IL-1H, an interleukin 1-related protein that binds IL-18 receptor/IL-1Rrp

IL-37 isoform D downregulates pro-inflammatory cytokines expression in a Smad3-dependent manner

IL-37 is a new member of IL-1 family and possesses five different isoforms (named as IL-37 a–e). IL-37b has been demonstrated as a physiological suppressor of immune responses. However, the function of other isoforms remains unknown. Here, we show that IL-37d possesses anti-inflammatory roles both in vitro and in vivo. Firstly, IL-37d is expressed in peripheral blood mononuclear cells (PBMCs) and umbilical cords-derived mesenchymal stem cells (UCMSCs). Secondly, IL-37d overexpression markedly inhibits IL-1β-induced IL-6 production in A549 cells. Consistently, bone marrow-derived macrophages (BMDMs) from IL-37d transgenic mice express low levels of pro-inflammatory cytokines (such as IL-6 and TNF-α) following LPS stimulation, compared with those from wild-type mice. Furthermore, IL-37d transgenic mice produce less pro-inflammatory cytokines, and show much less degree of LPS-induced endotoxemia in vivo. Mechanistically, IL-37d interacts with Smad3 and promotes nuclear translocation of pSmad3. SIS3 (a specific Smad3 inhibitor) treatment completely blocks the inhibitory effects of IL-37d. Thus, our data indicate that IL-37d is a functional cytokine that negatively regulates pro-inflammatory cytokines expression in a Smad3-dependent manner.

Elevated plasma interleukin-37 playing an important role in acute coronary syndrome through suppression of ROCK activation

OBJECTIVE

The plasma level of interleukin-37 is elevated in patients with acute coronary syndrome, however, its function during the onset and progress of the disease remains unclear. This study aimed to investigate the clinical significance of IL-37 in acute coronary syndrome and its underlying mechanism.

METHODS

124 patients with acute coronary syndrome and 40 healthy controls were recruited in this study. Plasma interleukin-37 levels were measured in 41 patients with ST elevation myocardial infarction (STEMI), 41 patients with non-STEMI, 42 patients with unstable angina, and 40 controls. Mortality was defined as an event.

RESULTS

In this study, the mean follow-up period was 824±306 days (2-1077 days). 22% (n=27) of patients died. The mortality rate was significantly lower in patients with interleukin-37 serum levels below the median (6.4 pg/mL) than those with interleukin-37 serum levels above 6.4 pg/mL at 36-month follow-up (16% vs. 24%, p=0.02, log rank X2=5.39). Highly concentration of the anti-inflammatory interleukin-37 exerted a protective effect by suppressing the activated Rho Kinase (ROCK) activity in the peripheral blood mononuclear cells in vivo and in vitro after ischemia/reperfusion injury and stimulation of the Rho activator, calpeptin.

CONCLUSIONS

The interleukin-37 level is significantly increased in acute coronary syndrome. Elevated baseline interleukin-37 levels in patients on admission are associated with poor outcomes. Thus, we propose that interleukin-37 could be a biomarker predictive of mortality in acute coronary syndrome. Moreover, this study reveals that the protective effect of interleukin-37 against atherosclerosis may involve the inhibition of ROCK activity.

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.

Suppression of innate inflammation and immunity by interleukin-37

IL-37 is unique in the IL-1 family in that unlike other members of the family, IL-37 broadly suppresses innate immunity. IL-37 can be elevated in humans with inflammatory and autoimmune diseases where it likely functions to limit inflammation. Transgenic mice expressing human IL-37 (IL37-tg) exhibit less severe inflammation in models of endotoxin shock, colitis, myocardial infarction, lung, and spinal cord injury. IL37-tg mice have reduced antigen-specific responses and dendritic cells (DCs) from these mice exhibit characteristics of tolerogenic DCs. Compared to aging wild-type (WT) mice, aging IL37-tg mice are protected against B-cell leukemogenesis and heart failure. Treatment of WT mice with recombinant human IL-37 has been shown to be protective in several models of inflammation and injury. IL-37 binds to the IL-18 receptor but then recruits the orphan IL-1R8 (formerly TIR8 or SIGIRR) in order to function as an inhibitor. Here, we review the discovery of IL-37, its production, release, and mechanisms by which IL-37 reduces inflammation and suppresses immune responses. The data reviewed here suggest a therapeutic potential for IL-37.

Exogenous interleukin 37 ameliorates atherosclerosis via inducing the Treg response in ApoE-deficient mice

Our previous study indicated that interleukin (IL)-37 is involved in atherosclerosis. In the present study, Anterior tibial arteries were collected from diabetes patients and controls. A histopathological analysis showed that IL-37 was over-expressed in human atherosclerotic plaques. Many types of cells including macrophages, vascular smooth muscle cells (VSMCs), endothelial cells and T lymphocyte expressed IL-37 in human atherosclerotic plaques. ApoE-/- mice were divided into a control group and a recombinant human IL-37-treated group. The IL-37 treatment resulted in a significant decrease in macrophages and CD4+ T lymphocytes and a substantial increase in VSMCs and collagen in atherosclerotic plaques, resulting in a reduction in atherosclerotic plaque size. Furthermore, the IL-37 treatment modulated the CD4+ T lymphocyte activity, including a decrease in T helper cell type 1 (Th1) and Th17 cells and an increase in regulatory T (Treg) cells, and inhibited the maturity of dendritic cells both in vivo and in vitro. In addition, treatment with anti-IL-10 receptor monoclonal antibody abrogated the anti-atherosclerotic effects of IL-37. These data suggest that exogenous IL-37 ameliorates atherosclerosis via inducing the Treg response. IL-37 may be a novel therapeutic to prevent and treat atherosclerotic disease.

Role of Anti-inflammatory Cytokines IL-35 and IL-37 in Asthma

Asthma is a chronic airway inflammation that is characterized by intense eosinophil infiltrates, mucus hypersecretion, airway remodeling, and airway hyperresponsiveness. Interleukin (IL)-35 and IL-37 are two cytokines with anti-inflammatory effects found in immune response. Recent findings suggested that expressions of IL-35 and IL-37 are abnormal in asthma. Functional analysis further confirmed the important roles of them in the pathogenesis of asthma. The present study reviewed the updated evidence indicating the roles of IL-35 and IL-37 in asthma. Hopefully, the information obtained may lead to a better understanding of the pathogenesis of the disease.

Interleukin-37 suppresses the osteogenic responses of human aortic valve interstitial cells in vitro and alleviates valve lesions in mice

Calcific aortic valve disease is a chronic inflammatory process, and aortic valve interstitial cells (AVICs) from diseased aortic valves express greater levels of osteogenic factors in response to proinflammatory stimulation. Here, we report that lower cellular levels of IL-37 in AVICs of diseased human aortic valves likely account for augmented expression of bone morphogenetic protein-2 (BMP-2) and alkaline phosphatase (ALP) following stimulation of Toll-like receptor (TLR) 2 or 4. Treatment of diseased AVICs with recombinant human IL-37 suppresses the levels of BMP-2 and ALP as well as calcium deposit formation. In mice, aortic valve thickening is observed when exposed to a TLR4 agonist or a high fat diet for a prolonged period; however, mice expressing human IL-37 exhibit significantly lower BMP-2 levels and less aortic valve thickening when subjected to the same regimens. A high fat diet in mice results in oxidized low-density lipoprotein (oxLDL) deposition in aortic valve leaflets. Moreover, the osteogenic responses in human AVICs induced by oxLDL are suppressed by recombinant IL-37. Mechanistically, reduced osteogenic responses to oxLDL in human AVICs are associated with the ability of IL-37 to inhibit NF-κB and ERK1/2. These findings suggest that augmented expression of osteogenic factors in AVICs of diseased aortic valves from humans is at least partly due to a relative IL-37 deficiency. Because recombinant IL-37 suppresses the osteogenic responses in human AVICs and alleviates aortic valve lesions in mice exposed to high fat diet or a proinflammatory stimulus, IL-37 has therapeutic potential for progressive calcific aortic valve disease.

Interleukin-37 and Dendritic Cells Treated With Interleukin-37 Plus Troponin I Ameliorate Cardiac Remodeling After Myocardial Infarction

BACKGROUND

Excessive immune-mediated inflammatory reactions play a deleterious role in postinfarction ventricular remodeling. Interleukin-37 (IL-37) emerges as an inhibitor of both innate and adaptive immunity. However, the exact role of IL-37 and IL-37 plus troponin I (TnI)-treated dendritic cells (DCs) in ventricular remodeling after myocardial infarction (MI) remains elusive.

METHODS AND RESULTS

MI was induced by permanent ligation of the left anterior descending artery. Our results showed that treatment with recombinant human IL-37 significantly ameliorated ventricular remodeling after MI, as demonstrated by decreased infarct size, better cardiac function, lower mortality, restricted inflammatory responses, decreased myocardial fibrosis, and inhibited cardiomyocyte apoptosis. In vitro, we examined the phenotype of IL-37 plus TnI-conditioned DCs of male C57BL/6 mice and their capacity to influence the number of regulatory T cells. Our results revealed that IL-37 plus TnI-conditioned DCs obtained the characteristics of tolerogenic DCs (tDCs) and expanded the number of regulatory T cells when co-cultured with splenic CD4+ T cells. Interestingly, we also found that adoptive transfer of these antigen-loaded tDCs markedly increased the number of regulatory T cells in the spleen, attenuated the infiltration of inflammatory cells in the infarct hearts, decreased myocardial fibrosis, and improved cardiac function.

CONCLUSIONS

Our results reveal a beneficial role of IL-37 or tDCs treated with IL-37 plus TnI in post-MI remodeling that is possibly mediated by reestablishing a tolerogenic immune response, indicating that IL-37 or adoptive transfer of IL-37 plus TnI-treated tDCs may be a novel therapeutic strategy for ventricular remodeling after MI.

Interleukin 37 expression in mice alters sleep responses to inflammatory agents and influenza virus infection

Multiple interactions between the immune system and sleep are known, including the effects of microbial challenge on sleep or the effects of sleep loss on facets of the immune response. Cytokines regulate, in part, sleep and immune responses. Here we examine the role of an anti-inflammatory cytokine, interleukin-37 (IL-37) on sleep in a mouse strain that expresses human IL-37b (IL37tg mice). Constitutive expression of the IL-37 gene in the brains of these mice under resting conditions is low; however, upon an inflammatory stimulus, expression increases dramatically. We measured sleep in three conditions; (a) under baseline conditions and after 6 h of sleep loss, (b) after bolus intraperitoneal administration of lipopolysaccharide (LPS) or IL-1β and (c) after intranasal influenza virus challenge. Under baseline conditions, the IL37tg mice had 7% more spontaneous non-rapid eye movement sleep (NREMS) during the light period than wild-type (WT) mice. After sleep deprivation both WT mice and IL37tg mice slept an extra 21% and 12%, respectively, during the first 6 h of recovery. NREMS responses after sleep deprivation did not significantly differ between WT mice and IL37tg mice. However, in response to either IL-1β or LPS, the increases in time spent in NREMS were about four-fold greater in the WT mice than in the IL37tg mice. In contrast, in response to a low dose of mouse-adapted H1N1 influenza virus, sleep responses developed slowly over the 6 day recording period. By day 6, NREMS increased by 10% and REMS increased by 18% in the IL37tg mice compared to the WT mice. Further, by day 4 IL37tg mice lost less weight, remained more active, and retained their body temperatures closer to baseline values than WT mice. We conclude that conditions that promote IL-37 expression attenuate morbidity to severe inflammatory challenge.

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Sleep responses to mild acute sleep deprivation are similar in mice transgenic for interleukin-37 (IL37tg) IL37tg and wild type (WT) mice.

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Sleep responses induced by either IL-β or LPS are greatly attenuated in IL37tg mice compared to WT mice.

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After influenza virus challenge, IL37tg mice have reduced morbidities and enhanced sleep responses.

Treating experimental arthritis with the innate immune inhibitor interleukin-37 reduces joint and systemic inflammation

OBJECTIVES

The IL-1 family member IL-37 was recently characterized as a fundamental inhibitor of innate inflammation. We investigated the effects of recombinant IL-37 in joint inflammation and joint pathology in a mouse model of arthritis. In addition, we explored the potential for therapeutic use in human joint inflammation.

METHODS

Wild-type mice were treated systemically with a recombinant form of the naturally occurring human IL-37, and then the knee joints were injected with streptococcal cell wall fragments; joint inflammation, synovial cytokine concentrations and histology were evaluated after 24 h. Mice deficient in the IL-1 family decoy receptor IL-1R8 were treated in a similar manner. The effects of IL-37 treatment were also assessed in a model of streptococcal cell wall-induced systemic inflammation. Changes in IL37 and IL1R8 gene expression were evaluated in the synovia of patients with rheumatoid arthritis.

RESULTS

In wild-type mice, low doses (40 µg/kg) of IL-37 suppressed joint inflammation by 51.7% (P < 0.001) and significantly decreased synovial IL-1β by 84%, IL-6 by 73%, TNF-α by 33%, chemokine (C-X-C motif) ligand 1 by 58%, Chemokine (C-C motif) ligand 3 or macrophage inflammatory protein 1-alpha by 64%, IL-1α by 40% and MPO by 60%. These reductions were associated with a lower recruitment of neutrophils into the joint. The anti-inflammatory properties of IL-37 were dependent on the presence of IL-1R8, also in streptococcal cell wall-induced peritonitis. We found that gene expression of IL1R8, but not IL37, is markedly increased in the synovia of patients with rheumatoid arthritis.

CONCLUSION

IL-37 emerges as a key suppressor of joint and systemic inflammation. These findings indicate a rationale for using recombinant IL-37 in the treatment of arthritis.

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.

Interleukin-37 expression and its potential role in oral leukoplakia and oral squamous cell carcinoma

Interleukin 37 (IL-37) has been reported to play a significant role in innate immune response and to be involved in several kinds of cancers. However, the investigation of association between IL-37 and oral mucosa carcinogenesis hasn't been clearly established. The aim of the study was to assess IL-37 expression and explore its role in oral mucosa carcinogenesis. The expression of IL-37 increased from normal control (NC) to Oral leukoplakia (OLK) and oral squamous cell carcinoma (OSCC). Moreover, statistically highly significant difference was present between scores of OLK with and without mild/moderate dysplasia (P < 0.001). In addition, IL-37 expression was lower in OSCC with lymph node metastasis than those without metastasis (P < 0.01). What's more, overexpression of IL-37 in RAW264.7 cells remarkably reduced the pseudopodia, vacuolization and the expression of IL-6, TNF-α, and IL-1β. Finally, we found IL-37 and its receptor IL-18Rα but not its binding partner IL-18BP have similar tissue location and expression trend in different stages of oral mucosa carcinogenesis. Overall, IL-37 can be used as a biomarker for early oral tumorigenesis and for malignant transformation risk assessment of premalignant lesions.

IL-37 inhibits lipopolysaccharide-induced osteoclast formation and bone resorption in vivo

IL-37 is a newly defined member of the IL-1 cytokine family. It has been reported that IL-37 inhibited innate immunity and inflammatory responses in autoimmune diseases and tumors. IL-37 also inhibited Lipopolysaccharide (LPS)-induced immunological reaction. LPS is a bacterial cell wall component that is capable of inducing osteoclast formation and pathological bone resorption. However, there is no study to investigate the effect of IL-37 on LPS-induced osteoclast formation and bone resorption. The purpose of this study is to investigate the effect of IL-37 in LPS-induced osteoclast formation and bone resorption. LPS was administrated with or without IL-37 by subcutaneous injection on mice calvariae. The number of osteoclasts, the level of tartrate-resistant acid phosphatase (TRAP) and cathepsin K mRNA, the ratio of the bone resorption pits and the level of C-terminal telopeptide fragments of type I collagen cross-Links as a marker of bone resorption in mice administrated both LPS and IL-37 were lower than that in mice administrated LPS alone. Real-time RT-PCR was performed to analyze osteoclast related cytokines RANKL, TNF-α and IL-1β mRNA levels in vivo. RANKL, TNF-α and IL-1β mRNAs were increased in the LPS alone administrated mice as compared with PBS administrated groups. On the other hand, RANKL, TNF-α and IL-1β mRNAs were inhibited in the IL-37 and LPS administrated mice as compared with LPS alone administrated group. In vitro analysis, there was no effect of IL-37 in RANKL-induced osteoclast formation, TNF-α-induced osteoclast formation and cell viability from bone marrow macrophages as osteoclast precursor and LPS-induced RANKL expression from stromal cells. These results indicated that IL-37 inhibited LPS-induced osteoclast formation and bone resorption via inhibition of LPS-induced osteoclast related cytokines, but might not directly inhibit osteoclast formation on osteoclast precursor and RANKL expression on stromal cells.

Elevated serum levels of Interleukin-37 are associated with inflammatory cytokines and disease activity in rheumatoid arthritis

Interleukin-37 (IL-37) is closely associated with several inflammatory diseases. However, the role of IL-37 in the pathogenesis of rheumatoid arthritis (RA) remains unclear. The aim of this study was to assess the associations between serum levels of IL-37 and disease activity, inflammatory cytokines, and bone loss in patients with RA. Serum cytokines levels were examined by Enzyme-linked immunosorbent assay (ELISA). Radiographic bone erosion was assessed using the van der Heijde-modified Sharp score and bone mineral density (BMD) was measured using DXA. Serum IL-37 levels in RA patients were significantly higher than those in HCs (p < 0.001), and were significantly positively correlated with clinical parameters of disease activity and serum levels of IL-17 and IL-23. In addition, serum IL-37 levels were significantly higher in patients with stage IV of radiographic bone erosion than those with stage III and stage I-II, and they were significantly higher in those with osteopenia and osteoporosis than in those with normal BMD. Our results suggest that serum IL-37 levels were increased in patients with RA and were positively associated with disease activity, IL-17/IL-23 and bone loss in RA, suggesting that IL-37 may play a critical role in the pathogenesis of RA.

Interleukin-37 suppresses tumor growth through inhibition of angiogenesis in non-small cell lung cancer

BACKGROUND

Interleukin-37 (IL-37), a newly identified member of the IL-1 family, has been known to play an immunosuppressive role in a variety of inflammatory disorders, but whether it participates in the regulation of pathogenesis of non-small cell lung cancer (NSCLC) has not been investigated.

METHODS

Real-time polymerase chain reaction (PCR), western blotting, and immunohistochemical staining were employed to detect IL-37 expression in NSCLC tissues and corresponding adjacent tissues. The correlations between IL-37 expression and clinicopathological characteristics, prognosis were analyzed. Stable clone with overexpression of IL-37 was generated in H1299 cell lines. Cell growth, cell cycle and cell apoptosis assays were carried out for detecting proliferation and apoptosis of H1299 cells. The effects of IL-37 on NSCLC progression in vivo was performed in a xenografted lung tumor model in nude mice. The concentrations of IL-37 and VEGF in the s growth medium supernatants were quantified by ELISA. The antiangiogenic effect of IL-37 on HUVEC was measured by tube formation assay.

RESULTS

IL-37 mRNA and protein expressions were significantly decreased in NSCLC tissues, and decreased intratumoral IL-37 expression was significantly associated with tumor state, TNM stage and poor prognosis in NSCLC patients. In addition, intratumoral IL-37 expression was an independent prognostic factors for Overall survival (hazard ratio = 2.047; P = 0.011). Overexpression of IL-37 exerted no direct effect on cell proliferation and apoptosis of H1299 lung cancer cells in vitro, but significantly inhibited tumor growth in a H1299 xenograft model in vivo. Furthermore, there was no significant change in immune cell infiltration in IL-37 over-expressing tumors; instead, we found decreased microvessel density (MVD) and VEGF levels in IL-37-expressing tumors. Additional studies showed IL-37 could directly inhibit HUVEC cells growth and capillary structure formation. Finally, we found that decreased IL-37 expression was associated with high MVD in NSCLC patients.

CONCLUSIONS

Our findings demonstrate a protective role for IL-37 in lung cancer development, possibly through inhibiting tumor angiogenesis. IL-37 could serve as a promising therapeutic target for NSCLC.

Beneficial effects of IL-37 after spinal cord injury in mice

IL-37, a member of the IL-1 family, broadly reduces innate inflammation as well as acquired immunity. Whether the antiinflammatory properties of IL-37 extend to the central nervous system remains unknown, however. In the present study, we subjected mice transgenic for human IL-37 (hIL-37tg) and wild-type (WT) mice to spinal cord contusion injury and then treated them with recombinant human IL-37 (rIL-37). In the hIL-37tg mice, the expression of IL-37 was barely detectable in the uninjured cords, but was strongly induced at 24 h and 72 h after the spinal cord injury (SCI). Compared with WT mice, hIL-37tg mice exhibited increased myelin and neuronal sparing and protection against locomotor deficits, including 2.5-fold greater speed in a forced treadmill challenge. Reduced levels of cytokines (e.g., an 80% reduction in IL-6) were observed in the injured cords of hIL-37tg mice, along with lower numbers of blood-borne neutrophils, macrophages, and activated microglia. We treated WT mice with a single intraspinal injection of either full-length or processed rIL-37 after the injury and found that the IL-37-treated mice had significantly enhanced locomotor skills in an open field using the Basso Mouse Scale, as well as supported faster speed on a mechanical treadmill. Treatment with both forms of rIL-37 led to similar beneficial effects on locomotor recovery after SCI. This study presents novel data indicating that IL-37 suppresses inflammation in a clinically relevant model of SCI, and suggests that rIL-37 may have therapeutic potential for the treatment of acute SCI.

Polymorphism of IL37 gene as a protective factor for autoimmune thyroid disease

Autoimmune thyroid disease (AITD) comprises Graves' disease (GD) and Hashimoto's thyroiditis (HT). IL37 has been recently proved to be a natural suppressor for innate immunity and acquired immunity. Therefore, this study was conducted to identify the association of IL37 genetic polymorphisms with AITD in Chinese Han population. Polymorphisms of rs3811046/rs3811047/rs2723176/rs272186 in the IL37 gene were assessed in a case-control study comprising 701 GD patients, 301 HT patients and 939 controls. Genetic variants were genotyped by multiplex polymerase chain reaction and ligase detection reaction. The frequencies of the minor allele A of rs2723176 and A of rs2723186 were significantly lower in the GD patients than in the controls (P=0.014, OR=0.774; P=0.014, OR=0.777). After gender stratification, the rs3811046 G allele and the rs3811047/rs2723186 A allele were both significantly associated with a decreased risk of GD in female patients (P=0.030, OR=0.777; P=0.023, OR=0.774; P=0.029, OR=0.761). However, none of the four single nucleotide polymorphisms of IL37 gene showed any significant association with HT. Moreover, haplotype analysis revealed the GCG haplotype conferred increased risk for GD as a whole and in female GD patients (OR=1.213; OR=1.320). The ACG haplotype was associated with an increased risk of HT as a whole (OR=1.567) and in male GD patients (OR=1.820). In contrast, the AAA haplotype showed a protective role for GD as a whole (OR=0.760) and in female GD patients (OR=0.765). Our study strongly supports that the IL37 gene variants are associated with the susceptibility to AITD.

Allergic airway inflammation: unravelling the relationship between IL-37, IL-18Rα and Tir8/SIGIRR

The hallmarks of allergic bronchial asthma arise from chronic airway inflammation. Thus, elucidating the mechanisms regulating the maintenance of this chronic inflammatory response is key to understanding asthma pathogenesis. To date, it is not clear whether a predominance of proinflammatory factors or a reduced capacity of counterbalancing anti-inflammatory mediators is the pivotal factor predisposing individuals towards asthma development. The IL-1 cytokine family and its receptor systems comprise a variety of proinflammatory cytokines like IL-1β and IL-18 and anti-inflammatory molecules such as the Toll/interleukin-1 receptor 8/single Ig IL-1 receptor (IL-R)-related molecule (Tir8/SIGIRR) and the recently established cytokine IL-37. This article reviews the functions of these IL-1 cytokine family members in the regulation of allergic airway inflammation and asthma as they have been assessed clinically, in vitro and in mouse models.

IL-37 Is a Novel Proangiogenic Factor of Developmental and Pathological Angiogenesis

OBJECTIVE

Angiogenesis is tightly controlled by growth factors and cytokines in pathophysiological settings. Interleukin 37 (IL-37) is a newly identified cytokine of the IL-1 family, some members of which are important in inflammation and angiogenesis. However, the function of IL-37 in angiogenesis remains unknown. We aimed to explore the regulatory role of IL-37 in pathological and physiological angiogenesis.

APPROACH AND RESULTS

We found that IL-37 was expressed and secreted in endothelial cells and upregulated under hypoxic conditions. IL-37 enhanced endothelial cell proliferation, capillary formation, migration, and vessel sprouting from aortic rings with potency comparable with that of vascular endothelial growth factor. IL-37 activates survival signals including extracellular signal-regulated kinase 1/2 and AKT in endothelial cells. IL-37 promoted vessel growth in implanted Matrigel plug in vivo in a dose-dependent manner with potency comparable with that of basic fibroblast growth factor. In the mouse model of retinal vascular development, neonatal mice administrated with IL-37 displayed increased neovascularization. We demonstrated further that IL-37 promoted pathological angiogenesis in the mouse model of oxygen-induced retinopathy.

CONCLUSIONS

Our findings suggest that IL-37 is a novel and potent proangiogenic cytokine with essential role in pathophy siological settings.

Anti-inflammatory properties and expression in selected organs of canine interleukin-1β splice variant 1

The IL-1β gene can be also be spliced with the intron 4 retention; the result is a IL-1β splice variant 1 (IL-1βsv1), which was significantly up-regulated in failing myocardium of dogs suffering from chronic degenerative valvular disease (CDVD). Expression of IL-1βsv1 was assessed, at both RNA and protein levels, in organs affected by heart failure, namely, kidneys, liver, and lungs from 35 dogs suffering chronic degenerative valvular disease (CDVD) and in 20 disease free control dogs. IL-1βsv1 RNA was detected in the dogs from both groups. In the CDVD group, the highest RNA and protein IL-1βsv1 levels were observed in lungs, followed, in that order, by the liver and kidneys. IL-1βsv1 protein was found in the cytoplasm of hepatocytes and IL-1βsv1-overexpressing DH82 cells. In lungs, IL-1βsv1 was localized in the cytoplasm and in the nuclei of bronchiolar epithelial and smooth-muscle cells. Cytoplasmic and nuclear IL-1βsv1 expression was observed in macrophages, and a strong nuclear signal was detected in epithelial cells of the alveolar sacs. Following lipopolysaccharide (LPS) stimulation, overexpression of IL-1βsv1 in DH82 cells decreased the pro-inflammatory response. Our results indicate that IL-1βsv1 is constitutively expressed in both normal tissues and in tissues from cases of heart failure. The presence of IL-1βsv1 in tissues exposed to invading agents and its anti-inflammatory activity in DH82 cells may point to its immunomodulatory role in vivo.

Interleukin-1 Family Cytokines in Liver Diseases

The gene encoding IL-1 was sequenced more than 30 years ago, and many related cytokines, such as IL-18, IL-33, IL-36, IL-37, IL-38, IL-1 receptor antagonist (IL-1Ra), and IL-36Ra, have since been identified. IL-1 is a potent proinflammatory cytokine and is involved in various inflammatory diseases. Other IL-1 family ligands are critical for the development of diverse diseases, including inflammatory and allergic diseases. Only IL-1Ra possesses the leader peptide required for secretion from cells, and many ligands require posttranslational processing for activation. Some require inflammasome-mediated processing for activation and release, whereas others serve as alarmins and are released following cell membrane rupture, for example, by pyroptosis or necroptosis. Thus, each ligand has the proper molecular process to exert its own biological functions. In this review, we will give a brief introduction to the IL-1 family cytokines and discuss their pivotal roles in the development of various liver diseases in association with immune responses. For example, an excess of IL-33 causes liver fibrosis in mice via activation and expansion of group 2 innate lymphoid cells to produce type 2 cytokines, resulting in cell conversion into pro-fibrotic M2 macrophages. Finally, we will discuss the importance of IL-1 family cytokine-mediated molecular and cellular networks in the development of acute and chronic liver diseases.

IL-37b suppresses T cell priming by modulating dendritic cell maturation and cytokine production via dampening ERK/NF-κB/S6K signalings

Interleukin 37b (IL-37b) plays a key role in suppressing immune responses, partially by modulating the function of dendritic cells (DCs). However, the precise mechanisms are still largely unknown. Here, we investigated the effects of IL-37b on DC maturation and T cell responses induced by DCs, and explored the involved signaling pathways. It was found that IL-37b down-regulated the expressions of co-stimulatory molecules CD80 and CD86 on DCs in vitro. At the same time, the expressions of pro-inflammatory cytokines, such as TNF-α and IL-6, were suppressed, while the expression of the T cell inhibitory cytokine TGF-β was increased in IL-37b-treated DCs. In addition, the activation effect of DCs on T cells was impaired by IL-37b. We further revealed that extracellular single-regulated kinase (ERK), nuclear factor-κB (NF-κB), and mTOR-S6K signaling pathways were involved in the inhibition of DCs induced by IL-37b. This was confirmed by the similarly suppressive effect of chemical inhibitors against NF-κB, ERK, and S6K on the expressions of IL-6 and TNF-α in DCs. In conclusion, these results demonstrated that IL-37b suppressed DC maturation and immunostimulatory capacity in T cell priming by involving in ERK, NF-κB, and S6K-based inhibitory signaling pathways.

The interleukin (IL)-1 cytokine family--Balance between agonists and antagonists in inflammatory diseases

The interleukin (IL)-1 family of cytokines comprises 11 members, including 7 pro-inflammatory agonists (IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β, IL-36γ) and 4 defined or putative antagonists (IL-1R antagonist (IL-1Ra), IL-36Ra, IL-37, and IL-38) exerting anti-inflammatory activities. Except for IL-1Ra, IL-1 cytokines do not possess a leader sequence and are secreted via an unconventional pathway. In addition, IL-1β and IL-18 are produced as biologically inert pro-peptides that require cleavage by caspase-1 in their N-terminal region to generate active proteins. N-terminal processing is also required for full activity of IL-36 cytokines. The IL-1 receptor (IL-1R) family comprises 10 members and includes cytokine-specific receptors, co-receptors and inhibitory receptors. The signaling IL-1Rs share a common structure with three extracellular immunoglobulin (Ig) domains and an intracellular Toll-like/IL-1R (TIR) domain. IL-1 cytokines bind to their specific receptor, which leads to the recruitment of a co-receptor and intracellular signaling. IL-1 cytokines induce potent inflammatory responses and their activity is tightly controlled at the level of production, protein processing and maturation, receptor binding and post-receptor signaling by naturally occurring inhibitors. Some of these inhibitors are IL-1 family antagonists, while others are IL-1R family members acting as membrane-bound or soluble decoy receptors. An imbalance between agonist and antagonist levels can lead to exaggerated inflammatory responses. Several genetic modifications or mutations associated with dysregulated IL-1 activity and autoinflammatory disorders were identified in mouse models and in patients. These findings paved the road to the successful use of IL-1 inhibitors in diseases that were previously considered as untreatable.

Interleukin-1 family cytokines and their regulatory proteins in normal pregnancy and pre-eclampsia

Maternal systemic inflammation is a feature of pre-eclampsia, a condition in pregnancy characterized by hypertension and proteinuria. Pre-eclampsia is caused by the placenta; many placental factors contribute to the syndrome's progression, and proinflammatory cytokines have been identified previously as one such mediator. The interleukin (IL)-1 family of cytokines are key regulators of the inflammatory network, and two naturally occurring regulatory molecules for IL-1 family cytokines, IL-1RA and sST2, have been found previously to be elevated in maternal blood from women with pre-eclampsia. Here we investigate more recently identified IL-1 family cytokines and regulatory molecules, IL-1RAcP, IL-37, IL-18BP, IL-36α/β/γ/Ra and IL-38 in pre-eclampsia. Pregnant women have more circulating IL-18BP and IL-36Ra than non-pregnant women, and sIL-1RAcP is elevated from women with pre-eclampsia compared to normal pregnancies. The placenta expresses all the molecules, and IL-37 and IL-18BP are up-regulated significantly in pre-eclampsia placentas compared to those from normal pregnancies. Together, these changes contribute to the required inhibition of maternal systemic cytotoxic immunity in normal pregnancy; however, in pre-eclampsia the same profile is not seen. Interestingly, the increased circulating levels of sIL-1RAcP and increased placental IL-18BP and IL-37, the latter of which we show to be induced by hypoxic damage to the placenta, are all factors which are anti-inflammatory. While the placenta is often held responsible for the damage and clinical symptoms of pre-eclampsia by the research community, here we show that the pre-eclampsia placenta is also trying to prevent inflammatory damage to the mother.

Interleukin-37 Expression Is Increased in Chronic HIV-1-Infected Individuals and Is Associated with Inflammation and the Size of the Total Viral Reservoir

Interleukin-37 (IL-37) is a recently identified cytokine with potent antiinflammatory and immunosuppressive functions. The objective of this study was to compare levels of IL-37 mRNA in immunological subgroups of chronic human immunodeficiency virus-1 (HIV-1)-infected individuals and noninfected controls, to determine IL-37's association with biomarkers of inflammation and reservoir size. This was a cross-sectional study. The HIV-1-infected patients were categorized in three subgroups depending on their combination antiretroviral therapy (cART) treatment status and CD4(+) T-cell count. Quantitative RT-PCR was used for the detection of IL-37 mRNA and HIV-1 DNA in peripheral blood mononuclear cells (PBMCs). Biomarkers in plasma were quantified by enzyme-linked immunosorbent assay (ELISA), whereas T-cell activation was determined by flow cytometry. Lastly, lipopolysaccharide (LPS) stimulations of patients PBMCs were carried out to determine differences in IL-37 mRNA response between the subgroups. Sixty HIV-1-infected patients and 20 noninfected controls were included in the study. Steady-state IL-37 mRNA levels in PBMCs were significantly higher in HIV-1-infected individuals compared with noninfected controls: 2.4-fold (p ≤ 0.01) cART-naïve subjects; 3.9-fold (p ≤ 0.0001) inadequate immunological responders; and 4.0-fold (p ≤ 0.0001) in immunological responders compared with non-infected controls. Additionally, levels of the monocyte inflammatory marker sCD14 correlated with IL-37 mRNA (p = 0.03), whereas there was no association with T-cell activation. Finally, we observed a significant correlation between total viral HIV-1 DNA and IL-37 mRNA in PBMCs (p < 0.0001). Collectively, our data shows that the level of IL-37 mRNA is affected by chronic HIV-1-infection. A relationship with the activation of the monocyte compartment is suggested by the correlation with sCD14 and, interestingly, IL-37 could be related to the size of the total viral HIV-1 reservoir.

IL-37 requires IL-18Rα and SIGIRR/IL-1R8 to diminish allergic airway inflammation in mice

BACKGROUND

Interleukin (IL) 37 has been described as a negative regulator of innate immunity, as it reduces the activation and cytokine production of different innate immune cells. Recently, results from the CLARA childhood asthma cohort suggested an implication of IL-37 for human asthma pathogenesis. This study aimed to investigate the effects of IL-37 on allergic airway inflammation in a mouse model of experimental asthma.

METHODS

Peripheral blood mononuclear cells (PBMCs) of children were cultured for 48 h (anti-CD3/anti-CD28 stimulation or unstimulated), and IL-37 concentrations in supernatants were determined. Wild-type, IL-18Rα-deficient ((-/-) ), and SIGIRR(-/-) C57BL/6 mice were sensitized to ovalbumin (OVA) and challenged with OVA aerosol to induce acute experimental asthma, and IL-37 was applied intranasally prior to each OVA challenge. Airway hyper-responsiveness (AHR), airway inflammation, cytokine levels in broncho-alveolar lavage fluid, and mucus production were determined.

RESULTS

IL-37 production of human PBMCs was significantly lower in allergic asthmatics vs healthy children. In wild-type mice, intranasal administration of IL-37 ablated allergic airway inflammation as well as cytokine production and subsequently diminished the hallmarks of experimental asthma including mucus hyperproduction and AHR. In contrast, local application of IL-37 produced none of these effects in mice lacking either IL18Rα or SIGIRR/IL-1R8.

CONCLUSIONS

This study demonstrates that IL-37 is able to ablate a TH2 cell-directed allergic inflammatory response and the hallmarks of experimental asthma in mice, suggesting that IL-37 may be critical for asthma pathogenesis. Furthermore, these data suggest a mode of action of IL-37 that involves IL18Rα as well as the orphan receptor SIGIRR/IL-1R8.

Transfer of the IL-37b gene elicits anti-tumor responses in mice bearing 4T1 breast cancer

AIM

IL-37b has shown anti-cancer activities in addition to its anti-inflammatory properties. In this study, we investigated the effects of IL-37b on breast carcinoma growth in mice and to determine the involvement of T cell activation in the effects.

METHODS

IL-37b gene was transferred into mouse breast carcinoma cell line 4T1 (4T1-IL37b cells), the expression of secretory IL-37b by the cells was detected, and the effects of IL-37b expression on the cell proliferation in vitro was evaluated. After injection of 4T1 cells or 4T1-IL37b cells into immunocompetent BALB/c mice, immunodeficient BALB/c nude mice and NOD-SCID mice, the tumor growth and survival rate were measured. The proliferation of T cells in vitro was also detected.

RESULTS

IL-37b was detected in the supernatants of 4T1-IL37b cells with a concentration of 12.02 ± 0.875 ng/mL. IL-37b expression did not affect 4T1 cell proliferation in vitro. BALB/c mice inoculated with 4T1-IL37b cells showed significant retardation of tumor growth. BALB/c mice inoculated with both 4T1 cells and mitomycin C-treated 4T1-IL37b cells also showed significant retardation of tumor growth. But the anti-cancer activity of IL-37b was abrogated in BALB/c nude mice and NOD-SCID mice inoculated with 4T1-IL37b cells. Recombinant IL-37b slightly promoted CD4(+) T cell proliferation without affecting CD8(+) T cell proliferation.

CONCLUSION

IL-37b exerts anti-4T1 breast carcinoma effects in vivo by modulating the tumor microenvironment and influencing T cell activation.

IL-37 requires the receptors IL-18Rα and IL-1R8 (SIGIRR) to carry out its multifaceted anti-inflammatory program upon innate signal transduction

Interleukin 37 (IL-37) and IL-1R8 (SIGIRR or TIR8) are anti-inflammatory orphan members of the IL-1 ligand family and IL-1 receptor family, respectively. Here we demonstrate formation and function of the endogenous ligand-receptor complex IL-37-IL-1R8-IL-18Rα. The tripartite complex assembled rapidly on the surface of peripheral blood mononuclear cells upon stimulation with lipopolysaccharide. Silencing of IL-1R8 or IL-18Rα impaired the anti-inflammatory activity of IL-37. Whereas mice with transgenic expression of IL-37 (IL-37tg mice) with intact IL-1R8 were protected from endotoxemia, IL-1R8-deficient IL-37tg mice were not. Proteomic and transcriptomic investigations revealed that IL-37 used IL-1R8 to harness the anti-inflammatory properties of the signaling molecules Mer, PTEN, STAT3 and p62(dok) and to inhibit the kinases Fyn and TAK1 and the transcription factor NF-κB, as well as mitogen-activated protein kinases. Furthermore, IL-37-IL-1R8 exerted a pseudo-starvational effect on the metabolic checkpoint kinase mTOR. IL-37 thus bound to IL-18Rα and exploited IL-1R8 to activate a multifaceted intracellular anti-inflammatory program.

Extracellular forms of IL-37 inhibit innate inflammation in vitro and in vivo but require the IL-1 family decoy receptor IL-1R8

Similar to IL-1α and IL-33, IL-1 family member IL-37b translocates to the nucleus and is associated with suppression of innate and adaptive immunity. Here we demonstrate an extracellular function of the IL-37 precursor and a processed form. Recombinant IL-37 precursor reduced LPS-induced IL-6 by 50% (P < 0.001) in highly inflammatory human blood-derived M1 differentiated macrophages derived from selective subjects but not M2 macrophages. In contrast, a neutralizing monoclonal anti-IL-37 increased LPS-induced IL-6, TNFα and IL-1β (P < 0.01). The suppression by IL-37 was consistently observed at low picomolar but not nanomolar concentrations. Whereas LPS induced a 12-fold increase in TNFα mRNA, IL-37 pretreatment decreased the expression to only 3-fold over background (P < 0.01). Mechanistically, LPS-induced p38 and pERK were reduced by IL-37. Recombinant IL-37 bound to the immobilized ligand binding α-chain of the IL-18 receptor as well as to the decoy receptor IL-1R8. In M1 macrophages, LPS increased the surface expression of IL-1R8. Compared with human blood monocytes, resting M1 cells express more surface IL-1R8 as well as total IL-1R8; there was a 16-fold increase in IL-1R8 mRNA levels when pretreated with IL-37. IL-37 reduced LPS-induced TNFα and IL-6 by 50-55% in mouse bone marrow-derived dendritic cells, but not in dendritic cells derived from IL-1R8-deficient mice. In mice subjected to systemic LPS-induced inflammation, pretreatment with IL-37 reduced circulating and organ cytokine levels. Thus, in addition to a nuclear function, IL-37 acts as an extracellular cytokine by binding to the IL-18 receptor but using the IL-1R8 for its anti-inflammatory properties.

IL-37 inhibits IL-18-induced tubular epithelial cell expression of pro-inflammatory cytokines and renal ischemia-reperfusion injury

Cytokines and chemokines produced by tubular epithelial and infiltrating cells are critical to inflammation in renal ischemia-reperfusion injury. IL-37, a newly described IL-1 family member, inhibits IL-18-dependent pro-inflammatory cytokine production by its binding to IL-18 receptors and IL-18 binding protein. The potential role of IL-37 in renal ischemia-reperfusion injury is unknown. Here we found that exposure of tubular epithelial cells to exogenous IL-37 downregulated hypoxia and the IL-18-induced expression of TNFα, IL-6, and IL-1β. Importantly, human PT-2 tubular epithelial cells have inducible expression of IL-37. Moreover, pro-inflammatory cytokine expression was augmented in IL-37 mRNA-silenced tubular epithelial cells and inhibited by transfection with pCMV6-XL5-IL-37. In a mouse ischemic injury model, transgenic expression of human IL-37 inhibited kidney expression of TNFα, IL-6, and IL-1β and improved mononuclear cell infiltration, kidney injury, and function. Thus, human tubular epithelial cells express the IL-18 contra-regulatory protein IL-37 as an endogenous control mechanism to reduce inflammation. Augmenting kidney IL-37 may represent a novel strategy to suppress renal injury responses and promote kidney function after renal ischemic injury and transplantation.

Interleukin-37 gene variants segregated anciently coexist during hominid evolution

IL37 is a member of IL-1 cytokine family but conveys anti-inflammatory functions. The biological characteristic and genetic heterogeneity of IL37 are not fully understood yet. Here using the whole-genome sequencing data from 1000 Genomes Project, we performed population and evolutionary genetic analysis of human IL37 gene. First, 2184 IL37 gene sequences from different human populations were retrieved. The IL37 protein sequences were inferred from the coding DNA sequences and multiple species alignment was made. Then, the phylogenetic tree of IL37 was built and dN/dS ratios were calculated for each evolutionary branch, the classic McDonald and Kreitman test was also performed. Next, we conducted intraspecific evolutionary genetic analysis and built the genealogy network of 116 unique IL37 haplotypes through median-joining network analysis. Finally, we compared IL37 sequences between the modern and archaic humans. Our results for the first time provide solid evidence that common IL37 variants other than NCBI reference sequence are present worldwide. Our data also supports that IL37 variants are shaped and maintained by selection instead of neutral evolution. We further identified that human IL37 variants consist of two major haplogroups and their presence in archaic humans corroborates its ancient origin in hominid evolution. In conclusion, these data indicate that common IL37 variants are maintained among human populations by selective force, suggesting their potential involvements in immune regulation and human diseases. In addition, the ancient history of IL37 variants reveals interesting insight into the complicated human evolutionary history.

Interleukin-37 is increased in ankylosing spondylitis patients and associated with disease activity

Background

Interleukin-37 (IL-37) has been known to play an immunosuppressive role in various inflammatory disorders, but whether it participates in the regulation of pathogenesis of ankylosing spondylitis (AS) has not been investigated. Here, we examined the serum levels of IL-37 and its clinical association in AS, and explored the anti-inflammatory effects of IL-37 on peripheral blood mononuclear cells (PBMCs) from AS patients.

Methods

The mRNA levels of IL-37, TNF-α, IL-6, IL-17, and IL-23 in PBMCs and their serum concentrations from 46 AS patients were examined by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunoassay (ELISA), respectively. The correlations between serum IL-37 levels with disease activity, laboratory values and pro-inflammatory cytokines in AS were analyzed by Spearman correlation test. PBMCs from 46 AS patients were stimulated with recombinant IL-37 protein, expressions of TNF-α, IL-6, IL-17 and IL-23 were determined by RT-PCR and ELISA.

Results

Compared to healthy controls (HC), AS patients and active AS patients showed higher levels of IL-37 in PBMCs and serum respectively. Strikingly, serum IL-37 levels were higher in AS patients with osteoporosis than those without. Serum levels of IL-37 were correlated with laboratory values as well as TNF-α, IL-6 and IL-17, but not IL-23 in patients with AS. The productions of pro-inflammatory cytokines such as TNF-α, IL-6, IL-17, IL-23 in PBMCs from AS patients were obviously attenuated after recombinant IL-37 stimulation, but not in the HC.

Conclusion

The higher levels of IL-37 were found in AS patients, which were correlated with disease activity and AS related pro-inflammatory cytokines. More importantly, IL-37 inhibits the expressions of the pro-inflammatory cytokines from PBMCs in AS patients, indicating the potential anti-inflammatory role of IL-37 in AS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0394-3) contains supplementary material, which is available to authorized users.

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.

High-level expression and one-step purification of a soluble recombinant human interleukin-37b in Escherichia coli

Interleukin (IL)-37 is a novel member of the IL-1 cytokine family. However, as a result of lacking efficient method to generate relatively large quantity of IL-37, little is known of its functions in man. In the present study, the recombinant human IL-37b containing a C-hexahistidine tag was expressed in Escherichia coli (E. coli). The expression level of IL-37b in E. coli was very high after induction with IPTG. Furthermore, IL-37b protein was largely found in the soluble fraction. The expressed protein was readily purified by one-step immobilized metal-ion affinity chromatography using Ni(2+)-nitrilotriacetic acid agarose. The purified IL-37b appeared as a single band on SDS-PAGE and the purity was more than 97%. The yield was 90mg IL-37b from 1l of bacterial culture. Western blotting and N-terminal sequencing confirmed the identity of the purified protein. The purified IL-37b inhibited significantly the release of tumor necrosis factor-α and IL-1β in lipopolysaccharide-activated THP-1 cells. Thus, this method provides an efficient way to obtain an active IL-37 with high yield and high purity.

The growing spectrum of anti-inflammatory interleukins and their potential roles in the development of sepsis

Sepsis, recognized as a deadly immunological disorder, is one of the major causes of death in intensive care units globally. Traditionally, sepsis was characterized by an excessive systemic proinflammatory response to invasive microbial pathogens. However, failures of highly sophisticated trials directed toward the uncontrolled inflammatory reaction have led to an appeal by experts for reevaluation of the present approach toward sepsis. With accumulated evidence, a principal role for immunosuppression in severe sepsis has been evaluated. Different pathways of negative regulation in the pathophysiological process of sepsis have been investigated. Significant among these regulatory elements are the anti-inflammatory cytokines. In the past few years, several interleukins (ILs) have been identified and characterized, among which IL-35 and IL-37 represent newly identified ones in the spectrum of anti-inflammatory cytokines. In this study, we focus on regulatory cytokines of the IL family (including the old members: IL-4, IL-10, and IL-13, and newly discovered ones: IL-35 and IL-37) to address current knowledge regarding their structural and functional characteristics as well as their roles in the development of sepsis. Although the exact roles for these cytokines are pending further elucidation, the current advances in our understanding of mechanisms that regulate the immune responses during severe sepsis may lead to the identification of new diagnostic or treatment targets.

Human β-defensin-3 increases the expression of interleukin-37 through CCR6 in human keratinocytes

BACKGROUND

Interleukin (IL)-37, a new member of the IL-1 family, is characterized as a fundamental inhibitor of innate immunity: it dampens the production of proinflammatory cytokines, protects against inflammatory and autoimmune diseases, and plays a potent immunosuppressive role in the pathogenesis of psoriasis. IL-37 is highly expressed in psoriatic skin, in which human β-defensins (hBDs) have been detected. Although hBDs enhance the production of cytokines, including IL-1 cytokines, whether they stimulate the production of IL-37 remains unclear.

OBJECTIVES

To assess the ability of hBDs to stimulate IL-37 expression/production by human keratinocytes and to determine the mechanism involved.

METHODS

Real-time PCR and Western blotting were used to evaluate IL-37 expression. Caspase activities were assessed using colorimetric assay kits. A CCR6 antibody, siRNA, and caspase, Smad3, MAPK and NF-κB inhibitors were used to investigate the signaling mechanism of hBDs.

RESULTS

Among the four hBDs used, only hBD-3 up-regulated the mRNA and protein expression of IL-37. The combination of TNF-α, EGF and poly (I:C) with hBD-3 synergistically enhanced the mRNA but not the protein expression of IL-37. Furthermore, hBD-3 increased the release of IL-37 into the culture supernatants. Evaluation of the signaling mechanism of hBD-3 suggested that caspases 1 and 4, Smad3, CCR6, MAPKs and NF-κB were required for hBD-3-mediated IL-37 expression.

CONCLUSIONS

The finding that hBD-3 stimulates IL-37 expression, a novel target for the pathogenesis and therapy of cutaneous inflammatory diseases, provides evidence that hBDs contribute to the suppression of inflammatory and innate immune responses through the regulation of IL-37 expression.

Suppression of antigen-specific adaptive immunity by IL-37 via induction of tolerogenic dendritic cells

IL-1 family member IL-37 limits innate inflammation in models of colitis and LPS-induced shock, but a role in adaptive immunity remains unknown. Here, we studied mice expressing human IL-37b isoform (IL-37tg) subjected to skin contact hypersensitivity (CHS) to dinitrofluorobenzene. CHS challenge to the hapten was significantly decreased in IL-37tg mice compared with wild-type (WT) mice (-61%; P < 0.001 at 48 h). Skin dendritic cells (DCs) were present and migrated to lymph nodes after antigen uptake in IL-37tg mice. When hapten-sensitized DCs were adoptively transferred to WT mice, antigen challenge was greatly impaired in mice receiving DCs from IL-37tg mice compared with those receiving DCs from WT mice (-60%; P < 0.01 at 48 h). In DCs isolated from IL-37tg mice, LPS-induced increase of MHC II and costimulatory molecule CD40 was reduced by 51 and 31%, respectively. In these DCs, release of IL-1β, IL-6, and IL-12 was reduced whereas IL-10 secretion increased (37%). Consistent with these findings, DCs from IL-37tg mice exhibited a lower ability to stimulate syngeneic and allogeneic naive T cells as well as antigen-specific T cells and displayed enhanced induction of T regulatory (Treg) cells (86%; P < 0.001) in vitro. Histological analysis of CHS skin in mice receiving hapten-sensitized DCs from IL-37tg mice revealed a marked reduction in CD8(+) T cells (-74%) but an increase in Treg cells (2.6-fold). Together, these findings reveal that DCs expressing IL-37 are tolerogenic, thereby impairing activation of effector T-cell responses and inducing Treg cells. IL-37 thus emerges as an inhibitor of adaptive immunity.

Immunobiology of IL-37: mechanism of action and clinical perspectives

This article provides an overview of the biological function of a recently discovered cytokine, IL-37, formerly referred to as IL-1F7, and its role in chronic inflammation and autoimmune disease. Much has been discovered about IL-37 in the past decade, including its ability to down-regulate systemic and local inflammation by lowering levels of pro-inflammatory molecules. Here, we critically review the published reports. Future research is necessary to understand the receptor-dependent effects of IL-37, its intracellular and extracellular functions in both normal and diseased states and its potential role as a biomarker and pharmacological target in human disease.

Increased expression of IL-37 in patients with Graves' disease and its contribution to suppression of proinflammatory cytokines production in peripheral blood mononuclear cells

Background

Intreleukin-37 (IL-37), a member of IL-1 family, is primarily an anti-inflammatory cytokine, which reduces systemic and local inflammation. However, the expression and role of IL-37 in Graves' disease (GD) remains unknown. This study aims to measure the levels of serum and peripheral blood mononuclear cells (PBMCs) IL-37 in patients with Graves' disease and to examine its association with disease activity. Furthermore, we investigate the effect of IL-37 on proinflammatory cytokines involved in the pathogenesis of GD.

Methods

The expressions of IL-37, TNF-α, IL-6, and IL-17 mRNA in peripheral blood mononuclear cells (PBMCs) of 40 patients with Graves' disease were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR), and the levels of IL-37, TNF-α, IL-6, and IL-17 in serum were detected by enzyme-linked immunoassay (ELISA). The correlation of serum IL-37 levels with cytokines and disease activity in Graves' disease patients were investigated. The expressions of cytokines TNF-α, IL-6, and IL-17 in PBMCs under recombinant IL-37 stimulation were determined by RT-PCR and ELISA respectively.

Results

The levels of IL-37, TNF-α, IL-6, and IL-17 in PBMCs and serum were significantly increased in patients with GD compared with healthy controls (HC). Serum IL-37 were closely correlated with TNF-α, IL-6, IL-17, thyrotropin (TSH), free thyroxine (FT4),free triiodothyronine (FT3) and thyrotropin receptor antibody (TRAB). GD patients with active disease showed higher IL-37 mRNA and serum protein levels compared with those with inactive disease as well as HC. Moreover, IL-37 suppressed the production of IL-6, IL-17 and TNF-α in PBMCs of patients with GD.

Conclusions

Increased level of IL-37 in patients with GD are associated with TNF-α, IL-6, IL-17 and disease activity, and it plays a protective role against inflammatory effect in GD by inhibiting the production of proinflammatory cytokines. Thus, IL-37 may provide a novel research target for the pathogenesis and therapy of GD.