Paracrine IL-33 stimulation enhances lipopolysaccharide-mediated macrophage activation

Development and dysfunction of structural cells in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a disorder characterized by dysfunction and chronic local inflammation of the esophagus. The incidence and prevalence of EoE are increasing worldwide. The mechanisms responsible are poorly understood, and effective treatment options are limited. From the lumen outward, the esophagus comprises stratified squamous epithelium, lamina propria, and muscle. The tissue-specific nature of EoE strongly suggests that structural cells in the esophagus are involved in the EoE diathesis. Epithelial basal cell hyperplasia and dilated intercellular spaces are cardinal features of EoE. Some patients with EoE develop lamina propria fibrosis, strictures, or esophageal muscle dysmotility. Clinical symptoms of EoE are only weakly correlated with peak eosinophil count, implying that other cell types contribute to EoE pathogenesis. Epithelial, endothelial, muscle, and fibroblast cells can each initiate inflammation and repair, regulate tissue resident immune cells, recruit peripheral leukocytes, and tailor adaptive immune cell responses. A better understanding of how structural cells maintain tissue homeostasis, respond to cell-intrinsic and cell-extrinsic stressors, and exacerbate and/or resolve inflammatory responses in the esophagus is needed. This knowledge will facilitate the development of more efficacious treatment strategies for EoE that can restore homeostasis of both hematopoietic and structural elements in the esophagus.

Soluble ST2 as a Potential Biomarker for Abdominal Aortic Aneurysms-A Single-Center Retrospective Cohort Study

The maximal aortic diameter is the only clinically applied predictor of abdominal aortic aneurysm (AAA) progression and indicator for surgical repair. Circulating biomarkers resulting from AAA pathogenesis are attractive candidates for the diagnosis and prognosis of aneurysmal disease. Due to the reported role of interleukin 33 in AAA development, we investigated the corresponding circulating receptor molecules of soluble suppression of tumorigenesis 2 (sST2) in AAA patients regarding their marker potential in diagnosis and prognosis. We conducted a single-center retrospective cohort study in a diagnostic setting, measuring the circulating serum sST2 protein levels of 47 AAA patients under surveillance, matched with 25 peripheral artery disease (PAD) patients and 25 healthy controls. In a prognostic setting, we analyzed the longitudinal monitoring data of 50 monitored AAA patients. Slow versus fast AAA progression was defined as a <2 or ≥2 mm increase in AAA diameter over 6 months and a <4 or ≥4 mm increase over 12 months. Additionally, the association of circulating serum sST2 and AAA growth was investigated using a specifically tailored log-linear mixed model. Serum sST2 concentrations were significantly increased in AAA patients compared with healthy individuals: the median of AAA patient cohort was 112.72 ng/mL (p = 0.025) and that of AAA patient cohort 2 was 14.32 ng/mL (p = 0.039) versus healthy controls (8.82 ng/mL). Likewise, PAD patients showed significantly elevated sST2 protein levels compared with healthy controls (the median was 12.10 ng/mL; p = 0.048) but similar concentrations to AAA patients. Additionally, sST2 protein levels were found to be unsuited to identifying fast AAA progression over short-term periods of 6 or 12 months, which was confirmed by a log-linear mixed model. In conclusion, the significantly elevated protein levels of sST2 detected in patients with vascular disease may be useful in the early diagnosis of AAA but cannot distinguish between AAA and PAD or predict AAA progression.

Epidermis-Intrinsic Transcription Factor Ovol1 Coordinately Regulates Barrier Maintenance and Neutrophil Accumulation in Psoriasis-Like Inflammation

Skin epidermis constitutes the exterior barrier that protects the body from dehydration and environmental assaults. Barrier defects underlie common inflammatory skin diseases, but the molecular mechanisms that maintain barrier integrity and regulate epidermal-immune cell cross-talk in inflamed skin are not fully understood. In this study, we show that skin epithelia-specific deletion of Ovol1, which encodes a skin disease‒linked transcriptional repressor, impairs the epidermal barrier and aggravates psoriasis-like skin inflammation in mice in part by enhancing neutrophil accumulation and abscess formation. Through molecular studies, we identify IL-33, a cytokine with known pro-inflammatory and anti-inflammatory activities, and Cxcl1, a neutrophil-attracting chemokine, as potential weak and strong direct targets of Ovol1, respectively. Furthermore, we provide functional evidence that elevated Il33 expression reduces disease severity in imiquimod-treated Ovol1-deficient mice, whereas persistent accumulation and epidermal migration of neutrophils exacerbate it. Collectively, our study uncovers the importance of an epidermally expressed transcription factor that regulates both the integrity of the epidermal barrier and the behavior of neutrophils in psoriasis-like inflammation.

The Paradigm Change of IL-33 in Vascular Biology

In this review, we focus on the actual understanding of the role of IL-33 in vascular biology in the context of the historical development since the description of IL-33 as a member of IL-1 superfamily and the ligand for ST2 receptor in 2005. We summarize recent data on the biology, structure and signaling of this dual-function factor with both nuclear and extracellular cytokine properties. We describe cellular sources of IL-33, particularly within vascular wall, changes in its expression in different cardio-vascular conditions and mechanisms of IL-33 release. Additionally, we summarize the regulators of IL-33 expression as well as the effects of IL-33 itself in cells of the vasculature and in monocytes/macrophages in vitro combined with the consequences of IL-33 modulation in models of vascular diseases in vivo. Described in murine atherosclerosis models as well as in macrophages as an atheroprotective cytokine, extracellular IL-33 induces proinflammatory, prothrombotic and proangiogenic activation of human endothelial cells, which are processes known to be involved in the development and progression of atherosclerosis. We, therefore, discuss that IL-33 can possess both protective and harmful effects in experimental models of vascular pathologies depending on experimental conditions, type and dose of administration or method of modulation.

The diterpene from Sphagneticola trilobata (L.) Pruski, kaurenoic acid, reduces lipopolysaccharide-induced peritonitis and pain in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Sphagneticola trilobata (L.) Pruski is a plant species belonging to the Asteraceae family. Kaurenoid acid (KA) is a diterpene metabolite and one of the active ingredients of Sphagneticola trilobata (L.) Pruski. Extracts containing KA are used in traditional medicine to treat pain, inflammation, and infection.

AIM

The goal of the present study was to investigate the in vivo effects of KA (1-10 mg/kg, per oral gavage) upon LPS inoculation in mice by intraperitoneal (i.p.) or intraplantar (i.pl.; subcutaneous plantar injection) routes at the dose of 200 ng (200 μL or 25 μL, respectively).

METHODS

In LPS paw inflammation, mechanical and thermal hyperalgesia MPO activity and oxidative imbalance (TBARS, GSH, ABTS and FRAP assays) were evaluated. In LPS peritonitis we evaluated leukocyte migration, cytokine production, oxidative stress, and NF-κB activation.

RESULTS

KA inhibited LPS-induced mechanical and thermal hyperalgesia, MPO activity and modulated redox status in the mice paw. Pre- and post-treatment with KA inhibited migration of neutrophils and monocytes in LPS peritonitis. KA inhibited the pro-inflammatory/hyperalgesic cytokine (e.g., TNF-α, IL-1β and IL-33) production while enhanced anti-inflammatory/analgesic cytokine IL-10 in peritoneal cavity. In agreement with the effect of KA over pro-inflammatory cytokines it inhibited oxidative stress (total ROS, superoxide production and superoxide positive cells) and NF-κB activation during peritonitis.

CONCLUSION

KA efficiently dampens LPS-induced peritonitis and hyperalgesia in vivo, suggesting it as a suitable candidate to control excessive inflammation and pain during gram-negative bacterial infections and bringing mechanistic explanation to the ethnopharmacological application of Sphagneticola trilobata (L.) Pruski in inflammation and infection.

The Effect of Unconventional Cytokine Combinations on NK-Cell Responses to Viral Infection

Cytokines are soluble and membrane-bound factors that dictate immune responses. Dogmatically, cytokines are divided into families that promote type 1 cell-mediated immune responses (e.g., IL-12) or type 2 humoral responses (e.g., IL-4), each capable of antagonizing the opposing family of cytokines. The discovery of additional families of cytokines (e.g., IL-17) has added complexity to this model, but it was the realization that immune responses frequently comprise mixtures of different types of cytokines that dismantled this black-and-white paradigm. In some cases, one type of response may dominate these mixed milieus in disease pathogenesis and thereby present a clear therapeutic target. Alternatively, synergistic or blended cytokine responses may obfuscate the origins of disease and perplex clinical decision making. Most immune cells express receptors for many types of cytokines and can mediate a myriad of functions important for tolerance, immunity, tissue damage, and repair. In this review, we will describe the unconventional effects of a variety of cytokines on the activity of a prototypical type 1 effector, the natural killer (NK) cell, and discuss how this may impact the contributions of these cells to health and disease.

Proregenerative Activity of IL-33 in Gastric Tissue Cells Undergoing Helicobacter Pylori-Induced Apoptosis

Interleukin (IL)-33 is a proinflammatory mediator that alerts the host immune system to disorders in tissue homeostasis. Aim. To understand the role of IL-33 in modulating gastric tissue cell growth affected by Helicobacter pylori (H. pylori). Methods. IL-33 production in guinea pigs (Caviae porcellus) experimentally infected with H. pylori was evaluated by ELISA or immunohistochemical staining. The proregenerative activity of IL-33 was evaluated using gastric epithelial cells and fibroblasts that were naive or transfected with IL-33 siRNA exposed to H. pylori glycine acid extract antigenic complex (GE), as well as by measuring cell migration, proliferation, metabolic activity and apoptosis. Animals infected by H. pylori responded with increased production of IL-33. Also, cells treated in vitro with GE released more IL-33 than cells that were unstimulated. Silencing IL-33 in cells resulted in downregulation of metabolic activity, adhesion, migration and proliferation, especially after treatment with H. pylori GE, as well as upregulation of cells apoptosis associated with caspase 3 increase and Bcl-xL decrease, suggesting proregenerative activity of IL-33. Interestingly, upregulation of cell proliferation by IL-33 was Erk independent. Our results indicate that IL-33 may protect gastric tissue from loss of homeostasis caused by deleterious effects of H. pylori components and the inflammatory response developed during infection.

IL-33 – positive or negative role in cancer progression?

Interleukin-33 (IL-33) is a IL-1 family member of cytokines which binds the ST2 (suppression of tumorigenicity 2) receptor. This cytokine has a dual function. It may act both as a traditional cytokine and as an intracellular nuclear factor. IL-33 plays a role in many diseases such as: allergy, inflammatory diseases, diabetes and heart diseases. The role of IL-33 in the development of cancer has been intensively studied in recent years and researchers observe both its pro- -and anti-cancer effects. IL-33 promotes the development of tumors by affecting expression of cytokines promoting proliferation, angiogenesis, migration, matrix remodeling, the inhibition of apoptosis and recruitment of individual cells of the immune system. Antitumor action of IL-33 is carried out by recruiting and activating CD8+T lymphocytes, natural killer (NK) cells and by promoting second type immune response by the type 2 innate lymphoid cells (ILC2). Despite numerous studies on the role of IL-33 in the development of cancer, we still do not fully understand the mechanisms by which IL-33 impacts the development and malignancy of various types of cancers. This review summarizes the dual role of IL-33 in the development of the most common cancers in the world to better understand its importance in the carcinogenesis.

IL-33 induction and signaling are controlled by glutaredoxin-1 in mouse macrophages

Interleukin (IL)-33 is an interleukin-1 like cytokine that enhances Th2 responses and mediates mucosal immunity and allergic inflammation but the mechanism regulating endogenous IL-33 production are still under investigation. In macrophages, lipopolysaccharide (LPS) administration resulted in marked induction of IL-33 mRNA that was blunted in macrophages from glutaredoxin-1 (Glrx) knockout mice and in RAW264.7 macrophages with Glrx knockdown by siRNA. Glutaredoxin-1 is a small cytosolic thioltransferase that controls a reversible protein thiol modification, S-glutationylation (protein-GSH adducts), thereby regulating redox signaling. In this study, we examined the mechanism of Glrx regulation of endogenous IL-33 induction in macrophages. Glrx knockdown resulted in impaired de-glutathionylation of TRAF6, which is required for TRAF6 activation, and inhibited downstream IKKβ and NF-κB activation. Inhibitors of NF-κB suppressed IL-33 induction and chromatin IP sequencing data analysis confirmed that IL-33 is an NF-κB-responsive gene. Since TRAF6-NF-κB activation is also essential for IL-33 signaling through its receptor, ST2L, we next tested the involvement of Glrx in exogenous IL-33 responses in RAW264.7 cells. Recombinant IL-33 (rIL-33) administration induced IL-33 mRNA expression in RAW264.7 macrophages, and this was inhibited by Glrx knockdown. Interestingly, rIL-33-induced IL-33 protein was identified as the 20 kDa cleaved form whereas LPS-induced IL-33 protein was identified as full-length IL-33, which may be less active than the cleaved form. In a clinically-relevant mouse model of asthma, intra-tracheal cockroach antigen treatment induced Glrx protein in wild type mouse lungs but Glrx induction was attenuated in IL-33 knockout mouse lungs, suggesting that IL-33 may regulate Glrx induction in vivo in response to allergen challenge. In summary, our data reveal a novel mechanism by which Glrx controls both LPS- and IL-33-mediated NF-κB activation leading to IL-33 production, and paracrine IL-33 can induce Glrx to further regulate inflammatory reactions.

Elevated IL-33 promotes expression of MMP2 and MMP9 via activating STAT3 in alveolar macrophages during LPS-induced acute lung injury

Background

Pulmonary inflammation and endothelial barrier permeability increase in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) induced by pro-inflammatory cytokines and matrix metalloproteinases (MMPs). However, the relationship between pro-inflammatory cytokines and MMPs in ALI/ARDS remains poorly understood.

Methods

A lipopolysaccharide (LPS)-induced ALI rat model was established through intratracheal instillation. The wet/dry ratios of lung tissues were measured, and bronchoalveolar lavage fluid (BALF) was collected to test protein concentrations, total cell/macrophage numbers, and pro-inflammatory cytokine levels. LPS-treated alveolar macrophages were utilized in in vitro experiments. The expression and secretion of MMPs were respectively detected using quantitative PCR, Western blotting and ELISA assays.

Results

The levels of IL-33 and MMP2/9 in BALF increased in all the ALI rats with severe lung injury. LPS-induced IL-33 autocrine upregulated the expression of MMP2 and MMP9 through activating STAT3. Neutralizing IL-33 in culture medium with specific antibodies suppressed the expression and secretion of MMP2 and MMP9 in LPS-treated alveolar macrophages. Consistently, eliminating IL-33 decreased the levels of MMP2 and MMP9 in BALF and alleviated lung injury in ALI rats.

Conclusion

The IL-33/STAT3/MMP2/9 regulatory pathway is activated in alveolar macrophages during acute lung injury, which may exacerbate the pulmonary inflammation.

The Role of Interleukin-33 in Pathogenesis of Bronchial Asthma. New Experimental Data

Interleukin-33 (IL-33) belongs to the IL-1 cytokine family and plays an important role in modulating immune system by inducing Th2 immune response via the ST2 membrane receptor. Epithelial cells are the major producers of IL-33. However, IL-33 is also secreted by other cells, e.g., bone marrow cells, dendritic cells, macrophages, and mast cells. IL-33 targets a broad range of cell types bearing the ST2 surface receptor. Many ST2-positive cells, such as Th2 cells, mast cells, basophils, and eosinophils, are involved in the development of allergic bronchial asthma (BA). This suggests that IL-33 directly participates in BA pathogenesis. Currently, the role of IL-33 in pathogenesis of inflammatory disorders, including BA, has been extensively investigated using clinical samples collected from patients, as well as asthma animal models. In particular, numerous studies on blocking IL-33 and its receptor by monoclonal antibodies in asthma mouse model have been performed over the last several years; IL-33- and ST2-deficient transgenic mice have also been generated. In this review, we summarized and analyzed the data on the role of IL-33 in BA pathogenesis and the prospects for creating new treatments for BA.

Regulation of the IL-33/ST2 pathway contributes to the anti-inflammatory effect of acupuncture in the ovalbumin-induced murine asthma model

BACKGROUND

Bronchial asthma is a chronic airway inflammatory disease which has three main pathological features: airway hyperresponsiveness (AHR), airway remodelling, and chronic inflammation. Acupuncture is known to be an effective integrative medical therapy that has been used in the treatment of several chronic diseases, including bronchial asthma. The aim of the current study was to evaluate the effects of acupuncture on inflammation and regulation of the IL-33/ST2 pathway in a mouse model of asthma.

METHODS

The murine asthma model was established by both injection and inhalation of ovalbumin (OVA). Within 24 hours of the last OVA challenge, lung function was assessed by measurement of the airway resistance (R_L) and lung dynamic compliance (Cdyn). Pulmonary tissues were collected for the detection of pathological changes and mucus secretion. Serum levels of tumour necrosis factor α (TNF-α), interleukin (IL)-1β, IL-33 and sST2 (secreted ST2) were detected by ELISA. Th17 cell proportions and counts in bronchoalveolar lavage fluid (BALF) were analysed by flow cytometry.

RESULTS

The results showed that AHR, chronic inflammation and mucus secretion were significantly suppressed by acupuncture treatment. R_L decreased while Cdyn increased after acupuncture treatment. There was an apparent decrease in the serum concentrations of certain pro-inflammatory cytokines, such as TNF-α, IL-1β and IL-33, and an increase in sST2 level compared with untreated asthmatic mice. Acupuncture also reduced the CD4 +IL-17A+ cell proportion and counts in BALF.

CONCLUSION

Acupuncture effectively protects lung function and attenuates airway inflammation in the OVA-induced mouse model of asthma, which supports the role of acupuncture as a potential therapy in asthma treatment.

IL-33/ST2 signalling and crosstalk with FcεRI and TLR4 is targeted by the parasitic worm product, ES-62

ES-62 is a secreted parasitic worm-derived immunomodulator that exhibits therapeutic potential in allergy by downregulating aberrant MyD88 signalling to normalise the inflammatory phenotype and mast cell responses. IL-33 plays an important role in driving mast cell responses and promoting type-2 allergic inflammation, particularly with respect to asthma, via MyD88-integrated crosstalk amongst the IL-33 receptor (ST2), TLR4 and FcεRI. We have now investigated whether ES-62 targets this pathogenic network by subverting ST2-signalling, specifically by characterising how the functional outcomes of crosstalk amongst ST2, TLR4 and FcεRI are modulated by the worm product in wild type and ST2-deficient mast cells. This analysis showed that whilst ES-62 inhibits IL-33/ST2 signalling, the precise functional modulation observed varies with receptor usage and/or mast cell phenotype. Thus, whilst ES-62’s harnessing of the capacity of ST2 to sequester MyD88 appears sufficient to mediate its inhibitory effects in peritoneal-derived serosal mast cells, downregulation of MyD88 expression appears to be required to dampen the higher levels of cytokine production typically released by bone marrow-derived mucosal mast cells.

Toll-Interacting Protein, Tollip, Inhibits IL-13-Mediated Pulmonary Eosinophilic Inflammation in Mice

Toll-interacting protein (Tollip) is a key negative regulator of innate immunity by preventing excessive proinflammatory responses. Tollip genetic variation has been associated with airflow limitation in asthma subjects and Tollip expression. Whether Tollip regulates lung inflammation in a type 2 cytokine milieu (e.g., IL-13) is unclear. Our goal was to determine the in vivo role of Tollip in IL-13-mediated lung eosinophilic inflammation and the underlying mechanisms. Tollip-knockout (KO) and wild-type (WT) mice were inoculated intranasally with recombinant mouse IL-13 protein to examine lung inflammation. To determine how Tollip regulates inflammation, alveolar macrophages and bone marrow-derived macrophages from Tollip KO and WT mice were cultured with or without IL-13 and/or IL-33. IL-13-treated Tollip KO mice significantly increased lung eosinophilic inflammation and eotaxin-2 (CCL24) levels compared with the WT mice. IL-13- treated Tollip KO (vs. WT) macrophages, in the absence and particularly in the presence of IL-33, increased expression of the IL-33 receptor ST2L and CCL24, which was in part dependent on enhanced activation of interleukin (IL)-1 receptor-associated kinase 1 (IRAK1) and signal transducer and activator of transcription 6 (STAT6). Our results suggest that Tollip downregulates IL-13-mediated pulmonary eosinophilia in part through inhibiting the activity of the ST2L/IL-33/IRAK1 axis and STAT6.

Alarmins and Their Receptors as Modulators and Indicators of Alloimmune Responses

Cell damage and death releases alarmins, self-derived immunomodulatory molecules that recruit and activate the immune system. Unfortunately, numerous processes critical to the transplantation of allogeneic materials result in the destruction of donor and recipient cells and may trigger alarmin release. Alarmins, often described as damage-associated molecular patterns, together with exogenous pathogen-associated molecular patterns, are potent orchestrators of immune responses; however, the precise role that alarmins play in alloimmune responses remains relatively undefined. We examined evolving concepts regarding how alarmins affect solid organ and allogeneic hematopoietic cell transplantation outcomes and the mechanisms by which self molecules are released. We describe how, once released, alarmins may act alone or in conjunction with nonself materials to contribute to cytokine networks controlling alloimmune responses and their intensity. It is becoming recognized that this class of molecules has pleotropic functions, and certain alarmins can promote both inflammatory and regulatory responses in transplant models. Emerging evidence indicates that alarmins and their receptors may be promising transplantation biomarkers. Developing the therapeutic ability to support alarmin regulatory mechanisms and the predictive value of alarmin pathway biomarkers for early intervention may provide opportunities to benefit graft recipients.

Role of the IL-33-ST2 axis in sepsis

Sepsis remains a major clinical problem with high morbidity and mortality. As new inflammatory mediators are characterized, it is important to understand their roles in sepsis. Interleukin 33 (IL-33) is a recently described member of the IL-1 family that is widely expressed in cells of barrier tissues. Upon tissue damage, IL-33 is released as an alarmin and activates various types of cells of both the innate and adaptive immune system through binding to the ST2/IL-1 receptor accessory protein complex. IL-33 has apparent pleiotropic functions in many disease models, with its actions strongly shaped by the local microenvironment. Recent studies have established a role for the IL-33-ST2 axis in the initiation and perpetuation of inflammation during endotoxemia, but its roles in sepsis appear to be organism and model dependent. In this review, we focus on the recent advances in understanding the role of the IL-33/ST2 axis in sepsis.

Inflammation elevated IL-33 originating from the lung mediates inflammation in acute lung injury

Excessive inflammatory reactions occur with acute respiratory distress syndrome (ARDS), however, the underlying mechanisms of ARDS remain incompletely understood. Here we investigated whether interleukin (IL)-33 was elevated in ARDS patients. Serum samples were obtained from 14 ARDS patients and 24 control healthy volunteers. ELISA was used to measure the concentrations of IL-33. Besides, we established pulmonary ARDS and extrapulmonary ARDS models in mice, and serum and lung tissue samples were collected for analyses. The results showed that serum IL-33 concentrations were significantly higher in pulmonary ARDS patients compared to controls. Also, the levels of IFN-γ and IL-2 were positively correlated with IL-33 levels. We also showed that there were increased IL-33 levels in both the serum and lungs in the pulmonary ARDS model. This was not the case, however, in the extrapulmonary ARDS model. Pulmonary inflammation and injury in the pulmonary ARDS model was reduced with IL-33 neutralizing antibody treatment.

MicroRNA-487b Is a Negative Regulator of Macrophage Activation by Targeting IL-33 Production

MicroRNAs (miRNAs) are short noncoding RNAs that regulate a broad spectrum of biological processes, including immune responses. Although the contributions of miRNAs to the function of immune cells are beginning to emerge, their specific roles remain largely unknown. IL-33 plays an important role in macrophage activation for innate host defense and proinflammatory responses. In this study, we report that miR-487b can suppress the levels of mRNA and protein for IL-33 during the differentiation of bone marrow-derived macrophages (BMDMs). This results in inhibition of IL-33-induced expression of Ag-presenting and costimulatory molecules and proinflammatory mediators. A luciferase assay showed that miR-487b binds to the IL-33 3'-untranslated region. We also confirmed that IL-33 directly promotes the activation of BMDMs by increasing the expression of MHC class I, MHC class II, CD80/CD86, and inducible NO synthase (iNOS) in a dose-dependent manner. Exposure of BMDMs to the TLR4 ligand, LPS, decreased miR-487b expression, increased IL-33 transcript levels, and induced the production of proinflammatory mediators (e.g., iNOS, IL-1β, IL-6, and TNF-α). Treatment with a specific inhibitor of miR-487b function also resulted in increased levels of IL-33 mRNA, which augmented LPS-induced expression of these inflammatory mediators in macrophages. Collectively, our results indicate that miR-487b plays a negative regulatory role in macrophages by controlling the levels of IL-33 transcript and protein to fine-tune innate immune host defense and proinflammatory responses of these cells. Thus, miR-487b plays an important role in the regulation of macrophage homeostasis and activation by targeting IL-33 transcripts.

Cigarette smoke silences innate lymphoid cell function and facilitates an exacerbated type I interleukin-33-dependent response to infection

Cigarette smoking is a major risk factor for chronic obstructive pulmonary disease and is presumed to be central to the altered responsiveness to recurrent infection in these patients. We examined the effects of smoke priming underlying the exacerbated response to viral infection in mice. Lack of interleukin-33 (IL-33) signaling conferred complete protection during exacerbation and prevented enhanced inflammation and exaggerated weight loss. Mechanistically, smoke was required to upregulate epithelial-derived IL-33 and simultaneously alter the distribution of the IL-33 receptor ST2. Specifically, smoke decreased ST2 expression on group 2 innate lymphoid cells (ILC2s) while elevating ST2 expression on macrophages and natural killer (NK) cells, thus altering IL-33 responsiveness within the lung. Consequently, upon infection and release, increased local IL-33 significantly amplified type I proinflammatory responses via synergistic modulation of macrophage and NK cell function. Therefore, in COPD, smoke alters the lung microenvironment to facilitate an alternative IL-33-dependent exaggerated proinflammatory response to infection, exacerbating disease.

Ambient particulate matter induces an exacerbation of airway inflammation in experimental asthma: role of interleukin-33

High levels of ambient environmental particulate matter (PM10 i.e. < 10 μm median aerodynamic diameter) have been linked to acute exacerbations of asthma. We examined the effects of delivering a single dose of Sydney PM10 by intranasal instillation to BALB/c mice that had been sensitized to ovalbumin and challenged repeatedly with a low (≈3 mg/m(3)) mass concentration of aerosolized ovalbumin for 4 weeks. Responses were compared to animals administered carbon black as a negative control, or a moderate (≈30 mg/m(3)) concentration of ovalbumin to simulate an allergen-induced acute exacerbation of airway inflammation. Delivery of PM10 to mice, in which experimental mild chronic asthma had previously been established, elicited characteristic features of enhanced allergic inflammation of the airways, including eosinophil and neutrophil recruitment, similar to that in the allergen-induced exacerbation. In parallel, there was increased expression of mRNA for interleukin (IL)-33 in airway tissues and an increased concentration of IL-33 in bronchoalveolar lavage fluid. Administration of a monoclonal neutralizing anti-mouse IL-33 antibody prior to delivery of particulates significantly suppressed the inflammatory response induced by Sydney PM10, as well as the levels of associated proinflammatory cytokines in lavage fluid. We conclude that IL-33 plays a key role in driving airway inflammation in this novel experimental model of an acute exacerbation of chronic allergic asthma induced by exposure to PM10.

The balance between pro- and anti-inflammatory cytokines is crucial in human allergic contact dermatitis pathogenesis: the role of IL-1 family members

The interleukin (IL)-1 family includes 11 members that are important in inflammatory processes. It includes various agonists and two antagonists, IL-1Ra and IL-36Ra. Our aim was to investigate whether the IL-1 family is involved in allergic contact dermatitis (ACD). The expression of IL-1 family members was evaluated by PCR and immunohistochemistry in the positive patch test reaction site (involved skin) and in the uninvolved skin of ACD patients. We also examined these cytokines in an ex vivo model of ACD. The antagonistic activity of IL-36Ra was evaluated by injecting recombinant IL-36Ra in uninvolved skin biopsies of ACD patients. IL-1Ra and IL-36Ra expression was quantified in mononuclear cells of nickel-sensitized patients challenged in vitro with nickel. IL-33 involvement in ACD was investigated by intra-dermal injection of anti-IL-33 in the uninvolved skin of patients ex vivo. Results showed that IL-1β, IL-1Ra, IL-36α, IL-36β, IL-36γ and IL-33 expression, but not IL-36Ra expression, was enhanced in ACD-involved skin. Immunohistochemical analysis and ex vivo skin cultures confirmed these results. Injection of anti-IL-33 in ACD-uninvolved skin inhibited IL-8 expression, whereas IL-36Ra inhibited IL-36α, IL-36β, IL-36γ and IL-8 expression. Nickel induced IL-1Ra expression in lymphocytes of nickel-sensitized patients. Hence, various IL-1 agonists and antagonists may be involved in ACD pathogenesis.

IL-33/ST2 axis promotes mast cell survival via BCLXL

Mast cells (MC) are potent innate immune cells that accumulate in chronically inflamed tissues. MC express the IL-33 receptor IL-1 receptor-related protein ST2 at high level, and this IL-1 family cytokine both activates MC directly and primes them to respond to other proinflammatory signals. Whether IL-33 and ST2 play a role in MC survival remains to be defined. In skin-derived human MC, we found that IL-33 attenuated MC apoptosis without altering proliferation, an effect mediated principally through the antiapoptotic molecule B-cell lymphoma-X large (BCLXL). Murine MC demonstrated a similar mechanism, dependent entirely on ST2. In line with these observations, St2(-/-) mice exhibited reduced numbers of tissue MC in inflamed arthritic joints, in helminth-infected intestine, and in normal peritoneum. To confirm an MC-intrinsic role for ST2 in vivo, we performed peritoneal transfer of WT and St2(-/-) MC. In St2(-/-) hosts treated with IL-33 and in WT hosts subjected to thioglycollate peritonitis, WT MC displayed a clear survival advantage over coengrafted St2(-/-) MC. IL-33 blockade specifically attenuated this survival advantage, confirming IL-33 as the relevant ST2 ligand mediating MC survival in vivo. Together, these data reveal a cell-intrinsic role for the IL-33/ST2 axis in the regulation of apoptosis in MC, identifying thereby a previously unappreciated pathway supporting expansion of the MC population with inflammation.

Immune modulation by the IL-33/ST2 system in ulcerative colitis

The immune system prevents pathogens from entering and spreading in the body. Dysfunction of the immune system can activate an intestinal inflammatory response, leading to chronic diseases including inflammatory bowel diseases (IBD). Ulcerative colitis (UC) is a form of IBD of unknown etiology with increasing prevalence. There is an imbalance in the interleukin-33/homolog of sulfotransferase 2 (IL-33/ST2) axis in UC intestinal mucosa. This paper reviews the role of the IL-33/ST2 system in immunity of the intestinal mucosa and its importance in IBD, especially UC.

Involvement of ERK and p38 MAPK pathways on Interleukin-33-induced RANKL expression in osteoblastic cells

The receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) system is a well-known key factor in osteoclast differentiation, and osteoblastic lineage cells are the major sources of RANKL and OPG in local bone tissue. Recently, a new molecule from the interleukin (IL)-1 family, IL-33, was identified. Here, we report the possible involvement of IL-33 in RANKL and OPG expression, and the signaling pathways that are required for maximal IL-33-induced RANKL expression in MC3T3-E1 osteoblastic cells. Stimulation with IL-33 increased the mRNA expression and secretion of RANKL in MC3T3-E1 cells. The IL-33-induced RANKL mRNA expression was inhibited by an anti-IL-33 monoclonal antibody. Furthermore, ERK and p38 MAPK inhibitors, but not a JNK inhibitor, suppressed IL-33-induced RANKL mRNA expression. On the other hand, IL-33 had no effect on OPG mRNA expression and protein secretion. These results taken together suggest that IL-33 stimulates RANKL expression through mechanisms dependent on the ERK and p38 MAPK pathways in MC3T3-E1 cells.

Interleukin-33 drives activation of alveolar macrophages and airway inflammation in a mouse model of acute exacerbation of chronic asthma

We investigated the role of interleukin-33 (IL-33) in airway inflammation in an experimental model of an acute exacerbation of chronic asthma, which reproduces many of the features of the human disease. Systemically sensitized female BALB/c mice were challenged with a low mass concentration of aerosolized ovalbumin for 4 weeks to induce chronic asthmatic inflammation and then received a single moderate-level challenge to trigger acute airway inflammation simulating an asthmatic exacerbation. The inflammatory response and expression of cytokines and activation markers by alveolar macrophages (AM) were assessed, as was the effect of pretreatment with a neutralizing antibody to IL-33. Compared to chronically challenged mice, AM from an acute exacerbation exhibited significantly enhanced expression of markers of alternative activation, together with enhanced expression of proinflammatory cytokines and of cell surface proteins associated with antigen presentation. In parallel, there was markedly increased expression of both mRNA and immunoreactivity for IL-33 in the airways. Neutralization of IL-33 significantly decreased both airway inflammation and the expression of proinflammatory cytokines by AM. Collectively, these data indicate that in this model of an acute exacerbation of chronic asthma, IL-33 drives activation of AM and has an important role in the pathogenesis of airway inflammation.

Components of the interleukin-33/ST2 system are differentially expressed and regulated in human cardiac cells and in cells of the cardiac vasculature

Interleukin-33 (IL-33) is a recently described member of the IL-1 family of cytokines, which was identified as a ligand for the ST2 receptor. Components of the IL-33/ST2 system were shown to be expressed in normal and pressure overloaded human myocardium, and soluble ST2 (sST2) has emerged as a prognostic biomarker in myocardial infarction and heart failure. However, expression and regulation of IL-33 in human adult cardiac myocytes and fibroblasts was not tested before. In this study we found that primary human adult cardiac fibroblasts (HACF) and human adult cardiac myocytes (HACM) constitutively express nuclear IL-33 that is released during cell necrosis. Tumor necrosis factor (TNF)-α, interferon (IFN)-γ and IL-1β significantly increased both IL-33 protein and IL-33 mRNA expression in HACF and HACM as well as in human coronary artery smooth muscle cells (HCASMC). The nuclear factor-κB (NF-κB) inhibitor dimethylfumarate inhibited TNF-α- and IL-1β-induced IL-33 production as well as nuclear translocation of p50 and p65 NF-κB subunits in these cells. Mitogen-activated protein/extracellular signal-regulated kinase inhibitor U0126 abrogated TNF-α-, IFN-γ-, and IL-1β-induced and Janus-activated kinase inhibitor I reduced IFN-γ-induced IL-33 production. We detected IL-33 mRNA in human myocardial tissue from patients undergoing heart transplantation (n=27) where IL-33 mRNA levels statistically significant correlated with IFN-γ (r=0.591, p=0.001) and TNF-α (r=0.408, p=0.035) mRNA expression. Endothelial cells in human heart expressed IL-33 as well as ST2 protein. We also reveal that human cardiac and vascular cells have different distribution patterns of ST2 isoforms (sST2 and transmembrane ST2L) mRNA expression and produce different amounts of sST2 protein. Both human macrovascular (aortic and coronary artery) and heart microvascular endothelial cells express specific mRNA for both ST2 isoforms (ST2L and sST2) and are a source for sST2 protein, whereas cardiac myocytes, cardiac fibroblasts and vascular SMC express only minor amounts of ST2 mRNA and do not secrete detectable amounts of sST2 antigen. In accordance with the cellular distribution of ST2 receptor, human cardiac fibroblasts and myocytes as well as HCASMC did not respond to treatment with IL-33, as recombinant human IL-33 did not induce NF-κB p50 and p65 subunits nuclear translocation or increase IL-6, IL-8, and monocyte chemoattractant protein (MCP-1) level in HACF, HACM and HCASMC. In summary, we found that endothelial cells seem to be the source of sST2 and the target for IL-33 in the cardiovascular system. IL-33 is expressed in the nucleus of human adult cardiac fibroblasts and myocytes and released during necrosis. Proinflammatory cytokines TNF-α, IFN-γ and IL-1β increase IL-33 in these cells in vitro, and IL-33 mRNA levels correlated with TNF-α and IFN-γ mRNA expression in human myocardial tissue.

IL-33 causes selective mast cell tolerance to bacterial cell wall products by inducing IRAK1 degradation

Mast cells are important cellular constituents of epithelial-mesenchymal interactions, densely located at sites of microbial entry into the host where they are continuously exposed to products from commensals. In order to avoid excessive activation and the associated pathology, mast cell responses to TLR agonists must be tightly regulated. Here, we show that exposure in vitro to subactivating levels of the epithelial cell product, IL-33, renders mast cells insensitive to bacterial cell wall products. Mast cell responsiveness to Ag, cytoplasmic dsDNA, and TLR7/8 agonists is unaffected or enhanced by IL-33. The IL-33-induced mast cell selective tolerance requires the IL-33 receptor ST2 and peritoneal mast cells from St2(-/-) mice display a constitutively activated phenotype, demonstrated by increased expression of activation markers including CD11b and CD28. IL-33 exposure neither affects the levels of TLR4, MyD88, TIRAP, IL-1R associated kinase 2 (IRAK2), or IRAK4, nor induces persistent A20 or Tollip expression, but potently causes ST2-dependent IRAK1 degradation. We show that while IRAK2 is redundant for TLR4 signaling, IRAK1 is essential for TLR4 signaling in mast cells. We suggest that IL-33 produced during homeostasis retains mast cells in an unresponsive state to bacterial cell wall products via IRAK1 degradation, thus preventing chronic inflammation and tissue destruction.

IL-33 promotes eosinophilia in vivo and antagonizes IL-5-dependent eosinophil hematopoiesis ex vivo

IL-33 is an IL-1 family cytokine that elicits IL-5-dependent eosinophilia in vivo. We show here that IL-33 promotes minimal eosinophil hematopoiesis via direct interactions with mouse bone marrow progenitors ex vivo and that it antagonizes eosinophil hematopoiesis promoted by IL-5 on SCF and Flt3L primed bone marrow progenitor cells in culture. SCF and Flt3L primed progenitors respond to IL-33 by acquiring an adherent, macrophage-like phenotype, and by releasing macrophage-associated cytokines into the culture medium. IL-33-mediated antagonism of IL-5 was reproduced in part by the addition of GM-CSF and was inhibited by the actions of neutralizing anti-GM-CSF antibody. These findings suggest that the direct actions of IL-33 on bone marrow progenitors primed with SCF and Flt3L are antagonistic to the actions of IL-5 and are mediated in part by GM-CSF.

Innate immunity modulation by the IL-33/ST2 system in intestinal mucosa

Innate immunity prevents pathogens from entering and spreading within the body. This function is especially important in the gastrointestinal tract and skin, as these organs have a large surface contact area with the outside environment. In the intestine, luminal commensal bacteria are necessary for adequate food digestion and play a crucial role in tolerance to benign antigens. Immune system damage can create an intestinal inflammatory response, leading to chronic disease including inflammatory bowel diseases (IBD). Ulcerative colitis (UC) is an IBD of unknown etiology with increasing worldwide prevalence. In the intestinal mucosa of UC patients, there is an imbalance in the IL-33/ST2 axis, an important modulator of the innate immune response. This paper reviews the role of the IL-33/ST2 system in innate immunity of the intestinal mucosa and its importance in inflammatory bowel diseases, especially ulcerative colitis.

Interleukin-33 primes mast cells for activation by IgG immune complexes

Mast cells (MCs) are heterogeneous cells whose phenotype is modulated by signals received from the local microenvironment. Recent studies have identified the mesenchymal-derived cytokine IL-33 as a potent direct activator of MCs, as well as regulator of their effector phenotype, and have implicated this activity in the ability of mast cells to contribute to murine experimental arthritis. We explored the hypothesis that IL-33 enables participation of synovial MCs in murine K/BxN arthritis by promoting their activation by IgG immune complexes. Compared to wild-type (WT) control mice, transgenic animals lacking the IL-33 receptor ST2 exhibited impaired MC-dependent immune complex-induced vascular permeability (flare) and attenuated K/BxN arthritis. Whereas participation of MCs in this model is mediated by the activating IgG receptor FcγRIII, we pre-incubated bone marrow-derived MCs with IL-33 and found not only direct induction of cytokine release but also a marked increase in FcγRIII-driven production of critical arthritogenic mediators including IL-1β and CXCL2. This "priming" effect was associated with mRNA accumulation rather than altered expression of Fcγ receptors, could be mimicked by co-culture of WT but not ST2(-/-) MCs with synovial fibroblasts, and was blocked by antibodies against IL-33. In turn, WT but not ST2(-/-) MCs augmented fibroblast expression of IL-33, forming a positive feedback circuit. Together, these findings confirm a novel role for IL-33 as an amplifier of IgG immune complex-mediated inflammation and identify a potential MC-fibroblast amplification loop dependent on IL-33 and ST2.

Interleukin-33 in allergy

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, which includes IL-1 and IL-18, and is considered to be important for host defense against nematodes by inducing Th2 cytokine production via the IL-33 receptor. IL-33 receptor is a heterodimer of IL-1 receptor-like 1 (IL-1RL1; also called ST2, T1, Der4, and fit-1) and IL-1 receptor accessory protein (IL-1RAcP). On the other hand, excessive and/or inappropriate production of IL-33 is considered to be involved in the development of various disorders, such as allergic and autoimmune diseases. Unlike IL-1β and IL-18, IL-33 does not seem to be secreted through the activation of inflammasomes in events such as apoptosis. However, IL-33 is localized in the nucleus of cells and is released during tissue injury associated with necrosis. This suggests that it acts as an alarmin, like IL-1α and high-mobility group box chromosomal protein-1 (HMGB-1). This review summarizes current knowledge regarding the roles of IL-33 in the functions of various cell types and the pathogenesis of allergy.

Deletion of IL-33R (ST2) abrogates resistance to EAE in BALB/C mice by enhancing polarization of APC to inflammatory phenotype

The administration of interleukin 33 and deletion of IL-33 receptor, ST2 molecule, affects the induction of autoimmunity in different experimental models of human autoimmune diseases. The aim of this study was to analyze the effect of ST2 deletion on the induction of experimental autoimmune encephalomyelitis (EAE) in resistant BALB/c mice. Mice were immunized with MOG(35-55) peptide or disease was induced by passive transfer of encephalitogenic singenic cells and EAE was clinically and histologically evaluated. Expression of intracellular inflammatory cytokines, markers of activation and chemokine receptors on lymphoid tissue and CNS infiltrating mononuclear cells was analyzed by flow cytometry. We report here that deletion of ST2(-/-) molecule abrogates resistance of BALB/c mice to EAE induction based on clinical and histopathological findings. Brain and spinal cord infiltrates of ST2(-/-) mice had significantly higher number of CD4(+) T lymphocytes containing inflammatory cytokines compared to BALB/c WT mice. Adoptive transfer of ST2(-/-) primed lymphocytes induced clinical signs of the disease in ST2(-/-) as well as in WT mice. MOG(35-55) restimulated ST2(-/-) CD4(+) cells as well as ex vivo analyzed lymph node cells had higher expression of T-bet and IL-17, IFN-γ, TNF-α and GM-CSF in comparison with WT CD4(+) cells. ST2(-/-) mice had higher percentages of CD4(+) cells expressing chemokine receptors important for migration to CNS in comparison with WT CD4(+) cells. Draining lymph nodes of ST2(-/-) mice contained higher percentage of CD11c(+)CD11b(+)CD8(-) cells containing inflammatory cytokines IL-6 and IL-12 with higher expression of activation markers. Transfer of ST2(-/-) but not WT dendritic cells induced EAE in MOG(35-55) immunized WT mice. Our results indicate that ST2 deficiency attenuates inherent resistance of BALB/c mice to EAE induction by enhancing differentiation of proinflammatory antigen presenting cells and consecutive differentiation of encephalitogenic T cells in the draining lymph node rather than affecting their action in the target tissue.

IL-33/ST2 axis in inflammation and immunopathology

Interleukin-33 (IL-33), a member of the IL-1 family of cytokines, binds to its plasma membrane receptor, heterodimeric complex consisted of membrane-bound ST2L and IL-1R accessory protein, inducing NFkB and MAPK activation. IL-33 exists as a nuclear precursor and may act as an alarmin, when it is released after cell damage or as negative regulator of NFκB gene transcription, when acts in an intracrine manner. ST2L is expressed on several immune cells: Th2 lymphocytes, NK, NKT and mast cells and on cells of myeloid lineage: monocytes, dendritic cells and granulocytes. IL-33/ST2 axis can promote both Th1 and Th2 immune responses depending on the type of activated cell and microenvironment and cytokine network in damaged tissue. We previously described and discuss here the important role of IL-33/ST2 axis in experimental models of type 1 diabetes, experimental autoimmune encephalomyelitis, fulminant hepatitis and breast cancer. We found that ST2 deletion enhance the development of T cell-mediated autoimmune disorders, EAE and diabetes mellitus type I. Disease development was accompanied by dominantly Th1/Th17 immune response but also higher IL-33 production, which suggest that IL-33 in receptor independent manner could promote the development of inflammatory autoreactive T cells. IL-33/ST2 axis has protective role in Con A hepatitis. ST2-deficient mice had more severe hepatitis with higher influx of inflammatory cells in liver and dominant Th1/Th17 systemic response. Pretreatment of mice with IL-33 prevented Con A-induced liver damage through prevention of apoptosis of hepatocytes and Th2 amplification. Deletion of IL-33/ST2 axis enhances cytotoxicity of NK cells, production of IFN-γ in these cells and systemic production of IFN-γ, IL-17 and TNF-α, which leads to attenuated tumor growth. IL-33 treatment of tumor-bearing mice suppresses activity of NK cells, dendritic cell maturation and enhances alternative activation of macrophages. In conclusion, we observed that IL-33 has attenuated anti-inflammatory effects in T cell-mediated responses and that both IL-33 and ST2 could be further explored as potential therapeutic targets in treatment of immune-mediated diseases.

IL-33: a novel danger signal system in atopic dermatitis

IL-33 is a newly recognized cytokine of the IL-1 cytokine family that has recently been attributed to the epithelial "alarmin" defense system. IL-33 is released by the epithelial cells in various tissues and organs, including keratinocytes, endothelial cells, and immune cells. Recent reports have suggested that IL-33 might be a critical part of the innate immunity, although its precise role is as yet poorly understood. In several organs, IL-33 appears to drive T helper type 2 (Th2) responses, suggesting roles in allergic and atopic diseases, as well as in fibrosis. IL-33 exerts its effects by activating the ST2 (suppression of tumorigenicity 2)/IL-1 aR receptor on different types of cells, including mast cells and Th2 cells. The ST2 receptor is either expressed on the cell surface or shed from these cells (soluble ST2, sST2), thereby functioning as a "decoy" receptor. After binding to its receptor, IL-33 activates NF-κB, suggesting that it regulates the outcome of diseases such as atopic dermatitis. On the other hand, several studies have reported on the inhibitory effects of sST2 in inflammatory and fibrotic diseases, suggesting that IL-33/ST2 is a unique cytokine with potential pro- and anti-inflammatory effects.

F-box protein FBXL19-mediated ubiquitination and degradation of the receptor for IL-33 limits pulmonary inflammation

The ST2L receptor for interleukin 33 (IL-33) mediates pulmonary inflammation and immune system-related disorders, such as asthma and rheumatoid arthritis. At present, very little is known about the molecular regulation of ST2L expression. Here we found that FBXL19, an 'orphan' member of the Skp1-Cullin-F-box family of E3 ubiquitin ligases, selectively bound to ST2L to mediate its polyubiquitination and elimination in the proteasome. Degradation of ST2L involved phosphorylation of ST2L at Ser442 catalyzed by the kinase GSK3β. Overexpression of FBXL19 abrogated the proapoptotic and inflammatory effects of IL-33 and lessened the severity of lung injury in mouse models of pneumonia. Our results suggest that modulation of the IL-33-ST2L axis by ubiquitin ligases might serve as a unique strategy for lessening pulmonary inflammation.

Dynamic role of epithelium-derived cytokines in asthma

Asthma is an inflammatory disorder of the airways, characterized by infiltration of mast cells, eosinophils, and Th2-type CD4+ T cells in the airway wall. Airway epithelium constitutes the first line of interaction with our atmospheric environment. The protective barrier function of the airway epithelium is likely impaired in asthma. Furthermore, recent studies suggest critical immunogenic and immunomodulatory functions of airway epithelium. In particular, a triad of cytokines, including IL-25, IL-33 and TSLP, is produced and released by airway epithelial cells in response to various environmental and microbial stimuli or by cellular damage. These cytokines induce and promote Th2-type airway inflammation and cause remodeling and pathological changes in the airway walls, suggesting their pivotal roles in the pathophysiology of asthma. Thus, the airway epithelium can no longer be regarded as a mere structural barrier, but must be considered an active player in the pathogenesis of asthma and other allergic disorders.

Interleukin-33 upregulation in peripheral leukocytes and CNS of multiple sclerosis patients

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system (CNS). Here we document for the first time that the cytokine IL-33 is upregulated in both the periphery and the CNS of MS patients. Plasma IL-33 was elevated in MS patients compared to normal subjects and a three-month treatment of MS patients with interferon β-1a resulted in a significant decrease of IL-33 levels. Similarly, stimulated cultured lymphocytes and macrophages from MS patients had elevated IL-33 levels compared to normal subjects. In parallel, the transcription factor NF-κB that mediates IL-33 transcription was also elevated in leukocytes of MS patients. IL-33 was elevated in normal-appearing white matter and plaque areas from MS brains and astrocytes were identified as an important source of IL-33 expression in the CNS. In summary, IL-33 levels are elevated in the periphery and CNS of MS patients, implicating IL-33 in the pathogenesis of MS.

Interleukin-33 induces expression of adhesion molecules and inflammatory activation in human endothelial cells and in human atherosclerotic plaques

OBJECTIVE

Interleukin (IL)-33 is the most recently described member of the IL-1 family of cytokines and it is a ligand of the ST2 receptor. While the effects of IL-33 on the immune system have been extensively studied, the properties of this cytokine in the cardiovascular system are much less investigated. Methods/Results- We show here that IL-33 promoted the adhesion of human leukocytes to monolayers of human endothelial cells and robustly increased vascular cell adhesion molecule-1, intercellular adhesion molecule-1, endothelial selectin, and monocyte chemoattractant protein-1 protein production and mRNA expression in human coronary artery and human umbilical vein endothelial cells in vitro as well as in human explanted atherosclerotic plaques ex vivo. ST2-fusion protein, but not IL-1 receptor antagonist, abolished these effects. IL-33 induced translocation of nuclear factor-κB p50 and p65 subunits to the nucleus in human coronary artery endothelial cells and human umbilical vein endothelial cells and overexpression of dominant negative form of IκB kinase 2 or IκBα in human umbilical vein endothelial cells abolished IL-33-induced adhesion molecules and monocyte chemoattractant protein-1 mRNA expression. We detected IL-33 and ST2 on both protein and mRNA level in human carotid atherosclerotic plaques.

CONCLUSIONS

We hypothesize that IL-33 may contribute to early events in endothelial activation characteristic for the development of atherosclerotic lesions in the vessel wall, by promoting adhesion molecules and proinflammatory cytokine expression in the endothelium.