The new IL-1 family member IL-1F8 stimulates production of inflammatory mediators by synovial fibroblasts and articular chondrocytes

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.

Serum Interleukin-36 α as a Candidate Biomarker to Distinguish Behçet's Syndrome and Psoriatic Arthritis

Behçet's syndrome (BS) is a rare systemic vasculitis characterized by different clinical manifestations. As no specific laboratory tests exist, the diagnosis relies on clinical criteria, and the differential diagnosis with other inflammatory diseases can be challenging. Indeed, in a relatively small proportion of patients, BS symptoms include only mucocutaneous, articular, gastrointestinal, and non-typical ocular manifestations, which are frequently found also in psoriatic arthritis (PsA). We investigate the ability of serum interleukin (IL)-36α-a pro-inflammatory cytokine involved in cutaneous and articular inflammatory diseases-to differentiate BS from PsA. A cross-sectional study was performed on 90 patients with BS, 80 with PsA and 80 healthy controls. Significantly lower IL-36α concentrations were found in patients with BS as compared to PsA, although in both groups IL-36α was significantly increased compared to healthy controls. An empirical cut-off of 420.6 pg/mL displayed a specificity of 0.93, with a sensitivity of 0.70 (AUC 0.82) in discriminating PsA from BS. This cut-off displayed a good diagnostic performance also in BS patients lacking highly specific BS manifestations. Our results indicate that IL-36α might be involved in the pathogenesis of both BS and PsA, and might be a candidate biomarker to support the differential diagnosis of BS.

Role of Interleukin-36 in inflammatory joint diseases

Interleukin (IL)-36 is a family of cytokines that belongs to the larger IL-1 superfamily. IL-36 agonist/antagonist binds to the interleukin-36 receptor involving in physiological inflammation regulation and pathogenesis of many inflammatory diseases. In inflammatory joint diseases, the expression of IL-36 changes, and some studies have initially explored the role of IL-36 in these diseases. In psoriatic arthritis, IL-36 signal mediates plasma cell and fibroblast-like synoviocyte crosstalk presenting IL-36 agonist/antagonist imbalance. In rheumatoid arthritis, IL-36 agonists induce fibroblast-like synoviocyte to produce pro-inflammatory factors, while IL-36 antagonist deficiency leads to lesion progression. In osteoarthritis, IL-36 agonists induce chondrocytes to produce catabolic enzymes and pro-inflammatory factors. This article reviews the expression and function of IL-36 in different inflammatory joint diseases to provide a reference for revealing their pathogenic mechanisms and discovering therapeutic targets.

Injectable Temperature-Sensitive Hydrogel Loaded with IL-36Ra for the Relief of Osteoarthritis

Osteoarthritis (OA) is an inflammatory disease accompanied by synovial joint inflammation, and IL-36 plays an important role in this process. Local application of IL-36 receptor antagonist (IL-36Ra) can effectively control the inflammatory response, thereby protecting cartilage and slowing down the development of OA. However, its application is limited by the fact that it is rapidly metabolized locally. We designed and prepared a temperature-sensitive poly(lactic-co-glycolic acid)-poly(ethylene glycol)-poly(lactic-co-glycolic acid) (PLGA-PEG-PLGA) hydrogel (IL-36Ra@Gel) system carrying IL-36Ra and evaluated its basic physicochemical characteristics. The drug release curve of IL-36Ra@Gel indicated that this system could slowly release the drug over a longer period. Furthermore, degradation experiments showed that it could be largely degraded from the body within 1 month. The biocompatibility-related results showed that it had no significant effect on cell proliferation compared to the control group. In addition, the expression of MMP-13 and ADAMTS-5 was lower in IL-36Ra@Gel-treated chondrocytes than in the control group, and the opposite results appeared in aggrecan and collagen X. After 8 weeks of treatment with IL-36Ra@Gel by joint cavity injection, HE and Safranin O/Fast green staining showed that the degree of cartilage tissue destruction in the IL-36Ra@Gel-treated group was less than those in other groups. Meanwhile, the joints of mice in the IL-36Ra@Gel group had the most intact cartilage surface, the smallest thickness of cartilage erosion, and the lowest OARSI and Mankins score among all groups. Consequently, the combination of IL-36Ra and PLGA-PLEG-PLGA temperature-sensitive hydrogels can greatly improve the therapeutic effect and prolong the drug duration time, thus effectively delaying the progression of degenerative changes in OA, providing a new feasible nonsurgical treatment for OA.

Plasma IL-36α and IL-36γ as Potential Biomarkers in Interstitial Lung Disease Associated with Rheumatoid Arthritis: a Pilot Study in the Chinese Population

Interstitial lung disease (ILD) is a frequent extra-articular manifestation of rheumatoid arthritis (RA) and increases mortality in patients with RA. Early identification of ILD, especially the usual interstitial pneumonia (UIP) pattern with a poor prognosis, is important for guiding treatment of RA-ILD and preventing damage resulting from a delay in diagnosis. Interleukin-36 (IL-36) cytokines are involved in connective tissue diseases. However, IL-36 expression in RA-ILD is unknown. In this study, the clinical relevance of plasma IL-36 cytokines was evaluated in 39 patients with RA-ILD and three other groups (30 healthy controls [HCs], 35 RA patients without ILD, and 27 patients with idiopathic pulmonary fibrosis [IPF]) in the Chinese population. Plasma IL-36α and IL-36γ concentrations were elevated in patients with RA-ILD compared with those in HCs and patients with RA. RA-ILD patients with UIP pattern had higher plasma IL-36γ concentrations than those with RA-ILD without UIP, but these were lower than those in patients with IPF. Receiver operating curve analysis suggested that IL-36α and IL-36γ were potential biomarkers for identifying ILD in patients with RA. Additionally, the optimal cutoff value of IL-36γ for distinguishing RA-ILD with the UIP pattern from RA-ILD without UIP was 555.40 pg/mL and that for distinguishing RA-ILD from IPF was 655.10 pg/mL. No significant difference in plasma IL-36β or IL-36Ra concentrations was found between patients with RA-ILD and the three other groups. We also found that the lungs originating from different types of patients with PF, including RA-ILD and IPF, and those from mice following bleomycin-induced PF were characterized by increased IL-36γ expression. Our findings suggest that using IL-36 cytokines to identify patients with RA for further ILD workups may provide additional diagnostic value to the current clinically available assays. Moreover, IL-36γ may help to identify the presence of the UIP pattern in patients with RA-ILD and to discriminate RA-ILD from IPF.

Plasma Levels of Interleukins 36α, 36β, and 37 in Patients with Psoriasis and Their Correlation with Disease Activity Parameters

Psoriasis is a chronic, proliferative, inflammatory skin disease characterised by skin lesions and systemic symptoms. Numerous cytokines are produced in psoriasis as a result of inflammation. The aim of this study was to examine the plasma concentrations of IL-36α, IL-36β, and IL-37 in psoriasis and their correlations with disease activity parameters. This study recruited 84 individuals, 53 with plaque-type psoriasis and 31 healthy controls. The plaque type of psoriasis is the most common type and is typically characterized by circular-to-oval red plaques distributed over body surfaces of the extremities and scalp. In patients with psoriasis, we observed statistically significantly decreased plasma concentrations of IL-36β and IL-37. The concentrations of IL-36α were increased in comparison with control group. The plasma concentrations of IL-36α and IL-36β were statistically significantly correlated with all tested parameters of disease activity: the Psoriasis Activity Severity Index, Dermatology Life Quality Index, and Body Surface Area Index. There were no statistically significant correlations between plasma levels of IL-37 and the tested parameters of disease activity. These results indicate a role of IL36α, IL-36β, and IL-37 in the pathogenesis of psoriasis.

Regulation of Interleukin-36γ/IL-36R Signaling Axis by PIN1 in Epithelial Cell Transformation and Breast Tumorigenesis

Simple Summary

Members of the interleukin (IL)-1 cytokine family exhibit dual functions in the regulation of inflammation and cancer. Recent studies have shown the critical role of IL-36γ, the newly identified IL-1 family member, in the regulation of cellular processes implicated in the progression of cancer. Therefore, the underlying mechanism of IL-36γ in tumor development is of considerable interest. Here, we identified the pivotal role of IL-36γ in the proliferation of breast cancer cells. Consistently, IL-36γ was found to promote epithelial cell transformation via the activation of c-Fos, c-Jun, and AP-1 transcription factors, followed by the IL36R-mediated MEK/ERK and JNK/c-Jun cascades. Furthermore, our findings demonstrate the critical role of PIN1 in the regulation of IL-36γ-induced mammary gland tumorigenesis.

Abstract

Given the increasing recognition of the relationship between IL-1 cytokines, inflammation, and cancer, the significance of distinct members of the IL-1 cytokine family in the etiology of cancer has been widely researched. In the present study, we investigated the underlying mechanism of the IL-36γ/IL-36R axis during breast cancer progression, which has not yet been elucidated. Initially, we determined the effects of IL-36γ on the proliferation and epithelial cell transformation of JB6 Cl41 mouse epidermal and MCF7 human breast cancer cells using BrdU incorporation and anchorage-independent growth assays. We found that treatment with IL-36γ increased the proliferation and colony formation of JB6 Cl41 and MCF7 cells. Analysis of the mechanism underlying the neoplastic cell transformation revealed that IL-36γ induced IL-36R-mediated phosphorylation of MEK1/2, ERK1/2, JNK1/2, and c-Jun, resulting in increased c-Fos, c-Jun, and AP-1 activities in JB6 Cl41 and MCF7 cells. Furthermore, the IL-36γ-induced tumorigenic capacity of MCF7 cells was considerably enhanced by PIN1, following MEK/ERK and JNK/c-Jun signaling. Interestingly, blocking PIN1 activity using juglone suppressed the IL-36γ-induced increase in the anchorage-independent growth of 4T1 metastatic mouse breast cancer cells. Finally, in a syngeneic mouse model, IL-36γ-induced tumor growth in the breast mammary gland was significantly inhibited following PIN1 knockout.

Interleukin-36α is elevated in diffuse systemic sclerosis and may potentiate fibrosis

Systemic sclerosis (SSc) is an autoimmune prototypical connective tissues disease that results in alterations in vasculature, inflammation and fibrosis of the skin. Interleukin-1 family cytokines has been implicated in the disease including IL-1. IL-36α is an IL-1 family member that is clearly implicated in psoriatic skin disease but its role in systemic sclerosis disease is not clear. The aim of this work is to evaluate the levels and role of IL-36α in systemic sclerosis. Early diffuse SSc patients sera was isolated along with healthy controls and IL-36 levels quantified by ELISA. In vitro analysis was also undertaken with primary dermal fibroblasts with recombinant IL-36α and keratinocyte cells were also incubated with IL-36α. Cytokines were measured by ELISA. Serum IL-36 was significantly elevated compared to healthy controls. Elevated neutrophil elastase was also elevated in the matched sera. IL-36 was not directly pro-fibrotic in dermal fibroblasts but did induce pro-inflammatory cytokines that were dependant on the MAPK pathway for their release. IL-36α also led to release of CCL20 and CCL2 in keratinocytes which may potentiate fibrosis. IL-36α is elevated in SSc serum and whilst not directly pro-fibrotic it may through keratinocytes, potentiate fibrosis through keratinocyte-immune fibroblast cross-talk.

IL-36 is Closely Related to Neutrophilic Inflammation in Chronic Obstructive Pulmonary Disease

Background

Interleukin (IL)-36α, IL-36β, and IL-36γ belong to the IL-36 family and play an important role in the pathogenesis of many diseases. Chronic obstructive pulmonary disease (COPD) may be correlated with IL-36; however, the specific role of IL-36 in COPD is unclear. In this study, we aimed to clarify whether IL-36 could be an indicator for determining COPD severity and the specific nature of the pro-inflammatory effects of IL-36 in COPD.

Methods

A total of 70 patients with COPD and 20 control subjects were included in this study. We collected peripheral blood samples from both the groups, analyzed the blood cell fractions by routine blood examination, and measured the serum levels of IL-36α, IL-36β, and IL-36γ by performing polymerase chain reaction and enzyme-linked immunosorbent assay. In addition, the correlation between the number of neutrophils and eosinophils and the level of IL-36 was also analyzed.

Results

We found that level of IL-36 in patients with COPD was positively correlated with the number of neutrophils but not with eosinophils, whereas the correlation was not found in the control group. Moreover, the level of IL-36 was negatively correlated with the level of lung function of patients with COPD, and the levels of IL-36α, IL-36β, and IL-36γ increased with advancing disease severity.

Conclusion

In COPD, the pro-inflammatory effect of IL-36 is closely related to neutrophils, and hence, IL-36 might be considered a novel biomarker for determining COPD severity.

Serum Levels of Interleukin-36 Alpha and Interleukin-36 Receptor Antagonist In Behcet’s Syndrome

Background Behcet’s syndrome (BS) is a systemic vasculitic disorder. This study aimed to investigate the levels of serum IL-36α and IL-36Ra in patients with BS.

Material and Methods A total of 80 subjects (60 BS patients and 20 healthy controls [HC]) were included.

Results The median IL-36α level was 0.11 ng/ml in the BS group and 0.09 ng/ml in the HC group (p=0.058). The mean IL-36Ra level was 13.62 pg/ml in the BS group and 13.26 pg/ml in the HC group (p=0.348). Serum IL-36Ra levels of the active group were significantly higher (p=0.037). Patients with oral ulcers and central nervous system involvement had higher serum IL36Ra levels. In the BS group, a positive correlation was found between serum IL-36Ra and CRP. In a multivariate analysis, the IL-36Ra level (OR=1.067; 95% CI=1.001–1.137; p=0.045) was independently associated with disease activity.

Conclusion According to these findings, it is not clear whether such a slight difference is clinically significant, but they suggest that the IL-36 cytokine family may play a role in the course of the disease.

IL-36 in chronic inflammation and fibrosis - bridging the gap?

IL-36 is a member of the IL-1 superfamily and consists of three agonists and one receptor antagonist (IL-36Ra). The three endogenous agonists, IL-36α, -β, and -γ, act primarily as proinflammatory cytokines, and their signaling through the IL-36 receptor (IL-36R) promotes immune cell infiltration and secretion of inflammatory and chemotactic molecules. However, IL-36 signaling also fosters secretion of profibrotic soluble mediators, suggesting a role in fibrotic disorders. IL-36 isoforms and IL-36 have been implicated in inflammatory diseases including psoriasis, arthritis, inflammatory bowel diseases, and allergic rhinitis. Moreover, IL-36 has been connected to fibrotic disorders affecting the kidney, lung, and intestines. This review summarizes the expression, cellular source, and function of IL-36 in inflammation and fibrosis in various organs, and proposes that IL-36 modulation may prove valuable in preventing or treating inflammatory and fibrotic diseases and may reveal a mechanistic link between inflammation and fibrosis.

NF-κB: At the Borders of Autoimmunity and Inflammation

The transcription factor NF-κB regulates multiple aspects of innate and adaptive immune functions and serves as a pivotal mediator of inflammatory response. In the first part of this review, we discuss the NF-κB inducers, signaling pathways, and regulators involved in immune homeostasis as well as detail the importance of post-translational regulation by ubiquitination in NF-κB function. We also indicate the stages of central and peripheral tolerance where NF-κB plays a fundamental role. With respect to central tolerance, we detail how NF-κB regulates medullary thymic epithelial cell (mTEC) development, homeostasis, and function. Moreover, we elaborate on its role in the migration of double-positive (DP) thymocytes from the thymic cortex to the medulla. With respect to peripheral tolerance, we outline how NF-κB contributes to the inactivation and destruction of autoreactive T and B lymphocytes as well as the differentiation of CD4⁺-T cell subsets that are implicated in immune tolerance. In the latter half of the review, we describe the contribution of NF-κB to the pathogenesis of autoimmunity and autoinflammation. The recent discovery of mutations involving components of the pathway has both deepened our understanding of autoimmune disease and informed new therapeutic approaches to treat these illnesses.

The Role of IL-36 in Infectious Diseases: Potential Target for COVID-19?

IL-36 is a member of the interleukin 1 cytokine family, which is currently experiencing a renaissance due to the growing understanding of its context-dependent roles and advances in our understanding of the inflammatory response. The immunological role of IL-36 has revealed its profound and indispensable functional roles in psoriasis, as well as in several inflammatory diseases, including inflammatory bowel disease (IBD), systemic lupus erythematosus, rheumatoid arthritis (RA) and cancer. More recently, an increasing body of evidence suggests that IL-36 plays a crucial role in viral, bacterial and fungal infections. There is a growing interest as to whether IL-36 contributes to host protective immune responses against infection as well as the potential implications of IL-36 for the development of new therapeutic strategies. In this review, we summarize the recent progress in understanding cellular expression, regulatory mechanisms and biological roles of IL-36 in infectious diseases, which suggest more specific strategies to maneuver IL-36 as a diagnostic or therapeutic target, especially in COVID-19.

IL36 is a critical upstream amplifier of neutrophilic lung inflammation in mice

IL-36, which belongs to the IL-1 superfamily, is increasingly linked to neutrophilic inflammation. Here, we combined in vivo and in vitro approaches using primary mouse and human cells, as well as, acute and chronic mouse models of lung inflammation to provide mechanistic insight into the intercellular signaling pathways and mechanisms through which IL-36 promotes lung inflammation. IL-36 receptor deficient mice exposed to cigarette smoke or cigarette smoke and H1N1 influenza virus had attenuated lung inflammation compared with wild-type controls. We identified neutrophils as a source of IL-36 and show that IL-36 is a key upstream amplifier of lung inflammation by promoting activation of neutrophils, macrophages and fibroblasts through cooperation with GM-CSF and the viral mimic poly(I:C). Our data implicate IL-36, independent of other IL-1 family members, as a key upstream amplifier of neutrophilic lung inflammation, providing a rationale for targeting IL-36 to improve treatment of a variety of neutrophilic lung diseases.

Targeted drug delivery of Methotrexate in situ gels for the treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is considered a debilitating disease that increases the risk of significant morbidity and premature mortality. To circumvent drug-related toxicity and ineffectiveness of anti-inflammatory drugs, there is a significant need for an advanced delivery system that increases bioavailability. The feasibility of in situ gel of methotrexate sodium (MTS) as an effective management for Rheumatoid arthritis was investigated. It was formulated with pluronic F-127 (PLF-127) as primary polymer, hydroxypropyl methylcellulose K4M (HK4M), and polycarbophil (PCL) as a copolymer and characterized by various parameters. The efficacy evaluation by Freund's complete adjuvant (FCA) model, biocompatibility assessment by histopathological studies conducted. The optimized in situ gel (M4) was thermoresponsive, released 93.26 ± 2.39% MTS at 96 hours. In addition, distribution of MTS was even in the optimized sterile and syringeable in situ gel. In vivo studies on wistar rats demonstrated a substantial reduction in paw oedema during the 28-day study period and were biocompatible with the tissues at the injection site. The study was successful in formulating, optimizing MTS in situ gel for effective management of RA.

Regulation of gene expression by MF63, a selective inhibitor of microsomal PGE synthase 1 (mPGES1) in human osteoarthritic chondrocytes

Background and Purpose

mPGES1 catalyses the production of PGE₂, the most abundant prostanoid related to inflammation and pain in arthritis. mPGES1 is suggested to be a safer and more selective drug target in inflammatory conditions compared to the COX enzymes inhibited by NSAIDs. In the present study, we investigated the effects of the selective mPGES1 inhibitor MF63 on gene expression in primary human chondrocytes from patients with osteoarthritis (OA).

Experimental Approach

Chondrocytes were isolated from articular cartilage obtained from osteoarthritis patients undergoing knee replacement surgery. The effects of MF63 were studied in the primary chondrocytes with RNA‐sequencing based genome‐wide expression analysis. The main results were confirmed with qRT‐PCR and compared with the effects of the NSAID ibuprofen. Functional analysis was performed with the GO database and interactions between the genes were studied with STRING.

Key Results

MF63 enhanced the expression of multiple metallothionein 1 (MT1) isoforms as well as endogenous antagonists of IL‐1 and IL‐36. The expression of IL‐6, by contrast, was down‐regulated. These genes were also essential in functional and interaction network analyses. The effects of MF63 were consistent in qRT‐PCR analysis, whereas the effects of ibuprofen overlapped only partly with MF63. There were no evident findings of catabolic effects by MF63.

Conclusion and Implications

Metallothionein 1 has been suggested to have anti‐inflammatory and protective effects in cartilage. Up‐regulation of the antagonists of IL‐1 superfamily and down‐regulation of the pro‐inflammatory cytokine IL‐6 also support novel anti‐inflammatory and possibly disease‐modifying effects of mPGES1 inhibitors in arthritis.

Interleukin-36 family dysregulation drives joint inflammation and therapy response in psoriatic arthritis

OBJECTIVES

IL-36 agonists are pro-inflammatory cytokines involved in the pathogenesis of psoriasis. However, their role in the pathogenesis of arthritis and treatment response to DMARDs in PsA remains uncertain. Therefore, we investigated the IL-36 axis in the synovium of early, treatment-naïve PsA, and for comparison RA patients, pre- and post-DMARDs therapy.

METHODS

Synovial tissues were collected by US-guided biopsy from patients with early, treatment-naïve PsA and RA at baseline and 6 months after DMARDs therapy. IL-36 family members were investigated in synovium by RNA sequencing and immunohistochemistry, and expression levels correlated with DMARDs treatment response ex vivo. Additionally, DMARDs effects on IL-36 were investigated in vitro in fibroblast-like synoviocytes.

RESULTS

PsA synovium displayed a reduced expression of IL-36 antagonists, while IL-36 agonists were comparable between PsA and RA. Additionally, neutrophil-related molecules, which drive a higher activation of the IL-36 pathway, were upregulated in PsA compared with RA. At baseline, the synovial expression of IL-36α was significantly higher in PsA non-responders to DMARDs treatment, with the differential expression being sustained at 6 months post-treatment. In vitro, primary PsA-derived fibroblasts were more responsive to IL-36 stimulation compared with RA and, importantly, DMARDs treatment increased IL-36 expression in PsA fibroblasts.

CONCLUSION

The impaired balance between IL-36 agonists-antagonists described herein for the first time in PsA synovium and the decreased sensitivity to DMARDs in vitro may explain the apparent lower efficacy of DMARDs in PsA compared with RA. Exogenous replacement of IL-36 antagonists may be a novel promising therapeutic target for PsA patients.

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.

Function and Regulation of IL-36 Signaling in Inflammatory Diseases and Cancer Development

The IL-36 subfamily of cytokines belongs to the IL-1 superfamily and consists of three pro-inflammatory agonists IL-36α, IL-36β, IL-36γ, and an IL-36 receptor (IL-36R) antagonist, IL-36Ra. These IL-36 cytokines function through a common receptor to modulate innate and adaptive immune responses. IL-36 cytokines are expressed as inactive precursors and require proteolytic processing to become fully active. Upon binding to IL-36R, IL-36 agonists augment the expression and production of inflammatory cytokines via activating signaling pathways. IL-36 is mainly expressed in epidermal, bronchial, and intestinal epithelial cells that form the barrier structures of the body and regulates the balance between pro-inflammatory and anti-inflammatory cytokine production at these tissue sites. Dysregulation of IL-36 signaling is a major etiological factor in the development of autoimmune and inflammatory diseases. Besides its critical role in inflammatory skin diseases such as psoriasis, emerging evidence suggests that aberrant IL-36 activities also promote inflammatory diseases in the lung, kidneys, and intestines, underscoring the potential of IL-36 as a therapeutic target for common inflammatory diseases. The role of IL-36 signaling in cancer development is also under investigation, with limited studies suggesting a potential anti-tumor effect. In this comprehensive review, we summarize current knowledge regarding the expression, activation, regulatory mechanisms, and biological functions of IL-36 signaling in immunity, inflammatory diseases, and cancer development.

IL-36β Promotes Inflammatory Activity and Inhibits Differentiation of Keratinocytes In Vitro

Objective Psoriasis is an immune-mediated inflammatory disease. Despite advances in the study of its pathogenesis, the exact development mechanism of psoriasis remains to be fully elucidated. Hyperproliferative epidermis plays a crucial role in psoriasis. This study aimed to investigate the effects of interleukin-36β (IL-36β) on keratinocyte dysfunction in vitro. Methods Human keratinocyte cell lines, HaCaT cells, were treated with 0 (control), 50 or 100 ng/ml IL-36β respectively for 24 h. Cell viability was determined with a cell counting kit-8 assay. Flow cytometry was used to assess the effects of IL-36β on apoptosis and cell cycle distribution. Expressions of the differentiation markers, such as keratin 10 and involucrin, were evaluated by quantitative real-time polymerase chain reaction (RT-qPCR). Expressions of the inflammatory cytokines, IL-1β and IL-6 were tested by ELISA. Results CCK8 assay showed the survival rate had no significant difference between the control and treated group (P > 0.05). Flow cytometry analysis showed cell cycle arrest at S phase in the IL-36β-treated groups compared with the control group (P < 0.05). RT-qPCR verified the decreased mRNA expressions of keratin 10 and involucrin in the IL-36β-treated groups compared with the negative control (P < 0.01). ELISA showed 100 ng/ml IL-36β enhanced levels of IL-1β and IL-6 in culture supernatants of HaCaT cells compared with the negative control (P < 0.05). Conclusion Taken together, these findings suggest that IL-36β could induce cell cycle arrest at S phase, inhibit keratin 10 and involucrin expressions and promote inflammatory activity in HaCaT cell lines.

IL-38: A New Player in Inflammatory Autoimmune Disorders

Interleukin (IL)-38, a newly discovered IL-1 family cytokine, is expressed in several tissues and secreted by various cells. IL-38 has recently been reported to exert an anti-inflammatory function by binding to several receptors, including interleukin-36 receptor (IL-36R), interleukin-1 receptor accessory protein-like 1 (IL-1RAPL1), and interleukin-1 receptor 1 (IL-1R1) to block binding with other pro-inflammatory cytokines and inhibit subsequent signaling pathways; thereby regulating the differentiation and function of T cells, peripheral blood mononuclear cells, macrophages, and dendritic cells. Inflammatory autoimmune diseases, which are common immune-mediated inflammatory syndromes, are characterized by an imbalance between T helper cells (Ths), especially Th1s and Th17s, and regulatory T cells (Tregs). Recent findings have shown that abnormal expression of IL-38 in inflammatory autoimmune diseases, such as rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, primary Sjogren's syndrome, psoriasis, inflammatory bowel disease, hidradenitis suppurativa, ankylosing spondylitis, and glaucoma, involves Th1s, Th17s, and Tregs. In this review, the expression, regulation, and biological function of IL-38 are discussed, as are the roles of IL-38 in various inflammatory autoimmune disorders. Current data support that the IL-38/IL-36R and/or IL-38/IL-1RAPL1 axis primarily play an anti-inflammatory role in the development and resolution of inflammatory autoimmune diseases and indicate a possible therapeutic benefit of IL-38 in these diseases.

TGF-β type 2 receptor-mediated modulation of the IL-36 family can be therapeutically targeted in osteoarthritis

Mechanisms that govern the shift from joint homeostasis to osteoarthritis (OA) remain unknown. Here, we identify a pathway used for joint development and homeostasis, and its role in OA. Using a combination of transgenic, pharmacological, and surgical conditions in mouse and human tissues, we found that TGF-β signaling promotes joint homeostasis through regulation of the IL-36 family. We identified IL-36 receptor antagonist (IL-36 in mice and IL-36RN in humans) as a potential disease-modifying OA drug. Specifically, OA development was associated with IL-36α up-regulation and IL-36Ra down-regulation in mice with tissue-specific postnatally induced ablation of Tgfbr2, mice treated with a TGF-β signaling inhibitor, mice with posttraumatic OA, and aging mice with naturally occurring OA. In human cartilage, OA severity was associated with decreased TGFBR2 and IL-36RN, whereas IL-36α increased. Functionally, intra-articular treatment with IL-36Ra attenuated OA development in mice, and IL-36RN reduced MMP13 in human OA chondrocytes. These findings highlight the relevance of TGFBR2-IL-36 interplay in joint homeostasis and IL-36RN as a potential therapeutic agent for OA.

IL-36 Cytokines: Regulators of Inflammatory Responses and Their Emerging Role in Immunology of Reproduction

The IL-36 subfamily of cytokines has been recently described as part of the IL-1 superfamily. It comprises three pro-inflammatory agonists (IL-36α, IL-36β, and IL-36γ), their receptor (IL-36R), and one antagonist (IL-36Ra). Although expressed in a variety of cells, the biological relevance of IL-36 cytokines is most evident in the communication between epithelial cells, dendritic cells, and neutrophils, which constitute the common triad responsible for the initiation, maintenance, and expansion of inflammation. The immunological role of IL-36 cytokines was initially described in studies of psoriasis, but novel evidence demonstrates their involvement in further immune and inflammatory processes in physiological and pathological situations. Preliminary studies have reported a dynamic expression of IL-36 cytokines in the female reproductive tract throughout the menstrual cycle, as well as their association with the production of immune mediators and cellular recruitment in the vaginal microenvironment contributing to host defense. In pregnancy, alteration of the placental IL-36 axis has been reported upon infection and pre-eclampsia suggesting its pivotal role in the regulation of maternal immune responses. In this review, we summarize current knowledge regarding the regulatory mechanisms and biological actions of IL-36 cytokines, their participation in different inflammatory conditions, and the emerging data on their potential role in normal and complicated pregnancies.

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.

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.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

IL-36 cytokines in autoimmunity and inflammatory disease

The inteleukin-36 (IL-36) cytokines include IL-36α, IL-36β, IL-36γ and IL-36Ra, which belong to the IL-1 family and exert pro-inflammatory effects on various target cells such as keratinocytes, synoviocytes, dendritic cells and T cells. Emerging evidence has suggested a role of IL-36 in the pathogenesis of many inflammatory diseases. Here, we provide a brief review on the activation of IL-36 family cytokines and their involvement in autoimmunity and inflammatory diseases, which will provide further insights in understanding the functions of IL-36 family cytokines in the pathophysiology of autoimmunity and inflammatory diseases.

Cytokines in the pathogenesis of rheumatoid arthritis: new players and therapeutic targets

In recent years, the landscape of pro- and anti-inflammatory cytokines has rapidly expanded with the identification of new members proven to be involved at different extent in the pathogenesis of chronic immune mediated inflammatory diseases including rheumatoid arthritis (RA). The advance of our understanding of mediators involved in the pathogenesis of RA and in consequence, the development of novel targeted therapies is necessary to provide patients not responding to currently available strategies with novel compounds. The aim of this review article is to provide an overview on recently identified cytokines, emphasizing their pathogenic role and therapeutic potential in RA. A systematic literature review was performed to retrieve articles related to every cytokine discussed in the review. In some cases, evidence from animal models and RA patients is already consistent to move forward into drug development. In others, conflicting observation and the paucity of data require further investigations.Forty years after the discovery of IL-1, the landscape of cytokines is continuously expanding with increasing possibilities to develop novel therapeutic strategies in RA.

The emergence of the IL-36 cytokine family as novel targets for inflammatory diseases

The recently discovered interleukin (IL)-36 family of cytokines form part of the broader IL-1 family and are emerging as important mediators of inflammatory disease. The IL-36 subfamily consists of three ligands-IL-36α, IL-36β, and IL-36γ-and the natural antagonist IL-36Ra. The cytokines exert their effects through a specific IL-36 receptor consisting of IL-36R and IL-1RAcP chains. IL-36 cytokines can direct both innate and adaptive immune responses by acting on parenchymal, stromal, and specific immune cell subsets. In humans, inactivating mutations in the gene encoding the IL-36R antagonist, which lead to unregulated IL-36R signaling, lead to an autoinflammatory condition termed deficiency of the IL-36R antagonist, which primarily manifests as a severe form of pustular psoriasis. While such discoveries have prompted deeper mechanistic studies highlighting the important role of IL-36 cytokines in psoriatic skin inflammation, it is now evident that IL-36 cytokines can also play important roles in inflammatory disorders in other organs, such as the gastrointestinal tract and the lungs. Given these emerging roles, strategies to specifically target the expression and activity of the IL-36 family have the potential to uncover novel therapeutic approaches aimed at treating inflammatory diseases in humans.

The IL-1 cytokine family and its role in inflammation and fibrosis in the lung

The IL-1 cytokine family comprises 11 members (7 ligands with agonist activity, 3 receptor antagonists and 1 anti-inflammatory cytokine) and is recognised as a key mediator of inflammation and fibrosis in multiple tissues including the lung. IL-1 targeted therapies have been successfully employed to treat a range of inflammatory conditions such as rheumatoid arthritis and gouty arthritis. This review will introduce the members of the IL-1 cytokine family, briefly discuss the cellular origins and cellular targets and provide an overview of the role of these molecules in inflammation and fibrosis in the lung.

The role of IL-37 in cancer

Interleukin 37 (IL-37) is a new member of the IL-1 family which all have a similar β-barrel structure. Since its discovery, IL-37 has been studied extensively in immunological field. It has been established that IL-37 possesses anti-inflammatory characteristics both in innate immune response as well as in acquired immune responses by downregulating pro-inflammatory molecules. This review will discuss the role of IL-37 in immunological processes and neoplastic pathogenesis.

Chitosan-clodronate nanoparticles loaded in poloxamer gel for intra-articular administration

This work was based on the study of an intra-articular delivery system constituted by a poloxamer gel vehiculating clodronate in chitosan nanoparticles. This system has been conceived to obtain a specific and controlled release of clodronate in the joints to reduce the arthritis rheumatoid degenerative effect. Clodronate (CLO) is a first-generation bisphosphonate with anti-inflammatory properties, inhibiting the cytokine and NO secretion from macrophages, therefore causing apoptosis in these cells. This is related to its ability to be metabolized by cells and converted into a cytotoxic intermediate as a non-hydrolysable analogue of ATP. Chitosan (CHI) was used to develop nanosystems, by ionotropic gelation induced by clodronate itself. A fractional factorial experimental design allowed us to obtain nanoparticles, the diameter of which ranged from 200 to 300nm. Glutaraldehyde was used to increase nanoparticle stability and modify the drug release profile. The zeta potential value of crosslinked nanopaparticles was 21.0mV±1.3, while drug loading was 31.0%±5.4 w/w; nanoparticle yield was 18.2%±1.8 w/w, the encapsulation efficiency was 48.8%±9.9 w/w. Nanoparticles were homogenously loaded in a poloxamer sol, and the drug delivery system is produced in-situ after local administration, when sol become gel at physiological temperature. The properties of poloxamer gels containing CHI-CLO nanoparticles, such as viscosity, gelation temperature and drug release properties, were evaluated. In vitro studies were conducted to evaluate the effects of these nanoparticles on a human monocytic cell line (THP1). The results showed that this drug delivery system is more efficient, with respect to the free drug, to counteract the inflammatory process characteristic of several degenerative diseases.

Distinct expression of interleukin (IL)-36α, β and γ, their antagonist IL-36Ra and IL-38 in psoriasis, rheumatoid arthritis and Crohn's disease

Interleukin (IL)-36α, IL-36β and IL-36γ are expressed highly in skin and are involved in the pathogenesis of psoriasis, while the antagonists IL-36Ra or IL-38, another potential IL-36 inhibitor, limit uncontrolled inflammation. The expression and role of IL-36 cytokines in rheumatoid arthritis (RA) and Crohn's disease (CD) is currently debated. Here, we observed that during imiquimod-induced mouse skin inflammation and in human psoriasis, expression of IL-36α, γ and IL-36Ra, but not IL-36β and IL-38 mRNA, was induced and correlated with IL-1β and T helper type 17 (Th17) cytokines (IL-17A, IL-22, IL-23, CCL20). In mice with collagen-induced arthritis and in the synovium of patients with RA, IL-36α, β, γ, IL-36Ra and IL-38 were all elevated and correlated with IL-1β, CCL3, CCL4 and macrophage colony-stimulating factor (M-CSF), but not with Th17 cytokines. In the colon of mice with dextran sulphate sodium-induced colitis and in patients with CD, only IL-36α, γ and IL-38 were induced at relatively low levels and correlated with IL-1β and IL-17A. We suggest that only a minor subgroup of patients with RA (17-29%) or CD (25%) had an elevated IL-36 agonists/antagonists ratio, versus 93% of patients with psoriasis. By immunohistochemistry, IL-36 cytokines were produced by various cell types in skin, synovium and colonic mucosa such as keratinocytes, CD68⁺ macrophages, dendritic/Langerhans cells and CD79α⁺ plasma cells. In primary cultures of monocytes or inflammatory macrophages (M1), IL-36β and IL-36Ra were produced constitutively, but IL-36α, γ and IL-38 were produced after lipopolysaccharide stimulation. These distinct expression profiles may help to explain why only subgroups of RA and CD patients have a potentially elevated IL-36 agonists/antagonists ratio.

Increased Expression of Interleukin-36, a Member of the Interleukin-1 Cytokine Family, in Inflammatory Bowel Disease

BACKGROUND

Interleukin (IL)-36 (IL-36α, IL-36β, and IL-36γ) is a recently reported member of the IL-1 cytokine family. In this study, we investigated IL-36 expression in the inflamed mucosa of patients with inflammatory bowel disease and characterized the proinflammatory actions of IL-36 cytokines in human colonic epithelial cells.

METHODS

IL-36 mRNA expression was evaluated using real-time PCR. IL-36 protein expression was analyzed using immunoblotting and immunohistochemical technique. Intracellular signaling pathways were evaluated by immunoblotting and by specific siRNA-transfected cells.

RESULTS

The mRNA expression of IL-36α and IL-36γ, but not of IL-36β, was enhanced in the inflamed mucosa of patients with inflammatory bowel disease, in particular, in ulcerative colitis. Immunohistochemical analysis showed that T cells, monocytes, and plasma cells are the source of IL-36α and IL-36γ in colonic mucosa. DNA microarray analysis indicated that IL-36α induces the mRNA expression of CXC chemokines and acute phase proteins in intestinal epithelial cell line, HT-29 cells. IL-36α and IL-36γ dose-dependently and time-dependently induced the mRNA and protein expression of CXC chemokines (CXCL1, CXCL2, CXCL3 etc.) in HT-29 and Widr cells. Stimulation with IL-36α and IL-36γ assembled MyD88 adaptor proteins (MyD88, TRAF6, IRAK1, and TAK1) into a complex and induced the activation of NF-κB and AP-1 and also the phosphorylation of MAPKs. MAPK inhibitors and siRNAs specific for NF-κB and c-Jun AP-1 significantly reduced IL-36-induced CXC chemokine expression.

CONCLUSIONS

IL-36α and IL-36γ may play a proinflammatory role in the pathophysiology of inflammatory bowel disease through induction of CXC chemokines and acute phase proteins.

Interleukin (IL)-1β Is a Strong Inducer of IL-36γ Expression in Human Colonic Myofibroblasts

BACKGROUNDS AND AIMS

Interleukin (IL)-36 cytokines are members of the IL-1 cytokine family. In this study, we investigated the expression of IL-36γ in human colonic myofibroblasts to explore the molecular mechanisms underlying IL-36γ induction.

MATERIALS AND METHODS

IL-36 mRNA was analyzed by real-time PCR method. Secretion of IL-36γ protein was evaluated by Western blot and ELISA analyses. Molecular mechanism of IL-36γ induction was evaluated by siRNA analyses and immunofluorescence experiments.

RESULTS

IL-36γ mRNA expression was scarcely detected in the cells without stimulation. IL-1β induced a marked increase of IL-36γ mRNA expression. TNF-α markedly enhanced IL-1β-induced IL-36γ mRNA expression. These responses were confirmed at the protein levels. The inhibitors for ERK1/2 (PD98059 and U0216) and a p38 MAPK (SB203580) significantly reduced the IL-1β-induced IL-36γ mRNA expression. In addition, the siRNAs specific for NF-κB p65 and AP-1 (c-Jun) significantly reduced the expression of IL-1β-induced IL-36γ mRNA.

CONCLUSIONS

Colonic myofibroblasts are cellular source of IL-36γ in the intestine. IL-36γ expression was induced by the combination of IL-1β and TNF-α via activation of MAPKs and transcription factors, NF-κB and AP-1.

IL-36α: a novel cytokine involved in the catabolic and inflammatory response in chondrocytes

Recent studies confer to IL-36α pro-inflammatory properties. However, little is known about the expression and function of IL-36α in cartilage. This study sought to analyze the expression of IL-36α in healthy and OA cartilage. Next, we determined the effects of recombinant IL-36α on catabolism and inflammation in chondrocytes. For completeness, part of the signaling pathway elicited by IL-36α was also explored. IL-36α expression was evaluated by immunohistochemistry and RT-qPCR. Expression of MMP-13, NOS2 and COX-2 was also determined in OA articular chondrocytes treated with recombinant IL-36α. IκB-α and P-p38 was explored by western blot. We observed a low constitutive expression of IL-36α in healthy human chondrocytes. However, OA chondrocytes likely expressed more IL-36α than healthy chondrocytes. In addition, immune cells infiltrated into the joint and PBMCs express higher levels of IL-36α in comparison to chondrocytes. OA chondrocytes, treated with IL-36α, showed significant increase in the expression of MMP-13, NOS2 and COX-2. Finally, IL-36α stimulated cells showed NFκB and p38 MAPK activated pathways. IL-36α acts as a pro-inflammatory cytokine at cartilage level, by increasing the expression of markers of inflammation and cartilage catabolism. Like other members of IL-1 family, IL-36α acts through the activation of NFκB and p38 MAPK pathway.

Elevated Expression and Pro-Inflammatory Activity of IL-36 in Patients with Systemic Lupus Erythematosus

We investigated the expression and proinflammatory activity of interleukin (IL)-36 in patients with systemic lupus erythematosus (SLE). The expression level of IL-36, its putative receptors and the frequency of CD19⁺CD24^highCD27⁺ regulatory B (Breg) lymphocytes of peripheral blood from 43 SLE patients and 16 normal control (NC) subjects were studied using ELISA and flow cytometry. Plasma cytokines/chemokines and ex vivo productions of cytokine/chemokine from peripheral blood mononuclear cells (PBMC) stimulated with recombinant IL-36 were determined by Luminex multiplex assay. Plasma concentrations of IL-36α, IL-36γ and the proportions of circulating IL-36R-positive CD19⁺ B lymphocytes in total B lymphocytes and PBMC were significantly increased in active SLE patients compared with NC (all p < 0.05). Plasma IL-36α and IL-36γ correlated positively with SLE disease activity and elevated plasma IL-10 concentration (all p < 0.05). The frequencies of circulating Breg lymphocytes in total B lymphocytes and PBMC were significantly decreased in both inactive and active SLE patients compared with NC (all p < 0.01). The frequency of Breg lymphocytes in total B lymphocytes correlated negatively with the proportion of IL-36R-positive B lymphocytes (p < 0.05). IL-36α exerted substantial proinflammatory effect in PBMC from SLE patients by inducing the production of IL-6 and CXCL8. Upon stimulation with IL-36α and IL-36γ, ex vivo productions of IL-6 and CXCL8 were significantly increased in SLE patients compared with NC (all p < 0.05). This cross-sectional study demonstrated that over expression of circulating IL-36α may exert a proinflammatory effect as observed in human SLE.

Modern anti-cytokine therapy of autoimmune diseases

The emergence of genetically engineered biological agents opened new prospects in the treatment of autoimmune and inflammatory diseases. Cytokines responsible for regulation of a wide range of processes during development of the normal immune response are among the most successful therapeutic targets. Studies carried out in recent decades and accompanied by rapid development of biotechnology have promoted establishing in detail the role and place of cytokines in autoimmune and inflammatory pathologies. Nevertheless, mechanisms that underlie anti-cytokine therapy are still not fully understood. This review examines the role of such cytokines as TNF, IL-1, and IL-6 in the development of inflammatory processes and the action mechanisms of their inhibitors.

Role of IL-38 and its related cytokines in inflammation

Interleukin- (IL-) 38 is a recently discovered cytokine and is the tenth member of the IL-1 cytokine family. IL-38 shares structural features with IL-1 receptor antagonist (IL-1Ra) and IL-36Ra. IL-36R is the specific receptor of IL-38, a partial receptor antagonist of IL-36. IL-38 inhibits the production of T-cell cytokines IL-17 and IL-22. IL-38 also inhibits the production of IL-8 induced by IL-36γ, thus inhibiting inflammatory responses. IL-38-related cytokines, including IL-1Ra and IL-36Ra, are involved in the regulation of inflammation and immune responses. The study of IL-38 and IL-38-related cytokines might provide new insights for developing anti-inflammatory treatments in the near future.

Specific therapy to regulate inflammation in rheumatoid arthritis: molecular aspects

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which persistent inflammation of synovial tissue results in a progressive functional decline of the joint and premature mortality. TNF inhibitors were the first biological disease-modifying antirheumatic drugs (DMARDs) used to treat RA. Since then, new biological drugs have emerged, such as inhibitors of IL-1, IL-6 and others, with different mechanisms of action that include the depletion of B cells and the inhibition of T-cell costimulation. Recently, RA treatments have incorporated the use of synthetic DMARDs. This review describes the molecular aspects of the mechanisms of action of biological and synthetic DMARDs, discusses the adverse effects and limitations of established therapies and analyses the alternative approaches to RA treatment.

Cytokines in psoriasis

Psoriasis is a common inflammatory skin disease with an incompletely understood etiology. The disease is characterized by red, scaly and well-demarcated skin lesions formed by the hyperproliferation of epidermal keratinocytes. This hyperproliferation is driven by cytokines secreted by activated resident immune cells, an infiltrate of T cells, dendritic cells and cells of the innate immune system, as well as the keratinocytes themselves. Psoriasis has a strong hereditary character and has a complex genetic background. Genome-wide association studies have identified polymorphisms within or near a number of genes encoding cytokines, cytokine receptors or elements of their signal transduction pathways, further implicating these cytokines in the psoriasis pathomechanism. A considerable number of inflammatory cytokines have been shown to be elevated in lesional psoriasis skin, and the serum concentrations of a subset of these also correlate with psoriasis disease severity. The combined effects of the cytokines found in psoriasis lesions likely explain most of the clinical features of psoriasis, such as the hyperproliferation of keratinocytes, increased neovascularization and skin inflammation. Thus, understanding which cytokines play a pivotal role in the disease process can suggest potential therapeutic targets. A number of cytokines have been therapeutically targeted with success, revolutionizing treatment of this disease. Here we review a number of key cytokines implicated in the pathogenesis of psoriasis.

Inflammasome-independent regulation of IL-1-family cytokines

Induction, production, and release of proinflammatory cytokines are essential steps to establish an effective host defense. Cytokines of the interleukin-1 (IL-1) family induce inflammation and regulate T lymphocyte responses while also displaying homeostatic and metabolic activities. With the exception of the IL-1 receptor antagonist, all IL-1 family cytokines lack a signal peptide and require proteolytic processing into an active molecule. One such unique protease is caspase-1, which is activated by protein platforms called the inflammasomes. However, increasing evidence suggests that inflammasomes and caspase-1 are not the only mechanism for processing IL-1 cytokines. IL-1 cytokines are often released as precursors and require extracellular processing for activity. Here we review the inflammasome-independent enzymatic processes that are able to activate IL-1 cytokines, paying special attention to neutrophil-derived serine proteases, which subsequently induce inflammation and modulate host defense. The inflammasome-independent processing of IL-1 cytokines has important consequences for understanding inflammatory diseases, and it impacts the design of IL-1-based modulatory therapies.