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

Interleukin-37 exacerbates liver inflammation and promotes IFN-γ production in NK cells

Interleukin (IL)-37, a unique member of the IL-1 family, is known for its anti-inflammatory properties. However, its effects on immune-mediated liver diseases, such as primary biliary cholangitis (PBC) and acute immune-mediated hepatitis, remain unclear. Using mouse models of autoimmune cholangitis and hepatitis induced by 2-OA-OVA and concanavalin A (Con A) respectively, we introduced the human IL-37 gene via a liver-preferred adeno-associated virus vector (AAV-IL-37) to mice, as mice lack endogenous IL-37. Our findings reveal that IL-37 did not affect autoimmune cholangitis. Surprisingly, IL-37 exacerbated inflammation in Con A-induced hepatitis rather than mitigating it. Mechanistic insights suggest that this exacerbation involves the interferon (IFN)-γ pathway, supported by elevated serum IFN-γ levels in AAV-IL-37-treated Con A mice. Specifically, IL-37 heightened the number of hepatic NK and NKT cells, increased the production of the NK cell chemoattractant CCL5, and elevated the frequency of hepatic NK and NKT cells expressing IFN-γ. Moreover, IL-37 enhanced IFN-γ secretion from NK cells when combined with other proinflammatory cytokines, highlighting its synergistic effect in promoting IFN-γ production. These unexpected outcomes underscore a novel role for IL-37 in exacerbating liver inflammation during immune-mediated liver diseases, implicating its influence on NK cells and the production of IFN-γ by these cells.

The role of IL-37 in gastrointestinal diseases

Gastrointestinal mucosal surface is frequently under challenge due to it's the large surface area and most common entry of microbes. IL-37, an anti-inflammatory cytokine, regulates local and systemic host immunity. H. pylori infection leads to the inhibition of IL-37 in the gastric mucosa, contributing to heightened mucosal inflammation and destruction, thereby facilitating increased proliferation of H. pylori. Food allergy, due to immune dysregulation, also contribute to GI injury. On the other hand, elevated levels of IL-37 observed in gastric cancer patients align with reduced host immunity at the cellular and humoral levels, indicating that IL-37 may contribute to the development of gastric cancer via suppressing pro-inflammatory responses. While IL-37 provides protection in an IBD animal model, the detection of highly produced IL-37 in IBD patients suggests a stage-dependent role, being protective in acute inflammation but potentially exacerbates the development of IBD in chronic conditions. Moreover, elevated colonic IL-37 in CRC correlates with overall survival time and disease time, indicating a protective role for IL-37 in CRC. The differential regulation and expression of IL-37 between upper- and lower-GI organs may be attributed to variations in the microbial flora. This information suggests that IL-37 could be a potential therapeutic agent, depending on the stage and location.

A Narrative Review of the IL-18 and IL-37 Implications in the Pathogenesis of Atopic Dermatitis and Psoriasis: Prospective Treatment Targets

Atopic dermatitis and psoriasis are prevalent inflammatory skin conditions that significantly impact the quality of life of patients, with diverse treatment options available. Despite advances in understanding their underlying mechanisms, recent research highlights the significance of interleukins IL-18 and IL-37, in Th1, Th2, and Th17 inflammatory responses, closely associated with the pathogenesis of psoriasis and atopic dermatitis. Hence, IL-18 and IL-37 could potentially become therapeutic targets. This narrative review synthesizes knowledge on these interleukins, their roles in atopic dermatitis and psoriasis, and emerging treatment strategies. Findings of a literature search up to 30 May 2024, underscore a research gap in IL-37-targeted therapies. Conversely, IL-18-focused treatments have demonstrated promise in adult-onset Still's Disease, warranting further exploration for their potential efficacy in psoriasis and atopic dermatitis.

IL-37 possesses both anti-inflammatory and antiviral effects against Middle East respiratory syndrome coronavirus infection

BACKGROUND

The aim was to elucidate the function of IL-37 in middle east respiratory syndrome coronavirus (MERS-CoV) infection, thereby providing a novel therapeutic strategy for managing the clinical treatment of inflammatory response caused by respiratory virus infection.

METHODS

We investigated the development of MERS by infecting hDPP4 mice with hCoV-EMC (107 TCID50 [50% tissue culture infectious dose]) intranasally. We infected A549 cells with MERS-CoV, which concurrently interfered with IL-37, detecting the viral titer, viral load, and cytokine expression at certain points postinfection. Meanwhile, we administered IL-37 (12.5 μg/kg) intravenously to hDPP4 mice 2 h after MERS-CoV-2 infection and collected the serum and lungs 5 days after infection to investigate the efficacy of IL-37 in MERS-CoV infection.

RESULTS

The viral titer of MERS-CoV-infected A549 cells interfering with IL-37 was significantly reduced by 4.7-fold, and the viral load of MERS-CoV-infected hDPP4 mice was decreased by 59-fold in lung tissue. Furthermore, the administration of IL-37 suppressed inflammatory cytokine and chemokine (monocyte chemoattractant protein 1, interferon-γ, and IL-17A) expression and ameliorated the infiltration of inflammatory cells in hDPP4 mice.

CONCLUSION

IL-37 exhibits protective properties in severe pneumonia induced by MERS-CoV infection. This effect is achieved through attenuation of lung viral load, suppression of inflammatory cytokine secretion, reduction in inflammatory cell infiltration, and mitigation of pulmonary injury.

Therapeutic induction of antigen-specific immune tolerance

The development of therapeutic approaches for the induction of robust, long-lasting and antigen-specific immune tolerance remains an important unmet clinical need for the management of autoimmunity, allergy, organ transplantation and gene therapy. Recent breakthroughs in our understanding of immune tolerance mechanisms have opened new research avenues and therapeutic opportunities in this area. Here, we review mechanisms of immune tolerance and novel methods for its therapeutic induction.

Tape strips detect molecular alterations and cutaneous biomarkers in skin of patients with hidradenitis suppurativa

BACKGROUND

Hidradenitis suppurativa (HS) has a high unmet need for better treatments. Biopsies are considered the gold standard for studying molecular alterations in skin. A reproducible, minimally invasive approach is needed for longitudinal monitoring in trials and in pediatric populations.

OBJECTIVE

To determine whether skin tape strips can detect molecular alterations in HS and identify biomarkers of disease activity.

METHODS

We performed RNA sequencing on tape strips collected from lesional and healthy-appearing (nonlesional) HS skin (n = 22) and healthy controls (n = 21). We correlated the expression of skin biomarkers between tape strips and a previously published gene-signature of HS biopsies.

RESULTS

Tape strips detected upregulation of known HS biomarkers (eg, Interleukin[IL]-17A) in nonlesional and/or lesional skin and also identified novel clinically actionable targets, including OX40 and JAK3. The expression of Th17 and tumor necrosis factor-α pathways were highly correlated between tape strips and biopsies. HS clinical severity was significantly associated with expression of biomarkers (eg tumor necrosis factor-α , IL-17 A/F, OX40, JAK1-3, IL-4R) in HS lesional and/or nonlesional skin.

LIMITATIONS

Sample size. Tape stripping is limited in depth.

CONCLUSION

This study validates tape strips as a minimally-invasive approach to identify cutaneous biomarkers in HS. This provides a novel avenue for monitoring treatment efficacy and a potential step toward individualized therapy in HS.

IL-37 dampens immunosuppressive functions of MDSCs via metabolic reprogramming in the tumor microenvironment

Interleukin-37 (IL-37) has been shown to inhibit tumor growth in various cancer types. However, the immune regulatory function of IL-37 in the tumor microenvironment is unclear. Here, we established a human leukocyte antigen-I (HLA-I)-matched humanized patient-derived xenograft hepatocellular carcinoma (HCC) model and three murine orthotopic HCC models to study the function of IL-37 in the tumor microenvironment. We found that IL-37 inhibited HCC growth and promoted T cell activation. Further study revealed that IL-37 impaired the immunosuppressive capacity of myeloid-derived suppressor cells (MDSCs). Pretreatment of MDSCs with IL-37 before adoptive transfer attenuated their tumor-promoting function in HCC tumor-bearing mice. Moreover, IL-37 promoted both glycolysis and oxidative phosphorylation in MDSCs, resulting in the upregulation of ATP release, which impaired the immunosuppressive capacity of MDSCs. Collectively, we demonstrated that IL-37 inhibited tumor development through dampening MDSCs' immunosuppressive capacity in the tumor microenvironment via metabolic reprogramming, making it a promising target for future cancer immunotherapy.

The role of IL-36 and 37 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has garnered considerable attention due to its morbidity and mortality. Although the precise mechanisms underlying HCC tumorigenesis remain to be elucidated, evidence suggests that host immunity plays a pivotal role in its development. IL-36 and IL-37 are important immunoregulatory cytokines classified as pro-inflammatory and anti-inflammatory respectively. In the context of HCC, the downregulation of intrahepatic IL-36 is inversely correlated with cirrhosis, but positively correlated with 5-year survival rates, suggesting that IL-36 offers protection during HCC development. However, IL-36 may lose its hepatoprotective effects as the disease progresses to HCC in the context of dysregulated immunity in cirrhotic patients. Substantially increased circulating IL-36 in HCC patients is likely a systemic response to HCC stimulation, but is insufficient to suppress progression towards HCC. Intrahepatic IL-37 is suppressed in HCC patients, consistent with the inverse correlation between intrahepatic IL-37 and the level of AFP in HCC patients, suggesting IL-37 exerts hepatoprotection. There is no significant difference in IL-37 among differentiations of HCC or with respect to clinical BCLC stages or cirrhosis status in HCC patients. However, IL-37 protection is demonstrated in an IL-37 transfected HCC animal model, showing significantly reduced tumour size. IL-36/37 may inhibit HCC by enhancing M1 tumour-associated macrophages while not affecting M2 macrophages. The interplay between IL-36 (pro-inflammatory) and IL-37 (anti-inflammatory) is emerging as a crucial factor in host protection against the development of HCC. Further research is needed to investigate the complex mechanisms involved and the therapeutic potential of targeting these cytokines in HCC management.

Interleukin-37 relieves PM2.5-triggered lung injury by inhibiting autophagy through the AKT/mTOR signaling pathway in vivo and in vitro

Autophagy mediates PM2.5-related lung injury (LI) and is tightly linked to inflammation and apoptosis processes. IL-37 has been demonstrated to regulate autophagy. This research aimed to examine the involvement of IL-37 in the progression of PM2.5-related LI and assess whether autophagy serves as a mediator for its effects.To create a model of PM2.5-related LI, this research employed a nose-only PM2.5 exposure system and utilized both human IL-37 transgenic mice and wild-type mice. The hIL-37tg mice demonstrated remarkable reductions in pulmonary inflammation and pathological LI compared to the WT mice. Additionally, they exhibited activation of the AKT/mTOR signaling pathway, which served to regulate the levels of autophagy and apoptosis.Furthermore, in vitro experiments revealed a dose-dependent upregulation of autophagy and apoptotic proteins following exposure to PM2.5 DMSO extraction. Simultaneously, p-AKT and p-mTOR expression was found to decrease. However, pretreatment with IL-37 demonstrated a remarkable reduction in the levels of autophagy and apoptotic proteins, along with an elevation of p-AKT and p-mTOR. Interestingly, pretreatment with rapamycin, an autophagy inducer, weakened the therapeutic impact of IL-37. Conversely, the therapeutic impact of IL-37 was enhanced when treated with 3-MA, a potent autophagy inhibitor. Moreover, the inhibitory effect of IL-37 on autophagy was successfully reversed by administering AKT inhibitor MK2206. The findings suggest that IL-37 can inhibit both the inflammatory response and autophagy, leading to the alleviation of PM2.5-related LI. At the molecular level, IL-37 may exert its anti autophagy and anti apoptosis effects by activating the AKT/mTOR signaling pathway.

Potential Role of IL-37 in Atopic Dermatitis

Interleukin 37 (IL-37) is a recently discovered member of the IL-1 cytokine family that appears to have anti-inflammatory and immunosuppressive effects in various diseases. IL-37 acts as a dual-function cytokine, exerting its effect extracellularly by forming a complex with the receptors IL-18 α (IL-18Rα) and IL-1R8 and transmitting anti-inflammatory signals, as well as intracellularly by interacting with Smad3, entering the nucleus, and inhibiting the transcription of pro-inflammatory genes. Consequently, IL-37 is linked to IL-18, which plays a role in the pathogenesis of atopic dermatitis (AD), consistent with our studies. Some isoforms of IL-37 are expressed by keratinocytes, monocytes, and other skin immune cells. IL-37 has been found to modulate the skewed T helper 2 (Th2) inflammation that is fundamental to the pathogenesis of AD. This review provides an up-to-date summary of the function of IL-37 in modulating the immune system and analyses its potential role in the pathogenesis of AD. Moreover, it speculates on IL-37's hypothetical value as a therapeutic target in the treatment of AD.

The nuclear cytokine IL-37a controls lethal cytokine storms primarily via IL-1R8-independent transcriptional upregulation of PPARγ

Cytokine storms are crucial in the development of various inflammatory diseases, including sepsis and autoimmune disorders. The immunosuppressive cytokine INTERLEUKIN (IL)-37 consists of five isoforms (IL-37a-e). We identified IL-37a as a nuclear cytokine for the first time. Compared to IL-37b, IL-37a demonstrated greater efficacy in protecting against Toll-like receptor-induced cytokine hypersecretion and lethal endotoxic shock. The full-length (FL) form of IL-37a and the N-terminal fragment, which is processed by elastase, could translocate into cell nuclei through a distinctive nuclear localization sequence (NLS)/importin nuclear transport pathway. These forms exerted their regulatory effects independent of the IL-1R8 receptor by transcriptionally upregulating the nuclear receptor peroxisome proliferator-activated receptor (PPARγ). This process involved the recruitment of the H3K4 methyltransferase complex WDR5/MLL4/C/EBPβ and H3K4me1/2 to the enhancer/promoter of Pparg. The receptor-independent regulatory pathway of the nuclear IL-37a-PPARγ axis and receptor-dependent signaling by secreted IL-37a maintain homeostasis and are potential therapeutic targets for various inflammatory diseases, including sepsis.

Novel insights into IL-37: an anti-inflammatory cytokine with emerging roles in anti-cancer process

Interleukin-37 (IL-37) is a newly discovered member of IL-1 family. The cytokine was proved to have extensive protective effects in infectious diseases, allergic diseases, metabolic diseases, autoimmune diseases and tumors since its discovery. IL-37 was mainly produced by immune and some non-immune cells in response to inflammatory stimulus. The IL-37 precursors can convert into the mature forms after caspase-1 cleavage and activation intracellularly, and then bind to Smad-3 and transfer to the nucleus to inhibit the production and functions of proinflammatory cytokines; extracellularly, IL-37 binds to cell surface receptors to form IL-37/IL-18Rα/IL-1R8 complex to exert immunosuppressive function via inhibiting/activating multiple signal pathways. In addition, IL-37 can attenuate the pro-inflammatory effect of IL-18 through directly or forming an IL-37/IL-18BP/IL-18Rβ complex. Therefore, IL-37 has the ability to suppress innate and acquired immunity of the host, and effectively control inflammatory stimulation, which was considered as a new hallmark of cancer. Specifically, it is concluded that IL-37 can inhibit the growth and migration of tumor cells, prohibit angiogenesis and mediate the immunoregulation in tumor microenvironment, so as to exert effective anti-tumor effects. Importantly, latest studies also showed that IL-37 may be a novel therapeutic target for cancer monitoring. In this review, we summarize the immunoregulation roles and mechanisms of IL-37 in anti-tumor process, and discuss its progress so far and potential as tumor immunotherapy.

Regulatory Mechanism of the IL-33-IL-37 Axis via Aryl Hydrocarbon Receptor in Atopic Dermatitis and Psoriasis

Interleukin (IL)-33 and IL-37 have been identified as novel cytokines involved in various inflammatory diseases. However, their specific roles remain largely unknown. Recent studies have shown that IL-33, which triggers inflammation, and IL-37, which suppresses it, cooperatively regulate the balance between inflammation and anti-inflammation. IL-33 and IL-37 are also deeply involved in the pathogenesis of inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis. Furthermore, a signaling pathway by which aryl hydrocarbon receptor (AHR), a receptor for dioxins, regulates the expression of IL-33 and IL-37 has been revealed. Here, we outline recent findings on the mechanisms regulating IL-33 and IL-37 expression in AD and psoriasis. IL-33 expression is partially dependent on mitogen-activated protein kinase (MAPK) activation, and IL-37 has a role in suppressing MAPK in human keratinocytes. Furthermore, IL-33 downregulates skin barrier function proteins including filaggrin and loricrin, thereby downregulating the expression of IL-37, which colocalizes with these proteins. This leads to an imbalance of the IL-33-IL-37 axis, involving increased IL-33 and decreased IL-37, which may be associated with the pathogenesis of AD and psoriasis. Therefore, AHR-mediated regulation of the IL-33-IL-37 axis may lead to new therapeutic strategies for the treatment of AD and psoriasis.

Exogenous Interleukin-37 Alleviates Hepatitis with Reduced Dendritic Cells and Induced Regulatory T Cells in Acute Murine Cytomegalovirus Infection

Human cytomegalovirus (HCMV) infection is globally distributed, and the liver is one of the major targeting organs. So far, the mechanisms for cell and organ damage have not fully been elucidated and the treatments for the infection are mainly at symptoms. IL-37 has shown a protective role in certain inflammatory diseases. In the present study, potential protective effect of exogenous IL-37 on murine cytomegalovirus- (MCMV-) infected hepatitis was evaluated through analyses of serum transaminases, the liver histopathology and cytokine expression, and functional state of dendritic cells (DCs) and regulatory T cells (Tregs). These analyses showed a significant decrease in serum transaminase levels and a lower Ishak histopathologic score at the early stage of MCMV-infected mice with exogenous IL-37 pretreatment. The frequencies of MHC-Ⅱ, CD40, CD80, and CD86 positive DCs in the liver and spleen were decreased significantly at 7 days postinfection (dpi) in MCMV-infected mice with IL-37 pretreatment when compared with those without the pretreatment, while the total number of DCs in the liver was reduced in IL-37-pretreated mice. The induction of Tregs in the spleen was enhanced at dpi 3 with IL-37 pretreatment in MCMV-infected mice. The mRNA expression levels of cytokines in the liver were decreased significantly (IL-1β, IL-6, IL-10, IL-4) or to some extent (TGF-β and TNF-α). The present study suggested that exogenous IL-37 can alleviate MCMV-infected hepatitis, likely through reduced DCs and induced Tregs with a weaker cytokine storm, demonstrating its potential value in clinical management for HCMV-infected hepatitis.

Interleukin-37 promotes DMBA/TPA skin cancer through SIGIRR-mediated inhibition of glycolysis in CD103+DC cells

Interleukin 37 (IL-37), a member of the IL-1 family, is considered a suppressor of innate and adaptive immunity and, hence is a regulator of tumor immunity. However, the specific molecular mechanism and role of IL-37 in skin cancer remain unclear. Here, we report that IL-37b-transgenic mice (IL-37tg) treated with the carcinogenic 7,12-dimethylbenzoanthracene (DMBA)/12-o-tetradecylphorbol-13-acetate (TPA) exhibited enhanced skin cancer and increased tumor burden in the skin by inhibiting the function of CD103+ dendritic cells (DCs). Notably, IL-37 induced rapid phosphorylation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), and via single immunoglobulin IL-1-related receptor (SIGIRR), inhibited the long-term Akt activation. Specifically, by affecting the SIGIRR-AMPK-Akt signaling axis, which is related to the regulation of glycolysis in CD103+DCs, IL-37 inhibited their anti-tumor function. Our results show that a marked correlation between the CD103+DC signature (IRF8, FMS-like tyrosine kinase 3 ligand, CLEC9A, CLNK, XCR1, BATF3, and ZBTB46) and chemokines C-X-C motif chemokine ligand 9, CXCL10, and CD8A in a mouse model with DMBA/TPA-induced skin cancer. In a word, our results highlight that IL-37 as an inhibitor of tumor immune surveillance through modulating CD103+DCs and establishing an important link between metabolism and immunity as a therapeutic target for skin cancer.

A Nanoparticle-Based Anticaries Vaccine Enhances the Persistent Immune Response To Inhibit Streptococcus mutans and Prevent Caries

Caries vaccines have been identified as a good strategy for the prevention of caries through the mechanism of inoculation against Streptococcus mutans, which is the main etiological bacterium causing caries. Protein antigen c (PAc) of S. mutans has been administered as an anticaries vaccine but shows relatively weak immunogenicity to elicit a low-level immune response. Here, we report a zeolitic imidazolate framework-8 nanoparticle (ZIF-8 NP)-based adjuvant with good biocompatibility, pH responsiveness, and high loading performance for PAc that was used as an anticaries vaccine. In this study, we prepared a ZIF-8@PAc anticaries vaccine and investigated the immune responses and anticaries efficacy induced by this vaccine in vitro and in vivo. ZIF-8 NPs substantially improved the internalization of PAc in lysosomes for further processing and presentation to T lymphocytes. In addition, significantly higher IgG antibody titers, cytokine levels, splenocyte proliferation indices, and percentages of mature dendritic cells (DCs) and central memory T cells were detected in mice subcutaneously immunized with ZIF-8@PAc than in mice subcutaneously immunized with PAc alone. Finally, rats were immunized with ZIF-8@PAc, and ZIF-8@PAc elicited a strong immune response to inhibit colonization by S. mutans and improve prophylactic efficacy against caries. Based on the results, ZIF-8 NPs are promising as an adjuvant for anticaries vaccine development. IMPORTANCE Streptococcus mutans is the main etiologic bacterium of dental caries, whose protein antigen c (PAc) has been administered as an anticaries vaccine. However, the immunogenicity of PAc is relatively weak. To improve the immunogenicity of PAc, ZIF-8 NP was used as an adjuvant, and the immune responses and protective effect elicited by ZIF-8@PAc anticaries vaccine were evaluated in vitro and in vivo. The findings will help in prevention of dental caries and provide new insight for the development of anticaries vaccine in the future.

Integrating Untargeted and Targeted Metabolomics Coupled with Pathway Analysis Reveals Muscle Disorder in Osteoporosis on Orchiectomized Mice

Most osteoporosis (OP) fracture accidents in men are due not only to a low BMD but also because of unhealthy muscle support. However, there has been a limited number of reports about how muscle metabolism is disturbed by OP in males. In this work, a pathway analysis based on metabolomic research was carried out to fill this gap. A classical orchiectomy procedure was adapted to create an OP animal model. A micro-CT and pathological section were applied for a bone and muscle phenotype assessment and a pathology analysis. UPLC-Q-TOF/MS and UPLC-QQQ-MS/MS were applied to measure metabolites in skeletal muscle samples among groups. In total, 31 significantly differential metabolites were detected by comparing healthy models and OP animals, and 7 representative metabolites among the 31 significantly differential metabolites were identified and validated experimentally by UPLC-QQQ-MS/MS (xanthine, L-phenylalanine, choline, hypoxanthine, L-tryptophan, succinic acid, and L-tyrosine). An ingenuity pathway analysis (IPA) analysis revealed significantly enriched pathways involved in inflammation, oxidative stress, and necrosis. To our best knowledge, this is the first study to investigate early muscle disorder processes in Cases of OP at a metabolic level, facilitating early intervention and protection from OP fractures for aged men.

The pH-responsive zeolitic imidazolate framework nanoparticle as a promising immune-enhancing adjuvant for anti-caries vaccine

OBJECTIVES

Streptococcus mutans (S. mutans) is the main aetiologic bacterium of dental caries, whose protein antigen (PAc) has been administered as an anti-caries vaccine. In addition, several fusion proteins or PAc combined with adjuvants were used as anti-caries vaccines to improve the relatively weak immunogenicity of PAc. However, there are no nanoparticle-based adjuvants with good biocompatibility, excellent biodegradability, or the high loading performance of antigens used for anti-caries vaccines. This study aimed to prepare an innovative nanoparticle-based anti-caries vaccine and evaluate immune responses elicited by this vaccine in vitro and in vivo.

METHODS

In this study, an anti-caries vaccine was prepared by an antigen of recombinant protein PAc from S. mutans and an adjuvant of zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs) synthesized using a hydrothermal method. Then, mice were administrated intranasally by ZIF-8@PAc vaccine, and immune responses were evaluated.

RESULTS

ZIF-8 NPs not only greatly improved the internalization of the antigen but also released the PAc protein after degradation of ZIF-8 NPs in lysosomes for the further processing and presentation of antigen-presenting cells. In addition, ZIF-8@PAc induced significantly more potent PAc-specific serum IgG and saliva IgA antibodies, a higher splenocyte proliferation index, higher levels of the cytokines IL-4, IL-6, IL-10, IL-17A and IFN-γ, and a higher percentage of mature DCs and CD4⁺ memory T cells in vivo.

CONCLUSIONS

The ZIF-8 NPs, as an anti-caries vaccine adjuvant-assisted antigen PAc, elicit significantly potent immune responses, aiding in the further prevention of dental caries.

CLINICAL SIGNIFICANCE

Vaccine immunotherapy is an attractive strategy for prevention and treatment of dental caries. The ZIF-8@PAc vaccine can induce significantly high level of immune responses in this study, which indicates great potential for prevention and treatment of caries.

Persistent Inflammation in Cerebral Palsy: Pathogenic Mediator or Comorbidity? A Scoping Review

Research has established inflammation in the pathogenesis of brain injury and the risk of developing cerebral palsy (CP). However, it is unclear if inflammation is solely pathogenic and primarily contributes to the acute phase of injury, or if inflammation persists with consequence in CP and may therefore be considered a comorbidity. We conducted a scoping review to identify studies that analyzed inflammatory biomarkers in CP and discuss the role of inflammation in the pathogenesis of CP and/or as a comorbidity. Twelve included studies reported a range of analytes, methods and biomarkers, including indicators of inflammatory status, immune function and genetic changes. The majority of controlled studies concluded that one or more systemic biomarkers of inflammation were significantly different in CP versus controls; most commonly serum or plasma cytokines such as tumor necrosis factor, Interleukin (IL)-6 and IL-10. In addition, differences in inflammation were noted in distinct subgroups of CP (e.g., those with varying severity). The available evidence supports the pathogenic role of inflammation and its ongoing role as a comorbidity of CP. This review shows that inflammation may persist for decades, driving functional impairment across development and into adulthood. However, inflammation is complex, thus further research will increase our understanding.

The role of IL-35 and IL-37 in breast cancer - potential therapeutic targets for precision medicine

Breast cancer is still a major concern due to its relatively poor prognosis in women, although there are many approaches being developed for the management of breast cancer. Extensive studies demonstrate that the development of breast cancer is determined by pro versus anti tumorigenesis factors, which are closely related to host immunity. IL-35 and IL-37, anti-inflammatory cytokines, play an important role in the maintenance of immune homeostasis. The current review focuses on the correlation between clinical presentations and the expression of IL-35 and IL-37, as well as the potential underlying mechanism during the development of breast cancer in vitro and in vivo. IL-35 is inversely correlated the differentiation and prognosis in breast cancer patients; whereas IL-37 shows dual roles during the development of breast cancer, and may be breast cancer stage dependent. Such information might be useful for both basic scientists and medical practitioners in the management of breast cancer patients.

The intellectual base and research fronts of IL-37: A bibliometric review of the literature from WoSCC

Background

IL-37 is a recently identified cytokine with potent immunosuppressive functions. The research fronts of IL-37 are worth investigating, and there is no bibliometric analysis in this field. The purpose of this study is to construct the intellectual base and predict research hotspots of IL-37 research both quantitatively and qualitatively according to bibliometric analysis.

Methods

The articles were downloaded from the Web of Science Core Collection (WoSCC) database from the inception of the database to 1 April 2022. CiteSpace 5.8.R3 (64-bit, Drexel University, Philadelphia, PA, USA) and Online Analysis Platform of Literature Metrology (https://bibliometric.com/) were used to perform bibliometric and knowledge-map analyses.

Results

A total of 534 papers were included in 200 academic journals by 2,783 authors in 279 institutions from 50 countries/regions. The journal Cytokine published the most papers on IL-37, while Nature Immunology was the most co-cited journal. The publications belonged mainly to two categories of Immunology and Cell Biology. USA and China were the most productive countries. Meanwhile, the University of Colorado Denver in USA produced the highest number of publications followed by Radboud University Nijmegen in the Netherlands and Monash University in Australia. Charles A. Dinarello published the most papers, while Marcel F. Nold had the most co-citations. Top 10 co-citations on reviews, mechanisms, and diseases were regarded as the knowledge base. The keyword co-occurrence and co-citations of references revealed that the mechanisms and immune-related disorders were the main aspects of IL-37 research. Notably, the involvement of IL-37 in various disorders and the additional immunomodulatory mechanisms were two emerging hotspots in IL-37 research.

Conclusions

The research on IL-37 was thoroughly reviewed using bibliometrics and knowledge-map analyses. The present study is a benefit for academics to master the dynamic evolution of IL-37 and point out the direction for future research.

IL-37 overexpression promotes endometrial regenerative cell-mediated inhibition of cardiac allograft rejection

BACKGROUND

Endometrial regenerative cells (ERCs) play an important role in attenuation of acute allograft rejection, while their effects are limited. IL-37, a newly discovered immunoregulatory cytokine of the IL-1 family, can regulate both innate and adaptive immunity. Whether IL-37 overexpression can enhance the therapeutic effects of ERCs in inhibition of acute cardiac allograft rejection remains unknown and will be explored in this study.

METHODS

C57BL/6 mice recipients receiving BALB/c mouse heterotopic heart allografts were randomly divided into the phosphate-buffered saline (untreated), ERC treated, negative lentiviral control ERC (NC-ERC) treated, and IL-37 overexpressing ERC (IL-37-ERC) treated groups. Graft pathological changes were assessed by H&E staining. The intra-graft cell infiltration and splenic immune cell populations were analyzed by immunohistochemistry and flow cytometry, respectively. The stimulatory property of recipient DCs was tested by an MLR assay. Furthermore, serum cytokine profiles of recipients were measured by ELISA assay.

RESULTS

Mice treated with IL-37-ERCs achieved significantly prolonged allograft survival compared with the ERC-treated group. Compared with all the other control groups, IL-37-ERC-treated group showed mitigated inflammatory response, a significant increase in tolerogenic dendritic cells (Tol-DCs), regulatory T cells (Tregs) in the grafts and spleens, while a reduction of Th1 and Th17 cell population. Additionally, there was a significant upregulation of immunoregulatory IL-10, while a reduction of IFN-γ, IL-17A, IL-12 was detected in the sera of IL-37-ERC-treated recipients.

CONCLUSION

IL-37 overexpression can promote the therapeutic effects of ERCs to inhibit acute allograft rejection and further prolong graft survival. This study suggests that gene-modified ERCs overexpressing IL-37 may pave the way for novel therapeutic options in the field of transplantation.

Biology of interleukin‑37 and its role in autoimmune diseases (Review)

Autoimmune diseases (AIDs) are characterized by dysfunction and tissue destruction, and recent studies have shown that interleukin (IL)-37 expression is dysregulated in AIDs. Among cytokines of the IL-1 family, most are pro-inflammatory agents, and as an anti-inflammatory cytokine, IL-37 may have the potential to alleviate excessive inflammation and can be used as a ligand or transcription factor that is involved in regulating innate and adaptive immunity. IL-37 plays important roles in the development of AIDs. This review summarizes the biological characteristics and functions of IL-37 and discusses the potential of IL-37 as a therapeutic target for effective cytokine therapy and as a biomarker in AIDs.

IL-37 regulates allergic inflammation by counterbalancing pro-inflammatory IL-1 and IL-33

BACKGROUND

Children with asthma have impaired production of interleukin (IL) 37; in mice, IL-37 reduces hallmarks of experimental allergic asthma (EAA). However, it remains unclear how IL-37 exerts its inhibitory properties in asthma. This study aimed to identify the mechanism(s) by which IL-37 controls allergic inflammation.

METHODS

IL-37 target cells were identified by single-cell RNA-seq of IL-1R5 and IL-1R8. Airway tissues were isolated by laser-capture microdissection and examined by microarray-based gene expression analysis. Mononuclear cells (MNC) and airway epithelial cells (AECs) were isolated and stimulated with allergen, IL-1β, or IL-33 together with recombinant human (rh) IL-37. Wild-type, IL-1R1- and IL-33-deficient mice with EAA were treated with rhIL-37. IL-1β, IL-33, and IL-37 levels were determined in sputum and nasal secretions from adult asthma patients without glucocorticoid therapy.

RESULTS

IL-37 target cells included AECs, T cells, and dendritic cells. In mice with EAA, rhIL-37 led to differential expression of >90 genes induced by IL-1β and IL-33. rhIL-37 reduced production of Th2 cytokines in allergen-activated MNCs from wild-type but not from IL-1R1-deficient mice and inhibited IL-33-induced Th2 cytokine release. Furthermore, rhIL-37 attenuated IL-1β- and IL-33-induced pro-inflammatory mediator expression in murine AEC cultures. In contrast to wild-type mice, hIL-37 had no effect on EAA in IL-1R1- or IL-33-deficient mice. We also observed that expression/production ratios of both IL-1β and IL-33 to IL-37 were dramatically increased in asthma patients compared to healthy controls.

CONCLUSION

IL-37 downregulates allergic airway inflammation by counterbalancing the disease-amplifying effects of IL-1β and IL-33.

The Role of IL-37 and IL-38 in Colorectal Cancer

Colorectal cancer (CRC) is a major killer. Dysregulation of IL-37 and IL-38, both anti-inflammatory cytokines, is observed in auto-immune diseases. The precise regulatory mechanisms of IL-37/IL-38 during the development of CRC remains unclear, but chronic intestinal inflammation is involved in the carcinogenesis of CRC. Constitutive production of colonic IL-37 and IL-38 is substantially reduced in CRC, consistent with an inverse correlation with CRC differentiation. Reduced colonic IL-37 and IL-38 is relating to CRC invasion and distant metastasis, suggesting a protective role for IL-38 within the tumor micro-environment. IL-38 is reduced in right-sided CRC compared to left-sided CRC, which is in line with multiple risk factors for right-sided CRC, including the embryonic development of the colon, and genetic differences in CRC between these two sides. Finally, colonic IL-37 and tumor associated neutrophils (TAN) seem to be independent biomarkers of prognostic value, whereas colonic IL-38 seems to be a reliable and independent biomarker in predicting the 5-year survival post-surgery in CRC. However, there is room for improvement in available studies, including the extension of these studies to different regions/countries incorporating different races, evaluation of the role of multi-drug resistance, and different subsets of CRC. It would be useful to determine the kinetics of circulating IL-38 and its relationship with drug resistance/targeted therapy. The measurement of colonic IL-38 at the molecular and cellular level is required to explore the contribution of IL-38 pathways during the development of CRC. These approaches could provide insight for the development of personalized medicine.

Interleukin-37 promotes colitis-associated carcinogenesis via SIGIRR-mediated cytotoxic T cells dysfunction

Interleukin-37b (hereafter called IL-37) was identified as fundamental inhibitor of natural and acquired immunity. The molecular mechanism and function of IL-37 in colorectal cancer (CRC) has been elusive. Here, we found that IL-37 transgenic (IL-37tg) mice were highly susceptible to colitis-associated colorectal cancer (CAC) and suffered from dramatically increased tumor burdens in colon. Nevertheless, IL-37 is dispensable for intestinal mutagenesis, and CRC cell proliferation, apoptosis, and migration. Notably, IL-37 dampened protective cytotoxic T cell-mediated immunity in CAC and B16-OVA models. CD8⁺ T cell dysfunction is defined by reduced retention and activation as well as failure to proliferate and produce cytotoxic cytokines in IL-37tg mice, enabling tumor evasion of immune surveillance. The dysfunction led by IL-37 antagonizes IL-18-induced proliferation and effector function of CD8⁺ T cells, which was dependent on SIGIRR (single immunoglobulin interleukin-1 receptor-related protein). Finally, we observed that IL-37 levels were significantly increased in CRC patients, and positively correlated with serum CRC biomarker CEA levels, but negatively correlated with the CD8⁺ T cell infiltration in CRC patients. Our findings highlight the role of IL-37 in harnessing antitumor immunity by inactivation of cytotoxic T cells and establish a new defined inhibitory factor IL-37/SIGIRR in cancer-immunity cycle as therapeutic targets in CRC.

The Role of IL-37 and IL-38 in Obstetrics Abnormalities

There are two fairly common complications during pregnancy, i.e., gestational diabetes mellitus (GDM) and pre-eclampsia, which are independent, but are also closely linked in prevalence in pregnant women, with potential serious adverse consequences. IL-37 and IL-38, which belong to the IL-1 superfamily, participate in anti-inflammatory responses. Dysregulation of IL-37 and IL-38 has been observed in many auto-immune diseases. IL-37 is substantially reduced in the umbilical cords and placentas of GDM subjects, but IL-37 is significantly induced in the placentas of pre-eclampsia patients, suggesting there are differential regulatory roles of IL-37 in obstetrics, despite IL-37 being an anti-inflammatory mediator. Furthermore, IL-38 is substantially increased in the umbilical cords and placentas of GDM subjects, but minimal difference is observed in the placentas from pre-eclampsia patients. These data imply that IL-38 is also regulated independently within the diseased placentas. This review provides some insight for both basic scientists and medical practitioners to manage these patients effectively.

Role of IL-37- and IL-37-Treated Dendritic Cells in Acute Coronary Syndrome

As a chronic inflammatory disease, atherosclerosis is a leading cause of morbidity and mortality in most countries. Inflammation is responsible for plaque instability and the subsequent onset of acute coronary syndrome (ACS), which is one of the leading causes of hospitalization. Therefore, exploring the potential mechanism underlying ACS is of considerable concern, and searching for alternative therapeutic targets is very urgent. Interleukin-37 (IL-37) inhibits the production of proinflammatory chemokines and cytokines and acts as a natural inhibitor of innate and adaptive immunity. Interestingly, our previous study with murine models showed that IL-37 alleviated cardiac remodeling and myocardial ischemia/reperfusion injury. Of note, our clinical study revealed that IL-37 is elevated and plays a beneficial role in patients with ACS. Moreover, dendritic cells (DCs) orchestrate both immunity and tolerance, and tolerogenic DCs (tDCs) are characterized by more secretion of immunosuppressive cytokines. As expected, IL-37-treated DCs are tolerogenic. Hence, we speculate that IL-37- or IL-37-treated DCs is a novel therapeutic possibility for ACS, and the precise mechanism of IL-37 requires further study.

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

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

IL-37 overexpression enhances the therapeutic effect of endometrial regenerative cells in concanavalin A-induced hepatitis

BACKGROUND AIMS

Mesenchymal stromal cells and immunosuppressive factor IL-37 can both suppress concanavalin A (Con A)-induced hepatitis in mice. Endometrial regenerative cells (ERCs), novel types of mesenchymal-like stromal cells, possess powerful immunomodulatory effects and are effective in treating various diseases. The aim of this study was to explore the effects of ERCs in suppressing Con A-induced hepatitis and determine whether IL-37 overexpression could enhance the therapeutic effect of ERCs in this process.

METHODS

ERCs were extracted from the menstrual blood of healthy female volunteer donors. The IL-37 gene was transferred into ERCs, and the expression of IL-37 in cells was detected by western blot and enzyme-linked immunosorbent assay. Hepatitis was induced by Con A in C57BL/6 mice that were randomly divided into groups treated with phosphate-buffered saline, ERCs, IL-37 or ERCs transfected with the IL-37 gene (IL-37-ERCs). Cell tracking, liver function, histopathological and immunohistological changes, immune cell proportions and levels of cytokines were measured 24 h after Con A administration.

RESULTS

Compared with ERC or IL-37 treatment, IL-37-ERCs further reduced levels of liver enzymes (alanine aminotransferase and aspartate aminotransferase) and improved histopathological changes in the liver. In addition, IL-37-ERC treatment further reduced the proportions of M1 macrophages and CD4+ T cells and increased the proportion of regulatory T cells. Moreover, IL-37-ERC treatment resulted in lower levels of IL-12 and interferon gamma, and higher level of transforming growth factor beta.

CONCLUSIONS

The results of this study suggest that ERCs can effectively alleviate Con A-induced hepatitis. Furthermore, IL-37 overexpression can significantly enhance the therapeutic efficacy of ERCs by augmenting the immunomodulatory and anti-inflammatory properties of ERCs. This study may provide a promising strategy for treatment of T-cell-dependent hepatitis.

Current Understanding of IL-37 in Human Health and Disease

IL-37 is a recently discovered cytokine in the IL-1 family exerting broad protective effects on inflammatory diseases, autoimmune diseases, and cancer. Immune and non-immune cells produce the IL-37 precursor upon pro-inflammatory stimuli. Intracellularly, caspase-1 cleaves and activates IL-37, and its mature form binds to Smad3; this complex translocates into the nucleus where it suppresses cytokine production, consequently reducing inflammation. Extracellularly, IL-37 forms a complex with IL-18Rα and IL-1R8 (formerly TIR8 or SIGIRR) that transduces anti-inflammatory signals by the suppression of NF-κB and MAPK and the activation of Mer-PTEN-DOK pathways. During inflammation, IL-37 suppresses the expression of several pro-inflammatory cytokine in favor to the expression of the anti-inflammatory ones by the regulation of macrophage polarization, lipid metabolism, inflammasome function, TSLP synthesis and miRNAs function. Moreover, IL-37 not only regulates the innate and acquired immunity, but also improves aging-associated immunosenescence. Furthermore, IL-37 exerts an inhibitory effect on tumor angiogenesis and metastasis, and progression. Finally, IL-37 may have a potential ability to reduce excessive inflammation since it is aberrantly expressed in patients with inflammatory diseases, autoimmune diseases, and cancer, thus, it may be used as a marker for different types of diseases. Therefore, this review provides an updated view of the role of IL-37 in human health and disease, and discusses the potential of IL-37 as a therapeutic target and biomarker in inflammatory diseases, autoimmune diseases, and cancer.

Reduced CXCL1 production by endogenous IL-37 expressing dendritic cells does not affect T cell activation

The dendritic cell (DC)-derived cytokine profile contributes to naive T cell differentiation, thereby directing the immune response. IL-37 is a cytokine with anti-inflammatory characteristics that has been demonstrated to induce tolerogenic properties in DC. In this study we aimed to evaluate the influence of IL-37 on DC–T cell interaction, with a special focus on the role of the chemokine CXCL1. DC were cultured from bone marrow of human IL-37 transgenic (hIL-37Tg) or WT mice. The phenotype of unstimulated and LPS-stimulated DC was analyzed (co-stimulatory molecules and MHCII by flow cytometry, cytokine profile by RT-PCR and ELISA), and T cell stimulatory capacity was assessed in mixed lymphocyte reaction. The role of CXCL1 in T cell activation was analyzed in T cell stimulation assays with anti-CD3 or allogeneic DC. The expression of the co-stimulatory molecules CD40, CD80 and CD86, and of MHCII in LPS-stimulated DC was not affected by endogenous expression of IL-37, whereas LPS-stimulated hIL-37Tg DC produced less CXCL1 compared to LPS-stimulated WT DC. T cell stimulatory capacity of LPS-matured hIL-37Tg DC was comparable to that of WT DC. Recombinant mouse CXCL1 did not increase T cell proliferation either alone or in combination with anti-CD3 or allogeneic DC, nor did CXCL1 affect the T cell production of interferon-γ and IL-17. Endogenous IL-37 expression does not affect mouse DC phenotype or subsequent T cell stimulatory capacity, despite a reduced CXCL1 production. In addition, we did not observe an effect of CXCL1 in T cell proliferation or differentiation.

The Associations of Serum IL-37 With the Severity and Prognosis in Patients With Community-Acquired Pneumonia: A Retrospective Cohort Study

Background

Recent evidences suggested that IL-37 may participate in the pathophysiology of community-acquired pneumonia (CAP). Nevertheless, its exact biological role was unknown. The objective of this study was to determine the associations of serum IL-37 with the severity and prognosis in CAP patients based on a retrospective cohort study.

Methods

The whole of 120 healthy subjects and 240 CAP patients were summoned. Peripheral blood was collected and IL-37 was detected using ELISA.

Results

Serum IL-37 was obviously decreased in CAP patients on admission. In addition, serum IL-37 was gradually decreased in parallel with CAP severity scores. Correlative analysis revealed that serum IL-37 was negatively associated with CAP severity scores and inflammatory cytokines. Further logistical regression found that reduction of serum IL-37 augmented the severity of CAP patients. Moreover, the follow-up research was performed in CAP patients. Serum lower IL-37 on admission prolonged the hospital stay in CAP patients. Serum IL-37 combination with PSI and CURB-65 had a stronger predictive capacity for death than IL-37 and CAP severity score alone in CAP patients.

Conclusion

There are remarkably negative correlations between serum IL-37 with the severity and prognosis in CAP patients. Serum IL-37 on admission prolongs the hospital stay, demonstrating that IL-37 may involve in the process of CAP. Serum IL-37 may be regarded as a biomarker for diagnosis and prognosis for CAP patients.

No association of genetic variants in TLR4, TNF-α, IL10, IFN-γ, and IL37 in cytomegalovirus-positive renal allograft recipients with active CMV infection-Subanalysis of the prospective randomised VIPP study

Background

Cytomegalovirus (CMV) infection is amongst the most important factors complicating solid organ transplantation. In a large prospective randomized clinical trial, valganciclovir prophylaxis reduced the occurrence of CMV infection and disease compared with preemptive therapy in CMV-positive renal allograft recipients (VIPP study; NCT00372229). Here, we present a subanalysis of the VIPP study, investigating single nucleotide polymorphisms (SNPs) in immune-response-related genes and their association with active CMV infection, CMV disease, graft loss or death, rejection, infections, and leukopenia.

Methods

Based on literature research ten SNPs were analyzed for TLR4, three for IFN-γ, six for IL10, nine for IL37, and two for TNF-α. An asymptotic independence test (Cochran-Armitage trend test) was used to examine associations between SNPs and the occurrence of CMV infection or other negative outcomes. Statistical significance was defined as p<0.05 and Bonferroni correction for multiple testing was performed.

Results

SNPs were analyzed on 116 blood samples. No associations were found between the analyzed SNPs and the occurrence of CMV infection, rejection and leukopenia in all patients. For IL37 rs2723186, an association with CMV disease (p = 0.0499), for IL10 rs1800872, with graft loss or death (p = 0.0207) and for IL10 rs3024496, with infections (p = 0.0258) was observed in all patients, however did not hold true after correction for multiple testing.

Conclusion

The study did not reveal significant associations between the analyzed SNPs and the occurrence of negative outcomes in CMV-positive renal transplant recipients after correction for multiple testing. The results of this association analysis may be of use in guiding future research efforts.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

IL-37 exerts therapeutic effects in experimental autoimmune encephalomyelitis through the receptor complex IL-1R5/IL-1R8

Background: Interleukin 37 (IL-37), a member of IL-1 family, broadly suppresses inflammation in many pathological conditions by acting as a dual-function cytokine in that IL-37 signals via the extracellular receptor complex IL1-R5/IL-1R8, but it can also translocate to the nucleus. However, whether IL-37 exerts beneficial actions in neuroinflammatory diseases, such as multiple sclerosis, remains to be elucidated. Thus, the goals of the present study were to evaluate the therapeutic effects of IL-37 in a mouse model of multiple sclerosis, and if so, whether this is mediated via the extracellular receptor complex IL-1R5/IL-1R8.

Methods: We used a murine model of MS, the experimental autoimmune encephalomyelitis (EAE). We induced EAE in three different single and double transgenic mice (hIL-37tg, IL-1R8 KO, hIL-37tg-IL-1R8 KO) and wild type littermates. We also induced EAE in C57Bl/6 mice and treated them with various forms of recombinant human IL-37 protein. Functional and histological techniques were used to assess locomotor deficits and demyelination. Luminex and flow cytometry analysis were done to assess the protein levels of pro-inflammatory cytokines and different immune cell populations, respectively. qPCRs were done to assess the expression of IL-37, IL-1R5 and IL-1R8 in the spinal cord of EAE, and in blood peripheral mononuclear cells and brain tissue samples of MS patients.

Results: We demonstrate that IL-37 reduces inflammation and protects against neurological deficits and myelin loss in EAE mice by acting via IL1-R5/IL1-R8. We also reveal that administration of recombinant human IL-37 exerts therapeutic actions in EAE mice. We finally show that IL-37 transcripts are not up-regulated in peripheral blood mononuclear cells and in brain lesions of MS patients, despite the IL-1R5/IL-1R8 receptor complex is expressed.

Conclusions: This study presents novel data indicating that IL-37 exerts therapeutic effects in EAE by acting through the extracellular receptor complex IL-1R5/IL-1R8, and that this protective physiological mechanism is defective in MS individuals. IL-37 may therefore represent a novel therapeutic avenue for the treatment of MS with great promising potential.

Characterization of the pathoimmunology of necrotizing enterocolitis reveals novel therapeutic opportunities

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

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

Validation in a Brazilian population of gene markers of periodontitis previously investigated by GWAS and bioinformatic studies

BACKGROUND

Bioinformatic tools and genome-wide association studies (GWAS) have led to comprehensive identification of single nucleotide polymorphisms (SNPs) associated with periodontitis in diverse populations. Here we aimed to detect and validate the association of seven SNPs as genetic markers of susceptibility to periodontitis in a Brazilian population.

METHODS

This case-control study assessed complete periodontal parameters of 714 subjects with periodontal status classified as healthy/mild periodontitis (n = 356) and moderate/severe periodontitis (n = 358). Genotyping for rs187238, rs352140, rs1360573, rs2521634, rs3811046, rs3826782, and rs7762544 SNPs were evaluated. Genetic-phenotype associations, and sex or smoking effects of SNPs on periodontitis were tested using multiple logistic regressions adjusted for covariates.

RESULTS

The rs2521634-AA (close to NPY gene) presented increased risk for severe periodontitis (OR = 2.34; 95% CI = 1.19-4.59). The rs3811046-GG (IL37 gene) demonstrated increased risk for moderate periodontitis (OR = 2.58; 95% CI = 1.28-5.18). Higher risk for moderate periodontitis was found in male with rs7762544-AG close to NCR2 gene. The rs352140-TT in the TLR9 gene proved to be associated with lower risk to severe periodontitis in men. The rs2521634-AA was associated with higher percentage of interproximal probing pocket depth (P = .004).

CONCLUSIONS

This is the first evidence of validation in a Brazilian population of genetic markers of periodontitis previously investigated by GWAS and bioinformatics studies. SNPs in the NPY, IL37, and NCR2 genes were associated with susceptibility to moderate or severe periodontitis; whereas the TLR9 marker was associated with lower chance to develop severe periodontitis. Those SNPs had sex- and smoking-habit-specific effects on periodontitis; reinforcing the genetic profile predisposing to periodontitis.

Natural and Induced Tolerogenic Dendritic Cells

Dendritic cells (DCs) are highly susceptible to extrinsic signals that modify the functions of these crucial APCs. Maturation of DCs induced by diverse proinflammatory conditions promotes immune responses, but certain signals also induce tolerogenic functions in DCs. These "induced tolerogenic DCs" help to moderate immune responses such as those to commensals present at specific anatomical locations. However, also under steady-state conditions, some DCs are characterized by inherent tolerogenic properties. The immunomodulatory mechanisms constitutively present in such "natural tolerogenic DCs" help to promote tolerance to peripheral Ags. By extending tolerance initially established in the thymus, these functions of DCs help to regulate autoimmune and other immune responses. In this review we will discuss the mechanisms and functions of natural and induced tolerogenic DCs and offer further insight into how their possible manipulations may ultimately lead to more precise treatments for various immune-mediated conditions and diseases.

Novel immune biomarkers in complex regional pain syndrome

We investigated serum levels of 29 cytokines and immune-activated kynurenine and tetrahydrobiopterin pathway metabolites in 15 complex regional pain syndrome (CRPS) subjects and 14 healthy controls. Significant reductions in interleukin-37 and tryptophan were found in CRPS subjects, along with positive correlations between kynurenine/tryptophan ratio and TNF-α levels with kinesiophobia, tetrahydrobiopterin levels with McGill pain score, sRAGE, and xanthurenic acid and neopterin levels with depression, anxiety and stress scores. Using machine learning, we identified a set of binary variables, including IL-37 and GM-CSF, capable of distinguishing controls from established CRPS subjects. These results suggest possible involvement of various inflammatory markers in CRPS pathogenesis.

Potential methods for improving the efficacy of mesenchymal stem cells in the treatment of inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a group of chronic recurrent gastrointestinal inflammatory diseases, including ulcerative colitis (UC), Crohn's disease (CD) and IBD unclassified. The pathogenesis may be related to the mucosal immune dysfunction in genetically susceptible hosts affected by environmental factors. Current therapeutic agents mainly include aminosalicylates, corticosteroids, immunosuppressive drugs and novel biological agents. The purpose of treatment is to suppress inflammation and prevent irreversible structural damage. However, long-term application of these drugs may lead to multiple adverse effects and is not always effective. Mesenchymal stem cells (MSCs) are multipotent progenitors with low immunogenicity, which can be obtained and expanded easily. They play an important role in regulating immune responses and repairing damaged tissues in vivo. Therefore, MSCs are considered to be a promising option for the treatment of IBD. Nonetheless, there are many factors that can reduce the efficacy of MSCs, such as gradual deterioration of functional stem cells with age, low recruitment and persistence in vivo and different routes of administration. In recent years, researchers have been able to improve the efficacy of MSCs by pretreatment, genetic modification or co-application with other substances, as well as using different tissue-derived cells, administration methods or doses. This article reviews these methods to provide references for more effective application of MSCs in the treatment of IBD in the future.

The novel role of IL-37 to enhance the anti-inflammatory response of regulatory T cells in patients with peripheral atherosclerosis

OBJECTIVES

Regulatory T cells (Tregs) mediate immunomodulation and protect against atherosclerosis. It is considered that reducing the amount of pro-inflammatory mediators could be achieved by enhancing the anti-inflammatory response, and this may be considered one of the main targets for therapy development. The inhibitory cytokines secreted by Tregs mainly include interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β). Based on its known immunosuppressive involvement with other inflammatory disorders, we hypothesized that the newly characterized cytokine interleukin-37 (IL-37) might be associated with the inhibitory functions of Treg in atherosclerosis. Immune regulatory functions of IL-37 have not been completely clarified. Accordingly, we speculated that IL-37 might play a regulatory role in the immunosuppression of Tregs in atherosclerotic disease.

METHODS

Real-time polymerase chain reaction and enzyme linked immunosorbent assay were used to test gene expression and protein levels of IL-37 in peripheral blood and localized freshly resected arterial tissues from 84 patients with peripheral arterial occlusive disease and 50 non-atherosclerotic subjects. Results were correlated to disease hallmarks. We also evaluated the ability of recombinant IL-37 to modulate Treg cytokine secretion and T cell inhibition in relation to atherosclerotic disorder in vitro.Results: Our results revealed that IL-37 was increased in patients with chronic lower limb atherosclerotic ischemia, compared to non-atherosclerotic controls. In addition, the expression levels of circulating IL-37 correlated with disease severity of chronic lower limb ischemia. Supplementation with rIL-37 augmented levels of released IL-10 and TGF-β in supernatants of T cells co-cultured with Tregs in the enrolled patients.Conclusions: Results suggest a role for IL-37 in mediating anti-inflammatory functions in the atherosclerotic process, potentially involving enhancement of Treg inhibitory function and anti-inflammatory cytokine secretion with a particularly marked direct response in severe disease.

IL-37 is protective in allergic contact dermatitis through mast cell inhibition

Allergic contact dermatitis (ACD), characterized predominantly by erythema, vesiculation, and pruritus, is a T cell-mediated skin inflammatory condition. Among immune cells involved in ACD, mast cells (MCs) play an essential role in its pathogenesis. As an inhibitor of proinflammatory IL-1 family members, interleukin 37 (IL-37) has been shown to ameliorate inflammatory responses in various allergic diseases. In this study, we assessed the immunomodulatory effect of IL-37 on allergic inflammation using a 2,4-dinitrofluorobenzene (DNFB)-induced ACD rat model and isolated rat peritoneal mast cells (RPMCs). Systematic application of IL-37 significantly relieved ear swelling, reduced inflammatory cell infiltration, decreased inflammatory cytokine production (TNF-α, IL-1β, IFN-γ, and IL-13), inhibited MC recruitment, lowered IgE levels, and reduced IL-33 production in the local ear tissues with DNFB challenge. Additionally, RPMCs isolated from ACD rats with IL-37 intervention showed downregulation of IL-6, TNF-α, IL-13, and MCP-1 production following IL-33 stimulation, and reduction of β-hexosaminidase and histamine release under DNP-IgE/HSA treatment. Moreover, IL-37 treatment also significantly restrained NF-κB activation and P38 phosphorylation in ACD RPMCs. SIS3, a specific Smad3 inhibitor, abolished the suppressive effects of IL-37 on MC-mediated allergic inflammation, suggesting the participation of Smad3 in the anti-ACD effect of IL-37. These findings indicated that IL-37 protects against IL-33-regulated MC inflammatory responses via inhibition of NF-κB and P38 MAPK activation accompanying the regulation of Smad3 in rats with ACD.

IL-37 Represses the Autoimmunity in Myasthenia Gravis via Directly Targeting Follicular Th and B Cells

IL-37 is a newly identified immune-suppressive factor; however, the function, cellular sources, and mechanism of IL-37 in humoral immunity and Myasthenia gravis (MG) are still unclear. In this study, we found IL-37 were substantially downregulated in the serum and PBMCs of MG patients compared with healthy controls. The lower IL-37 was associated with severer disease (quantitative MG score) and higher follicular Th (Tfh)/Tfh17 and B cell numbers. Flow cytometry analysis revealed that IL-37 was mainly produced by CD4⁺ T cells without overlapping with Th1, Th17, and Tfh subsets in MG patients. Regulatory IL-37⁺ T cell rarely expressed Foxp3 and CD25 but produced numerous IL-4. Tfh and B cell expressed high levels of SIGIRR, the receptor of IL-37, in MG patients. Mechanically, IL-37 directly bond to SIGIRR, repressed the proliferation, cytokine production of Tfh and B cells, and the secretion of autoantibody via inhibition of STAT3 signaling in Tfh and B cells.

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

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

Parsing the IL-37-Mediated Suppression of Inflammasome Function

Interleukin (IL)-37 is a member of the IL-1 family of cytokines. Although its broad anti-inflammatory properties are well described, the effects of IL-37 on inflammasome function remain poorly understood. Performing gene expression analyses, ASC oligomerization/speck assays and caspase-1 assays in bone marrow-derived macrophages (BMDM), and employing an in vivo endotoxemia model, we studied how IL-37 affects the expression and maturation of IL-1β and IL-18, inflammasome activation, and pyroptosis in detail. IL-37 inhibited IL-1β production by NLRP3 and AIM2 inflammasomes, and IL-18 production by the NLRP3 inflammasome. This inhibition was partially attributable to effects on gene expression: whereas IL-37 did not affect lipopolysaccharide (LPS)-induced mRNA expression of Il18 or inflammasome components, IL-37-transgenic BMDM displayed an up to 83% inhibition of baseline and LPS-stimulated Il1b compared to their wild-type counterparts. Importantly, we observed that IL-37 suppresses nigericin- and silica-induced ASC oligomerization/speck formation (a step in inflammasome activation and subsequent caspase-1 activation), and pyroptosis (-50%). In mice subjected to endotoxemia, IL-37 inhibited plasma IL-1β (-78% compared to wild-type animals) and IL-18 (-61%). Thus, our study adds suppression of inflammasome activity to the portfolio of anti-inflammatory pathways employed by IL-37, highlighting this cytokine as a potential tool for treating inflammasome-driven diseases.

The role of IL-37 in skin and connective tissue diseases

IL-37 was discovered as an anti-inflammatory and immunosuppressive cytokine of the IL-1 family. Significant advancements in the understanding of signaling pathways associated with IL-37 have been made in recent years. IL-37 binds to IL-18R and recruits IL-1R8 to form the IL-37/IL-1R8/IL-18Rα complex. Capase-1 plays a key role in the nuclear transduction of IL-37 signal, processing precursor IL-37 into the mature isoform, and interacting with Smad3. IL-37 exerts its role by activating anti-inflammation pathways including AMPK, PTEN, Mer, STAT3 and p62, and promoting tolerogenic dendritic cells and Tregs. In addition, IL-37 inhibits pro-inflammatory cytokines such as IL-1, IL-6, IL-8, IL-17, IL-23, TNF-α, and IFN-γ, and suppresses Fyn, MAPK, TAK1, NFκB, and mTOR signaling. The final effects of IL-37 depend on the interaction among IL-18R, IL-1R8, IL-37 and IL-18BP. Previous studies have deciphered the role of IL-37 in the development and pathogenesis of autoimmune diseases, chronic infections and cancer. In this review, we discuss the role of IL-37 in psoriasis, atopic dermatitis, Behcet's diseases, systemic lupus erythematosus, and other skin and connective tissue diseases.

BMP7 aberrantly induced in the psoriatic epidermis instructs inflammation-associated Langerhans cells

BACKGROUND

Epidermal hyperplasia represents a morphologic hallmark of psoriatic skin lesions. Langerhans cells (LCs) in the psoriatic epidermis engage with keratinocytes (KCs) in tight physical interactions; moreover, they induce T-cell-mediated immune responses critical to psoriasis.

OBJECTIVE

This study sought to improve the understanding of epidermal factors in psoriasis pathogenesis.

METHODS

BMP7-LCs versus TGF-β1-LCs were phenotypically characterized and their functional properties were analyzed using flow cytometry, cell kinetic studies, co-culture with CD4 T cells, and cytokine measurements. Furthermore, immunohistology of healthy and psoriatic skin was performed. Additionally, in vivo experiments with Jun^f/fJunB^f/fK5cre-ER^T mice were carried out to assess the role of bone morphogenetic protein (BMP) signaling in psoriatic skin inflammation.

RESULTS

This study identified a KC-derived signal (ie, BMP signaling) to promote epidermal changes in psoriasis. Whereas BMP7 is strictly confined to the basal KC layer in the healthy skin, it is expressed at high levels throughout the lesional psoriatic epidermis. BMP7 instructs precursor cells to differentiate into LCs that phenotypically resemble psoriatic LCs. These BMP7-LCs exhibit proliferative activity and increased sensitivity to bacterial stimulation. Moreover, aberrant high BMP signaling in the lesional epidermis is mediated by a KC intrinsic mechanism, as suggested from murine data and clinical outcome after topical antipsoriatic treatment in human patients.

CONCLUSIONS

These data indicate that available TGF-β family members within the lesional psoriatic epidermis preferentially signal through the canonical BMP signaling cascade to instruct inflammatory-type LCs and to promote psoriatic epidermal changes. Targeting BMP signaling might allow to therapeutically interfere with cutaneous psoriatic manifestations.