IL-37 is a fundamental inhibitor of innate immunity

Divergent responses to thermogenic stimuli in BAT and subcutaneous adipose tissue from interleukin 18 and interleukin 18 receptor 1-deficient mice

Brown and beige adipocytes recruitment in brown (BAT) or white adipose tissue, mainly in the inguinal fat pad (iWAT), meet the need for temperature adaptation in cold-exposure conditions and protect against obesity in face of hypercaloric diets. Using interleukin18 (Il18) and Il18 receptor 1- knockout (Il18r1-KO) mice, this study aimed to investigate the role of IL18 signaling in BAT and iWAT activation and thermogenesis under both stimuli. Il18-KO, extremely dietary obesity-prone as previously described, failed to develop diet-induced thermogenesis as assessed by BAT and iWAT Ucp1 mRNA levels. Overweight when fed standard chow but not HFD, HFD-fed Il18r1-KO mice exhibited increased iWAT Ucp1 gene expression. Energy expenditure was reduced in pre-obese Il18r1-KO mice and restored upon HFD-challenge. Cold exposure lead to similar results; Il18r1-KO mice were protected against acute body temperature drop, displaying a more brown-like structure, alternative macrophage activation and thermogenic gene expression in iWAT than WT controls. Opposite effects were observed in Il18-KO mice. Thus, Il18 and Il18r1 genetic ablation disparate effects on energy homeostasis are likely mediated by divergent BAT responses to thermogenic stimuli as well as iWAT browning. These results suggest that a more complex receptor-signaling system mediates the IL18 adipose-tissue specific effects in energy expenditure.

Increased serum level of IL-37 in patients with multiple sclerosis and neuromyelitis optica

Multiple sclerosis (MS) is a common autoimmune disease of central nervous system in which neurodegenerative and inflammatory mechanisms cause alternate neurological impairments. Many inflammatory and anti-inflammatory cytokines were suggested as contributor in MS pathogenesis, and the balance between these opposing cytokines can regulate MS severity. IL-37, an anti-inflammatory cytokine, is the most recently identified member of IL-1 family, which acts as a natural inhibitor of innate immunity. However, the role of IL-37 in MS has not investigated so far. Therefore, in this study, we aimed to measure serum level of IL-37 in patients with relapsing remitting multiple sclerosis (RRMS) and neuromyelitis optica (NMO). In a case-control study, plasma was collected from healthy controls (n = 49) and also patients with RRMS (n = 122) and NMO (n = 31). Serum level measurement of IL-37 was performed using enzyme-linked immunoassay (ELISA) method. The serum levels of IL-37 were 247.46 ± 74.02 and 312.00 ± 86.72 and 114.63 ± 20.58 in RRMS and NMO patients and healthy controls, respectively, showing statistically significant difference between them (P = 0.00). Furthermore, we found a positive correlation between the serum levels of IL-37 and EDSS of patients (r = +0.31 and P = 0.00). In summary, the serum level of IL-37 was found to be significantly increased in MS patients compared to healthy controls. Furthermore, the mean serum level of IL-37 was correlated with disease severity. This suggests that IL-37 may be part of a feed-back loop to control underlying inflammation in MS pathogenesis. However, further studies will be required to indicate exact role of IL-37 in the MS pathomechanisms.

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.

Systemic Cytokine Profiles in Strongyloides stercoralis Infection and Alterations following Treatment

Strongyloides stercoralis is a soil-transmitted helminth organism that infects ~50 to 100 million people worldwide. Despite its widespread prevalence, very little is known about the immune response that characterizes human S. stercoralis infection. To study the systemic cytokine profile characteristic of Strongyloides infection, we measured the circulating levels of a large panel of pro- and anti-inflammatory cytokines in asymptomatic, infected individuals (n = 32) and compared them to those in uninfected, controls (n = 24). Infected individuals exhibited significantly lower circulating levels of proinflammatory cytokines (gamma interferon [IFN-γ], tumor necrosis factor alpha [TNF-α], and interleukin-1β [IL-1β]) and significantly higher levels of anti-inflammatory cytokines (IL-4, IL-5, IL-9, IL-10, IL-13, IL-27, IL-37, and transforming growth factor β [TGF-β]). Moreover, treatment of Strongyloides infection resulted in a significant reversal of the cytokine profile, with increased levels of proinflammatory (IFN-γ, TNF-α, IL-2, IL-17A, IL-17F, IL-22, IL-23, and IL-1β) and decreased levels of anti-inflammatory (IL-4, IL-5, IL-9, IL-10, IL-13, IL-27, IL-37, and TGF-β) cytokines following treatment. Thus, S. stercoralis infection is characterized by alterations in the levels of systemic cytokines, reflecting major alterations in the underlying immune response to this chronic helminth infection.

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.

Aging-associated inflammation promotes selection for adaptive oncogenic events in B cell progenitors

The incidence of cancer is higher in the elderly; however, many of the underlying mechanisms for this association remain unexplored. Here, we have shown that B cell progenitors in old mice exhibit marked signaling, gene expression, and metabolic defects. Moreover, B cell progenitors that developed from hematopoietic stem cells (HSCs) transferred from young mice into aged animals exhibited similar fitness defects. We further demonstrated that ectopic expression of the oncogenes BCR-ABL, NRAS(V12), or Myc restored B cell progenitor fitness, leading to selection for oncogenically initiated cells and leukemogenesis specifically in the context of an aged hematopoietic system. Aging was associated with increased inflammation in the BM microenvironment, and induction of inflammation in young mice phenocopied aging-associated B lymphopoiesis. Conversely, a reduction of inflammation in aged mice via transgenic expression of α-1-antitrypsin or IL-37 preserved the function of B cell progenitors and prevented NRAS(V12)-mediated oncogenesis. We conclude that chronic inflammatory microenvironments in old age lead to reductions in the fitness of B cell progenitor populations. This reduced progenitor pool fitness engenders selection for cells harboring oncogenic mutations, in part due to their ability to correct aging-associated functional defects. Thus, modulation of inflammation--a common feature of aging--has the potential to limit aging-associated oncogenesis.

IL-37b gene transfer enhances the therapeutic efficacy of mesenchumal stromal cells in DSS-induced colitis mice

AIM

To investigate whether the transfer of the IL-37b gene, a newly identified inhibitor of both innate and adaptive immunity, could improve the therapeutic efficacy of mesenchumal stromal cells (MSCs) in inflammatory bowel disease (IBD).

METHODS

The expression of IL-37 in biopsied specimens of the patients with active ulcerative colitis (UC) was detected using RT-PCR and immunohistochemistry. Mice were treated with 3% dextran sulfate sodium (DSS) for 8 days to induce colitis. Before DSS treatment, the mice were injected with MSCs, MSC-eGFP or MSC-IL37b. Their body weight was measured each day, and the colons and spleens were harvested on d 10 for pathological and biochemical analyses.

RESULTS

In biopsied specimens of the patients with active UC, the expression of IL-37 was dramatically elevated in inflamed mucosa, mainly in epithelial cells and infiltrating immune cells. Compared to MSC-eGFP or MSCs, MSC-IL37b administration significantly attenuated the body weight and colon length reduction, and decreased the histological score in DSS-induced colitis mice. Furthermore, MSC-IL37b administration increased the percentage of myeloid-derived suppressor cells (MDSCs) among total splenic mononuclear cells as well as the percentage of regulatory T cells (Tregs) among splenic CD4+ T cells in the mice. Moreover, MSC-IL37b administration increased the IL-2+ cells and decreased the IFN-γ+ cells among splenic CD4+ T cells.

CONCLUSION

IL-37 is involved in the pathophysiology of UC. IL-37b gene transfer enhances the therapeutic efficacy of MSCs in DSS-induced colitis mice by inducing Tregs and MDSCs and regulating cytokine production.

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-37 mediates the antitumor activity in renal cell carcinoma

Interleukin (IL)-37 is a natural suppressor of innate inflammatory and immune responses. IL-37 plays an important role in renal function and antitumor activity. The aim of this study was to investigate the role of IL-37 in renal cell carcinoma (Rcc). Serum IL-37 levels in 120 Rcc patients and 50 healthy controls were measured by enzyme-linked immunosorbent assay (ELISA). The Rcc cell lines A498 and Caki-1 were cultured with 0-100 ng/mL of recombinant human IL-37 protein (rhIL-37). Cancer cells were transfected with or without pcDNA3.1-IL-6 to alter IL-6 expression. Cell migration, proliferation, and apoptosis were tested by wound-healing assay, MTT, and flow cytometry, respectively. Levels of IL-6, pSTAT3 Y705, Bcl-2, cyclin D1, and HIF-1α were detected by qRT-PCR, ELISA, or western blot. Additionally, therapeutic effect of rhIL-37 was also confirmed in SCID mice. The expression of IL-37 was decreased in Rcc patients and was negatively correlated with tumor progression. In vitro, IL-37 markedly inhibited the migration and proliferation, and promoted apoptosis in Rcc cells. Furthermore, the expressions of IL-6, pSTAT3 Y705, HIF-1α, Bcl-2, and cyclin D1 were decreased by IL-37. However, these effects were reversed by the transfection of pcDNA3.1-IL-6. In vivo, tumor growth and gene expressions of IL-6 and HIF-1α were suppressed by IL-37. In conclusion, IL-37 might serve as a novel tumor suppressor in Rcc and exert its antitumor activity through inhibiting IL-6/STAT3 signaling.

Meta-analysis derived atopic dermatitis (MADAD) transcriptome defines a robust AD signature highlighting the involvement of atherosclerosis and lipid metabolism pathways

Background

Atopic dermatitis (AD) is a common inflammatory skin disease with limited treatment options. Several microarray experiments have been conducted on lesional/LS and non-lesional/NL AD skin to develop a genomic disease phenotype. Although these experiments have shed light on disease pathology, inter-study comparisons reveal large differences in resulting sets of differentially expressed genes (DEGs), limiting the utility of direct comparisons across studies.

Methods

We carried out a meta-analysis combining 4 published AD datasets to define a robust disease profile, termed meta-analysis derived AD (MADAD) transcriptome.

Results

This transcriptome enriches key AD pathways more than the individual studies, and associates AD with novel pathways, such as atherosclerosis signaling (IL-37, selectin E/SELE). We identified wide lipid abnormalities and, for the first time in vivo, correlated Th2 immune activation with downregulation of key epidermal lipids (FA2H, FAR2, ELOVL3), emphasizing the role of cytokines on the barrier disruption in AD. Key AD “classifier genes” discriminate lesional from nonlesional skin, and may evaluate therapeutic responses.

Conclusions

Our meta-analysis provides novel and powerful insights into AD disease pathology, and reinforces the concept of AD as a systemic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0133-x) contains supplementary material, which is available to authorized users.

Elevated Circulating Levels of Inflammatory Markers in Patients with Acute Coronary Syndrome

Objective. We evaluated inflammatory cytokines and chemokine in peripheral blood mononuclear cells (PBMCs) in patients with either acute coronary syndrome (ACS) or stable coronary artery disease (CAD). Methods. We enrolled 20 ACS patients and 50 stable CAD patients without previous history of ACS who underwent cardiac catheterization. Patients with an estimated glomerular filtration rate of ≤30 mL/min/1.73 m(2) and C-reactive protein of ≥1.0 mg/dL were excluded. Blood samples were collected from the patients just before catheterization, and PBMCs were isolated from the whole blood. The levels of inflammatory cytokines and chemokine were measured by using real-time quantitative polymerase chain reaction and immunoassays. Results. The expression of tumor necrosis factor alpha (TNF-α), interleukin- (IL-) 6, IL-10, IL-23A, IL-27, and IL-37 was significantly higher in the ACS group than in the CAD group (P < 0.05). In contrast, the expression of IL-33 was significantly lower in the ACS group than in the CAD group (P < 0.05). The ACS patients had higher plasma levels of TNF-α, IL-6, and IL-10 in the ACS group than in the CAD group. Conclusion. Circulating levels of pro-/anti-inflammatory cytokines, including IL-23A, IL-27, IL-33, and IL-37, may be associated with the pathogenesis of atherosclerosis in ACS patients.

IL-1 family members in the pathogenesis and treatment of metabolic disease: Focus on adipose tissue inflammation and insulin resistance

Obesity is characterized by a chronic, low-grade inflammation that contributes to the development of insulin resistance and type 2 diabetes. Cytokines and chemokines produced by immunocompetent cells influence local as well as systemic inflammation and are therefore critical contributors to the pathogenesis of type 2 diabetes. Hence, cytokines that modulate inflammatory responses are emerging as potential targets for intervention and treatment of the metabolic consequences of obesity. The interleukin-1 (IL-1) family of cytokines and receptors are key mediators of innate inflammatory responses and exhibit both pro- and anti-inflammatory functions. During the last decades, mechanistic insights into how the IL-1 family affects the initiation and progression of obesity-induced insulin resistance have increased significantly. Here, we review the current knowledge and understanding, with emphasis on the therapeutic potential of individual members of the IL-1 family of cytokines for improving insulin sensitivity in patients with diabetes.

Expression of IL-37 contributes to the immunosuppressive property of human CD4+CD25+ regulatory T cells

Interleukin-37 (IL-37) possesses the function of down-regulate systemic and local inflammation. It is unknown whether IL-37 is expressed in human regulatory T cells (Tregs) and its role in modulating the immune response of Tregs. In the present study, cell surface molecules and secretory cytokines were analyzed in order to determine the function of IL-37 in regulating inhibitory effect of human CD4⁺CD25⁺Tregs. Meanwhile, the effects of IL-37 on T cell differentiation and proliferation as co-culture of CD4⁺CD25⁺Treg/CD4⁺CD25⁻T cell were also investigated. It was showed that IL-37 was expressed in cytoplasm of CD4⁺CD25⁺Tregs, and the levels of IL-37 were gradually elevated with the enhanced activity of CD4⁺CD25⁺Tregs. Secretory cytokines such as transforming growth factor (TGF)-β and interleukin (IL)-10, and expressions of cell surface molecules, including forkhead/winged helix transcription factor p3 (FOXP3) and cytotoxic T-lymphocyte associated antigen (CTLA)-4, were significantly decreased when IL-37 gene was silenced by siRNA. Furthermore, down-regulation of IL-37 expression in human CD4⁺CD25⁺Tregs obviously promoted proliferation of co-cultured T cell and differentiation, together with observably enhancement of IL-2 formation. These results demonstrated that IL-37 might manifest as a critical protein involving in immunosuppression of human CD4⁺CD25⁺Tregs.

Anti-inflammatory activity of IL-37 in asthmatic children: Correlation with inflammatory cytokines TNF-α, IL-β, IL-6 and IL-17A

BACKGROUND

The aim of this study was to assess interleukin (IL)-37 production in asthmatic children in serum and induced sputum and to look to the impact of IL-37 on pro-inflammatory cytokines production (TNF-α, IL-6, IL-1β and IL-17).

METHODS

Forty children with well-controlled asthma (20 moderate and 20 mild asthmatics) were studied. IL-37 was measured by ELISA in serum and induced sputum (IS) samples, and compared with 22 age- and sex-matched healthy controls. Real-time quantitative PCR was used to determine IL-37 mRNA expression in induced sputum cells. Induced sputum mononuclear cells from 10 moderate asthmatics and 10 healthy controls were stimulated either with lipopolysaccharides (LPS) or LPS plus recombinant IL-37 (rIL-37) comparing pro-inflammatory cytokines production. TNF-α, IL-1β, IL-6 and IL-17 were measured by RT-PCR and ELISA.

FINDINGS

The expression of IL-37 mRNA in asthmatic patients was significantly lower than that observed in healthy controls (P=0.0001). IL37 mRNA expression depended on asthma severity. Serum and IS IL-37 levels were significantly lower in asthma patients compared to healthy controls. LPS-stimulated sputum cells from asthma patients produced higher levels of IL-1β, IL-6, and TNF-α than those from HC. Adding rIL-37 suppressed TNF-α, IL-1β and IL-6 production in IS cells. In the same way, stimulating IS CD4(+) T cells in the presence of rIL-37 inhibited IL-17 production both in asthma patients and HC. IL-37 effect on IL-17 was more pronounced in patients than controls.

INTERPRETATION

The decrease in IL-37 level observed in IS was found to correlate with disease severity. The increased pro-inflammatory cytokines production from asthma IS cells was abrogated by the addition of rIL-37. IL-37 could be an important cytokine in the control of asthma by suppressing the production of inflammatory cytokines.

Plasma Interleukin-37 Is Elevated in Patients with Rheumatoid Arthritis: Its Correlation with Disease Activity and Th1/Th2/Th17-Related Cytokines

Interleukin- (IL-) 37 is a novel anti-inflammatory cytokine that suppresses immune response and inflammation. This study was performed to determine whether IL-37 was elevated in patients with rheumatoid arthritis (RA) and investigate the correlation between IL-37 level and disease activity and the concentration of Th1/Th2/Th17-related cytokines. Clinical parameters of disease activity, including the 28-joint disease activity score (DAS28) and C-reactive protein (CRP), were collected in 34 RA patients and 34 age- and sex-matched healthy controls. Plasma IL-37 was measured by ELISA. Plasma levels of TNF-α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-17, G-CSF, GM-CSF, IFN-γ, MCP-1, and MIP-1β were analyzed using the Bio-Plex suspension array system. It was found that IL-37 levels were elevated markedly in RA patients and almost undetectable in healthy controls. In addition, IL-37 levels in patients with active RA were significantly enhanced as compared with those in patients of remission. More importantly, IL-37 showed a significant correlation with disease activity (DAS28) and IL-4, IL-7, IL-10, IL-12, and IL-13 concentrations in RA patients. These findings suggest that IL-37 plays an important role in the pathogenesis of RA and may prove to be a potential biomarker of active RA.

Immunology of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is primarily a malignancy of the liver, advancing from a damaged, cirrhotic liver to HCC. Globally, HCC is the sixth most prevalent cancer and the third-most prevalent reason for neoplastic disease-related deaths. A diverse array of infiltrating immunocytes regulates the development and progression of HCC, as is the case in many other cancers. An understanding of the various immune components during HCC becomes necessary so that novel therapeutic strategies can be designed to combat the disease. A dysregulated immune system (including changes in the number and/or function of immune cells, cytokine levels, and the expression of inhibitory receptors or their ligands) plays a key role in the development of HCC. Alterations in either the innate or adaptive arm of the immune system and cross-talk between them make the immune system tolerant to tumors, leading to disease progression. In this review, we have discussed the status and roles of various immune effector cells (e.g., dendritic cells, natural killer cells, macrophages, and T cells), their cytokine profile, and the chemokine-receptor axis in promoting or impeding HCC.

Interleukin 37 Expression Inhibits STAT3 to Suppress the Proliferation and Invasion of Human Cervical Cancer Cells

Objectives: The most recently discovered cytokine interleukin 37 (IL-37) received growing attention. Its function on tumor is largely unknown. Here, we investigated the biological function of IL-37 on cervical cancer (CC).

Materials and methods: HPV⁺ Hela cells and HPV^- C33A cells were used. RT-qPCR was performed to detect the transcription of IL-37, STAT3, TNF-αand IL-1β. Western blotting was used for protein detection. CCK-8 assay and transwell assay were employed for cell proliferation and invasion detection, respectively.

Results: Successful gene transfection of IL-37 suppressed the proliferation and invasion of CC. Interestingly, IL-37 showed higher anticancer ability in HPV⁺ Hela cells than that in HPV^- C33A cells. Then, the molecular mechanism of IL-37 anticancer was explored. Firstly, we found that IL-37 inhibited STAT3 expression at both mRNA and protein levels. IL-37 also down regulated the phosphorylation of STAT3. Secondly, blockage of STAT3 using siRNAs reduced significantly the ability of IL-37 to suppress cell proliferation and invasion. Thirdly, STAT3 knockdown reduced markedly the inhibition of IL-37 on the transcription of tumor-derived TNF-α and IL-1β, indicating the contribution of STAT3 for the cancer associated antiinflammation of IL-37. Finally, STAT3 up regulation restored the ability of cell proliferation, cell invasion and the expression of inflammatory cytokines, TNF-α and IL-1β.

Conclusions: IL-37 suppressed cell proliferation and invasion of CC and STAT3 is involved in this process. Thus, IL-37 emerges as a new anticancer cytokine for CC. This study demonstrated a new biological function of IL-37 and offered a potential molecule for CC treatment.

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.

Cytokine Dysregulation in MECP2- and CDKL5-Related Rett Syndrome: Relationships with Aberrant Redox Homeostasis, Inflammation, and ω-3 PUFAs

An involvement of the immune system has been suggested in Rett syndrome (RTT), a devastating neurodevelopmental disorder related to oxidative stress, and caused by a mutation in the methyl-CpG binding protein 2 gene (MECP2) or, more rarely, cyclin-dependent kinase-like 5 (CDKL5). To date, it is unclear whether both mutations may have an impact on the circulating cytokine patterns. In the present study, cytokines involved in the Th1-, Th2-, and T regulatory (T-reg) response, as well as chemokines, were investigated in MECP2- (MECP2-RTT) (n = 16) and CDKL5-Rett syndrome (CDKL5-RTT) (n = 8), before and after ω-3 polyunsaturated fatty acids (PUFAs) supplementation. A major cytokine dysregulation was evidenced in untreated RTT patients. In MECP2-RTT, a Th2-shifted balance was evidenced, whereas in CDKL5-RTT both Th1- and Th2-related cytokines (except for IL-4) were upregulated. In MECP2-RTT, decreased levels of IL-22 were observed, whereas increased IL-22 and T-reg cytokine levels were evidenced in CDKL5-RTT. Chemokines were unchanged. The cytokine dysregulation was proportional to clinical severity, inflammatory status, and redox imbalance. Omega-3 PUFAs partially counterbalanced cytokine changes, as well as aberrant redox homeostasis and the inflammatory status. RTT is associated with a subclinical immune dysregulation as the likely consequence of a defective inflammation regulatory signaling system.

Phenylbutyrate Is Bacteriostatic against Mycobacterium tuberculosis and Regulates the Macrophage Response to Infection, Synergistically with 25-Hydroxy-Vitamin D3

Adjunctive vitamin D treatment for pulmonary tuberculosis enhances resolution of inflammation but has modest effects on bacterial clearance. Sodium 4-phenylbutyrate (PBA) is in clinical use for a range of conditions and has been shown to synergise with vitamin D metabolites to upregulate cathelicidin antimicrobial peptide (CAMP) expression. We investigated whether clinically attainable plasma concentrations of PBA (0.4-4 mM) directly affect Mycobacterium tuberculosis (Mtb) growth and human macrophage and PBMC response to infection. We also tested the ability of PBA to enhance the immunomodulatory actions of the vitamin D metabolite 25(OH)D3 during infection and synergistically inhibit intracellular Mtb growth. PBA inhibited Mtb growth in broth with an MIC99 of 1 mM, which was reduced to 0.25 mM by lowering pH. During human macrophage infection, PBA treatment restricted Mtb uptake, phagocytic receptor expression and intracellular growth in a dose-dependent manner. PBA independently regulated CCL chemokine secretion and induced expression of the antimicrobial LTF (lactoferrin), the anti-inflammatory PROC (protein C) and multiple genes within the NLRP3 inflammasome pathway. PBA co-treatment with 25(OH)D3 synergistically modulated expression of numerous vitamin D-response genes, including CAMP, CYP24A1, CXCL10 and IL-37. This synergistic effect was dependent on MAPK signalling, while the effect of PBA on LTF, PROC and NLRP3 was MAPK-independent. During PBA and 25(OH)D3 co-treatment of human macrophages, in the absence of exogenous proteinase 3 (PR3) to activate cathelicidin, Mtb growth restriction was dominated by the effect of PBA, while the addition of PR3 enhanced growth restriction by 25(OH)D3 and PBA co-treatment. This suggests that PBA augments vitamin D-mediated cathelicidin-dependent Mtb growth restriction by human macrophages and independently induces antimicrobial and anti-inflammatory action. Therefore through both host-directed and bacterial-directed mechanisms PBA and vitamin D may prove an effective combinatorial adjunct therapy for tuberculosis to both resolve immunopathology and enhance bacterial clearance.

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.

Expression profile of IL-1 family cytokines in aqueous humor and sera of patients with HLA-B27 associated anterior uveitis and idiopathic anterior uveitis

The purpose of this study was to evaluate the cytokine expression profile of specific IL-1 family members in the aqueous humor and sera of patients with HLA-B27 associated acute anterior uveitis (AAU) and idiopathic AAU. Following informed consent, a total of 13 patients with HLA-B27 associated AAU, 12 patients with idiopathic AAU and 9 controls were recruited to this study from May 2013 to July 2014. Each individual received a complete ophthalmologic examination. Aqueous humor and sera samples were collected and 11 inflammation-related cytokines of the IL-1 family (IL-1α, IL-1β, IL-1 receptor antagonist [IL-1Ra], IL-18, IL-36 receptor antagonist [IL-36Ra], IL-33, IL-36α, IL-36β, IL-36γ, IL-37, IL-38) were quantitatively measured and analyzed for statistical significance between groups. The degree of inflammation, anterior chamber cell or flare, correlated with expression of IL-1β, IL-1Ra, and IL-18. The highest levels of IL-1β, IL-1Ra, IL-18, and IL-36Ra were seen in the aqueous of patients with HLA-B27 associated AAU and this was statically significant when compared to the controls, but not to idiopathic AAU. Expression of IL-18 was statistically higher in the aqueous of patients with HLA-B27 associated AAU in comparison to either idiopathic AAU or controls, but this may reflect greater inflammation in this patient group. In the sera only IL-1α was statistically higher in the HLA-B27 associated AAU in comparison to the control. Cytokine analysis reveals elevation of multiple IL-1 family members in the aqueous humor of patients with AAU as compared to controls. The specific signature of inflammation may potentially be useful in developing new future therapies for AAU.

Caspase-1: an integral regulator of innate immunity

Caspase-1 is a unique cysteine protease playing central roles in innate immunity. Pathogens, stress, and damage signals induce activation of caspase-1, typically mediated by proximity-induced autoproteolysis in multimeric protein complexes called the inflammasome. Active caspase-1 induces secretion of pro-inflammatory cytokines and mediates pyroptosis, a programmed pro-inflammatory cell death, thereby initiating an immune response finally leading to pathogen clearance. Excessive activation of caspase-1 is the underlying cause for rare diseases such as periodic fever syndromes, and more common disorders, including atherosclerosis, type 2 diabetes, and gout. Beside these well-known pro-inflammatory functions, active caspase-1 also has anti-inflammatory and protective functions contributing to cell survival, reduced inflammatory cytokine signaling, and improved outcomes in mouse models of burn injury or trauma and shock. Furthermore, naturally occurring procaspase-1 variants with reduced or abrogated enzymatic activity mediate enhanced inflammatory signaling and have been associated to autoinflammatory symptoms. Here, we review functions of caspase-1 focusing on anti-inflammatory signaling pathways and discuss the role of enzymatically inactive caspase-1 as disease-promoting factors in autoinflammatory diseases. Moreover, we illustrate differential requirements for autoproteolysis and enzymatic activity in caspase-1 functions.

Effects of interleukin-37 on cardiac function after myocardial infarction in mice

BACKGROUND

Interleukin-37 (IL-37) is a new discovered member of the interleukin family and plays anti-inflammatory effect in some inflammatory disease. A recent study found that IL-37 elevated significantly in peripheral blood of patients with acute myocardial infarction. We aimed to explore the effect IL-37 on cardiac function after mice myocardial infarction (MI) and its mechanism.

METHODS

Acute MI mouse model was established and divided into three groups: sham group, MI group and IL-37 treatment group. MPO expression was detected by immunohistochemistry; NF-κB signaling pathway was tested by Western blot; and cardiac function was measured by echocardiography.

RESULTS

Compared with MI mice, IL-37 treatment showed an obvious decrease of MPO expression, suppression of p-p65 expression, and improved cardiac function by decreasing left ventricular shortening fraction (LVFS).

CONCLUSION

IL-37 may improve MI mice cardiac function via inhibition of inflammatory NF-κB signaling pathway.

RNA-Seq Analysis of the Host Response to Staphylococcus aureus Skin and Soft Tissue Infection in a Mouse Model

Staphylococcus aureus is a leading cause of skin and soft tissue infections (SSTI), which are primarily self-limiting. We conducted a comprehensive analysis of the host transcriptome during a S. aureus SSTI to provide insight on the protective mechanisms that thwart these infections. We utilized a murine SSTI model in which one ear is epicutaneously challenged while the other is not. We then harvested these infected and uninfected ears, as well as ears from naïve mice, at one, four, and seven days post-challenge, and performed RNA sequencing (RNA-seq) using the Illumina platform. RNA-seq data demonstrated a robust response at the site of infection. Comparison of gene expression profiles between infected ears and the non-infected ears of challenged mice defined the local response to infection, while comparisons of expression profiles of non-infected ears from challenged mice to ears of naïve mice revealed changes in gene expression levels away from the site indicative of a systemic response. Over 1000 genes exhibited increased expression locally at all tested time points. The local response was more robust than the systemic response. Through evaluation of the RNA-seq data using the Upstream Regulator Analytic as part of the Ingenuity Pathway Analysis software package, we found that changes in the activation and inhibition of regulatory pathways happen first locally, and lag behind systemically. The activated pathways are highly similar at all three time points during SSTI, suggesting a stable global response over time. Transcript increases and pathway activation involve pro- and anti-inflammatory mediators, chemotaxis, cell signaling, keratins, and TH1/TH17 cytokines. Transcript decreases and pathway inhibition demonstrate that metabolic genes and anti-inflammatory pathways are repressed. These data provide insight on the host responses that may aid in resolution of this self-limited S. aureus infection, and may shed light on potential immune correlates of protection for staphylococcal SSTI.

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.

Molecular and Morphological Characterization of Inflammatory Infiltrate in Rosacea Reveals Activation of Th1/Th17 Pathways

Rosacea is a common chronic inflammatory skin disease of unknown etiology. Our knowledge about an involvement of the adaptive immune system is very limited. We performed detailed transcriptome analysis, quantitative real-time reverse-transcriptase-PCR, and quantitative immunohistochemistry on facial biopsies of rosacea patients, classified according to their clinical subtype. As controls, we used samples from patients with facial lupus erythematosus and healthy controls. Our study shows significant activation of the immune system in all subtypes of rosacea, characterizing erythematotelangiectatic rosacea (ETR) already as a disease with significant influx of proinflammatory cells. The T-cell response is dominated by Th1/Th17-polarized immune cells, as demonstrated by significant upregulation of IFN-γ or IL-17, for example. Chemokine expression patterns support a Th1/Th17 polarization profile of the T-cell response. Macrophages and mast cells are increased in all three subtypes of rosacea, whereas neutrophils reach a maximum in papulopustular rosacea. Our studies also provide evidence for the activation of plasma cells with significant antibody production already in ETR, followed by a crescendo pattern toward phymatous rosacea. In sum, Th1/Th17 polarized inflammation and macrophage infiltration are an underestimated hallmark in all subtypes of rosacea. Therapies directly targeting the Th1/Th17 pathway are promising candidates in the future treatment of this skin disease.

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.

Role of IL-38 and its related cytokines in inflammation

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

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.