The role of IL-33/ST2L signals in the immune cells

The Mechanism of Interleukin 33-Induced Stimulation of Interleukin 6 in MLO-Y4 Cells

The differentiation and function of osteocytes are controlled by surrounding cells and mechanical stress; however, the detailed mechanisms are unknown. Recent findings suggest that IL-33 is highly expressed in periodontal tissues in orthodontic tooth movement. The present study aimed to elucidate the effect of IL-33 on the expression of regulatory factors for bone remodeling and their molecular mechanisms in the osteocyte-like cell line MLO-Y4. MLO-Y4 cells were treated with IL-33, and the activation of intracellular signaling molecules and transcriptional factors was determined using Western blot analysis and chromatin immunoprecipitation assay. IL-33 treatment enhanced the expression of IL-6 in MLO-Y4 cells, which was suppressed by the knockdown of the IL-33 receptor ST2L. Additionally, IL-33 treatment induced activation of NF-κB, JNK/AP-1, and p38 MAPK signaling pathways in MLO-Y4 cells. Moreover, pretreatment with specific inhibitors of NF-κB, p38 MAPK, and JNK/AP-1 attenuated the IL-33-induced expression of IL-6. Furthermore, chromatin immunoprecipitation indicated that IL-33 increased c-Jun recruitment to the IL-6 promoter. Overall, these results suggest that IL-33 induces IL-6 expression and regulates osteocyte function via activation of the NF-κB, JNK/AP-1, and p38 MAPK pathways through interaction with ST2L receptors on the plasma membrane.

A novel anti-IL-33 antibody recognizes an epitope FVLHN of IL-33 and has a therapeutic effect on inflammatory diseases

As a crucial member of the Interleukin-1 (IL-1) family, IL-33 plays an indispensable role in modulating inflammatory responses. Here, we developed an effective anti-human IL-33 monoclonal antibody (mAb) named 5H8. Importantly, we have identified an epitope (FVLHN) of IL-33 protein as a recognition sequence for 5H8, which plays an important role in mediating the biological activity of IL-33. We observed that 5H8 significantly suppressed IL-33-induced IL-6 expression in bone marrow cells and mast cells in a dose-dependent manner in vitro. Furthermore, 5H8 effectively relievedHDM-induced asthma and PR8-induced acute lung injury in vivo. These findings indicate that targeting the FVLHN epitope is critical for inhibiting IL-33 function. In addition, wedetected that the Tm value of 5H8 was 66.47℃ and the KD value was 173.0 pM, which reflected that 5H8 had good thermal stability and high affinity. Taken together, our data suggest that our newly developed 5H8 antibody has potential as a therapeutic antibody for treating inflammatory diseases.

IL-33-ST2 signaling promotes stemness in subtypes of myeloid leukemia cells through the Wnt and Notch pathways

Cell stemness is characterized by quiescence, pluripotency, and long-term self-renewal capacity. Therapy-resistant leukemic stem cells (LSCs) are the primary cause of relapse in patients with chronic and acute myeloid leukemia (CML and AML). However, the same signaling pathways frequently support stemness in both LSCs and normal hematopoietic stem cells (HSCs), making LSCs difficult to therapeutically target. In cell lines and patient samples, we found that interleukin-33 (IL-33) signaling promoted stemness only in leukemia cells in a subtype-specific manner. The IL-33 receptor ST2 was abundant on the surfaces of CD34+ BCR/ABL1 CML and CD34+ AML cells harboring AML1/ETO and DEK/NUP214 translocations or deletion of chromosome 9q [del(9q)]. The cell surface abundance of ST2, which was lower or absent on other leukemia subtypes and HSCs, correlated with stemness, activated Wnt signaling, and repressed Notch signaling. IL-33-ST2 signaling promoted the maintenance and expansion of AML1/ETO-, DEK/NUP214-, and BCR/ABL1-positive LSCs in culture and in mice by activating Wnt, MAPK, and NF-κB signaling. Wnt signaling and its inhibition of the Notch pathway up-regulated the expression of the gene encoding ST2, thus forming a cell-autonomous loop. IL-33-ST2 signaling promoted the resistance of CML cells to the tyrosine kinase inhibitor (TKI) nilotinib and of AML cells to standard chemotherapy. Thus, inhibiting IL-33-ST2 signaling may target LSCs to overcome resistance to chemotherapy or TKIs in these subtypes of leukemia.

Is There Any Difference in the In Situ Immune Response in Active Localized Cutaneous Leishmaniasis That Respond Well or Poorly to Meglumine Antimoniate Treatment or Spontaneously Heal?

Localized cutaneous leishmaniasis caused by Leishmania braziliensis can either respond well or poorly to the treatment or heal spontaneously; It seems to be dependent on the parasite and/or host factors, but the mechanisms are not fully understood. We evaluated the in situ immune response in eighty-two active lesions from fifty-eight patients prior to treatment classified as early spontaneous regression (SRL-n = 14); treatment responders (GRL-n = 20); and non-responders (before first treatment/relapse, PRL1/PRL2-n = 24 each). Immunohistochemistry was used to identify cell/functional markers which were correlated with the clinical characteristics. PRL showed significant differences in lesion number/size, clinical evolution, and positive parasitological examinations when compared with the other groups. SRL presented a more efficient immune response than GRL and PRL, with higher IFN-γ/NOS2 and a lower percentage of macrophages, neutrophils, NK, B cells, and Ki-67+ cells. Compared to SRL, PRL had fewer CD4+ Tcells and more CD163+ macrophages. PRL1 had more CD68+ macrophages and Ki-67+ cells but less IFN-γ than GRL. PRL present a less efficient immune profile, which could explain the poor treatment response, while SRL had a more balanced immune response profile for lesion healing. Altogether, these evaluations suggest a differentiated profile of the organization of the inflammatory process for lesions of different tegumentary leishmaniasis evolution.

Sex and age differences in sST2 in cardiovascular disease

Aims

The goal of this study was to determine whether sex and age differences exist for soluble ST2 (sST2) for several cardiovascular diseases (CVDs).

Methods

We examined sST2 levels using an ELISA kit for myocarditis (n = 303), cardiomyopathy (n = 293), coronary artery disease (CAD) (n = 239), myocardial infarct (MI) (n = 159), and congestive heart failure (CHF) (n = 286) and compared them to controls that did not have CVDs (n = 234).

Results

Myocarditis occurred in this study in relatively young patients around age 40 while the other CVDs occurred more often in older individuals around age 60. We observed a sex difference in sST2 by age only in myocarditis patients (men aged 38, women 46, p = 0.0002), but not for other CVDs. Sera sST2 levels were significantly elevated compared to age-matched controls for all CVDs: myocarditis (p ≤ 0.0001), cardiomyopathy (p = 0.0009), CAD (p = 0.03), MI (p = 0.034), and CHF (p < 0.0001) driven by elevated sST2 levels in females for all CVDs except myocarditis, which was elevated in both females (p = 0.002) and males (p ≤ 0.0001). Sex differences in sST2 levels were found for myocarditis and cardiomyopathy but no other CVDs and were higher in males (myocarditis p = 0.0035; cardiomyopathy p = 0.0047). sST2 levels were higher in women with myocarditis over 50 years of age compared to men (p = 0.0004) or women under 50 years of age (p = 0.015). In cardiomyopathy and MI patients, men over 50 had significantly higher levels of sST2 than women (p = 0.012 and p = 0.043, respectively) but sex and age differences were not detected in other CVDs. However, women with cardiomyopathy that experienced early menopause had higher sST2 levels than those who underwent menopause at a natural age range (p = 0.02).

Conclusion

We found that sex and age differences in sera sST2 exist for myocarditis, cardiomyopathy, and MI, but were not observed in other CVDs including CAD and CHF. These initial findings in patients with self-reported CVDs indicate that more research is needed into sex and age differences in sST2 levels in individual CVDs.

The IL-1 Family and Its Role in Atherosclerosis

The IL-1 superfamily of cytokines is a central regulator of immunity and inflammation. The family is composed of 11 cytokines (with agonist, antagonist, and anti-inflammatory properties) and 10 receptors, all tightly regulated through decoy receptor, receptor antagonists, and signaling inhibitors. Inflammation not only is an important physiological response against infection and injury but also plays a central role in atherosclerosis development. Several clinical association studies along with experimental studies have implicated the IL-1 superfamily of cytokines and its receptors in the pathogenesis of cardiovascular disease. Here, we summarize the key features of the IL-1 family, its role in immunity and disease, and how it helps shape the development of atherosclerosis.

Heterogeneity of Group 2 Innate Lymphoid Cells Defines Their Pleiotropic Roles in Cancer, Obesity, and Cardiovascular Diseases

Group 2 innate lymphoid cells (ILC2s) are typically known for their ability to respond rapidly to parasitic infections and play a pivotal role in the development of certain allergic disorders. ILC2s produce cytokines such as Interleukin (IL)-5 and IL-13 similar to the type 2 T helper (Th2) cells. Recent findings have highlighted that ILC2s, together with IL-33 and eosinophils, participate in a considerably broad range of physiological roles such as anti-tumor immunity, metabolic regulation, and vascular disorders. Therefore, the focus of the ILC2 study has been extended from conventional Th2 responses to these unexplored areas of research. However, disease outcomes accompanied by ILC2 activities are paradoxical mostly in tumor immunity requiring further investigations. Although various environmental factors that direct the development, activation, and localization of ILC2s have been studied, IL-33/ILC2/eosinophil axis is presumably central in a multitude of inflammatory conditions and has guided the research in ILC2 biology. With a particular focus on this axis, we discuss ILC2s across different diseases.

The Controversial Role of IL-33 in Lung Cancer

Interleukin-33 (IL-33) belongs to the interleukin-1 (IL-1) family, and its structure is similar to IL-18. When cells are damaged or undergo necrosis, mature form of IL-33 is secreted as a cytokine, which can activate the immune system and provide danger signals. The IL-33/ST2 signaling pathway is composed of IL-33, suppression of tumorigenicity 2 (ST2), and IL-1 receptor accessory protein (IL-1RAcP). IL-33 has been reported to be strongly associated with lung cancer progression, and can exhibit opposite effects on lung cancer under different conditions. In this review, we have summarized the structure and basic functions of IL-33, its possible function in immune regulation, and its role in pulmonary fibrosis as well as in lung cancer. We have highlighted the dual regulation of IL-33 in lung cancer and proposed potential lung cancer treatment regimens, especially new immunotherapies, based on its mechanism of action.

Inflammatory Mediators in Atherosclerotic Vascular Remodeling

Atherosclerotic vascular disease remains the most common cause of ischemia, myocardial infarction, and stroke. Vascular function is determined by structural and functional properties of the arterial vessel wall, which consists of three layers, namely the adventitia, media, and intima. Key cells in shaping the vascular wall architecture and warranting proper vessel function are vascular smooth muscle cells in the arterial media and endothelial cells lining the intima. Pathological alterations of this vessel wall architecture called vascular remodeling can lead to insufficient vascular function and subsequent ischemia and organ damage. One major pathomechanism driving this detrimental vascular remodeling is atherosclerosis, which is initiated by endothelial dysfunction allowing the accumulation of intimal lipids and leukocytes. Inflammatory mediators such as cytokines, chemokines, and modified lipids further drive vascular remodeling ultimately leading to thrombus formation and/or vessel occlusion which can cause major cardiovascular events. Although it is clear that vascular wall remodeling is an elementary mechanism of atherosclerotic vascular disease, the diverse underlying pathomechanisms and its consequences are still insufficiently understood.

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.

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.

Serum soluble suppression of tumorigenicity 2 as a novel inflammatory marker predicts the severity of acute pancreatitis

BACKGROUND

Acute pancreatitis (AP) is an inflammatory disease in which the regulatory pathway is complex and not well understood. Soluble suppression of tumorigenicity 2 (sST2) protein receptor functions as a decoy receptor for interleukin (IL)-33 to prevent IL-33/suppression of tumorigenicity 2L (ST2L)-pathway-mediated T helper (Th)2 immune responses.

AIM

To investigate the role of sST2 in AP.

METHODS

We assessed the association between sST2 and severity of AP in 123 patients enrolled in this study. The serum levels of sST2, C-reactive protein (CRP) and Th1- and Th2-related cytokines, including interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-2, IL-4, IL-5 and IL-13, were measured by highly sensitive ELISA, and the severity of AP in patients was evaluated by the 2012 Atlanta Classification Criteria.

RESULTS

Serum sST2 levels were significantly increased in AP patients, and further, these levels were significantly elevated in severe AP (SAP) patients compared to moderately severe AP (MSAP) and mild AP (MAP) patients. Logistic regression showed sST2 was a predictor of SAP [odds ratio (OR): 1.003 (1.001–1.006), P = 0.000]. sST2 cutoff point was 1190 pg/mL, and sST2 above this cutoff was associated with SAP. sST2 was also a predictor of any organ failure and mortality during AP [OR: 1.006 (1.003–1.009), P = 0.000, OR: 1.002 (1.001–1.004), P = 0.012, respectively]. Additionally, the Th1-related cytokines IFN-γ and TNF-α in the SAP group were higher and the Th2-related cytokine IL-4 in the SAP group was significantly lower than those in MSAP and MAP groups.

CONCLUSION

sST2 may be used as a novel inflammatory marker in predicting AP severity and may regulate the function and differentiation of IL-33/ST2-mediated Th1 and Th2 Lymphocytes in AP homeostasis.

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.

Airway Exposure to Polyethyleneimine Nanoparticles Induces Type 2 Immunity by a Mechanism Involving Oxidative Stress and ATP Release

Polyethyleneimine (PEI) induced immune responses were investigated in human bronchial epithelial (hBE) cells and mice. PEI rapidly induced ATP release from hBE cells and pretreatment with glutathione (GSH) blocked the response. PEI activated two conductive pathways, VDAC-1 and pannexin 1, which completely accounted for ATP efflux across the plasma membrane. Moreover, PEI increased intracellular Ca²⁺ concentration ([Ca²⁺]_i), which was reduced by the pannexin 1 inhibitor, ¹⁰Panx (50 μM), the VDAC-1 inhibitor, DIDS (100 μM), and was nearly abolished by pretreatment with GSH (5 mM). The increase in [Ca²⁺]_i involved Ca²⁺ uptake through two pathways, one blocked by oxidized ATP (oATP, 300 μM) and another that was blocked by the TRPV-1 antagonist A784168 (100 nM). PEI stimulation also increased IL-33 mRNA expression and protein secretion. In vivo experiments showed that acute (4.5 h) PEI exposure stimulated secretion of Th2 cytokines (IL-5 and IL-13) into bronchoalveolar lavage (BAL) fluid. Conjugation of PEI with ovalbumin also induced eosinophil recruitment and secretion of IL-5 and IL-13 into BAL fluid, which was inhibited in IL-33 receptor (ST2) deficient mice. In conclusion, PEI-induced oxidative stress stimulated type 2 immune responses by activating ATP-dependent Ca²⁺ uptake leading to IL-33 secretion, similar to allergens derived from Alternaria.

Anti-Tumorigenic Activities of IL-33: A Mechanistic Insight

Interleukin-33 (IL-33) is an epithelial-derived cytokine that can be released upon tissue damage, stress, or infection, acting as an alarmin for the immune system. IL-33 has long been studied in the context of Th2-related immunopathologies, such as allergic diseases and parasitic infections. However, its capacity to stimulate also Th1-type of immune responses is now well established. IL-33 binds to its specific receptor ST2 expressed by most immune cell populations, modulating a variety of responses. In cancer immunity, IL-33 can display both pro-tumoral and anti-tumoral functions, depending on the specific microenvironment. Recent findings indicate that IL-33 can effectively stimulate immune effector cells (NK and CD8⁺ T cells), eosinophils, basophils and type 2 innate lymphoid cells (ILC2) promoting direct and indirect anti-tumoral activities. In this review, we summarize the most recent advances on anti-tumor immune mechanisms operated by IL-33, including the modulation of immune checkpoint molecules, with the aim to understand its potential as a therapeutic target in cancer.

Early Treatment of Interleukin-33 can Attenuate Lupus Development in Young NZB/W F1 Mice

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, has been recently associated with the development of autoimmune diseases, including systemic lupus erythematosus (SLE). IL-33 is an alarmin and a pleiotropic cytokine that affects various types of immune cells via binding to its receptor, ST2. In this study, we determine the impact of intraperitoneal IL-33 treatments in young lupus, NZB/W F1 mice. Mice were treated from the age of 6 to 11 weeks. We then assessed the proteinuria level, renal damage, survival rate, and anti-dsDNA antibodies. The induction of regulatory B (Breg) cells, changes in the level of autoantibodies, and gene expression were also examined. In comparison to the control group, young NZB/W F1 mice administered with IL-33 had a better survival rate as well as reduced proteinuria level and lupus nephritis. IL-33 treatments significantly increased the level of IgM anti-dsDNA antibodies, IL-10 expressing Breg cells, and alternatively-induced M2 macrophage gene signatures. These results imply that IL-33 exhibits a regulatory role during lupus onset via the expansion of protective IgM anti-dsDNA as well as regulatory cells such as Breg cells and M2 macrophages.

The Effect of Statins through Mast Cells in the Pathophysiology of Atherosclerosis: a Review

PURPOSE OF REVIEW

In this review, we discuss the evidence supporting the effects of statins on mast cells (MCs) in atherosclerosis and their molecular mechanism of action.

RECENT FINDINGS

Statins or HMG-CoA reductase inhibitors are known for their lipid-lowering properties and are widely used in the prevention and treatment of cardiovascular diseases. There is growing evidence that statins have an inhibitory effect on MCs, which contributes to the pleiotropic effect of statins in various diseases. MCs are one of the crucial effectors of the immune system which play an essential role in the pathogenesis of multiple disorders. Recent studies have shown that MCs are involved in the development of atherosclerotic plaques. MCs secrete various inflammatory cytokines (IL-6, IL4, TNF-α, and IFNγ) and inflammatory mediators (histamine, tryptase, proteoglycans) after activation by various stimulants. This, in turn, will exacerbate atherosclerosis. Statins suppress the activation of MCs via IgE inhibition which leads to inhibition of inflammatory mediators and cytokines which are involved in the development and progression of atherosclerosis. In keeping with this evidence presented here, MCs can be considered as one of the therapeutic targets for statins in the treatment of atherosclerosis.

Epithelial cells expressed IL-33 to promote degranulation of mast cells through inhibition on ST2/PI3K/mTOR-mediated autophagy in allergic rhinitis

Nasal epithelial cells are the first barrier against allergen infiltration in allergic rhinitis (AR), and the relationship between nasal epithelial cells and mast cell-mediated hypersensitivity remains unclear. This study aimed to investigate the possible association between allergen-challenged nasal epithelial cells (AR-HNEpC) and mast cell degranulation in AR. Our data revealed that calcium influx and degranulation were increased in AR-HNEpC-co-cultured mast cells. Expression of IL-33, a factor that binds to ST2 receptors on mast cells and regulates their degranulation, was elevated in AR-HNEpC. Blocking IL-33/ST2 pathway activated autophagy and inhibited degranulation and inflammatory factor release in mast cells. Furthermore, PI3K/mTOR was increased in IL-33-treated mast cells. Inhibition on PI3K/mTOR pathway enhanced autophagy and inhibited degranulation. Analysis using an in vivo AR model supported the above findings. In conclusion, IL-33 from epithelial cells promotes degranulation of mast cells in AR through inhibition on ST2/PI3K/mTOR-mediated autophagy, which provides a potential therapeutic target for the disease.Abbreviations: AR: allergic rhinitis; IL: interleukin; TNF-α: tumor necrosis factor-alpha; INF-γ: interferon-gamma; HNEpC: human nasal epithelial cell line; ATCC: American Type Culture Collection; C48/80: compound 48/80; 3-MA: 3-methyladenine; qPCR: quantitative PCR; AR-HNEpC: dust mite allergen-treated nasal epithelial cells; IgE: immunoglobulin E; Atg7: autophagy-related gene 7.

Fungal allergen-induced IL-33 secretion involves cholesterol-dependent, VDAC-1-mediated ATP release from the airway epithelium

KEY POINTS

Alternaria aeroallergens induce the release of ATP from human bronchial epithelial (HBE) cells by activating a conductive pathway involving voltage-dependent anion channel-1 (VDAC-1) and by exocytosis of ATP localized within membrane vesicles. Inhibition of VDAC-1 blocked Alternaria-evoked Ca²⁺ uptake across the plasma membrane of HBE cells and interleukin (IL)-33 release into the extracellular media. Reducing cholesterol content with a cholesterol scavenger (β-methylcyclodextrin) or statin compound (simvastatin) blocked ATP and IL-33 release by lowering the expression of VDAC-1 in the plasma membrane. Pretreatment with simvastatin for 24 h also inhibited the increase in tight junction macromolecule permeability that occurs following Alternaria exposure. These results establish a novel role for VDAC-1 as a mechanism underlying ATP release induced by fungal allergens and suggests a possible therapeutic use for cholesterol lowering compounds in reducing Alternaria-stimulated allergic inflammation.

ABSTRACT

Human bronchial epithelial (HBE) cells exposed to allergens derived from the common saprophytic fungus, Alternaria alternata release ATP, which in turn stimulates P2X₇ receptor-mediated Ca²⁺ uptake across the plasma membrane. The subsequent increase in intracellular calcium concentration induces proteolytic processing and secretion of interleukin (IL)-33, a critical cytokine involved in the initiation of allergic airway inflammation. A major objective of the present study was to identify the mechanism responsible for conductive ATP release. The results show that pretreatment of HBE cells with inhibitors of the voltage-dependent anion channel-1 (VDAC-1) or treatment with a VDAC-1 selective blocking antibody or silencing mRNA expression of the channel by RNA interference, inhibit Alternaria-evoked ATP release. Moreover, inhibition of VDAC-1 channel activity or reducing protein expression blocked the secretion of IL-33. Similarly, reducing the cholesterol content of HBE cells with simvastatin or the cholesterol scavenger β-methylcyclodextrin also blocked ATP release and IL-33 secretion by decreasing the level of VDAC-1 expression in the plasma membrane. In addition, simvastatin inhibited the increase in tight junction macromolecule permeability that was previously observed after Alternaria exposure. These results demonstrate a novel function for VDAC-1 as the conductive mechanism responsible for Alternaria-induced ATP release, an essential early step in the processing, mobilization and secretion of IL-33 by the airway epithelium. Furthermore, the simvastatin-evoked reduction of VDAC-1 expression in the plasma membrane, suggests the possibility that cholesterol lowering compounds may be beneficial in alleviating allergic airway inflammation induced by fungal allergens.

ST2 and regulatory T cells in the colorectal adenoma/carcinoma microenvironment: implications for diseases progression and prognosis

ST2 (also known as IL1RL1) is the critical functional receptor for interleukin (IL)-33 in stimulating regulatory T cell (Treg) expansion and function in physiological and pathological conditions. We examined the correlation between ST2 cell expression and FoxP3 positive Tregs in both colorectal adenoma and cancer (CRC) microenvironment by real-time PCR, immunohistochemistry (IHC) and double immunofluorescences. The clinicopathological and prognostic significance of cellular ST2-positive cells and FoxP3-positive Tregs in patients with adenoma and CRC were evaluated. Real-time PCR results revealed increased expression levels of ST2 and FoxP3 mRNAs in both adenoma and CRC tissues as compared with control tissues. IHC analysis confirmed increased densities of ST2-positive cells in both the adenoma/CRC epithelium and stroma, which show a close positive linear association with the densities of FoxP3-positive Tregs in respective compartments. Pathological feature analysis showed that densities of ST2-positive cells in the tumor stroma were notably associated with degree of dysplastic grading in patients with adenoma, and disease stages and lymph node metastasis in patients with CRC. Kaplan-Meier survival curves suggested that CRC patients with high densities of ST2-positive cells in the stroma tend to have a shorter overall survival. We therefore concluded that increased densities of ST2-postive cells relate to Treg accumulation within the adenoma/CRC microenvironment, suggesting the IL-33/ST2 pathway as a potential contributor for immunosuppressive milieu formation that impact disease stage and prognosis in patients with CRC.

Induction of IκBζ Augments Cytokine and Chemokine Production by IL-33 in Mast Cells

IκBζ (encoded by the Nfkbiz) is a member of the nuclear IκB family, which is involved in the expression of secondary response genes based on signals from TLR or IL-1R. ST2L, an IL-33R, is a member of the IL-1R family and abundantly expressed in tissue-resident immune cells, such as mast cells and innate lymphoid cells; however, its downstream signaling pathway remains unelucidated. In this study, we examined the role of IκBζ in ST2L-mediated cytokine and chemokine production in mast cells. Murine bone marrow cells were differentiated ex vivo into bone marrow-derived mast cells (BMMCs). The treatment of BMMCs with IL-33 transiently induced robust IκBζ expression. Of the 40 cytokines and chemokines examined using a cytokine and chemokine array, the concentrations of IL-6, IL-13, CCL2, CCL3, and TNF-α in the supernatant were augmented by IL-33. The deletion of IκBζ in BMMCs resulted in a significant reduction of the production of these mediators and the expression of their mRNA. NF-κB p50 but not p65 translocated to the nucleus by IL-33 and was not affected by the deletion of IκBζ. However, induction of IκBζ and the resultant cytokine and chemokine productions were significantly inhibited by pretreatment with an NF-κB inhibitor. The deletion of IκBζ did not affect the phosphorylation of ERK, p38 MAPK, or JNK by IL-33, and the treatment with inhibitors of these mitogen-activated kinases failed to abolish the expression of Nfkbiz Our findings suggest that IκBζ augments IL-33-dependent cytokine and chemokine production in BMMCs through the action of NF-κB.

Interleukin-33 delays recovery of mucosal inflammation via downregulation of homeostatic ABCG5/8 in the colon

Previous studies have suggested that interleukin-33 (IL-33) is involved in the pathogenesis of ulcerative colitis (UC), though the detailed mechanisms are not fully known. We investigated IL-33-mediated colonic homeostasis using a mechanistic method. Il33^-/- mice were more tolerant to dextran sulfate sodium-induced acute colitis than the wild type and also showed delayed recovery from colitis with recombinant IL-33 (rIL-33) administration. Unexpectedly, microarray analysis identified significant downregulation of the Abcg5/8 genes in mouse colons following rIL-33 treatment. ABCG5/8 are known cholesterol transporters in the small intestine and liver, though their colon activities have not been elucidated, thus their role in IL-33-mediated inflammation was investigated. In vitro, toll-like receptor (TLR) stimulation upregulated ABCG5/8 mRNA expression in Caco2 and HCT-15 cells, with subsequent downregulation by rIL-33, while inhibition of ABCG5/8 along with their siRNA increased TLR-stimulated IL-8 production. Together, these results indicated that colonic ABCG5/8 play a regulatory role in TLR-induced inflammation, while histological inflammation in human UC was correlated positively with the level of mucosal IL-33 and inversely with that of colonic ABCG5/8. This is the first report of IL-33-mediated downregulation of colonic ABCG5/8 in a colitis recovery phase, indicating their involvement in UC pathogenesis and potential as a therapeutic target.

Elevated Sera sST2 Is Associated With Heart Failure in Men ≤50 Years Old With Myocarditis

Background

Myocarditis is an important cause of acute and chronic heart failure. Men with myocarditis have worse recovery and an increased need for transplantation compared with women, but the reason for the sex difference remains unclear. Elevated sera soluble (s)ST2 predicts mortality from acute and chronic heart failure, but has not been studied in myocarditis patients.

Methods and Results

Adults with a diagnosis of clinically suspected myocarditis (n=303, 78% male) were identified according to the 2013 European Society of Cardiology position statement. Sera sST2 levels were examined by ELISA in humans and mice and correlated with heart function according to sex and age. Sera sST2 levels were higher in healthy men (P=8×10⁻⁶) and men with myocarditis (P=0.004) compared with women. sST2 levels were elevated in patients with myocarditis and New York Heart Association class III‐IV heart failure (P=0.002), predominantly in men (P=0.0003). Sera sST2 levels were associated with New York Heart Association class in men with myocarditis who were ≤50 years old (r=0.231, P=0.0006), but not in women (r=0.172, P=0.57). Sera sST2 levels were also significantly higher in male mice with myocarditis (P=0.005) where levels were associated with cardiac inflammation. Gonadectomy with hormone replacement showed that testosterone (P<0.001), but not estradiol (P=0.32), increased sera sST2 levels in male mice with myocarditis.

Conclusions

We show in a well‐characterized subset of heart failure patients with clinically suspected and biopsy‐confirmed myocarditis that elevated sera sST2 is associated with an increased risk of heart failure based on New York Heart Association class in men ≤50 years old.

Possible Roles of IL-33 in the Innate-Adaptive Immune Crosstalk of Psoriasis Pathogenesis

Background

IL-33 belongs to the IL-1 family, playing a role in several biologic processes as well as in the pathogenesis of different diseases, including skin pathologies. It acts as an alarmin, released by damaged cells. Binding to a ST2 receptor, it stimulates many immune cells such as ILC2 and Th2 cells. IL-33/ST2 axis seems to be involved in Th17 response. According to this, a review was performed to analyze if IL-33 even interplay in the onset of psoriasis, a Th1/Th17 inflammatory disease.

Methods

Data obtained from the included articles are study author name, publication date, group studied, clinical and biological variables, laboratory tests, and outcome of interest of the study.

Results

Data are obtained from the 19 studies identified, which assessed the association between IL-33 and psoriasis.

Discussion

It seems to promote the innate-adaptive immune crosstalk: it could induce mast cells and neutrophil response after being released by injured keratinocytes and after stimulation by some cytokines, in particular TNFα, INFγ, and IL-17A. In addition, it seems to be involved from the onset of disease to the development of comorbidities, as psoriatic arthritis.

Conclusion

The core of the future research on psoriasis could be to fully understand the role of this complex cytokine, in order also to find a new therapeutic approach.

Interleukin 33/ST2 Axis Components Are Associated to Desmoplasia, a Metastasis-Related Factor in Colorectal Cancer

In colorectal cancer (CRC), cancer-associated fibroblasts (CAFs) are the most abundant component from the tumor microenvironment (TM). CAFs facilitate tumor progression by inducing angiogenesis, immune suppression and invasion, thus altering the organization/composition of the extracellular matrix (i.e., desmoplasia) and/or activating epithelial-mesenchymal transition (EMT). Soluble factors from the TM can also contribute to cell invasion through secretion of cytokines and recently, IL-33/ST2 pathway has gained huge interest as a protumor alarmin, promoting progression to metastasis by inducing changes in TM. Hence, we analyzed IL-33 and ST2 content in tumor and healthy tissue lysates and plasma from CRC patients. Tissue localization and distribution of these molecules was evaluated by immunohistochemistry (using localization reference markers α-smooth muscle actin or α-SMA and E-cadherin), and clinical/histopathological information was obtained from CRC patients. In vitro experiments were conducted in primary cultures of CAFs and normal fibroblasts (NFs) isolated from tumor and healthy tissue taken from CRC patients. Additionally, migration and proliferation analysis were performed in HT29 and HCT116 cell lines. It was found that IL-33 content increases in left-sided CRC patients with lymphatic metastasis, with localization in tumor epithelia associated with abundant desmoplasia. Although ST2 content showed similarities between tumor and healthy tissue, a decreased immunoreactivity was observed in left-sided tumor stroma, associated to metastasis related factors (advanced stages, abundant desmoplasia, and presence of tumor budding). A principal component analysis (including stromal and epithelial IL-33/ST2 and α-SMA immunoreactivity with extent of desmoplasia) allowed us to distinguish clusters of low, intermediate and abundant desmoplasia, with potential to develop a diagnostic signature with benefits for further therapeutic targets. IL-33 transcript levels from CAFs directly correlated with CRC cell line migration induced by CAFs conditioned media, with rhIL-33 inducing a mesenchymal phenotype in HT29 cells. These results indicate a role of IL-33/ST2 in tumor microenvironment, specifically in the interaction between CAFs and epithelial tumor cells, thus contributing to invasion and metastasis in left-sided CRC, most likely by activating desmoplasia.

IL33/ST2 Axis in Diabetic Kidney Disease: A Literature Review

Interleukin-33 (IL-33) is a cytokine belonging to the IL-1 family, playing a role in inflammatory, infectious and autoimmune diseases and expressed in the cellular nucleus in several tissues. High levels of IL-33 are expressed in epithelial barrier tissues and endothelial barriers. ST2 is a receptor for IL-33, expressed selectively on a subset of Th2 cells, mediating some of their functions. The IL-33/ST2 axis plays an important role in several acute and chronic inflammatory diseases, including asthma and rheumatoid arthritis. Different disorders are related to the activity of IL-33, ST2, or their axis, including cardiovascular disease or renal disturbances. Therefore, in the present work, a literature review was conducted, covering the period from 1 January 2000 to 30 November 2018, in PubMed, ScienceDirect, and Google Scholar database, to assess the involvement of the IL-33/ST2 axis in diabetic kidney disease. 6 articles directly dealing with the argument were identified, highlighting a clear link between IL-33/ST2 axis and diabetic kidney disease or related nephropathy. Overall, the involvement of ST2 seems to be more predictive than IL-33, especially in investigating the deterioration of kidney function; however, both compounds are pivotal in the field of renal diseases. Future studies are required to confirm the scientific evidences on larger and more heterogeneous cohorts.

Contribution of IL-33 to the Pathogenesis of Colorectal Cancer

The development of colorectal cancer (CRC) is not only determined by transformed cells per se, but also by factors existing in their immune microenvironment. Accumulating scientific evidence has revealed that interleukin (IL)-33, an IL-1 family member, plays an essential role in the regulation of immune response and is relevant in CRC pathogenesis. Data from both human and experimental studies demonstrated that IL-33 inhibits host anti-tumor immunity, remodels tumor stroma and enhances angiogenesis, thereby promoting the development of CRC. These pro-tumor effects of IL-33 are mainly mediated by IL-33 receptor ST2 (also known as IL-1RL1). Based on those findings, it is currently hypothesized that the IL-33/ST2 pathway is a potential biomarker and therapeutic target for colorectal tumorigenesis. Herein, we summarize the recent discoveries in understanding the critical role of the IL-33/ST2 pathway in contributing to the pathogenesis of colorectal tumorigenesis and discuss its potential implications for the future development of effective anti-tumor strategies.

IL-33 Upregulates Cysteinyl Leukotriene Receptor Type 1 Expression in Human Peripheral Blood CD4+ T Lymphocytes

IL-33 and cysteinyl leukotrienes (cysLTs) are key components of asthma pathogenesis, and both contribute to the initiation and maintenance of the type 2 inflammatory environment. However, little is known about the potential interactions between the two mediators. In this work, we aimed at studying the regulation of expression of the cysLT receptors CysLT1 and CysLT2 by IL-33 in human PBLs. Our results show that the IL-33/ST2L axis increases CysLT1 but not CysLT2 expression in a concentration- and time-dependent manner in PBLs. IL-33-induced CysLT1 upregulation was observed at the protein but not at the mRNA level and was accompanied by an increase in LTD₄-induced calcium mobilization and migration of CD4⁺ T lymphocytes. We also show that purified naive CD4⁺ T lymphocytes expressed ST2L and responded to IL-33 in the absence of Ag or TCR stimulation, suggesting a mechanism independent of Ag presentation. These results contribute to expanding our knowledge in the field of IL-33 by proposing a new mode of action of the cytokine on T cells and by extending its role to the regulation of naive T cell trafficking, therefore reinforcing its interest as a potential therapeutic target for the treatment of asthma.

Interleukin 33 regulates gene expression in intestinal epithelial cells independently of its nuclear localization

Interleukin 33 (IL33) is a cytokine found in the extracellular space (mature IL33) or in the cell nucleus (full-length IL33). Nuclear accumulation of IL33 has been reported in intestinal epithelial cells (IEC) during intestinal inflammation and cancer, but a functional role for this nuclear form remains unclear. To study the role of nuclear IL33 in IEC, we generated transgenic mice expressing full-length IL33 in the intestinal epithelium (Vfl33 mice). Expression of full-length IL33 in the epithelium resulted in accumulation of IL33 protein in the nucleus and secretion of IL33. Over-expression of full-length IL33 by IEC did not promote gut inflammation, but induced expression of genes in the IEC and lamina propria lymphocytes (LPL) that correlated negatively with genes expressed in inflammatory bowel diseases (IBD). Because the IL33 receptor ST2 is expressed by IEC, there was the potential that both the mature and full-length forms could mediate this effect. To specifically interrogate the transcriptional role of nuclear IL33, we intercrossed the Vfl33 mice with ST2- deficient mice. ST2 deficiency completely abrogated the transcriptional effects elicited by IL33 expression, suggesting that the transcriptional effects of IL33 on IEC are mediated by its mature, not its nuclear form.

Inflammatory milieu in contrast-induced nephropathy: a prospective single-center study

Background

Acute kidney injury (AKI) caused by contrast exposure is a common problem, which may cause a significant increase in patients in-hospital stay and therefore the cost of treatment. This study was conducted to evaluate the role of inflammation, inflammatory markers in predicting contrast induced nephropathy (CIN). This is a prospective study that was carried out in a major tertiary referral hospital in Jordan.

Methods

Clinical data, blood and urine samples were collected from all patients admitted to the cardiology unit. All patients who agreed to participate in the study had creatinine level analysis 48-72 hours after the procedure. The CIN was defined as an increase in serum creatinine by 25% or 44 μmol/L from the baseline within 48-72 hours after the contrast administration. Patients with stage 4, 5 renal failure, patients on dialysis, and patients with recent intravenous contrast use, active infection or cancer were excluded from the study.

Results

Of the total 202 patients, 30 (14.8%) developed CIN. The incidence rate was 21.1% among females and 12.4% among males. In the multivariate analysis, beside eGFR, diuretics, and alkaline phosphatase, IL-33 was significantly associated with CIN, while the other cytokines did not to show this an association.

Conclusion

Serum level of IL-33 was a significant predictor for development of CIN. Good clinical judgment and high serum levels of IL-33 may stratify patients into low and high risk for CIN.

Investigation of IL-33 serum levels in patients with benign and malignant salivary gland tumors

BACKGROUND

Interleukin-33 (IL-33) has been recently discovered as an influential factor in the process of tumor immunity, and is presented in cancer pathogenesis.

OBJECTIVE

This study aimed to determine the serum levels of IL-33 in patients with benign and malignant Salivary gland tumors (SGTs).

METHODS

This descriptive cross-sectional study was performed on 47 samples of malignant SGTs including 18 mucoepidermoid carcinoma (MEC), 8 adenoid cystic carcinoma (ADCC), 21 malignant mixed tumor (MMT), and 14 benign pleomorphic adenoma (PA). A control group was considered consisting of 28 healthy subjects. The serum level of IL-33 was measured by using sandwich ELISA method. The data were statistically analyzed through Kruskal-Wallis and Mann-Whitney tests.

RESULTS

The median concentration of IL-33 was 6.91 in malignant, 5.14 in benign, and 5.01 in healthy cases, with a statistically significant difference (P= 0.001). The median serum levels of IL-33 increased significantly in ADCC (7.15), MEC (7.03), and MMT (6.91) compared with the control group (5.01) (P< 0.05). The mean rank of MEC was significantly higher than PA (P= 0.01). IL-33 concentration was positively and significantly correlated with the tumor stage (P= 0.02) and tumor size (P= 0.03).

CONCLUSIONS

IL-33 could be suggested as a novel biomarker to distinguish different types of SGTs.

IL-33/ST2 Pathway and Galectin-3 as a New Analytes in Pathogenesis and Cardiometabolic Risk Evaluation in Psychosis

Schizophrenia and treatment of this disorder are often accompanied with metabolic syndrome and cardiovascular issues. Alterations in the serum level of innate immune mediators, such as interleukin-33 (IL-33) and its receptor IL-33R (ST2) and Galectin-3 (Gal-3) were observed in these conditions. Moreover, these parameters are potential prognostic and therapeutic markers. There is also accumulating evidence that these molecules play a role in neuroinflammation. Therefore, in this study we have investigated the serum level of Gal-3, IL-33 and soluble ST2 (sST2) in different stages of schizophrenia. Gal-3 levels were elevated in remission and lower in schizophrenia exacerbation in comparison with controls. Levels of IL-33 and sST2 are higher in schizophrenia exacerbation in comparison with controls and patients in remission. This initial analysis of new markers of neuroinflammation suggested their involvement in schizophrenia pathophysiology and/or cardiometabolic comorbidity.

Interplay of Brain-Derived Neurotrophic Factor and Cytokines in Schizophrenia

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family and plays an important role in neuroplasticity, differentiation and survival of neurons, as well as their function. Neuroinflammation has been explored in the pathophysiology of many mental disorders, such as schizophrenia. Cytokines representing different types of immune responses have an impact on neurogenesis and BDNF expression. Cross-regulation of BDNF and cytokines is accomplished through several signalling pathways. Also, typical and atypical antipsychotic drugs variously modulate the expression of BDNF and serum levels of cytokines, which can possibly be used in evaluation of therapy effectiveness. Comorbidity of metabolic syndrome and atopic diseases has been considered in the context of BDNF and cytokines interplay in schizophrenia.

Critical Roles of IL-33/ST2 Pathway in Neurological Disorders

Interleukin-33 (IL-33) is an IL-1 family member, which exhibits both pro- and anti-inflammatory properties solely based on the type of the disease itself. Generally, IL-33 is expressed by both endothelial and epithelial cells and mediates its function based on the interaction with various receptors, mainly with ST2 variants. IL-33 is a potent inducer for the Th2 immune response which includes defence mechanism in brain diseases. Thus, in this paper, we review the biological features of IL-33 and the critical roles of IL-33/ST2 pathway in selected neurological disorders including Alzheimer's disease, multiple sclerosis, and malaria infection to discuss the involvement of IL-33/ST2 pathway during these brain diseases and its potential as future immunotherapeutic agents or for intervention purposes.

First-Breath-Induced Type 2 Pathways Shape the Lung Immune Environment

From birth onward, the lungs are exposed to the external environment and therefore harbor a complex immunological milieu to protect this organ from damage and infection. We investigated the homeostatic role of the epithelium-derived alarmin interleukin-33 (IL-33) in newborn mice and discovered the immediate upregulation of IL-33 from the first day of life, closely followed by a wave of IL-13-producing type 2 innate lymphoid cells (ILC2s), which coincided with the appearance of alveolar macrophages (AMs) and their early polarization to an IL-13-dependent anti-inflammatory M2 phenotype. ILC2s contributed to lung quiescence in homeostasis by polarizing tissue resident AMs and induced an M2 phenotype in transplanted macrophage progenitors. ILC2s continued to maintain the M2 AM phenotype during adult life at the cost of a delayed response to Streptococcus pneumoniae infection in mice. These data highlight the homeostatic role of ILC2s in setting the activation threshold in the lung and underline their implications in anti-bacterial defenses.

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The first breath triggers IL-33 induction by AEC2 in lungs of newborn mice

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IL-33 promotes the perinatal expansion and activation of ST2-expressing ILC2s

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ILC2-derived IL-13 polarizes newborn’s AMs into an M2 phenotype

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This homeostatic type 2 pathway delays antibacterial effector responses

IL-33/ST2 Pathway as a Rational Therapeutic Target for CNS Diseases

Interleukin (IL)-33 is a member of the interleukin-1 cytokine family that is produced by many different types of tissues including the central nervous system (CNS). IL-33 mediates its effects via its heterodimeric receptor complex, comprised of ST2 and the IL-1 receptor accessory protein (IL-1RAcp). As a pleiotropic nuclear cytokine, IL-33 is a crucial factor in the development of cardiovascular diseases, allergic diseases, infectious diseases, and autoimmune diseases. Recently, accumulated evidence shows that the IL-33/ST2 axis plays a crucial and diverse role in the pathogenesis of CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, infectious diseases, traumatic CNS injury, chronic pain, etc. In this review, we discuss the recent findings in the cellular signaling of IL-33 and advancement of the role of IL-33 in several CNS diseases, as well as its therapeutic potential for the treatment of those diseases.

Pulmonary Susceptibility of Neonates to Respiratory Syncytial Virus Infection: A Problem of Innate Immunity?

Human respiratory syncytial virus (RSV) is a common and highly contagious viral agent responsible for acute lower respiratory infection in infants. This pathology characterized by mucus hypersecretion and a disturbed T cell immune response is one of the major causes of infant hospitalization for severe bronchiolitis. Although different risk factors are associated with acute RSV bronchiolitis, the immunological factors contributing to the susceptibility of RSV infection in infants are not clearly elucidated. Epidemiological studies have established that the age at initial infection plays a central role in the severity of the disease. Thus, neonatal susceptibility is intrinsically linked to the immunological characteristics of the young pulmonary mucosa. Early life is a critical period for the lung development with the first expositions to external environmental stimuli and microbiota colonization. Furthermore, neonates display a lung immune system that profoundly differs to those from adults, with the predominance of type 2 immune cells. In this review, we discuss the latest information about the lung immune environment in the early period of life at a steady state and upon RSV infection and how we can modulate neonatal susceptibility to RSV infection.

IL-33 and IgE stimulate mast cell production of IL-2 and regulatory T cell expansion in allergic dermatitis

BACKGROUND

We have previously shown that mast cells (MCs) suppress chronic allergic dermatitis in mice. The underlying mechanism involves MC-derived IL-2, which supports regulatory T cell (Treg) response at the site of inflammation. However, it is not clear what are the factors that drive MCs to produce IL-2.

OBJECTIVE

To understand the mechanisms that lead to IL-2 production from MCs in chronic allergic dermatitis.

METHODS

Isolated murine bone marrow-derived MCs (BMMCs) were incubated with various stimulators, and IL-2 production was assessed by RT-PCR and ELISA. The response of signalling pathways was evaluated by MAPK inhibitors and Western blot analysis. The effect of MC-IL-2 on Tregs was studied by incubation of splenic T cells with conditioned media obtained from activated BMMCs. Dermatitis was elicited by repeated exposures of mouse ears to oxazolone. MCs in mouse and human skin samples were evaluated by immunostaining.

RESULTS

BMMCs released IL-2 in response to IL-33, and IL-2 production was further enhanced by concomitant FcεRI activation. The effect of IL-33 was mediated by activation of the MAPK family members. IL-2 in conditioned media from IL-33 and IgE-stimulated BMMCs led to considerable expansion of Tregs in vitro. IL-33 levels were elevated in oxazolone-challenged ears along with increased numbers of IL-2-expressing MCs. Human skin with chronic inflammation also contained IL-2-expressing MCs that colocalized with IL-33 staining in the dermis.

CONCLUSIONS

IL-33, in collaboration with IgE, is critical for MC-IL-2 production in allergic skin disease, thus leading to Treg stimulation and suppression of allergic dermatitis.

The effect of diabetes on ovaries in a rat model: the role of interleukin-33 and apoptosis

Interleukin-33 (IL-33) is a novel cytokine involved in diabetes mellitus (DM) but its role in diabetic ovarian injury is unknown. As IL-33 is modulated by apoptosis, we aimed at investigating the effect of diabetes on ovaries in terms of evaluating apoptosis and IL-33 in a rat model. In this prospective experimental study, 16 female, nonpregnant Sprague-Dawley albino rats (12 weeks, 220-240 g) were randomly divided into two groups. Group 1 included eight healthy nondiabetic rats as controls and group 2 included eight rats in which diabetes was induced by intraperitoneal (i.p) injection of streptozotocin (STZ). After overt DM occurred (blood glucose >400 mgr/dl), all animals were euthanized and blood samples were collected by cardiac puncture for biochemical analysis. Bilateral oophorectomy was performed for histopathological examination. Serum levels of IL-33 and ovarian IL-33 and caspase-3 immunoexpressions were assessed. Immunoexpressions of caspase-3 and IL-33 were significantly higher in ovarian stromal cells of the diabetic rats compared to the controls. Also, in diabetic group, serum IL33 levels were significantly higher than the control group. In conclusion, increased IL-33 was observed both in serum and ovaries of STZ-induced diabetic rats as well as increased apoptosis in these diabetic rats. IL-33 may contribute to the apoptosis in diabetic ovarian injury.

IL-33-matured dendritic cells promote Th17 cell responses via IL-1β and IL-6

IL-33 is associated with a variety of autoimmune diseases, such as sclerosis, inflammatory bowel disease, and rheumatoid arthritis. Although IL-33 is mainly involved in the induction of Th2 cells, however, the relationship between IL-33 and Th17 cells is still largely unknown. In this study, we investigated the effects of IL-33 on DC-mediated CD4⁺ T cell activation and Th17 cell differentiation because DCs are essential cells for presenting self-antigens to CD4⁺ T cells in autoimmune disease conditions. OT-II mice were injected with IL-33-treated DCs or untreated DCs that were primed by OVA_323-339 peptide, and their Th17 cell responses were compared. Th17 cell population and IL-17 expression levels were significantly increased in draining lymph nodes of mice injected with IL-33-treated DCs, compared with those in mice injected with untreated DCs. IL-33 treatment maturated DCs to present self-antigens and to increase production of proinflammatory cytokines such as IL-1β and IL-6, which have a crucial role in Th17 cell differentiation. We found that the IL-33-matured DCs enhanced the expression of an early T cell activation marker (CD69) and the Th17 master transcription factor (RORγt), but IL-33 did not directly affect CD4⁺ T cell differentiation or increase Th17 polarization. Notably, neutralizing IL-1β and/or IL-6 significantly decreased IL-17 expression levels and Th17 cell population which were increased by the coculture of CD4⁺ T cells with IL-33-matured DCs, indicating that IL-33 may induce Th17 cell responses via IL-1β and IL-6 derived from IL-33-matured DCs.

Epithelial-derived IL-33 promotes intestinal tumorigenesis in Apc Min/+ mice

Increased expression of Interleukin (IL)-33 has been detected in intestinal samples of patients with ulcerative colitis, a condition associated with increased risk for colon cancer, but its role in the development of colorectal cancer has yet to be fully examined. Here, we investigated the role of epithelial expressed IL-33 during development of intestinal tumors. IL-33 expression was detected in epithelial cells in colorectal cancer specimens and in the Apc^Min/+ mice. To better understand the role of epithelial-derived IL-33 in the intestinal tumorigenesis, we generated transgenic mice expressing IL-33 in intestinal epithelial cells (V33 mice). V33 Apc^Min/+ mice, resulting from the cross of V33 with Apc^Min/+ mice, had increased intestinal tumor burden compared with littermate Apc^Min/+ mice. Consistently, Apc^Min/+ mice deficient for IL-33 receptor (ST2), had reduced polyp burden. Mechanistically, overexpression of IL-33 promoted expansion of ST2⁺ regulatory T cells, increased Th2 cytokine milieu, and induced alternatively activated macrophages in the gut. IL-33 promoted marked changes in the expression of antimicrobial peptides, and antibiotic treatment of V33 Apc^Min/+ mice abrogated the tumor promoting-effects of IL-33 in the colon. In conclusion, elevated IL-33 signaling increases tumor development in the Apc^Min/+ mice.

The Role of IL-33 on LPS-Induced Acute Lung Injury in Mice

The objective of the study is to investigate the role and specific molecular mechanism of interleukin-33 (IL-33) acted on acute lung injury (ALI) induced by lipopolysaccharide (LPS). C57BL/6 mice intratracheally instilled LPS to induce ALI model. The mice were randomly divided into three groups: the sham operation group (Sham), ALI group (ALI), and pretreatment with IL-33 of ALI group (IL-33). By observing the survival rate, inflammatory cytokines in bronchoalveolar lavage fluid (BALF), myeloperoxidase (MPO) levels in lung tissue, lung histopathological examination, pulmonary capillary leakage, lung wet/dry (W/D) weight ratio, fibrosis levels in lung tissue, and associated pathways changes among the different groups, comparing to explore the role of IL-33 pretreatment on ALI mice and the possible molecular mechanisms. IL-33 pretreatment overall decreased the survival rate of ALI mice. IL-33 aggravated inflammation reaction showing as increasing the release of proinflammatory cytokines TNF-α and IL-6, increasing MPO levels in lung tissue, and aggravating lung pathology injury. In addition, IL-33 pretreatment further destroyed adherens junctions (AJs) by increasing the phosphorylation of VE-cadherin, resulting in the concomitantly pulmonary capillary barrier damage and pulmonary edema. During this process, mitogen-activated protein kinase (MAPK) pathways further activated. However, IL-33 pretreatment had no significant impact on collagen content of lung tissue. Our results indicated that IL-33 aggravated inflammatory reaction and increased microvascular permeability, but had little effect on pulmonary fibrosis, associated with the further activation of MAPK family proteins in the process. To sum up, IL-33 decreased survival rate and aggravated LPS-induced ALI.

IL-33 restricts tumor growth and inhibits pulmonary metastasis in melanoma-bearing mice through eosinophils

The alarmin IL-33 is an IL-1 family member that stimulates pleiotropic immune reactions depending on the target tissue and microenvironmental factors. In this study, we have investigated the role of IL-33/ST2 axis in antitumor response to melanoma. Injection of IL-33 in mice-bearing subcutaneous B16.F10 melanoma resulted in significant tumor growth delay. This effect was associated with intratumoral accumulation of CD8⁺ T cells and eosinophils, decrease of immunosuppressive myeloid cells, and a mixed Th1/Th2 cytokine expression pattern with local and systemic activation of CD8⁺ T and NK cells. Moreover, intranasal administration of IL-33 determined ST2-dependent eosinophil recruitment in the lung that prevented the onset of pulmonary metastasis after intravenous injection of melanoma cells. Accordingly, ST2-deficient mice developed pulmonary metastasis at higher extent than wild-type counterparts, associated with lower eosinophil frequencies in the lung. Of note, depletion of eosinophils by in vivo treatment with anti-Siglec-F antibody abolished the ability of IL-33 to both restrict primary tumor growth and metastasis formation. Finally, we show that IL-33 is able to activate eosinophils resulting in efficient killing of target melanoma cells, suggesting a direct antitumor activity of eosinophils following IL-33 treatment. Our results advocate for an eosinophil-mediated antitumoral function of IL-33 against melanoma, thus opening perspectives for novel cancer immunotherapy strategies.

Divide, Conquer, and Sense: CD8+CD28- T Cells in Perspective

Understanding the rationale for the generation of a pool of highly differentiated effector memory CD8⁺ T cells displaying a weakened capacity to scrutinize for peptides complexed with major histocompatibility class I molecules via their T cell receptor, lacking the “signal 2” CD28 receptor, and yet expressing a highly diverse array of innate receptors, from natural killer receptors, interleukin receptors, and damage-associated molecular pattern receptors, among others, is one of the most challenging issues in contemporary human immunology. The prevalence of these differentiated CD8⁺ T cells, also known as CD8⁺CD28⁻, CD8⁺KIR⁺, NK-like CD8⁺ T cells, or innate CD8⁺ T cells, in non-lymphoid organs and tissues, in peripheral blood of healthy elderly, namely centenarians, but also in stressful and chronic inflammatory conditions suggests that they are not merely end-of-the-line dysfunctional cells. These experienced CD8⁺ T cells are highly diverse and capable of sensing a variety of TCR-independent signals, which enables them to respond and fine-tune tissue homeostasis.

IL-33-Induced Cytokine Secretion and Survival of Mouse Eosinophils Is Promoted by Autocrine GM-CSF

Eosinophils are major effector cells during allergic responses and helminth infections. Recent studies further highlight eosinophils as important players in many other biological processes. Therefore it is important to understand how these cells can be modulated in terms of survival and effector function. In the present study we investigated how eosinophils respond to the alarmin IL-33. We show that IL-33 promotes eosinophil survival in a ST2- and MyD88-dependent manner. IL-33-mediated protection from apoptosis was dependent on autocrine GM-CSF release. In addition, GM-CSF increased the IL-33-induced secretion of IL-4 and IL-13 from eosinophils. Unexpectedly, this effect was further enhanced by cross-linking of Siglec-F, a proposed inhibitory and apopotosis-inducing receptor on eosinophils. Co-culture experiments with eosinophils and macrophages revealed that the IL-33-induced release of IL-4 and IL-13 from eosinophils was required for differentiation of alternatively activated macrophages (AAMs). The differentiation of AAMs could be further increased in the presence of GM-CSF. These results indicate that cross-talk between Siglec-F and the receptors for IL-33, LPS and GM-CSF plays an important role for efficient secretion of IL-4 and IL-13. Deciphering the molecular details of this cross-talk could lead to the development of new therapeutic option to treat eosinophil-associated diseases.

Lactic Acid Suppresses IL-33-Mediated Mast Cell Inflammatory Responses via Hypoxia-Inducible Factor-1α-Dependent miR-155 Suppression

Lactic acid (LA) is present in tumors, asthma, and wound healing, environments with elevated IL-33 and mast cell infiltration. Although IL-33 is a potent mast cell activator, how LA affects IL-33-mediated mast cell function is unknown. To investigate this, mouse bone marrow-derived mast cells were cultured with or without LA and activated with IL-33. LA reduced IL-33-mediated cytokine and chemokine production. Using inhibitors for monocarboxylate transporters (MCT) or replacing LA with sodium lactate revealed that LA effects are MCT-1- and pH-dependent. LA selectively altered IL-33 signaling, suppressing TGF-β-activated kinase-1, JNK, ERK, and NF-κB phosphorylation, but not p38 phosphorylation. LA effects in other contexts have been linked to hypoxia-inducible factor (HIF)-1α, which was enhanced in bone marrow-derived mast cells treated with LA. Because HIF-1α has been shown to regulate the microRNA miR-155 in other systems, LA effects on miR-155-5p and miR-155-3p species were measured. In fact, LA selectively suppressed miR-155-5p in an HIF-1α-dependent manner. Moreover, overexpressing miR-155-5p, but not miR-155-3p, abolished LA effects on IL-33-induced cytokine production. These in vitro effects of reducing cytokines were consistent in vivo, because LA injected i.p. into C57BL/6 mice suppressed IL-33-induced plasma cytokine levels. Lastly, IL-33 effects on primary human mast cells were suppressed by LA in an MCT-dependent manner. Our data demonstrate that LA, present in inflammatory and malignant microenvironments, can alter mast cell behavior to suppress inflammation.

Ablation of interaction between IL-33 and ST2+ regulatory T cells increases immune cell-mediated hepatitis and activated NK cell liver infiltration

The IL-33/ST2 axis plays a protective role in T-cell-mediated hepatitis, but little is known about the functional impact of endogenous IL-33 on liver immunopathology. We used IL-33-deficient mice to investigate the functional effect of endogenous IL-33 in concanavalin A (Con A)-hepatitis. IL-33(-/-) mice displayed more severe Con A liver injury than wild-type (WT) mice, consistent with a hepatoprotective effect of IL-33. The more severe hepatic injury in IL-33(-/-) mice was associated with significantly higher levels of TNF-α and IL-1β and a larger number of NK cells infiltrating the liver. The expression of Th2 cytokines (IL-4, IL-10) and IL-17 was not significantly varied between WT and IL-33(-/-) mice following Con A-hepatitis. The percentage of CD25(+) NK cells was significantly higher in the livers of IL-33(-/-) mice than in WT mice in association with upregulated expression of CXCR3 in the liver. Regulatory T cells (Treg cells) strongly infiltrated the liver in both WT and IL-33(-/-) mice, but Con A treatment increased their membrane expression of ST2 and CD25 only in WT mice. In vitro, IL-33 had a significant survival effect, increasing the total number of splenocytes, including B cells, CD4(+) and CD8(+) T cells, and the frequency of ST2(+) Treg cells. In conclusion, IL-33 acts as a potent immune modulator protecting the liver through activation of ST2(+) Treg cells and control of NK cells.