Serum- and oncoprotein-mediated induction of a gene with sequence similarity to the gene encoding carcinoembryonic antigen

Interleukin-33 and Obesity-Related Inflammation and Cancer

Interleukin-33 (IL-33) is a cytokine belonging to the IL-1 family. It is primarily associated with type 2 immune responses. It interacts with a receptor complex on immune cells in reaction to tissue damage or cellular injury. IL-33 is crucial in immune responses and is involved in various autoimmune and inflammatory diseases. Obesity is marked by chronic inflammation and is a known risk factor for several types of cancer. Recent studies have shown that IL-33 and its receptor complex are expressed in adipose (fat) tissue, suggesting they may play a role in obesity. While inflammation connects obesity and cancer, it is not yet clear whether IL-33 contributes to cancer associated with obesity. Depending on the cellular context, inflammatory environment, expression levels, and bioactivity, IL-33 can exhibit both protumorigenic and antitumorigenic effects. This review will explore the various functions of IL-33 in the inflammation linked to obesity and its relationship with cancer.

Correlations of sST2 and Gal-3 with Cardiothoracic Ratio in Patients with Chronic Kidney Disease

Chronic kidney disease (CKD) frequently correlates with cardiovascular complications. Soluble suppression of tumorigenicity 2 (sST2) and Galectin-3 (Gal-3) are emerging as cardiac markers with potential relevance in cardiovascular risk prediction. The cardiothoracic ratio (CTR), a metric easily obtainable from chest radiographs, has traditionally been used to assess cardiac size and the potential for cardiomegaly. Understanding the correlation between these cardiac markers and the cardiothoracic ratio (CTR) could provide valuable insights into the cardiovascular prognosis of CKD patients. This study aimed to explore the relationship between sST2, Gal-3, and the CTR in individuals with CKD. Plasma concentrations of sST2 and Gal-3 were assessed in a cohort of 123 CKD patients by enzyme-linked immunosorbent assay (ELISA). On a posterior-to-anterior chest X-ray view, the CTR was determined by comparing the widths of the heart to that of the thorax. The mean concentration of sST2 in the study participants ranged from 775.4 to 4475.6 pg/mL, and the mean concentration of Gal-3 ranged from 4.7 to 9796.0 ng/mL. Significant positive correlations were observed between sST2 and the CTR (r = 0.291, p < 0.001) and between Gal-3 and the CTR (r = 0.230, p < 0.01). Our findings indicate that elevated levels of sST2 and Gal-3 are associated with an increased CTR in CKD patients. This relationship may enable better cardiovascular risk evaluation for CKD patients. Further studies are warranted to explore the clinical implications of these associations.

A type 1 immunity-restricted promoter of the IL-33 receptor gene directs antiviral T-cell responses

The pleiotropic alarmin interleukin-33 (IL-33) drives type 1, type 2 and regulatory T-cell responses via its receptor ST2. Subset-specific differences in ST2 expression intensity and dynamics suggest that transcriptional regulation is key in orchestrating the context-dependent activity of IL-33-ST2 signaling in T-cell immunity. Here, we identify a previously unrecognized alternative promoter in mice and humans that is located far upstream of the curated ST2-coding gene and drives ST2 expression in type 1 immunity. Mice lacking this promoter exhibit a selective loss of ST2 expression in type 1- but not type 2-biased T cells, resulting in impaired expansion of cytotoxic T cells (CTLs) and T-helper 1 cells upon viral infection. T-cell-intrinsic IL-33 signaling via type 1 promoter-driven ST2 is critical to generate a clonally diverse population of antiviral short-lived effector CTLs. Thus, lineage-specific alternative promoter usage directs alarmin responsiveness in T-cell subsets and offers opportunities for immune cell-specific targeting of the IL-33-ST2 axis in infections and inflammatory diseases.

The ST2/IL-33 Pathway in Adult and Paediatric Heart Disease and Transplantation

ST2 is a member of interleukin 1 receptor family with soluble sST2 and transmembrane ST2L isoforms. The ligand of ST2 is IL-33, which determines the activation of numerous intracytoplasmic mediators following the binding with ST2L and IL-1RAcP, leading to nuclear signal and cardiovascular effect. Differently, sST2 is released in the blood and works as a decoy receptor, binding IL-33 and blocking IL-33/ST2L interaction. sST2 is mainly involved in maintaining homeostasis and/or alterations of different tissues, as counterbalance/activation of IL-33/ST2L axis is typically involved in the development of fibrosis, tissue damage, inflammation and remodeling. sST2 has been described in different clinical reports as a fundamental prognostic marker in patients with cardiovascular disease, as well as marker for the treatment monitoring of patients with heart failure; however, further studies are needed to better elucidate its role. In this review we reported the current knowledge about its role in coronary artery disease, heart failure, heart transplantation, heart valve disease, pulmonary arterial hypertension, and cardiovascular interventions.

Growth stimulation expressed gene 2 (ST2): Clinical research and application in the cardiovascular related diseases

As an interleukin (IL)-1 receptor family member, scientists found that when circulating soluble growth stimulation expressed gene 2 (sST2) is low, its ligand, IL-33, will bind to ST2L to exert protective effects on various types of cells. On the other hand, competitive binding of IL-33 occurs when sST2 concentrations are increased, followed by a reduction in the amount available for cell protection. Based on this mechanism, the usage of sST2 is to identify the population of high-risk patients with cardiovascular disease. In recent years, the role of serum sST2 in the occurrence, diagnosis, prognosis, and treatment of cardiovascular diseases has been gradually accepted by doctors. This manuscript systemically reviews the biological functions and applications of sST2 in disease diagnosis and treatment, especially for cardiovascular diseases. In clinical testing, since IL-33 can negatively impact sST2 measurement accuracy, the properties of current assay kits have been summarized and discussed to provide a clear view of the clinical chemistry results. Although sST2 is a promising biomarker, there are few quantitative approaches available for clinical testing. In this context, a mass spectrometry (MS)-based approach might be an option, as this is a powerful analytical tool to distinguish structurally related molecules in the matrix and decrease false-positive results in clinical testing. Moreover, approaches developed based on MS would be an ideal way to further study sST2 standardization.

IL-33 and Soluble ST2 Are Associated With Recurrent Spontaneous Abortion in Early Pregnancy

Normal pregnancy is related to the successful transition from type 1 cellular immunity to type 2 cellular immunity. Therefore, this study aimed to investigate whether there is abnormal expression of cytokines in the process of inducing Recurrent spontaneous abortion (RSA). Interleukin (IL)-33 is a new member of the IL-1 family, and ST2, as IL-33’s receptor, induced the production of type 2 cytokines. In this study, blood samples were collected from 19 non-pregnant women of normal childbearing age, 28 normal pregnant women, and 33 women with RSA. The serum concentrations of IL-33 and ST2 were detected by flow cytometry. Our results showed that the serum concentrations of IL-33 and ST2 in the RSA group were significantly higher than those in the healthy control group (IL-33: P < 0.05; ST2: P < 0.0001), and IL-33 and ST2 had a higher level in the process of RSA predictive value. In addition, this study initially found that the serum concentrations of IL-33 and ST2 were not significantly correlated with the number of weeks of pregnancy, and there was a lower correlation between IL-33 and ST2 during RSA. This result may be related to the small number of cases. This study is the first time to correlate the changes in serum concentrations of IL-33 and ST2 with RSA, which may be a novel biomarker for the prediction and treatment of RSA.

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.

Diagnostic Value of sST2 in Cardiovascular Diseases: A Systematic Review and Meta-Analysis

Biomarkers such as B-type natriuretic peptide (BNP), N-terminal pro-BNP (NT-proBNP), cardiac troponin (cTn), and CK-MB contribute significantly to the diagnosis of cardiovascular disease (CVD). Recent studies have demonstrated that suppression of tumorigenicity 2 (ST2) is associated with CVD, but a meta-analysis of ST2 levels in different CVDs has yet to be conducted. Therefore, the present study aimed to investigate soluble ST2 (sST2) levels in patients with ischemic heart disease (IHD), myocardial infarction (MI), and heart failure (HF). A total of 1,425 studies were searched across four databases, of which 16 studies were included in the meta-analysis. The Newcastle-Ottawa Quality Assessment Scale (NOS) values of all 16 studies were ≥7. The meta-analysis results indicated that the sST2 level was not correlated with IHD (standard mean difference [SMD] = 0.58, 95% confidence interval [95% CI] = 0.00 to 1.16, p = 0.05) or MI (weighted mean difference [WMD] = 0.17, 95% CI = -0.22 to 0.55, p = 0.40) but was significantly associated with HF (WMD = 0.21, 95% CI = 0.04 to 0.38, p = 0.02; I 2 = 99%, p < 0.00001). sST2 levels did not differ significantly between patients with IHD or MI and healthy individuals; however, we believe that ST2 could be used as an auxiliary diagnostic biomarker of HF.

Role of Interleukin-1 Receptor-Like 1 (ST2) in Cerebrovascular Disease

Following both ischemic and hemorrhagic stroke, innate immune cells initiate a proinflammatory response that further exacerbate tissue injury in the acute phase, but these cells also play an important reparative role thereafter. Numerous cytokines and signaling pathways have been implicated in driving the deleterious proinflammatory response, but less is known about the mediators that connect the initial vascular injury to the systemic immune response and the relationship between proinflammatory and reparative immune responses. The Interleukin-33 (IL-33) and serum stimulation-2 (ST2) axis is an interleukin signaling pathway that is a prime candidate to fulfill this role. In this review, we describe the biology of the IL-33/ST2 system, present evidence that its soluble decoy receptor, soluble ST2 (sST2), plays a key role in secondary neurologic injury after stroke, and discuss this in the context of the known role of IL-33/ST2 in other disease.

Soluble ST2 levels for predicting the presence and severity of metabolic syndrome

To explore the relationship between soluble ST2 (sST2) and metabolic syndrome (MetS) and determine whether sST2 levels can predict the presence and severity of MetS. We evaluated 550 consecutive subjects (58.91 ± 9.69 years, 50% male) with or without MetS from the Department of Vascular & Cardiology, Shanghai Jiao Tong University-Affiliated Ruijin Hospital. Serum sST2 concentrations were measured. The participants were divided into three groups according to the sST2 tertiles. Univariate and multivariable logistic regression models were used to evaluate the association between serum sST2 concentrations and the presence of MetS. Serum sST2 concentrations were significantly higher in the MetS group than in those in the no MetS group (14.80 ± 7.01 vs 11.58 ± 6.41 ng/mL, P < 0.01). Subjects with more MetS components showed higher levels of sST2. sST2 was associated with the occurrence of MetS after multivariable adjustment as a continuous log-transformed variable (per 1 SD, odds ratio (OR): 1.42, 95% CI: 1.13-1.80, P < 0.01). Subgroup analysis showed that individuals with MetS have significantly higher levels of sST2 than those without MetS regardless of sex and age. High serum sST2 levels were significantly and independently associated with the presence and severity of MetS. Thus, sST2 levels may be a novel biomarker and clinical predictor of MetS.

The Functional Roles of IL-33/ST2 Axis in Ocular Diseases

Interleukin-33 (IL-33), an important member of the IL-1 family, plays a pivotal role in regulating immune responses via combining with its receptor suppression of tumorigenicity 2 (ST2). We have already known IL-33/ST2 axis participates in the pathogenesis of various diseases, including liver diseases, renal diseases, and neurological diseases. Recently, emerging studies are indicating that IL-33/ST2 is also involved in a wide range of ocular diseases, such as allergic eye disease, keratitis and corneal regeneration, dry eye disease, uveitis, vitreoretinal diseases, and neuromyelitis optica spectrum disorder. In this review, we will summarize and discuss the current understanding about the functional roles of IL-33/ST2 in eyes, with an attempt to explore the possible study perspectives and therapeutic alternatives in the future.

Soluble ST2: A complex and diverse role in several diseases

The Suppression of Tumorigenicity 2 protein (ST2) is a member of the interleukin (IL) 1 receptor family with transmembrane (ST2L) and soluble (sST2) isoforms that are (over)expressed in several cells in different conditions and following various triggers (e.g. inflammation, stress). The ligand of ST2 is IL-33, which on binding to ST2L results in nuclear signalling and immunomodulatory action in various cells (tumour, immune, heart). sST2, that is released in the circulation, functions as a »decoy« receptor of IL-33 and inhibits IL-33/ST2L signalling and beneficial effects. The importance and role of the ST2/IL-33 axis and sST2 have been evaluated and confirmed in several inflammatory, cancer and cardiac diseases. sST2 is involved in homeostasis/pathogenesis of these diseases, as the counterbalance/response on IL-33/ST2L axis activation, which is triggered and expressed during developing fibrosis, tissue damage/inflammation and remodelling. In clinical studies, sST2 has been recognised as an important prognostic marker in patients with cardiac disease, including patients with chronic kidney disease where specific characteristics of sST2 enable better assessment of the risk of End-Stage Renal Disease patients on dialysis. sST2 is also recognised as an important marker for monitoring treatment in heart failure patients. However, accurate measurement and interpretation of ST2 concentration in serum/plasma samples for routine and research applications require the use of appropriate methods and recognition of essential characteristics of both the methods and the analyte that may influence the result. sST2, as one of the most promising disease biomarkers, is deserving of further study and wider application in clinical practice.

[Soluble ST2 - biomarker for prognosis and monitoring in decompensated heart failure]

The review aims to appraise the value of determining the concentrations of the new biomarker sST2 for assessing prognosis and monitoring treatment effectiveness of patients with decompensated heart failure during an episode of decompensation and during long-term follow-up after discharge from the hospital. The article analyses in detail the expedience of sST2 measurement in a patient with ADHF on admission and discharge from the hospital and the changes in the biomarker level during the period of active treatment for risk-stratification in patients, presents the optimal threshold values of sST2, which should be oriented when selecting patients with high and very high risk. The importance of subsequent monitoring of the marker concentration during long-term observation in emphasized to predict the risk of death, HF re-decompensation / HF rehospitalization. The potential benefits of choosing sST2 as the optimal marker for serial measurement during long-term follow-up, as well as evaluating the treatment effectiveness in patients with HF, compared to the "classical" variant - natriuretic peptides are shown.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

CEA Serum Levels in Non-Neoplastic Disease

Several non-neoplastic conditions, i.e., acute and chronic inflammations, benign tumors, renal or hepatic insufficiency, are associated with elevated plasma levels of Carcinoembryonic Antigen (CEA). Usually, CEA elevation in these pathologies is less than 10 ng/ml.

CEA values in non-malignant disease can be affected by many factors, which can be classified into five main categories: a) tissular, b) physiological, c) metabolic, d) circulating and e) methodological factors. Synthesis, expression and realease are the most important tissular factors. Among the metabolic ones liver, biliary and renal functions play a primary role in the determination of CEA concentrations. In addition, other factors such as the presence of circulating CEA-like substances, autoantibodies and immunocomplexes or the characteristics of the assay method can influence the diagnostic value of the CEA test.

All these factors must be carefully considered when the marker is used in clinical practice.

Runx2 mediated Induction of Novel Targets ST2 and Runx3 Leads to Cooperative Regulation of Hypertrophic Differentiation in ATDC5 Chondrocytes

Knowledge concerning expression and function of Suppression of Tumorigenicity 2 (ST2) in chondrocytes is at present, limited. Analysis of murine growth plates and ATDC5 chondrocytes indicated peak expression of the ST2 transmembrane receptor (ST2L) and soluble (sST2) isoforms during the hypertrophic differentiation concomitant with the expression of the hypertrophic markers Collagen X (Col X), Runx2 and MMP-13. Gain- and loss-of-function experiments in ATDC5 and primary human growth plate chondrocytes (PHCs), confirmed regulation of ST2 by the key transcription factor Runx2, indicating ST2 to be a novel Runx2 target. ST2 knock-out mice (ST2−/−) exhibited noticeable hypertrophic zone (HZ) reduction in murine growth plates, accompanied by lower expression of Col X and Osteocalcin (OSC) compared to wild-type (WT) mice. Likewise, ST2 knockdown resulted in decreased Col X expression and downregulation of OSC and Vascular Endothelial Growth Factor (VEGF) in ATDC5 cells. The ST2 suppression was also associated with upregulation of the proliferative stage markers Sox9 and Collagen II (Col II), indicating ST2 to be a new regulator of ATDC5 chondrocyte differentiation. Runx3 was, furthermore, identified as a novel Runx2 target in chondrocytes. This study suggests that Runx2 mediates ST2 and Runx3 induction to cooperatively regulate hypertrophic differentiation of ATDC5 chondrocytes.

Maternal plasma-soluble ST2 concentrations are elevated prior to the development of early and late onset preeclampsia - a longitudinal study

OBJECTIVE

The objectives of this study were to determine (1) the longitudinal profile of plasma soluble ST2 (sST2) concentrations in patients with preeclampsia and those with uncomplicated pregnancies; (2) whether the changes in sST2 occur prior to the diagnosis of preeclampsia; and (3) the longitudinal sST2 profile of women with early or late preeclampsia.

MATERIALS AND METHODS

This longitudinal nested case-control study included singleton pregnancies in the following groups: (1) uncomplicated pregnancies (n = 160); and (2) those complicated by early (<34 weeks, n = 9) and late (≥34 weeks, n = 31) preeclampsia. sST2 concentrations were determined by enzyme-linked immunosorbent assays. Mixed-effects models were used for the longitudinal analysis.

RESULTS

(1) Plasma sST2 concentration profiles across gestation differed significantly among cases and controls (p < 0.0001); (2) women with early preeclampsia had higher mean sST2 concentrations than controls at >22 weeks of gestation; cases with late preeclampsia had higher mean concentrations at >33 weeks of gestation (both p < 0.05); and (3) these changes started approximately 6 weeks prior to clinical diagnosis.

CONCLUSIONS

Maternal plasma sST2 concentrations are elevated 6 weeks prior to the clinical diagnosis of preeclampsia. An increase in the maternal plasma concentration of sST2 may contribute to an exaggerated intravascular inflammatory response and/or the Th1/Th2 imbalance in some cases.

Interleukin-33 Expression does not Correlate with Survival of Gastric Cancer Patients

The aim of the study was to investigate IL-33 expression in gastric cancer (GC) and its association with the clinical characteristics and the prognosis. IL-33 protein in tumor and corresponding adjacent tissues were detected by immunohistochemistry in 179 GC patients and clinical features plus prognostic value were analyzed via Pearson's chi-square test and Kaplan-Meier test in Cox proportional hazards model, respectively. IL-33 protein levels were significantly lower in tumor tissues than adjacent tissues (29.05% vs. 78.77%, χ ²  = 89.05, P < 0.001). The positive rate of IL-33 in the ulcerative type group was the lowest among all groups (P < 0.05). IL-33 levels were correlated with age (P = 0.025) and invasion depth (P = 0.030) while not significantly associated with the overall survival of GC patients. IL-33 expression is associated with age and invasive depth of GC patients but not an independent risk factor of prognosis.

Prognostic biomarkers in acute coronary syndrome

The acute coronary syndrome (ACS) is a leading cause of death around the globe. Beside a still high mortality rate, additional complications of ACS include arrhythmias, left ventricular mural thrombus, cardiac fibrosis, heart failure (HF), cardiogenic shock, mitral valve dysfunction, aneurysms, up to cardiac rupture. Despite many prognostic tools have been developed over the past decades, efforts are still ongoing to identify reliable and predictive biomarkers, which may help predict the prognosis of these patients and especially the risk of HF. Recent evidence suggests that the value of a discrete number of biomarkers of myocardial fibrosis, namely the soluble form of suppression of tumorigenicity 2 (sST2) and galectin-3 (GAL-3), may be predictive of HF and death in patients with ACS. Interestingly, the already promising predictive value of these biomarkers when measured alone was shown to be consistently magnified when combined with other and well-established cardiac biomarkers such natriuretic peptides and cardiac troponins. This article is hence aimed to review the current knowledge about cardiac biomarkers of fibrosis and adverse remodeling.

Reconstitution of ST2 (IL-1R4) specific for IL-33 activity; no suppression by IL-1Ra though a common chain IL-1R3 (IL-1RAcP) shared with IL-1

Interleukin-33 (IL-33) receptors are composed of ST2 (also known as IL-1R4), a ligand binding chain, and IL-1 receptor accessory protein (IL-1RAcP, also known as IL-1R3), a signal transducing chain. IL-1R3 is a common receptor for IL-1α, and IL-1β, IL-33, and three IL-36 isoforms. A549 human lung epithelial cells are highly sensitive to IL-1α and IL-1β but not respond to IL-33. The lack of responsiveness to IL-33 is due to ST2 expression. ST2 was stably transfected into A549 cells to reconstitute its activity. RT-PCR and FACS analysis confirmed ST2 expression on the cell surface of A549/ST2 cells. Upon IL-33 stimulation, A549/ST2 cells induced IL-8 and IL-6 production in a dose dependent manner while A549/mock cells remained unresponsive. There was no difference in IL-1α and IL-1β activity in A549/ST2 cells compared to A549/mock cells despite the fact that IL-33 shares IL-1R3 with IL-1α/β. IL-33 activated inflammatory signaling molecules in a time- and dose-dependent manner. Anti-ST2 antibody and soluble recombinant ST2-Fc abolished IL-33-induced IL-6 and IL-8 production in A549/ST2 cells but the IL-1 receptor antagonist failed to block IL-33-induced cytokines. This result demonstrates for the first time the reconstitution of ST2 in A549 human lung epithelial cell line and verified its function in IL-33-mediated cytokine production and signal transduction.

Conformational Sampling and Binding Site Assessment of Suppression of Tumorigenicity 2 Ectodomain

Suppression of Tumorigenicity 2 (ST2), a member of the interleukin-1 receptor (IL-1R) family, activates type 2 immune responses to pathogens and tissue damage via binding to IL-33. Dysregulated responses contribute to asthma, graft-versus-host and autoinflammatory diseases and disorders. To study ST2 structure for inhibitor development, we performed the principal component (PC) analysis on the crystal structures of IL1-1R1, IL1-1R2, ST2 and the refined ST2 ectodomain (ST2ECD) models, constructed from previously reported small-angle X-ray scattering data. The analysis facilitates mapping of the ST2ECD conformations to PC subspace for characterizing structural changes. Extensive coverage of ST2ECD conformations was then obtained using the accelerated molecular dynamics simulations started with the IL-33 bound ST2ECD structure as instructed by their projected locations on the PC subspace. Cluster analysis of all conformations further determined representative conformations of ST2ECD ensemble in solution. Alignment of the representative conformations with the ST2/IL-33 structure showed that the D3 domain of ST2ECD (containing D1-D3 domains) in most conformations exhibits no clashes with IL-33 in the crystal structure. Our experimental binding data informed that the D1-D2 domain of ST2ECD contributes predominantly to the interaction between ST2ECD and IL-33 underscoring the importance of the D1-D2 domain in binding. Computational binding site assessment revealed one third of the total detected binding sites in the representative conformations may be suitable for binding to potent small molecules. Locations of these sites include the D1-D2 domain ST2ECD and modulation sites conformed to ST2ECD conformations. Our study provides structural models and analyses of ST2ECD that could be useful for inhibitor discovery.

IL-33 Signaling in Lung Injury

Interleukin (IL)-33, a member of the IL-1 cytokine super-family, acts as both a traditional cytokine and an intracellular nuclear factor. It is generally released from damaged immune cells and signals through its receptor ST2 in an autocrine and paracrine fashion, plays important roles in type-2 innate immunity, and functions as an "alarmin" or a danger signal for cellular damage or cellular stress. Here, we review recent advances of the role of IL-33 in lung injury and explore its potential significance as an attractive therapeutic target.

The biology of ST2: the International ST2 Consensus Panel

ST2 is a member of the interleukin 1 receptor family with 2 main isoforms: transmembrane or cellular (ST2L) and soluble or circulating (sST2) forms. ST2 is the receptor of the IL-33, which is an IL-1-like cytokine that can be secreted by living cells in response to cell damage. IL-33 exerts its cellular functions by binding a receptor complex composed of ST2L and IL-1R accessory protein. The IL-33/ST2 system is upregulated in cardiomyocytes and fibroblasts as response to mechanical stimulation or injury. The interaction between IL33 and ST2L has been demonstrated to be cardioprotective: in experimental models, this interaction reduces myocardial fibrosis, prevents cardiomyocyte hypertrophy, reduces apoptosis, and improves myocardial function. The beneficial effects of IL-33 are specifically through the ST2L receptor. sST2 avidly binds IL-33 which results in interruption of the interaction between IL-33/ST2L and consequently eliminates the antiremodeling effects; thus, sST2 is viewed as a decoy receptor. In recent years, knowledge about ST2 role in the pathophysiology of cardiovascular diseases has broadly expanded, with strong links to myocardial dysfunction, fibrosis, and remodeling. Beyond its myocardial role, the IL-33/ST2 system could have an additional role in the development and progression of atherosclerosis. In conclusion, IL-33/ST2L signaling is a mechanically activated, cardioprotective fibroblast-cardiomyocyte paracrine system, which may have therapeutic potential for beneficially regulating the myocardial response to overload and injury. In contrast, sST2 acts as a decoy receptor and, by sequestering IL-33, antagonizes the cardioprotective effects of IL-33/ST2L interaction.

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.

Novel Biomarkers in Heart Failure Beyond Natriuretic Peptides - The Case for Soluble ST2

Despite more effective management of heart failure over the past few decades, its burden as a chronic disease has grown and is expected to continue to rise, representing a major health problem for years to come. Having reliable tools for early diagnosis and risk stratification can help managing the condition more efficiently. In this context, the interest for biomarkers has increased considerably in the last years following the useful clinical role of B-type natriuretic peptides. These biomarkers have been extensively studied and have become established diagnostic and prognostic biomarkers in heart failure. Despite their usefulness, limitations still remain a problem in clinical practice and the search for new biomarkers has therefore continued. Amongst the most promising newer biomarkers, soluble ST2 deserves further consideration. The present review will focus on the role of this new biomarker in the context of heart failure.

Cytokines (interleukin-9, IL-17, IL-22, IL-25 and IL-33) and asthma

Asthma is a reversible airway obstruction that is characterized by constriction of airway smooth muscle, hyper secretion of mucus, edema and airway hyper responsiveness (AHR), mucus secretion and thickening of the basement membrane underlying the airway epithelium. During the process of airway inflammation, complex interactions of innate and adaptive immune cells as well as structural cells and their cytokines have many important roles. It was believed that airway inflammation is orchestrated by allergen specific T helper (Th) 2 cells, which recruit and accumulate in the lungs and produce a range of different effector cytokines. However, more recent studies have revealed the potential collaboration of other helper T cells and their cytokines in this process. Th17 cell may have a role in severe asthma and chronic obstructive pulmonary disease (COPD). Interleukin (IL)-9-producing subset called Th9 cell, Th22 cells which primarily secrete IL-22, IL-13 and tumor necrosis factor-α and Th25 cells via producing IL-25 are believed to be important for initiating allergic reactions and developing airway inflammation. Cytokines are important in asthma and play a critical role in orchestrating the allergic inflammatory response, although the precise role of each cytokine remains to be determined. The aim of this review is to summarize the current knowledge about the possible roles of newly identified helper T cells derived cytokines (IL-9, 17, 22, 25 and IL-33) in asthma. The potential therapeutic applications emerging from the roles of these cytokines will be discussed as well.

Serum soluble ST2 is associated with ER-positive breast cancer

BACKGROUND

ST2, a member of the interleukin (IL)-1receptor family, regulates Th1/Th2 immune responses in autoimmune and inflammatory conditions. However, the role of ST2 signaling in tumor growth and metastasis of breast cancers has not been investigated. This study investigated the possible role of soluble ST2 (sST2) in breast cancer.

METHODS

The serum levels of IL-33, sST2, and vascular endothelial growth factor (VEGF) in 150 breast cancer patients and 90 healthy women were measured by enzyme-linked immunosorbent assay. Estrogen receptor(ER), progesterone receptor, human epithelial receptor (HER)-2, and cell cycle regulated protein Ki-67 were measured. Clinical stage, tumor size, lymph node metastasis, and histological type were also recorded.

RESULTS

The serum levels of sST2, IL-33, and VEGF were significantly higher in breast cancer patients than in the control group (P < 0.05, each). Serum sST2 levels in ER-positive breast cancer patients were significantly associated with age, histological type, clinical stage, tumor size, and Ki-67 status (P < 0.05, each). Moreover, the serum levels of IL-33 and sST2 in breast cancers significantly correlated with VEGF levels (IL-33: r = 0.375, P < 0.0001; sST2: r = 0.164, P = 0.045). Serum levels of sST2, IL-33, and VEGF decreased after modified radical mastectomy in ER-positive breast cancers. Serum levels of IL-33, sST2, and VEGF and clinicopathological factors were not significantly correlated with disease-free survival and overall survival of ER-positive breast cancer women during follow-up.

CONCLUSION

Serum sST2 levels in ER-positive breast cancer patients are significantly associated with factors that indicate poor prognosis.

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.

The inhibitory function of Fc-ST2 depends on cell type; IL-1RAcP and ST2 are necessary but insufficient for IL-33 activity

IL-33 (IL-1F11) is a member of IL-1 family ligand, which stimulates the production of inflammatory cytokines. IL-33 receptor complex is comprised of IL-1 receptor accessory protein (IL-1RAcP) and ST2 that are activated by IL-33 ligand binding. ST2 is a ligand-binding chain of the IL-33 receptor component, and the soluble ST2 form possesses antagonistic activity. Here, we expressed the extracellular domain of ST2-fused to the immunoglobulin of IgG1 constant region in order to generate a soluble recombinant Fc-ST2. Human and mouse recombinant Fc-ST2 protein were expressed in Chinese hamster ovary cells and purified using a mini-protein A affinity chromatography. The recombinant Fc-ST2 protein was used to examine inhibitory function in IL-33-induced cytokine production in different cell types. The human Fc-ST2 abolished IL-33-induced IL-8 production in human mast cells, but mouse Fc-ST2 failed to inhibit IL-33-induced TNFα production in mouse Raw 264.7 macrophage cells. We further investigated the expression of IL-33 receptor component with various cell lines. IL-33 receptors expression pattern and Fc-ST2 inhibitory activity in different cell types suggest that IL-1RAcP and ST2 are necessary but insufficient for IL-33 activity. Our results suggest that an additional receptor component may participate in the biological activity of IL-33.

Maternal plasma concentrations of sST2 and angiogenic/anti-angiogenic factors in preeclampsia

OBJECTIVES

Angiogenic/anti-angiogenic factors have emerged as one of the promising biomarkers for the prediction of preeclampsia. Since not all patients with preeclampsia can be identified by these analytes, the search for additional biomarkers continues. The soluble form of ST2 (sST2), a protein capable of binding to interleukin (IL)-33 and thus contributing to a Th1-biased immune response, has been reported to be elevated in maternal plasma of women with preeclampsia. The aims of this study were to examine: (1) differences in maternal plasma concentrations of sST2 and IL-33 between women diagnosed with preeclampsia and those having uncomplicated pregnancies; (2) the relationship between sST2, umbilical and uterine artery Doppler velocimetry, and the severity of preeclampsia; and (3) the performance of sST2 and angiogenic/anti-angiogenic factors in identifying patients with preeclampsia at the time of diagnosis.

METHODS

This cross-sectional study included women with preeclampsia (n = 106) and women with an uncomplicated pregnancy (n = 131). Plasma concentrations of sST2, IL-33, soluble vascular endothelial growth factor receptor (sVEGFR)-1, soluble endoglin (sEng) and placental growth factor (PlGF) were determined by enzyme linked immune sorbent assay. Area under the receiver operating characteristic curve (AUC) for the identification of preeclampsia was examined for each analyte.

RESULTS

(1) Patients with preeclampsia had a higher mean plasma concentrations of sST2 than those with an uncomplicated pregnancy (p < 0.0001), while no significant difference in the mean plasma concentration of IL-33 between the two groups was observed; (2) the magnitude of this difference was greater in early-onset, compared to late-onset disease, and in severe compared to mild preeclampsia; (3) sST2 plasma concentrations did not correlate with the results of uterine or umbilical artery Doppler velocimetry (p = 0.7 and p = 1, respectively) among women with preeclampsia; (4) sST2 correlated positively with plasma concentrations of sVEGFR1-1 and sEng (Spearman's Rho = 0.72 and 0.63; each p < 0.0001), and negatively with PlGF (Spearman's Rho = -0.56, p < 0.0001); and (5) while the AUC achieved by sST2 and angiogenic/anti-angiogenic factors in identifying women with preeclampsia at the time of diagnosis were non-significantly different prior to term (<37 weeks of gestation), thereafter the AUC achieved by sST2 was significantly less than that achieved by angiogenic/anti-angiogenic factors.

CONCLUSIONS

Preeclampsia is associated with increased maternal plasma concentrations of sST2. The findings that sST2 concentrations do not correlate with uterine or umbilical artery Doppler velocimetry in women with preeclampsia suggest that elevated maternal plasma sST2 concentrations in preeclampsia are not related to the increased impedance to flow in the utero-placental circulation. The performance of sST2 in identifying preeclampsia at the time of diagnosis prior to 37 weeks of gestation was comparable to that of angiogenic/anti-angiogenic factors. It remains to be elucidated if an elevation of maternal plasma sST2 concentrations in pregnancy is specific to preeclampsia.

Interleukin-33 and the function of innate lymphoid cells

Interleukin (IL)-33 is a member of the IL-1 cytokine family that has been shown to play an important role in the induction and effector phases of type 2 immune responses. Both innate and adaptive immunity are regulated by IL-33, and many studies have shown disease-associated functions for this cytokine. Recently, IL-33 has been implicated in the function of novel innate lymphocyte populations that regulate both protective responses in parasitic infections and allergic airway inflammation. Here, we discuss recent data highlighting the dual roles of IL-33 in protective and deleterious immune responses.

Effects of interleukin-33 on cardiac fibroblast gene expression and activity

Interleukin-33 (IL-33) is a recently described member of the interleukin-1 (IL-1) family. It is produced by diverse cell types in response to a variety of stresses including hemorrhage and increased mechanical load. Though only relatively recently discovered, IL-33 has been shown to participate in several pathological processes including promoting type 2 T helper cell-associated autoimmune diseases. In contrast, IL-33 has been also found to have protective effects in cardiovascular diseases. Recent studies have illustrated that IL-33 attenuates cardiac fibrosis induced by increased cardiovascular load in mice (transaortic constriction). Since cardiac fibrosis is largely dependent on increased production of extracellular matrix by cardiac fibroblasts, we hypothesized that IL-33 directly inhibits pro-fibrotic activities of these cells. Experiments have been carried out with isolated rat cardiac fibroblasts to evaluate the effects of IL-33 on the modulation of cardiac fibroblast gene expression and function to test this hypothesis. The expression of the IL-33 receptor, interleukin-1 receptor-like 1 (ST2), was detected at the mRNA and protein levels in isolated adult rat cardiac fibroblasts. Subsequently, the effects of IL-33 treatment (0-100 ng/ml) on the expression of extracellular matrix proteins and pro-inflammatory cytokines/chemokines were examined as well as the effects on rat cardiac fibroblast activities including proliferation, collagen gel contraction and migration. While IL-33 did not directly inhibit collagen I and collagen III production, it yielded a dose-dependent increase in the expression of interleukin-6 and monocyte chemotactic protein-1. Treatment of rat cardiac fibroblasts with IL-33 also impaired the migratory activity of these cells. Further experiments illustrated that IL-33 rapidly activated multiple signaling pathways including extracellular signal-regulated kinases, p38 mitogen-activated protein kinase, c-Jun N-terminal kinases and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) in a dose-dependent manner. Experiments were carried out with pharmacological inhibitors to determine the role of specific signaling pathways in the response of fibroblasts to IL-33. These experiments illustrated that the activation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinases are critical to the increased production of interleukin-6 and monocyte chemotactic protein-1 in response to IL-33. These studies suggest that IL-33 has an important role in the modulation of fibroblast function and gene expression. Surprisingly, IL-33 had no effect on the expression of genes encoding extracellular matrix components or on proliferation, markers typical of fibrosis. The major effects of IL-33 detected in these studies included inhibition of cell migration and activation of cytokine/chemokine expression. The previously reported inhibition of cardiac fibrosis may include more complicated mechanisms that involve other cardiac cell types. Future studies aimed at determining the effects of IL-33 on other cardiac cell types are warranted.

Contradictory functions (activation/termination) of neutrophil proteinase 3 enzyme (PR3) in interleukin-33 biological activity

IL-1 family ligand does not possess a typical hydrophobic signal peptide and needs a processing enzyme for maturation. The maturation process of IL-33 (IL-1F11), a new member of the IL-1 family ligand, remains unclear. Precursor IL-33 ligand affinity column isolates neutrophil proteinase 3 (PR3) from human urinary proteins. PR3 is a known IL-1 family ligand-processing enzyme for IL-1β (IL-1F2) and IL-18 (IL-1F4), including other inflammatory cytokines. We investigated PR3 in the maturation process of precursor IL-33 because we isolated urinary PR3 by using the precursor IL-33 ligand affinity column. PR3 converted inactive human and mouse precursor IL-33 proteins to biological active forms; however, the increase of PR3 incubation time abrogated IL-33 activities. Unlike caspase-1-cleaved precursor IL-18, PR3 cut precursor IL-33 and IL-18 at various sites and yielded multibands. The increased incubation period of PR3 abated mature IL-33 in a time-dependent manner. The result is consistent with the decreased bioactivity of IL-33 along with the increased PR3 incubation time. Six different human and mouse recombinant IL-33 proteins were expressed by the predicted consensus amino acid sequence of PR3 cleavage sites and tested for bioactivities. The human IL-33/p1 was highly active, but human IL-33/p2 and p3 proteins were inactive. Our results suggest the dual functions (activation/termination) of PR3 in IL-33 biological activity.

In silico approach to inhibition of signaling pathways of Toll-like receptors 2 and 4 by ST2L

Toll-like receptors (TLRs) activate a potent immunostimulatory response. There is clear evidence that overactivation of TLRs leads to infectious and inflammatory diseases. Recent biochemical studies have shown that the membrane-bound form of ST2 (ST2L), a member of the Toll-like/IL-1 receptor superfamily, negatively regulates MyD88-dependent TLR signaling pathways by sequestrating the adapters MyD88 and Mal (TIRAP). Specifically, ST2L attenuates the recruitment of Mal and MyD88 adapters to their receptors through its intracellular TIR domain. Thus, ST2L is a potent molecule that acts as a key regulator of endotoxin tolerance and modulates innate immunity. So far, the inhibitory mechanism of ST2L at the molecular level remains elusive. To develop a working hypothesis for the interactions between ST2L, TLRs (TLR1, 2, 4, and 6), and adapter molecules (MyD88 and Mal), we constructed three-dimensional models of the TIR domains of TLR4, 6, Mal, and ST2L based on homology modeling. Since the crystal structures of the TIR domains of TLR1, 2 as well as the NMR solution structure of MyD88 are known, we utilized these structures in our analysis. The TIR domains of TLR1, 2, 4, 6, MyD88, Mal and ST2L were subjected to molecular dynamics (MD) simulations in an explicit solvent environment. The refined structures obtained from the MD simulations were subsequently used in molecular docking studies to probe for potential sites of interactions. Through protein-protein docking analysis, models of the essential complexes involved in TLR2 and 4 signaling and ST2L inhibiting processes were developed. Our results suggest that ST2L may exert its inhibitory effect by blocking the molecular interface of Mal and MyD88 adapters mainly through its BB-loop region. Our predicted oligomeric signaling models may provide a basis for the understanding of the assembly process of TIR domain interactions, which has thus far proven to be difficult via in vivo studies.

Discovery of the DIGIRR gene from teleost fish: a novel Toll-IL-1 receptor family member serving as a negative regulator of IL-1 signaling

Toll-IL-1R (TIR) family members play crucial roles in a variety of defense, inflammatory, injury, and stress responses. Although they have been widely investigated in mammals, little is known about TIRs in ancient vertebrates. In this study, we report a novel double Ig IL-1R related molecule (DIGIRR) from three model fish (Tetraodon nigroviridis, Gasterosteus aculeatus, and Takifugu rubripes), adding a previously unknown homolog to the TIR family. This DIGIRR molecule contains two Ig-like domains in the extracellular region, one Arg-Tyr-mutated TIR domain in the intracellular region, and a unique subcellular distribution within the Golgi apparatus. These characteristics distinguish DIGIRR from other known family members. In vitro injection of DIGIRR into zebrafish embryos dramatically inhibited LPS-induced and IL-1β-induced NF-κB activation. Moreover, in vivo knockdown of DIGIRR by small interfering RNA significantly promoted the expression of IL-1β-stimulated proinflammatory cytokines (IL-6 and IL-1β) in DIGIRR-silenced liver and kidney tissues and in leukocytes. These results strongly suggest that DIGIRR is an important negative regulator of LPS-mediated and IL-1β-mediated signaling pathways and inflammatory responses. The Arg-Tyr-mutated site disrupted the signal transduction ability of DIGIRR TIR. Evolutionally, we propose a hypothesis that DIGIRR and single Ig IL-1R related molecule (SIGIRR) might originate from a common ancient IL-1R-like molecule that lost one (in DIGIRR) or two (in SIGIRR) extracellular Ig-like domains and intracellular Ser and Arg-Tyr amino acids. DIGIRR might be an evolutionary "transitional molecule" between IL-1R and SIGIRR, representing a shift from a potent receptor to a negative regulator. These results help define the evolutionary history of TIR family members and their associated signaling pathways and mechanisms.

ST2 deletion enhances innate and acquired immunity to murine mammary carcinoma

ST2 is a member of the IL-1 receptor family and IL-33 was recently identified as its natural ligand. The IL-33/ST2 pathway regulates Th1/Th2 immune responses in autoimmune and inflammatory conditions, but the role of ST2 signaling in tumor growth and metastasis has not been investigated. We aimed to investigate whether ST2 gene deletion affects tumor appearance, growth, and metastasis, and antitumor immunity in an experimental metastatic breast cancer model. Deletion of ST2 in BALB/c mice bearing mammary carcinoma attenuated tumor growth and metastasis, which was accompanied by increased serum levels of IL-17, IFN-γ, and TNF-α and decreased IL-4. Tumor-bearing ST2-/- mice had significantly higher percentages of activated CD27high CD11bhigh NK cells, CD69+ and KLRG- NK cells and higher cytotoxic activity of splenocytes, NK cells, and CD8+ T cells in vitro. A significantly higher number of NK cells expressing IFN-γ were found in ST2-/- mice compared with WT recipients. In vivo depletion of CD8+ or NK cells revealed a key role for NK cells in enhanced antitumor immunity in ST2-/- mice. We report for the first time that suppressed breast cancer progression and metastasis in mice lacking ST2 corresponds mainly with enhanced cytotoxic activity of NK cells, and increased systemic Th1/Th17 cytokines.

Nuocytes and beyond: new insights into helminth expulsion

T helper 2 (Th2) responses, characterized by the expression of the type-2 cytokines interleukin (IL)-4, IL-5, IL-9 and IL-13, are essential for the control of parasitic helminth infections and also drive the pathogenesis of allergy and asthma. Such responses are initiated, maintained and regulated, in part, by an array of innate effector cells and cytokines. However, relatively little is known about how the initiation of type-2 immune responses occurs in vivo. The recent discovery, using helminth models, of several novel innate immune cells capable of shaping type-2 immune responses allows us to reflect on the progress made in this area. It also affords us the opportunity to highlight the diversity of immune responses that can be driven by innate cells responding rapidly to early cytokine cues.

Identification of constitutively active interleukin 33 (IL-33) splice variant

IL-33/IL-1F11 is a new member of the IL-1 family ligand and provokes T helper-type immune responses. IL-33 is the ligand of ST2 and IL-1 receptor accessory protein (IL-1RAcP) that triggers nuclear factor-κ light chain enhancer of activated B cells (NF-κB) and MAPK signaling. We discovered a novel short splice variant of IL-33 that was termed spIL-33. The new spIL-33 lacks exon 3 containing a proposed caspase-1 cleavage site. We isolated spIL-33 cDNA from the Huh7 human hepatocarcinoma cell line and expressed the recombinant spIL-33 protein in Escherichia coli. The recombinant spIL-33 and pro-IL-33 were not cleaved by caspase-1, unlike IL-18 (IL-1F4). The recombinant spIL-33 was constitutively active, and spIL-33-induced inflammatory cytokine production was caspase-1-independent in HMC-1 and Raw 264.7 cells. The recombinant spIL-33 induced the phosphorylation of IL-1 receptor-associated kinase (IRAK1), NF-κB, p38 MAPK, p44/42 MAPK, and JNK in a time- and dose-dependent manner. Anti-ST2 monoclonal antibody specifically blocked the spIL-33-induced cytokine production. In this study, we identified and characterized a new IL-33 splice variant, which was a constitutively active IL-33 isoform. The existence of constitutively active spIL-33 suggests that the biological activity of IL-33 could be triggered by diverse stimulations during immune responses. Further investigation of the spIL-33 expression pattern may contribute to understanding the involvement of IL-33 in inflammatory disorders.

Interleukin-33 in asthma: how big of a role does it play?

In complex disorders such as asthma and allergic disease, the goal for developing disease-modifying biotherapeutics is to find a target that is a central instigator of immunologic activity. Interleukin (IL)-33 seems to be such a molecule, as it is one of the earliest-released signaling molecules following epithelial damage and can orchestrate the recruitment and activation of the cells responsible for disease. Unregulated IL-33 activity leads to activation of T-helper type 2 cells, mast cells, dendritic cells, eosinophils, and basophils, ultimately leading to increased expression of cytokines and chemokines that define the disease. As such, IL-33 is an attractive candidate for therapeutic intervention with the goal of ameliorating disease. This review focuses on the role of IL-33 in promoting and maintaining the asthma phenotype.