Epithelial expression of interleukin-37b in inflammatory bowel disease

Intestinal Inflammation and Regeneration-Interdigitating Processes Controlled by Dietary Lipids in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a disease of chronic inflammatory conditions of the intestinal tract due to disturbance of the inflammation and immune system. Symptoms of IBD include abdominal pain, diarrhea, bleeding, reduced weight, and fatigue. In IBD, the immune system attacks the intestinal tract's inner wall, causing chronic inflammation and tissue damage. In particular, interlukin-6 and interlukin-17 act on immune cells, including T cells and macrophages, to amplify the immune responses so that tissue damage and morphological changes occur. Of note, excessive calorie intake and obesity also affect the immune system due to inflammation caused by lipotoxicity and changes in lipids supply. Similarly, individuals with IBD have alterations in liver function after sustained high-fat diet feeding. In addition, excess dietary fat intake, along with alterations in primary and secondary bile acids in the colon, can affect the onset and progression of IBD because inflammatory cytokines contribute to insulin resistance; the factors include the release of inflammatory cytokines, oxidative stress, and changes in intestinal microflora, which may also contribute to disease progression. However, interfering with de novo fatty acid synthase by deleting the enzyme acetyl-CoA-carboxylase 1 in intestinal epithelial cells (IEC) leads to the deficiency of epithelial crypt structures and tissue regeneration, which seems to be due to Lgr5+ intestinal stem cell function. Thus, conflicting reports exist regarding high-fat diet effects on IBD animal models. This review will focus on the pathological basis of the link between dietary lipids intake and IBD and will cover the currently available pharmacological approaches.

Recent Advances in Cell-Based In Vitro Models to Recreate Human Intestinal Inflammation

Inflammatory bowel disease causes a major burden to patients and healthcare systems, raising the need to develop effective therapies. Technological advances in cell culture, allied with ethical issues, have propelled in vitro models as essential tools to study disease aetiology, its progression, and possible therapies. Several cell-based in vitro models of intestinal inflammation have been used, varying in their complexity and methodology to induce inflammation. Immortalized cell lines are extensively used due to their long-term survival, in contrast to primary cultures that are short-lived but patient-specific. Recently, organoids and organ-chips have demonstrated great potential by being physiologically more relevant. This review aims to shed light on the intricate nature of intestinal inflammation and cover recent works that report cell-based in vitro models of human intestinal inflammation, encompassing diverse approaches and outcomes.

Modulation of intestinal IL-37 expression and its impact on the epithelial innate immune response and barrier integrity

Background and Aims

Intestinal epithelial cells separate the luminal flora from lamina propria immune cells and regulate innate immune responses in the gut. An imbalance of the mucosal immune response and disrupted intestinal barrier integrity contribute to the evolution of inflammatory bowel diseases. Interleukin (IL)-37 has broad anti- inflammatory activity and is expressed by the human intestinal epithelium. Mice ectopically expressing human IL-37 show reduced epithelial damage and inflammation after DSS-induced colitis. Here, we investigated the impact of IL-37 on the innate immune response and tight junction protein expression of mouse intestinal organoids and the modulation of IL37 expression in human intestinal organoids.

Methods

Murine intestinal organoids were generated from IL-37tg and wildtype mice. Human ileal organoids were generated from healthy young donors.

Results

Expression of transgene IL-37 or recombinant IL-37 protein did not significantly reduce overall proinflammatory cytokine mRNA expression in murine intestinal organoids. However, higher IL37 expression correlated with a reduced proinflammatory cytokine response in murine colonic organoids. IL37 mRNA expression in human ileal organoids was modulated by proinflammatory cytokines showing an increased expression upon TNF-α-stimulation and decreased expression upon IFN-gamma stimulation. Transgene IL-37 expression did not rescue TNF-α-induced changes in morphology as well as ZO-1, occludin, claudin-2, and E-cadherin expression patterns of murine jejunal organoids.

Conclusions

We speculate that the anti-inflammatory activity of IL-37 in the intestine is mainly mediated by lamina propria immune cells protecting intestinal epithelial integrity.

Elevated Interleukin-37 Associated with Dengue Viral Load in Patients with Dengue Fever

Dengue remains a public health issue worldwide. Similar to chronic infectious diseases, stimulation of cytokine production is not enough to drive immune effector cells for effective virus clearance. One possible mechanism is the virus induces a large number of negative stimulatory cytokines inhibiting immune response. Interleukin 37 (IL-37) plays a crucial regulatory role in infection and immunity, inhibits innate and adaptive immunity as an anti-inflammatory cytokine by inhibiting proinflammatory mediators and pathways. To date, there are few studies reporting correlations between dengue fever (DF) and IL-37. In this study we found that the serum IL-37b and IL-37b-producing monocytes in patients were significantly increased in DF patients. A majority of the IL-37b produced by DF patients was produced by monocytes, not lymphocytes. Increased levels of IL-6, IL-10, and IFN-α were also found in DF patients. However, we failed to detect IL-1β, IL-17A and TNF-α in plasma, because of off-target. In our study, there was no relation between IL-6, IL-10, and IFN-α expressions and IL-37b in serum (P > 0.05). The IL-37b-producing monocytes were negatively correlated with the level of IFN-α in serum and platelet count, and positively correlated with lymphocytes percentage (P < 0.05, respectively). Additionally, serum DENV nonstructural protein 1 levels were positively correlated with monocytes percentages (P < 0.05). Our data represents findings for IL-37b expression and its potential mechanisms in DF patients' immune response.

Interleukin-35 and Interleukin-37 anti-inflammatory effect on inflammatory bowel disease: Application of non-coding RNAs in IBD therapy

Inflammatory bowel disease (IBD) is a widespread autoimmune disease that may even be life-threatening. IBD is divided into two major subtypes: ulcerative colitis and Crohn's disease. Interleukin (IL)-35 and IL-37 are anti-inflammatory cytokines that belong to IL-12 and IL-1 families, respectively. Their recruitment relieves inflammation in various autoimmune diseases, including psoriasis, multiple sclerosis, rheumatoid arthritis, and IBD. Regulatory T cells (Tregs) and regulatory B cells (Bregs) are the primary producers of IL-35/IL-37. IL-35 and IL-37 orchestrate the regulation of the immune system through two main strategies: Blocking nuclear transcription factor kappa-B (NF-kB) and mitogen-activated protein kinase (MAPK) signaling pathways or promoting the proliferation of Tregs and Bregs. Moreover, IL-35 and IL-37 can also inhibit inflammation by adjusting the T helper (Th)17/Treg ratio balance. Among the anti-inflammatory cytokines, IL-35 and IL-37 have significant potential to reduce intestinal inflammation. Therefore, administering IL-35/IL-37-based drugs or blocking their inhibitor microRNAs could be a promising approach to alleviate IBD symptoms. Overall, in this review article, we summarized the therapeutic application of IL-35 and IL-37 in both human and experimental models of IBD. Also, it is hoped that this practical information will reach beyond IBD therapy and shed some light on treating all intestinal inflammations.

Interleukin-37 ameliorates cigarette smoke-induced lung inflammation in mice

Cigarette smoking (CS) is the leading cause of chronic obstructive pulmonary disease, and its severity is closely related to lung inflammation. Interleukin (IL)-37 is a newly discovered member of the IL-1 family with anti-inflammatory activity. Our study aimed to elucidate the effect of IL-37 on CS-induced lung inflammation in mice. In this study, mice were exposed to six cigarettes for 1 h three times daily (4 h smoke-free intervals) for 10 consecutive days. Mice were treated intranasally with IL-37-expressing lentivirus and empty lentivirus particles 1 day before the first CS or sham exposure. Mice were sacrificed on day 11 to evaluate the effect of IL-37 on CS-induced pulmonary inflammation in mice. Administering IL-37-expressing lentivirus significantly reduced CS-induced weight loss in mice compared to empty lentivirus controls (P < 0.05). Histological analysis showed that IL-37 significantly alleviated inflammatory cell recruitment, alveolar septum enlargement, alveolar wall attenuation, mucus hypersecretion, and goblet cell metaplasia in mouse lungs (P < 0.001). IL-37 expression also significantly inhibited CS-induced increases in inflammatory cells (including lymphocytes, neutrophils, and macrophages) in mouse lungs (P < 0.05), as well as pro-inflammatory cytokines such as IL-1β, IL-6, IL-17, monocyte chemotactic protein-1 and tumor necrosis factor-α production (P < 0.05). IL-37 also significantly reduced myeloperoxidase activity in mouse serum (P < 0.01) and lung tissues (P < 0.001). Therefore, IL-37 can ameliorate CS-induced pulmonary inflammation in mice and IL-37 may be a potential therapeutic strategy for CS-induced lung inflammatory diseases.

Macrophage orchestration of epithelial and stromal cell homeostasis in the intestine

The intestinal tract is a complex ecosystem where numerous cell types of epithelial, immune, neuronal, and endothelial origin coexist in an intertwined, highly organized manner. The functional equilibrium of the intestine relies heavily on the proper crosstalk and cooperation among each cell population. Furthermore, macrophages are versatile, innate immune cells that participate widely in the modulation of inflammation and tissue remodeling. Emerging evidence suggest that macrophages are central in orchestrating tissue homeostasis. Herein, we describe how macrophages interact with epithelial cells, neurons, and other types of mesenchymal cells under the context of intestinal inflammation, followed by the therapeutic implications of cellular crosstalk pertaining to the treatment of inflammatory bowel disease.

Clinical Implications of IL-32, IL-34 and IL-37 in Atherosclerosis: Speculative Role in Cardiovascular Manifestations of COVID-19

Atherosclerosis, which is a primary cause of cardiovascular disease (CVD) deaths around the world, is a chronic inflammatory disease that is characterised by the accumulation of lipid plaques in the arterial wall, triggering inflammation that is regulated by cytokines/chemokines that mediate innate and adaptive immunity. This review focuses on IL-32, -34 and -37 in the stable vs. unstable plaques from atherosclerotic patients. Dysregulation of the novel cytokines IL-32, -34 and -37 has been discovered in atherosclerotic plaques. IL-32 and -34 are pro-atherogenic and associated with an unstable plaque phenotype; whereas IL-37 is anti-atherogenic and maintains plaque stability. It is speculated that these cytokines may contribute to the explanation for the increased occurrence of atherosclerotic plaque rupture seen in patients with COVID-19 infection. Understanding the roles of these cytokines in atherogenesis may provide future therapeutic perspectives, both in the management of unstable plaque and acute coronary syndrome, and may contribute to our understanding of the COVID-19 cytokine storm.

Circulating Interleukin-37 Levels in Healthy Adult Humans - Establishing a Reference Range

Interleukin (IL)-37 has an important function in limiting excessive inflammation. Its expression is increased in numerous inflammatory and autoimmune conditions and correlates with disease activity, suggesting it could have potential as a disease biomarker. Nevertheless, a reference range has yet to be determined. Our aim was to establish the first reference range of circulating IL-37 levels in healthy adult humans. PubMed was searched for studies reporting blood IL-37 concentrations in healthy adult subjects as measured by enzyme-linked immunosorbent assay. Nineteen studies were included in the analysis. Mean IL-37 levels were weighted by sample sizes, and weighted mean lower and upper levels ( ± 2SD of means) were calculated to provide a weighted mean and reference range. IL-37 levels were quantified in either serum or plasma from a total of 1035 (647 serum; 388 plasma) healthy subjects. The serum, plasma and combined matrix weighted means (reference ranges) were 72.9 (41.5 – 104.4) pg/mL, 83.9 (41.1 – 126.8) pg/mL, and 77.1 (41.4 – 112.8) pg/mL, respectively. There were no significant differences between serum and plasma means and upper and lower limits. Study means and upper IL-37 levels were significantly higher in Chinese population studies. From our analysis, a preliminary reference range for circulating IL-37 levels in healthy human adults has been established. In order to determine a reliable reference range for clinical application, large, prospective, multi-ethnic, healthy population studies are necessary. In addition, demographics, sample matrix, collection, processing and storage methods potentially affecting IL-37 detection levels should be thoroughly investigated.

IL-37 As a Potential Biotherapeutics of Inflammatory Diseases

Interleukin-37 (IL-37) was discovered as a new member of pro-inflammatory IL-1 superfamily. However, further studies suggested that IL-37 plays a critical anti-inflammatory role in innate and adaptive immunity. IL-37 may suppress the inflammatory process via intracellular SMAD family member 3 (SMAD3) and extracellular IL-18 Receptor alpha (IL-18Rα) signaling pathway, respectively. Meanwhile, the abnormal expression of IL-37 was observed in immune-mediated inflammatory diseases, such as inflammatory bowel disease, rheumatoid arthritis, atherosclerosis, systemic lupus erythematosus, asthma, and multiple sclerosis, which suggest IL-37 is a potential therapeutic target for these diseases. In this review, we summarize the anti-inflammatory mechanism of IL-37 and discuss the critical roles of IL-37 in the pathogenesis of these diseases. Further studies are required to confirm the effectiveness of IL-37 as a novel target for these inflammatory diseases.

Interleukin-37 regulates innate immune signaling in human and mouse colonic organoids

Intestinal epithelial cells (IEC) reside in close proximity to the gut microbiota and are hypo-responsive to bacterial products, likely to prevent maladaptive inflammatory responses. This is in part due to their strong expression of Single Ig IL-1 related receptor (SIGIRR), a negative regulator of interleukin (IL)-1 and toll-like receptor signaling. IL-37 is an anti-inflammatory cytokine that inhibits innate signaling in diverse cells by signaling through SIGIRR. Despite the strong expression of SIGIRR by IEC, few studies have examined whether IL-37 can suppress their innate immune signaling. We characterized innate immune responses of human and murine colonoids to bacteria (FliC, LPS) and host (IL-1β) products and the role of IL-37/SIGIRR in regulating these responses. We demonstrated that human colonoids responded only to FliC, but not to LPS or IL-1β. While colonoids derived from different donors displayed significant inter-individual variability in the magnitude of their innate responses to FliC stimulation, all colonoids released a variety of chemokines. Interestingly, IL-37 attenuated these responses through inhibition of p38 and NFκB signaling pathways. We determined that this suppression by IL-37 was SIGIRR dependent, in murine organoids. Along with species-specific differences in IEC innate responses, we show that IL-37 can promote IEC hypo-responsiveness by suppressing inflammatory signaling.

Characterization of the pathoimmunology of necrotizing enterocolitis reveals novel therapeutic opportunities

Necrotizing enterocolitis (NEC) is a severe, currently untreatable intestinal disease that predominantly affects preterm infants and is driven by poorly characterized inflammatory pathways. Here, human and murine NEC intestines exhibit an unexpected predominance of type 3/T_H17 polarization. In murine NEC, pro-inflammatory type 3 NKp46⁻RORγt⁺Tbet⁺ innate lymphoid cells (ILC3) are 5-fold increased, whereas ILC1 and protective NKp46⁺RORγt⁺ ILC3 are obliterated. Both species exhibit dysregulation of intestinal TLR repertoires, with TLR4 and TLR8 increased, but TLR5-7 and TLR9-12 reduced. Transgenic IL-37 effectively protects mice from intestinal injury and mortality, whilst exogenous IL-37 is only modestly efficacious. Mechanistically, IL-37 favorably modulates immune homeostasis, TLR repertoires and microbial diversity. Moreover, IL-37 and its receptor IL-1R8 are reduced in human NEC epithelia, and IL-37 is lower in blood monocytes from infants with NEC and/or lower birthweight. Our results on NEC pathomechanisms thus implicate type 3 cytokines, TLRs and IL-37 as potential targets for novel NEC therapies.

Necrotizing Enterocolitis (NEC) is an untreatable intestinal disease in infants. Here the authors show that human and experimental mouse NEC is associated with altered toll-like receptor expression in the intestine, enhanced Th17/type 3 polarization in adaptive immune and innate lymphoid cells, dysregulated microbiota, and reduced interleukin-37 signaling.

IL-18 and infections: Is there a role for targeted therapies?

Interleukin (IL)-18 is a pro-inflammatory cytokine belonging to the IL-1 family, first identified for its interferon-γ-inducing properties. IL-18 regulates both T helper (Th) 1 and Th2 responses. It acts synergistically with IL-12 in the Th1 paradigm, whereas with IL-2 and without IL-12 it can induce Th2 cytokine production from cluster of differentation (CD)4⁺ T cells, natural killer (NK cells, NKT cells, as well as from Th1 cells. IL-18 also plays a role in the hemophagocytic lymphohistiocytosis, a life-threatening condition characterized by a cytokine storm that can be secondary to infections. IL-18-mediated inflammation was largely studied in animal models of bacterial, viral, parasitic, and fungal infections. These studies highlight the contribution of either IL-18 overproduction by the host or overresponsiveness of the host to IL-18 causing an exaggerated inflammatory burden and leading to tissue injury. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19). The damage in the later phase of the disease appears to be driven by a cytokine storm, including interleukin IL-1 family members and secondary cytokines like IL-6. IL-18 may participate in this hyperinflammation, as it was previously found to be able to cause injury in the lung tissue of infected animals. IL-18 blockade has become an appealing therapeutic target and has been tested in some IL-18-mediated rheumatic diseases and infantile-onset macrophage activation syndrome. Given its role in regulating the immune response to infections, IL-18 blockade might represent a therapeutic option for COVID-19, although further studies are warranted to investigate more in detail the exact role of IL-18 in SARS-CoV-2 infection.

Inflammasome signaling and regulation of interleukin-1 family cytokines

Specific IL-1 family cytokines are initially expressed as inactive, cytosolic pro-forms. Chan and Schroder review inflammasome signaling and cell death decisions, mechanisms underpinning IL-1α, IL-1β, IL-18, and IL-37 maturation and release, and the functions of these cytokines in protective and pathological inflammation.

Specific IL-1 family cytokines are expressed by cells as cytosolic pro-forms that require cleavage for their activity and cellular release. IL-1β, IL-18, and IL-37 maturation and secretion is governed by inflammatory caspases within signaling platforms called inflammasomes. By inducing pyroptosis, inflammasomes can also drive the release of the alarmin IL-1α. Recent advances have transformed our mechanistic understanding of inflammasome signaling, cell death decisions, and cytokine activation and secretion. Here, we provide an updated view of inflammasome signaling; mechanisms underpinning IL-1α, IL-1β, IL-18, and IL-37 maturation and release; and the functions of these cytokines in protective and pathological inflammation.

A new target for the treatment of inflammatory bowel disease: Interleukin-37

Interleukin (IL)-37 belongs to the IL-1 cytokine family. It has anti-inflammatory effects on numerous autoimmune diseases such as asthma, psoriasis, inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE), multiple sclerosis (MS) and rheumatoid arthritis (RA). Mechanistically, IL-37 plays an anti-inflammatory role by regulating the expression of inflammatory factors in two ways: binding extracellular receptors IL-18R or transferring into the nucleus with Smad3. IBD is a kind of idiopathic intestinal inflammatory disease with unknown etiology and pathogenesis. Recent researches had proved that IL-37 is negatively involved in the pathogenesis and development of IBD. Among various inflammatory diseases, IL-37 has been shown to regulate inflammatory development by acting on various immune cells such as neutrophils, macrophages (Mϕ), dendritic cells (DCs), T cells and intestinal epithelial cells. This review summarizes the biological role of IL-37, and its immunoregulatory effects on the immune cells, especially anti-inflammatory function in both human and experimental models of IBD.

Chloroquine and Rapamycin Augment Interleukin-37 Expression via the LC3, ERK, and AP-1 Axis in the Presence of Lipopolysaccharides

IL-37 is a cytokine that plays critical protective roles in many metabolic inflammatory diseases, and its therapeutic potential has been confirmed by exogenous IL-37 administration. However, its regulatory mechanisms remain unclear. U937 cells were treated with autophagy-modifying reagents (3-MA, chloroquine, and rapamycin) with or without LPS stimulation. Thereafter, IL-37 expression and autophagic markers (Beclin1, P62/SQSTM1, and LC3) were determined. For regulatory signal pathways, phosphorylated proteins of NF-κB (p65 and IκBα), AP-1 (c-Fos/c-Jun), and MAPK signal pathways (Erk1/2 and p38 MAPK) were quantified, and the agonists and antagonists of MAPK and NF-κB pathways were also used. Healthy human peripheral blood mononuclear cells were treated similarly to confirm our results. Four rhesus monkeys were also administered chloroquine to evaluate IL-37 induction in vivo and its bioactivity on CD4 proliferation and activation. IL-37 was upregulated by rapamycin and chloroquine in both U937 cells and human PBMCs in the presence of LPS. IL-37 was preferentially induced in autophagic cells associated with LC3 conversion. AP-1 and p65 binding motifs could be deduced in the sequence of the IL-37 promoter. Inductive IL-37 expression was accompanied with increased phosphorylated Erk1/2 and AP-1 and could be completely abolished by an Erk1/2 inhibitor or augmented by Erk1/2 agonists. In monkeys, chloroquine increased IL-37 expression, which was inversely correlated with CD4 proliferation and phosphorylated STAT3. IL-37 levels were induced by rapamycin and chloroquine through the LC3, Erk1/2, and NF-κB/AP-1 pathways. Functional IL-37 could also be induced in vivo.

Interleukin-37 Inhibits Colon Carcinogensis During Chronic Colitis

Inflammatory bowel disease increases the risk of developing colon cancer. Interleukin (IL-) 37 is a fundamental inhibitor of innate immunity by reducing systemic and local inflammation. IL-37 protein is expressed in healthy and diseased bowel and liver tissue. Here, we tested whether transgenic expression of human IL-37 protects IL-10 deficient (IL-10KO) mice from chronic colitis. IL-37tg mice were crossbred with IL-10KO mice. Homozygous IL-10KO/IL-37tg and IL10KO drank 2% dextran sulfate sodium (DSS) in water for 5 days to induce mild colitis. Colon carcinogenesis was triggered by intragastric administration of celecoxib. Endpoints were clinical parameters of colitis, cytokine responses in LPS-stimulated whole blood and explanted colon specimen and qPCR analysis of colon biopsies. Colon inflammation and number of adenoma-carcinoma were analyzed by histology. During the DSS-induction phase IL-10KO and IL-10KO/IL-37tg mice had a similar weight loss due to mild acute colitis. From day 115 there was a significantly improved weight gain in IL-10KO/IL37-tg mice, though colon length was similar. After ex vivo LPS stimulation whole blood of IL-10KO/IL-37tg compared to IL-10KO mice released less IL-6, IL-17, IFNγ, and TNFα and ex vivo colon cultures showed reduced IL-6 production both indicative of reduced inflammatory conditions under the influence of IL-37. Six out of 10 IL-10KO mice developed colon adenoma and carcinoma. Only one adenoma but no carcinoma was detected in colons of IL-10KO/IL-37tg mice. In conclusion, IL-37 transgene expression protects IL-10KO mice from colon carcinogenesis. It remains unclear whether IL-37 has direct tumor suppressing properties.

Interleukin‑37 is increased in peripheral blood mononuclear cells of coronary heart disease patients and inhibits the inflammatory reaction

It has been universally acknowledged that interleukin-37 (IL-37) has an immunosuppressive effect on various inflammatory disorders. However, whether IL-37 participates in the acute inflammation associated with coronary heart disease (CHD) has not yet been clarified. In the present study, the association between the serum levels of IL-37 and the clinical indexes of CHD were analysed. In addition, the anti-inflammatory effects of IL-37 on peripheral blood mononuclear cells (PBMCs) were studied in CHD patients. PBMCs from 46 healthy controls (HCs) and 92 CHD patients were cultured in vitro and stimulated using the recombinant IL-37 protein. The protein levels, as well as the mRNA expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-17) were analysed by enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (RT-PCR). Spearman's correlation test was performed to examine the association between the serum level of IL-37 and the levels of pro-inflammatory cytokines, certain clinical indexes, and disease activity during CHD. Compared to the HCs, the CHD patients, especially those with acute myocardial infarction, exhibited higher levels of IL-37 in their PBMCs and sera. Serum levels of IL-37 were associated with the levels of IL-17, IL-6, and TNF-α, and clinical indexes such as the left ventricular ejection fraction (LVEF), amino-N-terminal pro-plasma brain natriuretic peptide (NT-proBNP) levels, and cardiac troponin T (cTnT) levels in CHD patients. Compared to the HC group, the production of inflammatory cytokines such as IL-17, IL-6, TNF-α, and IL-1β increased in the PBMCs of CHD patients and significantly decreased after the stimulation of the cells with recombinant IL-37. The IL-37 levels in CHD patients were high, and were correlated with the levels of CHD-related pro-inflammatory cytokines and disease activity. Notably, the expression of CHD-related pro-inflammatory cytokines in the PBMCs of CHD patients decreased following the stimulation of the cells with recombinant IL-37, indicating that IL-37 exerts anti-inflammatory effects during CHD.

Interleukin 30 to Interleukin 40

Cytokines are important molecules that regulate the ontogeny and function of the immune system. They are small secreted proteins usually produced upon activation of cells of the immune system, including lymphocytes and myeloid cells. Many cytokines have been described, and several have been recognized as pivotal players in immune responses and in human disease. In fact, several anticytokine antibodies have proven effective therapeutics, especially in various autoimmune diseases. In the last 15 years, new cytokines have been described, and many remain poorly understood. Among the most recent cytokines discovered are interleukins-30 (IL-30) to IL-40. Several of these are members of other cytokine superfamilies, including several IL-1 superfamily members (IL-33, IL-36, IL-37, and IL-38) as well as several new members of the IL-12 family (IL-30, IL-35, and IL-39). The rest (IL-31, IL-32, IL-34, and IL-40) are encoded by genes that do not belong to any cytokine superfamily. Our aim of this review was to present a concise version of the information available on these novel cytokines to facilitate their understanding by members of the immunological community.

Insight into interleukin-37: The potential therapeutic target in allergic diseases

Allergic diseases are ubiquitous diseases with detrimental effects on the quality of life of people worldwide. Common allergic diseases include asthma, allergic rhinitis (AR) and allergic dermatitis (AD). Recently, studies have shown that interleukin (IL)-37, a novel cytokine in the IL-1 family, exhibits broad protective properties in various diseases, such as autoimmune diseases and cancer. IL-37 displays its anti-inflammatory effect on diseases by curbing innate and acquired immunity as well as inflammatory reactions. IL-37 functions by forming a complex with IL-18Rα and IL-1R8 extracellularly and can be translocated to the nucleus upon forming a complex with mothers against decapentaplegic homolog 3 (Smad3) intracellularly, thereby affecting gene transcription and signaling pathway activation. In addition, increasing evidence confirms that IL-37 expression is aberrant in asthma, AR and AD, which indicates that IL-37 may also play essential roles in allergic diseases. Furthermore, accumulating data obtained from recombinant IL-37 (rIL-37)-treated mice and from IL-37 transgenic (IL-37tg) mice suggest a protective role for IL-37. This review will detail the role of IL-37 in the occurrence and development of allergic diseases and discuss the potential of IL-37 as a therapeutic target in allergic diseases.

Inflammatory cytokines: from discoveries to therapies in IBD

Introduction: Although the etiology of inflammatory bowel diseases (IBD) remains unknown, accumulating evidence suggests that the intestinal tissue damage in these disorders is due to a dynamic interplay between immune cells and non-immune cells, which is mediated by cytokines produced within the inflammatory microenvironment. Areas covered: We review the available data about the role of inflammatory cytokines in IBD pathophysiology and provide an overview of the therapeutic options to block the function of such molecules. Expert opinion: Genome studies, in vitro experiments with patients' samples and animal models of colitis, have largely advanced our understanding of how cytokines modulate the ongoing mucosal inflammation in IBD. However, not all the cytokines produced within the damaged gut seem to play a major role in the amplification and perpetuation of the IBD-associated inflammatory cascade. Indeed, while some of the anti-cytokine compounds are effective in some subgroups of IBD patients, others have no benefit. In this complex scenario, a major unmet need is the identification of biomarkers that can predict response to therapy and facilitate a personalized therapeutic approach, which maximizes the benefits and limits the adverse events.

Plasma levels and expression of interleukin-37 in patients with immune thrombocytopenia

Interleukin (IL)-37 has an important role in autoimmune diseases by suppressing immunity and inflammation; however, the role of IL-37 in immune thrombocytopenia (ITP) has remained largely elusive. The present study aimed to investigate the expression of IL-37 and its potential role in the pathogenesis of ITP. The plasma levels and expression of IL-37 in the peripheral blood mononuclear cells of patients with active ITP, ITP patients in remission and healthy controls were measured by ELISA and reverse transcription-quantitative PCR, respectively. The levels of IL-37 in patients with ITP treated with and without glucocorticoids were also determined by ELISA. Specific anti-platelet glycoprotein (GP)IIb/IIIa and/or GPIb/IX autoantibodies were assayed by modified monoclonal antibody-specific immobilization of platelet antigens. The mean value of plasma IL-37 in ITP patients was slightly higher than that in healthy controls, but this was not statistically significant. There was no correlation between IL-37 and anti-platelet autoantibodies, and no significant difference in the IL-37 concentration was identified between patients treated with and without glucocorticoids. In addition, the correlation between IL-37 and the platelet count was analyzed, with no statistical significance observed. It was therefore concluded that IL-37 may not have a pivotal role in the development of ITP. However, the lack of significant differences may be due to the limited number of patients in different groups. A larger number of ITP patients should be enrolled in the future work and achieve more accurate results.

Targeting immune cell circuits and trafficking in inflammatory bowel disease

Inflammatory bowel diseases (IBDs) such as Crohn's disease and ulcerative colitis are characterized by uncontrolled activation of intestinal immune cells in a genetically susceptible host. Due to the progressive and destructive nature of the inflammatory process in IBD, complications such as fibrosis, stenosis or cancer are frequently observed, which highlights the need for effective anti-inflammatory therapy. Studies have identified altered trafficking of immune cells and pathogenic immune cell circuits as crucial drivers of mucosal inflammation and tissue destruction in IBD. A defective gut barrier and microbial dysbiosis induce such accumulation and local activation of immune cells, which results in a pro-inflammatory cytokine loop that overrides anti-inflammatory signals and causes chronic intestinal inflammation. This Review discusses pathogenic cytokine responses of immune cells as well as immune cell trafficking as a rational basis for new translational therapies in IBD.

Divergent Roles for the IL-1 Family in Gastrointestinal Homeostasis and Inflammation

Inflammatory disorders of the gastro-intestinal tract are a major cause of morbidity and significant burden from a health and economic perspective in industrialized countries. While the incidence of such conditions has a strong environmental component, in particular dietary composition, epidemiological studies have identified specific hereditary mutations which result in disequilibrium between pro- and anti-inflammatory factors. The IL-1 super-family of cytokines and receptors is highly pleiotropic and plays a fundamental role in the pathogenesis of several auto-inflammatory conditions including rheumatoid arthritis, multiple sclerosis and psoriasis. However, the role of this super-family in the etiology of inflammatory bowel diseases remains incompletely resolved despite extensive research. Herein, we highlight the currently accepted paradigms as they pertain to specific IL-1 family members and focus on some recently described non-classical roles for these pathways in the gastrointestinal tract. Finally, we address some of the shortcomings and sources of variance in the field which to date have yielded several conflicting results from similar studies and discuss the potential effect of these factors on data interpretation.

IL-37 affects the occurrence and development of endometriosis by regulating the biological behavior of endometrial stromal cells through multiple signaling pathways

Endometriosis (EMs) is a chronic inflammatory condition. Interleukin (IL)-37 is a member of the IL-1 family and an anti-inflammatory cytokine. This study aimed to evaluate the possible role of IL-37 in the EMs pathogenesis. We investigated the in vivo effect of IL-37 on EMs by injection with recombinant human IL-37 (rhIL-37) into EMs mice. Furthermore, we evaluated the in vitro effects of IL-37 on proliferation, adhesion, migration and invasiveness of endometrial stromal cells (ESCs), and explored whether Wnt/β-catenin and mitogen-activated protein kinase (MAPK) pathways were involved in this process. In cultured ESCs, IL-37 overexpression significantly suppressed both protein and mRNA expression of the inflammation-associated cytokines, including IL-1β, IL-6, IL-10 and tumor necrosis factor (TNF-α). Furthermore, IL-37 overexpression significantly inhibited ESCs proliferation, adhesion, migration, invasion and the activity of matrix metalloproteinase (MMP)-2 and MMP-9. In contrast, knockdown of IL-37 exerted the opposite effects. Importantly, the IL-37-mediated action in ESCs was through inactivation of Wnt/β-catenin, p38 MAPK, extracellular signal-related kinases MAPK and c-Jun N-terminal kinase MAPK pathways. Moreover, EMs mice treated with rhIL-37 showed the decreased endometriotic-like lesion size and lesion weight, lower expression of IL-1β, IL-6, IL-10, TNF-α, vascular endothelial growth factor (VEGF), soluble intercellular adhesion molecule-I (ICAM-I) and MMP-2/9 activity in peritoneal fluid compared with the wide type (WT) EMs mice. These findings suggest that IL-37 suppresses cell proliferation, adhesion, migration and invasion of human ESCs through multiple signaling pathways, thereby affecting the occurrence and development of EMs.

Human gut derived-organoids provide model to study gluten response and effects of microbiota-derived molecules in celiac disease

Celiac disease (CD) is an immune-mediated disorder triggered by gluten exposure. The contribution of the adaptive immune response to CD pathogenesis has been extensively studied, but the absence of valid experimental models has hampered our understanding of the early steps leading to loss of gluten tolerance. Using intestinal organoids developed from duodenal biopsies from both non-celiac (NC) and celiac (CD) patients, we explored the contribution of gut epithelium to CD pathogenesis and the role of microbiota-derived molecules in modulating the epithelium’s response to gluten. When compared to NC, RNA sequencing of CD organoids revealed significantly altered expression of genes associated with gut barrier, innate immune response, and stem cell functions. Monolayers derived from CD organoids exposed to gliadin showed increased intestinal permeability and enhanced secretion of pro-inflammatory cytokines compared to NC controls. Microbiota-derived bioproducts butyrate, lactate, and polysaccharide A improved barrier function and reduced gliadin-induced cytokine secretion. We concluded that: (1) patient-derived organoids faithfully express established and newly identified molecular signatures characteristic of CD. (2) microbiota-derived bioproducts can be used to modulate the epithelial response to gluten. Finally, we validated the use of patient-derived organoids monolayers as a novel tool for the study of CD.

Immune response and inflammatory pathway of ulcerative colitis

Ulcerative colitis (UC) is an idiopathic relapsing inflammatory disease. Although the etiology of UC remains unclear, it could be characterized by inflammation of the intestinal mucosa, starting from the rectum and potentially involving the entire colon. The immune response and inflammatory pathway of UC have shown that tissue damage is driven by dynamic and complexes of cells and cytokines. Various types of cells, including antigen-presenting cells (dendritic cells and macrophages), T helper cells, regulatory T cells, and natural killer T cells, play a crucial role in UC pathogenesis by regulation, suppression, and maintenance of inflammation. Moreover, cytokine networks become an important part due to their signaling function, which is indispensable for cell communication. Pro-inflammatory cytokines [tumor necrosis factor-α, interleukin (IL)-1, IL-6, IL-9, IL-13, and IL-33] play significant roles in upregulation, while anti-inflammatory cytokines (transforming growth factor-β, IL-10, and IL-37) play significant roles in downregulation of disease progression. The pathogenesis of UC consists of immuno-inflammatory pathways related to the multiple components of the intestine, including the epithelial barrier, commensal microflora, antigen recognition, dysregulation of immunological responses, leukocyte recruitment, and genetic factors. The understanding of immuno-inflammatory pathways of UC might lead to the development of a specific therapy and/or a novel treatment that could be more efficient.

Anti-Inflammatory Effect of IL-37-Producing T-Cell Population in DSS-Induced Chronic Inflammatory Bowel Disease in Mice

Inflammatory bowel disease (IBD) is a chronic inflammatory disease that is thought to arise in part from abnormal adaptive immune responses against intestinal microbiota. T lymphocytes play significant roles in triggering mucosal inflammation and/or maintaining gut immune homeostasis. It has been demonstrated that IL-37 expresses in a variety of cells and exerts a protective function involved in both innate immunity and adaptive immunity. In the present study, a population of IL-37-producing T-cells was detected in the spleen and mesenteric lymph nodes (MLNs) in IL-37^+/+ mice after dextran sodium sulfate (DSS) induction. Adoptive transfer of the T-cells from the spleen of IL-37^+/+ mice following DSS treatment partly recovered the body weight, improved the disease activity index (DAI) and macroscopic damage score, and attenuated the intestinal inflammation. In addition, colon shortening, an indirect marker of inflammation, was decreased, consistent with the decreased IFN-γ level and the increased IL-10 level in the colonic tissue. Collectively, our data uncovered a subset of T-lymphocytes expressing IL-37, which represents a potent regulation of immunity and serves as the protective role in chronic IBD.

IL-37: An anti-inflammatory cytokine with antitumor functions

BACKGROUND

IL-37 is a newly identified IL-1 family cytokine. Unlike other members in IL-1 family, IL-37 has been demonstrated to be an anti-inflammatory cytokine in many inflammatory and autoimmune diseases. IL-37 is regarded as a dual-function cytokine as both the extracellular and intracellular IL-37 are biologically functional. Extracellular IL-37 can bind to IL-18Rα and IL-1R8 to form a triple complex, regulating the downstream STAT3 and PTEN signaling. Intracellular IL-37 can interact with Smad3, translocate into nucleus, and regulate downstream target gene expressions. Recently, the role of IL-37 in tumor development has been extensively studied.

RECENT FINDINGS

IL-37 has been found to play an antitumor role in various types of tumors, such as non-small cell lung cancer, hepatocellular carcinoma, and renal cell carcinoma. Many mechanism studies have been carried out to elaborate the possible effects of IL-37 on tumor growth, immune responses, and tumor angiogenesis. More importantly, the function of IL-37 may be dependent on its concentration and receptor expression. It can form dimers at high concentrations to be inactivated, thus inhibiting its anti-inflammatory function. We focused on the role of IL-37 in various tumor types and provided the hypothesis regarding the underlying mechanisms.

CONCLUSION

IL-37 may affect tumor development through multiple mechanisms: (1) IL-37 directly influences tumor cell viability; (2) IL-37 regulates the immune response to promote the antitumor immunity; and (3) IL-37 suppresses tumor angiogenesis in the tumor microenvironment. Future studies are warranted to further investigate the mechanisms of these multifaceted functions of IL-37 in animal models and cancer patients.

Plasma interleukin-37 is increased and inhibits the production of inflammatory cytokines in peripheral blood mononuclear cells in systemic juvenile idiopathic arthritis patients

Background

Interleukin (IL)-37 has emerged as a novel anti-inflammatory cytokine that play an immunosuppressive role in regulating inflammatory response. This study aimed to measure IL-37 levels in the plasma and peripheral blood mononuclear cells (PBMCs) of patients with systemic juvenile idiopathic arthritis (sJIA), and to establish the correlation between IL-37 levels and disease activity, laboratory parameters and inflammatory cytokines.

Methods

The mRNA levels of IL-37 in PBMCs and plasma IL-37 concentrations in 46 sJIA patients and 30 age- and sex-matched healthy controls were measured by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The correlations between plasma IL-37 levels and disease activity, laboratory parameters and inflammatory cytokines in sJIA were analyzed by Spearman correlation test. PBMCs from the sJIA patients were stimulated with recombinant human IL-37 (rhIL-37) protein, expressions of IL-1β, IL-6, TNF-α and IL-17 were detected by RT-PCR and ELISA.

Results

Plasma levels of IL-37 and relative IL-37 mRNA expression were significantly elevated in sJIA patients, especially in active sJIA patients, when compared with the healthy controls (P < 0.001). Furthermore, patients with active disease showed higher IL-37 mRNAs and plasma protein levels than those with inactive disease as well as healthy controls. Plasma IL-37 levels were correlated with disease activity and inflammatory cytokines (IL-6, TNF-α, IL-17 and GM-CSF) in sJIA patients. The productions of inflammatory cytokines such as IL-6, TNF-α, IL-17 in PBMCs from sJIA patients were obviously decreased after recombinant IL-37 stimulation, whereas the production of IL-1β was not changed.

Conclusions

Our results demonstrate that levels of IL-37 were higher in sJIA patients, which were correlated with disease activity and sJIA related inflammatory cytokines. In addition, rhIL-37 down-regulates the expressions of inflammatory cytokines form PBMCs in sJIA patients, suggesting that IL-37 may have the potential role as a natural inhibitor for the pathogenesis and therapy of sJIA.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1655-8) contains supplementary material, which is available to authorized users.

Can We Target Endogenous Anti-inflammatory Responses as a Therapeutic Strategy for Inflammatory Bowel Disease?

Inflammatory bowel disease (IBD) describes chronic relapsing remitting inflammation of the gastrointestinal tract including ulcerative colitis and Crohn's disease. The prevalence of IBD is rising across the globe. Despite a growing therapeutic arsenal, current medical treatments are not universally effective, do not induce lasting remission in all, or are accompanied by short- and long-term adverse effects. Therefore, there is a clinical need for novel therapeutic strategies for IBD. Current treatments for IBD mainly manipulate the immune system for therapeutic gain by inhibiting pro-inflammatory activity. There is a robust endogenous immunoregulatory capacity within the repertoire of both innate and adaptive immune responses. An alternative treatment strategy for IBD is to hijack and bolster this endogenous capability for therapeutic gain. This review explores this hypothesis and presents current evidence for this therapeutic direction in immune cell function, cytokine biology, and alternative mechanisms of immunoregulation such as microRNA, oligonucleotides, and the endocannabinoid system.

Advances in understanding the role of cytokines in inflammatory bowel disease

Cytokines represent the key pathophysiologic elements that govern the initiation, progression, and, in some circumstances, the resolution of the inflammation occurring in inflammatory bowel disease (IBD). Areas covered: In this review, we will focus on the main effector and anti-inflammatory cytokines produced in IBD and discuss the results of recent trials in which cytokine-based therapy has been used for treating IBD patients. Expert commentary: The possibility to sample mucosal biopsies from IBD patients and analyze which molecular pathways are prominent during the active phases of the disease and the easy access to various models of experimental colitis has largely advanced our understanding about the role of cytokines in IBD. These progresses have facilitated the development of several therapeutic compounds, which either target inflammatory cytokines or enhance the regulatory function of immunosuppressive cytokines. While some of such drugs are effective in the induction and maintenance of remission of the disease, other compounds are not useful for attenuating the ongoing mucosal inflammation, thus establishing a hierarchical scale of the relevance of cytokines in IBD. Further work is needed to identify biomarkers, which could help personalize cytokine-targeted therapy and minimize potential side effects.

IL1F7 Gene Polymorphism Is not Associated with Rheumatoid Arthritis Susceptibility in the Northern Chinese Han Population: A Case-Control Study

Background:

Interleukin (IL)-37, also called IL1F7, is a natural inhibitor of inflammatory and immune responses. It is involved in the pathogenesis of rheumatoid arthritis (RA). This study aimed to investigate the role of IL1F7 gene polymorphism in RA susceptibility in a large cohort of patients.

Methods:

Five selected single-nucleotide polymorphisms in IL1F7 genes (rs2723186, rs3811046, rs4241122, rs4364030, and rs4392270) were genotyped by TaqMan Allelic Discrimination in Northern Chinese Han population. The allele and the genotype were compared between patients with RA and healthy controls. Association analyses were performed on the entire data set and on different RA subsets based on the status of the anti-cyclic citrullinated peptide antibody and the rheumatoid factor by logistic regression, adjusting for age and gender.

Results:

Trend associations were detected between rs2723186, rs4241122, rs4392270, and RA in Stage I (160 patients with RA; 252 healthy controls). Further validation in Stage II comprised 730 unrelated patients with RA (mean age: 54.9 ± 12.6 years; 81.6% females) and 778 unrelated healthy individuals (mean age: 53.5 ± 15.7 years; 79.5% females). No significant differences in the distributions of alleles and genotypes were observed between the case and control groups in both the entire set and the different RA subsets. Disease activity and age of RA onset were also not associated with genotype distributions.

Conclusion:

IL1F7 gene polymorphism does not significantly influence RA susceptibility in the Northern Chinese Han population.

Cigarette smoke upregulates SPRR3 by favoring c-Jun/Fra1 heterodimerization in human bronchial epithelial cells

AIM

The airway epithelium of smokers exhibits upregulated SPRR3, an indicator of pathogenic keratinization. The mechanisms underlying this phenomenon require investigation.

PATIENTS & METHODS

Human bronchial epithelial (HBE) SPRR3 expression was analyzed by smoking status. Primary HBE cells were exposed to cigarette smoke (CS). SPRR3 expression, SPRR3 promoter activity, AP-1 factor binding and AP-1 factors' effects were analyzed.

RESULTS

Current smokers display SPRR3 upregulation relative to never smokers. CS upregulates SPRR3 transcription in an exposure-dependent manner. CS promotes c-Jun and Fra1 binding to the SPRR3-AP-1/TRE site. Wild-type c-Jun and Fra1 upregulate, whereas c-Jun and Fra1, dominant-negative mutants, suppress SPRR3 promoter activity.

CONCLUSION

CS induces SPRR3 upregulation in HBE cells by promoting aberrant c-Jun/Fra1 dimerization.

IL-37 Expression Reduces Lean Body Mass in Mice by Reducing Food Intake

The human cytokine interleukin (IL)-37 is an anti-inflammatory member of the IL-1 family of cytokines. Transgenic expression of IL-37 in mice protects them from diet-induced obesity and associated metabolic complications including dyslipidemia, inflammation and insulin resistance. The precise mechanism of action leading to these beneficial metabolic effects is not entirely known. Therefore, we aimed to assess in detail the effect of transgenic IL-37 expression on energy balance, including food intake and energy expenditure. Feeding homozygous IL-37 transgenic mice and wild-type (WT) control mice a high-fat diet (HFD; 45% kcal palm fat) for 6 weeks showed that IL-37 reduced body weight related to a marked decrease in food intake. Subsequent mechanistic studies in mice with heterozygous IL-37 expression versus WT littermates, fed the HFD for 18 weeks, confirmed that IL-37 reduces food intake, which led to a decrease in lean body mass, but did not reduce fat mass and plasma lipid levels or alterations in energy expenditure independent of lean body mass. Taken together, this suggests that IL-37 reduces lean body mass by reducing food intake.

Suppression of inflammation and acquired immunity by IL-37

IL-37 is a unique member of the IL-1 family of cytokines, which functions as a natural suppressor of inflammatory and immune responses. Immune and non-immune cells produce IL-37 precursor following pro-inflammatory stimuli. Following activating cleavage by caspase-1, mature IL-37 translocates to the nucleus, where it suppresses transcription of pro-inflammatory genes. Both precursor and mature IL-37 are also secreted in the extracellular space, where they bind IL-18Rα and recruit the IL-1R8 (formerly TIR8 or SIGIRR), which transduces anti-inflammatory signals by suppressing NF-kB and MAPK and by activating Mer-PTEN-DOK pathways. During inflammation, IL-37 restores the metabolism of the cell by reducing succinate, inhibiting mTOR, and activating AMPK. Transgenic mice expressing human IL-37 and wild type mice treated with recombinant human IL-37 are protected from several experimental models of inflammation, including endotoxin shock, colitis, lung and spinal cord injury, coronary artery disease, arthritis and inflammation-induced fatigue, while also exhibiting reduced adaptive immune responses. In humans, IL-37 likely functions to limit excessive inflammation: accordingly, IL-37 levels are abnormal in patients with inflammatory and autoimmune diseases. In this review, we provide an overview of the discovery and biology of IL-37, and discuss the potential for development of this cytokine as a therapeutic agent.

Genetic Variation at Chromosome 2q13 and Its Potential Influence on Endometriosis Susceptibility Through Effects on the IL-1 Family

Endometriosis is characterized by the growth of epithelial and stromal cells outside the uterine cavity. It has a complex etiology and affects ∼10% of reproductive age women. It is accompanied by a chronic inflammatory response with substantial evidence to indicate genetic susceptibility. The causal genes and their pathways leading to endometriosis, however, are still unknown. Recently, genomewide association studies on endometriosis identified 14 genomic risk loci in women of European and Japanese ancestry. It is becoming increasingly clear that these risk regions are intergenic and thus contribute to disease susceptibility through regulatory mechanisms, most likely mediated through regulation of genes within a restricted distance from the risk variants. One endometriosis risk locus has been detected at chromosome 2q13 within an inflammatory-rich region of gene transcripts and thus may play a role in the inflammation component of the disease. We carried out detailed analysis of the genomic region 250 kb on either side of sentinel SNP rs10167914 and identified 21 transcripts which contained 6 interleukin (IL)-1 family genes, 3 previously reported coding genes that have a relationship to inflammation, 4 novel coding, or pseudogenes, and 8 noncoding RNA transcripts. Through an extensive literature search, we examined the roles these genes and their resultant proteins play in endometriosis pathogenesis. The results suggest alteration in the expression the IL-1 family transcripts either alone or as a complex milieu could have a significant influence on endometriosis and should be prioritized for future study on the implications of inflammation on endometriotic lesions.

Reviews of Interleukin-37: Functions, Receptors, and Roles in Diseases

Interleukin-37 (IL-37) is an IL-1 family cytokine discovered in recent years and has 5 different isoforms. As an immunosuppressive factor, IL-37 can suppress excessive immune response. IL-37 plays a role in protecting the body against endotoxin shock, ischemia-reperfusion injury, autoimmune diseases, and cardiovascular diseases. In addition, IL-37 has a potential antitumor effect. IL-37 and its receptors may serve as novel targets for the study, diagnosis, and treatment of immune-related diseases and tumors.

Interleukin-37 is increased in adult-onset Still's disease and associated with disease activity

Background

Interleukin (IL)-37 has been known to play an immunosuppressive role in various inflammatory disorders, but whether it participates in the regulation of pathogenesis of adult-onset Still’s disease (AOSD) has not been investigated. In this study, we examined serum IL-37 levels and their clinical association with AOSD, and we explored the anti-inflammatory effects of IL-37 on peripheral blood mononuclear cells (PBMCs) from patients with AOSD.

Methods

Blood samples were collected from 62 patients with AOSD and 50 healthy control subjects (HC). The serum IL-37 levels were determined using an enzyme-linked immunosorbent assay (ELISA). The correlations of serum IL-37 levels with disease activity, laboratory values, and inflammatory cytokines in AOSD were analyzed by Spearman’s correlation test. The correlations between serum IL-37 levels and clinical manifestations were analyzed by Mann-Whitney U test. PBMCs from ten patients with AOSD were stimulated with recombinant human IL-37 protein, and expression levels of tumor necrosis factor (TNF)-α, IL-6, IL-10, IL-1β, and IL-18 were determined by qRT-PCR and ELISA.

Results

A significantly higher IL-37 protein level was observed in patients with AOSD than in HC. Serum IL-37 levels correlated with systemic score, laboratory values, IL-1β, IL-18, and IL-10 in patients with AOSD. The expression levels of IL-37 were closely related to the patients with AOSD who also had fever, skin rash, lymphadenopathy, splenomegaly, myalgia, and arthralgia. Moreover, the production of proinflammatory cytokines such as IL-6, IL-1β, TNF-α, and IL-18 in PBMCs from patients with AOSD was obviously attenuated after recombinant human IL-37 stimulation.

Conclusions

Increased expression of IL-37 and its positive correlation with disease activity suggest its involvement in AOSD pathogenesis. More importantly, IL-37 inhibits the expression of proinflammatory cytokines in PBMCs from patients with AOSD, indicating the potential anti-inflammatory role of IL-37 in AOSD. Thus, IL-37 may be a novel disease activity biomarker and research target in AOSD.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1555-6) contains supplementary material, which is available to authorized users.

Interleukin-37: A crucial cytokine with multiple roles in disease and potentially clinical therapy

Interleukin (IL)-37, a new IL-1 family member, has received increasing attention in recent years. In the past decade, it has been determined that IL-37 is expressed in various normal cells and tissues and is regulated by inflammatory stimuli and pro-cytokines via different signal transduction pathways. Recently, it has been found that IL-37 is expressed in a variety of cancers, chronic inflammatory and autoimmune disorders, and exerts anti-inflammatory effects. Moreover, a growing body of literature demonstrates that IL-37 plays a vital role in inhibiting both innate and adaptive immune responses as well as inflammatory reactions. In addition, IL-37 may prove to be a new and potentially useful target for effective cytokine therapy. Further evidence is needed to clarify in more detail the effects of IL-37 in experimental and clinical studies. Based on an extensive summary of published data, the aim of this review is to outline the current knowledge of IL-37, including the location, structure, expression, regulation and function, as well as the potential clinical applications of this cytokine.

Overview of the IL-1 family in innate inflammation and acquired immunity

The interleukin-1 (IL-1) family of cytokines and receptors is unique in immunology because the IL-1 family and Toll-like receptor (TLR) families share similar functions. More than any other cytokine family, the IL-1 family is primarily associated with innate immunity. More than 95% of living organisms use innate immune mechanisms for survival whereas less than 5% depend on T- and B-cell functions. Innate immunity is manifested by inflammation, which can function as a mechanism of host defense but when uncontrolled is detrimental to survival. Each member of the IL-1 receptor and TLR family contains the cytoplasmic Toll-IL-1-Receptor (TIR) domain. The 50 amino acid TIR domains are highly homologous with the Toll protein in Drosophila. The TIR domain is nearly the same and present in each TLR and each IL-1 receptor family. Whereas IL-1 family cytokine members trigger innate inflammation via IL-1 family of receptors, TLRs trigger inflammation via bacteria, microbial products, viruses, nucleic acids, and damage-associated molecular patterns (DAMPs). In fact, IL-1 family member IL-1a and IL-33 also function as DAMPs. Although the inflammatory properties of the IL-1 family dominate in innate immunity, IL-1 family member can play a role in acquired immunity. This overview is a condensed update of the IL-1 family of cytokines and receptors.

Tripterygium wilfordii Glycosides Upregulate the New Anti-Inflammatory Cytokine IL-37 through ERK1/2 and p38 MAPK Signal Pathways

As a Chinese traditional patent medicine, Tripterygium wilfordii glycosides (TWG) have been approved by the China State Food and Drug Administration (Z32021007) for autoimmune and inflammatory diseases. Application of TWG leads to significant decrease of the inflammatory cytokines, such as IL-6, IL-1β, and TNF-α. However, little is known whether TWG could regulate the anti-inflammatory cytokines and what the mechanism is. Here, we found that TWG could induce the upregulation of IL-37 which is a new anti-inflammatory cytokine. Furthermore, the inhibitors of ERK1/2 and/or p38 MAPK pathways suppressed IL-37 expression induced by TWG, indicating that the two pathways took part in this process. In conclusion, TWG could upregulate the anti-inflammatory cytokine IL-37 and ERK1/2 and p38 MAPK signal pathways were involved in the upregulation of IL-37 induced by TWG. The results showed that TWG had a potent activity on promoting the expression of IL-37, a new anti-inflammatory cytokine, which help further understanding the anti-inflammatory mechanism for the clinical application of TWG in therapy of diseases.

The potential of interleukin-37 as an effective therapeutic agent in asthma

Interleukin (IL)-37 belongs to the IL-1 cytokine family. It binds to IL-18Rα and recruits the orphan decoy IL-1R8. Emerging evidence shows that IL-37 is a key player in the regulation of inflammation, cellular differentiation, and proliferation. Altered IL-37 expression has been demonstrated in many inflammatory disease conditions, including asthma. In rheumatoid arthritis, IL-37 is involved in the regulation of proliferation, production of inflammatory mediators, and activation of inflammatory cells. Furthermore, this cytokine acts as a negative regulator of inflammation in inflammatory bowel disease. Similarly, IL-37 also appears to suppress allergic inflammation in asthma. In a murine model of asthma, local administration of IL-37 markedly reduced the degree of inflammatory cell infiltration and airway hyper-responsiveness. IL-37 has also been shown to be involved in a number of aspects of allergic inflammation, such as eosinophil and neutrophil recruitment, as well as inhibition of Th1/Th2/Th17 inflammatory mediators. However, the exact molecular mechanisms underlying the function of IL-37 in human asthma have yet to be fully elucidated. This review describes the current evidence regarding the role of IL-37 in the pathophysiology of asthma and evaluates both the potential of IL-37 as a biomarker for airway inflammation and a therapeutic target for the treatment of asthma.

Potential role of IL-37 in atherosclerosis

IL-37 is a member of the IL-1 family, but unlike most other members of this family of cytokines, it has wide-ranging anti-inflammatory properties. Initially shown to bind IL-18 binding protein and prevent IL-18-mediated inflammation, its known role has been expanded to include distinct pathways, both intracellular involving the transcription factor Smad3, and extracellular via binding to the orphan receptor IL-1R8. A number of recent publications investigating the role of IL-37 in atherosclerosis and ischemic heart disease have revealed promising therapeutic value of the cytokine. Although research concerning the role of IL-37 and its mechanism in atherosclerosis is relatively scant, there are a number of well-known atherosclerotic processes that this cytokine can mediate with the potential of modulating the disease progression itself. This review will probe in detail the effects of IL-37 on important pathological processes such as inflammation, dysregulated lipid metabolism, and apoptosis, by analyzing existing data as well as exploring the potential of this cytokine to influence these properties.

Anti-inflammatory effects of hypoxia-preconditioned human periodontal ligament cell secretome in an experimental model of multiple sclerosis: a key role of IL-37

Recent research has widely investigated the anti-inflammatory effects of mesenchymal stem cells and their secretory products, termed the secretome, in the treatment of multiple sclerosis (MS). The present study examined the capacity of the conditioned medium (CM) from human periodontal ligament stem cells (hPLSCs) under hypoxia (H-hPDLSCs-CM) to suppress experimental autoimmune encephalomyelitis (EAE), a murine model of MS. To induce EAE, female C57BL/6 mice were immunized with myelin oligodendroglial glycoprotein peptide_35–55. At the onset of symptoms, H-hPDLSCs-CM was infused via the tail vein of mice. Our results demonstrate the efficacy of H-hPDLSCs-CM treatment in diminishing clinical and histologic disease score. A key finding from this study is the marked expression of anti-inflammatory cytokine IL-37, paralleled by the suppression of proinflammatory cytokines in mice with EAE that were treated with H-hPDLSCs-CM. In addition, a consequent modulation of oxidative stress, autophagic, and apoptotic markers was observed in mice with EAE after hPDLSCs-CM administration. In addition, to provide additional evidence of the molecular mechanisms that underlie H-hPDLSCs-CM, we investigated its therapeutic action in scratch injury–exposed NSC-34 neurons, an in vitro model of injury. This model reproduces severe inflammation and oxidative stress conditions as observed after EAE damage. In vitro results corroborate the ability of hPDLSCs-CM to modulate inflammatory, oxidative stress, and apoptotic pathways. Taken together, our findings suggest H-hPDLSCs-CM as a new pharmacologic opportunity for the management of MS.—Giacoppo, S., Thangavelu, S. R., Diomede, F., Bramanti, P., Conti, P., Trubiani, O., Mazzon, E. Anti-inflammatory effects of hypoxia-preconditioned human periodontal ligament cell secretome in an experimental model of multiple sclerosis: a key role of IL-37.