Construction of ELISA system to quantify human ST2 protein in sera of patients

Current Trends in Biohumoral Screening for the Risk of Sudden Cardiac Death: A Systematic Review

Background and Objectives: Sudden cardiac death (SCD) represents a challenge to health systems globally and is met with increased frequency in the population. Over time, multiple screening methods have been proposed, including the analysis of various plasma biomarkers. This article aims to analyze for illustrative purposes the specialized literature in terms of current biomarkers and testing trends, in the case of cardiovascular diseases and implicitly sudden cardiac death. Materials and Methods: In this regard, we searched the PubMed database from 2010 to the present time using the keywords "sudden cardiac death" and "biomarkers". The inclusion criteria were clinical trials that analyzed the effectiveness of screening methods in terms of biomarkers used in stratifying the risk of cardiac distress and/or sudden cardiac death. We excluded reviews, meta-analyses, and studies looking at the effectiveness of treatments. Results: An extended approach was found, through studies that brought to the forefront both classical markers analyzed by new, more performant methods, markers for other pathologies that also determined cardiovascular impact, non-specific molecules with effects on the cardiovascular system, and state-of-the-art markers, such as microRNA. Some molecules were analyzed simultaneously in certain groups of patients. Conclusion: The observed current trend revealed the tendency to define the clinical-biological particularities of the person to be screened.

In vitro evolution of diagnostic antibodies targeting native antigens in plasma by sandwich flow cytometry

Monoclonal antibodies (mAbs) that recognize and bind to specific antigens (Ags) have a wide range of applications in research, therapy, and diagnostics. However, many of these antibodies cannot bind well to the native Ags. In this study, based on the Chinese hamster ovary (CHO) cell display platform developed previously in our lab, we reported a novel artificial evolution procedure to improve the affinity of mAb against the native Ag directly using the plasma samples without purification of the native Ag. In this procedure, a pair of antibodies able to bind the Ag in sandwich manner are first confirmed (Ab1/Ab2) and the antibody (Ab) to be affinity-improved (Ab1) is displayed on CHO cells for Ab mutation. Then the cells were detected and sorted with flow cytometry in the form of Ab1-Ag-fluorescence labeled Ab2, which we named sandwich flow cytometry. Here, we used soluble isoform of suppression of tumorigenicity 2 (sST2) protein as model Ag, carried out "sandwich" maturation directly using the plasma samples containing the native sST2 protein and optimized a pair of antibodies with significantly improved sensitivity in the detection of the native sST2 in plasma. This method could be very useful in optimization of the diagnostic Ab pairs working in a "sandwich" manner if more antibodies were also successfully affinity-matured with this method.

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.

Role of IL-33/ST2 Axis in Chronic Inflammatory Neurological Disorderss

Interleukin-33 (IL-33) is a member of IL-1 family of cytokines, produced constitutively by fibroblasts, endothelial cells, and epithelial cells. IL-33 can be released passively from cells during tissue damage and cell necrosis, suggesting that it may act as an alarmin. Function of IL-33 is mediated by its interaction with ST2 molecule that is expressed on many immune cells: Th2 lymphocytes, NK, NKT and mast cells, monocytes, dendritic cells and granulocytes. IL-33/ST2 pathway plays, often dual, roles in different physiological and inflammatory processes, mediating both, pathological immune responses and tissue repair. Expression of IL-33 in the central nervous system (CNS) is significantly enhanced during various pathological processes, indicating its important role in the pathogenesis of neurological inflammatory and degenerative diseases. In this review the biological features, expression of IL-33 and its ligand ST2 in CNS, and the role of IL- 33/ST2 pathway in development of Alzheimer’s disease and multiple sclerosis are discussed.

Role of sST2 in predicting recurrence of atrial fibrillation after radiofrequency catheter ablation

INTRODUCTION

Atrial fibrosis is associated with atrial fibrillation (AF) recurrence after ablation. This study aims to determine the relationship between soluble ST2 (sST2), a profibrotic biomarker, and AF recurrence after radiofrequency catheter ablation (RFCA).

METHODS

AF patients referred for RFCA were consecutively included from October 2017 to May 2019. Baseline characteristics were collected, and sST2 levels were determined before ablation. Left atrial substrate mapping was performed after circumferential pulmonary vein isolation under sinus rhythm, and substrate was modified in low-voltage zones. A second procedure was recommended under recurrence.

RESULTS

Two hundred fifty-eight patients (146 males, average age 61.0 ± 8.8) were included. After a medium follow-up of 13.5 months, 52 patients (20.2%) had recurrence and received a second procedure. Preoperative sST2 level in patients with recurrence was significantly higher than that in patients without (31.3 ng/mL vs 20.3 ng/mL, P < .001). In those undergoing second ablation, sST2 level in patients with new abnormalities during endocardial mapping was significantly higher than that in patients without (43.0 ng/mL vs 22.1 ng/mL, P < .001). An sST2 level over 26.9 ng/mL could predict AF recurrence with new abnormalities during endocardial mapping with a sensitivity of 100% and a specificity of 75.9%. Multiple logistic analysis showed that sST2 level was an independent predictor of AF recurrence with new abnormalities during endocardial mapping (P < .001).

CONCLUSIONS

sST2 level was associated with new abnormalities during endocardial mapping and recurrence of AF after ablation. It might have significance in choosing treatment strategies for AF.

Lack of prognostic significance for major adverse cardiac events of soluble suppression of tumorigenicity 2 levels in patients with ST-segment elevation myocardial infarction

BACKGROUND

Elevation of soluble suppression of tumorigenicity 2 (sST2) is associated with cardiac fibrosis and hypertrophy. Under investigation herein, was whether sST2 level is associated with major adverse cardiac events (MACE) and left ventricular (LV) remodeling after primary percutaneous coronary intervention (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI).

METHODS

In total, this study included 184 patients who underwent successful primary PCI. A subsequent guideline-based medical follow-up was included (61.4 ± 11.8 years old, 85% male, 21% with Killip class ≥ I). sST2 concentration correlations with echocardiographic, angiographic, laboratory parameters, and clinical outcomes in STEMI patients were evaluated.

RESULTS

The median sST2 level was 60.3 ng/mL; 6 (3.2%) deaths occurred within 1 year. The sST2 level correlated with LV ejection fraction (LVEF) changes from baseline to 6 months (r= -0.273; p = 0.006) after adjustment for echocardiographic parameters including wall motions score index (WMSI). Recovery of LVEF at 6 months was highest in the tertile 1 group (Δ6 months - baseline LVEF; tertile 1, p = 0.001; tertile 2, p = 0.319; tertile 3, p = 0.205). The decrease in WMSI at 6 months was greater in the tertiles 1 and 2 groups than in the tertile 3 group (Δ6 months - baseline WMSI; tertile 1, p = 0.001; tertile 2, p = 0.013; tertile 3, p = 0.055). There was no association between sST2 levels and short-term (log rank p = 0.598) and long-term (p = 0.596) MACE.

CONCLUSIONS

sST2 concentration have predictive value for LV remodeling on echocardiography in patients with STEMI who underwent primary PCI. However, sST2 concentration was not associated with short-term and long-term MACE.

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.

Novel Biomarkers of Heart Failure

Although substantial improvements have been made in majority of cardiac disorders, heart failure (HF) remains a major health problem, with both increasing incidence and prevalence over the past decades. For that reason, the number of potential biomarkers that could contribute to diagnosis and treatment of HF patients is, almost exponentially, increasing over the recent years. The biomarkers that are, at the moment, more or less ready for use in everyday clinical practice, reflect different pathophysiological processes present in HF. In this review, seven groups of biomarkers associated to myocardial stretch (mid-regional proatrial natriuretic peptide, MR-proANP), myocyte injury (high-sensitive troponins, hs-cTn; heart-type fatty acid-binding protein, H-FABP; glutathione transferase P1, GSTP1), matrix remodeling (galectin-3; soluble isoform of suppression of tumorigenicity 2, sST2), inflammation (growth differentiation factor-15, GDF-15), renal dysfunction (neutrophil gelatinase-associated lipocalin, NGAL; kidney injury molecule-1, KIM-1), neurohumoral activation (adrenomedullin, MR-proADM; copeptin), and oxidative stress (ceruloplasmin; myeloperoxidase, MPO; 8-hydroxy-2'-deoxyguanosine, 8-OHdG; thioredoxin 1, Trx1) in HF will be overviewed. It is important to note that clinical value of individual biomarkers within the single time points in both diagnosis and outcome prediction in HF is limited. Hence, the future of biomarker application in HF lies in the multimarker panel strategy, which would include specific combination of biomarkers that reflect different pathophysiological processes underlying HF.

ST2 Predicts Mortality and Length of Stay in a Critically Ill Noncardiac Intensive Care Unit Population

OBJECTIVES

The biomarker suppression of tumorigenicity 2 (ST2) is a well-established clinical biomarker of cardiac strain and is frequently elevated in a variety of cardiac conditions. Here, we sought to evaluate the prognostic value of ST2 in critically ill medical intensive care unit (MICU) patients without primary cardiac illness.

METHODS

We measured ST2 and high-sensitivity troponin T (hsTnT) on plasma specimens collected on 441 patients following admission to a noncardiac MICU and evaluated the prognostic power of ST2 both alone and in multivariate models.

RESULTS

Of these critically ill patients, 96% exhibited ST2 concentrations above the reference interval. ST2 concentrations were highly predictive of intensive care unit and hospital length of stay, as well as in-hospital mortality, with high concentrations predicting a poor prognosis. Rates of in-hospital mortality were more than four times higher in patients with ST2 concentrations in the highest compared with the lowest quartile. In multivariate analysis, ST2 remained an important predictor of death after adjustment for age, hsTnT, and common diagnoses.

CONCLUSIONS

ST2 is increased and predictive of prognosis in critically ill patients without primary cardiac disease, suggesting that critically ill patients may often have unrecognized cardiac injury. Clinical decision support algorithms incorporating ST2 and hsTnT results may be useful in patient risk stratification.

Soluble form of the ST2 gene product exhibits growth promoting activity in NIH-3T3 cells

The ST2 gene is induced in murine fibroblast cells at the start of cell proliferation. Although IL-33 has been identified as a ligand for one of the two major gene products of ST2 – namely, the transmembrane receptor form ST2L – prompting immunological research on inflammation, the roles of the ST2 gene products in cell proliferation remain to be elucidated.

Using a cell proliferation assay system with NIH-3T3 cells, a normal murine fibroblast cell line, we found that treatment with recombinant ST2 caused an acceleration of cell proliferation, suggesting that ST2 acts in an autocrine/paracrine fashion. Strikingly, shRNA-induced knockdown of both ST2 gene products, ST2 and ST2L, reduced cell proliferation. This effect was effectively canceled by the expression of shRNA-resistant ST2, but not shRNA-resistant ST2L.

The novel enhancement of cell proliferation by ST2 appears to involve positive feedback. Since the ST2 level is increased in various diseases involving inflammation, future investigations into the role of ST2 gene products in relation to various diseases, including malignancies, may be warranted.

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Soluble ST2 enhanced cell proliferation of NIH-3T3 cells.

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Reduction of the ST2 gene products highly deteriorated cell growth of NIH-3T3 cells.

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Cell proliferation was recovered with supplementation of soluble ST2, but not ST2L.

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Positive feedback system of ST2 on cell proliferation is of great interest.

Interleukin-33 in Tissue Homeostasis, Injury, and Inflammation

Interleukin-33 (IL-33) is a nuclear-associated cytokine of the IL-1 family originally described as a potent inducer of allergic type 2 immunity. IL-33 signals via the receptor ST2, which is highly expressed on group 2 innate lymphoid cells (ILC2s) and T helper 2 (Th2) cells, thus underpinning its association with helminth infection and allergic pathology. Recent studies have revealed ST2 expression on subsets of regulatory T cells, and for a role for IL-33 in tissue homeostasis and repair that suggests previously unrecognized interactions within these cellular networks. IL-33 can participate in pathologic fibrotic reactions, or, in the setting of microbial invasion, can cooperate with inflammatory cytokines to promote responses by cytotoxic NK cells, Th1 cells, and CD8(+) T cells. Here, we highlight the regulation and function of IL-33 and ST2 and review their roles in homeostasis, damage, and inflammation, suggesting a conceptual framework for future studies.

Soluble ST2--analytical considerations

Suppression of tumorigenicity 2 (ST2, also known as interleukin [IL]-1 receptor-like-1) is an IL-1 receptor family member with transmembrane (ST2L) and soluble isoforms (sST2). ST2L is a membrane-bound receptor, and IL-33 is the functional ligand for ST2L. sST2, a soluble truncated form of ST2L, is secreted into the circulation and functions as a "decoy" receptor for IL-33, inhibiting IL-33/ST2L signaling. Blood concentrations of sST2 are increased in inflammatory diseases and heart disease and are considered a valuable prognostic marker in both conditions. In multiple clinical trials, sST2 has emerged as a clinically useful prognostic biomarker in patients with cardiac diseases. Interestingly, sST2 even provides prognostic information in low-risk community-based populations. In this review, we will discuss analytical considerations of measuring circulating sST2 including pre-analytical issues, such as in vitro stability of sST2, biological variation of sST2, and postanalytical issues, such as reference ranges and comparisons to diseased cohorts.

Soluble ST2 in heart failure

In addition to routine clinical laboratory tests (including natriuretic peptides and cardiac troponins), other biomarkers are gaining attention for their utility in heart failure (HF) management. Among them, soluble ST2 (sST2) a novel biomarker integrating inflammation, fibrosis, and cardiac stress has been included in the 2013 ACCF/AHA guideline for additive risk stratification of patients with acute and chronic HF. sST2 is an interleukin-1 (IL-1) receptor family member, is secreted into the circulation and functions as a "decoy" receptor for IL-33, inhibiting IL-33/ST2 signaling. Blood concentrations of sST2 are increased in various diseases such as inflammatory diseases and heart diseases and are considered a valuable prognostic marker in both conditions. sST2 lacks disease specificity and, therefore, is not a valuable marker for the diagnosis of HF. In acute and chronic HF, however, sST2 is strongly associated with measures of HF severity and poor outcome. Several studies in patients with HF indicate that serial measurement of sST2 has prognostic value and could have a potential role in future biomarker-directed therapy. In this review, the role of sST2 as a HF biomarker will be discussed, specifically addressing analytical considerations of measuring sST2 as well as the clinical applications of measurement of sST2 for the diagnosis, prognosis and monitoring of acute and chronic HF.

The Presage(®) ST2 Assay: analytical considerations and clinical applications for a high-sensitivity assay for measurement of soluble ST2

The Presage(®) ST2 Assay (Critical Diagnostics, CA, USA) is an in vitro diagnostic device that quantitatively measures soluble suppression of tumorigenicity 2 (sST2) in serum and plasma by ELISA. This assay is US FDA approved and is indicated to be used in conjunction with clinical evaluation as an aid in assessing the prognosis of patients diagnosed with chronic heart failure. sST2 binds to IL-33 and functions as a 'decoy' receptor for IL-33, thereby attenuating the systemic effects of IL-33. Due to the role of IL-33/transmembrane isoform of suppression of tumorigenicity 2 signaling in cardiac remodeling, sST2 has emerged as a novel cardiovascular biomarker. In recent studies, it was shown that sST2 is a valuable predictor of several end points in heart failure, in acute coronary syndromes and in critically ill patients. In this review, analytical considerations and clinical applications of the Presage ST2 Assay will be discussed, as well as probable future concepts for adoption of sST2 measurements into clinical practice.

ST2 requires Th2-, but not Th17-, type airway inflammation in epicutaneously antigen- sensitized mice

BACKGROUND

IL-33 is known to induce Th2-type cytokine production by various types of cells through its receptors, ST2 and IL-1RAcP. Polymorphism in the ST2 and/or IL-33 genes was found in patients with atopic dermatitis and asthma, implying that the IL-33/ST2 pathway is closely associated with susceptibility to these diseases. Exposure to allergens through damaged skin is suspected to be a trigger for allergen sensitization, resulting in development of such allergic disorders as asthma and atopic dermatitis.

METHODS

To elucidate the role(s) of the IL-33/ST2 pathway in asthma in individuals who had been epicutaneously sensitized to an antigen, wild-type and ST2-/- mice were epicutaneously sensitized with ovalbumin (OVA) and then were intranasally challenged with OVA. The degree of airway inflammation, the number of leukocytes and the activities of myeloperoxidase (MPO) and eosinophil peroxidase (EPO) in bronchoalveolar lavage fluids (BALFs), The levels of cytokines and chemokines in lungs and OVA-specific IgE levels in sera were determined by histological analysis, a hemocytometer, colorimetric assay, quantitative PCR or ELISA, respectively.

RESULTS

The number of eosinophils in BALFs, the levels of Th2 cytokines and chemoattractants in the lungs and OVA-specific IgE in sera from ST2-/- mice were significantly reduced compared with wild-type mice. Although the number of neutrophils in BALFs and the pulmonary levels of IL-17 were comparable in both mice, the levels of MPO activity in BALFs and neutrophil chemoattractants in the lung were reduced in ST2-/- mice.

CONCLUSIONS

The IL-33/ST2 pathway is crucial for Th2-cytokine-mediated eosinophilic, rather than Th17-cytokine-mediated neutrophilic, airway inflammation in mice that had been epicutaneously sensitized with antigens and then challenged with antigen.

Soluble ST2 as a Diagnostic and Prognostic Marker for Acute Heart Failure Syndromes

OBJECTIVES: We investigated the association of sST2 with diagnostic and prognostic outcomes and assessed whether it aids B-natriuretic peptide (BNP) in diagnosing and predicting outcomes in emergency department (ED) patients with suspected AHFS. METHODS: We recruited patients who presented to the ED of 3 tertiary hospitals with signs or symptoms of AHFS and met modified Framingham criteria for AHFS. Outcome measures were a final diagnosis of AHFS and 5-and 30-day adverse events. RESULTS: In the 295 subjects with sST2 available, the median sST2 was 0.20 ng/ml (IQR=0.10, 0.34). Although unadjusted analyses indicated sST2 was significantly associated with the diagnosis of AHFS (p=0.02), this was not so in the adjusted analysis (p=0.33). Moderately low diagnostic utility was noted with an AUC of 0.62 (95% CI=0.56, 0.69). Similar sST2 test characteristics were seen when BNP was restricted between 100 and 500 pg/ml. While sST2 was associated with AHFS readmission at 30-days (p=0.04), in the adjusted analyses it was not associated with adverse events. CONCLUSION: In patients with signs or symptoms of AHFS, unadjusted analyses indicated that sST2 was significantly associated with the diagnosis of AHFS and with 30-day AHFS recidivism. However, the associations did not carry over to adjusted analyses, and sST2 did not add significant information with regard to explaining the diagnostic and prognostic variability of BNP.

Paracrine IL-33 stimulation enhances lipopolysaccharide-mediated macrophage activation

Background

IL-33, a member of the IL-1 family of cytokines, provokes Th2-type inflammation accompanied by accumulation of eosinophils through IL-33R, which consists of ST2 and IL-1RAcP. We previously demonstrated that macrophages produce IL-33 in response to LPS. Some immune responses were shown to differ between ST2-deficient mice and soluble ST2-Fc fusion protein-treated mice. Even in anti-ST2 antibody (Ab)-treated mice, the phenotypes differed between distinct Ab clones, because the characterization of such Abs (i.e., depletion, agonistic or blocking Abs) was unclear in some cases.

Methodology/Principal Findings

To elucidate the precise role of IL-33, we newly generated neutralizing monoclonal Abs for IL-33. Exogenous IL-33 potentiated LPS-mediated cytokine production by macrophages. That LPS-mediated cytokine production by macrophages was suppressed by inhibition of endogenous IL-33 by the anti-IL-33 neutralizing mAbs.

Conclusions/Significance

Our findings suggest that LPS-mediated macrophage activation is accelerated by macrophage-derived paracrine IL-33 stimulation.

Soluble ST2 monitoring provides additional risk stratification for outpatients with decompensated heart failure

INTRODUCTION AND OBJECTIVES

The novel biomarker ST2 provides diagnostic information in a variety of clinical settings. The objective was to determine whether measurement of the soluble ST2 (sST2) concentration improves risk stratification in outpatients with decompensated heart failure (HF).

METHODS

The concentrations of sST2 and N-terminal probrain natriuretic peptide (NT-proBNP) and a heart failure severity score (HFSS), based on Framingham criteria, were determined at baseline and 2 weeks later in 48 outpatients with decompensated hf. The ratio of the value of each variable at week 2 relative to baseline was determined. Patients were followed for 1 year and cardiac events (i.e. death, HF admission and heart transplantation) were recorded.

RESULTS

By 1 year, 56% of patients had experienced a cardiac event. The sST2 ratio was significantly lower in patients who did not have a cardiac event (0.6 ± 0.39 vs. 1.39 ± 0.92; P< .001). After multivariable adjustment, the sST2 ratio remained an independent predictor of risk (odds ratio=1.054; 95% confidence interval, 1.01-1.09; P=.017). The optimum cut-point for the sST2 ratio determined by receiver operating curve [ROC] analysis was 0.75; this accounted for 25% of the change in sST2 by week 2. Among patients with an sST2 ratio >0.75 and a baseline NT-proBNP level >1000 ng/L, 72% had a cardiac event (P=.018), while no events occurred in patients with marker values below these reference levels.

CONCLUSIONS

Determination of the sST2 concentration in serial samples provided additional risk stratification in outpatients with decompensated HF. Repeated measurement of sST2 may aid clinical decision-making.

IL-33 and Airway Inflammation

Interleukin-33 (IL-33) is the 11th member of IL-1 cytokine family which includes IL-1 and IL-18. Unlike IL-1β and IL-18, IL-33 is suggested to function as an alarmin that is released upon endothelial or epithelial cell damage and may not enhance acquired immune responses through activation of inflammasome. ST2, a IL-33 receptor component, is preferentially expressed by T-helper type (Th) 2 cells, mast cells, eosinophils and basophils, compared to Th1 cells, Th17 cells and neutrophils. Thus, IL-33 profoundly enhances allergic inflammation through increased expression of proallergic cytokines and chemokines. Indeed, IL-33 and its receptor genes are recognized as the most susceptible genes for asthma by several recent genomewide association studies. It has also recently been shown that IL-33 plays a crucial role in innate eosinophilic airway inflammation rather than acquired immune responses such as IgE production. As such, IL-33 provides a unique therapeutic way for asthma, i.e., ameliorating innate airway inflammation.

IL-33 and IL-33 receptors in host defense and diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, which includes IL-1 and IL-18. IL-33 is considered to be crucial for induction of Th2-type cytokine-associated immune responses such as host defense against nematodes and allergic diseases by inducing production of such Th2-type cytokines as IL-5 and IL-13 by Th2 cells, mast cells, basophils and eosinophils. In addition, IL-33 is involved in the induction of non-Th2-type acute and chronic inflammation as a proinflammatory cytokine, similar to IL-1 and IL-18. In this review, we summarize and discuss the current knowledge regarding the roles of IL-33 and IL-33 receptors in host defense and disease development.

The carboxy-terminal fragment of alpha(1A) calcium channel preferentially aggregates in the cytoplasm of human spinocerebellar ataxia type 6 Purkinje cells

Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominant neurodegenerative disease caused by a small polyglutamine (polyQ) expansion (control: 4–20Q; SCA6: 20–33Q) in the carboxyl(C)-terminal cytoplasmic domain of the α_1A voltage-dependent calcium channel (Ca_v2.1). Although a 75–85-kDa Ca_v2.1 C-terminal fragment (CTF) is toxic in cultured cells, its existence in human brains and its role in SCA6 pathogenesis remains unknown. Here, we investigated whether the small polyQ expansion alters the expression pattern and intracellular distribution of Ca_v2.1 in human SCA6 brains. New antibodies against the Ca_v2.1 C-terminus were used in immunoblotting and immunohistochemistry. In the cerebella of six control individuals, the CTF was detected in sucrose- and SDS-soluble cytosolic fractions; in the cerebella of two SCA6 patients, it was additionally detected in SDS-insoluble cytosolic and sucrose-soluble nuclear fractions. In contrast, however, the CTF was not detected either in the nuclear fraction or in the SDS-insoluble cytosolic fraction of SCA6 extracerebellar tissues, indicating that the CTF being insoluble in the cytoplasm or mislocalized to the nucleus only in the SCA6 cerebellum. Immunohistochemistry revealed abundant aggregates in cell bodies and dendrites of SCA6 Purkinje cells (seven patients) but not in controls (n = 6). Recombinant CTF with a small polyQ expansion (rCTF-Q28) aggregated in cultured PC12 cells, but neither rCTF-Q13 (normal-length polyQ) nor full-length Ca_v2.1 with Q28 did. We conclude that SCA6 pathogenesis may be associated with the CTF, normally found in the cytoplasm, being aggregated in the cytoplasm and additionally distributed in the nucleus.

Soluble ST2 for predicting sudden cardiac death in patients with chronic heart failure and left ventricular systolic dysfunction

OBJECTIVES

We studied whether the measurement of the soluble form of ST2 (sST2), an interleukin-1 receptor family member, could identify heart failure (HF) patients at risk of sudden cardiac death (SCD).

BACKGROUND

The prediction of SCD remains an important challenge in patients with mild-to-moderate chronic HF. Concentrations of sST2 have been found increased and related to worse long-term outcomes in patients with acute HF. Whether sST2 has a prognostic role in SCD is unknown.

METHODS

A nested case-control study was performed on 36 cases of SCD and 63 control patients (matched for age, sex, and left ventricular ejection fraction) obtained from the MUSIC (MUerte Súbita en Insuficiencia Cardíaca) registry, a 3-year multicenter registry of ambulatory HF patients (New York Heart Association functional class II to III, left ventricular ejection fraction < or =45%). Demographic, clinical, echocardiographic, electrical, and biochemical data were collected at enrollment.

RESULTS

Concentrations of sST2 were greater among decedents (0.23 ng/ml [interquartile range 0.16 to 0.43 ng/ml] vs. 0.12 ng/ml [interquartile range 0.06 to 0.23 ng/ml], p = 0.001) and were predictive of experiencing SCD (+0.1 ng/ml, odds ratio: 1.39, 95% confidence interval: 1.09 to 1.78, p = 0.006). On the basis of a combined biomarker status, only 4% of patients experienced SCD for neither sST2 nor N-terminal pro-B-type natriuretic peptide (NT-proBNP) above receiver-operator characteristic-derived cut-off points (0.15 ng/ml and 2,000 ng/l, respectively), 34% for either biomarker above, and 71% for both biomarkers above (p < 0.001 for trend). This combined variable added incremental prognostic value to the multivariable regression model (p < 0.001).

CONCLUSIONS

Elevated sST2 concentrations are predictive of SCD in patients with chronic HF and provide complementary information to NT-proBNP levels. A combined biomarker approach may have an impact on clinical decision-making.

IL-33: a tissue derived cytokine pathway involved in allergic inflammation and asthma

Besides classic T cell-derived T-helper type 2 (Th2) cytokines such as IL-4, IL-5 and IL-13, tissue-produced cytokines such as thymic stromal lymphopoietin, IL-25 and IL-33 are now recognized as important contributors to allergic inflammation. IL-33 is produced by various tissue dwelling cells and broadly enhances allergic inflammation through its effects on hematopoietic cell types. The environmental or endogenous triggers that provoke IL-33 cellular release may be associated with infection, inflammation or tissue damage. This review summarizes the wide range of documented IL-33 activities on human cellular mediators of inflammation as well as genetic evidence that IL-33 contributes to disease. Finally, there will be a discussion of still unanswered questions regarding the mechanisms by which cytokine activity is generated and IL-33's relationship with other Th2-associated cytokines.

ST2 protein in heart disease: from discovery to mechanisms and prognostic value

Biomarkers aid in diagnosis by providing important information for the clinical assessment of patients that is not achieved by other means. This article focuses on the use of soluble ST2 as a biomarker in cardiovascular disease. Soluble ST2 is a secreted receptor belonging to the IL-1 receptor family that regulates inflammation and immunity. Recent studies have shown that soluble ST2 is a decoy receptor that disrupts the interaction of IL-33 with the full-length ST2L receptor. The rapidly evolving and expanding literature on ST2 and its ligand reveal emerging roles for this system in the regulation of inflammation in a variety of diseases. Elevated ST2 levels have been detected in cardiovascular diseases and levels provide useful prognostic information in many, but not all, of these diseases, which will be discussed here. Additional studies demonstrating elevated soluble ST2 levels in other human diseases will also be discussed.

Analytical and clinical evaluation of a novel high-sensitivity assay for measurement of soluble ST2 in human plasma--the Presage ST2 assay

BACKGROUND

The protein ST2 is a member of the interleukin-1 receptor family. Blood concentrations of the soluble isoform of ST2 (sST2) are increased in inflammatory diseases and in heart disease and are considered a prognostic marker in both. The aim of this study was the analytical and clinical evaluation of the novel Presage ST2 assay for the determination of sST2 in human plasma.

METHODS

We evaluated precision and linearity of the assay, analyte stability, and biological variability, determined reference values, performed a method comparison with an established ELISA, and quantified sST2 concentrations in various diseases.

RESULTS

Within-run and total coefficients of variation were <2.5% and <4.0%. The method was linear across the whole measurement range of the assay. The analyte was stable for 48 h at room temperature, for 7 days at 4 degrees C, and for at least 2 months at -20 degrees C and -80 degrees C. The reference change value for healthy individuals was 30%. Age-independent reference values were 3-28 U/mL in males, and 2-16 U/mL in females. The method comparison revealed a high proportional bias. sST2 plasma concentrations were increased modestly in heart failure and moderately in pneumonia and chronic obstructive pulmonary disease. Patients with sepsis exhibited highly elevated sST2 values. In patients with chronic renal disease, however, there was no difference compared to healthy individuals.

CONCLUSION

The Presage ST2 assay meets the needs of quality specifications of laboratory medicine. The results of the clinical assay evaluation are novel with respect to sST2 in various diseases and should initiate further studies.

Serum levels of the interleukin-1 receptor family member ST2, cardiac structure and function, and long-term mortality in patients with acute dyspnea

BACKGROUND

ST2, a biomarker of cardiomyocyte stretch, powerfully predicts poor outcomes in patients with acute dyspnea, but nothing is known about associations between soluble ST2 (sST2) and cardiac structure and function, or whether sST2 retains prognostic meaning in the context of such measures.

METHODS AND RESULTS

One hundred thirty-four dyspneic patients with and without decompensated heart failure had echocardiography during index admission and vital status was ascertained at 4 years. Echocardiographic and clinical correlates of sST2 as well as independent predictors of death at 4 years were identified. sST2 correlated with left ventricular end-systolic dimensions/volumes and left ventricular ejection fraction. sST2 was inversely associated with right ventricular fractional area change (rho=-0.18; P=0.046), higher right ventricular systolic pressure (rho=0.26; P=0.005), and right ventricular hypokinesis (P<0.001) and was correlated with tissue Doppler Ea wave peak velocity, but not to other indices of diastolic function. In multivariate regression, independent predictors of sST2 included right ventricular systolic pressure (t=2.29; P=0.002), left ventricular ejection fraction (t=-2.15; P=0.05) and dimensions (end systolic, t=2.57; end diastolic, t=2.98; both P<0.05), amino-terminal pro-B-type natriuretic peptide (t=3.31; P=0.009), heart rate (t=2.59; P=0.01), and presence of jugular venous distension (t=2.00; P=0.05). In a Cox proportional hazards model that included echocardiographic results and other biomarkers, sST2 independently predicted death at 4 years (hazard ratio=2.70; P=0.003).

CONCLUSIONS

Among dyspneic patients with and without acute heart failure, sST2 concentrations are associated with prevalent cardiac abnormalities on echocardiography, a more decompensated hemodynamic profile and are associated with long-term mortality, independent of echocardiographic, clinical, or other biochemical markers of risk.

The IL-1 receptor accessory protein (AcP) is required for IL-33 signaling and soluble AcP enhances the ability of soluble ST2 to inhibit IL-33

Interleukin (IL)-33 (or IL-1F11) was recently identified as a ligand for the orphan IL-1 receptor family member T1/ST2 (ST2). IL-33 belongs to the IL-1 cytokine family and, upon binding to ST2, induces intracellular signals similar to those utilized by IL-1. The effects of other IL-1 family cytokines are mediated by their binding to a specific receptor and the recruitment of a co-receptor required for elicitation of signaling. The aim of this study was to characterize the co-receptor involved in IL-33 signaling. Immunoprecipitation confirmed that IL-33 specifically binds ST2 and revealed that cellular IL-1 receptor accessory protein (AcP) associates with ST2 in a ligand-dependent manner. Receptor binding measurements demonstrated that the affinity of mouse (m)IL-33 for ST2 is increased by 4-fold in presence of AcP. IL-33 dose-dependently stimulated IL-6 secretion from wild-type (WT) mast cells, while no effect of IL-33 was observed with mast cells derived from AcP-deficient mice. Finally, soluble (s)ST2-Fc and sAcP-Fc acted synergistically to inhibit IL-33 activity. These observations identify AcP as a shared co-receptor within the IL-1 family that is essential for IL-33 signaling and suggest a novel role for sAcP in modulating the activity of IL-33.

Measurement of the interleukin family member ST2 in patients with acute dyspnea: results from the PRIDE (Pro-Brain Natriuretic Peptide Investigation of Dyspnea in the Emergency Department) study

OBJECTIVES

The aim of this study was to examine the value of measurement of the interleukin-1 receptor family member ST2 in patients with dyspnea.

BACKGROUND

Concentrations of ST2 have been reported to be elevated in patients with heart failure (HF).

METHODS

Five hundred ninety-three dyspneic patients with and without acute destabilized HF presenting to an urban emergency department were evaluated with measurements of ST2 concentrations. Independent predictors of death at 1 year were identified.

RESULTS

Concentrations of ST2 were higher among those with acute HF compared with those without (0.50 vs. 0.15 ng/ml; p < 0.001), although amino-terminal pro-brain natriuretic peptide (NT-proBNP) was superior to ST2 for diagnosis of acute HF. Median concentrations of ST2 at presentation to the emergency department were higher among decedents than survivors at 1 year (1.08 vs. 0.18 ng/ml; p < 0.001), and in multivariable analyses, an ST2 concentration > or =0.20 ng/ml strongly predicted death at 1 year in dyspneic patients as a whole (HR = 5.6, 95% confidence interval [CI] 2.2 to 14.2; p < 0.001) as well as those with acute HF (hazard ratio [HR] = 9.3, 95% CI 1.3 to 17.8; p = 0.03). This risk associated with an elevated ST2 in dyspneic patients with and without HF appeared early and was sustained at 1 year after presentation (log-rank p value <0.001). A multi-marker approach with both ST2 and NT-proBNP levels identified subjects with the highest risk for death.

CONCLUSIONS

Among dyspneic patients with and without acute HF, ST2 concentrations are strongly predictive of mortality at 1 year and might be useful for prognostication when used alone or together with NT-proBNP.

Elevation of ST2 protein levels in cerebrospinal fluid following subarachnoid hemorrhage

OBJECTIVE

To study the mode of appearance of ST2 in cerebrospinal fluid (CSF) after subarachnoid hemorrhage (SAH).

MATERIALS AND METHODS

Immunoprecipitation and subsequent immunoblotting were performed to reveal the existence of ST2 in CSF after SAH. CSF samples from 21 patients were analyzed for ST2 using an enzyme-linked immunosorbent assay system. The ST2 levels were compared between serum and CSF after SAH. The ST2 levels in CSF were measured in six patients operated with other than SAH.

RESULTS

ST2 was secreted into CSF after SAH. The concentration of ST2 was the highest in the samples of the first post-operative day and declined thereafter. The patients operated with other than SAH did not show the elevation of ST2 in CSF.

CONCLUSIONS

This study revealed the presence of ST2 in CSF for the first time and suggested a possibility that ST2 is related to the inflammatory reaction in the central nervous system after SAH.

ST2 suppresses IL-6 production via the inhibition of IκB degradation induced by the LPS signal in THP-1 cells

LPS induces the production of inflammatory cytokines via the stimulation of Toll-like receptors. In this study, we demonstrated that a soluble secreted form of the ST2 gene product (ST2), a member of the interleukin-1 receptor family, suppressed the production of IL-6 in an LPS-stimulated human monocytic leukemia cell line, THP-1. Immunofluorescence confocal microscopy revealed the binding of ST2 to the surface of the THP-1 cells, in which ST2 led to decreased binding of nuclear factor-kappaB to the IL-6 promoter. Furthermore, the degradation of IkappaB in the cytoplasm after LPS stimulation was reduced by pretreatment with ST2. These results demonstrated that ST2 negatively regulates LPS-induced IL-6 production via the inhibition of IkappaB degradation in THP-1 cells.

T-helper type 2 cell-specific expression of the ST2 gene is regulated by transcription factor GATA-3

ST2 is a member of the interleukin-1 receptor family and is expressed in type-2 T helper (Th2) cells. Here, we have studied the molecular mechanism responsible for the transcriptional regulation of the ST2 gene in Th2 cells using a mouse thymoma cell line, EL-4. The ST2 gene has distal and proximal promoters. ST2 mRNA was produced from the distal promoter in EL-4 cells stimulated with both phorbol 12-myristate 13-acetate (PMA) and dibutyryl cAMP (Bt2cAMP). The region of approximately 100 bp upstream of transcription start site, containing two GATA consensus sites, was indispensable for the activation of the distal promoter in reporter gene analysis. An electrophoretic mobility shift assay showed that transcription factor GATA-3 bound one of the GATA consensus sites (from -84 to -79) with nuclear extracts from PMA plus Bt2cAMP-stimulated EL-4 cells. The overexpression of GATA-3 enhanced the activity of the distal promoter. On the other hand, mutations of the GATA consensus site canceled out the enhancement by GATA-3. These data suggest that GATA-3 is an important transcription factor for the expression of the ST2 gene in Th2 cells.

Molecular cloning of the chicken ST2 gene and a novel variant form of the ST2 gene product, ST2LV

The ST2 gene encodes receptor-like molecules that are very similar to the interleukin-1 receptors. Three types of ST2 gene products, ST2, ST2L, and ST2V, can be produced by alternative splicing. In the course of cloning the chicken ST2 and ST2L cDNAs, we identified a novel variant cDNA other than ST2, ST2L, or ST2V, and tentatively named it ST2LV. ST2LV was produced by alternative splicing that deleted the transmembrane domain of ST2L. The chicken ST2 gene consisted of 13 exons and had two promoters followed by noncoding exons 1a and 1b, like the ST2 genes of human, mouse, and rat. The chicken ST2 mRNA was detected by RT-PCR as early as embryonic day 5. After that, the chicken ST2 mRNA was expressed in all examined organs, including the brain, eye, heart, lung, and liver. The chicken ST2LV mRNA was detected from embryonic day 10. The chicken ST2LV cDNA was transiently expressed in COS-7 cells. A protein of 69 kDa was detected in the culture supernatant, and the size of the protein was reduced to 53 kDa by treatment with peptide-N-glycosidase F, which suggested that ST2LV is a new soluble secreted and N-glycosylated variant of the ST2 gene product.

The Increase in Serum Soluble ST2 Protein Upon Acute Exacerbation of Idiopathic Pulmonary Fibrosis

BACKGROUND

The human ST2 gene can be specifically induced by growth stimulation in fibroblastic cells, and the soluble ST2 protein (ST2) is expressed preferentially in T-helper type 2 (Th2) cells. Furthermore, ST2 is induced by proinflammatory stimuli such as tumor necrosis factor-alpha and interleukin-1 beta. It has been reported that the inflammatory response in idiopathic pulmonary fibrosis (IPF) is thought to be associated with proinflammatory cytokines and Th2 immune response.

STUDY OBJECTIVE

The objective of this study was to evaluate the relevance of the serum ST2 levels in the pathogenesis of IPF.

DESIGN

Retrospective study.

SETTING

Inpatients in a college hospital.

PARTICIPANTS

Forty-nine patients with IPF admitted to our hospital 64 times: 36 patients were admitted once, 11 patients were admitted twice, and 2 patients were admitted three times. The participants also included 200 healthy control volunteers.

MEASUREMENTS AND RESULTS

Among 64 events in 49 patients with IPF, 50 of the events occurred in a stable state, and 14 events occurred during acute exacerbation. An acute exacerbation of IPF was defined as an accelerated phase of IPF. The serum ST2 levels were measured by enzyme-linked immunosorbent assay. The serum levels of ST2 in the stable state group did not differ from those in the healthy control group, while the serum levels of ST2 in the acute exacerbation group were significantly higher than those in the stable state group or the healthy control group (p < 0.001, acute exacerbation group vs stable state group or healthy control group; acute exacerbation group, 2.76 +/- 0.56 ng/mL; stable state group, 0.44 +/- 0.07 ng/mL; healthy control group, 0.42 +/- 0.03 ng/mL). Furthermore, serum ST2 statistically correlated with lactate dehydrogenase (r = 0.344, p = 0.005) and C-reactive protein (r = 0.496, p < 0.001), and inversely correlated with PaO(2) (r = - 0.356, p = 0.018) and the percentage of predicted vital capacity (r = - 0.346, p = 0.026).

CONCLUSIONS

These results suggest that ST2 protein may increase in the serum, reflecting severity in the inflammatory process and Th2 immune response in the IPF lung.

Identification of serum soluble ST2 receptor as a novel heart failure biomarker

BACKGROUND

Using genomic technology, we previously identified an interleukin-1 receptor family member, ST2, as a gene markedly induced by mechanical strain in cardiac myocytes. The soluble receptor form of ST2 is secreted and detectable in human serum. This study tested the hypothesis that soluble ST2 levels in the serum of patients with severe chronic heart failure are increased in patients with neurohormonal activation.

METHODS AND RESULTS

Serum samples, clinical variables, and neurohormone levels from the PRAISE-2 heart failure trial (NYHA functional class III-IV; end point, mortality or transplantation) were analyzed. ST2 serum measurements were performed with ELISA on samples from 161 patients obtained at trial enrollment and from 139 of the same patients obtained 2 weeks after trial enrollment. Baseline ST2 levels were correlated with baseline B-type natriuretic peptide (BNP) levels (r=0.36, P<0.0001), baseline proatrial natriuretic peptide (ProANP) levels (r=0.36, P<0.0001), and baseline norepinephrine levels (r=0.39, P<0.0001). The change in ST2 was significant as a univariate predictor of subsequent mortality or transplantation (P=0.048), as was baseline BNP (P<0.0001) and baseline ProANP (P<0.0001). In multivariate models including BNP and ProANP, the change in ST2 remained significant as a predictor of mortality or transplantation independent of BNP and ProANP.

CONCLUSIONS

Serum soluble ST2 is a novel biomarker for neurohormonal activation in patients with heart failure. In patients with severe chronic NYHA class III to IV heart failure, the change in ST2 levels is an independent predictor of subsequent mortality or transplantation.

The effect of ST2 gene product on anchorage-independent growth of a glioblastoma cell line, T98G

The ST2 gene, which is specifically induced by growth stimulation in fibroblasts, encodes interleukin-1 receptor-related proteins and is widely expressed in hematopoietic, helper T, and various cancer cells. However, the physiological as well as pathological functions of the ST2 gene products are not yet fully understood. In this study, we analyzed the expression of the ST2 gene in human glioma cell lines and human brain tumor samples with real-time polymerase chain reaction method, the results of which revealed that the expression level of the ST2 gene in glioma cell lines and glioblastoma samples is significantly lower than that in a fibroblastic cell line, TM12, and benign brain tumors, suggesting the reverse relationship between malignancy and ST2 expression. As we could not detect the soluble ST2 protein in the culture fluid of the T98G glioblastic cell line by ELISA, we established stable transformants of T98G that continuously produce and secrete the ST2 protein, in order to study the effect of the ST2 protein on malignancy. Although we could not detect a remarkable difference in proliferation between transformants and control cells in conventional tissue culture dishes, the efficiency of colony formation in soft agar was significantly decreased in the case of cells that continuously produce the ST2 protein. Furthermore, inhibition of colony formation in soft agar was observed in wild-type T98G cells when purified soluble ST2 protein was added to the culture, in a dose-dependent manner. Taken together, the results suggest that the expression of ST2 suppressed the anchorage-independent growth and malignancy.

Expression and regulation of ST2, an interleukin-1 receptor family member, in cardiomyocytes and myocardial infarction

BACKGROUND

We identified an interleukin-1 receptor family member, ST2, as a gene markedly induced by mechanical strain in cardiac myocytes and hypothesized that ST2 participates in the acute myocardial response to stress and injury.

METHODS AND RESULTS

ST2 mRNA was induced in cardiac myocytes by mechanical strain (4.7+/-0.9-fold) and interleukin-1beta (2.0+/-0.2-fold). Promoter analysis revealed that the proximal and not the distal promoter of ST2 is responsible for transcriptional activation in cardiac myocytes by strain and interleukin-1beta. In mice subjected to coronary artery ligation, serum ST2 was transiently increased compared with unoperated controls (20.8+/-4.4 versus 0.8+/-0.8 ng/mL, P<0.05). Soluble ST2 levels were increased in the serum of human patients (N=69) 1 day after myocardial infarction and correlated positively with creatine kinase (r=0.41, P<0.001) and negatively with ejection fraction (P=0.02).

CONCLUSIONS

These data identify ST2 release in response to myocardial infarction and suggest a role for this innate immune receptor in myocardial injury.

ST2 protein induced by inflammatory stimuli can modulate acute lung inflammation

We have investigated gene and protein expression of ST2/ST2L in a murine alveolar macrophage (AM) cell line, MH-S, reacting to inflammatory stimuli in vitro and in the lung tissue of an acute lung injury model in vivo. We have also analyzed the effect of soluble ST2 protein on inflammatory response of MH-S cells. Lipopolysaccharide (LPS) and proinflammatory cytokines such as IL-1beta, IL-6, and TNF-alpha induced ST2 mRNA expression in MH-S cells. In an acute lung injury model, protein and mRNA expression levels of ST2 increased to the maximal level at 24-72h after the LPS challenge. Furthermore, pretreatment with ST2 protein significantly reduced the protein production and gene expression of IL-1alpha, IL-6, and TNF-alpha in LPS-stimulated MH-S cells in vitro. These results suggest that increases in endogenous ST2 protein in AM, which is induced by inflammatory stimuli, such as LPS and proinflammatory cytokines, may modulate acute lung inflammation.

Expression and function of the ST2 gene in a murine model of allergic airway inflammation

BACKGROUND

We have recently reported that soluble ST2 protein levels are elevated in the sera of patients with asthma, and correlate well with the severity of asthma exacerbation. However, the role, function, and kinetics of soluble ST2 expression in asthma remain unclear.

OBJECTIVE

The objective of the present study was to clarify the function and kinetics of soluble murine (m) ST2 expression in a murine asthma model.

METHODS

We analyzed the kinetics of gene and protein expression of mST2 in sera or lung tissue after allergen (ovalbumin; OVA) challenge in a murine model of allergic airway inflammation, the effects of mST2 protein on OVA-induced Th2 cytokine production in vitro from splenocytes of sensitized mice, and the effects of soluble mST2 on Th2-dependent allergic airway inflammation by in vivo gene transfer of mST2.

RESULTS

Serum mST2 protein levels increased to the maximal level 3 h after the allergen challenge, before serum IL-5 levels peaked. The mRNA expression of mST2 in lung tissue was induced after the allergen challenge, while that in the spleen was constitutively detected. Furthermore, pre-treatment with mST2 protein significantly inhibited the production of IL-4 and IL-5, but not IFN-gamma, from OVA-stimulated splenocytes in vitro, and intravenous mST2 gene transfer resulted in a drastic reduction in the number of eosinophils and in the levels of IL-4 and IL-5 in bronchoalveolar lavage fluid, compared with those in response to transfer of non-coding plasmid vector or of lipid alone.

CONCLUSION

These results suggest that increases in endogenous mST2 protein after allergen exposure may modulate Th2-mediated airway inflammation, and that in vivo gene transfer of mST2 can be applicable to use in a novel immunotherapy for allergic diseases.

Expression of ST2 in helper T lymphocytes of malignant pleural effusions

The objective of this study was to test the hypothesis that accumulated helper T lymphocytes in malignant pleural effusions may shift to T-helper type 2 (Th2) and produce soluble ST2 protein. We took samples of serum and pleural effusions (p-) from patients with carcinomatous pleurisy (CA, n = 17), tuberculous pleurisy (TB, n = 8), and congestive heart failure (HF, n = 5) and compared the concentration of cytokines or ST2. Ex vivo production of interleukin (IL)-4 and IL-10, though not that of interferon (IFN)-gamma or IL-12, from CD4+ T cells isolated from pleural effusions was higher in the CA group than in the TB or HF group. The p-ST2 concentrations were significantly higher in the CA group than in the TB or HF group, positively correlated with the percentage of pleural effusion CD4+ T cells (r = 0.432, p = 0.016) and inversely correlated with p-IFN-gamma concentrations (r = -0.423, p = 0.019). Furthermore, mRNA expression of ST2 in CD4+ T cells isolated from group CA was upregulated, compared with that in those isolated from the TB group. These results suggest that CD4+ T cells in CA shift to Th2, which can produce soluble ST2 protein, resulting in increased concentrations of p-ST2 in malignant pleural effusion.

Tissue distribution and subcellular localization of a variant form of the human ST2 gene product, ST2V

The human ST2 gene has been known to encode three splice variants; namely, a soluble secreted form of ST2, a transmembrane form of ST2L, and ST2V of undetermined localization. Therefore, analysis of tissue distribution and subcellular localization of ST2V is important to elucidate functional relationships among the three splice variants of the human ST2 gene. RT-PCR procedure revealed that ST2V is predominantly expressed in the stomach, small intestine, and colon. Transfection of ST2V cDNA into COS7 cells in the presence of [(35)S] methionine and cysteine produced radiolabeled 40 kDa protein, which is recognized by specific monoclonal antibody against human ST2. Subcellular fractionation analysis showed that ST2V protein was distributed in the insoluble fraction of the cell lysate. Finally, ST2V protein was detected on the plasma membrane of COS7 cells, which had been transfected with ST2V cDNA, by confocal laser microscopic analysis. These findings taken together, indicate that ST2V protein localizes on the plasma membrane, suggesting its possible role in modification of the ST2L-signaling pathways.

Elevated soluble ST2 protein levels in sera of patients with asthma with an acute exacerbation

Previous studies have reported that ST2 is preferentially expressed on Th2 cells and plays a critical part in controlling airway inflammation in murine models of asthma. However, the clinical role of ST2 in patients with bronchial asthma remains unclear. In our study, we examined 56 patients with atopic asthma in a nonattack phase and 200 nonatopic normal volunteers for healthy control, and analyzed the relationship of their serum ST2 levels to asthma severity, pulmonary function, and laboratory data. Of the 56 patients with atopic asthma, 30 exhibited asthmatic exacerbation, and their serum ST2 levels were also analyzed. The serum ST2 levels were low, but a statistical difference was found between patients with nonattack asthma and the healthy control group (p < 0.05). We also found a differential rise of serum ST2 level that correlates well with the severity of asthma exacerbation. Furthermore, the serum ST2 levels during asthma exacerbation statistically correlated with the percentage of predicted peak expiratory flow (r = -0.634, p = 0.004) and Pa(CO(2)) (r = 0.516, p = 0.003). These results suggest that soluble human ST2 protein in sera may be related to Th2-mediated allergic inflammation inducing acute exacerbation in patients with atopic asthma.

Identification of human ST2 protein in the sera of patients with autoimmune diseases

Soluble human ST2 protein (IL1RL1-a) in the sera of patients with various autoimmune diseases was identified by a newly developed procedure using specific monoclonal antibodies. After immunoprecipitation and subsequent immunoblotting, a glycosylated protein of about 60 kDa was detected in the sera of SLE patients, but not in the sera of healthy controls. The experiments using gel filtration and SDS-PAGE under a nonreducing condition indicated the existence of the ST2 multimer in serum. The mobility of the natural protein was slower than that of the recombinant human ST2 protein produced by COS7 cells in SDS-PAGE, suggesting a difference of glycosylation between humans and monkeys. The identification of the natural human ST2 protein should be important both to fundamental researches and the further clarification of the clinical implications of the ST2 protein.

The cloning and nucleotide sequence of human ST2L cDNA

The ST2 gene is a member of the IL-1 receptor family and is hypothesized to be involved in helper T cell function, but its functional ligand and physiological role remain unknown. We have cloned the human ST2L cDNA that encodes a distinct type of membrane-bound ST2 protein. The predicted 556-amino-acid sequence showed 67% identity to the mouse ST2L protein. The human ST2 gene (IL1RL1) contains 13 exons and spans 40 kb in length. Its exon-intron organization was elucidated from a registered human genomic sequence derived from chromosome 2q, which contains three other genes belonging to the IL-1 receptor family in an approximately 202-kb genomic region. The tissue distribution of ST2 expression was examined by RT-PCR, and the soluble form (ST2, IL1RL1-a) and ST2L (IL1RL1-b) appear to be expressed differentially. We also established stable transfectants of a human glioblastoma cell line, T98G, that express human ST2L constitutively, and we confirmed cell-surface expression of human ST2L protein on the transfectants.