Suppression of innate inflammation and immunity by interleukin‐37

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

Association analysis of polymorphisms at the interleukin‐1 locus in essential hypertension

Infection with microorganisms such as Helicobacter pylori and Chlamidia pneumoniae has been associated with coronary heart disease (CAD) and hypertension (HT). Infection increases the release of pro‐inflammatory cytokines, thus facilitating interactions that lead to vascular damage and other effects. We hypothesized that genetically determined differences in activity or responsiveness of cytokine(s) might contribute to HT. The interleukin‐1 gene (IL1) cluster on chromosome 2q14 contains three related genes (IL1A, IL1B, and IL1RN) located within a 430‐kb region. These encode IL‐1α and IL‐1β, as well as their endogenous receptor antagonist, IL‐1ra. The IL1RN gene has a penta‐allelic 86‐bp tandem repeat in intron 2. Allele IL1RN* 2 is associated with a wide range of chronic inflammatory and autoimmune conditions, and its combination with the ? 31T variant of an IL1B C(? 31)T polymorphism constitutes a pro‐inflammatory haplotype that leads to vigorous IL‐1β production. We therefore tested each of these polymorphisms for association with HT. Subjects were white Anglo‐Celtic residents of Sydney, Australia. Frequencies of IL1B C(? 31)T genotypes CC, CT, and TT were 0.50, 0.40, and 0.10 in normotensive (NT) and 0.46, 0.46, and 0.08 in HT, respectively (χ² = 1.2, P = 0.55). T allele frequency in NT (0.30) was similar to that in HT (0.31). For the IL1RN variant, frequencies of alleles IL1RN* 1 and * 2 and combined minor alleles * 3, * 4, and * 5 were 0.61, 0.36, and 0.03 in NT and 0.54, 0.36, and 0.10 in HT, respectively (χ² = 11, P = 0.004). In conclusion, no association of the IL1B C(? 31)T with HT was found, whereas combined frequency of the minor alleles of the IL1RN polymorphism was increased in the HT cohort studied. © 2001 Wiley‐Liss, Inc.     

Overview of the IL-1 family in innate inflammation and acquired immunity

The interleukin-1 (IL-1) family of cytokines and receptors is unique in immunology because the IL-1 family and Toll-like receptor (TLR) families share similar functions. More than any other cytokine family, the IL-1 family is primarily associated with innate immunity. More than 95% of living organisms use innate immune mechanisms for survival whereas less than 5% depend on T- and B-cell functions. Innate immunity is manifested by inflammation, which can function as a mechanism of host defense but when uncontrolled is detrimental to survival. Each member of the IL-1 receptor and TLR family contains the cytoplasmic Toll-IL-1-Receptor (TIR) domain. The 50 amino acid TIR domains are highly homologous with the Toll protein in Drosophila. The TIR domain is nearly the same and present in each TLR and each IL-1 receptor family. Whereas IL-1 family cytokine members trigger innate inflammation via IL-1 family of receptors, TLRs trigger inflammation via bacteria, microbial products, viruses, nucleic acids, and damage-associated molecular patterns (DAMPs). In fact, IL-1 family member IL-1a and IL-33 also function as DAMPs. Although the inflammatory properties of the IL-1 family dominate in innate immunity, IL-1 family member can play a role in acquired immunity. This overview is a condensed update of the IL-1 family of cytokines and receptors.     

Interleukin‐32 production associated with biliary innate immunity and proinflammatory cytokines contributes to the pathogenesis of cholangitis in biliary atresia

Biliary atresia (BA) is thought to be associated with infections by viruses such as Reoviridae and is characterized histologically by fibrosclerosing cholangitis with proinflammatory cytokine‐mediated inflammation. Interleukin (IL)‐32 affects the continuous inflammation by increasing the production of proinflammatory cytokines. In this study, the role of IL‐32 in the cholangitis of BA was examined. Immunohistochemistry for IL‐32 and caspase 1 was performed using 21 samples of extrahepatic bile ducts resected from BA patients. Moreover, using cultured human biliary epithelial cells (BECs), the expression of IL‐32 and its induction on stimulation with a Toll‐like receptor [(TLR)‐3 ligand (poly(I:C)] and proinflammatory cytokines was examined. BECs composing extrahepatic bile ducts showing cholangitis expressed IL‐32 in BA, but not in controls. Caspase 1 was expressed constantly on BECs of both BA and control subjects. Furthermore, poly(I:C) and proinflammatory cytokines [(IL‐1β, interferon (IFN)‐γ and tumour necrosis factor (TNF)‐α] induced IL‐32 expression strongly in cultured BECs, accompanying the constant expression of TLR‐3 and caspase 1. Our results imply that the expression of IL‐32 in BECs was found in the damaged bile ducts of BA and induced by biliary innate immunity via TLR‐3 and proinflammatory cytokines. These findings suggest that IL‐32 is involved initially in the pathogenic mechanisms of cholangitis in BA and also plays an important role in the amplification and continuance of periductal inflammatory reactions. It is therefore tempting to speculate that inhibitors of IL‐32 could be useful for attenuating cholangitis in BA.     

High-mobility group box 1 protein orchestrates responses to tissue damage via inflammation,innate and adaptive immunity,and tissue repair

A single protein, HMGB1, directs the triggering of inflammation, innate and adaptive immune responses, and tissue healing after damage. HMGB1 is the best characterized damage-associated molecular pattern (DAMP), proteins that are normally inside the cell but are released after cell death, and allow the immune system to distinguish between antigens that are dangerous or not. Notably, cells undergoing severe stress actively secrete HMGB1 via a dedicated secretion pathway: HMGB1 is relocated from the nucleus to the cytoplasm and then to secretory lysosomes or directly to the extracellular space. Extracellular HMGB1 (either released or secreted) triggers inflammation and adaptive immunological responses by switching among multiple oxidation states, which direct the mutually exclusive choices of different binding partners and receptors. Immune cells are first recruited to the damaged tissue and then activated; thereafter, HMGB1 supports tissue repair and healing, by coordinating the switch of macrophages to a tissue-healing phenotype, activation and proliferation of stem cells, and neoangiogenesis. Inevitably, HMGB1 also orchestrates the support of stressed but illegitimate tissues: tumors. Concomitantly, HMGB1 enhances the immunogenicity of mutated proteins in the tumor (neoantigens), promoting anti-tumor responses and immunological memory. Tweaking the activities of HMGB1 in inflammation, immune responses and tissue repair could bring large rewards in the therapy of multiple medical conditions, including cancer.     

Lessons from interleukin‐deficient mice: the interleukin‐1 system

The study of cytokine‐deficient mice has provided important information for a better understanding of inflammatory processes. In this report, the characterization of mice deficient for various components of the interleukin (IL)‐1 system is reviewed. Results obtained by studying mice deficient for IL‐1α, IL‐1β, IL‐1 receptor antagonist, IL‐1 receptor type I, IL‐1 receptor accessory protein, IL‐1 receptor‐associated kinase, and the IL‐1β‐converting enzyme caspase‐1 are summarized. Because some of the components of the IL‐1 system are shared with IL‐18, similarities between IL‐1β and IL‐18 are also discussed.     

Galectin‐3 is an amplifier of the interleukin‐1β‐mediated inflammatory response in corneal keratinocytes

Interleukin‐1β (IL‐1β) is a potent mediator of innate immunity commonly up‐regulated in a broad spectrum of inflammatory diseases. When bound to its cell surface receptor, IL‐1β initiates a signalling cascade that cooperatively induces the expression of canonical IL‐1 target genes such as IL‐8 and IL‐6. Here, we present galectin‐3 as a novel regulator of IL‐1β responses in corneal keratinocytes. Using the SNAP‐tag system and digitonin semi‐permeabilization, we show that recombinant exogenous galectin‐3 binds to the plasma membrane of keratinocytes and is internalized into cytoplasmic compartments. We find that exogenous galectin‐3, but not a dominant negative inhibitor of galectin‐3 polymerization lacking the N‐terminal domain, exacerbates the response to IL‐1β by stimulating the secretion of inflammatory cytokines. The activity of galectin‐3 could be reduced by a novel d ‐galactopyranoside derivative targeting the conserved galactoside‐binding site of galectins and did not involve interaction with IL‐1 receptor 1 or the induction of endogenous IL‐1β. Consistent with these observations, we demonstrate that small interfering RNA‐mediated suppression of endogenous galectin‐3 expression is sufficient to impair the IL‐1β‐induced secretion of IL‐8 and IL‐6 in a p38 mitogen‐activated protein kinase‐independent manner. Collectively, our findings provide a novel role for galectin‐3 as an amplifier of IL‐1β responses during epithelial inflammation through an as yet unidentified mechanism.     

Mammalian Toll-like receptors: to immunity and beyond

Toll-like receptors (TLRs) constitute an archetypal pattern recognition system. Their sophisticated biology underpins the ability of innate immunity to discriminate between highly diverse microbial pathogens and self. However, the remarkable progress made in describing this biology has also revealed new immunological systems and processes previously hidden to investigators. In particular, TLRs appear to have a fundamental role in the generation of clonal adaptive immune responses, non-infectious disease pathogenesis and even in the maintenance of normal mammalian homeostasis. Although an understanding of TLRs has answered some fundamental questions at the host-pathogen interface, further issues, particularly regarding therapeutic modulation of these receptors, have yet to be resolved.     

Altered RIG‐I/DDX58‐mediated innate immunity in dermatomyositis

We investigated the molecular mechanisms involved in the pathogenesis of three inflammatory myopathies, dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). We performed microarray experiments^? using microdissected pathological muscle fibres from 15 patients with these disorders and five controls. Differentially expressed candidate genes were validated by immunohistochemistry on muscle biopsies, and the altered pathways were analysed in human myotube cultures. Up‐regulation of genes involved in viral and nucleic acid recognition were found in the three myopathies but not in controls. In DM, retinoic acid‐inducible gene 1 (RIG‐I, DDX58) and the novel antiviral factor DDX60, which promotes RIG‐I‐mediated signalling, were significantly up‐regulated, followed by IFIH1 (MDA5) and TLR3. Immunohistochemistry confirmed over‐expression of RIG‐I in pathological muscle fibres in 5/5 DM, 0/5 PM and 0/5 IBM patients, and in 0/5 controls. Stimulation of human myotubes with a ligand of RIG‐I produced a significant secretion of interferon‐β (IFNβ; p < 0.05) and up‐regulation of class I MHC, RIG‐I and TLR3 (p < 0.05) by IFNβ‐dependent and TLR3‐independent mechanisms. RIG‐I‐mediated innate immunity, triggered by a viral or damage signal, plays a significant role in the pathogenesis of DM, but not in that of PM or IBM. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd     

Bone marrow type 2 innate lymphoid cells: a local source of interleukin‐5 in interleukin‐33‐driven eosinophilia

T helper type 2 (Th2) cells, type 2 innate lymphoid cells (ILC2s) and eosinophil progenitors have previously been described to produce interleukin‐5 (IL‐5) in the airways upon allergen provocation or by direct administration of IL‐33. Eosinophilic airway inflammation is known to be associated with IL‐5‐dependent eosinophil development in the bone marrow, however, the source of IL‐5 remains unclear. T helper cells, ILC2s and CD34⁺ progenitors have been proposed to be involved in this process, therefore, we investigated whether these cells are taking part in eosinophilopoiesis by producing IL‐5 locally in the bone marrow in IL‐33‐driven inflammation. Airway exposure with IL‐33 led to eosinophil infiltration in airways and elevated eotaxin‐2/CCL24. Importantly, IL‐5 production as well as expression of the IL‐33 receptor increased in ILC2s in the bone marrow under this treatment. A small but significant induction of IL‐5 was also found in CD34⁺ progenitors but not in T helper cells. Similar results were obtained by in vitro stimulation with IL‐33 where ILC2s rapidly produced large amounts of IL‐5, which coincided with the induction of eosinophil hematopoiesis. IL‐33‐mediated eosinophil production was indeed dependent on IL‐5 as both airway and bone marrow eosinophils decreased in mice treated with anti‐IL‐5 in combination with IL‐33. Interestingly, the responsiveness of ILC2s to IL‐33 as well as IL‐33‐induced eotaxin‐2/CCL24 were independent of the levels of IL‐5. In summary, we demonstrate for the first time that IL‐33 acts directly on bone marrow ILC2s, making them an early source of IL‐5 and part of a process that is central in IL‐33‐driven eosinophilia.     

Epithelial expression of interleukin‐37b in inflammatory bowel disease

Interleukin (IL)‐37 is a member of the IL‐1 cytokine family. We investigated IL‐37b expression in the inflamed mucosa of inflammatory bowel disease (IBD) patients. Furthermore, we analysed IL‐37b expression in human colonic epithelial cells. The human colonic epithelial cell line T84 and human colonic subepithelial myofibroblasts (SEMFs) were used. IL‐37b expression in the IBD mucosa was evaluated by immunohistochemistry. IL‐37b mRNA and protein expression were determined by real time‐polymerase chain reaction (PCR) and Western blotting, respectively. IL‐37b was not detected in the normal colonic mucosa. In the inflamed mucosa of IBD patients, epithelial IL‐37b expression was increased markedly. In ulcerative colitis (UC) and Crohn's disease (CD) patients, IL‐37b expression was enhanced in the affected mucosa. In the intestinal epithelial cell line T84, the expression of IL‐37b mRNA and protein was enhanced by tumour necrosis factor (TNF)‐α. This IL‐37b induction by TNF‐α was mediated by nuclear factor (NF)‐κB and activator protein (AP)‐1 activation. Furthermore, IL‐37b inhibited TNF‐α‐induced interferon‐γ‐inducible protein (IP)‐10 expression significantly in human colonic SEMFs. Epithelial IL‐37b expression was increased in IBD patients, especially UC patients. IL‐37b may be involved in the pathophysiology of IBD as an anti‐inflammatory cytokine and an inhibitor of both innate and acquired immune responses.     

The association of interferon‐gamma,interleukin‐4 and interleukin‐17 single‐nucleotide polymorphisms with susceptibility to tuberculosis

Susceptibility to tuberculosis and progression of the disease depend on interactions between the bacterial agent, host immune system, and environmental and genetic factors. In this case‐controlled study, we aimed to determine the role of single‐nucleotide polymorphisms of interferon‐gamma, interleukin‐4 and interleukin‐17 in susceptibility to tuberculosis. Genomic DNA was extracted from peripheral blood samples of patients and controls. The association of single‐nucleotide polymorphisms in interleukin‐4 (?590C/T), interleukin‐17 (?152A/G) and interferon‐gamma (+874T/A) was investigated by polymerase chain reaction (PCR)‐restriction fragment length polymorphism and amplification refractory mutation system‐PCR. A total of 76 tuberculosis patients and 119 healthy individuals were included in this study. The interferon‐gamma (+874T/A) TA genotype was significantly associated with susceptibility to tuberculosis in patients compared to controls (OR = 1.76; 95%CI = 0.84–3.71; p = 0.007), while the interferon‐gamma (+874T/A) TT genotype (OR = 0.51; 95%CI = 0.19–1.36; p = 0.007) had protective effects against tuberculosis and was related to a low risk of tuberculosis development. The difference between allelic and genotypic frequencies of interleukin‐4 (?590C/T) between patients and controls was not significant (p = 0.46). Multivariate logistic regression analysis revealed that the interleukin‐17 (?152A/G) AG genotype (OR = 2.27; 95%CI = 1.19–4.34; p = 0.03) and AA genotype (OR = 1.03; 95%CI = 0.43–2.44; p = 0.03) were significantly different between patients and controls. In conclusion, single‐nucleotide mutations in different cytokine genes may have protective effects or increase the risk of tuberculosis.     

Mechanism of interleukin‐1β‐induced proliferation in rat hepatic stellate cells from different levels of signal transduction

Hepatic stellate cells (HSCs) are the major producers of collagen in the liver. Their conversion from resting cells to proliferative, contractile, and activated cells is a critical step leading to liver fibrosis that is characterized by the deposition of excessive extracellular matrix. Interleukin‐1 (IL‐1) may play a role in maintaining HSC in a proliferative state that is responsible for hepatic fibrogenesis. The aim of this study was to study the roles of the IL‐1 type I receptor (IL‐1R1), c‐Jun N‐terminal kinase (JNK), and activation protein‐1 (AP‐1) in IL‐1β–mediated proliferation in rat HSCs. We showed that IL‐1β can upregulate proliferation in rat HSCs; however, inhibition of the JNK pathway could inhibit HSCs proliferation. Furthermore, IL‐1β activated IL‐1R1 expression, the JNK signaling pathway, and AP‐1 activity in a time‐dependent manner in rat HSCs. These data demonstrate that IL‐1β could promote the proliferation of rat HSCs and that the IL‐1R1, JNK, and AP‐1 pathways were involved in this process. In summary, IL‐1β‐induced proliferation is possibly mediated by the IL‐1R1, JNK, and AP‐1 pathways in rat HSCs. Therefore, drugs that block these pathways may inhibit the proliferation of HSCs and suppress liver fibrosis.     

Synergistic effect of interleukin‐17 and tumour necrosis factor‐α on inflammatory response in hepatocytes through interleukin‐6‐dependent and independent pathways

The proinflammatory cytokines interleukin (IL)‐17 and tumour necrosis factor (TNF)‐α are targets for treatment in many chronic inflammatory diseases. Here, we examined their role in liver inflammatory response compared to that of IL‐6. Human hepatoma cells (HepaRG, Huh7.5 and HepG2 cells) and primary human hepatocytes (PHH) were cultured with IL‐6, IL‐17 and/or TNF‐α. To determine the contribution of the IL‐6 pathway in the IL‐17/TNF‐α‐mediated effect, an anti‐IL‐6 receptor antibody was used. IL‐17 and TNF‐α increased in synergy IL‐6 secretion by HepaRG cells and PHH but not by Huh7.5 and HepG2 cells. This IL‐17/TNF‐α synergistic cooperation enhanced the levels of C‐reactive protein (CRP) and aspartate aminotransferase (ASAT) in HepaRG cell and PHH cultures through the induction of IL‐6. IL‐17/TNF‐α also up‐regulated IL‐8, monocyte chemoattractant protein (MCP)‐1 and chemokine (C‐C motif) ligand 20 (CCL20) chemokines in synergy through an IL‐6‐independent pathway. Interestingly, first exposure to IL‐17, but not to TNF‐α, was crucial for the initiation of the IL‐17/TNF‐α synergistic effect on IL‐6 and IL‐8 production. In HepaRG cells, IL‐17 enhanced IL‐6 mRNA stability resulting in increased IL‐6 protein levels. The IL‐17A/TNF‐α synergistic effect on IL‐6 and IL‐8 induction was mediated through the activation of extracellular signal‐regulated kinase (ERK)‐mitogen‐activated protein kinase, nuclear factor‐κB and/or protein kinase B (Akt)–phosphatidylinositol 3‐kinase signalling pathways. Therefore, the IL‐17/TNF‐α synergistic interaction mediates systemic inflammation and cell damage in hepatocytes mainly through IL‐6 for CRP and ASAT induction. Independently of IL‐6, the IL‐17A/TNF‐α combination may also induce immune cell recruitment by chemokine up‐regulation. IL‐17 and/or TNF‐α neutralization can be a promising therapeutic strategy to control both systemic inflammation and liver cell attraction.     

IL‐2/IL‐6 ratio correlates with liver function and recovery in acute liver injury patients

Acute liver injury can result from a number of different diseases. Inflammatory cytokines are known to be involved in the development of this condition; however, their precise roles and effects on liver function remain unclear. The goal of this study was to determine the relationship between serum cytokine levels and both the severity of liver damage and recovery in acute liver injury. We enrolled 100 patients with acute liver injury caused by drug application who were hospitalized from September 2012 to September 2017 and measured serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and the cytokines, interleukin (IL)‐2 and IL‐6, before and after clinical therapy. Our results indicate that IL‐2 and IL‐6 levels are altered significantly following clinical therapy. However, with the exception of an association between IL‐2 and ALT, we found no correlation between the differences in cytokine levels pre‐ and post‐therapy and recovery of liver function. In contrast, we observed that pre‐ vs post‐treatment difference in the IL‐2/IL‐6 ratio negatively correlates with the pre‐ vs post‐treatment difference in ALT and AST values, and positively correlates with ALT and AST at 1‐month post‐discharge. Thus, our data suggest that IL‐2/IL‐6 ratio may represent a novel predictor for the prognosis of liver injury.