Interleukin-33 in health and disease. Nat Rev Immunol. 2016;16:676-689. [PMID: 27640624 DOI: 10.1038/nri.2016.95]

The ST2/Interleukin-33 Axis in Hematologic Malignancies: The IL-33 Paradox

Interleukin (IL)-33 is a chromatin-related nuclear interleukin that is a component of IL-1 family. IL-33 production augments the course of inflammation after cell damage or death. It is discharged into the extracellular space. IL-33 is regarded as an “alarmin” able to stimulate several effectors of the immune system, regulating numerous immune responses comprising cancer immune reactions. IL-33 has been demonstrated to influence tumorigenesis. However, as far as this cytokine is concerned, we are faced with what has sometimes been defined as the IL-33 paradox. Several studies have demonstrated a relevant role of IL-33 to numerous malignancies, where it may have pro- and—less frequently—antitumorigenic actions. In the field of hematological malignancies, the role of IL-33 seems even more complex. Although we can affirm the existence of a negative role of IL-33 in Chronic myelogenos leukemia (CML) and in lymphoproliferative diseases and a positive role in pathologies such as Acute myeloid leukemia (AML), the action of IL-33 seems to be multiple and sometimes contradictory within the same pathology. In the future, we will have to learn to govern the negative aspects of activating the IL-33/ST2 axis and exploit the positive ones.

Helicobacter pylori Induces IL-33 Production and Recruits ST-2 to Lipid Rafts to Exacerbate Inflammation

Helicobacter pylori colonizes human gastric epithelial cells and contributes to the development of several gastrointestinal disorders. Interleukin (IL)-33 is involved in various immune responses, with reported proinflammatory and anti-inflammatory effects, which may be associated with colitis and colitis-associated cancer. IL-33 induces the inflammatory cascade through its receptor, suppression of tumorigenicity-2 (ST-2). Binding of IL-33 to membrane-bound ST-2 (mST-2) recruits the IL-1 receptor accessory protein (IL-1RAcP) and activates intracellular signaling pathways. However, whether IL-33/ST-2 is triggered by H. pylori infection and whether this interaction occurs in lipid rafts remain unclear. Our study showed that both IL-33 and ST-2 expression levels were significantly elevated in H. pylori-infected cells. Confocal microscopy showed that ST-2 mobilized into the membrane lipid rafts during infection. Depletion of membrane cholesterol dampened H. pylori-induced IL-33 and IL-8 production. Furthermore, in vivo studies revealed IL-33/ST-2 upregulation, and severe leukocyte infiltration was observed in gastric tissues infected with H. pylori. Together, these results demonstrate that ST-2 recruitment into the lipid rafts serves as a platform for IL-33-dependent H. pylori infection, which aggravates inflammation in the stomach.

Calcitonin Gene-Related Peptide Negatively Regulates Alarmin-Driven Type 2 Innate Lymphoid Cell Responses

Neuroimmune interactions have emerged as critical modulators of allergic inflammation, and type 2 innate lymphoid cells (ILC2s) are an important cell type for mediating these interactions. Here, we show that ILC2s expressed both the neuropeptide calcitonin gene-related peptide (CGRP) and its receptor. CGRP potently inhibited alarmin-driven type 2 cytokine production and proliferation by lung ILC2s both in vitro and in vivo. CGRP induced marked changes in ILC2 expression programs in vivo and in vitro, attenuating alarmin-driven proliferative and effector responses. A distinct subset of ILCs scored highly for a CGRP-specific gene signature after in vivo alarmin stimulation, suggesting CGRP regulated this response. Finally, we observed increased ILC2 proliferation and type 2 cytokine production as well as exaggerated responses to alarmins in mice lacking the CGRP receptor. Together, these data indicate that endogenous CGRP is a critical negative regulator of ILC2 responses in vivo.

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.

Association of TREM-1, IL-1β, IL-33/ST2, and TLR Expressions With the Pathogenesis of Ocular Toxoplasmosis in Mouse Models on Different Genetic Backgrounds

Ocular toxoplasmosis (OT) is one of the most common causes of posterior uveitis. The signaling of triggering receptor expressed on myeloid cells (TREM)-1 amplifies inflammation, whereas TREM-2 signaling is anti-inflammatory. IL-1β is a major driver of inflammation during infection. Toll-like receptors (TLRs) play important roles in protective immune response during Toxoplasma gondii infection, and interleukin (IL)-33 receptor (T1/ST2) signaling prevents toxoplasmic encephalitis in mice. However, the pathogenic mechanisms of OT are not yet well elucidated. To investigate the role of TREM-1, TREM-2, IL-1β, IL-33/ST2, and TLRs in OT of susceptible C57BL/6 (B6) and resistant BALB/c mice, both strains of mice were intravitreally infected with 500 tachyzoites of the RH strain of T. gondii. Histopathological analysis showed that T. gondii-infected B6 mice had more severe ocular damage observed by light microscopy, higher number of neutrophil elastase-positive cells in the eyes detected by immunohistochemical staining, more T. gondii tachyzoites in the eyes observed by transmission electron microscopy, and higher mRNA expression levels of tachyzoite-specific surface antigen 1 detected by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) in comparison of T. gondii-infected BALB/c mice. Detected by using qRT-PCR, the mRNA expression levels of TREM-1, IL-1β, IL-33, ST2, TLR11, TLR12, and TLR13 were significantly higher in the eyes of T. gondii-infected B6 mice than those of T. gondii-infected BALB/c mice, whereas the mRNA expression levels of TLR3 and TLR9 were significantly higher in the eyes of T. gondii-infected BALB/c mice than those of T. gondii-infected B6 mice. Correlation analysis showed that significant positive correlations existed between TREM-1 and IL-1β/IL-33/ST2/TLR9/TLR11 in the eyes of B6 mice and existed between TREM-1 and IL-33/ST2/TLR3/TLR9/TLR13 in the eyes of BALB/c mice after ocular T. gondii infection. Our data revealed that, compared with T. gondii-resistant BALB/c mice, ocular T. gondii infection can stimulate higher production of TREM-1, IL-33, ST2, TLR11, TLR12, and TLR13 in the eyes of T. gondii-susceptible B6 mice, however, whether those lead to more severe ocular pathology in the susceptible B6 mice remain to be further studied.

RelB Deficiency in Dendritic Cells Protects from Autoimmune Inflammation Due to Spontaneous Accumulation of Tissue T Regulatory Cells

Foxp3⁺ regulatory T cells are well-known immune suppressor cells in various settings. In this study, we provide evidence that knockout of the relB gene in dendritic cells (DCs) of C57BL/6 mice results in a spontaneous and systemic accumulation of Foxp3⁺ T regulatory T cells (Tregs) partially at the expense of microbiota-reactive Tregs. Deletion of nfkb2 does not fully recapitulate this phenotype, indicating that alternative NF-κB activation via the RelB/p52 complex is not solely responsible for Treg accumulation. Deletion of RelB in DCs further results in an impaired oral tolerance induction and a marked type 2 immune bias among accumulated Foxp3⁺ Tregs reminiscent of a tissue Treg signature. Tissue Tregs were fully functional, expanded independently of IL-33, and led to an almost complete Treg-dependent protection from experimental autoimmune encephalomyelitis. Thus, we provide clear evidence that RelB-dependent pathways regulate the capacity of DCs to quantitatively and qualitatively impact on Treg biology and constitute an attractive target for treatment of autoimmune diseases but may come at risk for reduced immune tolerance in the intestinal tract.

ILC2 Activation by Protozoan Commensal Microbes

Group 2 innate lymphoid cells (ILC2s) are a member of the ILC family and are involved in protective and pathogenic type 2 responses. Recent research has highlighted their involvement in modulating tissue and immune homeostasis during health and disease and has uncovered critical signaling circuits. While interactions of ILC2s with the bacterial microbiome are rather sparse, other microbial members of our microbiome, including helminths and protozoans, reveal new and exciting mechanisms of tissue regulation by ILC2s. Here we summarize the current field on ILC2 activation by the tissue and immune environment and highlight particularly new intriguing pathways of ILC2 regulation by protozoan commensals in the intestinal tract.

Pilot-Scale Study Of Human Plasma Proteomics Identifies ApoE And IL33 As Markers In Atopic Asthma

Background

The pathobiology of atopic asthma is complex and the symptoms similar to other respiratory diseases. As such, identification of biomarkers of atopic asthma is of prime importance for better diagnosis and control of the disease.

Objectives

We sought to study the changes in plasma proteome and cytokine-expression profile across healthy and atopic asthmatics for identifying biomarkers and exploring aberrant pathways for atopic asthma.

Methods

A pilot-scale study in humans was performed to identify differentially expressed proteins in blood plasma of healthy controls (n=5) and treatment-naïve atopic asthma patients (n=5) using quantitative label-free liquid chromatography-tandem mass spectrometry proteomics and ELISA.

Results

Mass spectrometry-based proteomic analysis revealed ApoE to be significantly downregulated in atopic asthmatics compared to healthy volunteers. Decreased expression of ApoE in atopic asthmatics was validated by immunoblotting (50.74% decrease). Comparison with atopic asthmatics and COPD patients showed that ApoE was decreased (36.33%) in atopic asthma compared to COPD. IL33 was significantly upregulated in atopic asthmatics compared to healthy subjects (3.84-fold).

Conclusion

ApoE was downregulated and IL33 upregulated in atopic asthma patients compared to healthy volunteers. These two proteins' profiles were distinct in atopic asthma from healthy and COPD plasma samples. Differential expression of these proteins could serve as a probable candidate for a two-protein classifier-based prognostic biomarker of atopic asthma.

IL-33 Is a Cell-Intrinsic Regulator of Fitness during Early B Cell Development

IL-33 is an IL-1 family member protein that is a potent driver of inflammatory responses in both allergic and nonallergic disease. This proinflammatory effect is mediated primarily by extracellular release of IL-33 from stromal cells and binding of the C-terminal domain of IL-33 to its receptor ST2 on targets such as CD4+ Th2 cells, ILC2, and mast cells. Notably, IL-33 has a distinct N-terminal domain that mediates nuclear localization and chromatin binding. However, a defined in vivo cell-intrinsic role for IL-33 has not been established. We identified IL-33 expression in the nucleus of progenitor B (pro-B) and large precursor B cells in the bone marrow, an expression pattern unique to B cells among developing lymphocytes. The IL-33 receptor ST2 was not expressed within the developing B cell lineage at either the transcript or protein level. RNA sequencing analysis of wild-type and IL-33-deficient pro-B and large precursor B cells revealed a unique, IL-33-dependent transcriptional profile wherein IL-33 deficiency led to an increase in E2F targets, cell cycle genes, and DNA replication and a decrease in the p53 pathway. Using mixed bone marrow chimeric mice, we demonstrated that IL-33 deficiency resulted in an increased frequency of developing B cells via a cell-intrinsic mechanism starting at the pro-B cell stage paralleling IL-33 expression. Finally, IL-33 was detectable during early B cell development in humans and IL33 mRNA expression was decreased in B cell chronic lymphocytic leukemia samples compared with healthy controls. Collectively, these data establish a cell-intrinsic, ST2-independent role for IL-33 in early B cell development.

Acute Respiratory Barrier Disruption by Ozone Exposure in Mice

Ozone exposure causes irritation, airway hyperreactivity (AHR), inflammation of the airways, and destruction of alveoli (emphysema), the gas exchange area of the lung in human and mice. This review focuses on the acute disruption of the respiratory epithelial barrier in mice. A single high dose ozone exposure (1 ppm for 1 h) causes first a break of the bronchiolar epithelium within 2 h with leak of serum proteins in the broncho-alveolar space, disruption of epithelial tight junctions and cell death, which is followed at 6 h by ROS activation, AHR, myeloid cell recruitment, and remodeling. High ROS levels activate a novel PGAM5 phosphatase dependent cell-death pathway, called oxeiptosis. Bronchiolar cell wall damage and inflammation upon a single ozone exposure are reversible. However, chronic ozone exposure leads to progressive and irreversible loss of alveolar epithelial cells and alveoli with reduced gas exchange space known as emphysema. It is further associated with chronic inflammation and fibrosis of the lung, resembling other environmental pollutants and cigarette smoke in pathogenesis of asthma, and chronic obstructive pulmonary disease (COPD). Here, we review recent data on the mechanisms of ozone induced injury on the different cell types and pathways with a focus on the role of the IL-1 family cytokines and the related IL-33. The relation of chronic ozone exposure induced lung disease with asthma and COPD and the fact that ozone exacerbates asthma and COPD is emphasized.

Tokishakuyakusan, a Kampo medicine, attenuates endometriosis-like lesions and hyperalgesia in murine with endometriosis-like symptoms

PROBLEM

How are the effects of Tokishakuyakusan (TSS), a traditional Japanese medicine (Kampo) on murine endometriosis model?

METHODS

BALB/c mice were used for making the murine endometriosis model. Homogeneous uterus was surgically implanted with lipopolysaccharide (LPS) in peritoneal cavity. We administered 2 weeks of TSS (1.0 g/kg) orally. Upon treatment completion, we performed the hot plate test for all mice and collected blood samples before sacrifice. Then, the endometriosis-like lesions and uteri in the abdominal cavity were harvested. Concentrations of several cytokines in sera and cyst fluids were measured using Bio-Plex Suspension Array System. IL-33 localization was determined by immunohistochemistry. Gene expression of inflammatory cytokines in the endometriosis-like lesions or the eutopic endometrium was evaluated by real-time RT-PCR.

RESULTS

After 14 days of TSS treatment, the numbers of endometriosis-like cysts and cyst weight were significantly decreased. In TSS-treated mice, the latency against heat stimuli was extended. Inflammatory cytokine concentrations in sera were not changed by TSS treatment. TSS intake decreased IL-33 mRNA expression in endometriosis-like lesions and led to the tendency of attenuation of the elevated IL-33 synthesis in the cyst fluids of lesions.

CONCLUSION

These results suggest the TSS ameliorated the hyperalgesia and lesion formation on the LPS-accelerated endometriosis-like model. TSS represents a possible ideal target of novel therapeutics for endometriosis patients with dysmenorrhea.

Exogenous Interleukin-33 Contributes to Protective Immunity via Cytotoxic T-Cell Priming against Mucosal Influenza Viral Infection

Influenza is an infectious respiratory illness caused by the influenza virus. Though vaccines against influenza exist, they have limited efficacy. To additionally develop effective treatments, there is a need to study the mechanisms of host defenses from influenza viral infections. To date, the mechanism by which interleukin (IL)-33 modulates the antiviral immune response post-influenza infection is unclear. In this study, we demonstrate that exogenous IL-33 enhanced antiviral protection against influenza virus infection. Exogenous IL-33 induced the recruitment of dendritic cells, increased the secretion of pro-inflammatory cytokine IL-12, and promoted cytotoxic T-cell responses in the local microenvironment. Thus, our findings suggest a role of exogenous IL-33 in the antiviral immune response against influenza infection.

Possible role of interleukin 21 and interleukin 33 in patients with genital warts

Genital warts (GWs) are most prevalent sexually transmitted infections, presenting especially among the sexually active young population of both sexes. Efficient cell-mediated immunity is needed for regression of GWs. To clarify the reactivity of cellular immunity among patients with GWs by means of measurements of their levels of serum interleukin (IL)-21 and IL-33, hence, to identify the possible role of IL-21 and IL-33 in GWs, this study aimed to evaluate serum levels of IL-21 and IL-33 among patients with GWs in comparison with the results of the controls. Levels of serum IL-21 and IL-33 were assayed utilizing commercially enzyme-linked immune-sorbent assay kits in 45 patients with GWs and 45 healthy control subjects. Levels of serum IL-21 and IL-33 were significantly decreased among patients with GWs in comparison with the controls (p < .0001). There was a highly significant positive correlation between IL-21 and IL-33 (r = .73, p < .0001). Low levels of serum IL-21 and IL-33 could have a contributive role in development, persistence, severity, and recurrence of GWs which rely basically on the defectiveness of cell-mediated immunity. This could receive new light on nonconventional strategies for the prospective medical therapies of GWs by means of regulation of IL-21 and IL-33.

Fibro-Adipogenic Progenitors Cross-Talk in Skeletal Muscle: The Social Network

Skeletal muscle is composed of a large and heterogeneous assortment of cell populations that interact with each other to maintain muscle homeostasis and orchestrate regeneration. Although satellite cells (SCs) – which are muscle stem cells – are the protagonists of functional muscle repair following damage, several other cells such as inflammatory, vascular, and mesenchymal cells coordinate muscle regeneration in a finely tuned process. Fibro–adipogenic progenitors (FAPs) are a muscle interstitial mesenchymal cell population, which supports SCs differentiation during tissue regeneration. During the first days following muscle injury FAPs undergo massive expansion, which is followed by their macrophage-mediated clearance and the re-establishment of their steady-state pool. It is during this critical time window that FAPs, together with the other cellular components of the muscle stem cell niche, establish a dynamic network of interactions that culminate in muscle repair. A number of different molecules have been recently identified as important mediators of this cross-talk, and its alteration has been associated with different muscle pathologies. In this review, we will focus on the soluble factors that regulate FAPs activity, highlighting their roles in orchestrating the inter-cellular interactions between FAPs and the other cell populations that participate in muscle regeneration.

Inhibitors of class I histone deacetylases attenuate thioacetamide-induced liver fibrosis in mice by suppressing hepatic type 2 inflammation

BACKGROUND AND PURPOSE

Chronic liver diseases feature excessive collagen and matrix protein deposition or crosslinking that characterises fibrosis, leads to scar tissue, and disrupts liver functions. There is no effective treatment. This study investigated whether treatment with selective histone deacetylase (HDAC) inhibitors might specifically reduce type 2 inflammation in the injured liver, thereby attenuating fibrogenesis in mice.

EXPERIMENTAL APPROACH

Thioacetamide (TAA) was used to induce hepatic inflammation, fibrosis, and liver damage in female C57BL/6 mice, similar to the clinical features of chronic human liver disease. We used eight inhibitors of different human HDAC enzymes to probe histological (IHC and TUNEL), biochemical and immunological changes (flow cytometry, qPCR, Legendplex, and ELISA) in pathology, fibrosis, hepatic immune cell flux, and inflammatory cytokine expression.

KEY RESULTS

Inhibitors of class I, but not class II, HDAC enzymes potently suppressed chronic hepatic inflammation and fibrosis in mice, attenuating accumulation and activation of IL-33-dependent, but not IL-25-dependent, group 2 innate lymphoid cells (ILC2) and inhibiting type 2 inflammation that drives hepatic stellate cells to secrete excessive collagen and matrix proteins.

CONCLUSIONS AND IMPLICATIONS

The results show that potent and selective inhibitors of class I only HDAC enzymes profoundly inhibit hepatocyte death and type 2 inflammation to prevent TAA-induced liver fibrosis in mice. The specific HDAC enzymes identified here may be key promoters of inflammation in chronic liver fibrosis.

IL-33 promotes the progression of nonrheumatic aortic valve stenosis via inducing differential phenotypic transition in valvular interstitial cells

OBJECTIVE

Interleukin (IL)-33 is a mediator in the pathogenesis of several inflammatory diseases. Its receptor, ST2, is overexpressed in nonrheumatic aortic valve stenosis (NR-AS). This study compared smooth muscle α-actin (α-SMA), osteopontin (OPN), and suppression of tumorigenicity 2 (ST2) expression between specimens from fibrotic and calcific stages of NR-AS and observed the effects and mechanisms of phenotypic transition of porcine valvular interstitial cells (VICs) in the presence of IL-33.

METHODS

Peripheral blood IL-1 family mRNA and protein levels in NR-AS patients and healthy adults were quantified by real-time quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay. Immunohistochemistry and immunofluorescence were used to detect the expression and coexpression of α-SMA, OPN, and ST2 in NR-AS specimens. Porcine VICs were stimulated with IL-33, IL-33+SB203580, or IL-33+SC75741. mRNA and protein expression levels of porcine VICs were detected by RT-qPCR and western blot.

RESULTS

The mRNA and protein levels of IL-33 and sST2 in peripheral blood of NR-AS patients were higher than those in healthy adults. Immunohistochemistry and immunofluorescence showed higher expression of α-SMA, OPN, and ST2 in the calcific stage of NR-AS than in the fibrotic stage. Coexpression of ST2/α-SMA or ST2/OPN was found only in the calcific stage. Nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK) phosphorylation levels were associated with IL-33-induced porcine VIC differentiation into myofibroblasts and osteoblasts, respectively. IL-33 stimulation also promoted the coexpression of ST2/OPN or α-SMA/OPN/ST2.

CONCLUSION

IL-33 might be a potential biomarker for NR-AS. IL-33-induced porcine VIC differential phenotypic transition and differentiation into myofibroblasts and osteoblasts were dependent on the NF-κB and p38 MAPK signaling pathways, respectively.

Acute exanthemas: a prospective study of 98 adult patients with an emphasis on cytokinic and metagenomic investigation

BACKGROUND

Acute exanthemas (AEs) are frequently seen; they can be caused by drugs or viruses but often the cause is unknown.

OBJECTIVES

To describe the clinical, virological and histological aspects of AEs and explore their cytokinic and metagenomic profiles.

METHODS

This prospective study examined 98 patients with AE, from February to July 2014. Clinical data were recorded in a standardized chart. Virological investigation and skin biopsies were performed. In addition, blood and skin samples were analysed for cytokines and then by a shotgun metagenomic approach. We identified five groups of patients: those with maculopapular exanthemas (MPEs) that were virally induced (group 1); those with drug-induced MPEs (group 2), those with MPEs that were both viral and drug induced (group 3), those with idiopathic MPEs (group 4) and those with pityriasis rosea (group 5).

RESULTS

A virus was identified in 29 cases (human herpesvirus 6, 72%). Cytokinic analysis of the skin (n = 23 MPEs) showed higher levels of interferon-γ and interleukin-1 receptor-α in viral MPEs, higher interleukin-33 levels in idiopathic MPEs, and higher macrophage inflammatory protein 1α levels in drug-induced MPEs. By metagenomics analysis (n = 10 MPEs), viruses identified with routine practice methods were not found in group 1 (n = 4 MPEs). However, Enterovirus A was detected in two cases, especially in a group 1 patient for whom metagenomic analysis rectified the diagnosis of the culprit agent.

CONCLUSIONS

Human herpesvirus 6 was the virus most frequently identified, and histology did not discriminate MPEs. In addition, the level of interleukin-33 seen in idiopathic MPEs suggests that an environmental factor may be the trigger for these. The results bring into question the utility of routine polymerase chain reaction analysis and viral serology for determining cause in AE. What's already known about this topic? Acute exanthemas, especially maculopapular exanthemas, are a frequent reason for patients consulting emergency and dermatology departments. It is difficult to evaluate the aetiology of acute exanthema based on the clinical aspects. Few data are available on the investigations needed in routine practice, and no prospective series have been published. What does this study add? Our study provides a global and prospective description of acute exanthemas. Cytokine analysis could help to investigate the pathophysiology of idiopathic eruptions. Metagenomic analysis provides new insights about the value of routine practice virological investigations. We show for the first time the feasibility of metagenomics analysis in the skin, which results question the interest of routine PCR and viral sérologies for the exploration of such acute exanthemas.

Memory CD8+ T Cell Protection From Viral Reinfection Depends on Interleukin-33 Alarmin Signals

Memory CD8⁺ cytotoxic T lymphocytes (CTLs) can protect against viral reinfection. However, the signals driving rapid memory CTL reactivation have remained ill-defined. Viral infections can trigger the release of the alarmin interleukin-33 (IL-33) from non-hematopoietic cells. IL-33 signals through its unique receptor ST2 to promote primary effector expansion and activation of CTLs. Here, we show that the transcription factor STAT4 regulated the expression of ST2 on CTLs in vitro and in vivo in primary infections with lymphocytic choriomeningitis virus (LCMV). In the primary antiviral response, IL-33 enhanced effector differentiation and antiviral cytokine production in a CTL-intrinsic manner. Further, using sequential adoptive transfers of LCMV-specific CD8⁺ T cells, we deciphered the IL-33 dependence of circulating memory CTLs at various stages of their development. IL-33 was found dispensable for the formation and maintenance of memory CTLs, and its absence during priming did not affect their recall response. However, in line with the CTL-boosting role of IL-33 in primary LCMV infections, circulating memory CTLs required IL-33 for efficient secondary expansion, enhanced effector functions, and virus control upon challenge infection. Thus, beyond their effector-promoting activity in primary immune reactions, innate alarmin signals also drive memory T cell recall responses, which has implications for immunity to recurrent diseases.

The interleukin-33-mediated inhibition of expression of two key genes implicated in atherosclerosis in human macrophages requires MAP kinase, phosphoinositide 3-kinase and nuclear factor-κB signaling pathways

Atherosclerosis, a chronic inflammatory disorder of the walls of arteries, causes more deaths worldwide than any other disease. Cytokines, which are present at high levels in atherosclerotic plaques, play important roles in regulating the initiation and the progression of the disease. Previous studies using animal and cell culture model systems revealed protective, anti-atherogenic effects of the cytokine interleukin-33 (IL-33). The action of this cytokine involves both the induction and suppression of expression of many genes. Unfortunately, the signaling pathways that are responsible for the inhibition of gene expression by this cytokine are poorly understood. Further studies are required given the important roles of genes whose expression is inhibited by IL-33 in key cellular processes associated with atherosclerosis such as monocyte recruitment, foam cell formation and lipoprotein metabolism. We have investigated here the roles of various known IL-33 activated signaling pathways in such inhibitory actions using RNA interference-mediated knockdown assays and monocyte chemotactic protein-1 and intercellular adhesion molecule-1 as model genes. Key roles were identified for extracellular signal-regulated kinase-1/2, p38α kinase, c-Jun N-terminal kinase-1/2, phosphoinositide 3-kinase-γ, and p50 and p65 nuclear factor-κB in such inhibitory action of IL-33. These studies provide new insights on the signaling pathways through which IL-33 inhibits the macrophage expression of key atherosclerosis-associated genes.

Epithelial origin of eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic, allergen-driven inflammatory disease of the esophagus characterized predominantly by eosinophilic inflammation, leading to esophageal dysfunction. Converging data have placed the esophageal epithelium at the center of disease pathogenesis. In particular, the main EoE disease susceptibility loci at 2p23 and 5p22 encode for gene products that are produced by the esophageal epithelium: the intracellular protease calpain 14 and thymic stromal lymphopoietin, respectively. Furthermore, genetic and functional data establish a primary role for impaired epithelial barrier function in disease susceptibility and pathoetiology. Additionally, the EoE transcriptome, a set of genes dysregulated in the esophagi of patients with EoE, is enriched in genes that encode for proteins involved in esophageal epithelial cell differentiation. This transcriptome has a high proportion of esophagus-specific epithelial genes that are notable for the unexpected enrichment in genes encoding for proteases and protease inhibitors, as well as in IL-1 family genes, demonstrating a previously unappreciated role for innate immunity responses in the esophagus under homeostatic conditions. Among these pathways, basal production of the serine protease inhibitor, Kazal-type 7 (SPINK7) has been demonstrated to be part of the normal differentiation program of esophageal epithelium. Profound lost expression of SPINK7 occurs in patients with EoE and is sufficient for unleashing increased proteolytic activity (including urokinase plasminogen activator), impaired barrier function, and production of large quantities of proinflammatory and proallergic cytokines, including thymic stromal lymphopoietin. Collectively, we put forth a model in which the esophagus is normally equipped as an anti-inflammatory sensing organ and that defects in this pathway, mediated by epithelial protease/protease inhibitor imbalances, unleash inflammatory responses resulting in disorders, such as EoE.

IL-33 and its increased serum levels as an alarmin for imminent pulmonary complications in polytraumatized patients

Background

According to recently published findings, we hypothesized that serum interleukin-33 (IL-33) may qualify for predicting pulmonary complications in polytraumatized patients.

Methods

One hundred and thirty patients (age ≥ 18 years, ISS ≥ 16) were included in our prospective analysis after primary admission to our level I trauma center during the first post-traumatic hour. Serum samples immediately after admission and on day 2 after trauma were obtained and analyzed.

Results

Median initial IL-33 levels (in picograms per milliliter) were higher in polytrauma victims (1) with concomitant thoracic trauma [5.08 vs. 3.52; p = 0.036], (2) sustaining parenchymal lung injury (PLI) [5.37 vs. 3.71; p = 0.027], and (3) developing acute respiratory distress syndrome (ARDS) [6.19 vs. 4.48; p = 0.003], compared to the respective rest of the study group. The median initial IL-33 levels were higher in patients experiencing both PLI and ARDS compared to those sustaining PLI and not developing ARDS [6.99 vs. 4.69; p = 0.029]. ROC statistics provided an AUC of 0.666 (p = 0.003) and a cut-off value of 4.77 (sensitivity, 71.8%; specificity, 75.7%) for predicting ARDS. Moreover, a higher initial median IL-33 level was revealed in the deceased compared to the survivors [12.25 vs. 4.72; p = 0.021]. ROC statistics identified the initial level of IL-33 as a predictor of death with 11.19 as cut-off value (sensitivity, 80.0%; specificity, 80.0%; AUC = 0.805; p = 0.021).

Conclusions

Following tissue damage, IL-33 is abundantly released in the serum of polytraumatized patients immediately after their injuries occurred. As initial IL-33 levels were particularly high in individuals experiencing both PLI and ARDS, IL-33 release after trauma seems to be involved in the promotion of ARDS and might serve already at admission as a solid indicator of impending death in polytraumatized patients.

IL-1 Family Members Mediate Cell Death, Inflammation and Angiogenesis in Retinal Degenerative Diseases

Inflammation underpins and contributes to the pathogenesis of many retinal degenerative diseases. The recruitment and activation of both resident microglia and recruited macrophages, as well as the production of cytokines, are key contributing factors for progressive cell death in these diseases. In particular, the interleukin 1 (IL-1) family consisting of both pro- and anti-inflammatory cytokines has been shown to be pivotal in the mediation of innate immunity and contribute directly to a number of retinal degenerations, including Age-Related Macular Degeneration (AMD), diabetic retinopathy, retinitis pigmentosa, glaucoma, and retinopathy of prematurity (ROP). In this review, we will discuss the role of IL-1 family members and inflammasome signaling in retinal degenerative diseases, piecing together their contribution to retinal disease pathology, and identifying areas of research expansion required to further elucidate their function in the retina.

Immunomodulation in Pediatric Asthma

Childhood asthma is actually defined as a heterogeneous disease, including different clinical variants and partially sharing similar immune mechanisms. Asthma management is mainly focused on maintaining the control of the disease and reducing the risk of adverse outcomes. Most children achieve good control with standard therapies, such as low doses of inhaled corticosteroids (ICS) and/or one or more controller. These medications are targeted to suppress bronchial inflammation and to restore airway responsiveness. However, they are not disease-modifying and do not specifically target inflammatory pathways of asthma; in addition, they are not significantly effective in patients with severe uncontrolled asthma. The aim of this review is to update knowledge on current and novel therapeutic options targeted to immunomodulate inflammatory pathways underlying pediatric asthma, with particular reference on biologic therapies.

Shaping the diversity of Th2 cell responses in epithelial tissues and its potential for allergy treatment

Th2 cells have evolved to protect from large helminth infections and to exert tissue protective functions in response to nonmicrobial noxious stimuli. The initiation, maintenance, and execution of these functions depend on the integration of diverse polarizing cues by cellular sensors and molecular programs as well as the collaboration with cells that are coopted for signal exchange. The complexity of input signals and cellular collaboration generates tissue specific Th2 cell heterogeneity and specialization. In this review, we aim to discuss the advances and recent breakthroughs in our understanding of Th2 cell responses and highlight developmental and functional differences among T cells within the diversifying field of type 2 immunity. We will focus on factors provided by the tissue microenvironment and highlight factors with potential implications for the pathogenesis of allergic skin and lung diseases. Especially new insights into the role of immunometabolism, the microbiota and ionic signals enhance the complexity of Th2 cell regulation and warrant a critical evaluation. Finally, we will discuss how this ensemble of established knowledge and recent breakthroughs about Th2 immunobiology advance our understanding of the pathogenesis of allergic diseases and how this could be exploited for future immunotherapies.

Prostaglandin E2 (PGE2)-EP2 signaling negatively regulates murine atopic dermatitis-like skin inflammation by suppressing thymic stromal lymphopoietin expression

BACKGROUND

Atopic dermatitis (AD) is a common and chronic inflammatory skin disease of type 2 immunity. Keratinocyte-derived cytokines, including thymic stromal lymphopoietin (TSLP) and IL-33, are considered to induce the development of AD. Production of prostanoids, a family of lipid mediators, is increased in AD lesions. However, their physiologic functions remain to be clarified.

OBJECTIVES

We sought to elucidate the functions of prostanoids in the development of AD.

METHODS

The roles of prostanoids were investigated in a mouse model of AD induced by repeated application of hapten and PAM212, a keratinocyte cell line.

RESULTS

Application of indomethacin, which blocks prostanoid synthesis, leads to enhanced TSLP and IL-33 production in the skin, increased serum IgE levels, and exacerbation of skin inflammation in this AD model. The skin inflammation was attenuated in TSLP receptor-deficient mice but not in IL-33-deficient mice, and the indomethacin-enhanced type 2 immune responses were abolished in TSLP receptor-deficient mice. Indomethacin increased protease-activated receptor 2-mediated TSLP production in keratinocytes in vitro, and prostaglandin E₂ reversed the increase in TSLP levels through its receptor, the prostaglandin E₂ receptor (EP2), by downregulating surface expression of protease-activated receptor 2. Administration of an EP2 agonist canceled indomethacin-enhanced TSLP production and type 2 immune responses in the skin, whereas an EP2 antagonist caused an enhancement of TSLP production and type 2 immune responses in the skin.

CONCLUSION

Prostaglandin E₂-EP2 signaling negatively regulates murine AD-like skin inflammation by suppressing TSLP expression.

Advanced Molecular Knowledge of Therapeutic Drugs and Natural Products Focusing on Inflammatory Cytokines in Asthma

Asthma is a common respiratory disease worldwide. Cytokines play a crucial role in the immune system and the inflammatory response to asthma. Abnormal cytokine expression may lead to the development of asthma, which may contribute to pathologies of this disease. As cytokines exhibit pleiotropy and redundancy characteristics, we summarized them according to their biologic activity in asthma development. We classified cytokines in three stages as follows: Group 1 cytokines for the epithelial environment stage, Group 2 cytokines for the Th2 polarization stage, and Group 3 cytokines for the tissue damage stage. The recent cytokine-targeting therapy for clinical use (anti-cytokine antibody/anti-cytokine receptor antibody) and traditional medicinal herbs (pure compounds, single herb, or natural formula) have been discussed in this review. Studies of the Group 2 anti-cytokine/anti-cytokine receptor therapies are more prominent than the studies of the other two groups. Anti-cytokine antibodies/anti-cytokine receptor antibodies for clinical use can be applied for patients who did not respond to standard treatments. For traditional medicinal herbs, anti-asthmatic bioactive compounds derived from medicinal herbs can be divided into five classes: alkaloids, flavonoids, glycosides, polyphenols, and terpenoids. However, the exact pathways targeted by these natural compounds need to be clarified. Using relevant knowledge to develop more comprehensive strategies may provide appropriate treatment for patients with asthma in the future.

Elevations in Circulating sST2 Levels Are Associated With In-Hospital Mortality and Adverse Clinical Outcomes After Blunt Trauma

BACKGROUND

Soluble suppression of tumorigenicity 2 (sST2), a decoy receptor for interleukin (IL)-33, has emerged as a novel biomarker in various disease processes. Recent studies have elucidated the role of the sST2/IL-33 complex in modulating the balance of Th1/Th2 immune responses after tissue stress. However, the role of sST2 as a biomarker after traumatic injury remains unclear. To address this, we evaluated serum sST2 correlations with mortality and in-hospital adverse outcomes as endpoints in blunt trauma patients.

METHODS

We retrospectively analyzed clinical and biobank data of 493 blunt trauma victims 472 survivors (mean age: 48.4 ± 0.87; injury severity score [ISS]: 19.6 ± 0.48) and 19 nonsurvivors (mean age: 58.8 ± 4.5; ISS: 23.3 ± 2.1) admitted to the intensive care unit. Given the confounding impact of age on the inflammatory response, we derived a propensity-matched survivor subgroup (n = 19; mean age: 59 ± 3; ISS: 23.4 ± 2) using an IBM SPSS case-control matching algorithm. Serial blood samples were obtained from all patients (3 samples within the first 24 h and then once daily from day [D] 1 to D5 after injury). sST2 and twenty-nine inflammatory biomarkers were assayed using enzyme-linked immunosorbent assay and Luminex, respectively. Two-way analysis of variance on ranks was used to compare groups (P < 0.05). Spearman rank correlation was performed to determine the association of circulating sST2 levels with biomarker levels and in-hospital clinical outcomes.

RESULTS

Circulating sST2 levels of the nonsurvivor cohort were statistically significantly elevated at 12 h after injury and remained elevated up to D5 when compared either to the overall 472 survivor cohort or a matched 19 survivor subcohort. Admission sST2 levels obtained from the first blood draw after injury in the survivor cohort correlated positively with admission base deficit (correlation coefficient [CC] = 0.1; P = 0.02), international normalized ratio (CC = 0.1, P = 0.03), ISS (CC = 0.1, P = 0.008), and the average Marshall multiple organ dysfunction score between D2 and D5 (CC = 0.1, P = 0.04). Correlations with ISS revealed a positive correlation of ISS with plasma sST2 levels across the mild ISS (CC = 0.47, P < 0.001), moderate ISS (CC = 0.58, P < 0.001), and severe ISS groups (CC = 0.63, P < 0.001). Analysis of biomarker correlations in the matched survivor group over the initial 24 h after injury showed that sST2 correlates strongly and positively with IL-4 (CC = 0.65, P = 0.002), IL-5 (CC = 0.57, P = 0.01), IL-21 (CC = 0.52, P = 0.02), IL-2 (CC = 0.51, P = 0.02), soluble IL-2 receptor-α (CC = 0.5, P = 0.02), IL-13 (CC = 0.49, P = 0.02), and IL-17A (CC = 0.48, P = 0.03). This was not seen in the matched nonsurvivor group. sST2/IL-33 ratios were significantly elevated in nonsurvivors and patients with severe injury based on ISS ≥ 25.

CONCLUSIONS

Elevations in serum sST2 levels are associated with poor clinical trajectories and mortality after blunt trauma. High sST2 coupled with low IL-33 associates with severe injury, mortality, and worse clinical outcomes. These findings suggest that sST2 could serve as an early prognostic biomarker in trauma patients and that sustained elevations of sST2 could contribute to a detrimental suppression of IL-33 bioavailability in patients with high injury severity.

Reparative T lymphocytes in organ injury

Acute organ injuries such as acute cerebrovascular accidents, myocardial infarction, acute kidney injury, acute lung injury, and others are among the leading causes of death worldwide. Dysregulated or insufficient organ repair mechanisms limit restoration of homeostasis and contribute to chronic organ failure. Studies reveal that both humans and mice harness potent non-stem cells that are capable of directly or indirectly promoting tissue repair. Specific populations of T lymphocytes have emerged as important reparative cells with context-specific actions. These T cells can resolve inflammation and secrete reparative cytokines and growth factors as well as interact with other immune and stromal cells to promote the complex and active process of tissue repair. This Review focuses on the major populations of T lymphocytes known to mediate tissue repair, their reparative mechanisms, and the diseases in which they have been implicated. Elucidating and harnessing the mechanisms that promote the reparative functions of these T cells could greatly improve organ dysfunction after acute injury.

Group 2 Innate Lymphoid Cells in Airway Diseases

Group 2 innate lymphoid cells (ILC2s) are increasingly recognized as a key controller of type 2 inflammation, and are well known to be highly elevated in human airway type 2 inflammatory diseases including allergic rhinitis, chronic rhinosinusitis with nasal polyps, and asthma. ILC2-mediated production of type 2 cytokines initiates and amplifies airway inflammation via activation of eosinophils, B cells, mast cells, macrophages, fibroblasts, and epithelial cells in these diseases. ILC2s require at least three major signals to fully activate and robustly produce type 2 cytokines. IL-1 family cytokines (IL-1β, IL-18, IL-33), IL-25, and TNF superfamilies (TNF, TL1A, GITR-L, RANK-L) activate the NF-κB and AP-1 pathways that initiate production of IL-5 and IL-13. Lipid mediators (LTC4, LTD4, PGD2) and neuropeptide NMU promote production of IL-4 through the NFAT pathway. IL-2 and IL-7 family cytokines (IL-2, IL-7, IL-9, TSLP) activate the STAT5 pathway that induces survival of ILC2s and enhances cytokine production. The activation of STAT5 is necessary to potently induce cytokine- and lipid mediator-mediated production of type 2 cytokines. Inhibitory pathways for ILC2s have also become clearer. Type I and II interferons and IL-27 inhibit ILC2 functions through the activation of STAT1. Suppression mediated via β2-adrenergic receptor agonists, PGE2, and PGI2 occurs through cAMP and PKA. Glucocorticoid, testosterone, IL-10, and TGF-β are also able to inhibit ILC2-mediated production of type 2 cytokines. Blockage of ILC2 activators, activation of inhibitory pathways of ILC2s, and suppression of ILC2-mediated pathways including type 2 cytokines (IL-5, IL-13, IL-4Ra) may become therapeutic strategies for airway type 2 inflammatory diseases.

The group 2 innate lymphoid cell (ILC2) regulatory network and its underlying mechanisms

Group 2 innate lymphoid cells (ILC2s) play critical roles in the induction of type 2 inflammation, response to parasite infection, metabolic homeostasis, and tissue repair. These multifunctional roles of ILC2s are tightly controlled by complex regulatory systems in the local microenvironment, the disruption of which may cause various health problems. This review summarizes up-to-date knowledge regarding positive and negative regulators for ILC2s based on their function and signaling pathways, including activating cytokines (IL-33, IL-25; MAPK, NF-κB pathways), co-stimulatory cytokines (IL-2, IL-7, IL-9, TSLP; STAT5, IL-4; STAT6, TNF superfamily; MAPK, NF-κB pathways), suppressive cytokines (type1 IFNs, IFN-γ, IL-27; STAT1, IL-10, TGF-β), transdifferentiation cytokines (IL-12; STAT4, IL-1β, IL-18), lipid mediators (LTC4, LTD4, LTE4, PGD2; Ca²⁺ -NFAT pathways, PGE2, PGI2; AC/cAMP/PKA pathways, LXA4, LTB4), neuropeptides (NMU; Ca²⁺ -NFAT, MAPK pathways, VIP, CGRP, catecholamine, acetylcholine), sex hormones (androgen, estrogen), nutrients (butyrate; HDAC inhibitors, vitamins), and cell-to-cell interactions (ICOSL-ICOS; STAT5, B7-H6-NKp30, E-cadherin-KLRG1). This comprehensive review affords a better understanding of the regulatory network system for ILC2s, providing impetus to develop new treatment strategies for ILC2-related health problems.

Type 2 innate lymphoid cells in the induction and resolution of tissue inflammation

Type 2 immunity against pathogens is tightly regulated to ensure appropriate inflammatory responses that clear infection and prevent excessive tissue damage. Recent research has shown that type 2 innate lymphoid cells (ILC2s) contribute to steady-state tissue integrity and exert tissue-specific functions. However, upon exposure to inflammatory stimuli, they also initiate and amplify type 2 inflammation by inducing mucus production, eosinophilia, and Th2 differentiation. In this review, we discuss the regulation of ILC2 activation by transcription factors and metabolic pathways, as well as by extrinsic signals such as cytokines, lipid mediators, hormones, and neuropeptides. We also review recent discoveries about ILC2 plasticity and heterogeneity in different tissues, as revealed partly through single-cell RNA sequencing of transcriptional responses to various stimuli. Understanding the tissue-specific pathways that regulate ILC2 diversity and function is a critical step in the development of potential therapies for allergic diseases.

IL-33-mediated mast cell activation promotes gastric cancer through macrophage mobilization

The contribution of mast cells in the microenvironment of solid malignancies remains controversial. Here we functionally assess the impact of tumor-adjacent, submucosal mast cell accumulation in murine and human intestinal-type gastric cancer. We find that genetic ablation or therapeutic inactivation of mast cells suppresses accumulation of tumor-associated macrophages, reduces tumor cell proliferation and angiogenesis, and diminishes tumor burden. Mast cells are activated by interleukin (IL)-33, an alarmin produced by the tumor epithelium in response to the inflammatory cytokine IL-11, which is required for the growth of gastric cancers in mice. Accordingly, ablation of the cognate IL-33 receptor St2 limits tumor growth, and reduces mast cell-dependent production and release of the macrophage-attracting factors Csf2, Ccl3, and Il6. Conversely, genetic or therapeutic macrophage depletion reduces tumor burden without affecting mast cell abundance. Therefore, tumor-derived IL-33 sustains a mast cell and macrophage-dependent signaling cascade that is amenable for the treatment of gastric cancer.

Mast cells within the tumor microenvironment have controversial roles. Here, the authors show, using genetic mouse models, that in gastric cancer, mast cells at the periphery of the tumors are activated via cancer cell produced-IL33 and promote tumorigenesis by recruiting macrophages within the tumors.

Structural Basis of IL-1 Family Cytokine Signaling

Interleukin-1 (IL-1) family cytokines are key signaling molecules in both the innate and adaptive immune systems, mediating inflammation in response to a wide range of stimuli. The basic mechanism of signal initiation is a stepwise process in which an agonist cytokine binds its cognate receptor. Together, this cytokine-receptor complex recruits an often-common secondary receptor. Intracellularly, the Toll/IL-1 Receptor (TIR) domains of the two receptors are brought into close proximity, initiating an NF-κB signal transduction cascade. Due to the potent inflammatory response invoked by IL-1 family cytokines, several physiological mechanisms exist to inhibit IL-1 family signaling, including antagonist cytokines and decoy receptors. The numerous cytokines and receptors in the IL-1 superfamily are further classified into four subfamilies, dependent on their distinct cognate receptors—the IL-1, IL-33, and IL-36 subfamilies share IL-1RAcP as their secondary receptor, while IL-18 subfamily utilizes a distinct secondary receptor. Here, we describe how structural biology has informed our understanding of IL-1 family cytokine signaling, with a particular focus on molecular mechanisms of signaling complex formation and antagonism at the atomic level, as well as how these findings have advanced therapeutics to treat some chronic inflammatory diseases that are the result of dysregulated IL-1 signaling.

Divergent Effects of Acute and Prolonged Interleukin 33 Exposure on Mast Cell IgE-Mediated Functions

Background: Epithelial cytokines, including IL-33 and Thymic stromal lymphopoietin (TSLP), have attracted interest because of their roles in chronic allergic inflammation-related conditions such as asthma. Mast cells are one of the major targets of IL-33, to which they respond by secreting cytokines. Most studies performed thus far have investigated the acute effects of IL-33 on mast cells. In the current study, we investigated how acute vs. prolonged exposure of mast cells to IL-33 and TSLP affects mediator synthesis and IgE-mediated activation. Methods: Human lung mast cells (HLMCs), cord blood-derived mast cells (CBMCs), and the ROSA mast cell line were used for this study. Receptor expression and the levels of mediators were measured after treatment with IL-33 and/or TSLP. Results: IL-33 induced the release of cytokines. Prolonged exposure to IL-33 increased while TSLP reduced intracellular levels of tryptase. Acute IL-33 treatment strongly potentiated IgE-mediated activation. In contrast, 4 days of exposure to IL-33 decreased IgE-mediated activation, an effect that was accompanied by a reduction in FcεRI expression. Conclusion: We show that IL-33 plays dual roles in mast cells, in which its acute effects include cytokine release and the potentiation of IgE-mediated degranulation, whereas prolonged exposure to IL-33 reduces IgE-mediated activation. We conclude that mast cells act quickly in response to the alarmin IL-33 to initiate an acute inflammatory response, whereas extended exposure to IL-33 during prolonged inflammation reduces IgE-mediated responses. This negative feedback effect suggests the presence of a novel regulatory pathway that modulates IgE-mediated human mast cell responses.

Divergent Roles for the IL-1 Family in Gastrointestinal Homeostasis and Inflammation

Inflammatory disorders of the gastro-intestinal tract are a major cause of morbidity and significant burden from a health and economic perspective in industrialized countries. While the incidence of such conditions has a strong environmental component, in particular dietary composition, epidemiological studies have identified specific hereditary mutations which result in disequilibrium between pro- and anti-inflammatory factors. The IL-1 super-family of cytokines and receptors is highly pleiotropic and plays a fundamental role in the pathogenesis of several auto-inflammatory conditions including rheumatoid arthritis, multiple sclerosis and psoriasis. However, the role of this super-family in the etiology of inflammatory bowel diseases remains incompletely resolved despite extensive research. Herein, we highlight the currently accepted paradigms as they pertain to specific IL-1 family members and focus on some recently described non-classical roles for these pathways in the gastrointestinal tract. Finally, we address some of the shortcomings and sources of variance in the field which to date have yielded several conflicting results from similar studies and discuss the potential effect of these factors on data interpretation.

Interleukin‑33 promotes obstructive renal injury via macrophages

Chronic kidney disease is the outcome of most kidney diseases, and renal fibrosis is a pathological process involved in the progression of these disorders. The role of interleukin (IL)‑33 was previously investigated in fibrotic disorders affecting various organs, including liver, lungs and heart; however, its role in renal fibrosis remains unclear. Previous studies have demonstrated that macrophages are involved in obstructive renal injury. In the present study, the roles of IL‑33 and macrophages on renal fibrosis were investigated using a mouse model of unilateral ureteral obstruction (UUO). Compared with non‑obstructed kidneys, the expression levels of IL‑33 and its receptor, interleukin 1 receptor like 1, increased after UUO. Furthermore, the infiltration of macrophages and the degree of renal fibrosis increased after treatment with IL‑33. Additionally, the expression level of arginase‑1, a marker of M2 macrophages, increased in renal tissue. After depletion of macrophages, the administration of exogenous IL‑33 was not sufficient to reverse the reduction in fibrosis caused by elimination of these cells. Collectively, the present results suggested that IL‑33 promoted renal fibrosis in UUO‑induced renal injury by regulating macrophage polarization.

Role of IL-33 in transplant biology

Since the pro-inflammatory cytokine IL-33 and its receptor (ST2) are closely involved in regulating both innate and adaptive immune responses, it is conceivable that they may play an important role in organ transplantation. IL-33 is broadly expressed by multiple cell types such as fibroblasts, epithelial cells, and endothelial cells. As a strong inducer of type 2 helper T (Th2) cellular immune responses, IL-33 can significantly prolong allograft survival in organ transplantation partially via altering gene expression profiles and increasing frequency of regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). Nevertheless, the IL-33 signaling pathway and its underlying mechanisms remain largely undefined in transplant biology. This present mini-review summarizes recent advances in the studies concerning the IL-33/ST2 signaling pathway and the analysis of its biological function in the field transplantation. The literature points to a deleterious role of activation of the IL-33/ST2 signaling pathway, giving rise to ischemia/reperfusion, acute kidney injury and failure, acute heart rejection, as well as liver fibrosis. Under pro-inflammatory conditions, IL-33 expression is upregulated. Alteration of IL-33 levels has been suggested as a biomarker for predicting organ injury and ongoing allogeneic transplant outcome. These studies have deepened our understanding of immunobiological role of IL-33 and its receptor in organ transplantation. Modulation of the IL-33/ST2 signaling pathway might be utilized as a therapeutic target in the clinic.

Picroside II Isolated from Pseudolysimachion rotundum var. subintegrum Inhibits Glucocorticoid Refractory Serum Amyloid A (SAA) Expression and SAA-induced IL-33 Secretion

Chronic obstructive pulmonary disease (COPD) is a major inflammatory lung disease characterized by irreversible and progressive airflow obstruction. Although corticosteroids are often used to reduce inflammation, steroid therapies are insufficient in patients with refractory COPD. Both serum amyloid A (SAA) and IL-33 have been implicated in the pathology of steroid-resistant lung inflammation. Picroside II isolated from Pseudolysimachion rotundum var. subintegrum(Plantaginaceae) is a major bioactive component of YPL-001, which has completed phase-2a clinical trials in chronic obstructive pulmonary disease patients. In this study, we investigated whether picroside II is effective in treating steroid refractory lung inflammation via the inhibition of the SAA-IL-33 axis. Picroside II inhibited LPS-induced SAA1 expression in human monocytes, which are resistant to steroids. SAA induced the secretion of IL-33 without involving cell necrosis. Picroside II, but not dexamethasone effectively inhibited SAA-induced IL-33 expression and secretion. The inhibitory effect by picroside II was mediated by suppressing the mitogen-activated protein kinase (MAPK) p38, ERK1/2, and nuclear factor-κB pathways. Our results suggest that picroside II negatively modulates the SAA-IL-33 axis that has been implicated in steroid-resistant lung inflammation. These findings provide valuable information for the development of picroside II as an alternative therapeutic agent against steroid refractory lung inflammation in COPD.

IL-33/IL-33R in various types of carotid artery atherosclerotic lesions

OBJECTIVE

Inflammation plays a crucial role in the progression of atherosclerotic plaques. The aim of the study was to investigate serum levels and expression of Interleukin-33 (IL-33) and ST2 receptor in atherosclerotic plaques and to analyze correlation with the type of the carotid plaques in patients with carotid disease.

METHODS

This study included 191 consecutive patients submitted for carotid endarterectomy (CEA). Preoperative serum levels of IL-33 and soluble ST2 (sST2) were measured. Atherosclerotic plaques obtained during surgery were initially histologically classified and immunohistochemical analyzes of IL-33, IL-33R, CD68 and alpha-SMA expression was performed. Ultrasound assessment of the level of carotid stenosis in each patient was performed prior to carotid surgery. Demographic and clinical data such as gender, age, smoking status, blood pressure, glycaemia, hemoglobin and creatinine levels, and comorbidities were collected and the comparisons between variables were statistically evaluated.

RESULTS

Serum levels of IL-33 (35.86 ± 7.93 pg/ml vs.12.29 ± 1.8 pg/ml, p < 0.05) and sST2 (183 ± 8.03 pg/ml vs. 122.31 ± 15.89 pg/ml, p < 0.05) were significantly higher in the group of CEA patients vs. healthy subjects. We demonstrated abundant tissue expression of IL-33 and ST2 in atherosclerotic carotid artery lesions. The levels of IL-33 and IL-33R expression were significantly higher in vulnerable plaques and significantly correlated with the degree of inflammatory cells infiltration in these plaques (R = 0.579, p = 0.049). Immunohistochemical analysis also revealed that cells responsible for IL-33 expression are not only mononuclear cells confined to inflammatory atherosclerotic lesions, but also smooth muscle cells which gained phenotypic characteristics of foam cells and were loaded with lipid droplets.

CONCLUSION

The obtained results confirm the importance of IL-33/ST2 axis in the process of atherosclerosis, and indicate its ambiguous function in immune response, whether as proinflammatory cytokine in advanced atherosclerotic lesions, or as profibrotic, in early lesions.

[Interleukin-33: from biology to potential treatments]

Interleukin-33 is a member of the IL-1 cytokine family, expressed in the nucleus of endothelial cells and epithelial cells of barrier tissues. After cellular damage, IL-33 is released in the extracellular space and functions as an alarmin that alerts the immune system. IL-33 plays a critical role in type-2 innate immunity and allergic inflammation, by activating various target cells including mast cells and innate lymphoid cells that secrete high amounts of IL-5 and IL-13, two cytokines involved in allergic reactions. Recent studies suggest that IL-33 can also play other important roles, for example in homeostasis and during viral infection. It is implicated in numerous diseases, including allergic, inflammatory and infectious diseases and it constitutes a promising therapeutic target for treatment of severe asthma.

IL233, an IL-2-IL-33 hybrid cytokine induces prolonged remission of mouse lupus nephritis by targeting Treg cells as a single therapeutic agent

Lupus glomerulonephritis (GN) is an autoimmune disease characterized by immune complex-deposition, complement activation and glomerular inflammation. In lupus-prone NZM2328 mice, the occurrence of lupus GN was accompanied by a decrease in Treg cells and an increase in proinflammatory cytokine-producing T cells. Because IL-33 in addition to IL-2 has been shown to be important for Treg cell proliferation and ST2 (IL-33 receptor) positive Treg cells are more potent in suppressor activity, a hybrid cytokine with active domains of IL-2 and IL-33 was generated to target the ST2⁺ Treg cells as a therapeutic agent to treat lupus GN. Three mouse models were used: spontaneous and Ad-IFNα- accelerated lupus GN in NZM2328 and the lymphoproliferative autoimmune GN in MRL/lpr mice. Daily injections of IL233 for 5 days prevented Ad-IFNα-induced lupus GN and induced remission of spontaneous lupus GN. The remission was permanent in that no relapses were detected. The remission was accompanied by persistent elevation of Treg cells in the renal lymph nodes. IL233 is more potent than IL-2 and IL-33 either singly or in combination in the treatment of lupus GN. The results of this study support the thesis that IL233 should be considered as a novel agent for treating lupus GN.

Methionine enkephalin (MENK) regulates the immune pathogenesis of type 2 diabetes mellitus via the IL-33/ST2 pathway

The incidence and mortality of type 2 diabetes mellitus (T2DM) rank among the top ten worldwide. Emerging studies indicate pathological roles for the immune system in inflammation, insulin resistance and islet β-cell damage in subjects with T2DM. Methionine enkephalin (MENK) is present in endocrine cells of the pancreas and has been suggested to be an important mediator between the immune and neuroendocrine systems. Therefore, it may play a role in modulating insulin secretion from islet cells. Since little is known about the effect of MENK on T2DM, therefore it was the aim of this study to characterize the role and possible mechanism of action of MENK on plasma glucose and serum insulin levels in T2DM rats and INS-1 cells in vivo and in vitro. MENK significantly decreased the plasma glucose level and increased the serum insulin concentration in T2DM rats. It also increased the serum levels of the cytokines IL-5 and IL-10, while decreased TNF-α and IL-2 levels. We further confirmed that MENK regulated glucose metabolism by upregulating opioid receptor expression and modulating the IL-33/ST2 and MyD88-TRAF6-NF-κB p65 signaling pathways. Based on these results, an intraperitoneal injection of MENK represents a potentially new approach for T2DM.

Stromal cells maintain immune cell homeostasis in adipose tissue via production of interleukin-33

Obesity is driven by chronic low-grade inflammation resulting from dysregulated immune cell accumulation and function in white adipose tissue (WAT). Interleukin-33 (IL-33) is a key cytokine that controls innate and adaptive immune cell activity and immune homeostasis in WAT, although the sources of IL-33 have remained controversial. Here, we show that WAT-resident mesenchyme-derived stromal cells are the dominant producers of IL-33. Adipose stem and progenitor cells (ASPCs) produced IL-33 in all WAT depots, whereas mesothelial cells served as an additional source of IL-33 in visceral WAT. ASPC-derived IL-33 promoted a regulatory circuit that maintained an immune tone in WAT via the induction of group 2 innate lymphoid cell-derived type 2 cytokines and maintenance of eosinophils, whereas mesothelial IL-33 also acted as an alarmin by inducing peritoneal immune response upon infection. Together, these data reveal a previously unrecognized regulatory network between tissue-resident progenitor cells and innate lymphoid cells that maintains immune homeostasis in adipose tissue.

The alarmins IL-1 and IL-33 differentially regulate the functional specialisation of Foxp3+ regulatory T cells during mucosal inflammation

CD4⁺Foxp3⁺ regulatory T (T_REG) cells are critical mediators of peripheral tolerance and modulators of immune responses. Functional adaptation of T_REG cells, through acquisition of secondary transcription factors is critical for their effector differentiation towards local inflammatory stimuli including infections. The drivers and consequences of this adaptation of T_REG cell function remain largely unknown. Using an unbiased screen, we identified receptors of the IL-1 family controlling the adaptation of T_REG cells. Through respiratory infection models, we show that the IL-33 receptor (ST2) and the IL-1 receptor (IL1R1) selectively identify stable and unstable T_REG cells at mucosal surfaces, respectively. IL-33, not IL-1, is specifically required for maintaining the suppressive function of T_REG cells. In the absence of ST2, T_REG cells are prone to lose Foxp3 expression and acquire RORγT and IL1R1, while, in the absence of IL-1R1, they maintain Foxp3 expression and resist the acquisition of a Th17 phenotype. Finally, lack of IL-1 signalling enhances the accumulation of ST2⁺ T_REG over pro-inflammatory T_REG cells in a Cryptococcus neoformans infection. These observations show that IL-1 and IL-33 exert opposing functions in controlling the functional adaptation of T_REG cells, ultimately dictating the dynamics of adaptive immunity to pathogens.