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

Spaceflight effects on human vascular smooth muscle cell phenotype and function

The cardiovascular system is strongly impacted by the hazards of spaceflight. Astronauts spending steadily increasing lengths of time in microgravity are subject to cardiovascular deconditioning resulting in loss of vascular tone, reduced total blood volume, and diminished cardiac output. Appreciating the mechanisms by which the cells of the vasculature are altered during spaceflight will be integral to understanding and combating these deleterious effects as the human presence in space advances. In this study, we performed RNA-Seq analysis coupled with review by QIAGEN Ingenuity Pathway Analysis software on human aortic smooth muscle cells (HASMCs) cultured for 3 days in microgravity and aboard the International Space Station to assess the transcriptomic changes that occur during spaceflight. The results of our RNA-Seq analysis show that SMCs undergo a wide range of transcriptional alteration while in space, significantly affecting 4422 genes. SMCs largely down-regulate markers of the contractile, synthetic, and osteogenic phenotypes including smooth muscle alpha actin (αSMA), matrix metalloproteinases (MMPs), and bone morphogenic proteins (BMPs). Additionally, components of several cellular signaling pathways were strongly impacted including the STAT3, NFκB, PI3K/AKT, HIF1α, and Endothelin pathways. This study highlights the significant changes in transcriptional behavior SMCs exhibit during spaceflight and puts these changes in context to better understand vascular function in space.

A Critical Appraisal of the Diagnostic and Prognostic Utility of the Anti-Inflammatory Marker IL-37 in a Clinical Setting: A Case Study of Patients with Diabetes Type 2

BACKGROUND

The role of the cytokine interleukin-37 (IL-37) has been recognized in reversing inflammation-mediated metabolic costs. The aim was to evaluate the clinical utility of this cytokine as a diagnostic and prognostic marker in patients with type 2 diabetes (T2D).

METHODS

We included 170 older (median: 66 years) individuals with T2D (females: 95) and classified as primary care attenders to assess the association of factors that describe patients with plasma IL-37 levels (expressed as quartiles) using multinomial regression models. We determined the diagnostic ability of IL-37 cut-offs to identify diabetes-related complications or patient subgroups by using Receiver Operating Characteristic analysis (c-statistics).

RESULTS

Frailty status was shown to have a suppressive effect on IL-37 circulating levels and a major modifying effect on associations of metabolic and inflammatory factors with IL-37, including the effects of treatments. Situations in which IL-37 reached a clinically significant discriminating ability included the model of IL-37 and C-Reactive Protein in differentiating among diabetic patients with low-normal/high BMI ((<25/≥25 kg/m2), and the model of IL-37 and Thyroid Stimulating Hormone in discriminating between women with/without metabolic syndrome.

CONCLUSIONS

The study has revealed limitations in using classical approaches in determining the diagnostic and prognostic utility of the cytokine IL-37 in patients with T2D and lain a foundation for new methodology approaches.

NLRP3 inflammasome triggers interleukin-37 release from human monocytes

IL-37 is an anti-inflammatory member of the IL-1 family that dampens inflammation associated with many noncommunicable diseases. However, mechanisms of IL-37 regulation remain understudied. We aimed to investigate the enzymatic cleavage of IL-37 that potentiates extracellular signalling, as well as pathways of IL-37 secretion. In human monocytes, mature IL-37 (mIL-37) was released following canonical NLRP3 inflammasome activation. The release of IL-37 was blocked by inhibiting plasma membrane permeability and in gasdermin-D-deficient THP-1 cells. While the cleavage of IL-37 was found to be constitutive, the release of mIL-37 was blocked in NLRP3-deficient THP-1 cells and by NLRP3 inhibitor MCC950 in THP-1s and primary human monocytes. IL-37 secretion also occurred after 18-h exposure to LPS, independently of the alternative NLRP3 inflammasome. This LPS-dependent IL-37 secretion required plasma membrane permeability, but not conventional protein secretion apparatus. Mutagenesis of the suggested caspase-1 cleavage site (D20) or the proposed alternative cleavage site (V46) did not completely block IL-37 processing. Therefore, we propose a novel pathway in which IL-37 is cleaved by caspase-1-independent mechanisms and released following canonical and alternative NLRP3 inflammasome triggers by differential pathways.

Cross-Talk between the Cytokine IL-37 and Thyroid Hormones in Modulating Chronic Inflammation Associated with Target Organ Damage in Age-Related Metabolic and Vascular Conditions

Chronic inflammation is considered to be the main mechanism contributing to the development of age-related metabolic and vascular conditions. The phases of chronic inflammation that mediate the progression of target organ damage in these conditions are poorly known, however. In particular, there is a paucity of data on the link between chronic inflammation and metabolic disorders. Based on some of our own results and recent developments in our understanding of age-related inflammation as a whole-body response, we discuss the hypothesis that cross-talk between the cytokine IL-37 and thyroid hormones could be the key regulatory mechanism that justifies the metabolic effects of chronic tissue-related inflammation. The cytokine IL-37 is emerging as a strong natural suppressor of the chronic innate immune response. The effect of this cytokine has been identified in reversing metabolic costs of chronic inflammation. Thyroid hormones are known to regulate energy metabolism. There is a close link between thyroid function and inflammation in elderly individuals. Nonlinear associations between IL-37 and thyroid hormones, considered within the wider clinical context, can improve our understanding of the phases of chronic inflammation that are associated with target organ damage in age-related metabolic and vascular conditions.

Transcriptome-based identification of novel endotypes in adult atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a frequent and heterogeneous inflammatory skin disease, for which personalized medicine remains a challenge. High-throughput approaches have improved understanding of the complex pathophysiology of AD. However, a purely data-driven AD classification is still lacking.

METHODS

To address this question, we applied an original unsupervised approach on the largest available transcriptome dataset of AD lesional (n = 82) and healthy (n = 213) skin biopsies.

RESULTS

Taking into account pathological and physiological state, a variance-based filtering revealed 222 AD-specific hyper-variable genes that efficiently classified the AD samples into 4 clusters that turned out to be clinically and biologically distinct. Comparison of gene expressions between clusters identified 3 sets of upregulated genes used to derive metagenes (MGs): MG-I (19 genes) was associated with IL-1 family signaling (including IL-36A and 36G) and skin remodeling, MG-II (23 genes) with negative immune regulation (including IL-34 and 37) and skin architecture, and MG-III (17 genes) with B lymphocyte immunity. Sample clusters differed in terms of disease severity (p = .02) and S. aureus (SA) colonization (p = .02). Cluster 1 contained the most severe AD, highest SA colonization, and overexpressed MG-I. Cluster 2 was characterized by less severe AD, low SA colonization, and high MG-II expression. Cluster 3 included mild AD, mild SA colonization, and mild expression of all MGs. Cluster 4 had the same clinical features as cluster 3 but had hyper-expression of MG-III. Last, we successfully validated our method and results in an independent cohort.

CONCLUSION

Our study revealed unrecognized AD endotypes with specific underlying biological pathways, highlighting novel pathophysiological mechanisms. These data could provide new insights into personalized treatment strategies.

Interleukin-37: A Link Between COVID-19, Diabetes, and the Black Fungus

The COVID-19 pandemic involved millions of people and diabetes was identified as an associated comorbidity. Initiation of systemic corticosteroids in patients suffering from severe COVID-19 was associated with lower mortality. A surge of invasive fungal infections of the maxillofacial region, namely mucormycosis, was linked to a deadly infection known as black fungus. Black fungus, diabetes, corticosteroids, and coronavirus disease 2019 (COVID-19) all have a dysregulated immune response in common, which partly could also be attributed to interleukin 37 (IL-37). IL-37, a new cytokine of the IL-1 family, known for broadly reducing innate inflammation as well as acquired immune responses. The use of corticosteroids in diabetic COVID-19 patients, crowded hospitals, and lack of medical oxygen should be carefully considered to reduce COVID-associated secondary infections.

Immunobiological Properties and Clinical Applications of Interleukin-38 for Immune-Mediated Disorders: A Systematic Review Study

Exponential growth in the usage of "cytokines" (as seroimmunobiomarkers) has facilitated more accurate prognosis, early diagnosis, novel, and efficient immunotherapeutics. Numerous studies have reported immunopathophysiological and immunopathological processes of interleukin-38 (IL-38). Therefore, in this systematic review article, the authors aimed to present an updated comprehensive overview on the immunobiological mechanisms, diagnostic, and immune gene-based therapeutic potentials of IL-38. According to our inclusion and exclusion criteria, a total of 216 articles were collected from several search engines and databases from the January 2012 to July 2021 time interval by using six main keywords. Physiologic or pathologic microenvironments, optimal dosage, and involved receptors affect the functionalities of IL-38. Alterations in serum levels of IL-38 play a major role in the immunopathogenesis of a wide array of immune-mediated disorders. IL-38 shows anti-inflammatory activities by reduction or inhibition of pro-inflammatory cytokines, supporting the therapeutic aspects of IL-38 in inflammatory autoimmune diseases. According to the importance of pre-clinical studies, it seems that manipulation of the immune system by immunomodulatory properties of IL-38 can increase the accuracy of diagnosis, and decipher optimal clinical outcomes. To promote our knowledge, more collaboration is highly recommended among laboratory scientists, internal/infectious diseases specialists, oncologists, immunologists, diseases-specific biomarkers scientists, and basic medical researchers.

Activation of CpG-ODN-Induced TLR9 Signaling Inhibited by Interleukin-37 in U937 Human Macrophages

PURPOSE

Interleukin-37 (IL-37) is an anti-inflammatory cytokine that inhibits a broad spectrum of inflammatory responses in various human cells, including neutrophils, macrophages, and endothelial cells. The aim of this study was to identify the role of IL-37 in toll-like receptor 9 (TLR9) signaling in human macrophages.

MATERIALS AND METHODS

Human macrophage U937 cells treated with CpG-oligonucleotides (CpG-ODN), recombinant IL-37, or dexamethasone were used in an in vitro study. IL-37 small interfering RNA (siRNA) and TLR9 siRNA were used to silence endogenous IL-37 and TLR9, respectively. Expression levels of phosphorylated nuclear factor-κB (NF-κB), IκBα, IL-37, IL-1β, tumor necrosis factor-α (TNF-α), and IL-6 protein were assessed by real-time quantitative polymerase chain reaction and Western blotting. CpG-ODN-mediated IL-37 expression stimulated by dexamethasone was detected using immunofluorescent analysis.

RESULTS

U937 cells treated with CpG-ODN induced activation of the NF-κB pathway and increased the expression of the pro-inflammatory cytokines IL-1β, TNF-α, and IL-6, but reduced that of IL-37. Recombinant IL-37 attenuated phosphorylation of NF-κB and IκBα and the expression of IL-1β, TNF-α, and IL-6 stimulated by CpG-ODN. Human macrophages transfected with IL-37 siRNA augmented the expression of IL-1β, TNF-α, and IL-6 mRNA and protein in cells treated with CpG-ODN. Dexamethasone markedly inhibited expression of pro-inflammatory cytokines in U937 cells, whereas IL-37 expression was increased with the addition of dexamethasone. Inflammatory responses elicited by CpG-ODN were dependent on an MyD88-TRAF6 pathway. IL-37 inhibited CpG-ODN-induced ubiquitination of TRAF6 in U937 macrophages.

CONCLUSION

IL-37 inhibits CpG-ODN-mediated inflammatory responses through regulation of a TRAF6-NF-κB pathway in human macrophages.

Single-cell RNA-seq reveals a critical role of novel pro-inflammatory EndMT in mediating adverse remodeling in coronary artery-on-a-chip

A three-dimensional microengineered human coronary artery-on-a-chip was developed for investigation of the mechanism by which low and oscillatory shear stress (OSS) induces pro-atherogenic changes. Single-cell RNA sequencing revealed that OSS induced distinct changes in endothelial cells (ECs) including pro-inflammatory endothelial-to-mesenchymal transition (EndMT). OSS promoted pro-inflammatory EndMT through the Notch1/p38 MAPK-NF-κB signaling axis. Moreover, OSS-induced EC phenotypic changes resulted in proliferation and extracellular matrix (ECM) protein up-regulation in smooth muscle cells (SMCs) through the RANTES-mediated paracrine mechanism. IL-37 suppressed OSS-induced pro-inflammatory EndMT and thereby abrogated SMC proliferation and ECM protein remodeling. Overall, this study provides insights into endothelial heterogeneity under atheroprone shear stress and identifies the mechanistic role of a novel EC subtype in promoting adverse vascular remodeling. Further, this study demonstrates that anti-inflammatory approach is capable of mitigating vascular pathobiology evoked by atheroprone shear stress.

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

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

Elevated levels of interleukin-35 and interleukin-37 in adult patients with obstructive sleep apnea

Background

Systemic inflammation has a critical role in the pathogenesis of obstructive sleep apnea (OSA). Interleukin (IL)‐35 and IL‐37 have been identified as novel immune‐modulating cytokines with anti‐inflammatory activities in numerous types of inflammatory disease. The present study aimed to examine the serum levels of IL‐35 and IL‐37 in patients with OSA, and to investigate their associations with the severity of OSA.

Methods

A total of 97 patients, including 67 cases of OSA and 30 age‐ and gender‐matched healthy control subjects, were enrolled in the present study. All subjects were evaluated by overnight polysomnography. Serum IL‐35, IL‐37, and pro‐inflammatory cytokine IL‐1β levels were examined by ELISA.

Results

Compared with those in the control subjects, serum IL‐35, IL‐37, and IL‐1β levels were significantly elevated in patients with mild, moderate, or severe OSA. Furthermore, a severity‐dependent increase in serum IL‐35 and IL‐37 levels was observed in patients with OSA. IL‐35 and IL‐37 levels were positively correlated with the apnea‐hypopnea index (r = 0.742 and 0.578, respectively; both p < 0.001), while they were negatively correlated with the mean oxygen saturation (r = −0.461 and −0.339, respectively; both p < 0.001) and lowest oxyhaemoglobin saturation (r = −0.616 and −0.463, respectively; both p < 0.001) in patients with OSA. In addition, a positive correlation was observed between IL‐35 or IL‐37 and IL‐1β levels (all p < 0.001).

Conclusion

The serum levels of IL‐35 and IL‐37 were significantly increased in patients with OSA and associated with the severity of OSA, implying that IL‐35 and IL‐37 may have a protective role in OSA by counteracting inflammatory responses.

Cytokine Storm and Mucus Hypersecretion in COVID-19: Review of Mechanisms

Mucus is an integral part of the respiratory physiology. It protects the respiratory tract by acting as a physical barrier against inhaled particles and microbes. Excessive inflammation in conditions such as COVID-19 can result in over-production of mucus which obstructs the airway. Build-up of mucus can also contribute to recurrent airway infection, causing further obstruction. This article summarizes the current understanding and knowledge of respiratory mucus production and proposes the role of cytokine storm in inducing sudden mucus hypersecretion in COVID-19. Based on these cascades, the active constituents that inhibit or activate several potential targets are outlined for further research. These may be explored for the discovery and design of drugs to combat cytokine storm and its ensuing complications.

Extracellular and nuclear roles of IL-37 after spinal cord injury

Interleukin 37 (IL-37) is an anti-inflammatory cytokine of the interleukin 1 family. Transgenic mice expressing the human form of the IL37 gene (hIL-37Tg) display protective effects in several animal models of disease. Previous data from our group revealed that IL-37 limits inflammation after spinal cord injury (SCI) and ameliorates tissue damage and functional deficits. IL-37 can exert its anti-inflammatory effects by translocating to the nucleus or acting as an extracellular cytokine. However, whether this protection after SCI is mediated by translocating to the nucleus, activating of extracellular receptors, or both, is currently unknown. In the present study, we used different transgenic animals to answer this question. We demonstrated that the beneficial effects of IL-37 on functional and histological outcomes after SCI were lost in the lack of the extracellular receptor IL-1R8, indicating that IL-37 induces protection as an extracellular cytokine. On the other hand, transgenic mice with the nuclear function of IL-37 abolished (hIL-37D20ATg) showed significant improvement in locomotor skills and myelin sparing after SCI, indicating that nuclear pathway is not required for the protective actions of IL-37. Moreover, we also showed that the therapeutic effects of the recombinant IL-37 protein are produced only in the presence of the extracellular receptor IL-1R8, further highlighting the importance of the extracellular function of this cytokine after SCI. Finally, we revealed that the administration of recombinant IL-37 protein exerted therapeutic actions when administered in the lesion site but not systemically. This work demonstrated for the first time that translocation of IL-37 to the nucleus is not required for the beneficial actions of this cytokine after SCI and highlights the importance of the extracellular signaling of IL-37 to mediate neuroprotective actions.

Molecular and Immunological Mechanisms of Miana Leaf (Coleus Scutellariodes [L] Benth) in Infectious Diseases

Infectious disease is still a massive world burden of disease. It causes premature mortality and morbidity. Regardless of antibiotic therapy, the increased numbers of antibiotic resistance bring emerging problems in infectious disease. Several pathogens have unique roles to deactivate host immune response causing difficulty to treat the infection. Alack of antibiotic efficacy is crucial to modulate the immune response as a brilliant strategy to face infectious disease in years to come. Various herbal medicine has been known to have a pivotal role in enhancing immune response at the molecular level. Miana leaves extract (MLE) has a potential role in regulating the immune response to the infection. Besides its antimicrobial effect, MLE has other properties such as anti-inflammation, antioxidant. Several studies have revealedthe molecular mechanism of MLE in immune response, such as enhancing IL 37, IL 10, regulating TLR 4, and IFN-g. The objectives of this article are to review the molecular and immunological mechanism of Miana in treating various infective diseases comprehensively.

Antiviral properties of placental growth factors: A novel therapeutic approach for COVID-19 treatment

The current challenge of the COVID-19 pandemic is complicated by the limited therapeutic options against the virus, with many being anecdotal or still undergoing confirmatory trials, underlining the urgent need for novel strategies targeting the virus. The pulmotropic virus causes loss of oxygenation in severe cases with acute respiratory distress syndrome (ARDS) and need for mechanical ventilation. This work seeks to introduce placental extract-derived biologically active components as a therapeutic option and highlights their mechanism of action relevant to COVID-19 virus. Human placenta has been used in clinical practice for over a century and there is substantial experience in clinical applications of placental extract for different indications. Aqueous extract of human placentacontains growth factors, cytokines/chemokines, natural metabolic and other compounds, anti-oxidants, amino acids, vitamins, trace elements and biomolecules, which individually or in combination show accelerated cellular metabolism, immunomodulatory and anti-inflammatory effects, cellular proliferation and stimulation of tissue regeneration processes. Placental extract treatment is proposed as a suitable therapeutic approach consideringthe above properties which could protect against initial viral entry and acute inflammation of alveolar epithelial cells, reconstitute pulmonary microenvironment and regenerate the lung. We reviewed useful therapeutic information of placental biomolecules in relation to COVID-19 treatment. We propose the new approach of using placental growth factors, chemokines and cytokine which will execute antiviral activity in coordination with innate and humoral immunity and improve patient's immunological responses to COVID-19. Executing a clinical trial using placental extract as preventive, protective and/or therapeutic approach for COVID-19treatment could advance the development of a most promising therapeutic candidate that can join the armamentaria against the COVID-19 virus.

Plasma levels of IL-1β and IL-37 in patients with severe haemophilia

Objective

Haemophilia A and B are disorders caused by the lack of clotting factors VIII and IX, respectively. Repeated bleeding into the same joint leads to haemophilic arthropathy (HA). Interleukin (IL)-1β is responsible for the pro-inflammatory response and IL-37 is induced by IL-1β stimuli to have an anti-inflammatory response and prevent uncontrolled inflammation and tissue damage. Our objective was to investigate plasma levels of IL-1β and IL-37 in patients with severe haemophilia with different severities of HA.

Methods

Peripheral blood samples were collected from 14 patients with severe haemophilia A and 6 with severe haemophilia B, and 18 healthy individuals. Plasma levels of IL-1β and IL-37 were detected by immunoassay, and severity of HA was evaluated using the Pettersson scoring system. Plasma levels of IL-1β and IL-37 were analysed in patients with severe haemophilia grouped by Pettersson score and in healthy individuals.

Results

Plasma levels of IL-1β and IL-37 were significantly higher in patients with severe haemophilia compared with healthy individuals and significantly lower in those with moderate to severe HA than in those with no or mild HA.

Conclusions

Plasma levels of IL-1β and IL-37 may be useful to track HA progression in patients with severe haemophilia.

Interleukin-18, Functional IL-18 Receptor and IL-18 Binding Protein Expression in Active and Latent Tuberculosis

A thorough understanding of the processes modulating the innate and acquired immune response to Mycobacterium tuberculosis (M.tb) infection in the context of gene expression is still a scientific and diagnostic problem. The study was aimed to assess IL-18, IL-18 binding protein (IL-18BP), IL-18R, IFN-γ, and IL-37 mRNA expression in patients with active tuberculosis (ATB) and healthy volunteers with latent M.tb-infection (LTB) or M.tb-uninfected healthy controls (Control). The relative mRNA expression was assessed in the buffy coat blood fraction using the qPCR method. In total, 97 BCG-vaccinated Polish adults were enrolled in the study. The relative expression of IL-18 and IL-18BP mRNA was significantly elevated in the ATB and LTB groups. In ATB, but not LTB individuals, the overexpression of IL-18 and IL-18BP, as well as a significant increase in IFN-γ mRNA expression, might be considered as a manifestation of active tuberculosis disease. No statistically significant differences were observed in the IL-37 mRNA expression among the studied groups. Particularly noteworthy is the outstanding reduction in the relative expression of IL-18R mRNA in the LTB group as compared to the ATB and Control group. Reduced expression of IL-18R in LTB group may, at least partially, prevent the development of a pathological inflammatory reaction and promote the maintenance of homeostatic conditions between host immunity and M.tb.

In Silico and In Vivo Analysis of IL37 in Multiple Sclerosis Reveals Its Probable Homeostatic Role on the Clinical Activity, Disability, and Treatment with Fingolimod

We evaluated the in silico expression and circulating levels of interleukin (IL)37 in patients with different forms of multiple sclerosis (MS) and also upon treatment with different disease-modifying drugs. The combined interpretation of the resulting data strengthens and extends the current emerging concept that endogenous IL37 plays an important role in determining onset and progression of MS. The in silico analysis revealed that production of IL37 from cluster of differentiation (CD)4+ T cells from MS patients was reduced in vitro as compared to healthy controls. The analysis of the datasets also demonstrated that “higher” levels of IL37 production from PBMC entailed significant protection from MS relapses. In addition, the in vivo part of the study showed that IL37 was selectively augmented in the sera of MS patients during a relapse and that treatment with the high potency disease-modifying drug fingolimod significantly increased the frequency of patients with circulating blood levels of IL37 (6/9, 66%) as compared to patients receiving no treatment (n = 48) or platform therapy (n = 59) who had levels of IL37 below the limit of the sensitivity of the assay. This finding therefore anticipates that fingolimod may at least partially exert its beneficial effects in MS by upregulating the production of IL37.

Interleukin-37 Ameliorates Influenza Pneumonia by Attenuating Macrophage Cytokine Production in a MAPK-Dependent Manner

Viral pneumonitis caused by influenza A (H1N1) virus leads to high levels of morbidity and mortality. Given the limited treatment options for severe influenza pneumonia, it is necessary to explore effective amelioration approaches. Interleukin-37 (IL-37) has been reported to inhibit excessive immune responses and protect against a variety of inflammatory diseases. In this study, by using BALB/c mice intranasally infected with A/California/07/2009 (H1N1), we found that IL-37 treatment increases the survival rate and body weight, and reduces the pulmonary index, impaired the lung injury and decreased production of pro-inflammatory cytokines in the BALF and lung tissue. Moreover, IL-37 administration enhanced not only the percentage of macrophages, but also the percentage of IL-18Rα⁺ macrophages, suggesting that enhancing the macrophages function may improve outcomes in a murine model of H1N1 infection. Indeed, macrophages depletion reduced the protective effect of IL-37 during H1N1 infection. Furthermore, IL-37 administration inhibited MAPK signaling in RAW264.7 cells infected with H1N1. This study demonstrates that IL-37 treatment can ameliorate influenza pneumonia by attenuating cytokine production, especially by macrophages. Thus, IL-37 might serve as a promising new target for the treatment of influenza A-induced pneumonia.

IL-37 increases in patients after ischemic stroke and protects from inflammatory brain injury, motor impairment and lung infection in mice

Post-stroke inflammation may contribute to secondary brain injury and systemic immunosuppression. Interleukin(IL)-37 is an immunosuppressive cytokine belonging to the IL-1 superfamily with no mouse homologue yet identified, the effects of which have not been studied in stroke. Here we report: (1) the effect of ischemic stroke on circulating IL-37 in humans; and (2) the effect of IL-37 on stroke outcome measures in mice transgenic for human IL-37 (IL-37tg). We found that in the first 3 days after ischemic stroke in 55 patients, the plasma abundance of IL-37 was ~2-fold higher than in 24 controls. In IL-37tg mice, cerebral ischemia-reperfusion resulted in marked increases in plasma IL-37 (~9-fold) and brain IL-37 mRNA (~7,000-fold) at 24 h compared with sham-operated IL-37tg mice. Further, compared with wild-type (WT) mice subjected to cerebral ischemia-reperfusion, IL-37tg mice exhibited less severe locomotor deficit, smaller cerebral infarcts and reduced bacterial lung infection. In the ischemic hemisphere, there were 60% fewer pro-inflammatory microglia-macrophages and up to 4-fold higher expression of anti-inflammatory markers in IL-37tg compared to WT mice. Our data show that IL-37 expression is increased following ischemic stroke in humans and IL-37tg mice, and may exert protective effects by modulating post-stroke inflammation in the brain and periphery.