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

IL-37 attenuates allergic process via STAT6/STAT3 pathways in murine allergic rhinitis

Allergic rhinitis (AR) is a common upper airway allergic disease caused by allergens triggering a type 2 immune response. The imbalance of CD4+ T cell subsets is the essential immunological feature of AR, which is mainly characterized by the predominance of T helper (Th) 2 cells. Recent studies indicated that the anti-inflammatory factor interleukin (IL)-37 is involved in the immune regulation of AR. However, the mechanism of IL-37 acts on AR has not been fully elucidated. Thus, we sought to assess the protective role of IL-37 in AR and further explore the possible mechanism. An ovalbumin (OVA)-induced AR murine model was established. After IL-37 treatment, the allergic symptoms (sneezes and nasal rubbings), nasal mucosal infiltration with eosinophils, and serum IgE production were found significantly attenuated. For CD4+ T cell subsets, the proliferation and differentiation of Th2 and Th17 cells were restrained. The relevant effector cytokines of IL-4, IL-5, IL-6, and IL-17a protein expression and transcription factors GATA3 and RORγt mRNA levels were obviously decreased. However, IL-37 had no significant effect on Th1 and Treg response including in IFN-γ, IL-10, T-bet, and Foxp3 expression. Furthermore, IL-37 was found down-regulated the STAT6, STAT3, phospho-STAT6, and phospho-STAT3 expression. In conclusion, IL-37 alleviates allergic inflammation in AR possibly through repressing STAT6 and STAT3 signaling pathways.

Exploiting NK Cell Surveillance Pathways for Cancer Therapy

Natural killer (NK) cells can evoke potent anti-tumour activity. This function is largely mediated through a battery of specialised cell-surface receptors which probe the tissue microenvironment for changes in surface and secretory phenotypes that may alert to the presence of infection or malignancy. These receptors have the potential to arouse the robust cytotoxic and cytokine-secreting functions of NK cells and so must be tightly regulated to prevent autoimmunity. However, such functions also hold great promise for clinical intervention. In this review, we highlight some of the latest breakthroughs in fundamental NK cell receptor biology that have illuminated our understanding of the molecular strategies NK cells employ to perceive malignant cells from normal healthy cells. Moreover, we highlight how these sophisticated tumour recognition strategies are being harnessed for cancer immunotherapies in the clinic.

Interleukin-37: The Effect of Anti-Inflammatory Response in Human Coronary Artery Endothelial Cells

Interleukin-37 (IL-37) is unique in the IL-1 family since it broadly suppresses innate immunity and elevates in humans with inflammatory and autoimmune diseases. IL-37 shows definite groups and transcripts for human IL37 gene, but it is still not completely understood the effect and mechanisms of inflammatory response in endothelial cells. It is well accepted that endothelial dysfunction caused by inflammation is a key initiating event in atherosclerotic plaque formation, which leads to the occurrence and development of the cardiovascular adverse events in clinical since the inflammatory responses of endothelial cells could induce and enhance the deposition of extensive lipid and the formation of atherosclerotic plaque in the intima. Thus, it is essential to investigate the role and potential mechanisms in endothelial inflammatory response to prevent the formation and development of many cardiovascular diseases including atherosclerosis. So far, the recent studies have revealed that IL-37 is able to inhibit inflammatory response by suppressing the TLR2-NF-κB-ICAM-1 pathway intracellularly in human coronary artery endothelial cells (HCAECs). Further, the role of IL-37 may be related to the IL-18 pathway extracellularly and involved in the adhesion and transmigration of neutrophils in HCAECs.

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

BACKGROUND

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

RECENT FINDINGS

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

CONCLUSION

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

Interleukin-37 inhibits osteoclastogenesis and alleviates inflammatory bone destruction

Excessive osteoclast formation is one of the important pathological features of inflammatory bone destruction. Interleukin‐37 (IL‐37) is an anti‐inflammatory agent that is present throughout the body, but it displays low physiological retention. In our study, high levels of the IL‐37 protein were detected in clinical specimens from patients with bone infections. However, the impact of IL‐37 on osteoclast formation remains unclear. Next, IL‐37 alleviated the inflammatory bone destruction in the mouse in vivo. We used receptor activator of nuclear factor‐κB ligand and lipopolysaccharide to trigger osteoclastogenesis under physiological and pathological conditions to observe the role of IL‐37 in this process and explore the potential mechanism of this phenomenon. In both induction models, IL‐37 exerted inhibitory effects on osteoclast differentiation and bone resorption. Furthermore, IL‐37 decreased the phosphorylation of inhibitor of κBα and p65 and the expression of nuclear factor of activated T cells c1, while the dimerization inhibitor of myeloid differentiation factor 88 reversed the effects. These data provide evidence that IL‐37 modulates osteoclastogenesis and a theoretical basis for the clinical application of IL‐37 as a treatment for bone loss–related diseases.

Loss of the Chr16p11.2 ASD candidate gene QPRT leads to aberrant neuronal differentiation in the SH-SY5Y neuronal cell model

Background

Altered neuronal development is discussed as the underlying pathogenic mechanism of autism spectrum disorders (ASD). Copy number variations of 16p11.2 have recurrently been identified in individuals with ASD. Of the 29 genes within this region, quinolinate phosphoribosyltransferase (QPRT) showed the strongest regulation during neuronal differentiation of SH-SY5Y neuroblastoma cells. We hypothesized a causal relation between this tryptophan metabolism-related enzyme and neuronal differentiation. We thus analyzed the effect of QPRT on the differentiation of SH-SY5Y and specifically focused on neuronal morphology, metabolites of the tryptophan pathway, and the neurodevelopmental transcriptome.

Methods

The gene dosage-dependent change of QPRT expression following Chr16p11.2 deletion was investigated in a lymphoblastoid cell line (LCL) of a deletion carrier and compared to his non-carrier parents. Expression of QPRT was tested for correlation with neuromorphology in SH-SY5Y cells. QPRT function was inhibited in SH-SY5Y neuroblastoma cells using (i) siRNA knockdown (KD), (ii) chemical mimicking of loss of QPRT, and (iii) complete CRISPR/Cas9-mediated knock out (KO). QPRT-KD cells underwent morphological analysis. Chemically inhibited and QPRT-KO cells were characterized using viability assays. Additionally, QPRT-KO cells underwent metabolite and whole transcriptome analyses. Genes differentially expressed upon KO of QPRT were tested for enrichment in biological processes and co-regulated gene-networks of the human brain.

Results

QPRT expression was reduced in the LCL of the deletion carrier and significantly correlated with the neuritic complexity of SH-SY5Y. The reduction of QPRT altered neuronal morphology of differentiated SH-SY5Y cells. Chemical inhibition as well as complete KO of the gene were lethal upon induction of neuronal differentiation, but not proliferation. The QPRT-associated tryptophan pathway was not affected by KO. At the transcriptome level, genes linked to neurodevelopmental processes and synaptic structures were affected. Differentially regulated genes were enriched for ASD candidates, and co-regulated gene networks were implicated in the development of the dorsolateral prefrontal cortex, the hippocampus, and the amygdala.

Conclusions

In this study, QPRT was causally related to in vitro neuronal differentiation of SH-SY5Y cells and affected the regulation of genes and gene networks previously implicated in ASD. Thus, our data suggest that QPRT may play an important role in the pathogenesis of ASD in Chr16p11.2 deletion carriers.

IL-37b suppresses epithelial mesenchymal transition in hepatocellular carcinoma by inhibiting IL-6/STAT3 signaling

BACKGROUND

Interleukin-37b (IL-37b), a vital negative regulator of the innate immune system, has been reported to be a tumor inhibitor in different type of cancers. However, little is known about the relationship between IL-37b and hepatocellular carcinoma (HCC). The present study aimed to investigate the potential roles of IL-37b in HCC progression.

METHODS

Subjects (n = 237) were recruited, and serum IL-37b was measured using ELISA. The tumor-suppressive capacity and underlying mechanisms of IL-37b in HCC were investigated in vitro and in vivo.

RESULTS

Compared to healthy controls, serum IL-37b levels were elevated in chronic hepatitis B (CHB) patients but decreased significantly in HBV-HCC patients, especially for those with portal venous tumor thrombus. Low level serum IL-37b in HBV-HCC patients correlated with high HCC stage and poor overall survival and disease-free survival. In vitro and in vivo, recombinant human IL-37b inhibited proliferation and metastasis in HCC cells. Furthermore, IL-37b inhibited epithelial mesenchymal transition in HCC cells in vitro by downregulating IL-6, pSTAT3 (Y705), N-cadherin, and vimentin expression and by upregulating E-cadherin expression. These effects were partially reversed by transfection of adenovirus encoding human IL-6.

CONCLUSIONS

IL-37b inhibits HCC growth, metastasis and epithelial mesenchymal transition by regulating IL-6/STAT3 signaling. Serum IL-37b may be a biomarker for HBV-HCC and its staging.

Interleukin-37 treatment of mice with metabolic syndrome improves insulin sensitivity and reduces pro-inflammatory cytokine production in adipose tissue

Obesity and the metabolic syndrome are characterized by chronic, low-grade inflammation mainly originating from expanding adipose tissue and resulting in inhibition of insulin signaling and disruption of glycemic control. Transgenic mice expressing human interleukin 37 (IL-37), an anti-inflammatory cytokine of the IL-1 family, are protected against metabolic syndrome when fed a high-fat diet (HFD) containing 45% fat. Here, we examined whether treatment with recombinant IL-37 ameliorates established insulin resistance and obesity-induced inflammation. WT mice were fed a HFD for 22 weeks and then treated daily with IL-37 (1 μg/mouse) during the last 2 weeks. Compared with vehicle only-treated mice, IL-37-treated mice exhibited reduced insulin in the plasma and had significant improvements in glucose tolerance and in insulin content of the islets. The IL-37 treatment also increased the levels of circulating IL-1 receptor antagonist. Cultured adipose tissues revealed that IL-37 treatment significantly decreases spontaneous secretions of IL-1β, tumor necrosis factor α (TNFα), and CXC motif chemokine ligand 1 (CXCL-1). We also fed mice a 60% fat diet with concomitant daily IL-37 for 2 weeks and observed decreased secretion of IL-1β, TNFα, and IL-6 and reduced intracellular levels of IL-1α in the liver and adipose tissue, along with improved plasma glucose clearance. Compared with vehicle treatment, these IL-37-treated mice had no apparent weight gain. In human adipose tissue cultures, the presence of 50 pm IL-37 reduced spontaneous release of TNFα and 50% of lipopolysaccharide-induced TNFα. These findings indicate that IL-37's anti-inflammatory effects can ameliorate established metabolic disturbances during obesity.

GWAS for Interleukin-1β levels in gingival crevicular fluid identifies IL37 variants in periodontal inflammation

There is no agnostic GWAS evidence for the genetic control of IL-1β expression in periodontal disease. Here we report a GWAS for "high" gingival crevicular fluid IL-1β expression among 4910 European-American adults and identify association signals in the IL37 locus. rs3811046 at this locus (p = 3.3 × 10-22) is associated with severe chronic periodontitis (OR = 1.50; 95% CI = 1.12-2.00), 10-year incident tooth loss (≥3 teeth: RR = 1.33; 95% CI = 1.09-1.62) and aggressive periodontitis (OR = 1.12; 95% CI = 1.01-1.26) in an independent sample of 4927 German/Dutch adults. The minor allele at rs3811046 is associated with increased expression of IL-1β in periodontal tissue. In RAW macrophages, PBMCs and transgenic mice, the IL37 variant increases expression of IL-1β and IL-6, inducing more severe periodontal disease, while IL-37 protein production is impaired and shows reduced cleavage by caspase-1. A second variant in the IL37 locus (rs2708943, p = 4.2 × 10-7) associates with attenuated IL37 mRNA expression. Overall, we demonstrate that IL37 variants modulate the inflammatory cascade in periodontal disease.

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

Background:

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

Methods:

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

Results:

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

Conclusion:

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

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

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

IL-37 inhibits IL-4/IL-13-induced CCL11 production and lung eosinophilia in murine allergic asthma

BACKGROUND

IL-37 is emerging as an anti-inflammatory cytokine, particularly in innate inflammation. However, the role of IL-37 in Th2-mediated allergic lung inflammation remains uncertain. We sought to determine the role and the underlying mechanisms of IL-37 in the development of house dust mites (HDM)-induced murine asthma model.

METHODS

We examined the effect of IL-37 administration during the sensitization or challenge phase on Th2-mediated allergic asthma induced by inhaled HDM. Cellular source of CCL11 and distribution of IL-37 receptors, IL-18Rα and IL-1R8, were determined in HDM-exposed lungs. Finally, we examined the effect of IL-37 on CCL11 production and STAT6 activation in different primary lung structural cell types upon IL-4/IL-13 stimulation.

RESULTS

IL-37 had no effect on HDM sensitization, but when administrated during the challenge phase, significantly attenuated pulmonary eosinophilia, CCL11 production, and airway hyper-reactivity (AHR). Interestingly, IL-37 treatment had no significant effects on lung infiltrating T cells and Th2 cytokine production. Intranasal co-administration of CCL11 reversed the inhibiting effect of IL-37 on HDM-induced pulmonary eosinophilia and AHR. Furthermore, we demonstrated that CCL11 was primarily expressed by fibroblasts and airway smooth muscle cells (AMSC), while IL-37 receptors by tracheobronchial epithelial cells (TEC). In vitro study showed that IL-37 inhibited IL-4/IL-13-induced STAT6 activation and CCL11 production by fibroblasts and AMSC, which was dependent on its direct action on TEC. Moreover, cell contact was required for the inhibitory effect of IL-37-treated TEC.

CONCLUSIONS

IL-37 attenuates HDM-induced asthma, possibly by inhibiting IL-4/IL-13-induced CCL11 production by fibroblasts and AMSC via its direct act on TEC.

The family of the interleukin-1 receptors

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

IL-1 and IL-1 regulatory pathways in cancer progression and therapy

Inflammation is an important component of the tumor microenvironment. IL-1 is an inflammatory cytokine which plays a key role in carcinogenesis and tumor progression. IL-1 is subject to regulation by components of the IL-1 and IL-1 receptor (ILR) families. Negative regulators include a decoy receptor (IL-1R2), receptor antagonists (IL-1Ra), IL-1R8, and anti-inflammatory IL-37. IL-1 acts at different levels in tumor initiation and progression, including driving chronic non-resolving inflammation, tumor angiogenesis, activation of the IL-17 pathway, induction of myeloid-derived suppressor cells (MDSC) and macrophage recruitment, invasion and metastasis. Based on initial clinical results, the translation potential of IL-1 targeting deserves extensive analysis.

The role of the interleukin-1 family in trained immunity

Immunological memory was long considered a trait exclusive to cells of the adaptive immune system. However, recent studies have shown that after activation of the innate immune system, innate immune cells may undergo long-term functional reprogramming characterized by the ability to mount either a stronger or attenuated inflammatory response upon reactivation. This phenomenon, which has been termed trained immunity and is a de facto innate immune memory, is regulated by a network of integrated metabolic and epigenetic rewiring. The endogenous mediators that modulate trained immunity in the host are only partially understood, but increasing evidence supports the concept that the interleukin (IL)-1 family of cytokines plays an important role. In this review, we will highlight key findings from studies that provide insight into the multifaceted roles of members of the IL-1 family for trained immunity. Finally, we will discuss how the recent advances of our understanding on the role of IL-1 cytokines in this field may lead to new therapeutic strategies for treatment of common conditions, such as IL-1-driven autoinflammatory diseases.

Interleukin-18: Biological properties and role in disease pathogenesis

Initially described as an interferon (IFN)γ‐inducing factor, interleukin (IL)‐18 is indeed involved in Th1 and NK cell activation, but also in Th2, IL‐17‐producing γδ T cells and macrophage activation. IL‐18, a member of the IL‐1 family, is similar to IL‐1β for being processed by caspase 1 to an 18 kDa‐biologically active mature form. IL‐18 binds to its specific receptor (IL‐18Rα, also known as IL‐1R7) forming a low affinity ligand chain. This is followed by recruitment of the IL‐18Rβ chain. IL‐18 then uses the same signaling pathway as IL‐1 to activate NF‐kB and induce inflammatory mediators such as adhesion molecules, chemokines and Fas ligand. IL‐18 also binds to the circulating high affinity IL‐18 binding protein (BP), such as only unbound free IL‐18 is active. IL‐18Rα may also bind IL‐37, another member of the IL‐1 family, but in association with the negative signaling chain termed IL‐1R8, which transduces an anti‐inflammatory signal. IL‐18BP also binds IL‐37 and this acts as a sink for the anti‐inflammatory properties of IL‐37. There is now ample evidence for a role of IL‐18 in various infectious, metabolic or inflammatory diseases such as influenza virus infection, atheroma, myocardial infarction, chronic obstructive pulmonary disease, or Crohn's disease. However, IL‐18 plays a very specific role in the pathogenesis of hemophagocytic syndromes (HS) also termed Macrophage Activation Syndrome. In children affected by NLRC4 gain‐of‐function mutations, IL‐18 circulates in the range of tens of nanograms/mL. HS is treated with the IL‐1 Receptor antagonist (anakinra) but also specifically with IL‐18BP. Systemic juvenile idiopathic arthritis or adult‐onset Still's disease are also characterized by high serum IL‐18 concentrations and are treated by IL‐18BP.

Tuning inflammation and immunity by the negative regulators IL-1R2 and IL-1R8

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) are key players in immunity and inflammation and are tightly regulated at different levels. Most cell types, including cells of the innate and adaptive immune system express ILRs and TLRs. In addition, IL-1 family members are emerging as key players in the differentiation and function of innate and adaptive lymphoid cells. IL-1R2 and IL-1R8 (also known as TIR8 or SIGIRR) are members of the ILR family acting as negative regulators of the IL-1 system. IL-1R2 binds IL-1 and the accessory protein IL-1RAcP without activating signaling and can be released as a soluble form (sIL-1R2), thus modulating IL-1 availability for the signaling receptor. IL-1R8 dampens ILR- and TLR-mediated cell activation and it is a component of the receptor recognizing human IL-37. Here, we summarize our current understanding of the structure and function of IL-1R2 and IL-1R8, focusing on their role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation. We also address the emerging evidence regarding the role of IL-1R8 as a crucial checkpoint molecule in NK cells in anti-cancer and antiviral activity and the potential therapeutic implications of IL-1R8 blockade in specific pathological contexts.

Suppression of inflammation and acquired immunity by IL-37

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

Prognostic significance of nomograms integrating IL-37 expression, neutrophil level, and MMR status in patients with colorectal cancer

Interleukin (IL)‐37 and neutrophils are considered to be involved in human cancer, but their prognostic significance in colorectal cancer (CRC) has not been elucidated. The aim of this study was to evaluate the prognostic value of IL‐37 expression and neutrophil levels in CRC. We retrospectively analyzed IL‐37 expression, CD66b⁺ neutrophil levels, and mismatch repair (MMR) status in 337 paraffin‐embedded CRC specimens from the training cohort by immunohistochemistry. Their prognostic values were assessed using Kaplan‐Meier curves and multivariate Cox regression models. Moreover, several risk factors were used to form nomograms to evaluate survival, and the performance of the nomograms was assessed with respect to calibration, discrimination, and clinical usefulness. Further validation was performed in an independent cohort of 245 cases. Low IL‐37 expression and high CD66b⁺ neutrophil levels were significantly associated with diminished disease‐free survival (DFS) and overall survival (OS), and patients with MMR‐deficient CRC had better clinical outcomes. Furthermore, multivariate Cox analysis identified IL‐37, CD66b⁺ neutrophils, and MMR status as independent prognostic factors for DFS and OS. Two nomograms integrating the three markers with four clinicopathological risk factors were developed and validated for predicting DFS and OS with good calibration and discrimination (C‐index: training cohort, 0.798 (95% confidence interval:0.764‐0.832) and 0.828 (0.796‐0.860), respectively; validation cohort, 0.739 (0.696‐0.783) and 0.761 (0.715‐0.808), respectively). Decision curve analysis demonstrated that the nomograms were clinically useful. Intratumoral IL‐37, CD66b⁺ neutrophils, and MMR status were independent prognostic factors for CRC patients. Nomograms incorporating these biomarkers and clinicopathological features could be conveniently used to facilitate the individualized prediction of DFS and OS.

Adaptive NK Cells Resist Regulatory T-cell Suppression Driven by IL37

Natural killer (NK) cells are capable of fighting viral infections and cancer. However, these responses are inhibited by immune suppressor cells in the tumor microenvironment. Tumor progression promotes the recruitment and generation of intratumoral regulatory T cells (Treg), associated with a poor prognosis in cancer patients. Here, we show that canonical NK cells are highly susceptible to Treg-mediated suppression, in contrast to highly resistant CD57+ FcεRγ-NKG2C+ adaptive (CD56+CD3-) NK cells that expand in cytomegalovirus exposed individuals. Specifically, Tregs suppressed canonical but not adaptive NK-cell proliferation, IFNγ production, degranulation, and cytotoxicity. Treg-mediated suppression was associated with canonical NK-cell downregulation of TIM3, a receptor that activates NK-cell IFNγ production upon ligand engagement, and upregulation of the NK-cell inhibitory receptors PD-1 and the IL1 receptor family member, IL1R8 (SIGIRR or TIR8). Treg production of the IL1R8 ligand, IL37, contributed to the phenotypic changes and diminished function in Treg-suppressed canonical NK cells. Blocking PD-1, IL1R8, or IL37 abrogated Treg suppression of canonical NK cells while maintaining NK-cell TIM3 expression. Our data uncover new mechanisms of Treg-mediated suppression of canonical NK cells and identify that adaptive NK cells are inherently resistant to Treg suppression. Strategies to enhance the frequency of adaptive NK cells in the tumor microenvironment or to blunt Treg suppression of canonical NK cells will enhance the efficacy of NK-cell cancer immunotherapy. Cancer Immunol Res; 6(7); 766-75. ©2018 AACR.

Anti-Allergic Inflammatory Activity of Interleukin-37 Is Mediated by Novel Signaling Cascades in Human Eosinophils

IL-1 family regulatory cytokine IL-37b can suppress innate immunity and inflammatory activity in inflammatory diseases. In this study, IL-37b showed remarkable in vitro suppression of inflammatory tumor necrosis factor-α, IL-1β, IL-6, CCL2, and CXCL8 production in the coculture of human primary eosinophils and human bronchial epithelial BEAS-2B cells with the stimulation of bacterial toll-like receptor-2 ligand peptidoglycan, while antagonizing the activation of intracellular nuclear factor-κB, PI3K–Akt, extracellular signal-regulated kinase 1/2, and suppressing the gene transcription of allergic inflammation-related PYCARD, S100A9, and CAMP as demonstrated by flow cytometry, RNA-sequencing, and bioinformatics. Results therefore elucidated the novel anti-inflammation-related molecular mechanisms mediated by IL-37b. Using the house dust mite (HDM)-induced humanized asthmatic NOD/SCID mice for preclinical study, intravenous administration of IL-37b restored the normal plasma levels of eosinophil activators CCL11 and IL-5, suppressed the elevated concentrations of Th2 and asthma-related cytokines IL-4, IL-6, and IL-13 and inflammatory IL-17, CCL5, and CCL11 in lung homogenate of asthmatic mice. Histopathological results of lung tissue illustrated that IL-37b could mitigate the enhanced mucus, eosinophil infiltration, thickened airway wall, and goblet cells. Together with similar findings using the ovalbumin- and HDM-induced allergic asthmatic mice further validated the therapeutic potential of IL-37b in allergic asthma. The above results illustrate the novel IL-37-mediated regulation of intracellular inflammation mechanism linking bacterial infection and the activation of human eosinophils and confirm the in vivo anti-inflammatory activity of IL-37b on human allergic asthma.

Profiling of Canonical and Non-Traditional Cytokine Levels in Interferon-β-Treated Relapsing-Remitting-Multiple Sclerosis Patients

Background

Multiple sclerosis (MS) is a chronic, progressive autoimmune disease of the central nervous system in which inflammation plays a key role in the induction, development, and progression. Most of the MS patients present with relapsing–remitting (RR) form, characterized by flare-ups followed by periods of recovery. Many inflammatory and anti-inflammatory cytokines have been proposed as backers in MS pathogenesis, and the balance between these differing cytokines can regulate MS severity. Interferon (IFN)-β, a current disease-modifying therapy for MS, has demonstrated beneficial effects in reducing disease severity in MS patients. However, its immunoregulatory and anti-inflammatory actions in MS are not wholly understood. The aim of the study was to define, in clinically stable patients with RR-MS, the serum concentration of several cytokines, canonical or not, and their modulation by IFN-β therapy.

Methods

Relapsing–remitting-MS patients were enrolled and diagnosed according to revised Mc Donald Diagnostic Criteria. A set of cytokines [including non-canonical neurotransmitter acetylcholine (ACh) and adipokines] and B-cell differentiation molecules, as potential biomarkers, were evaluated in 30 non-treated RR-MS patients compared to 30 IFN-β-treated MS patients and 30 age, gender, and body mass index-matched healthy controls (HC).

Results

Naïve MS patients showed significantly higher levels of interleukin (IL)-1β, IL-12/IL-23p40, IL-18, high-mobility group box protein-1, and IL-18 binding protein (IL-18BP) than MS-treated patients (p < 0.001 for all) and HC (p < 0.01). IFN-β therapy has significantly downmodulated IL-1β, IL-12/IL-23p40, IL-18 to normal levels (p < 0.001), whereas it has decreased IL-18BP (p < 0.001). ACh was significantly higher in the IFN-β-treated than HC and non-treated MS patients (p < 0.001). No significant differences were observed either in adipokines concentration or in B-cell-associated molecules among the three study groups.

Conclusion

Although more experimental evidence are required, we speculate that the efficacy of treatment of MS with IFN-β is mediated, at least in part, by its ability to work on several levels to slow down the disease progression. Proposed actions include the modulation of IL-1–inflammasome axis and modulation of ACh, B-cell activating factor/a proliferation-inducing ligand system, and several adipokines.

Ethanol-mediated suppression of IL-37 licenses alcoholic liver disease

BACKGROUND & AIMS

Chronic alcohol consumption and alcoholic liver disease (ALD) afflicts individuals with substantial morbidity and mortality with limited treatment options available. Hepatic inflammation, triggered by activated Kupffer cells, is a driving force in alcoholic liver disease. Interleukin 37 (IL-37) exerts anti-inflammatory effects in hepatic diseases, however, the impact of Interleukin 37 on alcoholic liver disease is unknown. In this study, we addressed the role of Interleukin 37 in alcoholic liver disease.

METHODS

We utilized Interleukin 37 expressing transgenic mice and human recombinant Interleukin 37 in models of alcoholic liver disease. Interleukin 37 expression was measured in liver samples of 20 alcoholic steatohepatitis and 36 non-alcoholic fatty liver disease patients.

RESULTS

Interleukin 37 transgenic mice are not protected against hepatic injury and inflammation in alcoholic liver disease. Ethanol suppressed Interleukin 37 expression in transgenic mice. Alcoholic steatohepatitis (ASH) patients similarly exhibited reduced Interleukin 37 expression when compared to non-alcoholic fatty liver disease (NAFLD) patients. Human recombinant Interleukin 37 ameliorated hepatic inflammation in a binge drinking model of alcoholic liver disease.

CONCLUSION

We provide evidence for an exogenous noxae that suppresses Interleukin 37 expression which limits its anti-inflammatory effects in alcoholic liver disease.

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.

A Guide to IL-1 family cytokines in adjuvanticity

Growing awareness of the multiplicity of roles for the IL-1 family in immune regulation has prompted research exploring these cytokines in the context of vaccine-induced immunity. While tightly regulated, cytokines of the IL-1 family are normally released in response to cellular stress and in combination with other danger-/damage-associated molecular patterns (DAMPs), triggering potent local and systemic immune responses. In the context of infection or autoimmunity, engagement of IL-1 family receptors links robust innate responses to adaptive immunity. Clinical and experimental evidence has revealed that many vaccine adjuvants induce the release of one or multiple IL-1 family cytokines. The coordinated release of IL-1 family members in response to adjuvant-induced damage or cell death may be a determining factor in the transition from local inflammation to the induction of an adaptive response. Here, we analyse the effects of IL-1 family cytokines on innate and adaptive immunity with a particular emphasis on activation of antigen-presenting cells and induction of T cell-mediated immunity, and we address in detail the contribution of these cytokines to the modes of action of vaccine adjuvants including those currently approved for human use.

High IL-1R8 expression in breast tumors promotes tumor growth and contributes to impaired antitumor immunity

Tumors develop numerous strategies to fine-tune inflammation and avoid detection and eradication by the immune system. The identification of mechanisms leading to local immune dysregulation is critical to improve cancer therapy. We here demonstrate that Interleukin-1 receptor 8 (IL-1R8 - previously known as SIGIRR/TIR8), a negative regulator of Toll-Like and Interleukin-1 Receptor family signaling, is up-regulated during breast epithelial cell transformation and in primary breast tumors. IL-1R8 expression in transformed breast epithelial cells reduced IL-1-dependent NF-κB activation and production of pro-inflammatory cytokines, inhibited NK cell activation and favored M2-like macrophage polarization. In a murine breast cancer model (MMTV-neu), IL-1R8-deficiency reduced tumor growth and metastasis and was associated with increased mobilization and activation of immune cells, such as NK cells and CD8+ T cells. Finally, immune-gene signature analysis in clinical specimens revealed that high IL-1R8 expression is associated with impaired innate immune sensing and T-cell exclusion from the tumor microenvironment. Our results indicate that high IL-1R8 expression acts as a novel immunomodulatory mechanism leading to dysregulated immunity with important implications for breast cancer immunotherapy.

Unique Action of Interleukin-18 on T Cells and Other Immune Cells

Interleukin (IL)-18 was originally discovered as a factor that enhances interferon (IFN)-γ production by anti-CD3-stimulated Th1 cells, particularly in association with IL-12. IL-12 is a cytokine that induces development of Th1 cells. IL-18 cannot induce Th1 cell development, but has the capacity to activate established Th1 cells to produce IFN-γ in the presence of IL-12. Thus, IL-18 is regarded as a proinflammatory cytokine that facilitates type 1 responses. However, in the absence of IL-12 but presence of IL-2, IL-18 stimulates natural killer cells, NKT cells, and even established Th1 cells to produce IL-3, IL-9, and IL-13. Thus, IL-18 also facilitates type 2 responses. This unique function of IL-18 contributes to infection-associated allergic diseases. Together with IL-3, IL-18 stimulates mast cells and basophils to produce IL-4, IL-13, and chemical mediators such as histamine. Thus, IL-18 also induces innate-type allergic inflammation. IL-18 belongs to the IL-1 family of cytokines, which share similar molecular structures, receptors structures, and signal transduction pathways. Nevertheless, IL-18 shows a unique function by binding to a specific receptor expressed on distinct types of cells. In this review article, I will focus on the unique features of IL-18 in lymphocytes, basophils, and mast cells, particularly in comparison with IL-33.

The Role, Involvement and Function(s) of Interleukin-35 and Interleukin-37 in Disease Pathogenesis

The recently identified cytokines-interleukin (IL)-35 and interleukin (IL)-37-have been described for their anti-inflammatory and immune-modulating actions in numerous inflammatory diseases, auto-immune disorders, malignancies, infectious diseases and sepsis. Either cytokine has been reported to be reduced and in some cases elevated and consequently contributed towards disease pathogenesis. In view of the recent advances in utilizing cytokine profiles for the development of biological macromolecules, beneficial in the management of certain intractable immune-mediated disorders, these recently characterized cytokines (IL-35 and IL-37) offer potential as reasonable targets for the discovery of novel immune-modulating anti-inflammatory therapies. A detailed comprehension of their sophisticated regulatory mechanisms and patterns of expression may provide unique opportunities for clinical application as highly selective and target specific therapeutic agents. This review seeks to summarize the recent advancements in discerning the dynamics, mechanisms, immunoregulatory and anti-inflammatory actions of IL-35 and IL-37 as they relate to disease pathogenesis.

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

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

IL-37 suppresses hepatocellular carcinoma growth by converting pSmad3 signaling from JNK/pSmad3L/c-Myc oncogenic signaling to pSmad3C/P21 tumor-suppressive signaling

IL-37 has been characterized as a fundamental inhibitor of innate immunity and a tumor suppressor in several cancers. However, the molecular mechanism of IL-37 in hepatocellular carcinoma (HCC) is largely unclear. In this study we found IL-37 expression was down-regulated in human HCC tissues and cell lines, and was negatively correlated with tumor size, vascular invasion, as well as overall-survial and disease-free survival (OS and DFS) of HCC. Multivariate Cox analysis revealed that IL-37 was an independent prognostic indicator for OS and DFS in HCC. Functional studies further showed that IL-37 overexpression significantly suppressed tumor growth by confining HCC to G2/M cell cycle arrest in vitro and in vivo. Mechanistically, we determined that IL-37 promoted Smad3 phospho-isoform signaling conversion from JNK/pSmad3L/c-Myc oncogenic signaling to pSmad3C/p21 tumor-suppressive signaling. Consistently, we detected a significant negative correlation between IL-37 expression and pSmad3L levels in a cohort of HCC biopsies; and the expression of pSmad3L predicted poorer outcome. These data highlight the importance of IL-37 in the cell proliferation and progression of HCC, and suggests that IL-37 may be a valuable biomarker for HCC prognosis.

Role of the IL-23/IL-17 Axis in Psoriasis and Psoriatic Arthritis: The Clinical Importance of Its Divergence in Skin and Joints

Psoriasis is a chronic systemic inflammatory disease causing erythematosus and scaly skin plaques; up to 30% of patients with psoriasis develop Psoriatic Arthritis (PsA), which is characterised by inflammation and progressive damage of the peripheral joints and/or the spine and/or the entheses. The pathogenic mechanisms driving the skin disorder in psoriasis and the joint disease in PsA are sustained by the activation of inflammatory pathways that can be overlapping, but also, at least partially, distinct. Cytokines members of the IL-23/IL-17 family, critical in the development of autoimmunity, are abundantly expressed within the cutaneous lesions but also seem to be involved in chronic inflammation and damage of the synovium though, as it will be here discussed, not in all patients. In this review, we will focus on the state of the art of the molecular features of psoriatic skin and joints, focusing on the specific role of the IL-23/IL-17 pathway in each of these anatomical districts. We will then offer an overview of the approved and in-development biologics targeting this axis, emphasising how the availability of the “target” in the diseased tissues could provide a plausible explanation for the heterogeneous clinical efficacy of these drugs, thus opening future perspective of personalised therapies.

Activated Mast Cells Mediate Low-Grade Inflammation in Type 2 Diabetes: Interleukin-37 Could Be Beneficial

Mast cells (MCs) promote guest immune responses to parasites and play a critical role in allergic and inflammatory reactions. Once they have been activated, MCs release highly inflammatory compounds that can provoke serious pathologic signs that can lead to death. MCs generate a number of preformed, de novo synthesized compounds and inflammatory cytokine/chemokine synthesis in response to the high-affinity (Kd=10^-10 M) immunoglobulin E receptor triggering. Circulating MC progenitors migrate into arterial intima and develop lesions, mediating inflammation. They are involved in several disorders, including metabolic diseases, such as type 2 diabetes mellitus, in which endothelial cells release several inflammatory compounds during acute and chronic vascular damage. Certain inflammatory cytokines, such as interleukin (IL)-1 and IL-33, not only are produced by MCs but also may activate them. These effects mediate systemic inflammatory responses in metabolic disorders. Proinflammatory cytokines, such as tumor necrosis factor, IL-33 and IL-6, secreted by MCs and other immune cells, contribute to insulin resistance by activating kinases. IL-37 (IL-1 family member 7), one of the latest cytokines discovered, binds the IL-18 receptor alpha (IL-18Rα) chain and suppresses innate and acquired immunity, with a therapeutic effect. It also inhibits cytokine levels, including IL-6, IL-18, IL-33, tumor necrosis factor and IL-1, and may improve insulin production and, therefore, the pathogenesis of diabetes, stroke and cardiovascular health. This describes a new concept of inhibition of and cure for inflammatory diseases. However, the safety, dosage and tolerability of this novel therapeutic agent, IL-37, still remains to be determined.

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.

Interleukin-37 alleviates airway inflammation and remodeling in asthma via inhibiting the activation of NF-κB and STAT3 signalings

Asthma is a common respiratory inflammatory disorder disease of childhood, and airway smooth muscle cells (ASMCs) play an important role in this disease. Recently, studies have found that interleukin (IL)-37 inhibits allergic airway inflammation of asthmatic mouse models. The aim of this study was to investigate the exact mechanism of IL-37 in asthma. In this study, we found recombinant human IL-37 protein significantly reduced ovalbumin (OVA)-induced airway hyperresponsiveness, inflammatory cell infiltration, the epithelial-mesenchymal-transition (EMT) process, and levels of IL-4, IL-6 and IL-13, but increased interferon (IFN)-γ expression. Moreover, IL-37 treatment remarkably inhibited transforming growth factor (TGF)-β1-induced cell proliferation, migration, EMT, and inflammatory response in ASMCs. IL-37 notably upregulated IκB expression and downregulated levels of NF-κB p65, phospho-NF-κB p65, STAT3 and phospho-STAT3 both in OVA-induced mice and in TGF-β1-stimulated ASMCs. The effects of IL-37 on TGF-β1-induced ASMCs were abrogated by STAT3 upregulation. Additionally, PDTC, a NF-κB inhibitor, showed the similar effects as IL-37 in ASMCs. In conclusion, IL-37 may alleviate airway inflammation and remodeling in asthma through suppressing the activation of NF-κB and STAT3.

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

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

The 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.

Intracellular mature IL-37 suppresses tumor metastasis via inhibiting Rac1 activation

IL-37, a newly found anti-inflammatory cytokine of the IL-1 family, has both extracellular and intracellular functions. Accumulating evidences indicate that it is also involved in tumor progression. However, the mechanism and its intracellular target are unclear. In this study, clinical data from 84 patients showed that loss or reduced expression of IL-37 in lung adenocarcinoma tissues was significantly associated with tumor metastasis. We further provided evidence that IL-37 inhibited effectively tumor metastasis in vitro and in vivo. Moreover, we uncovered a novel mechanism by which IL-37 suppressed tumor cell migration via its intracellular mature form (amino acids 46-218). Intracellular mature form of IL-37, but not its extracellular form, markedly inhibited migration of multiple kinds of tumor cells through inhibiting Rac1 activation. Mechanistically, intracellular mature IL-37 directly bound to the CAAX motif in the C-terminal hypervariable region of Rac1, and then inhibited Rac1 membrane translocation and subsequent downstream signaling. Our research identifies intracellular mature IL-37 as a novel endogenous inhibitor of Rac1. Given the crucial roles of Rac1 in tumor angiogenesis and metastasis, intracellular mature IL-37 might serve as a potential strategy for the control of Rac1 activity and tumor progression.

IL-1R8 is a checkpoint in NK cells regulating anti-tumour and anti-viral activity

Interleukin-1 receptor 8 (IL-1R8, also known as single immunoglobulin IL-1R-related receptor, SIGIRR, or TIR8) is a member of the IL-1 receptor (ILR) family with distinct structural and functional characteristics, acting as a negative regulator of ILR and Toll-like receptor (TLR) downstream signalling pathways and inflammation. Natural killer (NK) cells are innate lymphoid cells which mediate resistance against pathogens and contribute to the activation and orientation of adaptive immune responses. NK cells mediate resistance against haematopoietic neoplasms but are generally considered to play a minor role in solid tumour carcinogenesis. Here we report that IL-1R8 serves as a checkpoint for NK cell maturation and effector function. Its genetic blockade unleashes NK-cell-mediated resistance to hepatic carcinogenesis, haematogenous liver and lung metastasis, and cytomegalovirus infection.

Wandering pathways in the regulation of innate immunity and inflammation

Tumor-associated macrophages (TAM) have served as a paradigm of cancer-related inflammation. Moreover, investigations on TAM have led to the dissection of macrophage plasticity and polarization and to the discovery and analysis of molecular pathways of innate immunity, in particular cytokines, chemokines and PTX3 as a prototypic fluid phase pattern recognition molecule. Mechanisms of negative regulation are complex and include decoy receptors, receptor antagonists, anti-inflammatory cytokines and the signalling regulator IL-1R8. In this review, topics and open issues in relation to regulation of innate immunity and inflammation are discussed: 1) how macrophage and neutrophil plasticity and polarization underlie diverse pathological conditions ranging from autoimmunity to cancer and may pave the way to innovative diagnostic and therapeutic approaches; 2) the key role of decoy receptors and negative regulators (e.g. IL-1R2, ACKR2, IL-1R8) in striking a balance between amplification of immunity and resolution versus uncontrolled inflammation and tissue damage; 3) role of humoral innate immunity, illustrated by PTX3, in resistance against selected microbes, regulation of inflammation and immunity and tissue repair, with implications for diagnostic and therapeutic translation.

IL-1 Family Cytokines Use Distinct Molecular Mechanisms to Signal through Their Shared Co-receptor

Within the interleukin 1 (IL-1) cytokine family, IL-1 receptor accessory protein (IL-1RAcP) is the co-receptor for eight receptor-cytokine pairs, including those involving cytokines IL-1β and IL-33. Unlike IL-1β, IL-33 does not have a signaling complex that includes both its cognate receptor, ST2, and the shared co-receptor IL-1RAcP, which we now present here. Although the IL-1β and IL-33 complexes shared structural features and engaged identical molecular surfaces of IL-1RAcP, these cytokines had starkly different strategies for co-receptor engagement and signal activation. Our data suggest that IL-1β binds to IL-1RI to properly present the cytokine to IL-1RAcP, whereas IL-33 binds to ST2 in order to conformationally constrain the cognate receptor in an IL-1RAcP-receptive state. These findings indicate that members of the IL-1 family of cytokines use distinct molecular mechanisms to signal through their shared co-receptor, and they provide the foundation from which to design new therapies to target IL-33 signaling.

Potential role of IL-37 in atherosclerosis

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

IL-37 is associated with osteoarthritis disease activity and suppresses proinflammatory cytokines production in synovial cells

The objective of this study is to investigate the correlation between IL-37 level and osteoarthritis activity and to determine the anti-inflammatory effects of IL-37 in peripheral blood mononuclear cells (PBMCs) and synovial cells (SCs) from osteoarthritis (OA) patients, which including 32 patients with erosive inflammatory OA (EIOA) and 40 patients with primary generalized OA (PGOA), 40 age and sex matched healthy volunteers were recruited as healthy controls (HCs). The protein and relative mRNA levels of IL-37 were significant increased in the blood of EIOA patients compared with those of PGOA patients and HCs. Serum IL-37 levels of OA patients were positively correlated with VAS score, as well as with CRP, ESR in blood. Positive correlations were also observed among IL-37 with IL-1β, TNF-α and IL-6 in synovial cells. Furthermore, the expression of IL-1β, TNF-α and IL-6 in PBMCs and SCs from EIOA patients was suppressed by IL-37 in vitro. In conclusion, our results indicated that IL-37 increased in EIOA patients and was positively correlated with disease activity, the pro-inflammatory cytokines such as IL-1β, TNF-α and IL-6 in PBMCs and synovial cells from EIOA patients were restrained by recombinant IL-37. Thus, IL-37 may serve as a novel therapeutic target for the treatment of OA inflammation.

Interleukin (IL)-18 Binding Protein Deficiency Disrupts Natural Killer Cell Maturation and Diminishes Circulating IL-18

The cytokine interleukin (IL)-18 is a crucial amplifier of natural killer (NK) cell function. IL-18 signaling is regulated by the inhibitory effects of IL-18 binding protein (IL-18BP). Using mice deficient in IL-18BP (IL-18BPKO), we investigated the impact of mismanaged IL-18 signaling on NK cells. We found an overall reduced abundance of splenic NK cells in the absence of IL-18BP. Closer examination of NK cell subsets in spleen and bone marrow using CD27 and CD11b expression revealed that immature NK cells were increased in abundance, while the mature population of NK cells was reduced. Also, NK cells were polarized to greater production of TNF-α, while dedicated IFN-γ producers were reduced. A novel subset of IL-18 receptor α- NK cells contributed to the expansion of immature NK cells in IL-18BPKO mice. Splenocytes cultured with IL-18 resulted in alterations similar to those observed in IL-18BP deficiency. NK cell changes were associated with significantly reduced levels of circulating plasma IL-18. However, IL-18BPKO mice exhibited normal weight gain and responded to LPS challenge with a >10-fold increase in IFN-γ compared to wild type. Finally, we identified that the source of splenic IL-18BP was among dendritic cells/macrophage localized to the T cell-rich regions of the spleen. Our results demonstrate that IL-18BP is required for normal NK cell abundance and function and also contributes to maintaining steady-state levels of circulating IL-18. Thus, IL-18BP appears to have functions suggestive of a carrier protein, not just an inhibitor.

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.