The role of the IL-33/ST2 axis in autoimmune disorders: Friend or foe?

Single-Cell Analysis Uncovers Striking Cellular Heterogeneity of Lung-Infiltrating Regulatory T Cells during Eosinophilic versus Neutrophilic Allergic Airway Inflammation

Allergic airway inflammation results from uncontrolled immune responses to environmental Ags. Although it is well established that allergic immune responses exhibit a high degree of diversity, driven by primary effector cell types such as eosinophils, neutrophils, or CD4 T cells with distinct effector signatures, the mechanisms responsible for such pathogenesis remain elusive. Foxp3+ regulatory T cells (Tregs) are essential immune regulators during chronic inflammation, including allergic airway inflammation. Emerging evidence suggests that Tregs infiltrating inflamed tissues exhibit distinct phenotypes dependent on the specific tissue sites and can display heterogeneity and tissue residency. Whether diverse allergic airway inflammatory responses influence infiltrating Treg heterogeneity or Treg lung residency has not been explored. We employed an unbiased single-cell RNA sequencing approach to investigate lung-infiltrating Tregs in models of eosinophilic and neutrophilic airway inflammation. We found that lung-infiltrating Tregs are highly heterogeneous, and that Tregs displaying lung-resident phenotypes are significantly different depending on the types of inflammation. Treg expression of ST2, a receptor for alarmin IL-33, was predominantly associated with eosinophilic inflammation and tissue residency. Nevertheless, Treg-specific ST2 deficiency did not affect the development of eosinophilic allergic inflammation or the generation of lung-resident Tregs. These results uncover a stark heterogeneity among Tregs infiltrating the lungs during allergic airway inflammation. The results indicate that varying types of inflammation may give rise to phenotypically distinct lung-resident Tregs, underscoring a (to our knowledge) novel mechanism by which inflammatory cues may shape the composition of infiltrating Tregs, allowing them to regulate inflammatory responses through tissue-adapted mechanisms.

Decoding Behcet's Uveitis: an In-depth review of pathogenesis and therapeutic advances

Behcet's disease (BD) is a rare but globally distributed vasculitis that primarily affects populations in the Mediterranean and Asian regions. Behcet's uveitis (BU) is a common manifestation of BD, occurring in over two-thirds of the patients. BU is characterized by bilateral, chronic, recurrent, non-granulomatous uveitis in association with complications such as retinal ischemia and atrophy, optic atrophy, macular ischemia, macular edema, and further neovascular complications (vitreous hemorrhage, neovascular glaucoma). Although the etiology and pathogenesis of BU remain unclear, numerous studies reveal that genetic factors (such as HLA-B51), dysregulated immune responses of both the innate and adaptive immune systems, infections (such as streptococcus), and environmental factors (such as GDP) are all involved in its development. Innate immunity, including hyperactivity of neutrophils and γδT cells and elevated NK1/NK2 ratios, has been shown to play an essential role in this disease. Adaptive immune system disturbance, including homeostatic perturbations, Th1, Th17 overaction, and Treg cell dysfunction, is thought to be involved in BU pathogenesis. Treatment of BU requires a tailored approach based on the location, severity of inflammation, and systemic manifestations. The therapy aims to achieve rapid inflammation suppression, preservation of vision, and prevention of recurrence. Systemic corticosteroids combined with other immunosuppressive agents have been widely used to treat BU, and beneficial effects are observed in most patients. Recently, biologics have been shown to be effective in treating refractory BU cases. Novel therapeutic targets for treating BU include the LCK gene, Th17/Treg balance, JAK pathway inhibition, and cytokines such as IL-17 and RORγt. This article summarizes the recent studies on BU, especially in terms of pathogenesis, diagnostic criteria and classification, auxiliary examination, and treatment options. A better understanding of the significance of microbiome composition, genetic basis, and persistent immune mechanisms, as well as advancements in identifying new biomarkers and implementing objective quantitative detection of BU, may greatly contribute to improving the adequate management of BU patients.

A Novel Bifunctional Fusion Protein (Anti-IL-17A-sST2) Protects against Acute Liver Failure, Modulating the TLR4/MyD88 Pathway and NLRP3 Inflammasome Activation

Acute liver failure (ALF) is a serious inflammatory disorder with high mortality rates, which poses a significant threat to human health. The IL-33/ST2 signal is a crucial regulator in inflammation responses associated with lipopolysaccharide (LPS)-induced macrophages. The IL-17A signaling pathway promotes the release of chemokines and inflammatory cytokines, recruiting neutrophils and T cells under LPS stimulation, thus facilitating inflammatory responses. Here, the potential therapeutic benefits of neutralizing the IL-17A signal and modulating the IL-33/ST2 signal in ALF were investigated. A novel dual-functional fusion protein, anti-IL-17A-sST2, was constructed, which displayed high purity and biological activities. The administration of anti-IL-17A-sST2 resulted in significant anti-inflammatory benefits in ALF mice, amelioration of hepatocyte necrosis and interstitial congestion, and reduction in TNF-α and IL-6. Furthermore, anti-IL-17A-sST2 injection downregulated the expression of TLR4 and NLRP3 as well as important molecules such as MyD88, caspase-1, and IL-1β. The results suggest that anti-IL-17A-sST2 reduced the secretion of inflammatory factors, attenuated the inflammatory response, and protected hepatic function by regulating the TLR4/MyD88 pathway and inhibiting the NLRP3 inflammasome, providing a new therapeutic approach for ALF.

Associations of MEFV gene variants, IL-33, and sST2 with the risk of Henoch-Schönlein purpura in children

Objective

Henoch-Schönlein purpura (HSP) is the most common systemic vasculitis in children. HSP is a multifactorial inflammatory disease, but its pathogenesis is still unclear. The pathogenicity of familial Mediterranean fever gene (MEFV) variants in HSP remains controversial. The objective of this study was to evaluate relationships between MEFV variants and susceptibility to HSP and their associations with clinical outcomes. We also investigated levels of IL-33 and soluble suppression of tumorigenicity 2 (sST2) in children with HSP and their clinical significance.

Methods

We selected 100 children with HSP as the case group. The control group consisted of 50 children who visited the hospital for physical health examinations. All subjects were screened for MEFV gene exon mutations, and levels of IL-33 and sST2 were measured.

Results

The frequency of MEFV variants was significantly greater in HSP patients than in healthy controls. The variant with the highest frequency was E148Q. The frequency of the C allele of the MEFV variant E148Q was 32 % in HSP patients and 18 % in controls (P-adjust = 0.04). Patients with the MEFV E148Q variant had more frequent joint involvement and recurrent purpura and higher levels of IL-33 and C-reactive protein (CRP). Levels of IL-33 and sST2 in children with HSP were significantly higher than those in the control group, and the sST2/IL-33 ratio in children with HSP was unbalanced (P-adjust <0.05). Logistic regression analysis revealed the presence of E148Q and an unbalanced sST2/IL-33 ratio to be independent risk factors for HSP.

Conclusion

The results of this study suggest that the MEFV variant E148Q is associated with HSP susceptibility in Chinese children and that carriers of the variant may have more severe clinical manifestations and greater inflammatory responses. E148Q and the sST2/IL-33 ratio may play important roles in the pathogenesis of HSP.

Interleukin (IL)-23, IL-31, and IL-33 Play a Role in the Course of Autoimmune Endocrine Diseases

BACKGROUND

Interleukins (IL)-23, 31, and 33 are involved in the regulation of T helper 17 (Th17)/regulatory T (Treg) cells balance. The role of IL-23, 31 and 33 in non-endocrine autoimmune diseases has been confirmed. Data on the involvement of these cytokines in endocrine autoimmune diseases are limited.

OBJECTIVE

This study aimed to determine the involvement of cytokines regulating the T helper 17 (Th17)/regulatory T (Treg) cells axis in the course of autoimmune endocrine diseases.

METHODS

A total number of 80 participants were divided into 4 groups: the autoimmune polyendocrine syndrome (APS) group consisting of APS type 2 (APS-2) and type 3 (APS-3) subgroups, the Hashimoto's thyroiditis (HT) group, the Graves' disease (GD) group and the control (C) group. Fifteen cytokines related to Th17 and Treg lymphocytes were determined in the serum of all participants.

RESULTS

Higher levels of IL-23 and IL-31 were found in the APS, GD, and HT groups compared to the C group. Higher levels of IL-23 and IL-31 were also observed in the APS-2 group, in contrast to the APS-3 group. Correlation analysis of variables in the groups showed a statistically significant correlation between the cytokines IL-23, IL-31, and IL-33 in the APS and APS-2 groups, but no correlation in the APS-3 and C groups.

CONCLUSION

IL-23 and IL-31 are independent factors in the course of HT, GD, and APS-2, in contrast to APS-3. The positive correlation between IL-23 and IL-31, IL-23 and IL-33, and between IL-31 and IL-33 in the APS, APS-2 groups, but the lack of correlation in the APS-3 and C groups may further suggest the involvement of these cytokines in the course of Addison's disease.

The IL-33/IL-31 Axis in Allergic and Immune-Mediated Diseases

Interleukin 31 (IL-31) belongs to the IL-6 superfamily [...].

Serum-soluble ST2 and systemic sclerosis arthropathy

Interleukin (IL)33 and its receptor ST2 have been involved in the pathogenesis of several conditions, including arthritis. The aim of the study was to evaluate the association between IL33 or soluble ST2 (sST2) serum levels and systemic sclerosis (SSc) articular involvement. IL33 and sST2 serum levels were measured in 64 SSc patients and 24 HC matched for sex and age. Articular involvement assessed by using Disease Activity Score 28 based on erythrocyte sedimentation rate (DAS28-ESR), presence of tendon friction rubs (TFRs) and finger-to-palm (FTP) distance. sST2 serum levels were significantly higher in SSc patients with DAS28-ESR > 3.2 than in SSc patients with DAS28-ESR⩽3.2 [9726.1 (IQR 7746.5 - 14,953.5) pg/mL vs 7611.7 (IQR 5162.6 -11,036.7) pg/mL; p < 0.05]. sST2 serum levels were significantly higher in SSc patients with TFRs compared to SSc patients without TFRs [9726.1 (IQR 7746.5 - 14,953.5) pg/mL vs 7426.4 (IQR 5145.9 - 10,593.5) pg/mL; p < 0.01] and in SSc patients with FTP ≥ 1 cm compared to SSc patients with FTP < 1 cm [9683.7 (IQR 8067.2 - 16,387.6) pg/mL vs 7679.1 (IQR 5246.1 - 11,472.2) pg/mL; p < 0.05]. No significant association was observed between IL33 and DAS28-ESR, TFRs and FTP. A slightly positive linear correlation was found between sST2 and Disease Activity Index (r = 0.294, p < 0.05) and Disease Severity Scale (r = 0.265, p < 0.05). sST2 serum levels were positively correlated with DAS28-ESR (r = 0.371, p < 0.01). Elevated sST2 serum levels were associated with higher articular disease activity, TFRs and hand dysfunction, suggesting that sST2 might have a role in the pathogenesis of SSc articular involvement. Key Points • In SSc patients elevated serum levels of sST2 were associated with higher articular disease activity • High serum levels of sST2 were reported in SSc patients with TFRs and hand dysfunction • sST2 might have a role in the pathogenesis of SSc articular involvement.

Interleukin-33: Metabolic checkpoints, metabolic processes, and epigenetic regulation in immune cells

Interleukin-33 (IL-33) is a pleiotropic cytokine linked to various immune cells in the innate and adaptive immune systems. Recent studies of the effects of IL-33 on immune cells are beginning to reveal its regulatory mechanisms at the levels of cellular metabolism and epigenetic modifications. In response to IL-33 stimulation, these programs are intertwined with transcriptional programs, ultimately determining the fate of immune cells. Understanding these specific molecular events will help to explain the complex role of IL-33 in immune cells, thereby guiding the development of new strategies for immune intervention. Here, we highlight recent findings that reveal how IL-33, acting as an intracellular nuclear factor or an extracellular cytokine, alters metabolic checkpoints and cellular metabolism, which coordinately contribute to cell growth and function. We also discuss recent studies supporting the role of IL-33 in epigenetic alterations and speculate about the mechanisms underlying this relationship.

The IL-33/ST2 Axis Promotes Primary Sjögren's Syndrome by Enhancing Salivary Epithelial Cell Activation and Type 1 Immune Response

The molecular mechanisms of primary Sjögren's syndrome (pSS) are poorly understood. In this study, we explored the role of the IL-33/ST2 axis in the development of pSS. In the mouse model of experimental Sjögren's syndrome, we found that the saliva flow rate at weeks 4 and 30 was preserved in IL-33^-/- and ST2^-/- mice, compared with that of wild-type mice. At week 30 of experimental Sjögren's syndrome induction, the histological score, anti-nuclear Ab levels, and numbers of Th1 and B cells in draining lymph nodes of the salivary gland were lower in the IL-33^-/- and ST2^-/- mice, whereas Th17 cells and regulatory T cells were not changed. Primary salivary gland epithelial cells expressed the IL-33 receptor ST2. After stimulation with rIL-33, salivary gland epithelial cells increased the transcriptional levels of CD86 and CCL2, accompanied by the activation of the NF-κB inflammatory pathway. There was a synergistic effect between rIL-33 and rIL-12 in augmenting the production of IFN-γ in CD4⁺ T cells. In the pSS patients, the expression of IL-33 was elevated in the labial salivary gland, with the number of IL-33⁺ cells positively correlated with the score of the EULAR (European Alliance of Associations for Rheumatology) Sjögren's syndrome disease activity index (ESSDAI). ST2 was highly expressed in the cytoplasm of ductal epithelial cells, with low levels of expression in lymphatic infiltration sites. Our data suggest that the IL-33/ST2 axis may promote the development of pSS by enhancing salivary epithelial cell activation and the type 1 immune response.

General Rehabilitation Program after Knee or Hip Replacement Significantly Influences Erythrocytes Oxidative Stress Markers and Serum ST2 Levels

The survival of erythrocytes in the circulating blood depends on their membranes' structural and functional integrity. One of the mechanisms that may underlie the process of joint degeneration is the imbalance of prooxidants and antioxidants, promoting cellular oxidative stress. The study is aimed at observing the effects of the 21-day general rehabilitation program on the erythrocytes redox status and serum ST2 marker in patients after knee or hip replacement in the course of osteoarthritis. Erythrocytes and serum samples were collected from 36 patients. We analyzed the selected markers of the antioxidant system in the erythrocytes: catalase (CAT), glutathione reductase (glutathione disulfide reductase (GR, GSR)), total superoxide dismutase activity (SOD), glutathione peroxidase (GPx), glutathione transferase (GST) activity, and cholesterol and lipofuscin (LPS) concentration. In serum, we analyzed the concentration of the suppression of tumorigenicity 2 (ST2) marker. After the 21-day general rehabilitation program, the total SOD and GPx activity, measured in the hemolysates, significantly increased (p < 0.001) while LPS, cholesterol, and ST2 levels in serum significantly decreased (p < 0.001). General rehabilitation reduces oxidative stress in patients after knee or hip replacement in the course of osteoarthritis. Individually designed, regular physical activity is the essential element of the postoperative protocol, which improves the redox balance helping patients recover after the s4urgery effectively.

Interleukin-33/ Suppression of Tumorigenicity 2 in Renal Fibrosis: Emerging Roles in Prognosis and Treatment

Chronic kidney disease (CKD) is a major public health problem that affects more than 10% of the population worldwide and has a high mortality rate. Therefore, it is necessary to identify novel treatment strategies for CKD. Incidentally, renal fibrosis plays a central role in the progression of CKD to end-stage renal disease (ESRD). The activation of inflammatory pathways leads to the development of renal fibrosis. In fact, interleukin-33 (IL-33), a newly discovered member of the interleukin 1 (IL-1) cytokine family, is a crucial regulator of the inflammatory process. It exerts pro-inflammatory and pro-fibrotic effects via the suppression of tumorigenicity 2 (ST2) receptor, which, in turn, activates other inflammatory pathways. Although the role of this pathway in cardiac, pulmonary, and hepatic fibrotic diseases has been extensively studied, its precise role in renal fibrosis has not yet been completely elucidated. Recent studies have shown that a sustained activation of IL-33/ST2 pathway promotes the development of renal fibrosis. However, with prolonged research in this field, it is expected that the IL-33/ST2 pathway will be used as a diagnostic and prognostic tool for renal diseases. In addition, the IL-33/ST2 pathway seems to be a new target for the future treatment of CKD. Here, we review the mechanisms and potential applications of the IL-33/ST2 pathway in renal fibrosis; such that it can help clinicians and researchers to explore effective treatment options and develop novel medicines for CKD patients.

IL-33 receptor expression on myeloid and plasmacytoid dendritic cells after allergen challenge in patients with allergic rhinitis

The diversity of immune responses in allergic diseases is critically mediated by dendritic cells (DCs), including myeloid and plasmacytoid DCs. Allergen inhalation increased the release of IL-33 from patients with allergic rhinitis (AR), which affecting the downstream cells by binding to its receptor (ST2). However, the effects of inhaled allergens on the expression of ST2 by DCs and IL-33 on the function of mDCs are unknown. The levels of ST2⁺mDCs and ST2⁺pDCs in the blood from patients with AR and healthy subjects were examined using flow cytometry. Moreover, the patients were challenged using the allergens and the levels of ST2⁺mDCs and ST2⁺pDCs were investigated at different time points. We found that there were higher levels of ST2⁺ mDCs and ST2⁺ pDCs in patients with AR, and these levels were further increased 0.5 h after allergen inhalation. Additionally, the type 2 immune response was upregulated after challenge. IL-33 treatment increased the expression of ST2 on mDCs. Our study demonstrated that ST2 was upregulated on DCs after allergen inhalation and that mDCs responded directly to IL-33 through ST2, suggesting that the IL-33/ST2 axis might play an important role in the pathogenesis of allergic rhinitis by DCs.

IL-33 in Rheumatic Diseases

Interleukin-33 (IL-33) is a nuclear factor mainly expressed in barrier epithelium, endothelial cells, and fibroblast reticular cells. Some inflammatory cells also express IL-33 under certain conditions. The important role of IL-33 in allergic reactions, helminth infection, cancer, tissue fibrosis, chronic inflammation, organ transplantation, and rheumatic immune diseases has been extensively studied in recent years. IL-33 primarily activates various circulating and tissue-resident immune cells, including mast cell, group 2 innate lymphoid cell (ILC2), regulatory T cell (Treg), T helper 2 cell (Th2), natural killer cell (NK cell), and macrophage. Therefore, IL-33 plays an immunomodulatory role and shows pleiotropic activity in different immune microenvironments. The IL-33/serum stimulation-2 (ST2) axis has been shown to have a detrimental effect on rheumatoid arthritis, systemic lupus erythematosus, and other rheumatic diseases. Interestingly, IL-33 also plays a protective role in the repair of barrier epithelium and the activation of Tregs. Therefore, the role of IL-33/ST2 depends on the underlying pathological conditions in rheumatic diseases. This review focuses on the dual role of the IL-33/ST2 axis in rheumatic diseases.

Increased serum level of interleukin-33 in Vogt-Koyanagi-Harada correlates with disease activity

OBJECTIVES

To measure the serum level of IL-33 in patients with Vogt-Koyanagi-Harada disease (VKH) and Behçet's uveitis (BU) in the Chinese Han population and investigate its associations with disease activity and clinical parameters.

METHODS

Serum was collected from 41 VKH patients (16 active and 25 inactive patients), 60 BU patients (24 active and 36 inactive patients), and 36 healthy controls. The serum level of IL-33 was measured using the enzyme-linked immunosorbent assay (ELISA) method. Demographic features, clinical manifestations, and intraocular inflammation activity scores (anterior chamber cells score, anterior chamber flare score, and vitreal haze score) were recorded.

RESULTS

The serum level of IL-33 significantly increased in all VKH patients, active VKH patients, and inactive VKH patients, as compared to healthy controls (p < 0.001, p < 0.001, and p = 0.002, respectively), and was higher in the active VKH than in the inactive VKH patients (p = 0.049). The serum level of IL-33 positively correlated with the anterior chamber cells score, vitreal haze score, and the annualized number of relapses in VKH patients (Rho = 0.359, p = 0.021; Rho = 0.344, p = 0.028; Rho = 0.537, p < 0.001, respectively). Serum IL-33 level was significantly associated with the annualized number of relapses in patients with BU (Rho = 0.361, p = 0.005).

CONCLUSION

Serum IL-33 level is significantly increased in VKH patients in the Chinese Han population. IL-33 level is in positive correlation with the activity and relapses of VKH. Increased IL-33 might contribute to the pathogenesis of VKH and serve as a potential biomarker for VKH disease.

The Clinical Significance of Serum IL-33 and sST2 Alterations in the Post-Stroke Depression

Introduction

This study was to test whether the serum levels of IL-33 and sST2 are correlated with the development of depression after acute ischemic stroke.

Methods

Patients diagnosed with acute ischemic stroke were selected. This study took the 24-item Hamilton Depression Rating Scale (HAMD) (score ≥20) as the diagnostic criteria for depression. On the 21st day after admission, patients who met the depression diagnostic criteria were included in the depression group, and patients who failed to meet the diagnostic criteria were included in the non-depression group. The serum levels of IL-33, sST2 and hsCRP were measured by enzyme-linked immunosorbent assay (ELISA).

Results

On 1st day after stroke, compared with the non-depression group, there was no significant difference in the serum IL-33, sST2 and hsCRP levels in the depression group; on 21st day after stroke, compared with the non-depression group, the serum IL-33 and hsCRP levels were significantly increased, while the sST2 level was significantly decreased in the depression group. Correlation analysis showed that IL-33 was positively correlated with the depression quantitative score and hsCRP, while sST2 was negatively correlated with the depression quantitative score and hsCRP. Regression analysis showed that IL-33 and sST2 were independent risk factors for the depression after acute ischemic stroke.

Discussion

The abnormal alterations of serum IL-33 and sST2 levels in the stroke patients may serve as one of the risk factors for the occurrence and exacerbation of the depression, and its mechanism may be related to the promotion of inflammatory factor production in vivo.

Interleukin-33 promotes invasiveness of human ovarian endometriotic stromal cells through the ST2/MAPK/MMP-9 pathway activated by 17β-estradiol

OBJECTIVE

Endometriosis is an estrogen-dependent, benign, and chronic gynecological disorder occurring in women of reproductive age. Although the pathogenesis of endometriosis is poorly understood, implantation theory indicates that viable endometrial cells shed from the endometrium into the pelvic peritoneum or ovaries, possibly through retrograde menstruation, and then reattach, invade, and damage other tissues. Interleukin (IL)-33, a new member of the IL-1 superfamily, is mainly upregulated by stromal cells following proinflammatory stimulation. Matrix metalloproteinases (MMPs) are involved in the degradation and reconstruction of the extracellular matrix. MMP-9 participates in the pathogenesis of endometriosis by promoting the invasion of endometriotic cells. This study investigated the effect of IL-33 on the cell invasion ability of and MMP-9 expression in human stromal cells derived from ovarian endometrioma (hOVEN-SCs).

MATERIALS AND METHODS

We isolated hOVEN-SCs from human ovarian endometrioma. Gene expression was analyzed using the Illumina Human WG-6 v2 Expression BeadChips microarray platform and through reverse transcription-polymerase chain reaction. Cell migration and invasion were examined by performing the transwell chamber assay.

RESULTS

We found that 17β-estradiol could increase the expression of IL-33 and ST2 through the estrogen receptor pathway in hOVEN-SCs. Moreover, IL-33 upregulated MMP-9 expression in and enhanced the invasion ability of hOVEN-SCs through the ST2/MAPK signaling pathway. Our results showed that MMP-9 expression was essential for IL-33-induced cell invasion.

CONCLUSION

Our main finding is that 17β-estradiol could increase IL-33 expression through the estrogen receptor pathway and activate MMP-9 expression in and invasion ability of hOVEN-SCs through the IL-33/ST2/MAPK signaling pathway. The results of this study and further related studies may provide new strategies for the prevention and treatment of endometriosis.

Inflammasomes and Fibrosis

Fibrosis is the final common pathway of inflammatory diseases in various organs. The inflammasomes play an important role in the progression of fibrosis as innate immune receptors. There are four main members of the inflammasomes, such as NOD-like receptor protein 1 (NLRP1), NOD-like receptor protein 3 (NLRP3), NOD-like receptor C4 (NLRC4), and absent in melanoma 2 (AIM2), among which NLRP3 inflammasome is the most studied. NLRP3 inflammasome is typically composed of NLRP3, ASC and pro-caspase-1. The activation of inflammasome involves both "classical" and "non-classical" pathways and the former pathway is better understood. The "classical" activation pathway of inflammasome is that the backbone protein is activated by endogenous/exogenous stimulation, leading to inflammasome assembly. After the formation of "classic" inflammasome, pro-caspase-1 could self-activate. Caspase-1 cleaves cytokine precursors into mature cytokines, which are secreted extracellularly. At present, the "non-classical" activation pathway of inflammasome has not formed a unified model for activation process. This article reviews the role of NLRP1, NLRP3, NLRC4, AIM2 inflammasome, Caspase-1, IL-1β, IL-18 and IL-33 in the fibrogenesis.

Group 2 innate lymphoid cells contribute to IL-33-mediated alleviation of cardiac fibrosis

Rationale: The major cause of heart failure is myocardium death consequent to detrimental cardiac remodeling and fibrosis following myocardial infarction. The cardiac protective cytokine interleukin (IL)-33, which signals by ST2 receptor binding, is associated with group 2 innate lymphoid cell (ILC2) activation and regulates tissue homeostasis and repair following tissue injury in various tissues. However, the distribution and role of IL-33-responsive ILC2s in cardiac fibrosis remain unclear. In this study, we elucidated the roles of IL-33-responsive cardiac-resident ILC2s and IL-33-mediated immunomodulatory functions in cardiac fibrosis.

Methods: We examined the distribution of cardiac ILC2s by using flow cytometry. The roles of IL-33-mediated ILC2 expansion in cardiac fibrosis was evaluated in the mouse model of catecholamine-induced cardiac fibrosis. ILC-deficient Rag2^‒/‒IL2Rγc^‒/‒ mice were implemented to determine the contribution of endogenous ILC in the progression of cardiac fibrosis. Histopathological assessments, speckle tracking echocardiography, and transcriptome profile analysis were performed to determine the effects of IL-33-mediated cardiac protective functions.

Results: We identified the resident cardiac ILC2s, which share similar cell surface marker and transcriptional factor expression characteristics as peripheral blood and lung tissue ILC2s. IL-33 treatment induced ILC2 expansion via ST2. In vivo, ILC-deficient Rag2^‒/‒IL2Rγc^‒/‒ mice developed exacerbated cardiac fibrosis following catecholamine-induced stress cardiac injury. IL-33 treatment expanded cardiac ILC2s and revealed protective effects against cardiac tissue damage with reduced cardiomyocyte death, immune cell infiltration, tissue fibrosis, and improved myocardial function. Transcriptome analysis revealed that IL-33 attenuated extracellular matrix synthesis- and fibroblast activation-associated gene expressions. IL13-knockout or epidermal growth factor receptor (EGFR) inhibition abolished IL-33-mediated cardiac protective function, confirming IL-13 and EGFR signaling as crucial for IL-33-mediated cardioprotective responses. Moreover, ILC2-produced BMP-7 served as a novel anti-fibrotic factor to inhibit TGF-β1-induced cardiac fibroblast activation.

Conclusion: Our findings indicate the presence of IL-33-responsive ILC2s in cardiac tissue and that IL-33-mediated ILC2 expansion affords optimal cardioprotective function via ILC2-derived factors. IL-33-mediated immunomodulation is thus a promising strategy to promote tissue repair and alleviate cardiac fibrosis following acute cardiac injury.

IL-33 Alarmin and Its Active Proinflammatory Fragments Are Released in Small Intestine in Celiac Disease

Initially described as Th2 promoter cytokine, more recently, IL-33 has been recognized as an alarmin, mainly in epithelial and endothelial cells. While localized in the nucleus acting as a gene regulator, it can be also released after injury, stress or inflammatory cell death. As proinflammatory signal, IL-33 binds to the surface receptor ST2, which enhances mast cell, Th2, regulatory T cell, and innate lymphoid cell type 2 functions. Besides these Th2 roles, free IL-33 can activate CD8⁺ T cells during ongoing Th1 immune responses to potentiate its cytotoxic function. Celiac Disease (CD) is a chronic inflammatory disorder characterized by a predominant Th1 response leading to multiple pathways of mucosal damage in the proximal small intestine. By immunofluorescence and western blot analysis of duodenal tissues, we found an increased expression of IL-33 in duodenal mucosa of active CD (ACD) patients. Particularly, locally digested IL-33 releases active 18/21kDa fragments which can contribute to expand the proinflammatory signal. Endothelial (CD31⁺) and mesenchymal, myofibroblast and pericyte cells from microvascular structures in villi and crypts, showed IL-33 nuclear location; while B cells (CD20⁺) showed a strong cytoplasmic staining. Both ST2 forms, ST2L and sST2, were also upregulated in duodenal mucosa of CD patients. This was accompanied by increased number of CD8⁺ST2⁺ T cells and the expression of T-bet in some ST2⁺ intraepithelial lymphocytes and lamina propria cells. IL-33 and sST2 mRNA levels correlated with IRF1, an IFN induced factor relevant in responses to viral infections and interferon mediated proinflammatory responses highly represented in duodenal tissues in ACD. These findings highlight the potential contribution of IL-33 and its fragments to exacerbate the proinflammatory circuit and potentiate the cytotoxic activity of CD8⁺ T cells in CD pathology.

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

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

Advances in Mast Cell Activation by IL-1 and IL-33 in Sjögren's Syndrome: Promising Inhibitory Effect of IL-37

Sjögren’s syndrome (SS) is a chronic autoimmune inflammatory disease that affects primarily older women and is characterized by irreversible damage of the exocrine glands, including tear (xerophthalmia) and salivary glands (xerostomia). Secretory glands lose their functionality due to the infiltration of immune cells, which produce cytokines and cause inflammation. Primary SS is characterized by dry syndrome with or without systemic commitment in the absence of other pathologies. Secondary SS is accompanied by other autoimmune diseases with high activation of B lymphocytes and the production of autoantibodies, including the rheumatoid factor. Other cells, such as CD4⁺ T cells and mast cells (MCs), participate in SS inflammation. MCs are ubiquitous, but are primarily located close to blood vessels and nerves and can be activated early in autoimmune diseases to express a wide variety of cytokines and chemokines. In the SS acute phase, MCs react by generating chemical mediators of inflammation, tumor necrosis factor (TNF), and other pro-inflammatory cytokines such as interleukin (IL)-1 and IL-33. IL-33 is the specific ligand for ST2 capable of inducing some adaptive immunity TH2 cytokines but also has pro-inflammatory properties. IL-33 causes impressive pathological changes and inflammatory cell infiltration. IL-1 family members can have paracrine and autocrine effects by exacerbating autoimmune inflammation. IL-37 is an IL-1 family cytokine that binds IL-18Rα receptor and/or Toll-like Receptor (TLR)4, exerting an anti-inflammatory action. IL-37 is a natural inhibitor of innate and acquired immunity, and the level is abnormal in patients with autoimmune disorders. After TLR ligand activation, IL-37 mRNA is generated in the cytoplasm, with the production of pro-IL-37 and later mature IL-37 caspase-1 mediated; both precursor and mature IL-37 are biologically active. Here, we discuss, for the first time, the current knowledge of IL-37 in autoimmune disease SS and propose a new therapeutic role.

The IL-33 Receptor/ST2 acts as a positive regulator of functional mouse bone marrow hematopoietic stem and progenitor cells

There is a paucity of information on a potential role for the IL-33 receptor/ST2 in the regulation of mouse bone marrow (BM) hematopoietic stem (HSC) and progenitor (HPC) cells. Comparing the BM of st2^−/− and wild type (WT) control mice using functional assays, it was found that st2^−/− BM cells had poorer engrafting capacity than WT BM in a competitive repopulating assay using congenic mice, with no changes in reconstitution of B-, T- and myeloid cells following transplantation. The BM of st2^−/− mice also had fewer granulocyte-macrophage, erythroid, and multipotential progenitors than that of WT BM and these st2^−/− HPC were in a slow cycling state compared to that of the rapidly cycling HPC of the WT mice. While functional assessment of HSC and HPC demonstrated that ST2 has a positive influence on regulation of HSC, we could not pick up differences in st2^−/− compared to WT BM using only phenotypic analysis of HSC and HPC populations prior to transplantation, again demonstrating that phenotypic analysis of HSC and HPC do not always recapitulate the functional assessments of these immature hematopoietic cells.

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ST2 is a positive modulator of hematopoiesis.

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ST2^-/- is a positive modulator of hematopoiesis

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Immunophenotyping of st2^-/- hematopoietic stem cell numbers does not recapitulate functional capability of these cells.

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

Parasitic infections pose a wide and varying threat globally, impacting over 25% of the global population with many more at risk of infection. These infections are comprised of, but not limited to, toxoplasmosis, malaria, leishmaniasis and any one of a wide variety of helminthic infections. While a great deal is understood about the adaptive immune response to each of these parasites, there remains a need to further elucidate the early innate immune response. Interleukin-33 is being revealed as one of the earliest players in the cytokine milieu responding to parasitic invasion, and as such has been given the name "alarmin." A nuclear cytokine, interleukin-33 is housed primarily within epithelial and fibroblastic tissues and is released upon cellular damage or death. Evidence has shown that interleukin-33 seems to play a crucial role in priming the immune system toward a strong T helper type 2 immune response, necessary in the clearance of some parasites, while disease exacerbating in the context of others. With the possibility of being a double-edged sword, a great deal remains to be seen in how interleukin-33 and its receptor ST2 are involved in the immune response different parasites elicit, and how those parasites may manipulate or evade this host mechanism. In this review article we compile the current cutting-edge research into the interleukin-33 response to toxoplasmosis, malaria, leishmania, and helminthic infection. Furthermore, we provide insight into directions interleukin-33 research may take in the future, potential immunotherapeutic applications of interleukin-33 modulation and how a better clarity of early innate immune system responses involving interleukin-33/ST2 signaling may be applied in development of much needed treatment options against parasitic invaders.

Emerging Roles of Interleukin-33-responsive Kidney Group 2 Innate Lymphoid Cells in Acute Kidney Injury

Interleukin (IL)-33, a member of the IL-1 family of cytokines, is involved in innate and adaptive immune responses. IL-33 triggers pleiotropic immune functions in multiple types of immune cells, which express the IL-33 receptor, ST2. Recent studies have revealed the potential applications of IL-33 for treating acute kidney injury in preclinical animal models. However, IL-33 and IL-33-responding immune cells are reported to exhibit both detrimental and beneficial roles. The IL-33-mediated immunomodulatory functions have been investigated using loss-of-function approaches, such as IL33-deficient mice, IL-33 antagonists, or administration of exogenous IL-33 recombinant protein. This review will discuss the key findings on IL-33-mediated activation of kidney resident group 2 innate lymphoid cells (ILC2s) and summarize the current understanding of the differential functions of endogenous IL-33 and exogenous IL-33 and their potential implications in treating acute kidney injury.

Short-Term Prognosis Value of sST2 for an Unfavorable Outcome in Hypertensive Patients

Background

sST2 represents a useful biomarker for the diagnosis and prognosis of patients with heart failure, but limited data is available on its role in patients with hypertension. The aim of this study is to evaluate the short-term prognosis value of sST2 for an unfavorable outcome in hypertensive patients.

Methods

This was a prospective observational study which enrolled 80 patients with hypertension, who were followed for one year. All patients underwent clinical, laboratory (including sST2), and echocardiographic assessment at baseline. The patients were grouped according to the cardiovascular (CV) events reported during the follow-up: group A (with CV events) and group B (without CV events).

Results

Overall, 59 CV events were reported during the follow-up period. Compared to group B, the patients in group A had significantly higher sST2 levels, a higher number of CV risk factors, and a higher left ventricle mass. Except for the diastolic dysfunction parameters, the echocardiographic findings were similar in the two groups. Patients in group A had a lower E/A ratio, larger deceleration time, and increased telediastolic pressure as quantified by the E/E/p = 0.006, Kaplan-Meier analysis).

Conclusions

sST2 levels were correlated with the risk of adverse CV outcomes in hypertensive patients and may represent a useful prognostic marker in these patients.

Correlation Profile of Suppression of Tumorigenicity 2 and/or Interleukin-33 with Biomarkers in the Adipose Tissue of Individuals with Different Metabolic States

PURPOSE

The suppression of tumorigenicity 2 (ST2) has two main splice variants including a membrane bound (ST2) form, which activates the myeloid differentiation primary response 88 (MyD88)/nuclear factor-kappa B (NF-κB) signaling pathway, and a secreted soluble form (sST2), which acts as a decoy receptor for ST2 ligand, interleukin (IL)-33. The IL-33/ST2 axis is protective against obesity, insulin resistance, and type 2 diabetes (T2D). In humans, adipose tissue IL-33 displays distinct correlation profiles with glycated hemoglobin, ST2, and other immunometabolic mediators, depending on the glycemic health of the individuals. We determined whether adipose tissue ST2 displays distinct correlation profiles with immunometabolic mediators and whether ST2 and/or IL-33 are correlated with intracellular signaling molecules.

PATIENTS AND METHODS

A total of 91 adults with normal glycemia, prediabetes, and T2D were included. After measuring their anthropometric and biochemical parameters, subcutaneous adipose tissues were isolated and mRNA expression of biomarkers was measured.

RESULTS

In individuals with normal glycemia, adipose tissue ST2 was directly correlated with chemokine (C-C motif) ligand (CCL)-2, CCL5, IL-12, fibrinogen-like protein 2 (FGL2) and interferon regulatory factor (IRF)-4, but inversely correlated with cytochrome C oxidase subunit 7A1. IL-33 and ST2 were directly correlated with tumor necrosis factor receptor-associated factor 6 (TRAF6), NF-κB, and nuclear factor of activated T-cells 5 (NFAT5). In individuals with prediabetes, ST2 was inversely correlated with IL-5, whereas IL-33 but not ST2 was directly correlated with MyD88 and NF-κB. In individuals with T2D, ST2 was directly correlated with CCL2, IL-1β, and IRF5. IL-33 and ST2 were directly correlated with MyD88, TRAF6, and NF-κB.

CONCLUSION

Adipose tissue ST2 and IL-33 show different correlation profiles with various immunometabolic biomarkers depending on the metabolic state of the individuals. Therefore, targeting the IL-33/ST2 axis might form the basis for novel therapies to combat metabolic disorders.

Effects of myeloid and plasmacytoid dendritic cells on ILC2s in patients with allergic rhinitis

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) were reported to serve a critical role in allergic diseases. Myeloid dendritic cells (mDCs) and plasmacytoid DCs (pDCs) play significant roles in allergic immune response. However, effects of DCs on ILC2s in allergic diseases, especially for patients with allergic rhinitis (AR), remain unclear.

OBJECTIVE

We sought to address the roles of mDCs and pDCs in regulating ILC2 function in AR.

METHODS

mDCs and pDCs were cocultured with human PBMCs isolated from patients with AR or ILC2s to measure soluble or intracellular T_H2 cytokines, transcription factors, signaling pathways in ILC2s, and the following mechanisms were further investigated. The levels of peripheral IL-33⁺mDCs, pDCs, and ILC2s were studied in patients under an inhaled allergen challenge.

RESULTS

We confirmed the presence of ILC2s, mDCs, and pDCs in the nasal mucosa of patients with AR. Both allogenic and autologous mDCs were found to activate ILC2s from patients with AR to produce T_H2 cytokines, and increase the levels of GATA-3 and signal transducer and activator of transcription signaling pathways, in which IL-33-producing mDCs exerted the major role by binding on ST2 on ILC2s. We further identified high levels of IL-33⁺mDCs and ILC2s in patients with AR under antigen challenge. Activated pDCs inhibited the cytokine production of ILC2s isolated from patients with AR by secretion of IL-6.

CONCLUSIONS

mDCs promote ILC2 function by the IL-33/ST2 pathway, and activation of pDCs suppresses ILC2 function through IL-6 in patients with AR. Our findings provide new understanding of the interplay between DCs and ILC2s in allergic diseases.