvement in acne and hidradenitis suppurativa (HS). Here, we have shown that IL-36α, IL-36β, and IL-36γ are increased in lesional skin of acne and HS, highlighting their possible pathogenetic contribution to these two skin conditions. In contrast, IL-36Ra (the anti-inflammatory member of IL-36 sub-family) was increased just in psoriasis, suggesting that an imbalance in IL-36/IL36Ra functions could play a role in the phenotype of skin damage. One of the consequences of this imbalance may be the increased induction of IL-8 that we found higher in acne, HS, and ACD respect to psoriasis.

Serum Levels of Interleukin 33 and Soluble ST2 Are Associated with the Extent of Disease Activity and Cutaneous Manifestations in Patients with Active Adult-onset Still's Disease

OBJECTIVE

Interleukin 33 (IL-33), a member of the IL-1 family and a ligand of the orphan receptor ST2, plays key roles in innate and adaptive immunity. We examined the associations between IL-33/ST2 levels and clinical manifestations of patients with active adult-onset Still's disease (AOSD).

METHODS

Blood samples were collected from 40 patients with active AOSD, 28 patients with rheumatoid arthritis (RA), and 27 healthy controls (HC). The serum levels of IL-33 and soluble ST2 were determined using ELISA. Expression levels of IL-33 and ST2 in biopsy specimens obtained from 34 AOSD patients with rash were immunohistochemically investigated.

RESULTS

IL-33 levels of patients with AOSD were higher than those of patients with RA and HC. Soluble ST2 levels of patients with AOSD were higher than those of HC, but not of patients with RA. Serum IL-33 levels correlated with systemic score, erythrocyte sedimentation rate, ferritin levels, and aspartate transaminase levels. However, serum soluble ST2 levels correlated only with ferritin levels. The numbers of inflammatory cells expressing IL-33 and ST2 were elevated in skin lesions of patients with AOSD compared to HC, but did not differ from those of the skin lesions of eczema or psoriasis.

CONCLUSION

We found significantly higher serum IL-33 and soluble ST2 levels in patients with active AOSD. Results indicate that the IL-33/ST2 signaling pathway may play a role in the pathogenesis of the acute inflammation and skin manifestations associated with AOSD.

Nickel-free vs conventional braces for patients allergic to nickel: Gingival and blood parameters during and after treatment

INTRODUCTION

Allergic and inflammatory reactions have commonly been associated with the release of metal ions during orthodontic treatment. Our objective was to evaluate prospectively gingival and blood status in patients allergic to nickel.

METHODS

Allergy to nickel was diagnosed using a patch test. Two groups were established: conventional braces (n = 21) and nickel-free braces (n = 21). The gingival index was used to determine gingival status before treatment, periodically for 12 months (evaluations every 3 months), and 1 month after the removal of the braces. Blood status was evaluated with a complete blood count, including the quantification of nickel and immunoglobin E before treatment, during treatment, and 1 month after removal of the braces. The data were analyzed using Mann-Whitney, Student t, Wilcoxon, repeated measures analysis of variance, Friedman, and chi-square tests. Either the Pearson or the Spearman correlation coefficients were calculated, when appropriate.

RESULTS

The number of basophils increased significantly among the evaluations in both groups (conventional, P = 0.002; nickel-free, P = 0.001), whereas the number of eosinophils and the immunoglobin E levels decreased significantly in the conventional group (P = 0.004). Plasma nickel levels were increased before and during treatment, and decreased 1 month after removing the braces in both groups, but the differences were significant only in the nickel-free group (P = 0.002). No correlations were found between the concentrations of nickel and immunoglobin E, basophils, or eosinophils, or between the gingival index and either bands or segmented neutrophils (P ≥ 0.05).

CONCLUSIONS

Patients treated with nickel-free braces had better gingival health and smaller blood changes than did those treated with conventional braces. All abnormalities tended to be eliminated after the removal of the braces.

IL-33/ST2 signaling excites sensory neurons and mediates itch response in a mouse model of poison ivy contact allergy

Poison ivy-induced allergic contact dermatitis (ACD) is the most common environmental allergic condition in the United States. Case numbers of poison ivy ACD are increasing due to growing biomass and geographical expansion of poison ivy and increasing content of the allergen, urushiol, likely attributable to rising atmospheric CO₂ Severe and treatment-resistant itch is the major complaint of affected patients. However, because of limited clinical data and poorly characterized models, the pruritic mechanisms in poison ivy ACD remain unknown. Here, we aim to identify the mechanisms of itch in a mouse model of poison ivy ACD by transcriptomics, neuronal imaging, and behavioral analysis. Using transcriptome microarray analysis, we identified IL-33 as a key cytokine up-regulated in the inflamed skin of urushiol-challenged mice. We further found that the IL-33 receptor, ST2, is expressed in small to medium-sized dorsal root ganglion (DRG) neurons, including neurons that innervate the skin. IL-33 induces Ca²⁺ influx into a subset of DRG neurons through neuronal ST2. Neutralizing antibodies against IL-33 or ST2 reduced scratching behavior and skin inflammation in urushiol-challenged mice. Injection of IL-33 into urushiol-challenged skin rapidly exacerbated itch-related scratching via ST2, in a histamine-independent manner. Targeted silencing of neuronal ST2 expression by intrathecal ST2 siRNA delivery significantly attenuated pruritic responses caused by urushiol-induced ACD. These results indicate that IL-33/ST2 signaling is functionally present in primary sensory neurons and contributes to pruritus in poison ivy ACD. Blocking IL-33/ST2 signaling may represent a therapeutic approach to ameliorate itch and skin inflammation related to poison ivy ACD.

Wounds that heal and wounds that don't - The role of the IL-33/ST2 pathway in tissue repair and tumorigenesis

IL-33 is a member of the IL-1 family of cytokines. IL-33 is predominantly located within the nucleus of cells where it plays a role in gene regulation. Given the right combination of signals and cellular damage, stored IL-33 is released from the cell where it can interact with its receptor ST2, triggering danger-associated responses and act as a cellular "alarmin". Whilst IL-33/ST2 signalling has been shown to induce potent pro-inflammatory responses that can be detrimental in certain disease states, a dichotomous, protective role of IL-33 in promoting wound healing has also emerged in multiple tissues types. This review will explore the current literature concerning this homeostatic role of IL-33/ST2 in tissue repair and also review its role in uncontrolled wound responses as seen in both fibrosis and tumorigenesis.