IL-33 is a crucial amplifier of innate rather than acquired immunity. Proc Natl Acad Sci U S A. 2010;107:18581-18586. [PMID: 20937871 DOI: 10.1073/pnas.1003059107]

IL-33 promotes the egress of group 2 innate lymphoid cells from the bone marrow

ILC2s are potent mucosal effector cells that participate in type 2 inflammatory responses. Stier et al. demonstrate that IL-33 negatively regulates CXCR4, mediating the egress of ILC2 lineage cells from the bone marrow for potential hematogenous trafficking.

Group 2 innate lymphoid cells (ILC2s) are effector cells within the mucosa and key participants in type 2 immune responses in the context of allergic inflammation and infection. ILC2s develop in the bone marrow from common lymphoid progenitor cells, but little is known about how ILC2s egress from the bone marrow for hematogenous trafficking. In this study, we identified a critical role for IL-33, a hallmark peripheral ILC2-activating cytokine, in promoting the egress of ILC2 lineage cells from the bone marrow. Mice lacking IL-33 signaling had normal development of ILC2s but retained significantly more ILC2 progenitors in the bone marrow via augmented expression of CXCR4. Intravenous injection of IL-33 or pulmonary fungal allergen challenge mobilized ILC2 progenitors to exit the bone marrow. Finally, IL-33 enhanced ILC2 trafficking to the lungs in a parabiosis mouse model of tissue disruption and repopulation. Collectively, these data demonstrate that IL-33 plays a critical role in promoting ILC2 egress from the bone marrow.

Combinatorial targeting of TSLP, IL-25, and IL-33 in type 2 cytokine-driven inflammation and fibrosis

Thymic stromal lymphopoietin (TSLP), interleukin-25 (IL-25), and IL-33 are important initiators of type 2-associated mucosal inflammation and immunity. However, their role in the maintenance of progressive type 2 inflammation and fibrosis is much less clear. Using chronic models of helminth infection and allergic lung inflammation, we show that collective disruption of TSLP, IL-25, and IL-33 signaling suppresses chronic and progressive type 2 cytokine-driven inflammation and fibrosis. In a schistosome lung granuloma model or during chronic Schistosoma mansoni infection in the liver, individual ablation of TSLP, IL-25, or IL-33/ST2 had no impact on the development of IL-4/IL-13-dependent inflammation or fibrosis. However, significant reductions in granuloma-associated eosinophils, hepatic fibrosis, and IL-13-producing type 2 innate lymphoid cells (ILC2s) were observed when signaling of all three mediators was simultaneously disrupted. Combined blockade through monoclonal antibody (mAb) treatment also reduced IL-5 and IL-13 expression during primary and secondary granuloma formation in the lungs. In a model of chronic house dust mite-induced allergic lung inflammation, combined mAb treatment did not decrease established inflammation or fibrosis. TSLP/IL-33 double-knockout mice treated with anti-IL-25 mAb during priming, however, displayed decreased inflammation, mucus production, and lung remodeling in the chronic phase. Together, these studies reveal partially redundant roles for TSLP, IL-25, and IL-33 in the maintenance of type 2 pathology and suggest that in some settings, early combined targeting of these mediators is necessary to ameliorate progressive type 2-driven disease.

Interleukin-33-Activated Islet-Resident Innate Lymphoid Cells Promote Insulin Secretion through Myeloid Cell Retinoic Acid Production

Pancreatic-islet inflammation contributes to the failure of β cell insulin secretion during obesity and type 2 diabetes. However, little is known about the nature and function of resident immune cells in this context or in homeostasis. Here we show that interleukin (IL)-33 was produced by islet mesenchymal cells and enhanced by a diabetes milieu (glucose, IL-1β, and palmitate). IL-33 promoted β cell function through islet-resident group 2 innate lymphoid cells (ILC2s) that elicited retinoic acid (RA)-producing capacities in macrophages and dendritic cells via the secretion of IL-13 and colony-stimulating factor 2. In turn, local RA signaled to the β cells to increase insulin secretion. This IL-33-ILC2 axis was activated after acute β cell stress but was defective during chronic obesity. Accordingly, IL-33 injections rescued islet function in obese mice. Our findings provide evidence that an immunometabolic crosstalk between islet-derived IL-33, ILC2s, and myeloid cells fosters insulin secretion.

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.

Developments in the field of allergy in 2016 through the eyes of Clinical and Experimental Allergy

In this article, we described the development in the field of allergy as described by Clinical and Experimental Allergy in 2016. Experimental models of allergic disease, basic mechanisms, clinical mechanisms, allergens, asthma and rhinitis, and clinical allergy are all covered.

Role of innate lymphoid cells in obesity and metabolic disease (Review)

The immune system has previously been demonstrated to be associated with the pathophysiological development of metabolic abnormalities. However, the mechanisms linking immunity to metabolic disease remain to be fully elucidated. It has previously been suggested that innate lymphoid cells (ILCs) may be involved in the progression of numerous types of metabolic diseases as these cells act as suppressors and promoters for obesity and associated conditions, and are particularly involved in adipose tissue inflammation, which is a major feature of metabolic imbalance. Group 2 ILCs (ILC2s) have been revealed as anti‑obese immune regulators by secreting anti‑inflammatory cytokines and promoting the polarization of M2 macrophages, whereas group 1 ILCs (ILC1s), including natural killer cells, may promote adipose tissue inflammation via production of interferon‑γ, which in turn polarizes macrophages toward the M1 type. The majority of studies to date have demonstrated the pathological association between ILCs and obesity in the context of adipose tissue inflammation, whereas the roles of ILCs in other organs which participate in obesity development have not been fully characterized. Therefore, identifying the roles of all types of ILCs as central components mediating obesity‑associated inflammation, is of primary concern, and may lead to the discovery of novel preventative and therapeutic interventions.

TH17 cells express ST2 and are controlled by the alarmin IL-33 in the small intestine

T_H17 cells are major drivers of inflammation and involved in several autoimmune diseases. Tissue inflammation is a beneficial host response to infection, but it can also contribute to autoimmunity. The crosstalk between a tissue and the immune system during an inflammatory response is key for preserving tissue integrity and restoring physiological processes. However, how the inflamed tissue regulates the magnitude of an immune response by controlling pro-inflammatory T cells is not well characterized so far. Here we show that T_H17 cells accumulating in the small intestine upon inflammation express the IL-33 receptor (ST2) and intestinal epithelial cells (IEC) are the main source of the alarmin interleukin-33 (IL-33). We show that pro-inflammatory T_H17 cells acquire a regulatory phenotype with immunosuppressive properties in response to IL-33. Absence of ST2 signaling promotes the secretion of pro-inflammatory cytokines by T_H17 cells and dampens the secretion of IL-10. Our results provide new insights into the mechanisms by which IEC, via IL-33/ST2 axis, may control pro-inflammatory T_H17 cells in the small intestine to sustain homeostasis.

Cyclosporin A indirectly attenuates activation of group 2 innate lymphoid cells in papain-induced lung inflammation

Cyclosporin A (CsA) is a well-known immunosuppressant that is used against steroid-resistant asthma. Group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells produce Th2 cytokines including IL-5 and play important roles in asthma pathogenesis. Here, we studied the effects of CsA in allergen-induced lung inflammation in mice and found that CsA decreased the number of lung ILC2s and attenuated papain-induced activation of ILC2s accompanied with IL-5 expression. The ILC2 suppression mediated by CsA was not observed in culture or in lymphocyte-deficient Rag2^-/- mice. Thus, we propose a new suppressive effect of CsA, i.e., administration of CsA indirectly suppresses maintenance and activation of lung ILC2s in addition to direct suppression of T-cell activation and cytokine production.

Type 2 cytokine responses: regulating immunity to helminth parasites and allergic inflammation

Purpose of Review

It is well established that T helper type 2 (T_H2) immune responses are necessary to provide protection against helminth parasites but also to promote the detrimental inflammation associated with allergies and asthma. Given the importance of type 2 immunity and inflammation, many studies have focused on better understanding the factors that regulate T_H2 cell development and activation. As a result, significant progress has been made in understanding the signaling pathways and molecular events necessary to promote T_H2 cell polarization. In addition to the adaptive compartment, emerging studies are better defining the innate immune pathways needed to promote T_H2 cell responses. Given the recent and substantial growth of this field, the purpose of this review is to highlight recent studies defining the innate immune events that promote immunity to helminth parasites and allergic inflammation.

Recent Findings

Emerging studies have begun to elucidate the importance of cytokine alarmins such as thymic stromal lymphopoietin (TSLP), IL-25 (IL-17E) and IL-33 in promoting type 2 immunity and inflammation following helminth challenge or exposure to allergens. Specifically, recent reports have begun to define the complex cellular networks these alarmins activate and their contribution to type 2 immunity and inflammation.

Summary

Our increased understanding of the pathways that regulate type 2 cytokine-mediated immunity and inflammation have revealed novel therapeutic targets to treat both helminth infections and allergic disease states.

The role of whey acidic protein four-disulfide-core proteins in respiratory health and disease

Members of the whey acidic protein (WAP) or WAP four-disulfide-core (WFDC) family of proteins are a relatively under-explored family of low molecular weight proteins. The two most prominent WFDC proteins, secretory leukocyte protease inhibitor (SLPI) and elafin (or the precursor, trappin-2), have been shown to possess multiple functions including anti-protease, anti-bacterial, anti-viral and anti-inflammatory properties. It is therefore of no surprise that both SLPI and elafin/trappin-2 have been developed as potential therapeutics. Given the abundance of SLPI and elafin/trappin-2 in the human lung, most work in the area of WFDC research has focused on the role of WFDC proteins in protecting the lung from proteolytic attack. In this review, we will outline the current evidence regarding the expanding role of WFDC protein function with a focus on WFDC activity in lung disease as well as emerging data regarding the function of some of the more recently described WFDC proteins.

IL-33 exacerbates liver sterile inflammation by amplifying neutrophil extracellular trap formation

BACKGROUND & AIMS

Neutrophils and liver sinusoidal endothelial cells (LSECs) both contribute to sterile inflammatory injury during ischemia/reperfusion (I/R), a well-known liver surgical stress. Interleukin-33 (IL-33) has been shown to drive neutrophil infiltration during inflammatory responses through its receptor ST2. We recently reported that infiltrating neutrophils form neutrophil extracellular traps (NETs), which exacerbate sterile inflammatory injury in liver I/R. Here, we sought to determine the role of IL-33 in NET formation during liver sterile inflammation.

METHODS

Evaluation of IL-33 forming NETs was investigated using a partial liver I/R model to generate sterile injury in healthy WT, IL-33 and ST2 knockouts. Serum levels of IL-33 and myeloperoxidase (MPO)-DNA complex were measured in both humans and mice after the first surgery. Liver damage was assessed. Mouse neutrophil depletion was performed by intraperitoneal injection of anti-Ly6G antibody before I/R.

RESULTS

Patients undergoing liver resection showed a significant increase in serum IL-33 compared to healthy volunteers. This coincided with higher serum MPO-DNA complexes. NET formation was decreased in IL-33 and ST2 knockout mice compared with control mice, after liver I/R. IL-33 or ST2 deficiency protected livers from I/R injury, whereas rIL-33 administration during I/R exacerbated hepatotoxicity and systemic inflammation. In vitro, IL-33 is released from LSECs to promote NET formation. IL-33 deficient LSECs failed to induce NETs. ST2 deficient neutrophils limited their capacity to form NETs in vitro and adoptive transfer of ST2 knockout neutrophils to neutrophil-depleted WT mice significantly decreased NET formation.

CONCLUSIONS

Data establish that IL-33, mainly released from LSECs, causes excessive sterile inflammation after hepatic I/R by inducing NET formation. Therapeutic targeting of IL-33/ST2 might extend novel strategies to minimize organ damage in various clinical settings associated with sterile inflammation.

LAY SUMMARY

Liver ischemia and reperfusion injury results in the formation of neutrophil extracellular traps, which contribute to organ damage in liver surgeries. Herein, we show that IL-33 is released from liver sinusoidal endothelial cells to promote NET formation during liver I/R, which exacerbates inflammatory cascades and sterile inflammation.

Secreted products of Fasciola hepatica inhibit the induction of T cell responses that mediate allergy

There is evidence from epidemiology studies of a negative association between infection with helminth parasites and the development of allergy and asthma. Here, we demonstrate that the excretory/secretory products of the helminth Fasciola hepatica (FHES) protected mice against ovalbumin (OVA)-induced allergic asthma when administered at time of allergen sensitization. FHES reduced the accumulation of mucus, eosinophils and lymphocytes into the airways of allergen-challenged mice. Furthermore, FHES treatment suppressed Th2 responses in the airways. Interestingly, systemic administration of FHES at allergen challenge had no effect on airway inflammation, demonstrating that alum-induced Th2 response is set following initial allergen sensitization. Our findings highlight the immunomodulatory potential of molecules secreted by F. hepatica.

Der f 31, a novel allergen from Dermatophagoides farinae, activates epithelial cells and enhances lung-resident group 2 innate lymphoid cells

Airway epithelial cell-derived thymic stromal lymphopoietin (TSLP) and IL-33 can enhance lung-resident group 2 innate lymphoid cells (ILC2s), and they play an important role in the development of allergic diseases. This study tests the hypothesis that Der f 31 (Dermatophagoides farinae-31), an allergen, modulates airway epithelial cell functions and increases the frequency of lung ILC2s. Our previous research identified cofilin (Der f 31) as a novel allergen. In this study, we found that recombinant Der f 31 (r-Der f 31) upregulated the expression of co-stimulatory molecules in DCs and promoted Th2-skewed polarization. The levels of TSLP and IL-33 in epithelial cells were upregulated by r-Der f 31 via the activation of Toll-like receptor 2. Furthermore, in in vivo studies, r-Der f 31 induced eosinophil-like airway allergy and increased the number of lung-resident ILC2s. In summary, Der f 31 can modulate the functions of airway epithelial cells and increase levels of lung-resident ILC2s.

IL-33 Drives Monocyte Recruitment to Lung Interstitium through Chemokine Upregulation

Tissue infiltration by circulating monocytes is a critical step in the initiation and augmentation of type 2 inflammatory responses in the lungs. Our studies demonstrate that IL-33-/- mice have a defect in monocyte extravasation from the vasculature to the lung interstitium during induction of type 2 inflammatory responses. This result suggests that monocyte migration to the lungs is IL-33 dependent, and we found that administration of exogenous recombinant IL-33 is sufficient to restore monocyte localization to the lung interstitium. Further investigation of the effect of early administration of recombinant IL-33 on the lungs identified upregulation of multiple chemokines including the monocyte chemoattractants CCL2, CCL7, and CCL22. Importantly, blockade of G-protein coupled receptor-dependent signaling, and thereby chemokine receptor activity, inhibited IL-33-driven monocyte recruitment. CCR2 deficiency prevented recruitment of monocytes to the lung extravascular space during allergic sensitization, and resulted in reduced eosinophilia after allergen challenge. Thus, IL-33 plays a critical role in the initiation of type 2 inflammatory responses by inducing upregulation of chemokines that promote monocyte recruitment to the lung interstitium.

Contributions of Interleukin-33 and TSLP in a papain-soaked contact lens-induced mouse conjunctival inflammation model

INTRODUCTION

Pathological changes of severe chronic allergic conjunctivitis are driven not only via acquired immunity but also via innate immunity. Type 2 immune response-initiating cytokines may play some roles as innate immunity-dependent components of the ocular surface inflammation. To investigate the involvement of type 2 immune response-initiating cytokines in innate immunity-dependent, papain-induced conjunctival inflammation model using IL-25-, IL-33-, and TSLP receptor (TSLPR)-knockout (KO) mice with reference to basophils and ILC2.

METHODS

Papain-soaked contact lenses (papain-CLs) were installed in the conjunctival sacs of C57BL/6-IL-25 KO, IL-33 KO, TSLPR KO, Rag2 KO, Bas-TRECK, and wild-type mice and their eyes were sampled at day 5. The eosinophil and basophil infiltration in papain-CL model was evaluated histologically and cytokine expression was examined. To clarify the roles of basophils and ILC2, basophil/ILC2-depletion experiments were carried out.

RESULTS

Papain-induced conjunctival inflammation exhibited eosinophil infiltration and upregulation of Th2 cytokine expression. Reduction of eosinophil and basophil infiltration and attenuated Th2 cytokine expression were observed in the papain-CL model using IL-33 KO and TSLPR KO mice. Depletion of basophils or ILC2s in the conjunctivae of the papain-CL model reduced eosinophil infiltration.

CONCLUSIONS

Innate immunity-driven type 2 immune responses of the ocular surface are dependent on IL-33, TSLP, basophils, and ILC2. These components may be possible therapeutic targets for refractory allergic keratoconjunctivitis.

Innate lymphoid cells in allergic and nonallergic inflammation

In the last decade, the full picture of the role of innate lymphoid cells (ILCs) has been gradually revealed. ILCs are classified into 3 groups based on their transcription factors and cytokine production patterns, which mirror helper T-cell subsets. Unlike T cells and B cells, ILCs do not have antigen receptors. They promptly respond to multiple tissue-derived factors, such as cytokines and alarmins, and produce multiple proinflammatory and immunoregulatory cytokines. It has been reported that ILC-derived cytokines are important for the induction and regulation of inflammation. Accumulating evidence suggests that ILCs play substantial roles in protection against infection and the pathogenesis of inflammatory diseases, such as allergic diseases and autoimmune diseases. Different ILC subsets localize in distinct tissue/organ niches and receive tissue-derived signals on different types of inflammation, which allows them to acquire diverse phenotypes with specialized effector capacities. In this review we highlight the roles of ILCs in a variety of organs, such as the airway, skin, and gastrointestinal tract, in the context of allergic and nonallergic inflammation.

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 Innate Cytokines IL-25, IL-33, and TSLP Cooperate in the Induction of Type 2 Innate Lymphoid Cell Expansion and Mucous Metaplasia in Rhinovirus-Infected Immature Mice

Early-life respiratory viral infection is a risk factor for asthma development. Rhinovirus (RV) infection of 6-d-old mice, but not mature mice, causes mucous metaplasia and airway hyperresponsiveness that are associated with the expansion of lung type 2 innate lymphoid cells (ILC2s) and are dependent on IL-13 and the innate cytokine IL-25. However, contributions of the other innate cytokines, IL-33 and thymic stromal lymphopoietin (TSLP), to the observed asthma-like phenotype have not been examined. We reasoned that IL-33 and TSLP expression are also induced by RV infection in immature mice and are required for maximum ILC2 expansion and mucous metaplasia. We inoculated 6-d-old BALB/c (wild-type) and TSLP receptor-knockout mice with sham HeLa cell lysate or RV. Selected mice were treated with neutralizing Abs to IL-33 or recombinant IL-33, IL-25, or TSLP. ILC2s were isolated from RV-infected immature mice and treated with innate cytokines ex vivo. RV infection of 6-d-old mice increased IL-33 and TSLP protein abundance. TSLP expression was localized to the airway epithelium, whereas IL-33 was expressed in epithelial and subepithelial cells. RV-induced mucous metaplasia, ILC2 expansion, airway hyperresponsiveness, and epithelial cell IL-25 expression were attenuated by anti-IL-33 treatment and in TSLP receptor-knockout mice. Administration of intranasal IL-33 and TSLP was sufficient for mucous metaplasia. Finally, TSLP was required for maximal ILC2 gene expression in response to IL-25 and IL-33. The generation of mucous metaplasia in immature RV-infected mice involves a complex interplay among the innate cytokines IL-25, IL-33, and TSLP.

IL-33 and the intestine: The good, the bad, and the inflammatory

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family that has been widely studied since its discovery in 2005 for its dichotomous functions in homeostasis and inflammation. IL-33, along with its receptor suppression of tumorigenicity 2 (ST2), has been shown to modulate both the innate and adaptive immune system. Originally, the IL-33/ST2 signaling axis was studied in the context of inducing type 2 immune responses with the expression of ST2 by T helper 2 (T_H2) cells. However, the role of IL-33 is not limited to T_H2 responses. Rather, IL-33 is a potent activator of T_H1 cells, group 2 innate lymphoid cells (ILC2s), regulatory T (Treg) cells, and CD8⁺ T cells. The intestine is uniquely important in this discussion, as the intestinal epithelium is distinctively positioned to interact with both pathogens and the immune cells housed in the mucosa. In the intestine, IL-33 is expressed by the pericryptal fibroblasts and its expression is increased particularly in disease states. Moreover, IL-33/ST2 signaling aberrancy is implicated in the pathogenesis of inflammatory bowel disease (IBD). Accordingly, for this review, we will focus on the role of IL-33 in the regulation of intestinal immunity, involvement in intestinal disease, and implication in potential therapeutics.

Interleukin33 deficiency causes tau abnormality and neurodegeneration with Alzheimer-like symptoms in aged mice

Late-onset Alzheimer's disease (AD) remains a medical mystery. Recent studies have linked it to impaired repair of aged neurons. Potential involvement of interleukin33 (IL33) in AD has been reported. Here we show that IL33, which was expressed by up to 75% astrocytes in the aged brains, was critical for repair of aged neurons. Mice lacking Il33 gene (Il33^-/-) developed AD-like disease after 60-80 weeks, which was characterized by tau abnormality and a heavy loss of neurons/neurites in the cerebral cortex and hippocampus accompanied with cognition/memory impairment. We detected an abrupt aging surge in the cortical and hippocampal neurons at middle age (40 weeks). To counter the aging surge, wild-type mice rapidly upregulated repair of DNA double-strand breaks (DSBs) and autophagic clearance of cellular wastes in these neurons. Il33^-/- mice failed to do so, but instead went on to develop rapid accumulation of abnormal tau, massive DSBs and abnormal autophagic vacuoles in these neurons. Thus, uncontrolled neuronal aging surge at middle age due to lack of IL33 resulted in neurodegeneration and late-onset AD-like symptome in Il33^-/- mice. Our study also suggests that the aging surge is a time to search for biomarkers for early diagnosis of AD before massive neuron loss.

IL33-mediated ILC2 activation and neutrophil IL5 production in the lung response after severe trauma: A reverse translation study from a human cohort to a mouse trauma model

BACKGROUND

The immunosuppression and immune dysregulation that follows severe injury includes type 2 immune responses manifested by elevations in interleukin (IL) 4, IL5, and IL13 early after injury. We hypothesized that IL33, an alarmin released early after tissue injury and a known regulator of type 2 immunity, contributes to the early type 2 immune responses after systemic injury.

METHODS AND FINDINGS

Blunt trauma patients admitted to the trauma intensive care unit of a level I trauma center were enrolled in an observational study that included frequent blood sampling. Dynamic changes in IL33 and soluble suppression of tumorigenicity 2 (sST2) levels were measured in the plasma and correlated with levels of the type 2 cytokines and nosocomial infection. Based on the observations in humans, mechanistic experiments were designed in a mouse model of resuscitated hemorrhagic shock and tissue trauma (HS/T). These experiments utilized wild-type C57BL/6 mice, IL33-/- mice, B6.C3(Cg)-Rorasg/sg mice deficient in group 2 innate lymphoid cells (ILC2), and C57BL/6 wild-type mice treated with anti-IL5 antibody. Severely injured human blunt trauma patients (n = 472, average injury severity score [ISS] = 20.2) exhibited elevations in plasma IL33 levels upon admission and over time that correlated positively with increases in IL4, IL5, and IL13 (P < 0.0001). sST2 levels also increased after injury but in a delayed manner compared with IL33. The increases in IL33 and sST2 were significantly greater in patients that developed nosocomial infection and organ dysfunction than similarly injured patients that did not (P < 0.05). Mechanistic studies were carried out in a mouse model of HS/T that recapitulated the early increase in IL33 and delayed increase in sST2 in the plasma (P < 0.005). These studies identified a pathway where IL33 induces ILC2 activation in the lung within hours of HS/T. ILC2 IL5 up-regulation induces further IL5 expression by CXCR2+ lung neutrophils, culminating in early lung injury. The major limitations of this study are the descriptive nature of the human study component and the impact of the potential differences between human and mouse immune responses to polytrauma. Also, the studies performed did not permit us to make conclusions about the impact of IL33 on pulmonary function.

CONCLUSIONS

These results suggest that IL33 may initiate early detrimental type 2 immune responses after trauma through ILC2 regulation of neutrophil IL5 production. This IL33-ILC2-IL5-neutrophil axis defines a novel regulatory role for ILC2 in acute lung injury that could be targeted in trauma patients prone to early lung dysfunction.

RORα-dependent type 2 innate lymphoid cells are required and sufficient for mucous metaplasia in immature mice

Early-life wheezing-associated respiratory tract infection by rhinovirus (RV) is considered a risk factor for asthma development. We have shown that RV infection of 6-day-old BALB/c mice, but not mature mice, induces an asthmalike phenotype that is associated with an increase in the population of type 2 innate lymphoid cells (ILC2s) and dependent on IL-13 and IL-25. We hypothesize that ILC2s are required and sufficient for development of the asthmalike phenotype in immature mice. Mice were infected with RV1B on day 6 of life and treated with vehicle or a chemical inhibitor of retinoic acid receptor-related orphan receptor-α (RORα), SR3335 (15 mg·kg-1·day-1 ip for 7 days). We also infected Rorasg/sg mice without functional ILC2s. ILC2s were identified as negative for lineage markers and positive for cluster of differentiation 25 (CD25)/IL-2Rα and CD127/IL-7Rα. Effects of SR3335 on proliferation and function of cultured ILC2s were determined. Finally, sorted ILC2s were transferred into naïve mice, and lungs were harvested 14 days later for assessment of gene expression and histology. SR3335 decreased the number of RV-induced lung lineage-negative, CD25+, CD127+ ILC2s in immature mice. SR3335 also attenuated lung mRNA expression of IL-13, Muc5ac, and Gob5 as well as mucous metaplasia. We also found reduced expansion of ILC2s in RV-infected Rorasg/sg mice. SR3335 also blocked IL-25 and IL-33-induced ILC2 proliferation and IL-13 production ex vivo. Finally, adoptive transfer of ILC2s led to development of asthmalike phenotype in immature and adult mice. RORα-dependent ILC2s are required and sufficient for type 2 cytokine expression and mucous metaplasia in immature mice.

Replicating viral vector platform exploits alarmin signals for potent CD8+ T cell-mediated tumour immunotherapy

Viral infections lead to alarmin release and elicit potent cytotoxic effector T lymphocyte (CTL^eff) responses. Conversely, the induction of protective tumour-specific CTL^eff and their recruitment into the tumour remain challenging tasks. Here we show that lymphocytic choriomeningitis virus (LCMV) can be engineered to serve as a replication competent, stably-attenuated immunotherapy vector (artLCMV). artLCMV delivers tumour-associated antigens to dendritic cells for efficient CTL priming. Unlike replication-deficient vectors, artLCMV targets also lymphoid tissue stroma cells expressing the alarmin interleukin-33. By triggering interleukin-33 signals, artLCMV elicits CTL^eff responses of higher magnitude and functionality than those induced by replication-deficient vectors. Superior anti-tumour efficacy of artLCMV immunotherapy depends on interleukin-33 signalling, and a massive CTL^eff influx triggers an inflammatory conversion of the tumour microenvironment. Our observations suggest that replicating viral delivery systems can release alarmins for improved anti-tumour efficacy. These mechanistic insights may outweigh safety concerns around replicating viral vectors in cancer immunotherapy.

Viruses trigger potent cytotoxic T cell responses, whereas anti-tumour immunity has been difficult to establish. Here the authors engineer a replicating viral delivery system for tumour-associated antigens, which induces alarmin release, innate activation and protective anti-tumour immunity in mice.

Macrophages produce IL-33 by activating MAPK signaling pathway during RSV infection

It has been reported that RSV infection can enhance IL-33 production in lung macrophages. However, little is known about specific signaling pathways for activation of macrophages during RSV infection. In the present study, by using real-time RT-PCR as well as western blot assay, it became clear that RSV infection can enhance not only the expression of mRNAs for MAPK molecules (including p38, JNK1/2, and ERK1/2), but also the levels of MAPK proteins in lung macrophages as well as RAW264.7 cells. Furthermore, infection with RSV resulted in an increased level of phosphorylated MAPK proteins in RAW264.7 cells, suggesting that MAPK signaling pathway may participate in the process of RSV-induced IL-33 secretion by macrophages. In fact, the elevated production of IL-33 in RAW264.7 was attenuated significantly by pretreatment of the cells with special MAPK inhibitor before RSV infection, further confirming the function of MAPKs pathway in RSV-induced IL-33 production in macrophages. In contrast, the expression of NF-κB mRNA as well as the production of NF-κB protein in lung macrophages and RAW264.7 cells was not enhanced markedly after RSV infection. Moreover, RSV infection failed to induce the phosphorylation of NF-κB in RAW264.7 cells, suggesting that NF-κB signaling pathway may be not involved in RSV-induced IL-33 production in macrophages. Conclusion, these results indicate that RSV-induced production of IL-33 in macrophages is dependent on the activation of MAPK signaling pathway.

IL-33 protects murine viral fulminant hepatitis by targeting coagulation hallmark protein FGL2/fibroleukin expression

Fulminant hepatitis (FH) is characterized by rapid liver failure and high mortality. The pathogenesis of viral FH includes virus-induced immune activation, inflammation, and subsequent hepatic apoptosis and necrosis. However, the mechanisms that underlie FH progression are unclear. IL-33 is a member of the IL-1-related cytokines, considered to be an "alarmin" that participates in various diseases, but its precise role in the coagulation of FH is not very clear. In our study, we found that IL-33 is significantly elevated in mice infected with murine hepatitis virus strain 3 (MHV-3). This is accompanied by an increase in pro-coagulant fibrinogen-like protein 2 (FGL2) in the liver. Previous studies have suggested that an increase in FGL2 is diagnostic of FH and liver necrosis, and animals with no FGL2 had better survivorship during FH. Our studies showed that IL-33 administration in a MHV-3 infection promoted survival during FH, with a significant reduction in FGL2 expression and liver inflammation. In vitro IL-33 treatment abrogated MHV-3 and IFN-γ induced FGL2 expression in RAW264.7 and THP-1 cells, respectively. In conclusion, our research suggests that IL-33 protects against viral fulminant hepatitis in mice by antagonizing expression of the pro-coagulant protein FGL2.

Innate immunity as the orchestrator of allergic airway inflammation and resolution in asthma

The respiratory system is constantly in direct contact with the environment and, has therefore, developed strong innate and adaptive immune responses to combat pathogens. Unlike adaptive immunity which is mounted later in the course of the immune response and is naive at the outset, innate immunity provides the first line of defense against microbial agents, while also promoting resolution of inflammation. In the airways, innate immune effector cells mainly consist of eosinophils, neutrophils, mast cells, basophils, macrophages/monocytes, dendritic cells and innate lymphoid cells, which attack pathogens directly or indirectly through the release of inflammatory cytokines and antimicrobial peptides, and coordinate T and B cell-mediated adaptive immunity. Airway epithelial cells are also critically involved in shaping both the innate and adaptive arms of the immune response. Chronic allergic airway inflammation and linked asthmatic disease is often considered a result of aberrant activation of type 2 T helper cells (Th2) towards innocuous environmental allergens; however, innate immune cells are increasingly recognized as key players responsible for the initiation and the perpetuation of allergic responses. Moreover, innate cells participate in immune response regulation through the release of anti-inflammatory mediators, and guide tissue repair and the maintenance of airway homeostasis. The scope of this review is to outline existing knowledge on innate immune responses involved in allergic airway inflammation, highlight current gaps in our understanding of the underlying molecular and cellular mechanisms and discuss the potential use of innate effector cells in new therapeutic avenues.

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.

Interleukin-33 regulates intestinal inflammation by modulating macrophages in inflammatory bowel disease

Interleukin 33 (IL-33) that signals through the ST2 receptor has emerged as a critical modulator in several inflammatory disorders, including inflammatory bowel disease (IBD). However, the precise mechanisms by which IL-33 modulates IBD are controversial. The aim of this study was thus to clarify the role of IL-33 in IBD. The plasma levels of IL-33 were significantly decreased, but soluble ST2 levels were increased in patients with IBD compared to healthy individuals. Moreover, IL-33 restored goblet cell numbers and induced macrophage switching from the M1 to the M2 phenotype. These effects were sufficient to ameliorate colitis in dextran sodium sulfate, trinitrobenzene sulfonic acid, and peritoneal cavity cell transfer models. IL-33 facilitated goblet cell restoration via modulating macrophages toward the M2 phenotype. In addition, wound healing was significantly faster in IL-33-treated human monocyte-derived macrophages than in control cells, which could be attributed to increased polarisation into M2 macrophages. We found that patients with IBD show decreased serum levels of IL-33 compared with healthy individuals and that IL-33 can attenuate colitis and aid tissue repair in mice. The mechanism by which IL-33 exerts these effects appears to involve the stimulation of differentiation of goblet cells and M2 macrophages.

Experimental atopic dermatitis depends on IL-33R signaling via MyD88 in dendritic cells

Atopic dermatitis (AD) is a chronic Th2 type inflammatory skin disorder. Here we report that MyD88 signaling is crucial in the pathogenesis of experimental AD induced by vitamin D3 analog MC903. The clinical signs and inflammation caused by MC903 are drastically reduced in MyD88^−/− mice with diminished eosinophil, neutrophil infiltration and Th2 cytokine expression. The biological effect of interleukin-1 (IL-1) family members relies on MyD88 signaling. We observed a strong upregulation of IL-1 family cytokine expression, including IL-1α, IL-1β, IL-33, IL-18, IL-36α, IL-36β, IL-36γ and IL-36Ra. Therefore, we asked which cytokine of the IL-1 family would be essential for MC903-induced AD syndrome. We find a significant reduction of AD in IL-33^−/− and IL-33R/ST2^−/− mice, only a minor reduction in double IL-1αβ^−/− mice and no difference in IL-36R^−/− and IL-36Ra^−/− mice. IL-33 is expressed in keratinocytes, and MyD88 signaling in dendritic cells (DCs) is crucial for AD development as inflammation was drastically reduced in DC-specific MyD88^−/− mice (CD11c-cre × MyD88-floxed). Taken together, the data demonstrate a critical role of MyD88 in DCs and of IL-33 signaling via ST2 in MC903-induced AD. These data suggest that IL-33/IL-33R may be a therapeutic target of AD.

Mechanisms involved in enhancement of matrix metalloproteinase-9 expression in macrophages by interleukin-33

Endothelial transmigration of macrophages is accomplished by matrix metalloproteinase (MMP)-induced degradation of the basement membrane and extracellular matrix components. Macrophages upregulate MMP-9 expression and secretion upon immunological challenges and require its activity for migration during inflammatory responses. Interleukin (IL)-33 is a recently discovered pro-inflammatory cytokine that belongs to the IL-1 family. The aim of this study was to elucidate the mechanisms underlying IL-33-induced MMP-9 expression in the mouse monocyte/macrophage line RAW264.7. IL-33 increased MMP-9 mRNA and protein expression in RAW264.7 cells. Blockage of IL-33-IL-33 receptor (ST2L) binding suppressed IL-33-mediated induction of MMP-9. IL-33 induced phosphorylation and nuclear translocation of extracellular signal-regulated kinase 1/2 (ERK1/2) and nuclear factor-kappa B (NF-κB). Chromatin immunoprecipitation indicated that IL-33 increased c-fos recruitment to the MMP-9 promoter. Reporter assay findings also revealed that IL-33 stimulated the transcriptional activity of activator protein 1 (AP-1). Pre-treatment of the cells with a specific inhibitor of ERK1/2 and NF-κB attenuated the IL-33-induced activation of AP-1 subunits, transcriptional activity of AP-1, and expression of MMP-9. We also demonstrated that ERK-dependent activation of cAMP response element binding protein (CREB) is a key step for AP-1 activation by IL-33. These results indicate an essential role of ERK/CREB and NF-κB cascades in the induction of MMP-9 in monocytes/macrophages through AP-1 activation.

Endogenous prostaglandin E2 amplifies IL-33 production by macrophages through an E prostanoid (EP)2/EP4-cAMP-EPAC-dependent pathway

When activated through toll-like receptors (TLRs), macrophages generate IL-33, an IL-1 family member that induces innate immune responses through ST2 signaling. LPS, a TLR4 ligand, induces macrophages to generate prostaglandin E₂ (PGE₂) through inducible COX-2 and microsomal PGE₂ synthase 1 (mPGES-1) (1). We demonstrate that IL-33 production by bone marrow-derived murine macrophages (bmMFs) requires the generation of endogenous PGE₂ and the intrinsic expression of EP₂ receptors to amplify NF-κB-dependent, LPS-induced IL-33 expression via exchange protein activated by cAMP (EPAC). Compared with WT cells, bmMFs lacking either mPGES-1 or EP₂ receptors displayed reduced LPS-induced IL-33 levels. A selective EP₂ agonist and, to a lesser extent, EP₄ receptor agonist potentiated LPS-induced IL-33 generation from both mPGES-1-null and WT bmMFs, whereas EP₁ and EP₃ receptor agonists were inactive. The effects of PGE₂ depended on cAMP, were mimicked by an EPAC-selective agonist, and were attenuated by EPAC-selective antagonism and knockdown. LPS-induced p38 MAPK and NF-κB activations were necessary for both IL-33 production and PGE₂ generation, and exogenous PGE₂ partly reversed the suppression of IL-33 production caused by p38 MAPK and NF-κB inhibition. Mice lacking mPGES-1 showed lower IL-33 levels and attenuated lung inflammation in response to repetitive Alternaria inhalation challenges. Cumulatively, our data demonstrate that endogenous PGE₂, EP₂ receptors, and EPAC are prerequisites for maximal LPS-induced IL-33 expression and that exogenous PGE₂ can amplify IL-33 production via EP₂ and EP₄ receptors. The ubiquitous induction of mPGES-1-dependent PGE₂ may be crucial for innate immune system activation during various IL-33 driven pathologic disorders.

Interleukin-33 plasma levels in patients with relapsing-remitting multiple sclerosis

Cytokines are implicated in the immunopathogenesis of multiple sclerosis (MS). Interleukin (IL)-33, one of the recently discovered members of the IL-1 superfamily, is a dual functional cytokine involved in various autoimmune disorders. In a case-control study, venous blood was collected from healthy subjects categorized as control group (n=44) and MS patients (n=44). All recruited patients were clinically diagnosed with relapsing-remitting MS (RRMS), including patients without treatment (new identified cases, n=16) and those treated with interferon beta (IFN-β) (n=28). The plasma levels of IL-33 in subjects were measured with ELISA. Significantly elevated IL-33 plasma levels were observed in RRMS patients (p=0.005). Furthermore, IFN-β-treated MS patients had lower levels of IL-33 compared to the untreated patients (p<0.001). Increased IL-33 plasma levels in the patient group might be associated with development of MS. These results could contribute to our better understanding about the role of IL-33 in the immunopathogenesis of MS.

ST2 from rainbow trout quenches TLR signalling, localises at the nuclear membrane and allows the nuclear translocation of MYD88

The mammalian interleukin 1 receptor-like 1 receptor (IL1RL1), commonly known as ST2, is thought to downregulate TLR signalling by sequestering the signalling adapter MYD88 (myeloid differentiation primary response protein 88). ST2 sequences are known in several fish species, but none of them have functionally been examined. We characterised ST2 from rainbow trout (Oncorhynchus mykiss) and the structure of its encoding gene. The primary sequence of ST2 is only weakly conserved from fish to human. However, the amino acid sequences forming the interfaces for ST2 and MYD88 interaction are well conserved throughout evolution. High similarity of the gene segmentation unambiguously proves the common ancestry of fish and mammalian ST2. Trout ST2 and trout MYD88 genes were constitutively expressed in embryonic, larval and adult trout. In vivo infection with Aeromonas salmonicida did not modulate the mRNA levels of both factors. Overexpressing trout ST2 in the mammalian HEK-293 reconstitution system of TLR2 signalling quenched the Escherichia coli-induced activation of NF-κB and SAA promoters in a dose-dependent fashion. The expression of GFP-tagged trout ST2 in human HEK-293 or trout CHSE-214 cells surprisingly revealed that (i) ST2 localised abundantly at the nuclear membrane rather than at the cell membrane and (ii) the coexpression of both ST2 and MYD88 allowed the translocation of trout MYD88 from cytoplasm to nucleus, as assessed using confocal microscopy and Western blotting. Hence, we validated that trout ST2 is a dampener of TLR signalling and interacts with MYD88. The spatial distribution of these factors raises questions about how this repressive mechanism functions.

A mechanism for the induction of type 2 immune responses by a protease allergen in the genital tract

The genital mucosa is a barrier that is constantly exposed to a variety of pathogens, allergens, and external stimuli. Although both allergen exposure and parasite infections frequently occur in the genital area, the mechanism by which immune responses-particularly type 2 immunity-are induced has rarely been studied in the genital mucosa. Here, we demonstrate the induction of T helper type 2 (Th2) immunity in the genital mucosa in response to a model allergen, the protease papain. Intravaginal papain immunization induced type 2 immunity in a manner that was dependent on protease activity and the estrous phase of the mice. In addition, IL-33 was released from the vaginal epithelia after intravaginal papain immunization, leading to the activation of type 2 innate lymphoid cells (ILC2s). Moreover, the IL-33-MyD88 (myeloid differentiation primary response gene 88) signaling pathway was critical for the induction of type 2 immunity. We also found that Th2 differentiation in response to intravaginal papain treatment requires a specific dendritic cell (DC) subset that is controlled by interferon regulatory factor 4 (IRF4). These findings suggest that type 2 immunity is induced by a unique mechanism in the genital tract, which is an important, but often overlooked, barrier surface.

Innate Immune Cytokines, Fibroblast Phenotypes, and Regulation of Extracellular Matrix in Lung

Chronic inflammation can be caused by adaptive immune responses in autoimmune and allergic conditions, driven by a T lymphocyte subset balance (TH1, TH2, Th17, Th22, and/or Treg) and skewed cellular profiles in an antigen-specific manner. However, several chronic inflammatory diseases have no clearly defined adaptive immune mechanisms that drive chronicity. These conditions include those that affect the lung such as nonatopic asthma or idiopathic pulmonary fibrosis comprising significant health problems. The remodeling of extracellular matrix (ECM) causes organ dysfunction, and it is largely generated by fibroblasts as the major cell controlling net ECM. As such, these are potential targets of treatment approaches in the context of ECM pathology. Fibroblast phenotypes contribute to ECM and inflammatory cell accumulation, and they are integrated into chronic disease mechanisms including cancer. Evidence suggests that innate cytokine responses may be critical in nonallergic/nonautoimmune disease, and they enable environmental agent exposure mechanisms that are independent of adaptive immunity. Innate immune cytokines derived from macrophage subsets (M1/M2) and innate lymphoid cell (ILC) subsets can directly regulate fibroblast function. We also suggest that STAT3-activating gp130 cytokines can sensitize fibroblasts to the innate cytokine milieu to drive phenotypes and exacerbate existing adaptive responses. Here, we review evidence exploring innate cytokine regulation of fibroblast behavior.

Factors associated with plasma IL-33 levels in patients with chronic obstructive pulmonary disease

BACKGROUND

Interleukin (IL)-33 promotes T helper (Th)2 immunity and systemic inflammation. The role of IL-33 in asthma has been widely investigated. IL-33 has also been suggested to play an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). This study investigated the clinical significance and usefulness of plasma IL-33 level in patients with COPD.

METHODS

A total of 307 patients with stable COPD from 15 centers, who were in the Korean Obstructive Lung Disease cohort, were enrolled in this study. Plasma IL-33 levels were measured by enzyme-linked immunosorbent assay. We analyzed the association between IL-33 level and other clinical characteristics related to COPD. We also examined the features of patients with COPD who exhibited high IL-33 levels.

RESULTS

IL-33 levels varied, but were very low in most patients. Eosinophil count was significantly correlated with a plasma IL-33 level. In addition, old age and current smoking were related to a low IL-33 level. Significantly more patients with a higher IL-33 level had chronic bronchitis compared with those with a low IL-33 level.

CONCLUSION

Plasma IL-33 level in patients with stable COPD was related to eosinophil count and chronic bronchitis phenotype. Further studies are needed to identify the precise mechanisms of IL-33/ST2 pathway in patients with COPD.

Development of chronic allergic responses by dampening Bcl6-mediated suppressor activity in memory T helper 2 cells

Mice deficient in the transcriptional repressor B-cell CLL/lymphoma 6 (Bcl6) exhibit similar T helper 2 (T_H2) immune responses as patients with allergic diseases. However, the molecular mechanisms underlying Bcl6-directed regulation of T_H2 cytokine genes remain unclear. We identified multiple Bcl6/STAT binding sites (BSs) in T_H2 cytokine gene loci. We found that Bcl6 is modestly associated with the BSs, and it had no significant effect on cytokine production in newly differentiated T_H2 cells. Contrarily, in memory T_H2 (mT_H2) cells derived from adaptively transferred T_H2 effectors, Bcl6 outcompeted STAT5 for binding to T_H2 cytokine gene loci, particularly Interleukin4 (Il4) loci, and attenuated GATA binding protein 3 (GATA3) binding to highly conserved intron enhancer regions in mT_H2 cells. Bcl6 suppressed cytokine production epigenetically in mT_H2 cells to negatively tune histone acetylation at T_H2 cytokine gene loci, including Il4 loci. In addition, IL-33, a pro-T_H2 cytokine, diminished Bcl6's association with loci to which GATA3 recruitment was inversely augmented, resulting in altered IL-4, but not IL-5 and IL-13, production in mT_H2 cells but no altered production in newly differentiated T_H2 cells. Use of a murine asthma model that generates high levels of pro-T_H2 cytokines, such as IL-33, suggested that the suppressive function of Bcl6 in mT_H2 cells is abolished in severe asthma. These findings indicate a role of the interaction between T_H2-promoting factors and Bcl6 in promoting appropriate IL-4 production in mT_H2 cells and suggest that chronic allergic diseases involve the T_H2-promoting factor-mediated functional breakdown of Bcl6, resulting in allergy exacerbation.

The Role of IL-33-Dependent Inflammation in the Tumor Microenvironment

There is compelling evidence that inflammation contributes to tumorigenesis. Inflammatory mediators within the tumor microenvironment can either promote an antitumor immune response or support tumor pathogenesis. Therefore, it is critical to determine the relative contribution of tumor-associated inflammatory pathways to cancer development. Interleukin-33 (IL-33) is a member of the IL-1 family of cytokines that is released upon tissue stress or damage to operate as an alarmin. IL-33 has been primarily implicated in the induction of type-2 immune responses. However, recent findings have shown a role of IL-33 in several cancers where it may exert multiple functions. In this review, we will present the current knowledge on the role of IL-33 in the microenvironment of different tumors. We will highlight which cells produce and which cells are activated by IL-33 in cancer. Furthermore, we will explain how IL-33 modulates the tumor-associated inflammatory microenvironment to restrain or promote tumorigenesis. Finally, we will discuss the issues to be addressed first before potentially targeting the IL-33 pathway for cancer therapy.

Expression of epithelial cell-derived cytokine genes in the duodenal and colonic mucosae of dogs with chronic enteropathy

It remains unclear whether epithelial cell-derived cytokines, including interleukin (IL)-25, IL-33 and thymic stromal lymphopoietin (TSLP), contribute to development of canine chronic enteropathy (CE), which includes antibiotic-responsive enteropathy (ARE), food-responsive enteropathy (FRE) and inflammatory bowel disease (IBD). In the present study, we examined mRNA expression of il-25, il-33 and tslp in the duodenal and colonic mucosae of dogs with ARE, FRE and IBD. Real-time PCR analysis revealed that mRNA expression of il-33 was significantly lower in the duodenum in dogs with FRE than in healthy dogs. The results suggest that epithelial cell-derived cytokines may not be an inducer of Th2-type immunity in the gut of dogs with CE, and decreased expression of IL-33 may be involved in induction of FRE. Further studies are required to clarify roles of epithelial cell-derived cytokines, especially IL-33, in the pathogenesis of canine CE.

The interleukin-33 receptor ST2 is important for the development of peripheral airway hyperresponsiveness and inflammation in a house dust mite mouse model of asthma

BACKGROUND

Several clinical and experimental studies have implicated IL-33 and its receptor ST2 in the development of asthma. However, the effect of IL-33/ST2 signalling on airway responses and inflammation in allergic asthma is not well established.

OBJECTIVE

To investigate the role of IL-33/ST2 signalling in promoting allergen-induced airway hyperresponsiveness (AHR), airway inflammation, antigen-specific IgE production and mast cell activity in a mouse model of asthma.

METHODS

ST2-deficient (ST2(-/-)) mice and control BALB/c mice were given house dust mite (HDM) extract over a 6-week period. Forty-eight hours after the final HDM administration, lung function and airway inflammation were evaluated. Airway responsiveness was determined in the central airways and peripheral lung. Cellular infiltration and mast cell protease mMCP-1 levels were quantified in bronchoalveolar lavage fluid (BALF). Recruitment of inflammatory cells and inflammatory cytokine profiles were assessed in pulmonary tissue, and HDM-specific IgE was measured in serum.

RESULTS

ST2 deficiency diminished HDM-induced AHR in the peripheral lung, while AHR in the central airways was unaffected. Inflammatory responses to HDM were also reduced in ST2(-/-) mice as reflected by the lower induction of HDM-specific serum IgE, inhibition of HDM-induced eosinophilia and reduced macrophage count in BALF, and a diminished influx of inflammatory cells and reduced goblet cell hyperplasia around the peripheral airways. Furthermore, the levels of the inflammatory cytokines IL-1β, IL-5, IL-13, IL-33, GM-CSF, thymic stromal lymphopoietin and mast cell protease mMCP-1 were reduced in HDM-treated ST2(-/-) mice compared with wild-type controls.

CONCLUSIONS

In addition to promoting Th2 inflammation, we now suggest a role for the IL-33/ST2 pathway for the induction of peripheral inflammation and mucus production that causes AHR in the peripheral lung. This mechanism for inducing AHR at distal parts of the lung may be of specific importance as asthma is considered as a small airway disease.

IL-33 regulates the IgA-microbiota axis to restrain IL-1α-dependent colitis and tumorigenesis

Inflammatory bowel diseases (IBD) affect over 5 million individuals in the industrialized world, with an increasing incidence rate worldwide. IBD also predisposes affected individuals to development of colorectal cancer, which is a leading cause of cancer-related deaths in adults. Mutations in genes encoding molecules in the IL-33 signaling pathway are associated with colitis and colitis-associated cancer (CAC), but how IL-33 modulates gut homeostasis is unclear. Here, we have shown that Il33-deficient mice are highly susceptible to colitis and CAC. Mechanistically, we observed that IL-33 promoted IgA production from B cells, which is important for maintaining microbial homeostasis in the intestine. Il33-deficient mice developed a dysbiotic microbiota that was characterized by increased levels of mucolytic and colitogenic bacteria. In response to chemically induced colitis, this microbial landscape promoted the release of IL-1α, which acted as a critical driver of colitis and CAC. Consequently, reconstitution of symbiotic microbiota or IL-1α ablation markedly ameliorated colitis susceptibility in Il33-deficient animals. Our results demonstrate that IL-33 promotes IgA production to maintain gut microbial homoeostasis and restrain IL-1α-dependent colitis and CAC. This study therefore highlights modulation of IL-33, IgA, IL-1α, and the microbiota as a potential therapeutic approach in the treatment of IBD and CAC.

Th2 Cells in Health and Disease

Helper T (Th) cell subsets direct immune responses by producing signature cytokines. Th2 cells produce IL-4, IL-5, and IL-13, which are important in humoral immunity and protection from helminth infection and are central to the pathogenesis of many allergic inflammatory diseases. Molecular analysis of Th2 cell differentiation and maintenance of function has led to recent discoveries that have refined our understanding of Th2 cell biology. Epigenetic regulation of Gata3 expression by chromatin remodeling complexes such as Polycomb and Trithorax is crucial for maintaining Th2 cell identity. In the context of allergic diseases, memory-type pathogenic Th2 cells have been identified in both mice and humans. To better understand these disease-driving cell populations, we have developed a model called the pathogenic Th population disease induction model. The concept of defined subsets of pathogenic Th cells may spur new, effective strategies for treating intractable chronic inflammatory disorders.

Soluble IL-33 receptor sST2 inhibits colorectal cancer malignant growth by modifying the tumour microenvironment

Interleukin-33 (IL-33) was recently shown to be involved in the inflammatory tumour microenvironment and the progression of colorectal cancer (CRC). We report here that the expression level of sST2, a soluble form of the IL-33 receptor (ST2L), is inversely associated with the malignant growth of CRC. sST2 is downregulated in high-metastatic cells compared with low-metastatic human and mouse CRC cells. Knockdown of sST2 in low-metastatic cells enhances tumour growth, metastasis and tumour angiogenesis, whereas its overexpression in high-metastatic cells suppresses these processes. Circulating and intratumourally administered sST2-Fc fusion protein reduce tumour growth, metastatic spread and tumour angiogenesis in mice bearing high-metastatic CRC. Mechanistically, sST2 suppresses IL-33-induced angiogenesis, Th1- and Th2-responses, macrophage infiltration and macrophage M2a polarization. In conclusion, we show that sST2 negatively regulates tumour growth and the metastatic spread of CRC through modification of the tumour microenvironment. Thus, the IL-33/ST2L axis may be a potential therapeutic target in CRC.

IL-33 is a pro-inflammatory cytokine with a role in colorectal cancer. Here, the authors show that circulating tumour-derived sST2, an IL-33 decoy receptor, delayed the growth and progression of colorectal cancer cells by inhibiting Th1/Th2 polarization, macrophage infiltration and angiogenesis.