The challenge of measuring IL-33 in serum using commercial ELISA: lessons from asthma

Interleukin-33/serum stimulation-2 pathway: Regulatory mechanisms and emerging implications in immune and inflammatory diseases

Interleukin (IL)- 33, a nuclear factor and pleiotropic cytokine of the IL-1 family, is gaining attention owing to its important role in chronic inflammatory and autoimmune diseases. This review extends our knowledge of the effects exerted by IL-33 on target cells by binding to its specific receptor serum stimulation-2 (ST2). Depending on the tissue context, IL-33 performs multiple functions encompassing host defence, immune response, initiation and amplification of inflammation, tissue repair, and homeostasis. The levels and activity of IL-33 in the body are controlled by complex IL-33-targeting regulatory pathways. The unique temporal and spatial expression patterns of IL-33 are associated with host homeostasis and the development of immune and inflammatory disorders. Therefore, understanding the origin, function, and processes of IL-33 under various conditions is crucial. This review summarises the regulatory mechanisms underlying the IL-33/ST2 signalling axis and its potential role and clinical significance in immune and inflammatory diseases, and discusses the current complex and conflicting findings related to IL-33 in host responses.

IL-33 Expression Is Lower in Current Smokers at both Transcriptomic and Protein Levels

Rationale: IL-33 is a proinflammatory cytokine thought to play a role in the pathogenesis of asthma and chronic obstructive pulmonary disease (COPD). A recent clinical trial using an anti-IL-33 antibody showed a reduction in exacerbation and improved lung function in ex-smokers but not current smokers with COPD. Objectives: This study aimed to understand the effects of smoking status on IL-33. Methods: We investigated the association of smoking status with the level of gene expression of IL-33 in the airways in eight independent transcriptomic studies of lung airways. Additionally, we performed Western blot analysis and immunohistochemistry for IL-33 in lung tissue to assess protein levels. Measurements and Main Results: Across the bulk RNA-sequencing datasets, IL-33 gene expression and its signaling pathway were significantly lower in current versus former or never-smokers and increased upon smoking cessation (P < 0.05). Single-cell sequencing showed that IL-33 is predominantly expressed in resting basal epithelial cells and decreases during the differentiation process triggered by smoke exposure. We also found a higher transitioning of this cellular subpopulation into a more differentiated cell type during chronic smoking, potentially driving the reduction of IL-33. Protein analysis demonstrated lower IL-33 levels in lung tissue from current versus former smokers with COPD and a lower proportion of IL-33-positive basal cells in current versus ex-smoking controls. Conclusions: We provide strong evidence that cigarette smoke leads to an overall reduction in IL-33 expression in transcriptomic and protein level, and this may be due to the decrease in resting basal cells. Together, these findings may explain the clinical observation that a recent antibody-based anti-IL-33 treatment is more effective in former than current smokers with COPD.

Exploring the significance of interleukin-33/ST2 axis in minimal change disease

Minimal change disease (MCD), a common cause of idiopathic nephrotic syndrome, has been postulated to exhibit an association with allergic conditions. Recent studies revealed the crucial role of interleukin (IL)-33 in type 2 innate immunity. We hypothesized that development of MCD involves an IL-33-related immune response. We examined 49 patients with biopsy-proven MCD, 6 healthy volunteers, and 29 patients in remission. In addition to clinical features, serum and urinary levels of IL-33 and soluble suppression of tumorigenicity 2 protein (sST2), a secreted form of the receptor of IL-33, were analyzed. Although IL-33 was barely detectable in either MCD or control samples, sST2 levels at diagnosis were elevated in MCD patients. Serum sST2 levels of MCD patients were correlated with serum total protein level (r =  - 0.36, p = 0.010) and serum creatinine level (r = 0.34, p = 0.016). Furthermore, the elevated sST2 levels were observed to decrease following remission. Immunofluorescence revealed IL-33 expression in the podocytes among MCD patients, with a significant increase compared with controls. In vitro, mouse podocyte cells incubated with serum from a MCD patient at disease onset showed increased IL-33 secretion. These results suggest an IL-33-related immune response plays a role in MCD.

Exposure to farm environment and its correlations with total IgE, IL-13, and IL-33 serum levels in patients with atopy and asthma

BACKGROUND

The aim of the study was to evaluate total immunoglobulin E (IgE), IL-13, and IL-33 serum level in people with bronchial asthma and atopy, and in healthy control group depending on their exposure to farm animals currently and in the first year of life.

METHODS

The study included 174 individuals living in rural areas and in a small town. Standardized questions from the International Study of Asthma and Allergy in Childhood and The European Community Respiratory Health Survey (ECRHS) questionnaires were used to define asthma. Atopic status was verified by skin prick tests. Rural exposure including contact with livestock was verified by adequate questionnaire. Total serum IgE, IL-13, and IL-33 levels were assessed by ELISA (enzyme-linked immunosorbent assay) tests.

RESULTS

Participants with atopy and bronchial asthma were characterized by high level of immunoglobulin E. Tendency to lower serum IgE level was observed among people reporting present contact with farm animals. Also, among those having contact with livestock in their first year of life, the analogous tendency was noticed. No difference in serum IL-13 levels in participants with asthma and atopy, and controls was observed, and there was no effect of exposure on farm animals on the concentration of IL-13. The highest IL-33 level was found in the atopic group, and the lowest in the control group. Participants currently exposed to farm animals were predisposed to have lower IL-33 serum level.

CONCLUSION

Exposure of farm animals currently and in first year of life may result in a lower level of total IgE. Correlation between IL-13 and IL-33 serum levels and contact with livestock was not confirmed.

Longitudinal proteomic profiling of the inflammatory response in dengue patients

BACKGROUND

The immunopathogenesis of dengue virus (DENV) infection remains incompletely understood. To increase our understanding of inflammatory response in non-severe dengue, we assessed longitudinal changes in the inflammatory proteome in patients with an acute DENV infection.

METHODS

Using a multiplex proximity extension assay (PEA), we measured relative levels of 368 inflammatory markers in plasma samples from hospitalized patients with non-severe DENV infection in the acute (n = 43) and convalescence (n = 35) phase of the infection and samples of healthy controls (n = 10).

RESULTS

We identified 203 upregulated and 39 downregulated proteins in acute versus convalescent plasma samples. The upregulated proteins had a strong representation of interferon (IFN) and IFN-inducible effector proteins, cytokines (e.g. IL-10, IL-33) and cytokine receptors, chemokines, pro-apoptotic proteins (e.g. granzymes) and endothelial markers. A number of differentially expressed proteins (DEPs) have not been reported in previous studies. Functional network analysis highlighted a central role for IFNγ, IL-10, IL-33 and chemokines. We identified different novel associations between inflammatory proteins and circulating concentrations of the endothelial glycocalyx disruption surrogate marker syndecan-1. Conclusion: This unbiased proteome analysis provides a comprehensive insight in the inflammatory response in DENV infection and its association with glycocalyx disruption.

IL1RAP expression and the enrichment of IL-33 activation signatures in severe neutrophilic asthma

BACKGROUND

Interleukin (IL)-33 is an upstream regulator of type 2 (T2) eosinophilic inflammation and has been proposed as a key driver of some asthma phenotypes.

OBJECTIVE

To derive gene signatures from in vitro studies of IL-33-stimulated cells and use these to determine IL-33-associated enrichment patterns in asthma.

METHODS

Signatures downstream of IL-33 stimulation were derived from our in vitro study of human mast cells and from public datasets of in vitro stimulated human basophils, type 2 innate lymphoid cells (ILC2), regulatory T cells (Treg) and endothelial cells. Gene Set Variation Analysis (GSVA) was used to probe U-BIOPRED and ADEPT sputum transcriptomics to determine enrichment scores (ES) for each signature according to asthma severity, sputum granulocyte status and previously defined molecular phenotypes.

RESULTS

IL-33-activated gene signatures were cell-specific with little gene overlap. Individual signatures, however, were associated with similar signalling pathways (TNF, NF-κB, IL-17 and JAK/STAT signalling) and immune cell differentiation pathways (Th17, Th1 and Th2 differentiation). ES for IL-33-activated gene signatures were significantly enriched in asthmatic sputum, particularly in patients with neutrophilic and mixed granulocytic phenotypes. IL-33 mRNA expression was not elevated in asthma whereas the expression of mRNA for IL1RL1, the IL-33 receptor, was up-regulated in the sputum of severe eosinophilic asthma. The mRNA expression for IL1RAP, the IL1RL1 co-receptor, was greatest in severe neutrophilic and mixed granulocytic asthma.

CONCLUSIONS

IL-33-activated gene signatures are elevated in neutrophilic and mixed granulocytic asthma corresponding with IL1RAP co-receptor expression. This suggests incorporating T2-low asthma in anti-IL-33 trials.

Elevated Plasma Soluble ST2 Levels are Associated With Neuronal Injury and Neurocognitive Impairment in Children With Cerebral Malaria

Background

Murine experimental cerebral malaria studies suggest both protective and deleterious central nervous system effects from alterations in the interleukin-33 (IL-33)/ST2 pathway.

Methods

We assessed whether soluble ST2 (sST2) was associated with neuronal injury or cognitive impairment in a cohort of Ugandan children with cerebral malaria (CM, n=224) or severe malarial anemia (SMA, n=193).

Results

Plasma concentrations of sST2 were higher in children with CM than in children with SMA or in asymptomatic community children. Cerebrospinal fluid (CSF) sST2 levels were elevated in children with CM compared with North American children. Elevated plasma and CSF ST2 levels in children with CM correlated with increased endothelial activation and increased plasma and CSF levels of tau, a marker of neuronal injury. In children with CM who were ≥5 years of age at the time of their malaria episode, but not in children <5 years of age, elevated risk factor-adjusted plasma levels of sST2 were associated with worse scores for overall cognitive ability and attention over a 2-year follow-up.

Conclusions

The study findings suggest that sST2 may contribute to neuronal injury and long-term neurocognitive impairment in older children with CM.

New drugs under development for COPD

The characteristic features of chronic obstructive pulmonary disease (COPD) include inflammation and remodelling of the lower airways and lung parenchyma together with activation of inflammatory and immune processes. Due to the increasing habit of cigarette smoking worldwide COPD prevalence is increasing globally. Current therapies are unable to prevent COPD progression in many patients or target many of its hallmark characteristics which may reflect the lack of adequate biomarkers to detect the heterogeneous clinical and molecular nature of COPD. In this chapter we review recent molecular data that may indicate novel pathways that underpin COPD subphenotypes and indicate potential improvements in the classes of drugs currently used to treat COPD. We also highlight the evidence for new drugs or approaches to treat COPD identified using molecular and other approaches including kinase inhibitors, cytokine- and chemokine-directed biologicals and small molecules, antioxidants and redox signalling pathway inhibitors, inhaled anti-infectious agents and senolytics. It is important to consider the phenotypes/molecular endotypes of COPD patients together with specific outcome measures to target new therapies to particular COPD subtypes. This will require greater understanding of COPD molecular pathologies and a focus on biomarkers of predicting disease subsets and responder/non-responder populations.

Soluble IL-33 receptor predicts survival in acute kidney injury

Introduction: The prediction of acute kidney injury (AKI)-related outcomes remains challenging. Herein we prospectively quantified soluble ST2 (sST2), the circulating isoform of the IL-33 receptor, in hospitalized patients with AKI. Methods: In-hospital subjects with AKI of various etiology were identified through the in-hospital AKI alert system of the Brandenburg University hospital. sST2 was measured within a maximum of 48 hours from the time of diagnosis of AKI. The following endpoints were defined: in-hospital death, dialysis, recovery of kidney function until demission. Results: In total, 151 individuals were included in the study. The in-hospital mortality was 16.6%, dialysis therapy became mandatory in 39.7%, no recovery of kidney function occurred in 27.8%. sST2 was significantly higher in nonsurvivors (p = 0.024) but did not differ in the two other endpoints. The level of sST2 increased significantly with the severity of AKI. Further differences were detected in subjects with heart insufficiency (lower sST2), and in patients that required ICU treatment, or ventilatory therapy, or vasopressors (all higher). Conclusions: The current study suggests sST2 as biomarker of “acute distress”: it predicts post-AKI survival and substantially increases in subjects with a higher degree of cumulative morbidity under acute circumstances (e.g., ICU therapy, vasopressor administration).

Development of an ultra-sensitive human IL-33 biomarker assay for age-related macular degeneration and asthma drug development

Background

Over the past decade, human Interleukin 33 (hIL-33) has emerged as a key contributor to the pathogenesis of numerous inflammatory diseases. Despite the existence of several commercial hIL-33 assays spanning multiple platform technologies, their ability to provide accurate hIL-33 concentration measurements and to differentiate between active (reduced) and inactive (oxidized) hIL-33 in various matrices remains uncertain. This is especially true for lower sample volumes, matrices with low hIL-33 concentrations, and matrices with elevated levels of soluble Interleukin 1 Receptor-Like 1 (sST2), an inactive form of ST2 that competes with membrane bound ST2 for hIL-33 binding.

Results

We tested the performance of several commercially available hIL-33 detection assays in various human matrices and found that most of these assays lacked the sensitivity to accurately detect reduced hIL-33 at biologically relevant levels (sub-to-low pg/mL), especially in the presence of human sST2 (hsST2), and/or lacked sufficient target specificity. To address this, we developed and validated a sensitive and specific enzyme-linked immunosorbent assay (ELISA) capable of detecting reduced and total hIL-33 levels even in the presence of high concentrations of sST2. By incorporating the immuno-polymerase chain reaction (iPCR) platform, we further increased the sensitivity of this assay for the reduced form of hIL-33 by ~ 52-fold. Using this hIL-33 iPCR assay, we detected hIL-33 in postmortem human vitreous humor (VH) samples from donors with age-related macular degeneration (AMD) and found significantly increased hIL-33 levels when compared to control individuals. No statistically significant difference was observed in aqueous humor (AH) from AMD donors nor in plasma and nasosorption fluid (NF) from asthma patients compared to control individuals.

Conclusions

Unlike existing commercial hIL-33 assays, our hIL-33 bioassays are highly sensitive and specific and can accurately quantify hIL-33 in various human clinical matrices, including those with high levels of hsST2. Our results provide a proof of concept of the utility of these assays in clinical trials targeting the hIL-33/hST2 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03189-3.

Serum IL-33 as a biomarker in different diseases: useful parameter or much need for clarification?

Interleukin-33 (IL-33), a member of the IL-1 family, is critically involved in the modulation of the activity of a diverse range of immunocompetent cells. Essential roles have been implicated in cardioprotection, in both innate and adaptive immune responses in mucosal organs, and in the maintenance of adipose tissue cells. Over the past 10 years, several studies evaluated the usability of IL-33 as a biomarker in diseases of inflammatory and noninflammatory origin. Our group is currently evaluating the predictive role of serum IL-33 in acute kidney injury (AKI). The aim of the article is to discuss selected studies on IL-33 in different diseases and its potential role as a biomarker molecule.

Quantitation of reduced IL-33 levels in human serum: mitigating interference from endogenous binding partners

Aim: IL-33 is a potential therapeutic target but commercially available assays for the quantitation of systemic IL-33 have poor reliability. Results: In commercial IL-33 kits, interference from endogenous binding partners (e.g., soluble ST2) causes under-quantitation. Mitigating this required acid dissociation and addition of the detection reagent simultaneously with the capture step. This enabled detection of total, reduced (active) levels of IL-33 in human serum (LLOQ 6.25 pg/ml). Conclusion: Acid treatment of serum samples dissociates IL-33 from endogenous binding partners, increasing soluble ST2 tolerance to >1000 ng/ml. The modified method was specific for reduced endogenous IL-33. Analysis of over 300 samples from individuals with and without asthma and with different smoking status revealed no difference in serum IL-33.

Role of the IL-33/ST2 axis in cardiovascular disease: A systematic review and meta-analysis

Interleukin (IL)-33 and its unique receptor, ST2, play a pivotal role in the immune response to infection and stress. However, there have been conflicting reports of the role of IL-33 in cardiovascular disease (CVD) and the potential of this axis in differentiating CVD patients and controls and with CVD disease severity, remains unclear.

AIMS

1) To quantify differences in circulating IL-33 and/or sST2 levels between CVD patients versus controls. 2) Determine association of these biomarkers with mortality in CVD and community cohorts.

METHODS AND RESULTS

Using Pubmed/MEDLINE, Web of Science, Prospero and Cochrane databases, systematic review of studies published on IL-33 and/or sST2 levels in patients with CVD (heart failure, acute coronary syndrome, atrial fibrillation, stroke, coronary artery disease and hypertension) vs controls, and in cohorts of each CVD subtype was performed. Pooled standardised mean difference (SMD) of biomarker levels between CVD-cases versus controls and hazard ratios (HRs) for risk of mortality during follow-up in CVD patients, were assessed by random effects meta-analyses. Heterogeneity was evaluated with random-effects meta-regressions. From 1071 studies screened, 77 were meta-analysed. IL-33 levels were lower in HF and CAD patients vs controls, however levels were higher in stroke patients compared controls [Meta-SMD 1.455, 95% CI 0.372-2.537; p = 0.008, I2 = 97.645]. Soluble ST2 had a stronger association with risk of all-cause mortality in ACS (Meta-multivariate HR 2.207, 95% CI 1.160-4.198; p = 0.016, I2 = 95.661) than risk of all-cause mortality in HF (Meta-multivariate HR 1.425, 95% CI 1.268-1.601; p<0.0001, I2 = 92.276). There were insufficient data to examine the association of IL-33 with clinical outcomes in CVD.

CONCLUSIONS

IL-33 and sST2 levels differ between CVD patients and controls. Higher levels of sST2 are associated with increased mortality in individuals with CVD. Further study of IL-33/ST2 in cardiovascular studies is essential to progress diagnostic and therapeutic advances related to IL-33/ST2 signalling.

Mechanisms and biomarkers of airway epithelial cell damage in asthma: A review

Bronchial asthma is a heterogeneous disease with complex pathological mechanisms representing different phenotypes, including severe asthma. The airway epithelium is a major site of complex pathological changes in severe asthma due, in part, to activation of inflammatory and immune mechanisms in response to noxious agents. Current imaging procedures are unable to accurately measure epithelial and airway remodeling. Damage of airway epithelial cells occurs is linked to specific phenotypes and endotypes which provides an opportunity for the identification of biomarkers reflecting epithelial, and airway, remodeling. Identification of patients with more severe epithelial disruption using biomarkers may also provide personalised therapeutic opportunities and/or markers of successful therapeutic intervention. Here, we review the evidence for ongoing epithelial cell dysregulation in the pathogenesis of asthma, the sentinel role of the airway epithelium and how understanding these molecular mechanisms provides the basis for the identification of candidate biomarkers for asthma prediction, prevention, diagnosis, treatment and monitoring.

The central role of IL-33/IL-1RL1 pathway in asthma: From pathogenesis to intervention

Interleukin-33 (IL-33), a member of the IL-1 family, and its cognate receptor, Interleukin-1 receptor like-1 (IL-1RL1 or ST2), are susceptibility genes for childhood asthma. In response to cellular damage, IL-33 is released from barrier tissues as an 'alarmin' to activate the innate immune response. IL-33 drives type 2 responses by inducing signalling through its receptor IL-1RL1 in several immune and structural cells, thereby leading to type 2 cytokine and chemokine production. IL-1RL1 gene transcript encodes different isoforms generated through alternative splicing. Its soluble isoform, IL-1RL1-a or sST2, acts as a decoy receptor by sequestering IL-33, thereby inhibiting IL1RL1-b/IL-33 signalling. IL-33 and its receptor IL-1RL1 are therefore considered as putative biomarkers or targets for pharmacological intervention in asthma. This review will provide an overview of the genetics and biology of the IL-33/IL-1RL1 pathway in the context of asthma pathogenesis. It will discuss the potential and complexities of targeting the cytokine or its receptor, how genetics or biomarkers may inform precision medicine for asthma targeting this pathway, and the possible positioning of therapeutics targeting IL-33 or its receptor in the expanding landscape of novel biologicals applied in asthma management.

Rapid systemic surge of IL-33 after severe human trauma: a prospective observational study

Background

Alarmins are considered proximal mediators of the immune response after tissue injury. Understanding their biology could pave the way for development of new therapeutic targets and biomarkers in human disease, including multiple trauma. In this study we explored high-resolution concentration kinetics of the alarmin interleukin-33 (IL-33) early after human trauma.

Methods

Plasma samples were serially collected from 136 trauma patients immediately after hospital admission, 2, 4, 6, and 8 h thereafter, and every morning in the ICU. Levels of IL-33 and its decoy receptor sST2 were measured by immunoassays.

Results

We observed a rapid and transient surge of IL-33 in a subset of critically injured patients. These patients had more widespread tissue injuries and a greater degree of early coagulopathy. IL-33 half-life (t_1/2) was 1.4 h (95% CI 1.2–1.6). sST2 displayed a distinctly different pattern with low initial levels but massive increase at later time points.

Conclusions

We describe for the first time early high-resolution IL-33 concentration kinetics in individual patients after trauma and correlate systemic IL-33 release to clinical data. These findings provide insight into a potentially important axis of danger signaling in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00288-1.

The Role of the IL-33/ST2 Immune Pathway in Autoimmunity: New Insights and Perspectives

Interleukin (IL)-33, a member of IL-1 cytokine family, is produced by various immune cells and acts as an alarm to alert the immune system after epithelial or endothelial cell damage during cell necrosis, infection, stress, and trauma. The biological functions of IL-33 largely depend on its ligation to the corresponding receptor, suppression of tumorigenicity 2 (ST2). The pathogenic roles of this cytokine have been implicated in several disorders, including allergic disease, cardiovascular disease, autoimmune disease, infectious disease, and cancers. However, alerted levels of IL-33 may result in either disease amelioration or progression. Genetic variations of IL33 gene may confer protective or susceptibility risk in the onset of autoimmune diseases. The purpose of this review is to discuss the involvement of IL-33 and ST2 in the pathogenesis of a variety of autoimmune disorders, such as autoimmune rheumatic, neurodegenerative, and endocrine diseases.

Association of Soluble Suppression of Tumorigenesis 2 (sST2) With Platelet Activation, Monocyte Tissue Factor and Ischemic Outcomes Following Angioplasty and Stenting

Background: Peripheral artery disease (PAD) patients undergoing infrainguinal angioplasty with stenting suffer high rates of target lesion restenosis and ischemic events. Blood-based prognostic markers in these patients are currently limited. The IL-33/ST2-system is involved in atherothrombosis. Soluble ST2 has been proposed as a biomarker in patients with cardiovascular disease. Aim: To investigate the association of sST2 with platelet activation and monocyte tissue factor (TF) in 316 patients undergoing elective angioplasty and stenting for cardiovascular disease, and its predictive value for ischemic outcomes following infrainguinal angioplasty with stent implantation in 104 PAD patients within this cohort. Methods and Results: Circulating levels of sST2, platelet surface P-selectin, monocyte TF expression as well as soluble P-selectin were determined in 316 consecutive patients on dual antiplatelet therapy following angioplasty and stenting. sST2 was independently associated with soluble P-selectin (B = 6.4, 95% CI 2.0-10.7, p = 0.004) and TF expression (B = 0.56, 95% CI 0.02-1.1, p = 0.041) but not with platelet surface P-selectin (B = 0.1, 95% CI -0.1-0.3, p = 0.307) after adjustment for age, sex, clinical risk factors and inflammatory parameters. During the follow-up of 24 months, the primary endpoint occurred in 41 of 104 PAD patients (39.4%). However, circulating levels of sST2 did not predict the primary endpoint in PAD patients (HR 1.1, 95% CI 0.76-1.71, p = 0.527). Conclusion: sST2 is associated with soluble P-selectin and monocyte TF expression in atherosclerosis but not with ischemic outcomes following infrainguinal angioplasty with stent implantation for PAD.

Evidence for eosinophil and IL-17 mediated inflammation in allergic rhinitis

Background

The aim was to determine the level of inflammatory cytokines, eosinophil cationic protein and IgE in allergic rhinitis (AR) patients.

Subjects and methods

Blood samples were taken from 88 AR patients and 88 healthy controls (HC). Each sample was analysed for eosinophil counts by flow cytometry, IgE by ECLIA, ECP, IL-17, and IL-33 by using ELISA test.

Results

There was no significant difference between AR patients and the control group in age and gender. Levels of eosinophils, IgE, ECP, IL-17, IL-33 and the total symptom scores were significantly higher in AR patients than the HC (P = 0.0001). Serum ECP correlated with IL-17 (P = 0.041, r = 0.42), IL-33 (P = 0.0001, r = 080), and IgE levels (P = 0.017, r = 0.45) in the R patients. There was no correlation between IL-17 and IL-33. There was a correlation between symptom scores and eosinophils (P = 0.026, r = 0.52), and IgE (P = 0.001, r = 0.60) in the patients. No correlation was observed between symptom scores and ECP, IL-17, and IL-33 in the AR patient.

Conclusions

Patients with AR have significant higher serum levels of ECP, IL-17, and IL-33 than healthy controls. This indicates that these markers could be used to in order to diagnose AR and to monitor disease. Inhibitory molecules to IL-17 and IL-33 may be considered as novel treatment strategies.

IL-33 in Chronic Respiratory Disease: From Preclinical to Clinical Studies

IL-33 has been deorphanized as a member of the IL-1 family and has key roles as an alarmin and cytokine with potent capacity to drive type 2 inflammation. This has led to a plethora of studies surrounding its role in chronic diseases with a type 2 inflammatory component. Here, we review the roles of IL-33 in two chronic respiratory diseases, asthma and chronic obstructive pulmonary disease (COPD). We discuss the hallmark and paradigm-shifting studies that have contributed to our understanding of IL-33 biology. We cover animal studies that have elucidated the mechanisms of IL-33 and assessed the role of anti-IL-33 treatment and immunization against IL-33. We highlight key clinical evidence for the potential of targeting increased IL-33 in respiratory diseases including exacerbations, and we outline current clinical trials using an anti-IL-33 monoclonal antibody in asthma patients. Finally, we discuss some of the challenges that have arisen in IL-33 biology and highlight potential future directions in targeting this cytokine in chronic respiratory diseases.

Customizable Implant-specific and Tissue-Specific Extracellular Matrix Protein Coatings Fabricated Using Atmospheric Plasma

Progression in implant science has benefited from ample amount of technological contributions from various disciplines, including surface biotechnology. In this work, we successfully used atmospheric plasma to enhance the biological functions of surgical implants by coating them with extracellular matrix proteins. The developed collagen and laminin coatings demonstrate advantageous material properties. Chemical analysis by XPS and morphological investigation by SEM both suggested a robust coating. Contact angle goniometry and dissolution study in simulated body fluid (SBF) elicited increased hydrophilicity and physiological durability. Furthermore, these coatings exhibited improved biological interactions with human mesenchymal and neural stem cells (NSCs). Cell adhesion, proliferation, and differentiation proved markedly refined as shown by enzymatic detachment, flow cytometry, and ELISA data, respectively. Most importantly, using the pathway-specific PCR array, our study discovered dozens of deregulated genes during osteogenesis and neurogenesis on our newly fabricated ECM coatings. The coating-induced change in molecular profile serves as a promising clue for designing future implant-based therapy. Collectively, we present atmospheric plasma as a versatile tool for enhancing surgical implants, through customizable implant-specific and tissue-specific coatings.

Serum levels of interleukin 33 and its receptor ST2 in patients treated with subcutaneous allergen immunotherapy in intermittent allergic rhinitis

Introduction

Interleukin 33 (IL-33) is a pleiotropic cytokine involved in pathological processes in seasonal allergic rhinitis. IL-33 binds to ST2 receptor, which is highly expressed on mast cells and selectively on Th2 cells. Information is lacking on the role of IL-33/ST2 axis in allergen subcutaneous immunotherapy.

Aim of the study

To determine if allergen immunotherapy changes the IL-33/ST2l axis in seasonal allergic rhinitis patients.

Material and methods

40 patients with intermittent allergic rhinitis sensitive to grass and/or tree pollen were studied. Among these, 10 patients were longitudinally assessed in the follow-up visit after completing the first course of immunotherapy. Twenty-two healthy subjects were included as controls. Immunotherapy was applied according to a perennial schedule comprising up-building and maintenance phases. Serum levels of ST2/IL-33 R and IL-33 were measured by ELISA (R&D Systems).

Results

Serum levels of IL-33 significantly rose after the first course of immunotherapy and reached the controls levels. Serum levels of ST2 were comparable before the pollen season and after the first course of immunotherapy.

Conclusions

Increase in serum levels of IL-33 after the first course of immunotherapy may suggest it is too short period to prevent the expected raise in serum IL-33 levels in the pollen season, and longer treatment is required to observe significant changes of this cytokine. ST2 serum levels are independent of immunotherapy and pollen season.

Downregulated Rac1 promotes apoptosis and inhibits the clearance of apoptotic cells in airway epithelial cells, which may be associated with airway hyper-responsiveness in asthma

The accumulation of airway apoptotic cells may be an important factor causing airway hyper-responsiveness (AHR). Whether the apoptotic cells can be promptly removed is related to the occurrence and course of asthma. In recent years, studies have shown that Rac1 is involved in many cellular biological activities including the formation and elimination of apoptotic cells. In this study, based on the analysis of airway local cells and related factors in asthmatic mice, we evaluated the expression of Rac1 in airway epithelial cells or phagocytes and analysed its relationship with the incidence of apoptosis or scavenging of apoptotic cells. Our data showed that the expression level of Rac1 in asthmatic mice decreased significantly, while the expression of IL-33 increased obviously. The airway epithelial cell line was stimulated by curcumin at 50 μmol/L for 24-48 hours; more than 50% of the cells were apoptotic, and of which, about 20% were late apoptosis. Rac1 inhibitor (NSC23766) can enhance the apoptosis effect. In addition, the ability of phagocytosis and migration in the epithelial cells or macrophages was increased following the application of Rac1 inhibitors or specific siRNA in a dose-dependent manner, and the expression level of IL-33 was simultaneously increased after blocking Rac1. It is suggested that the down regulation of Rac1 in asthma may contribute to the apoptosis of airway epithelial cells and affect the clearance of apoptotic cells, which will lead to the aggregation of the apoptotic cells in the respiratory tract and participate in AHR.

Plasma levels of interleukin-33 and soluble suppression of tumorigenicity 2 in patients with advanced pancreatic ductal adenocarcinoma undergoing systemic chemotherapy

Interleukin-33 (IL-33) and its "decoy" receptor soluble ST2 (sST2) are involved in the development of chronic inflammation and cancer. We explored IL-33 and sST2 as a potential prognostic marker in patients with metastatic and locally advanced pancreatic ductal adenocarcinoma (PDAC). IL-33 and sST2 plasma levels were assessed in 20 patients with advanced PDAC before start of systemic chemotherapy and were analyzed in relation to clinical outcome. Kaplan Meier and multivariable Cox proportional hazards model analysis revealed a significant association between sST2 plasma levels and survival (HR 2.10, 95% CI 1.33-3.41, p = 0.002) and link high sST2 plasma levels to inferior survival in patients with advanced PDAC undergoing chemotherapy.

New perspectives on IL-33 and IL-1 family cytokines as innate environmental sensors

Interleukin (IL)-1 family cytokines are important initiators of innate immunity and host defence; however, their uncontrolled activities can cause tissue-damaging inflammation. Consequently, IL-1 family cytokines have sophisticated regulatory mechanisms to control their activities including proteolytic processing for their activation and the deployment of soluble receptors and receptor antagonists to limit their activities. IL-33 is a promoter of type 2 immunity and allergic inflammation through its alarmin activity that can rapidly initiate local immune responses by stimulating innate immune cells following exposure to environmental insults, pathogens, or sterile injury. Recent publications have provided new insights into how the range and duration of IL-33 activity is regulated by direct sensing of host-derived and exogenous proteolytic activities as well as oxidative changes during tissue damage. Here, we discuss how this impacts our understanding of the roles of IL-33 in initiating immune responses and the evidence that these sensing mechanisms might regulate the activities of other IL-1 family cytokines and their biological functions. Finally, we discuss translational challenges these discoveries pose for the accurate detection of different forms of these cytokines.

Conflicting vascular and metabolic impact of the IL-33/sST2 axis

Interleukin 33 (IL-33), which is expressed by several immune cell types, endothelial and epithelial cells, and fibroblasts, is a cytokine of the IL-1 family that acts both intra- and extracellularly to either enhance or resolve the inflammatory response. Intracellular IL-33 acts in the nucleus as a regulator of transcription. Once released from cells by mechanical stress, inflammatory cytokines, or necrosis, extracellular IL-33 is proteolytically processed to act in an autocrine/paracrine manner as an 'alarmin' on neighbouring or various immune cells expressing the ST2 receptor. Thus, IL-33 may serve an important role in tissue preservation and repair in response to injury; however, the actions of IL-33 are dampened by a soluble form of ST2 (sST2) that acts as a decoy receptor and is produced by endothelial and certain immune cells. Accumulating evidence supports the conclusion that sST2 is a biomarker of vascular health with diagnostic and/or prognostic value in various cardiovascular diseases, including coronary artery disease, myocardial infarction, atherosclerosis, giant-cell arteritis, acute aortic dissection, and ischaemic stroke, as well as obesity and diabetes. Although sST2 levels are positively associated with cardiovascular disease severity, the assumption that IL-33 is always beneficial is naïve. It is increasingly appreciated that the pathophysiological importance of IL-33 is highly dependent on cellular and temporal expression. Although IL-33 is atheroprotective and may prevent obesity and type 2 diabetes by regulating lipid metabolism, IL-33 appears to drive endothelial inflammation. Here, we review the current knowledge of the IL-33/ST2/sST2 signalling network and discuss its pathophysiological and translational implications in cardiovascular diseases.

Elevated Expression of IL-33 and TSLP in the Airways of Human Asthmatics In Vivo: A Potential Biomarker of Severe Refractory Disease

The epithelial cytokines IL-33, thymic stromal lymphopoietin (TSLP), and IL-25 have been implicated in asthma pathogenesis because they promote Th2-type cytokine synthesis, but their expression is relatively poorly documented in "real-life" human asthma. Using bronchoalveolar lavage fluid (BALF), we measured airway concentrations of these mediators and compared them with those of Th1- and Th2-type cytokines, airway infiltration of neutrophils and eosinophils, and lung function in a large group of asthmatic patients with a range of disease severity (n = 70) and control subjects (n = 30). The median BALF concentrations of IL-33, TSLP, IL-4, IL-5, IL-13, and IL-12p70, but not IL-25, IL-2, or IFN-γ, were significantly elevated in asthmatics compared with controls (p < 0.05). The concentrations of IL-33 and TSLP, but not IL-25, correlated inversely with the lung function (forced expiratory volume in the first second) of asthmatics (IL-33: r = -0.488, p < 0.0001; TSLP: r = -0.565, p < 0.0001) independently of corticosteroid therapy. When divided according to disease severity and corticosteroid therapy, all subgroups of asthmatics had elevated median numbers of eosinophils in BALF, whereas the patients with more severe disease who were treated with corticosteroids had higher numbers of neutrophils compared with milder asthmatics not so treated and control subjects (p < 0.05). The data implicate TSLP and IL-33 in the pathogenesis of asthma that is characterized by persistent airway inflammation and impaired lung function despite intensive corticosteroid therapy, highlighting them as potential molecular targets.

TNF is required for TLR ligand-mediated but not protease-mediated allergic airway inflammation

Asthma is associated with exposure to a wide variety of allergens and adjuvants. The extent to which overlap exists between the cellular and molecular mechanisms triggered by these various agents is poorly understood, but it might explain the differential responsiveness of patients to specific therapies. In particular, it is unclear why some, but not all, patients benefit from blockade of TNF. Here, we characterized signaling pathways triggered by distinct types of adjuvants during allergic sensitization. Mice sensitized to an innocuous protein using TLR ligands or house dust extracts as adjuvants developed mixed eosinophilic and neutrophilic airway inflammation and airway hyperresponsiveness (AHR) following allergen challenge, whereas mice sensitized using proteases as adjuvants developed predominantly eosinophilic inflammation and AHR. TLR ligands, but not proteases, induced TNF during allergic sensitization. TNF signaled through airway epithelial cells to reprogram them and promote Th2, but not Th17, development in lymph nodes. TNF was also required during the allergen challenge phase for neutrophilic and eosinophilic inflammation. In contrast, TNF was dispensable for allergic airway disease in a protease-mediated model of asthma. These findings might help to explain why TNF blockade improves lung function in only some patients with asthma.

Emerging Roles of IL-33/ST2 Axis in Renal Diseases

Renal diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), have a great impact on health care systems worldwide. Similar to cardiovascular diseases, renal diseases are inflammatory diseases involving a variety of cytokines. Primary causes of renal injury include ischemia, uremic toxins, bacteremia, or nephrotoxicity. Inflammation represents an important component following kidney injury. Interleukin (IL)-33 is a member of the IL-1 cytokine family, which is widely expressed in epithelial barrier tissues and endothelial cells, and mediates both tissue inflammation and repair responses. IL-33 is released as a nuclear alarmin in response to tissue damage and triggers innate and adaptive immune responses by binding to its receptor, suppression of tumorigenicity 2 (ST2). Recent evidence from clinical and experimental animal studies indicates that the IL-33/ST2 axis is involved in the pathogenesis of CKD, renal graft injury, systemic lupus nephritis, and AKI. In this review, we discuss the pathological and tissue reparative roles of the IL-33/ST2 pathway in different types of renal diseases.