Inflammatory bowel disease-associated interleukin-33 is preferentially expressed in ulceration-associated myofibroblasts

Stromal and immune cells in gut fibrosis: the myofibroblast and the scarface

Post-inflammatory scarring is the end-result of excessive extracellular matrix (ECM) accumulation and tissue architectural destruction. It represents a failure to effectively remodel ECM and achieve proper reinstitution and healing during chronic relapsing inflammatory processes. Scarring may affect the functionality of any organ, and in the case of inflammatory bowel disease (IBD)-associated fibrosis leads to stricture formation and often surgery to remove the affected bowel. The activated myofibroblast is the final effector cell that overproduces ECM under the influence of various mediators generated by an intense interplay of classic and non-classic immune cells. This review focuses on how proinflammatory mediators from various sources produced in different stages of intestinal inflammation can form profibrotic pathways that eventually lead to tissue scarring through sustained activation of myofibroblasts.

Endothelial IL-33 Expression Is Augmented by Adenoviral Activation of the DNA Damage Machinery

IL-33, required for viral clearance by cytotoxic T cells, is generally expressed in vascular endothelial cells in healthy human tissues. We discovered that endothelial IL-33 expression was stimulated as a response to adenoviral transduction. This response was dependent on MRE11, a sensor of DNA damage that can also be activated by adenoviral DNA, and on IRF1, a transcriptional regulator of cellular responses to viral invasion and DNA damage. Accordingly, we observed that endothelial cells responded to adenoviral DNA by phosphorylation of ATM and CHK2 and that depletion or inhibition of MRE11, but not depletion of ATM, abrogated IL-33 stimulation. In conclusion, we show that adenoviral transduction stimulates IL-33 expression in endothelial cells in a manner that is dependent on the DNA-binding protein MRE11 and the antiviral factor IRF1 but not on downstream DNA damage response signaling.

Loss of interleukin 33 expression in colonic crypts - a potential marker for disease remission in ulcerative colitis

Interleukin 33 (IL-33) is a cytokine preferentially elevated in acute ulcerative colitis (UC), inferring a role in its pathogenesis. The role of IL-33 in intestinal inflammation is incompletely understood, with both pro-inflammatory and regulatory properties described. There are also conflicting reports on cellular sources and subcellular location of IL-33 in the colonic mucosa, justifying a closer look at IL-33 expression in well-defined clinical stages of UC. A total of 50 study participants (29 UC patients and 21 healthy controls) were included from a prospective cohort of inflammatory bowel disease patients treated to disease remission with infliximab, a tumour necrosis factor alpha (TNF) inhibitor. To our knowledge this is the first study examining mucosal IL-33 expression before and after anti-TNF therapy. In colonic mucosal biopsies we found a 3-fold increase in IL-33 gene expression comparing acute UC to healthy controls (p < 0.01). A significant reduction of IL33 between acute UC and disease remission was observed when TNF normalised in the mucosa (p = 0.02). Immunostaining revealed IL-33 in the nuclei of epithelial cells of scattered colonic crypts in acute disease, while at disease remission, IL-33 was undetectable, a novel finding suggesting that enterocyte-derived IL-33 is induced and maintained by inflammatory mediators.

Interleukin-33 in health and disease

Interleukin-33 (IL-33) - a member of the IL-1 family - was originally described as an inducer of type 2 immune responses, activating T helper 2 (T_H2) cells and mast cells. Now, evidence is accumulating that IL-33 also potently stimulates group 2 innate lymphoid cells (ILC2s), regulatory T (T_reg) cells, T_H1 cells, CD8⁺ T cells and natural killer (NK) cells. This pleiotropic nature is reflected in the role of IL-33 in tissue and metabolic homeostasis, infection, inflammation, cancer and diseases of the central nervous system. In this Review, we highlight the molecular and cellular characteristics of IL-33, together with its major role in health and disease and the potential therapeutic implications of these findings in humans.

GLP-1 Induces Barrier Protective Expression in Brunner's Glands and Regulates Colonic Inflammation

BACKGROUND

Beneficial roles for glucagon-like peptide 1 (GLP-1)/GLP-1R signaling have recently been described in diseases, where low-grade inflammation is a common phenomenon. We investigated the effects of GLP-1 in Brunner's glands and duodenum with abundant expression of GLP-1 receptors, as well as GLP-1 effect on colonic inflammation.

METHODS

RNA from Brunner's glands of GLP-1R knockout and wild-type mice were subjected to full transcriptome profiling. Array results were validated by quantitative reverse transcription polymerase chain reaction in wild-type mice and compared with samples from inflammatory bowel disease (IBD) patients and controls. In addition, we performed a detailed investigation of the effects of exogenous liraglutide dosing in a T-cell driven adoptive transfer (AdTr) colitis mouse model.

RESULTS

Analyses of the Brunner's gland transcriptomes of GLP-1R knockout and wild-type mice identified 722 differentially expressed genes. Upregulated transcripts after GLP-1 dosing included IL-33, chemokine ligand 20 (CCL20), and mucin 5b. Biopsies from IBD patients and controls, as well as data from the AdTr model, showed deregulated expression of GLP-1R, CCL20, and IL-33 in colon. Circulating levels of GLP-1 were found to be increased in mice with colitis. Finally, the colonic cytokine levels and disease scores of the AdTr model indicated reduced levels of colonic inflammation in liraglutide-dosed animals.

CONCLUSIONS

We demonstrate that IL-33, GLP-1R, and CCL20 are deregulated in human IBD, and that prophylactic treatment with 0.6 mg/kg liraglutide improves disease in AdTr colitis. In addition, GLP-1 receptor agonists upregulate IL-33, mucin 5b, and CCL20 in murine Brunner's glands. Taken together, our data indicate that GLP-1 receptor agonists affect gut homeostasis in both proximal and distal parts of the gut.

The RNA Binding Protein Mex-3B Is Required for IL-33 Induction in the Development of Allergic Airway Inflammation

Allergic airway inflammation is one of the primary features of allergic asthma. Interleukin-33 (IL-33) is recognized as a key pro-inflammatory cytokine that mediates allergic airway inflammation, and its expression is elevated in this condition, but little is known about the regulatory mechanisms underlying IL-33 induction. Here, we show that the RNA binding protein Mex-3B plays a critical role in the induction of IL-33 in the development of allergic airway inflammation. We generated Mex3b(-/-) mice and found that they develop significantly less airway inflammation than wild-type mice due to reduced induction of IL-33. Furthermore, we show that Mex-3B directly upregulates IL-33 expression by inhibiting miR-487b-3p-mediated repression of IL-33. Moreover, we show that inhalation of an antisense oligonucleotide targeting Mex-3B suppresses allergic airway inflammation. Our data identify a signaling pathway that post-transcriptionally regulates IL-33 expression and suggest that Mex-3B could be a promising molecular target for the treatment of allergic asthma.

Wounds that heal and wounds that don't - The role of the IL-33/ST2 pathway in tissue repair and tumorigenesis

IL-33 is a member of the IL-1 family of cytokines. IL-33 is predominantly located within the nucleus of cells where it plays a role in gene regulation. Given the right combination of signals and cellular damage, stored IL-33 is released from the cell where it can interact with its receptor ST2, triggering danger-associated responses and act as a cellular "alarmin". Whilst IL-33/ST2 signalling has been shown to induce potent pro-inflammatory responses that can be detrimental in certain disease states, a dichotomous, protective role of IL-33 in promoting wound healing has also emerged in multiple tissues types. This review will explore the current literature concerning this homeostatic role of IL-33/ST2 in tissue repair and also review its role in uncontrolled wound responses as seen in both fibrosis and tumorigenesis.

Programming of Intestinal Epithelial Differentiation by IL-33 Derived from Pericryptal Fibroblasts in Response to Systemic Infection

The intestinal epithelium constitutes an efficient barrier against the microbial flora. Here, we demonstrate an unexpected function of IL-33 as a regulator of epithelial barrier functions. Mice lacking IL-33 showed decreased Paneth cell numbers and lethal systemic infection in response to Salmonella typhimurium. IL-33 was produced upon microbial challenge by a distinct population of pericryptal fibroblasts neighboring the intestinal stem cell niche. IL-33 programmed the differentiation of epithelial progenitors toward secretory IEC including Paneth and goblet cells. Finally, IL-33 suppressed Notch signaling in epithelial cells and induced expression of transcription factors governing differentiation into secretory IEC. In summary, we demonstrate that gut pericryptal fibroblasts release IL-33 to translate bacterial infection into an epithelial response to promote antimicrobial defense.

Gut mucosal DAMPs in IBD: from mechanisms to therapeutic implications

Endogenous damage-associated molecular patterns (DAMPs) are released during tissue damage and have increasingly recognized roles in the etiology of many human diseases. The inflammatory bowel diseases (IBD), ulcerative colitis (UC) and Crohn's disease (CD), are immune-mediated conditions where high levels of DAMPs are observed. DAMPs such as calprotectin (S100A8/9) have an established clinical role as a biomarker in IBD. In this review, we use IBD as an archetypal common chronic inflammatory disease to focus on the conceptual and evidential importance of DAMPs in pathogenesis and why DAMPs represent an entirely new class of targets for clinical translation.

Cytokine-Induced Modulation of Colorectal Cancer

The emergence of novel immunomodulatory cancer therapies over the last decade, above all immune checkpoint blockade, has significantly advanced tumor treatment. For colorectal cancer (CRC), a novel scoring system based on the immune cell infiltration in tumors has greatly improved disease prognostic evaluation and guidance to more specific therapy. These findings underline the relevance of tumor immunology in the future handling and therapeutic approach of malignant disease. Inflammation can either promote or suppress CRC pathogenesis and inflammatory mediators, mainly cytokines, critically determine the pro- or anti-tumorigenic signals within the tumor environment. Here, we review the current knowledge on the cytokines known to be critically involved in CRC development and illustrate their mechanisms of action. We also highlight similarities and differences between CRC patients and murine models of CRC and point out cytokines with an ambivalent role for intestinal cancer. We also identify some of the future challenges in the field that should be addressed for the development of more effective immunomodulatory therapies.

IL-33 Drives Eosinophil Infiltration and Pathogenic Type 2 Helper T-Cell Immune Responses Leading to Chronic Experimental Ileitis

Although a clear association has been established between IL-33 and inflammatory bowel disease, mechanistic studies to date, primarily using acute murine models of colitis, have yielded contradicting results, demonstrating both pathogenic and protective roles. We used a well-characterized, spontaneous model of inflammatory bowel disease [ie, SAMP1/YitFc (SAMP) mice] to investigate the role of IL-33 during chronic intestinal inflammation. Our results showed marked eosinophil infiltration into the gut mucosa with increased levels of eotaxins and type 2 helper T-cell (Th2) cytokines as disease progressed and became more severe, which could be reversed upon either eosinophil depletion or blockade of IL-33 signaling. Exogenous IL-33 administration recapitulated these effects in ilea of uninflamed (parental) control AKR/J mice. Human data supported these findings, showing colocalization and up-regulation of IL-33 and eosinophils in the colonic mucosa of inflammatory bowel disease patients versus noninflamed controls. Finally, colonization of commensal flora by fecal material transplantation into germ-free SAMP and the presence of the gut microbiome induced IL-33, subsequent eosinophil infiltration, and mounting of Th2 immune responses, leading to exacerbation of chronic intestinal inflammation characteristic of SAMP mice. These data demonstrate a pathogenic role for IL-33-mediated eosinophilia and activation of Th2 immunity in chronic intestinal inflammation that is dependent on the gut microbiome. Targeting IL-33 may represent a novel therapeutic approach to treat patients with inflammatory bowel disease.

Interleukin-33 in tumorigenesis, tumor immune evasion, and cancer immunotherapy

Interleukin-33 (IL-33) is a member of the IL-1 gene family and mainly expressed in the nucleus of tissue lining cells, stromal cells, and activated myeloid cells. IL-33 is considered a damage-associated molecular pattern (DAMP) molecule and plays an important role in many physiological and pathological settings such as tissue repair, allergy, autoimmune disease, infectious disease, and cancer. The biological functions of IL-33 include maintaining tissue homeostasis, enhancing type 1 and 2 cellular immune responses, and mediating fibrosis during chronic inflammation. IL-33 exerts diverse functions through signaling via its receptor ST2, which is expressed in many types of cells including regulatory T cells (Treg), group 2 innate lymphoid cells (ILC2s), myeloid cells, cytotoxic NK cells, Th2 cells, Th1 cells, and CD8(+) T cells. Tumor development results in downregulation of IL-33 in epithelial cells but upregulation of IL-33 in the tumor stroma and serum. The current data suggest that IL-33 expression in tumor cells increases immunogenicity and promotes type 1 antitumor immune responses through CD8(+) T cells and NK cells, whereas IL-33 in tumor stroma and serum facilitates immune suppression via Treg and myeloid-derived suppressor cell (MDSC). Understanding the role of IL-33 in cancer immunobiology sheds lights on targeting this cytokine for cancer immunotherapy.

Interleukin-33 Expression Indicates a Favorable Prognosis in Malignant Salivary Gland Tumors

The cytokine interleukin-33 (IL-33) is abundantly expressed in epithelial barrier tissues such as salivary glands. Here, we characterized nuclear IL-33 protein expression by immunohistochemistry in benign and malignant salivary gland tumors and associated it with disease outcome. Most benign salivary gland tumors expressed IL-33, and all Warthin's tumors showed strong and consistent IL-33 expression in the basally oriented cells of their bilayered epithelium. In the malignant group of neoplasms, nuclear IL-33 expression was limited to specific tumor entities-for example, to epithelial-myopepithelial carcinomas (n = 9/11), acinic cell carcinomas (n = 13/27), and oncocytic carcinomas (n = 2/2). IL-33 expression in the combined group of malignant salivary gland neoplasms was significantly associated with favorable histological parameters, lack of metastasis, and longer overall survival, compared with IL-33-negative tumors. We conclude that IL-33 expression is a novel prognostic marker for malignant salivary gland tumors with potential use in clinical diagnostics.

Serum Interleukin-33 level in Saudi children with inflammatory bowel disease

Interleukin-33 (IL-33) is a cytokine that belongs to the interleukin-1 family and has been shown to be associated with mucosal inflammation. The aim of this study was to determine the serum level of IL-33 in children with ulcerative colitis (UC) and Crohn's disease (CD) and to correlate the level with the disease progression. In this cross sectional prospective study, we enrolled 50 children with IBD from KAUH, Jeddah, Saudi Arabia and 34 healthy control subjects between June 2012 and December 2012. Serum IL-33 was assessed by ELISA and CRP by immunonephelometric assay. Results from our study showed 32 CD and 18 UC patients included. The median age was 13.5 years for CD patients, 11.9 years for UC patients and 11.2 years for controls. Females constituted 53%, 66.7% and 59% of CD, UC and control subjects respectively. The median serum IL-33 in UC patients of 55.5 pg/mL was significantly higher than the median IL-33 level of 41 pg/mL in the healthy control (P=0.04) but no significant difference was found between the median IL-33 level in the sera of CD and the control group (P=0.7). A higher median IL-33 level was also found in active disease (P=0.03). In our cohort, the serum level of IL-33 was positively correlated with hs-CRP (r=0.48, P < 0.001). To conclude, our results support that serum IL-33 level is increased in children with UC as compared with control. Serum level is correlated with the disease activity; therefore it could be used as a potential biomarker for monitoring the severity of the disease in children with UC.

Development of Fibrosis in Acute and Longstanding Ulcerative Colitis

BACKGROUND

Intestinal fibrosis is a process driven by chronic inflammation leading to increased presence of myofibroblasts and collagen deposition. Although strictures are rarely seen in ulcerative colitis [UC], longstanding disease is believed to cause fibrosis resulting in altered bowel function.

METHODS

The presence of fibrosis was studied in colectomy specimens from patients with recent-onset UC refractory to medical treatment [n = 13] and longstanding UC [n = 16], and colon cancer patients without UC [n = 7] as controls. Severity of inflammation was scored according to the Geboes score on haematoxylin and eosin stainings. Immunohistochemistry was performed to detect α-smooth muscle actin, fibronectin and collagen I and III.

RESULTS

Colectomy specimens from patients with acute UC showed significantly more inflammation than those with longstanding disease [19 vs 9 points, p = 0.01]. Both acute and longstanding UC showed a thicker muscularis mucosa than controls [0.10 vs 0.10 vs 0.05 mm, respectively, p = 0.019]. An increase in collagen I and III deposition in the mucosa was observed in UC compared with controls (40% [30-75] vs 25% [10-25], p = 0.033), but this did not differ significantly among acute and longstanding UC patients.

CONCLUSIONS

Collagen deposition is enhanced in UC compared with controls. However, UC collagen deposition does not increase significantly over time and does not seem to aggravate the entire fibrotic process.

Interleukin-33 acts as a transcriptional repressor and extracellular cytokine in fibroblast-like synoviocytes in patients with rheumatoid arthritis

The present study aimed to assess the functions of interleukin (IL)-33 in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA). Enzyme-linked immunosorbent assays (ELISAs) were used to quantify interleukin (IL)-33 in plasma obtained from patients with RA and osteoarthritis (OA). To evaluate functions of intracellular IL-33, levels of inflammatory mediators and matric metalloproteinases (MMPs) were measured in RA FLS transfected with IL-33 small- interfering RNA (siRNA) or plasmids, and changes in the expression and regulation of nuclear factor kappaB (NF-κB) were determined using western blotting and reporter gene assays. In addition, to examine the extracellular effects of IL-33, IP10 and receptor activator of NF-κB ligand (RANKL) mRNA levels were measured after treatment with IL-33 and blocking antibodies to ST2, the IL-33 receptor. To evaluate whether extracellular IL-33 regulated osteoclastogenesis, human CD14(+) monocytes cocultured with IL-33-stimulated FLS were stained with tartrate-resistant acid phosphatase (TRAP). IL-33 levels were higher in plasma obtained from patients with RA than in those obtained from patients with OA. The expression levels of IL-33 were elevated in RA FLS that had been stimulated with poly I:C, IL-1β, and tumor necrosis factor (TNF)-α. Silencing of IL-33 increased the levels of pro-inflammatory molecules and MMPs, promoted inhibitor of kappaB (IκBα) degradation, and increased NF-κB activity; these effects were reversed in IL-33 plasmid-transfected FLS. Stimulation with exogenous IL-33 increased RANKL and IP-10 mRNA expression. These increases were blocked by anti-ST2 treatment. Furthermore, we confirmed that extracellular IL-33 stimulated the formation of TRAP(+) multinucleated osteoclasts through RA FLS. These results suggested that intracellular IL-33 acted as a transcriptional repressor of NF-κB, which may provide negative feedback against inflammatory responses, whereas, extracellular IL-33 functioned as an activator of osteoclastogenesis. Therefore, increased plasma IL-33 levels in patients with RA could be a possible biomarker to reflect the potential risks of bone erosion.

Eosinophils and IL-33 Perpetuate Chronic Inflammation and Fibrosis in a Pediatric Population with Stricturing Crohn's Ileitis

BACKGROUND

Fibrostenosis and stricture are well-recognized endpoints in Crohn's disease (CD). We hypothesized that stricturing CD is characterized by eosinophilia and epithelial IL-33. We proposed that eosinophil exposure to IL-33 would perpetuate inflammatory chronicity and subsequent fibrostenosis.

METHODS

We performed a retrospective study of 74 children with inflammatory and stricturing ileal CD comparing clinicopathological features to immunohistochemical measures of eosinophilia and IL-33. To scrutinize eosinophil patterns, we developed a novel eosinophil peroxidase score encompassing number, distribution, and degranulation. Human eosinophils and intestinal fibroblasts were cultured with IL-33 and IL-13, and inflammatory and remodeling parameters were assessed. Antieosinophil therapy was also administered to the Crohn's-like ileitis model (SAMP1/SkuSlc).

RESULTS

Our novel eosinophil peroxidase score was more sensitive than H&E staining, revealing significant differences in eosinophil patterns, comparing inflammatory and stricturing pediatric CD. A significant relationship between ileal eosinophilia and complicated clinical/histopathological phenotype including fibrosis was determined. IL-33 induced significant eosinophil peroxidase secretion and IL-13 production. Exposure to eosinophils in the presence of IL-33, "primed" fibroblasts to increase proinflammatory cytokines (TNF-α, IL-1β, and IL-6), eosinophil-associated chemokines (CCL24 and CCL26), and IL-13Rα2 production. Production of fibrogenic molecules (collagen 1A2, fibronectin, and periostin) increased after exposure of "primed" fibroblasts to IL-13. Epithelial-IL-33 was increased in pediatric Crohn's ileitis and strongly associated with clinical and histopathological activity, ileal eosinophilia, and complicated fibrostenotic disease. SAMP1/SkuSlc eosinophil-targeted treatment resulted in significant improvements in inflammation and remodeling.

CONCLUSIONS

Our study of specimens from pediatric patients with ileal CD linked eosinophil patterns and IL-33 to fibrosis and suggested that these may contribute to the perpetuation of inflammation and subsequent stricture in pediatric CD.

Rhinoviral stimuli, epithelial factors and ATP signalling contribute to bronchial smooth muscle production of IL-33

BACKGROUND

Bronchial smooth muscle cells (BSMCs) from severe asthmatics have been shown to overexpress the Th2-driving and asthma-associated cytokine IL-33. However, little is known regarding factors involved in BSMC production of IL-33. Rhinovirus (RV) infections cause asthma exacerbations, which exhibit features of Th2-type inflammation. Here, we investigated the effects of epithelial-derived media and viral stimuli on IL-33 expression in human BSMCs.

METHODS

Primary human BSMCs from healthy (n = 3) and asthmatic (n = 3) subjects were stimulated with conditioned media from primary human bronchial epithelial cells (BECs), double-stranded (ds)RNA, dsRNA/LyoVec, or infected with RV. BSMCs were also pretreated with the purinergic receptor antagonist suramin. IL-33 expression was analysed by RT-qPCR and western blot and ATP levels were determined in cell supernatants.

RESULTS

RV infection and activation of TLR3 by dsRNA increased IL-33 mRNA and protein in healthy and asthmatic BSMCs. These effects were inhibited by dexamethasone. BSMC expression of IL-33 was also increased by stimulation of RIG-I-like receptors using dsRNA/LyoVec. Conditioned media from BECs induced BSMC expression of IL-33, which was further enhanced by dsRNA. BEC-derived medium and viral-stimulated BSMC supernatants exhibited elevated ATP levels. Blocking of purinergic signalling with suramin inhibited BSMC expression of IL-33 induced by dsRNA and BEC-derived medium.

CONCLUSIONS

RV infection of BSMCs and activation of TLR3 and RIG-I-like receptors cause expression and production of IL-33. Epithelial-released factor(s) increase BSMC expression of IL-33 and exhibit positive interaction with dsRNA. Increased BSMC IL-33 associates with ATP release and is antagonised by suramin. We suggest that epithelial-derived factors contribute to baseline BSMC IL-33 production, which is further augmented by RV infection of BSMCs and stimulation of their pathogen-recognising receptors.

The IL-33/ST2 pathway contributes to intestinal tumorigenesis in humans and mice

Colorectal cancer (CRC) develops through a multistep process and is modulated by inflammation. However, the inflammatory pathways that support intestinal tumors at different stages remain incompletely understood. Interleukin (IL)-33 signaling plays a role in intestinal inflammation, yet its contribution to the pathogenesis of CRC is unknown. Using immunohistochemistry on 713 resected human CRC specimens, we show here that IL-33 and its receptor ST2 are expressed in low-grade and early-stage human CRCs, and to a lesser extent in higher-grade and more advanced-stage tumors. In a mouse model of CRC, ST2-deficiency protects from tumor development. Moreover, bone marrow (BM) chimera studies indicate that engagement of the IL-33/ST2 pathway on both the radio-resistant and radio-sensitive compartment is essential for CRC development. Mechanistically, activation of IL-33/ST2 signaling compromises the integrity of the intestinal barrier and triggers the production of pro-tumorigenic IL-6 by immune cells. Together, this data reveals a tumor-promoting role of IL-33/ST2 signaling in CRC.

Single high-dose irradiation aggravates eosinophil-mediated fibrosis through IL-33 secreted from impaired vessels in the skin compared to fractionated irradiation

We have revealed in a porcine skin injury model that eosinophil recruitment was dose-dependently enhanced by a single high-dose irradiation. In this study, we investigated the underlying mechanism of eosinophil-associated skin fibrosis and the effect of high-dose-per-fraction radiation. The dorsal skin of a mini-pig was divided into two sections containing 4-cm(2) fields that were irradiated with 30 Gy in a single fraction or 5 fractions and biopsied regularly over 14 weeks. Eosinophil-related Th2 cytokines such as interleukin (IL)-4, IL-5, and C-C motif chemokine-11 (CCL11/eotaxin) were evaluated by quantitative real-time PCR. RNA-sequencing using 30 Gy-irradiated mouse skin and functional assays in a co-culture system of THP-1 and irradiated-human umbilical vein endothelial cells (HUVECs) were performed to investigate the mechanism of eosinophil-mediated radiation fibrosis. Single high-dose-per-fraction irradiation caused pronounced eosinophil accumulation, increased profibrotic factors collagen and transforming growth factor-β, enhanced production of eosinophil-related cytokines including IL-4, IL-5, CCL11, IL-13, and IL-33, and reduced vessels compared with 5-fraction irradiation. IL-33 notably increased in pig and mouse skin vessels after single high-dose irradiation of 30 Gy, as well as in irradiated HUVECs following 12 Gy. Blocking IL-33 suppressed the migration ability of THP-1 cells and cytokine secretion in a co-culture system of THP-1 cells and irradiated HUVECs. Hence, high-dose-per-fraction irradiation appears to enhance eosinophil-mediated fibrotic responses, and IL-33 may be a key molecule operating in eosinophil-mediated fibrosis in high-dose-per fraction irradiated skin.

IL-33 activates tumor stroma to promote intestinal polyposis

Tumor epithelial cells develop within a microenvironment consisting of extracellular matrix, growth factors, and cytokines produced by nonepithelial stromal cells. In response to paracrine signals from tumor epithelia, stromal cells modify the microenvironment to promote tumor growth and metastasis. Here, we identify interleukin 33 (IL-33) as a regulator of tumor stromal cell activation and mediator of intestinal polyposis. In human colorectal cancer, IL-33 expression was induced in the tumor epithelium of adenomas and carcinomas, and expression of the IL-33 receptor, IL1RL1 (also referred to as IL1-R4 or ST2), localized predominantly to the stroma of adenoma and both the stroma and epithelium of carcinoma. Genetic and antibody abrogation of responsiveness to IL-33 in the Apc(Min/+) mouse model of intestinal tumorigenesis inhibited proliferation, induced apoptosis, and suppressed angiogenesis in adenomatous polyps, which reduced both tumor number and size. Similar to human adenomas, IL-33 expression localized to tumor epithelial cells and expression of IL1RL1 associated with two stromal cell types, subepithelial myofibroblasts and mast cells, in Apc(Min/+) polyps. In vitro, IL-33 stimulation of human subepithelial myofibroblasts induced the expression of extracellular matrix components and growth factors associated with intestinal tumor progression. IL-33 deficiency reduced mast cell accumulation in Apc(Min/+) polyps and suppressed the expression of mast cell-derived proteases and cytokines known to promote polyposis. Based on these findings, we propose that IL-33 derived from the tumor epithelium promotes polyposis through the coordinated activation of stromal cells and the formation of a protumorigenic microenvironment.

Interleukin-33 promotes inflammatory cytokine production in chronic airway inflammation

Interleukin (IL)-33, belonging to the IL-1 family, is a novel cytokine that plays an important role in several chronic inflammatory diseases. Its role in chronic airway inflammation that develops into COPD is widely unknown. To determine this, we identified the expression of IL-33 in human bronchial epithelial layer and detected the inflammatory effects of IL-33 stimulation and the relative signaling pathways in human bronchial epithelial (HBE) cells and peripheral blood mononuclear cells (PBMCs), respectively. In this study, the expression of IL-33 in human bronchial epithelial layer was upregulated in COPD patients compared with normal controls. The expressions of IL-6 and IL-8 were also increased in both HBE cells and PBMCs, stimulated by IL-33 alone or combining the cigarette smoke extract (CSE). And the increased expressions could be partially blocked by ST2-Fc and IL-1RacP-Fc in both HBE cells and PBMCs. The p42/p44 ERK inhibitor in HBE cells and the p38 MAPK inhibitor in PBMCs exerted similar effects. Our data showed that IL-33 could induce and enhance the expression of IL-6 and IL-8 in HBE cells and PBMCs of COPD patients via ST2/IL-1RacP pathway and MAPKs pathway. Thus, the IL-33 is a promoter of chronic airway inflammation that contributes to COPD development.

The potential role of IL-33/ST2 signaling in fibrotic diseases

IL-33, a new member of the IL-1F, is widely expressed throughout the body and can be up-regulated by stimulation with proinflammatory factors. It has been identified as a functional ligand for the plasma membrane receptor complex that is a heterodimer consisting of membrane-bound ST2L, which is a member of the IL-1R family, and IL-1RAcP. IL-33 is crucial for the induction of Th2 immune responses. Additionally, under other circumstances, it can also act as an endogenous danger signal. Recently, many studies have demonstrated that IL-33 may be related to the development and progression of fibrotic diseases. It has proinflammatory effects in some fibrotic diseases but has anti-inflammatory effects in others. In this review, the biologic characteristics of IL-33 and the role of the IL-33/ST2 signaling pathway in various fibrotic diseases will be discussed. We hope this overview will provide new insights for the treatment of these diseases.

Expression of interleukin-33 and its receptor ST2 in periapical granulomas and radicular cysts

BACKGROUND

Interleukin-33 (IL-33) is a recently identified cytokine belonging to the IL-1 family and ligand for the IL-1 receptor-related protein ST2. IL-33/ST2 signaling plays a critical role in allergy, autoimmunity, and chronic inflammatory disorders, but its role in the pathogenesis of periapical lesions is unknown. We aimed to investigate the expression patterns of IL-33 and ST2 in human periapical lesions.

METHODS

Periapical lesions (n = 36) and healthy periapical tissues (n = 10) were evaluated by immunohistochemistry using antibodies specific for human IL-33 and ST2. Lesion samples were further analyzed by double immunofluorescence to assess IL-33/ST2 co-expression.

RESULTS

The numbers of IL-33- and ST2-positive fibroblasts were significantly higher in periapical lesions compared to healthy periapical tissues (both P < 0.05), while the numbers of IL-33- and ST2-positive endothelial cells were similar (both P > 0.05). There were no significant differences in the numbers of IL-33- and ST2-positive fibroblasts and endothelial cells between periapical granulomas and radicular cysts (all P > 0.05). Similarly, numbers of ST2-positive mononuclear cells did not differ between periapical granulomas and radicular cysts (P > 0.05). The majority of epithelial cells in radicular cysts were IL-33 positive, while the small proportion of epithelial cells was ST2 positive. Double immunofluorescence analysis revealed IL-33/ST2 co-expression in fibroblasts and endothelial cells.

CONCLUSIONS

IL-33 and ST2 are expressed in periapical granulomas and radicular cysts. Increased numbers of IL-33- and ST2-positive fibroblasts in periapical lesions when compared to healthy periapical tissues suggest that IL-33/ST2 signaling may be involved in periapical inflammation and tissue fibrosis.

IL-33 promotes GATA-3 polarization of gut-derived T cells in experimental and ulcerative colitis

BACKGROUND

In the respiratory mucosa, interleukin (IL)-33, has been shown to enhance T helper 2 (TH2)-type responses through the master regulatory gene GATA-3. IL-33 is upregulated in ulcerative colitis (UC), and the aim was to assess if IL-33 holds a similar key position in the shaping of the immune response in experimental colitis (piroxicam-accelerated colitis (PAC) in IL-10 (-/-) mice, dextran sodium sulfate (DSS) model) and UC.

METHODS

Colonic IL-33 expression was determined in UC (8 active UC, 8 quiescent UC, and 7 controls) and experimental colitis. Mesenteric lymph node (MesLN) T cells were isolated from PAC IL-10 (-/-) mice and stimulated with IL-33.

RESULTS

The colonic IL-33 expression was significantly upregulated all forms of colitis (P < 0.01) and correlated with disease severity score and inflammation (P < 0.001), and with GATA-3 expression levels (P < 0.01); no correlation with the TH1-specific T-bet expression was observed. MesLN T cells stimulated with IL-33 had increased GATA-3 expression, and showed an IL-33 dose-dependent increase in secreted TH2-type cytokines, whereas this effect was abolished by blocking IL-33 signaling. The non-TH2-type cytokine IL-17 was upregulated by IL-33 but in a T cell receptor dependent manner, as opposed to TH2-type cytokines, which required only IL-33 stimulation.

CONCLUSIONS

The study demonstrates that intestinal IL-33 is capable of inducing GATA-3 in mucosal T cells, and suggests that IL-33 is a key mediator of pathological TH2 and non-TH2-type responses in intestinal inflammation. Blocking IL-33 signaling could be a feasible option in the treatment of UC.

Fibrosis in ulcerative colitis: mechanisms, features, and consequences of a neglected problem

Chronic intestinal inflammation and impaired tissue repair leading to intestinal fibrosis are a commonly observed complication in inflammatory bowel disease. This is particularly true for small bowel Crohn's disease. However, the development of fibrosis in ulcerative colitis has remained largely unexplored. This is surprising, given knowledge about its prevalence for decades, well described histopathologic features of fibrotic and stricturing ulcerative colitis, the relevance of the extracellular matrix for intestinal inflammation and fibrosis, and the clinical impact of fibrosis on stricture formation, motility, and the necessary discrimination from colonic malignancy. This systematic review summarizes the current knowledge of ulcerative colitis-related fibrosis, including epidemiology, basic mechanisms, histopathology, and clinical implications.

Impaired endothelium-mesenchymal stem cells cross-talk in systemic sclerosis: a link between vascular and fibrotic features

INTRODUCTION

To assess if an impaired cross-talk between endothelial cells (ECs) and perivascular/multipotent mesenchymal stem cells (MSCs) might induce a perturbation of vascular repair and leading to a phenotypic switch of MSC toward myofibroblast in Systemic Sclerosis (SSc).

METHODS

We investigated different angiogenic and profibrotic molecules in a tridimentional matrigel assay, performing co-cultures with endothelial cells (ECs) and bone marrow derived MSCs from patients and healthy controls (HC). After 48 hours of co-culture, cells were sorted and analyzed for mRNA and protein expression.

RESULTS

ECs-SSc showed a decreased tube formation ability which is not improved by co-cultures with different MSCs. After sorting, we showed: i. an increased production of vascular endothelial growth factor A (VEGF-A) in SSc-MSCs when co-cultured with SSc-ECs; ii. an increased level of transforming growth factor beta (TGF-β) and platelet growth factor BB (PDGF-BB) in SSc-ECs when co-cultured with both HC- and SSc-MSCs; iii. an increase of TGF-β, PDGF-R, alpha smooth muscle actin (α-SMA) and collagen 1 (Col1) in both HC- and SSc-MSCs when co-cultured with SSc-ECs.

CONCLUSION

We showed that during SSc, the ECs-MSCs crosstalk resulted in an altered expression of different molecules involved in the angiogenic processes, and mainly SSc-ECs seem to modulate the phenotypic switch of perivascular MSCs toward a myofibroblast population, thus supporting the fibrotic process.

Inflammatory bowel disease in pediatric and adolescent patients: A biomolecular and histopathological review

Crohn’s disease (CD) and ulcerative colitis (UC) are the two main forms of inflammatory bowel disease (IBD) with both overlapping and distinct clinical, pathological and biomolecular features. It has been suggested that pediatric IBD is a distinct disease entity, with probably different disease subtypes.The aim of this study is to review and summarize the evolution of the current concept of pediatric IBD. The results of this review reinforce the idea that pediatric CD and UC may be further classified in various clinicopathologic entities. For clinicians and pathologists convenience, practical algorithms for the distinction of the various subphenotypes of pediatric IBD are also provided.

Granulomas are a source of interleukin-33 expression in pulmonary and extrapulmonary sarcoidosis

Sarcoidosis is a chronic inflammatory disease characterized by noncaseating epithelioid granulomas. These granulomas consist of highly differentiated mononuclear phagocytes--epithelioid cells and multinucleated giant cells (MNGCs)--surrounded by a proinflammatory infiltrate. Interleukin-33 (IL-33) is an inflammatory cytokine that is constitutively expressed in barrier tissues such as skin and lung and up-regulated in inflammation. Because sarcoidosis occurs most frequently in lung and skin, we studied the expression of this cytokine by immunohistochemistry in these tissues from patients with sarcoidosis, with foreign body granulomas, with other granulomatous diseases, and in corresponding normal tissues. We identified nuclear IL-33 staining of epithelioid cells and MNGCs in biopsies of skin (18/25 patients, 72%) and lung (10/19 patients, 53%) sarcoidosis. In contrast, sarcoidal granulomas in lymph nodes did not show IL-33 expression. Other granulomatous diseases showed only occasional and weak IL-33 expression. In sarcoidosis, we found a strong correlation between IL-33 expression and systemic disease, presence of MNGCs, and an M2-like macrophage phenotype as assessed by CD163 staining. Therefore, we propose that IL-33 plays a critical role in pathogenesis and disease progression of sarcoidosis. Because IL-33 is less commonly and only weakly expressed in other granulomatous diseases, the detection of IL-33 might serve as an adjunctive diagnostic marker. IL-33 expression in sarcoidosis seems to be dependent on the specific tissue microenvironment of sarcoidal granulomas and represents a novel biomarker for systemic involvement.

Unique temporal and spatial expression patterns of IL-33 in ovaries during ovulation and estrous cycle are associated with ovarian tissue homeostasis

Ovaries are among the most active organs. Frequently occurring events such as ovulation and ovarian atresia are accompanied with tissue destruction and repairing. Critical roles of immune cells or molecules in those events have been well recognized. IL-33 is a new member of the IL-1 cytokine gene family. Recent studies suggest its roles beyond immune responses. We systemically examined its expression in ovaries for its potential roles in ovarian functions. During ovulation, a high level of IL-33 was transiently expressed, making it the most significantly upregulated immune gene. During estrous cycle, IL-33 expression levels fluctuated along with numbers of ovarian macrophages and atresia wave. Cells with nuclear form of IL-33 (nIL-33(+) cells) were mostly endothelial cells of veins, either in the inner layer of theca of ovulating follicles during ovulation, or surrounding follicles during estrous cycle. Changes in number of nIL-33(+) cells showed a tendency similar to that in IL-33 mRNA level during estrous cycle. However, the cell number sharply declined before a rapid increase of macrophages and a surge of atresia. The decline in nIL-33(+) cell number was coincident with detection of higher level of the cytokine form of IL-33 by Western blot, suggesting a release of cytokine form of IL-33 before the surge of macrophage migration and atresia. However, IL-33 Ab, either by passive transfer or immunization, showed a limited effect on ovulation or atresia. It raises a possibility of IL-33's role in tissue homeostasis after ovarian events, instead of a direct involvement in ovarian functions.

MFG-E8 regulates angiogenesis in cutaneous wound healing

Our research group recently demonstrated that pericytes are major sources of the secreted glycoprotein and integrin ligand lactadherin (MFG-E8) in B16 melanoma tumors, and that MFG-E8 promotes angiogenesis via enhanced PDGF-PDGFRβ signaling mediated by integrin-growth factor receptor crosstalk. However, sources of MFG-E8 and its possible roles in skin physiology are not well characterized. The objective of this study was to characterize the involvement of MFG-E8 in skin wound healing. In the dermis of normal murine and human skin, accumulations of MFG-E8 were found around CD31(+) blood vessels, and MFG-E8 colocalized with PDGFRβ(+), αSMA(+), and NG2(+) pericytes. MFG-E8 protein and mRNA levels were elevated in the dermis during full-thickness wound healing in mice. MFG-E8 was diffusely present in granulation tissue and was localized around blood vessels. Wound healing was delayed in MFG-E8 knockout mice, compared with the wild type, and myofibroblast and vessel numbers in wound areas were significantly reduced in knockout mice. Inhibition of MFG-E8 production with siRNA attenuated the formation of capillary-like structures in vitro. Expression of MFG-E8 in fibrous human granulation tissue with scant blood vessels was less than that in granulation tissue with many blood vessels. These findings suggest that MFG-E8 promotes cutaneous wound healing by enhancing angiogenesis.

IFN-γ directly controls IL-33 protein level through a STAT1- and LMP2-dependent mechanism

IL-33 contributes to disease processes in association with Th1 and Th2 phenotypes. IL-33 mRNA is rapidly regulated, but the fate of synthesized IL-33 protein is unknown. To understand the interplay among IL-33, IFN-γ, and IL-4 proteins, recombinant replication-deficient adenoviruses were produced and used for dual expression of IL-33 and IFN-γ or IL-33 and IL-4. The effects of such dual gene delivery were compared with the effects of similar expression of each of these cytokines alone. In lung fibroblast culture, co-expression of IL-33 and IFN-γ resulted in suppression of the levels of both proteins, whereas co-expression of IL-33 and IL-4 led to mutual elevation. In vivo, co-expression of IL-33 and IFN-γ in the lungs led to attenuation of IL-33 protein levels. Purified IFN-γ also attenuated IL-33 protein in fibroblast culture, suggesting that IFN-γ controls IL-33 protein degradation. Specific inhibition of caspase-1, -3, and -8 had minimal effect on IFN-γ-driven IL-33 protein down-regulation. Pharmacological inhibition, siRNA-mediated silencing, or gene deficiency of STAT1 potently up-regulated IL-33 protein expression levels and attenuated the down-regulating effect of IFN-γ on IL-33. Stimulation with IFN-γ strongly elevated the levels of the LMP2 proteasome subunit, known for its role in IFN-γ-regulated antigen processing. siRNA-mediated silencing of LMP2 expression abrogated the effect of IFN-γ on IL-33. Thus, IFN-γ, IL-4, and IL-33 are engaged in a complex interplay. The down-regulation of IL-33 protein levels by IFN-γ in pulmonary fibroblasts and in the lungs in vivo occurs through STAT1 and non-canonical use of the LMP2 proteasome subunit in a caspase-independent fashion.

Interleukin-33 and inflammatory bowel diseases: lessons from human studies

Interleukin- (IL-) 33 is a widely expressed cytokine present in different cell types, such as epithelial, mesenchymal, and inflammatory cells, supporting a predominant role in innate immunity. IL-33 can function as a proinflammatory cytokine inducing Th2 type of immune response being involved with the defense against parasitic infections of the gastrointestinal tract. In addition, it has been proposed that IL-33 can act as a signaling molecule alerting the immune system of danger or tissue damage. Recently, in the intestinal mucosa, overexpression of IL-33 has been reported in samples from patients with inflammatory bowel diseases (IBD). This review highlights the available data regarding IL-33 in human IBD and discusses emerging roles for IL-33 as a key modulator of intestinal inflammation.

Emerging role of interleukin-33 in autoimmune diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family. It predominantly induces type 2 immune responses and thus is protective against atherosclerosis and nematode infections but contributes to allergic airway inflammation. Interleukin-33 also plays a pivotal role in the development of many autoimmune diseases through mechanisms that are still not fully understood. In this review, we focus on the recent advances in understanding of the expression and function of IL-33 in some autoimmune disorders, aiming to provide insight into its potential role in disease development.

Neutralisation of the interleukin-33/ST2 pathway ameliorates experimental colitis through enhancement of mucosal healing in mice

OBJECTIVE

Inflammatory bowel diseases (IBD) have been intrinsically linked to a deregulated cytokine network, but novel therapeutic principles are urgently needed. Here we identify the interleukin (IL)-33 and its receptor ST2 as key negative regulators of wound healing and permeability in the colon of mice.

DESIGN

Expression of IL-33 and ST2 was determined by qRT-PCR, ELISA, immunohistochemistry and western-blot analysis. Wild-type and St2(-/-) mice were used in wound healing experiments and in two experimental models of IBD triggered by 2,4,6-trinitrobenzene sulphonic acid or dextran sodium sulphate (DSS). Neutralisation of ST2 was performed by using a specific blocking antibody.

RESULTS

Nuclear localisation and enhanced expression of IL-33 in myofibroblasts and enterocytes was linked to disease involvement independently of inflammation, while the expression of ST2 was primarily restricted to the colonic epithelia. In two experimental models of IBD, genetic ablation of ST2 significantly improved signs of colitis, while a sustained epithelial expression of the cyto-protective factor connexin-43 was observed in DSS-treated St2-deficient mice. Unexpectedly, absence of ST2 in non-hematopoietic cells was sufficient to protect against colitis. Consistently, specific inhibition of endogenous ST2-mediated signalling by treatment with neutralising antibody improved DSS-induced colitis. In addition, IL-33 treatment impaired epithelial barrier permeability in vitro and in vivo, whereas absence of ST2 enhanced wound healing response upon acute mechanical injury in the colon.

CONCLUSIONS

Our study unveiled a novel non-hematopoietic function of IL-33 in epithelial barrier function and wound healing. Therefore, blocking the IL-33/ST2 axis may represent an efficient therapy in IBD.

Role of lung pericytes and resident fibroblasts in the pathogenesis of pulmonary fibrosis

RATIONALE

The origin of cells that make pathologic fibrillar collagen matrix in lung disease has been controversial. Recent studies suggest mesenchymal cells may contribute directly to fibrosis.

OBJECTIVES

To characterize discrete populations of mesenchymal cells in the normal mouse lung and to map their fate after bleomycin-induced lung injury.

METHODS

We mapped the fate of Foxd1-expressing embryonic progenitors and their progeny during lung development, adult homeostasis, and after fibrosing injury in Foxd1-Cre; Rs26-tdTomato-R mice. We studied collagen-I(α)1-producing cells in normal and diseased lungs using Coll-GFP(Tg) mice.

MEASUREMENTS AND MAIN RESULTS

Foxd1-expressing embryonic progenitors enter lung buds before 13.5 days post-conception, expand, and form an extensive lineage of mesenchymal cells that have characteristics of pericytes. A collagen-I(α)1-expressing mesenchymal population of distinct lineage is also found in adult lung, with features of a resident fibroblast. In contrast to resident fibroblasts, Foxd1 progenitor-derived pericytes are enriched in transcripts for innate immunity, vascular development, WNT signaling pathway, and cell migration. Foxd1 progenitor-derived pericytes expand after bleomycin lung injury, and activate expression of collagen-I(α)1 and the myofibroblast marker αSMA in fibrotic foci. In addition, our studies suggest a distinct lineage of collagen-I(α)1-expressing resident fibroblasts that also expands after lung injury is a second major source of myofibroblasts.

CONCLUSIONS

We conclude that the lung contains an extensive population of Foxd1 progenitor-derived pericytes that are an important lung myofibroblast precursor population.

CD90(+) Stromal Cells are Non-Professional Innate Immune Effectors of the Human Colonic Mucosa

Immune responses at the intestinal mucosa must allow for host protection whilst simultaneously avoiding inappropriate inflammation. Although much work has focused on the innate immune functionality of hematopoietic immune cells, non-hematopoietic cell populations – including epithelial and stromal cells – are now recognized as playing a key role in innate defense at this site. In this study we examined the innate immune capacity of primary human intestinal stromal cells (iSCs). CD90⁺ iSCs isolated from human colonic mucosa expressed a wide array of innate immune receptors and functionally responded to stimulation with bacterial ligands. iSCs also sensed infection with live Salmonella typhimurium, rapidly expressing IL-1 family cytokines via a RIPK2/p38MAPK-dependent signaling process. In addition to responding to innate immune triggers, primary iSCs exhibited a capacity for bacterial uptake, phagocytosis, and antigen processing, although to a lesser extent than professional APCs. Thus CD90⁺ iSCs represent an abundant population of “non-professional” innate immune effector cells of the human colonic mucosa and likely play an important adjunctive role in host defense and immune regulation at this site.

Macrophage phenotype in the subclinical gut inflammation of patients with ankylosing spondylitis

OBJECTIVE

Long-term evolution of subclinical gut inflammation to overt Crohn's disease (CD) has been described in AS patients. The aim of this study was to evaluate macrophage polarization occurring in the inflamed gut of patients with AS.

METHODS

Twenty-seven HLA-B27(+) AS patients, 20 CD patients and 17 normal controls were consecutively enrolled. Classic M1 (iNOS(+)IL-10(-)), resolution phase (iNOS(+)IL-10(+)), M2 and CD14(+) macrophages were characterized by immunohistochemistry and flow cytometry. Quantitative gene expression analysis of IFN-γ, IL-4, IL-5, IL-33 and STAT6 was performed by real time PCR.

RESULTS

Classic M1 macrophages were expanded in CD and AS, where resolution phase macrophages predominate. A large increase in CD163(+) (M2) macrophages was observed in AS strictly correlated with the expression of IL-33, a Th2 cytokine involved in M2 polarization. Unlike in CD, CD14(+) macrophages were virtually absent in the gut of AS patients and controls.

CONCLUSION

The absence of CD14(+) macrophages together with the expansion of resolution phase and M2 macrophages is the immunological signature of subclinical ileal inflammation in AS.

Pathogenic mouse hepatitis virus or poly(I:C) induce IL-33 in hepatocytes in murine models of hepatitis

The IL-33/ST2 axis is known to be involved in liver pathologies. Although, the IL-33 levels increased in sera of viral hepatitis patients in human, the cellular sources of IL-33 in viral hepatitis remained obscure. Therefore, we aimed to investigate the expression of IL-33 in murine fulminant hepatitis induced by a Toll like receptor (TLR3) viral mimetic, poly(I:C) or by pathogenic mouse hepatitis virus (L2-MHV3). The administration of poly(I:C) plus D-galactosamine (D-GalN) in mice led to acute liver injury associated with the induction of IL-33 expression in liver sinusoidal endothelial cells (LSEC) and vascular endothelial cells (VEC), while the administration of poly(I:C) alone led to hepatocyte specific IL-33 expression in addition to vascular IL-33 expression. The hepatocyte-specific IL-33 expression was down-regulated in NK-depleted poly(I:C) treated mice suggesting a partial regulation of IL-33 by NK cells. The CD1d KO (NKT deficient) mice showed hepatoprotection against poly(I:C)-induced hepatitis in association with increased number of IL-33 expressing hepatocytes in CD1d KO mice than WT controls. These results suggest that hepatocyte-specific IL-33 expression in poly(I:C) induced liver injury was partially dependent of NK cells and with limited role of NKT cells. In parallel, the L2-MHV3 infection in mice induced fulminant hepatitis associated with up-regulated IL-33 expression as well as pro-inflammatory cytokine microenvironment in liver. The LSEC and VEC expressed inducible expression of IL-33 following L2-MHV3 infection but the hepatocyte-specific IL-33 expression was only evident between 24 to 32h of post infection. In conclusion, the alarmin cytokine IL-33 was over-expressed during fulminant hepatitis in mice with LSEC, VEC and hepatocytes as potential sources of IL-33.

Opposing Functions of Classic and Novel IL-1 Family Members in Gut Health and Disease

In addition to their well-established role(s) in the pathogenesis of gastrointestinal (GI)-related inflammatory disorders, including inflammatory bowel disease (IBD) and inflammation-associated colorectal cancer (CRC), emerging evidence confirms the critical involvement of the interleukin-1 (IL-1) cytokine family and their ligands in the maintenance of normal gut homeostasis. In fact, the paradigm that IBD occurs in two distinct phases is substantiated by the observation that classic IL-1 family members, such as IL-1, the IL-1 receptor antagonist (IL-1Ra), and IL-18, possess dichotomous functions depending on the phase of disease, as well as on their role in initiating vs. sustaining chronic gut inflammation. Another recently characterized IL-1 family member, IL-33, also possesses dual functions in the gut. IL-33 is upregulated in IBD and potently induces Th2 immune responses, while also amplifying Th1-mediated inflammation. Neutralization studies in acute colitis models, however, have yielded controversial results and recent reports suggest a protective role of IL-33 in epithelial regeneration and mucosal wound healing. Finally, although little is currently known regarding the potential contribution of IL-36 family members in GI inflammation/homeostasis, another IL-1 family member, IL-37, is emerging as a potent anti-inflammatory cytokine with the ability to down-regulate colitis. This new body of information has important translational implications for both the prevention and treatment of patients suffering from IBD and inflammation-associated CRC.

Profibrotic interleukin-33 is correlated with uterine leiomyoma tumour burden

STUDY QUESTION

Are interleukin-33 (IL-33) serum levels higher in women with uterine leiomyoma compared with controls without leiomyoma?

SUMMARY ANSWER

Serum IL-33 is elevated in women with uterine leiomyoma and correlated with features of uterine leiomyoma tumour burden, namely fibroid number, size and weight.

WHAT IS KNOWN ALREADY

Uterine leiomyomas are the most common benign tumours in premenopausal women associated with major tissue fibrosis. IL-33 is a cytokine involved in fibrotic disorders. The potential role of IL-33 in leiomyoma has not been reported before.

STUDY DESIGN, SIZE, DURATION

This is a prospective laboratory study conducted in a tertiary-care university hospital between January 2005 and December 2010. We investigated non-pregnant, 42-year-old patients (n = 151) during surgery for a benign gynaecological condition.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After complete surgical exploration of the abdominopelvic cavity, 59 women with histologically proved uterine leiomyoma and 92 leiomyoma-free control women were enrolled. Women with endometriosis or past history of ovarian malignancy and borderline tumours were not included. The control group included women with benign ovarian cysts, paratubal cysts or tubal defects without any evidence of uterine leiomyoma. For each patient, a structured questionnaire was completed during a face-to-face interview conducted by the surgeon during the month preceding surgery. Serum samples were obtained in the month preceding the surgical procedures according to the menstrual phase or hormonal therapy. IL-33 was measured in sera by enzyme-linked immunosorbent assay, and correlation of IL-33 concentration with the extent and severity of the disease was investigated.

MAIN RESULTS AND THE ROLE OF CHANCE

IL-33 was detected in 32 (54.2%) women with leiomyoma and 18 (19.6%) controls (P < 0.001). Serum IL-33 was higher in women with leiomyoma (median, 140.1 pg/ml; range, 7.5-2247.7) than in controls (median, 27.8 pg/ml; range, 7.5-71.6; P = 0.002). We found positive correlations between serum IL-33 concentration and leiomyoma features, such as fibroid weight (r = 0.630; P = 0.001) and size (r = 0.511; P = 0.018) and the number of fibroids (r = 0.503; P = 0.003).

LIMITATIONS, REASONS FOR CAUTION

There was a possible selection bias due to inclusion of only surgical patients. Therefore our control group consisted of women who underwent surgery for benign gynaecological conditions. This may lead to biases stemming from the fact that certain of these conditions, such as tubal infertility or ovarian cysts, might be associated with altered serum IL-33 levels.

WIDER IMPLICATIONS OF THE FINDINGS

We demonstrate for the first time that elevated serum IL-33 levels are associated with the existence of uterine leiomyoma. However, even if an association does not constitute proof of cause and effect, investigating the mechanisms that underlie fibrogenesis associated with leiomyomas is a step towards understanding this enigmatic disease. This study opens the doors to future, more mechanistics studies to establish the exact role of IL-33 in uterine leiomyomas pathogenesis.

STUDY FUNDING/COMPETING INTEREST(S)

No funding, no conflict of interest.

The role of IL-33 in gut mucosal inflammation

Interleukin (IL)-33 is a recently identified cytokine belonging to the IL-1 family that is widely expressed throughout the body and has the ability to induce Th2 immune responses. In addition, IL-33 plays a key role in promoting host defenses against parasites through the expansion of a novel population of innate lymphoid cells. In recent years, a growing body of evidence has shown that the proinflammatory properties displayed by IL-33 are detrimental in several experimental models of inflammation; in others, however, IL-33 appears to have protective functions. In 2010, four different research groups consistently described the upregulation of IL-33 in patients with inflammatory bowel disease (IBD). Animal models of IBD were subsequently utilized in order to mechanistically determine the precise role of IL-33 in chronic intestinal inflammation, without, however, reaching conclusive evidence demonstrating whether IL-33 is pathogenic or protective. Indeed, data generated from these studies suggest that IL-33 may possess dichotomous functions, enhancing inflammatory responses on one hand and promoting epithelial integrity on the other. This review focuses on the available data regarding IL-33/ST2 in the physiological and inflammatory states of the gut in order to speculate on the possible roles of this novel IL-1 family member in intestinal inflammation.

Associations between genetic polymorphisms in IL-33, IL1R1 and risk for inflammatory bowel disease

BACKGROUND

Recent evidence suggests that the IL-33/IL1RL1 axis plays a critical role in several autoimmune and inflammatory disorders; however, its mechanistic role in inflammatory bowel disease (IBD) has not been clearly defined. We investigated the contribution of IL-33 and IL1RL1 polymorphisms to IBD risk, and possible correlations with phenotype in an Italian cohort of adult and pediatric patients.

METHODS

We evaluated the association of six SNPs in IL-33 and IL1RL1 genes, in 805 Crohn's disease (CD), 816 ulcerative colitis (UC), and 752 controls, using Taqman. IL-33 and IL1RL1 mRNA expression was also analyzed.

RESULTS

Significant allele and genotype associations with IL-33 rs3939286 were found in CD (P = 0.004; P = 0.035) and UC patients (P = 0.002; P = 0.038). After stratifying the cohort for age at diagnosis, the differences remained significant only in the IBD adult-onset. Significant associations were also obtained in CD patients with two IL1RL1 polymorphisms (rs13015714 and rs2058660, P<0.015). By combining homo- and heterozygous carriers of the rs13015714 risk allele, differences were still significant for both CD adult- and pediatric-onset. Upon genotype-phenotype evaluation, an increased frequency of extensive colitis in adult UC (P = 0.019) and in steroid-responsive pediatric patients (P = 0.024) carrying the IL-33 rs3939286 risk genotype, was observed. mRNA expression of IL-33 and IL1RL1 in inflamed IBD biopsy samples was significantly increased.

CONCLUSIONS

Common IL-33 and IL1RL1 polymorphisms contribute to the risk of IBD in an Italian cohort of adult and pediatric patients, with some influence on sub-phenotypes.

Implications for Interleukin-33 in solid organ transplantation

Interleukin(IL)-33 is a member of the IL-1 cytokine family that has been attributed T helper (Th) type 2 immunity-promoting capacity. However, new studies indicate that IL-33 is a multifunctional protein that acts as transcriptional/signaling repressor, functions as an alarmin alerting the immune system to necrosis, as well as serves as a cytokine that targets cells expressing ST2, the IL-33 receptor. Interestingly, IL-33 is also emerging as a pleiotropic cytokine. Depending on the innate or adaptive immune cells targeted by IL-33, it can not only promote type 2, but also IFN-γ dominated type 1 immunity. In addition, IL-33 expands regulatory T cells. In this review, we assimilate the current knowledge of IL-33 immunobiology and discuss how IL-33 may mediate such diverse roles in the immune response to pathogens and development of immune-mediated pathologies. The function of IL-33 in shaping alloimmune responses to transplanted organs is poorly explored, but a particularly beneficial role of IL-33 in experimental heart transplant models is summarized. Finally, given the implication of IL-33 in pathologies of the lung and intestine, we discuss how IL-33 may contribute to the comparatively poor outcomes following transplantation of these two organs.

Intestinal stromal cells in mucosal immunity and homeostasis

A growing body of evidence suggests that non-hematopoietic stromal cells of the intestine have multiple roles in immune responses and inflammation at this mucosal site. Despite this, many still consider gut stromal cells as passive structural entities, with past research focused heavily on their roles in fibrosis, tumor progression, and wound healing, rather than their contributions to immune function. In this review, we discuss our current knowledge of stromal cells in intestinal immunity, highlighting the many immunological axes in which stromal cells have a functional role. We also consider emerging data that broaden the potential scope of their contribution to immunity in the gut and argue that these so-called "non-immune" cells are reclassified in light of their diverse contributions to intestinal innate immunity and the maintenance of mucosal homeostasis.