Macrophages as IL-25/IL-33-responsive cells play an important role in the induction of type 2 immunity

Estrogen contributes to sex differences in M2a macrophages during multi-walled carbon nanotube-induced respiratory inflammation

Lung diseases characterized by type 2 inflammation are reported to occur with a female bias in prevalence/severity in both humans and mice. This includes previous work examining multi-walled carbon nanotube (MWCNT)-induced eosinophilic inflammation, in which a more exaggerated M2a phenotype was observed in female alveolar macrophages (AMs) compared to males. The mechanisms responsible for this sex difference in AM phenotype are still unclear, but estrogen receptor (ER) signaling is a likely contributor. Accordingly, male AMs downregulated ERα expression after MWCNT exposure while female AMs did not. Thus, ER antagonist Fulvestrant was administered prior to MWCNT instillation. In females, Fulvestrant significantly attenuated MWCNT-induced M2a gene expression and eosinophilia without affecting IL-33. In males, Fulvestrant did not affect eosinophil recruitment but reduced IL-33 and M2a genes compared to controls. Regulation of cholesterol efflux and oxysterol synthesis is a potential mechanism through which estrogen promotes the M2a phenotype. Levels of oxysterols 25-OHC and 7α,25-OHC were higher in the airways of MWCNT-exposed males compared to MWCNT-females, which corresponds with the lower IL-1β production and greater macrophage recruitment previously observed in males. Sex-based changes in cholesterol efflux transporters Abca1 and Abcg1 were also observed after MWCNT exposure with or without Fulvestrant. In vitro culture with estrogen decreased cellular cholesterol and increased the M2a response in female AMs, but did not affect cholesterol content in male AMs and reduced M2a polarization. These results reveal the modulation of (oxy)sterols as a potential mechanism through which estrogen signaling may regulate AM phenotype resulting in sex differences in downstream respiratory inflammation.

MiR-548t-5p regulates pancreatic ductal adenocarcinoma metastasis through an IL-33-dependent crosstalk between cancer cells and M2 macrophages

IL-33 has been associated with pro- and anticancer functions in cancer. However, its role in pancreatic cancer metastasis remains unknown. This study aimed to explore the role of miR-548t-5p/IL-33 axis in the metastasis of pancreatic cancer. Luciferase activity assay, qRT-PCR, Western blot and ELISA were performed to prove whether IL-33 is the target of miR-548t-5p. In vivo metastasis assay and cellular transwell assay were performed to explore the role of miR-548t-5p/IL-33 axis in the invasion and metastasis of pancreatic cancer. Co-culture experiments and immunohistochemistry were performed to observe whether IL-33 affects cell invasion and metastasis dependent on the involvement of M2 macrophages. THP-1 cell induction experiment and flow cytometry were performed to explore the effect of IL-33 on macrophage polarization. CCK-8, colony formation, cell apoptosis, cell cycle, cell wound healing and transwell assay were performed to investigate the effect of IL-33 induced M2 macrophages on cell malignant biological behavior by coculturing pancreatic cancer cells with the conditioned medium (CM) from macrophages. We found that miR-548t-5p regulated the expression and secretion of IL-33 in pancreatic cancer cells by directly targeting IL-33 mRNA. IL-33 secreted by cancer cells promoted the recruitment and activation of macrophages to a M2-like phenotype. In turn, IL-33 induced M2 macrophages promoted the migration and invasion of cancer cells. Moreover, IL-33 affected pancreatic cancer cell invasion dependent on the involvement of M2 macrophages in the co-culture system. Thus, our study suggested that manipulation of this IL-33-dependent crosstalk has a therapeutic potential for the treatment of pancreatic cancer metastasis.

ATP functions as a primary alarmin in allergen-induced type 2 immunity

Environmental allergens that interact with the airway epithelium can activate cellular stress pathways that lead to the release of danger signals known as alarmins. The mechanisms of alarmin release are distinct from damage-associated molecular patterns (DAMPs), which typically escape from cells after loss of plasma membrane integrity. Oxidative stress represents a form of allergen-induced cellular stress that stimulates oxidant-sensing mechanisms coupled to pathways, which facilitate alarmin mobilization and efflux across the plasma membrane. In this review, we highlight examples of alarmin release and discuss their roles in the initiation of type 2 immunity and allergic airway inflammation. In addition, we discuss the concept of alarmin amplification, where "primary" alarmins, which are directly released in response to a specific cellular stress, stimulate additional signaling pathways that lead to secretion of "secondary" alarmins that include proinflammatory cytokines, such as IL-33, as well as genomic and mitochondrial DNA that coordinate or amplify type 2 immunity. Accordingly, allergen-evoked cellular stress can elicit a hierarchy of alarmin signaling responses from the airway epithelium that trigger local innate immune reactions, impact adaptive immunity, and exacerbate diseases including asthma and other chronic inflammatory conditions that affect airway function.

IL-33 Orchestrated the Interaction and Immunoregulatory Functions of Alternatively Activated Macrophages and Regulatory T Cells In Vitro

Our group has previously demonstrated elevated serum-soluble ST2 in patients with active systemic lupus erythematosus, suggesting a role of IL-33 in the underlying pathogenesis. However, inconsistent results have been reported on the effect of exogenous IL-33 on murine lupus activity, which may be mediated by concerted actions of various immune cells in vivo. This study aimed to examine the function of IL-33 on macrophage polarization and regulatory T cells (Treg) and their interactive effects in the lupus setting by in vitro coculture experiments of macrophages and T cells that were performed in the presence or absence of IL-33-containing medium. Compared to IL-4-polarized bone marrow-derived macrophages (BMDM) from MRL/MpJ mice, adding IL-33 enhanced mRNA expression of markers of alternatively activated macrophages, including CD206 and Arg1. IL-33 and IL-4 copolarized BMDM produced higher TGF-β but not IL-6 upon inflammatory challenge. These BMDM induced an increase in the Foxp3+CD25+ Treg population in cocultured allogeneic T cells from MRL/MpJ and predisease MRL/lpr mice. These copolarized BMDM also showed an enhanced suppressive effect on T cell proliferation with reduced IFN-γ and IL-17 release but increased TGF-β production. In the presence of TGF-β and IL-2, IL-33 also directly promoted inducible Treg that expressed a high level of CD25 and more sustained Foxp3. Unpolarized BMDM cocultured with these Treg displayed higher phagocytosis. In conclusion, TGF-β was identified as a key cytokine produced by IL-4 and IL-33 copolarized alternatively activated macrophages and the induced Treg, which may contribute to a positive feedback loop potentiating the immunoregulatory functions of IL-33.

Interleukin-33 Ameliorates Murine Systemic Lupus Erythematosus and Is Associated with Induction of M2 Macrophage Polarisation and Regulatory T Cells

The innate cytokine IL-33 is increasingly recognised to possess biological effects on various immune cells. We have previously demonstrated elevated serum level of soluble ST2 in patients with active systemic lupus erythematosus suggesting involvement of IL-33 and its receptor in the lupus pathogenesis. This study sought to examine the effect of exogenous IL-33 on disease activity of pre-disease lupus-prone mice and the underlying cellular mechanisms. Recombinant IL-33 was administered to MRL/lpr mice for 6 weeks, whereas control group received phosphate-buffered saline. IL-33-treated mice displayed less proteinuria, renal histological inflammatory changes, and had lower serum levels of pro-inflammatory cytokines including IL-6 and TNF-α. Renal tissue and splenic CD11b+ extracts showed features of M2 polarisation with elevated mRNA expression of Arg1, FIZZI, and reduced iNOS. These mice also had increased IL-13, ST2, Gata3, and Foxp3 mRNA expression in renal and splenic tissues. Kidneys of these mice displayed less CD11b+ infiltration, had downregulated MCP-1, and increased infiltration of Foxp3-expressing cells. Splenic CD4+ T cells showed increased ST2-expressing CD4+Foxp3+ population and reduced IFN-γ+ population. There were no differences in serum anti-dsDNA antibodies and renal C3 and IgG2a deposit in these mice. Exogenous IL-33 was found to ameliorate disease activity in lupus-prone mice with induction of M2 polarisation, Th2 response, and expansion of regulatory T cells. IL-33 likely orchestrated autoregulation of these cells through upregulation of ST2 expression.

Epithelial-intrinsic defects in TGFβR signaling drive local allergic inflammation manifesting as eosinophilic esophagitis

Allergic diseases are a global health challenge. Individuals harboring loss-of-function variants in transforming growth factor-β receptor (TGFβR) genes have an increased prevalence of allergic disorders, including eosinophilic esophagitis. Allergic diseases typically localize to mucosal barriers, implicating epithelial dysfunction as a cardinal feature of allergic disease. Here, we describe an essential role for TGFβ in the control of tissue-specific immune homeostasis that provides mechanistic insight into these clinical associations. Mice expressing a TGFβR1 loss-of-function variant identified in atopic patients spontaneously develop disease that clinically, immunologically, histologically, and transcriptionally recapitulates eosinophilic esophagitis. In vivo and in vitro, TGFβR1 variant-expressing epithelial cells are hyperproliferative, fail to differentiate properly, and overexpress innate proinflammatory mediators, which persist in the absence of lymphocytes or external allergens. Together, our results support the concept that TGFβ plays a fundamental, nonredundant, epithelial cell-intrinsic role in controlling tissue-specific allergic inflammation that is independent of its role in adaptive immunity.

STAT6-IP-Dependent Disruption of IL-33-Mediated ILC2 Expansion and Type 2 Innate Immunity in the Murine Lung

Recent interest has focused on innate-type cytokines as promoters of type 2 immunity and targets for drug development in asthma. IL-33 induces production of IL-4 and/or IL-13, which is associated with STAT6-dependent responses in innate cells, including group 2 innate lymphoid cells (ILC2s), macrophages, and eosinophils. Our published data show that STAT6-immunomodulatory peptide (STAT6-IP), an immunomodulatory peptide designed to inhibit the STAT6 transcription factor, reduces induction of Th2 adaptive immunity in respiratory syncytial virus infection and asthma models. Nevertheless, the mechanism of STAT6-IP-dependent inhibition has remained obscure. In this study, we demonstrate that STAT6-IP reduced IL-33-induced type 2 innate lung inflammation. Specifically, our data show that STAT6-IP reduced recruitment and activation of eosinophils as well as polarization of alternatively activated macrophages. Decreases in these cells correlated with reduced levels of IL-5 and IL-13 as well as several type 2 chemokines in the bronchoalveolar lavage fluid. STAT6-IP effectively inhibited expansion of ILC2s as well as the number of IL-5- and IL-13-producing ILC2s. Our data suggest that STAT6-IP effectively disrupts IL-13-dependent positive feedback loops, initiated by ILC2 activation, to suppress IL-33-induced type 2 innate immunity in the murine lung.

Soluble ST2 as a Potential Biomarker for Abdominal Aortic Aneurysms-A Single-Center Retrospective Cohort Study

The maximal aortic diameter is the only clinically applied predictor of abdominal aortic aneurysm (AAA) progression and indicator for surgical repair. Circulating biomarkers resulting from AAA pathogenesis are attractive candidates for the diagnosis and prognosis of aneurysmal disease. Due to the reported role of interleukin 33 in AAA development, we investigated the corresponding circulating receptor molecules of soluble suppression of tumorigenesis 2 (sST2) in AAA patients regarding their marker potential in diagnosis and prognosis. We conducted a single-center retrospective cohort study in a diagnostic setting, measuring the circulating serum sST2 protein levels of 47 AAA patients under surveillance, matched with 25 peripheral artery disease (PAD) patients and 25 healthy controls. In a prognostic setting, we analyzed the longitudinal monitoring data of 50 monitored AAA patients. Slow versus fast AAA progression was defined as a <2 or ≥2 mm increase in AAA diameter over 6 months and a <4 or ≥4 mm increase over 12 months. Additionally, the association of circulating serum sST2 and AAA growth was investigated using a specifically tailored log-linear mixed model. Serum sST2 concentrations were significantly increased in AAA patients compared with healthy individuals: the median of AAA patient cohort was 112.72 ng/mL (p = 0.025) and that of AAA patient cohort 2 was 14.32 ng/mL (p = 0.039) versus healthy controls (8.82 ng/mL). Likewise, PAD patients showed significantly elevated sST2 protein levels compared with healthy controls (the median was 12.10 ng/mL; p = 0.048) but similar concentrations to AAA patients. Additionally, sST2 protein levels were found to be unsuited to identifying fast AAA progression over short-term periods of 6 or 12 months, which was confirmed by a log-linear mixed model. In conclusion, the significantly elevated protein levels of sST2 detected in patients with vascular disease may be useful in the early diagnosis of AAA but cannot distinguish between AAA and PAD or predict AAA progression.

Nanocarriers for effective delivery: modulation of innate immunity for the management of infections and the associated complications

Innate immunity is the first line of defense against invading pathogens. Innate immune cells can recognize invading pathogens through recognizing pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs). The recognition of PAMPs by PRRs triggers immune defense mechanisms and the secretion of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. However, sustained and overwhelming activation of immune system may disrupt immune homeostasis and contribute to inflammatory disorders. Immunomodulators targeting PRRs may be beneficial to treat infectious diseases and their associated complications. However, therapeutic performances of immunomodulators can be negatively affected by (1) high immune-mediated toxicity, (2) poor solubility and (3) bioactivity loss after long circulation. Recently, nanocarriers have emerged as a very promising tool to overcome these obstacles owning to their unique properties such as sustained circulation, desired bio-distribution, and preferred pharmacokinetic and pharmacodynamic profiles. In this review, we aim to provide an up-to-date overview on the strategies and applications of nanocarrier-assisted innate immune modulation for the management of infections and their associated complications. We first summarize examples of important innate immune modulators. The types of nanomaterials available for drug delivery, as well as their applications for the delivery of immunomodulatory drugs and vaccine adjuvants are also discussed.

Nanoparticle-Induced Airway Eosinophilia Is Independent of ILC2 Signaling but Associated With Sex Differences in Macrophage Phenotype Development

The majority of lung diseases occur with a sex bias in terms of prevalence and/or severity. Previous studies demonstrated that, compared with males, female mice develop greater eosinophilic inflammation in the airways after multiwalled carbon nanotube (MWCNT) exposure. However, the mechanism by which this sex bias occurs is unknown. Two immune cells that could account for the sex bias are type II innate lymphoid cells (ILC2s) and alveolar macrophages (AMs). In order to determine which immune cell type was responsible for MWCNT-induced airway eosinophil recruitment and subsequent sex differences in inflammation and disease, male and female C57BL/6 mice were exposed to MWCNTs (2 mg/kg) via oropharyngeal aspiration, and the respiratory immune response was assessed 7 d later. Greater eosinophilia and eotaxin 2 levels were observed in MWCNT-treated females and corresponded with greater changes in airway hyperresponsiveness than those in MWCNT-treated males. In MWCNT-treated females, there was a significant increase in the frequency of ILC2s within the lungs compared with control animals. However, depletion of ILC2s via α-CD90.2 administration did not decrease eosinophil recruitment 24 h and 7 d after MWCNT exposure. AMs isolated from control and MWCNT-treated animals demonstrated that M2a macrophage phenotype gene expression, ex vivo cytokine production, and activation of (p)STAT6 were upregulated to a significantly greater degree in MWCNT-treated females than in males. Our findings suggest that sex differences in AM phenotype development, not ILC2 signaling, are responsible for the observed female bias in eosinophilic inflammation after MWCNT inhalation.

Could Interleukin-33 (IL-33) Govern the Outcome of an Equine Influenza Virus Infection? Learning from Other Species

Influenza A viruses (IAVs) are important respiratory pathogens of horses and humans. Infected individuals develop typical respiratory disorders associated with the death of airway epithelial cells (AECs) in infected areas. Virulence and risk of secondary bacterial infections vary among IAV strains. The IAV non-structural proteins, NS1, PB1-F2, and PA-X are important virulence factors controlling AEC death and host immune responses to viral and bacterial infection. Polymorphism in these proteins impacts their function. Evidence from human and mouse studies indicates that upon IAV infection, the manner of AEC death impacts disease severity. Indeed, while apoptosis is considered anti-inflammatory, necrosis is thought to cause pulmonary damage with the release of damage-associated molecular patterns (DAMPs), such as interleukin-33 (IL-33). IL-33 is a potent inflammatory mediator released by necrotic cells, playing a crucial role in anti-viral and anti-bacterial immunity. Here, we discuss studies in human and murine models which investigate how viral determinants and host immune responses control AEC death and subsequent lung IL-33 release, impacting IAV disease severity. Confirming such data in horses and improving our understanding of early immunologic responses initiated by AEC death during IAV infection will better inform the development of novel therapeutic or vaccine strategies designed to protect life-long lung health in horses and humans, following a One Health approach.

The Paradigm Change of IL-33 in Vascular Biology

In this review, we focus on the actual understanding of the role of IL-33 in vascular biology in the context of the historical development since the description of IL-33 as a member of IL-1 superfamily and the ligand for ST2 receptor in 2005. We summarize recent data on the biology, structure and signaling of this dual-function factor with both nuclear and extracellular cytokine properties. We describe cellular sources of IL-33, particularly within vascular wall, changes in its expression in different cardio-vascular conditions and mechanisms of IL-33 release. Additionally, we summarize the regulators of IL-33 expression as well as the effects of IL-33 itself in cells of the vasculature and in monocytes/macrophages in vitro combined with the consequences of IL-33 modulation in models of vascular diseases in vivo. Described in murine atherosclerosis models as well as in macrophages as an atheroprotective cytokine, extracellular IL-33 induces proinflammatory, prothrombotic and proangiogenic activation of human endothelial cells, which are processes known to be involved in the development and progression of atherosclerosis. We, therefore, discuss that IL-33 can possess both protective and harmful effects in experimental models of vascular pathologies depending on experimental conditions, type and dose of administration or method of modulation.

IL-33: A central cytokine in helminth infections

IL-33 is an alarmin cytokine which has been implicated in allergy, fibrosis, inflammation, tumorigenesis, metabolism, and homeostasis. However, amongst its strongest roles are in helminth infections, where IL-33 usually (but not always) is central to induction of an effective anti-parasitic immune response. In this review, we will summarise the literature around this fascinating cytokine, its activity on immune and non-immune cells, the unique (and sometimes counterintuitive) responses it induces, and how it can coordinate the immune response during infections by parasitic helminths. Finally, we will summarise some of the ways that parasites have developed to modulate the IL-33 pathway for their own benefit.

IL-13 Controls IL-33 Activity through Modulation of ST2

IL-33 is a multifunctional cytokine that mediates local inflammation upon tissue damage. IL-33 is known to act on multiple cell types including group 2 innate lymphoid cells (ILC2s), Th2 cells, and mast cells to drive production of Th2 cytokines including IL-5 and IL-13. IL-33 signaling activity through transmembrane ST2L can be inhibited by soluble ST2 (sST2), which acts as a decoy receptor. Previous findings suggested that modulation of IL-13 levels in mice lacking decoy IL-13Rα2, or mice lacking IL-13, impacted responsiveness to IL-33. In this study, we used Il13 ^-/- mice to investigate whether IL-13 regulates IL-33 activity by modulating the transmembrane and soluble forms of ST2. In Il13 ^-/- mice, the effects of IL-33 administration were exacerbated relative to wild type (WT). Il13 ^-/- mice administered IL-33 i.p. had heightened splenomegaly, more immune cells in the peritoneum including an expanded ST2L⁺ ILC2 population, increased eosinophilia in the spleen and peritoneum, and reduced sST2 in the circulation and peritoneum. In the spleen, lung, and liver of mice given IL-33, gene expression of both isoforms of ST2 was increased in Il13 ^-/- mice relative to WT. We confirmed fibroblasts to be an IL-13-responsive cell type that can regulate IL-33 activity through production of sST2. This study elucidates the important regulatory activity that IL-13 exerts on IL-33 through induction of IL-33 decoy receptor sST2 and through modulation of ST2L⁺ ILC2s.

Enteric Tuft Cells in Host-Parasite Interactions

Enteric tuft cells are chemosensory epithelial cells gaining attention in the field of host-parasite interactions. Expressing a repertoire of chemosensing receptors and mediators, these cells have the potential to detect lumen-dwelling helminth and protozoan parasites and coordinate epithelial, immune, and neuronal cell defenses against them. This review highlights the versatility of enteric tuft cells and sub-types thereof, showcasing nuances of tuft cell responses to different parasites, with a focus on helminths reflecting the current state of the field. The role of enteric tuft cells in irritable bowel syndrome, inflammatory bowel disease and intestinal viral infection is assessed in the context of concomitant infection with parasites. Finally, the review presents pertinent questions germane to understanding the enteric tuft cell and its role in enteric parasitic infections. There is much to be done to fully elucidate the response of this intriguing cell type to parasitic-infection and there is negligible data on the biology of the human enteric tuft cell—a glaring gap in knowledge that must be filled.

IL-25-induced shifts in macrophage polarization promote development of beige fat and improve metabolic homeostasis in mice

Beige fat dissipates energy and functions as a defense against cold and obesity, but the mechanism for its development is unclear. We found that interleukin (IL)-25 signaling through its cognate receptor, IL-17 receptor B (IL-17RB), increased in adipose tissue after cold exposure and β3-adrenoceptor agonist stimulation. IL-25 induced beige fat formation in white adipose tissue (WAT) by releasing IL-4 and IL-13 and promoting alternative activation of macrophages that regulate innervation and up-regulate tyrosine hydroxylase (TH) up-regulation to produce more catecholamine including norepinephrine (NE). Blockade of IL-4Rα or depletion of macrophages with clodronate-loaded liposomes in vivo significantly impaired the beige fat formation in WAT. Mice fed with a high-fat diet (HFD) were protected from obesity and related metabolic disorders when given IL-25 through a process that involved the uncoupling protein 1 (UCP1)-mediated thermogenesis. In conclusion, the activation of IL-25 signaling in WAT may have therapeutic potential for controlling obesity and its associated metabolic disorders.

Protective/reparative cytokines are suppressed at high injury severity in human trauma

Background

Trauma elicits a complex inflammatory response that, among multiple presenting factors, is greatly impacted by the magnitude of injury severity. Herein, we compared the changes in circulating levels of mediators with known proinflammatory roles to those with known protective/reparative actions as a function of injury severity in injured humans.

Methods

Clinical and biobank data were obtained from 472 (trauma database-1 (TD-1), University of Pittsburgh) and 89 (trauma database-2 (TD-2), Indiana University) trauma patients admitted to the intensive care unit (ICU) and who survived to discharge. Injury severity was estimated based on the Injury Severity Score (ISS), and this was used as both a continuous variable and for the purpose of grouping patients into severity-based cohorts. Samples within the first 24 hours were obtained from all patients and then daily up to day 7 postinjury in TD-1. Sixteen cytokines were assayed using Luminex and were analyzed using two-way analysis of variance (p<0.05).

Results

Patients with higher ISSs had longer ICU and hospital stays, days on mechanical ventilation and higher rates of nosocomial infection when compared with the mild and moderate groups. Time course analysis and correlations with ISS showed that 11 inflammatory mediators correlated positively with injury severity, consistent with previous reports. However, five mediators (interleukin (IL)-9, IL-21, IL-22, IL-23 and IL-17E/25) were suppressed in patients with high ISS and inversely correlated with ISS.

Discussion

These findings suggest that severe injury is associated with a suppression of a subset of cytokines known to be involved in tissue protection and regeneration (IL-9, IL-22 and IL-17E/25) and lymphocyte differentiation (IL-21 and IL-23), which in turn correlates with adverse clinical outcomes. Thus, patterns of proinflammatory versus protective/reparative mediators diverge with increasing ISS.

Schistosome and intestinal helminth modulation of macrophage immunometabolism

Macrophages are fundamental to sustain physiological equilibrium and to regulate the pathogenesis of parasitic and metabolic processes. The functional heterogeneity and immune responses of macrophages are shaped by cellular metabolism in response to the host's intrinsic factors, environmental cues and other stimuli during disease. Parasite infections induce a complex cascade of cytokines and metabolites that profoundly remodel the metabolic status of macrophages. In particular, helminths polarize macrophages to an M2 state and induce a metabolic shift towards reliance on oxidative phosphorylation, lipid oxidation and amino acid metabolism. Accumulating data indicate that helminth-induced activation and metabolic reprogramming of macrophages underlie improvement in overall whole-body metabolism, denoted by improved insulin sensitivity, body mass in response to high-fat diet and atherogenic index in mammals. This review aims to highlight the metabolic changes that occur in human and murine-derived macrophages in response to helminth infections and helminth products, with particular interest in schistosomiasis and soil-transmitted helminths.

Exploring the origin and regulatory role of mast cells in asthma

PURPOSE OF REVIEW

Mast cells have previously been thought to function solely as effector cells in asthma but more recent studies have indicated that mast cells may play a more central role in propagating and regulating lower airway inflammation in asthma.

RECENT FINDINGS

Initial studies have found increased numbers of mast cell progenitors (MCPs) in the peripheral blood of patients with asthma and these cells could contribute to the increased number of progenitors identified in the airways of patients with asthma. There are unique subpopulations of mast cells within the asthmatic airway, which are characterized by their physical location and distinguished by their expression profile of mast cell proteases. Intraepithelial mast cells are tightly associated with type-2 (T2) inflammation but additional studies have suggested a role for anti-mast cell therapies as a treatment for T2-low asthma. Mast cells have recently been shown to closely communicate with the airway epithelium and airway smooth muscle to regulate lower airway inflammation and airway hyperresponsiveness.

SUMMARY

Recent studies have better illuminated the central role of mast cells in regulating lower airway inflammation and airway hyperresponsiveness.

Interleukin (IL)-33 is dispensable for Schistosoma mansoni worm maturation and the maintenance of egg-induced pathology in intestines of infected mice

BACKGROUND

Schistosomes are trematode worms that dwell in their definitive host's blood vessels, where females lay eggs that need to be discharged into the environment with host excreta to maintain their life-cycle. Both worms and eggs require type 2 immunity for their maturation and excretion, respectively. However, the immune molecules that orchestrate such immunity remain unclear. Interleukin (IL)-33 is one of the epithelium-derived cytokines that induce type 2 immunity in tissues. The aim of this study was to determine the role of IL-33 in the maturation, reproduction and excretion of Schistosoma mansoni eggs, and in the maintenance of egg-induced pathology in the intestines of mice.

METHODS

The morphology of S. mansoni worms and the number of eggs in intestinal tissues were studied at different time points post-infection in S. mansoni-infected IL-33-deficient (IL-33-/-) and wild-type (WT) mice. IL-5 and IL-13 production in the spleens and mesenteric lymph nodes were measured. Tissue histology was performed on the terminal ilea of both infected and non-infected mice.

RESULTS

Worms from IL-33-/- and WT mice did not differ morphologically at 4 and 6 weeks post-infection (wpi). The number of eggs in intestinal tissues of IL-33-/- and WT mice differed only slightly. At 6 wpi, IL-33-/- mice presented impaired type 2 immunity in the intestines, characterized by a decreased production of IL-5 and IL-13 in mesenteric lymph nodes and fewer inflammatory infiltrates with fewer eosinophils in the ilea. There was no difference between IL-33-/- and WT mice in the levels of IL-25 and thymic stromal lymphopoietin (TSLP) in intestinal tissues.

CONCLUSIONS

Despite its ability to initiate type 2 immunity in tissues, IL-33 alone seems dispensable for S. mansoni maturation and its absence may not affect much the accumulation of eggs in intestinal tissues. The transient impairment of type 2 immunity observed in the intestines, but not spleens, highlights the importance of IL-33 over IL-25 and TSLP in initiating, but not maintaining, locally-induced type 2 immunity in intestinal tissues during schistosome infection. Further studies are needed to decipher the role of each of these molecules in schistosomiasis and clarify the possible interactions that might exist between them.

IL-25 Treatment Improves Metabolic Syndrome in High-Fat Diet and Genetic Models of Obesity

INTRODUCTION

Endemic obesity is considered the driving force for the dramatic increase in incidence of type 2 diabetes (T2D). There is mounting evidence that chronic, low-grade inflammation driven by Th1/Th17 cells and M1 macrophages, is a critical link between obesity and insulin resistance. IL-25 promotes development of a Th2 immune response and M2 macrophages that counteract the inflammation associated with obesity and T2D.

METHODS

Mice were fed a high-fat diet (HFD) for 16 weeks and then treated with IL-25 or BSA as a control for 21 days. Body weight, blood glucose levels, intraperitoneal glucose tolerance, and gene expression were evaluated in mice treated with BSA or IL-25. Ob/ob mice fed a normal control diet were also treated with BSA or IL-25 and body weight and blood glucose levels were measured. Transepithelial electrical resistance and sodium-linked glucose absorption were determined in muscle-free small intestinal tissue and glucose absorption assessed in vitro in intestinal epithelial and skeletal muscle cell lines.

RESULTS

Administration of IL-25 to HFD fed mice reversed glucose intolerance, an effect mediated in part by reduction in SGLT-1 activity and Glut2 expression. Importantly, the improved glucose tolerance in HFD mice treated with IL-25 was maintained for several weeks post-treatment indicating long-term changes in glucose metabolism in obese mice. Glucose intolerance was also reversed by IL-25 treatment in genetically obese ob/ob mice without inducing weight loss. In vitro studies demonstrated that glucose absorption was inhibited by IL-25 treatment in the epithelial IPEC-1 cells but increased glucose absorption in the L6 skeletal muscle cells. This supports a direct cell-specific effect of IL-25 on glucose metabolism.

CONCLUSION

These results suggest that the IL-25 pathway may be a useful target for the treatment of metabolic syndrome.

IL-25 Receptor Signaling Modulates Host Defense against Cryptococcus neoformans Infection

Cryptococcal meningitis is one of the most common life-threatening diseases caused by Cryptococcus infection. Increasing evidence indicates that type 2 immunity is associated with disease progression by promoting fungal growth and dissemination. However, factors that govern this pathogenic response during infection are still elusive. In this study, we investigated the role of IL-25, one of the type 2-inducing cytokines produced by epithelial cells, in contributing to the pathogenesis of cryptococcosis. We found that pulmonary but not systemic infection with a high-virulence strain of C. neoformans significantly induced pulmonary IL-25 expression in the lungs but not brains. In response to pulmonary infection, mice deficient in the surface IL-17 receptor B, a component of the IL-25R, exhibited improved survival with a decreased brain fungal burden. The absence of IL-25R signaling diminished the type 2 and enhanced the type 1 immune response that directed macrophage polarization toward M1 macrophages. Interestingly, Cryptococcus-mediated IL-25 signaling suppressed the expression of cytokines and chemokines associated with protection in the brain, including Ifng, Il1b, Ip10, and Nos2, without affecting brain cellular inflammation and microglia cell activation. Il17rb^-/- mice receiving cryptococcal-specific CD4⁺ T cells from wild-type had a shorter survival time with higher fungal burden within the brain and an elevated expression of M2 macrophage markers than those receiving cryptococcal-specific CD4⁺ T cells from Il17rb^-/- mice. Taken together, our data indicated that IL-25 signaling subverts the induction of protective immunity and amplifies the type 2 immune response that may favor the development of cryptococcal disease and the fungal dissemination to the CNS.

Group 2 Innate Lymphoid Cells Must Partner with the Myeloid-Macrophage Lineage for Long-Term Postviral Lung Disease

Group 2 innate lymphoid cells (ILC2s) are implicated in host defense and inflammatory disease, but these potential functional roles need more precise definition, particularly using advanced technologies to better target ILC2s and engaging experimental models that better manifest both acute infection and chronic, even lifelong, disease. In this study, we use a mouse model that applies an improved genetic definition of ILC2s via IL-7r-conditional Rora gene targeting and takes advantage of a distinct progression from acute illness to chronic disease, based on a persistent type 2 immune response to respiratory infection with a natural pathogen (Sendai virus). We first show that ILC2s are activated but are not required to handle acute illness after respiratory viral infection. In contrast, we find that this type of infection also activates ILC2s chronically for IL-13 production and consequent asthma-like disease traits that peak and last long after active viral infection is cleared. However, to manifest this type of disease, the Csf1-dependent myeloid-macrophage lineage is also active at two levels: first, at a downstream level, this lineage provides lung tissue macrophages (interstitial macrophages and tissue monocytes) that represent a major site of Il13 gene expression in the diseased lung; and second, at an upstream level, this same lineage is required for Il33 gene induction that is necessary to activate ILC2s for participation in disease at all, including IL-13 production. Together, these findings provide a revised scheme for understanding and controlling the innate immune response leading to long-term postviral lung diseases with features of asthma and related progressive conditions.

Interactions between macrophages and helminths

Macrophages, the major population of tissue-resident mononuclear phagocytes, contribute significantly to the immune response during helminth infection. Alternatively activated macrophages (AAM) are induced early in the anti-helminth response following tissue insult and parasite recognition, amplifying the early type 2 immune cascade initiated by epithelial cells and ILC2s, and subsequently driving parasite expulsion. AAM also contribute to functional alterations in tissues infiltrated with helminth larvae, mediating both tissue repair and inflammation. Their activation is amplified and occurs more rapidly following reinfection, where they can play a dual role in trapping tissue migratory larvae and preventing or resolving the associated inflammation and damage. In this review, we will address both the known and emerging roles of tissue macrophages during helminth infection, in addition to considering both outstanding research questions and new therapeutic strategies.

Early-life heterologous rhinovirus infections induce an exaggerated asthma-like phenotype

BACKGROUND

Early-life wheezing-associated respiratory tract infection by rhinovirus (RV) is a risk factor for asthma development. Infants are infected with many different RV strains per year.

OBJECTIVE

We previously showed that RV infection of 6-day-old BALB/c mice induces a mucous metaplasia phenotype that is dependent on type 2 innate lymphoid cells (ILC2s). We hypothesized that early-life RV infection alters the response to subsequent heterologous infection, inducing an exaggerated asthma-like phenotype.

METHODS

Wild-type BALB/c mice and Rora^fl/flIl7r^cre mice lacking ILC2s were treated as follows: (1) sham on day 6 of life plus sham on day 13 of life, (2) RV-A1B on day 6 plus sham on day 13, (3) sham on day 6 plus RV-A2 on day 13, and (4) RV-A1B on day 6 plus RV-A2 on day 13.

RESULTS

Mice infected with RV-A1B at day 6 and sham at day 13 showed an increased number of bronchoalveolar lavage eosinophils and increased expression of IL-13 mRNA but not expression of IFN-γ mRNA (which is indicative of a type 2 immune response), whereas mice infected with sham on day 6 and RV-A2 on day 13 of life demonstrated increased IFN-γ expression (which is a mature antiviral response). In contrast, mice infected with RV-A1B on day 6 before RV-A2 infection on day 13 showed increased expression of IL-13, IL-5, Gob5, Muc5b, and Muc5ac mRNA; increased numbers of eosinophils and IL-13-producing ILC2s; and exaggerated mucus metaplasia and airway hyperresponsiveness. Compared with Rora^fl/fl mice, Rora^fl/flIl7r^cre mice showed complete suppression of bronchoalveolar lavage eosinophils and mucous metaplasia.

CONCLUSION

Early-life RV infection alters the response to subsequent heterologous infection, inducing an intensified asthma-like phenotype that is dependent on ILC2s.

ST2 Signaling in the Tumor Microenvironment

Suppression of tumorigenicity 2 (ST2), also known as interleukin-1 receptor-like 1 (IL1RL1), is one of the natural receptors of IL-33. Three major isoforms, ST2L (transmembrane form), sST2 (soluble form), and ST2V, are generated by alternative splicing. Damage to stromal cells induces necrosis and release of IL-33, which binds to heterodimeric ST2L/IL-1RAcP complex on the membrane of a variety of immune cells. This IL-33/ST2L signal induces transcription of the downstream inflammatory and anti-inflammatory genes by activating diverse intracellular kinases and factors to mount an adequate immune response, even in tumor microenvironment. For example, activation of IL-33/ST2L signal may trigger Th2-dependent M2 macrophage polarization to facilitate tumor progression. Notably, sST2 is a soluble form of ST2 that lacks a transmembrane domain but preserves an extracellular domain similar to ST2L, which acts as a "decoy" receptor for IL-33. sST2 has been shown to involve in the inflammatory tumor microenvironment and the progression of colorectal cancer, non-small cell lung cancer, and gastric cancer. Therefore, targeting the IL-33/ST2 axis becomes a promising new immunotherapy for treatment of many cancers. This chapter reviews the recent findings on IL-33/ST2L signaling in tumor microenvironment, the trafficking mode of sST2, and the pharmacological strategies to target IL-33/ST2 axis for cancer treatment.

Deficiency of GATA3-Positive Macrophages Improves Cardiac Function Following Myocardial Infarction or Pressure Overload Hypertrophy

BACKGROUND

Macrophages are highly plastic cells that play an important role in the pathogenesis of cardiovascular disease.

OBJECTIVES

This study investigated the role of GATA3-positive macrophages in modulating cardiac function after myocardial infarction (MI) or in response to pressure overload hypertrophy.

METHODS

Myeloid-specific GATA3-deficient (mGATA3KO) mice were generated, MI or pressure overload was induced, and cardiac function was determined by echocardiography. GATA3-sufficient Cre mice were used as a control. Immunohistochemical staining, flow cytometry, MILLIPLEX Mouse Cytokine/Chemokine Assay, cultured macrophages, quantitative real-time polymerase chain reaction, and western blot were used to determine the role of GATA3 in macrophages.

RESULTS

GATA3-positive macrophages rapidly accumulated in the infarcted region of the myocardium after acute MI. Deficiency of GATA3-positive macrophages led to a significant improvement of cardiac function in response to acute MI or pressure overload hypertrophy compared with the control mice. This improvement was associated with the presence of a large number of proinflammatory Ly6C^hi monocytes/macrophages and fewer reparative Ly6C^lo macrophages in the myocardium of mGATA3KO mice compared with control mice. Analysis of serum proteins from the 2 mouse genotypes revealed no major changes in the profile of serum growth factors and cytokines between the 2 mice genotypes before and after MI. GATA3 was found to be specifically and transiently induced by interleukin 4 in cultured macrophages through activity of the proximal promoter, whereas the distal promoter remained silent. In addition, the absence of GATA3 in macrophages markedly attenuated arginase-1 expression in cultured macrophages.

CONCLUSIONS

We demonstrated that the presence of GATA3-positive macrophages adversely affects remodeling of the myocardium in response to ischemia or pressure overload, whereas the absence of these macrophages led to a significant improvement in cardiac function. Targeting of signaling pathways that lead to the expression of GATA3 in macrophages may have favorable cardiac outcomes.

Elevated Kallikrein-binding protein in diabetes impairs wound healing through inducing macrophage M1 polarization

Background

The accumulation of M1-polarized macrophages and excessive inflammation are important in the pathogenesis of diabetic foot ulcer (DFU). However, the underlying mechanism of DFU pathogenesis and the crucial regulators of DFU are less well known. Our previous study reported that kallikrein-binding protein (KBP), an angiogenesis inhibitor, was significantly upregulated in diabetic patients compared to its levels in controls. The effects of KBP on monocyte chemotaxis and macrophage M1 polarization were elucidated in this study.

Methods

Plasma KBP levels and monocyte counts were assessed by ELISA and flow cytometry. Wound closure rates in different groups were monitored daily. The phenotype and recruitment of macrophages were measured by real-time PCR, western blot and immunofluorescence assays. The expression of Notch and NF-κB signalling pathway members was determined by the methods mentioned above. ChIP and dual-luciferase reporter gene assays were employed to explore the binding and transcriptional regulation of Hes1 and iNOS.

Results

We found that plasma KBP levels and circulating monocytes were elevated in diabetic patients compared to those in nondiabetic controls, and both were higher in diabetic patients with DFU than in diabetic patients without DFU. KBP delayed wound healing in normal mice; correspondingly, KBP-neutralizing antibody ameliorated delayed wound healing in diabetic mice. Circulating monocytes and macrophage infiltration in the wound were upregulated in KBP-TG mice compared to those in control mice. KBP promoted the recruitment and M1 polarization of macrophages. Mechanistically, KBP upregulated iNOS by activating the Notch1/RBP-Jκ/Hes1 signalling pathway. Hes1 downregulated CYLD, a negative regulator of NF-κB signalling, and then activated the IKK/IκBα/NF-κB signalling pathway.

Conclusions

Our findings demonstrate that KBP is the key regulator of excessive inflammation in DFUs and provide a novel target for DFU therapy.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0376-9) contains supplementary material, which is available to authorized users.

Sex Differences in IL-33-Induced STAT6-Dependent Type 2 Airway Inflammation

Sex differences in asthma prevalence are well-documented but poorly understood. Murine models have contributed to our understanding of mechanisms that could regulate this sex disparity, though the majority of these studies have examined responses present after Th2 adaptive immunity is established. We have now investigated how sex influences acute activation of innate cell populations in the lung upon initial exposure to the model antigen, ovalbumin (OVA), in the presence of IL-33 (OVA+IL-33), to prime the lungs for type 2 immunity. We also examined how inflammatory responses induced by OVA+IL-33 were altered in mice lacking the STAT6 transcription factor, which is activated by IL-13, an effector cytokine of IL-33. Our data demonstrate that type 2 inflammation induced by OVA+IL-33 was more severe in female mice compared to males. Females exhibited greater cytokine and chemokine production, eosinophil influx and activation, macrophage polarization to the alternatively activated phenotype, and expansion of group 2 innate lymphoid cells (ILC2s). While increases in ILC2s and eosinophils were largely independent of STAT6 in both males and females, many other responses were STAT6-dependent only in female mice. Our findings indicate that a subset of type 2 inflammatory responses induced by OVA+IL-33 require STAT6 in both males and females and that enhanced type 2 inflammation in females, compared to males, is associated with greater IL-13 protein production. Our findings suggest blunted IL-13 production in males may protect against type 2 inflammation initiated by OVA+IL-33 delivery to the lung.

Innate Lymphoid Cells in Helminth Infections-Obligatory or Accessory?

ILCs burst onto the immunological scene with their involvement in bacterial and helminth infections. As their influence has emerged, it has become clear that they play a fundamental role in regulating barrier tissue homeostasis and the immune response during inflammation. A subset of ILCs, ILC2s, has become the focus of attention for many helminth biologists-stepping into the limelight as both the elusive initiator and amplifier of the type-2 response. In many of the early reports, conclusions as to their function were based on experiments using unadapted parasites or immune-compromised hosts. In this review we re-examine the generation and function of type-2 ILCs in helminth infection and the extent to which their roles may be essential or redundant, in both primary and challenge infections. ILC2s will be discussed in terms of a broader innate network, which when in dialogue with adaptive immunity, allows the generation of the anti-parasite response. Finally, we will review how helminths manipulate ILC2 populations to benefit their survival, as well as dampen systemic inflammation in the host, and how this understanding may be used to improve strategies to control disease.

IL-33 in obesity: where do we go from here?

IL-33 is a cytokine that belongs to the IL-1 family and is classically associated with type 2-like immune responses. In the adipose tissue, IL-33 is related to the beiging of adipocytes and to the maintenance of adipose tissue-resident immune cells, such as innate lymphoid cells 2, alternatively activated macrophages and regulatory T cells, which contribute to the maintenance of adipose tissue homeostasis. In the obese adipose tissue, the number of these cells is diminished, unlike the expression of IL-33, which is up-regulated. However, despite its increased expression, IL-33 is not able to maintain the homeostasis of the obese adipose tissue. IL-33 treatment, on the other hand, highly improves obesity-related inflammatory and metabolic alterations. The evidence that exogenous IL-33, but not adipose tissue-driven IL-33, regulates the inflammatory process in obesity leaves a gap in the understanding of IL-33 biology. Thus, in this review we discuss the potential mechanisms associated with the impaired action of IL-33 in obesity.

Expression of TSLP and IL-33 receptors on sputum macrophages of asthma patients and healthy subjects

Objective: Local cytokine milieu (especially Th2 inflammatory type) secreted into the asthmatic airways affect the alternative activated macrophages polarization (M2). TSLP and IL-33 are important alarmins of allergic response associated with Th2 inflammation. The aim of the study was to investigate the expression of the receptors for epithelial derived cytokines: TSLP (TSLPR) and IL-33 (ST2) on induced sputum CD206 positive macrophages from asthma and healthy subjects and analyze the relationships between these receptors and clinical features of the disease. Methods: Immunofluorescence staining for CD206 and TSLPR or ST2 on sputum macrophages was performed in 20 adult patients with stable asthma - 75% with atopy (3 intermittent, 12 mild-to-moderate, 5 severe, of which 11 were on biological anty-IgE treatment) and 23 healthy adult controls - 48% with atopy. Results: Our study demonstrated an increased expression of TSLP and IL-33 receptors on bronchial CD206 positive macrophages in asthma group. TSLPR but not ST2 had also greater expression on CD206 negative macrophages in asthma patients. Increased expression of both investigated receptors was related to longer disease duration and impaired lung function. We observed increased count of CD206_lowTSLP_high macrophages as well as positive correlation of these cells with total serum IgE in patients with atopy. Conclusions: The macrophage response during allergic reaction is likely to be connected with TSLP but rather not with IL-33 action. Our study indicates an important role of crosstalk between macrophages, TSLP and IL-33 in asthma pathophysiology.

Kupffer Cells Survive Plasmodium berghei Sporozoite Exposure and Respond with a Rapid Cytokine Release

The liver stage of the Plasmodium life cycle features sporozoite traversal of the liver sinusoidal barrier through Kupffer cells (KCs) followed by invasion of hepatocytes. Little is known about the interaction of Plasmodium sporozoites with KCs, the liver-resident macrophages. Previous reports suggest KCs do not mount a pro-inflammatory response and undergo cell death following this interaction. Our work explores this interaction using primary rat KCs (PRKCs) and Plasmodium berghei sporozoites. We analyzed PRKC culture supernatants for markers of an immunological response through cytokine arrays. Additionally, cell wounding and death were assessed by monitoring lactate dehydrogenase (LDH) levels in these supernatants and by live/dead cell imaging. We found that PRKCs mount an immunological response to P. berghei sporozoites by releasing a diverse set of both pro- and anti-inflammatory cytokines, including IFNγ, IL-12p70, Mip-3α, IL-2, RANTES, IL-1α, IL-4, IL-5, IL-13, EPO, VEGF, IL-7, and IL-17α. We also observed no difference in LDH level or live/dead staining upon sporozoite exposure, suggesting that the KCs are not deeply wounded or dying. Overall, our data suggest that sporozoites may be actively modulating the KC's reaction to their presence and altering the way the innate immune system is triggered by KCs.

IL-25 protects against high-fat diet-induced hepatic steatosis in mice by inducing IL-25 and M2a macrophage production

Interleukin (IL)-25 is a cytokine that has previously been shown to have a protective role against nonalcoholic fatty liver disease (NAFLD), which is associated with the induction of M2 macrophage differentiation. However, the direct relationships between IL-25 expression regulation, M2 induction and NAFLD remain unknown. In this study, we demonstrate that IL-25 promotes hepatic macrophage differentiation into M2a macrophages both in vivo and in vitro via the IL-13/STAT6 pathway. M2 macrophages that were differentiated in vitro were able to ameliorate high-fat diet HFD-induced hepatic steatosis. Furthermore, we found that IL-25 treatment, both in vitro and in vivo, promotes direct binding of STAT6 to the IL-25 gene promoter region. This binding of STAT6 in response to IL-25 treatment also resulted in the increase of IL-25 expression in hepatocytes. Together, these findings identify IL-25 as a protective factor against HFD-induced hepatic steatosis by inducing an increase of IL-25 expression in hepatocytes and through promotion of M2a macrophage production.

Biological Properties and the Role of IL-25 in Disease Pathogenesis

The interleukin- (IL-) 17 superfamily, a T cell-derived cytokine, consists of 6 ligands (IL-17A-IL-17F) and 5 receptors (IL-17RA-IL-17RE). IL-17A, a prototype member of this family, is involved in the pathogenesis of allergies, autoimmune diseases, allograft transplantations, and malignancies. By contrast, IL-17B is reported to be closely related to certain diseases, particularly tumors such as breast cancer, gastric cancer, and pancreatic cancer. Recently, the biological function of IL-17E (also called IL-25) in disease, particularly airway diseases, has attracted the attention of researchers. However, studies on IL-25 are scant. In this review, we detail the structural characteristics, expression patterns, responder cells, biological properties, and role of IL-25 in disease pathogenesis.

Concerted IL-25R and IL-4Rα signaling drive innate type 2 effector immunity for optimal helminth expulsion

Interleukin 25 (IL-25) is a major 'alarmin' cytokine, capable of initiating and amplifying the type immune response to helminth parasites. However, its role in the later effector phase of clearing chronic infection remains unclear. The helminth Heligmosomoides polygyrus establishes long-term infections in susceptible C57BL/6 mice, but is slowly expelled in BALB/c mice from day 14 onwards. We noted that IL-25R (Il17rb)-deficient BALB/c mice were unable to expel parasites despite type 2 immune activation comparable to the wild-type. We then established that in C57BL/6 mice, IL-25 adminstered late in infection (days 14-17) drove immunity. Moreover, when IL-25 and IL-4 were delivered to Rag1-deficient mice, the combination resulted in near complete expulsion of the parasite, even following administration of an anti-CD90 antibody to deplete innate lymphoid cells (ILCs). Hence, effective anti-helminth immunity during chronic infection requires an innate effector cell population that is synergistically activated by the combination of IL-4Rα and IL-25R signaling.

Mechanistic Basis for Obesity-related Increases in Ozone-induced Airway Hyperresponsiveness in Mice

Obesity is a risk factor for asthma, especially nonallergic asthma. Ozone, a common air pollutant, is a nonallergic asthma trigger. Importantly, ozone-induced decrements in lung function are greater in obese and overweight human subjects than in lean individuals. Obese mice also exhibit exaggerated pulmonary responses to ozone. Ozone causes greater increases in pulmonary resistance, in bronchoalveolar lavage neutrophils, and in airway hyperresponsiveness in obese than in lean mice. Our data indicate that IL-33 plays a role in mediating these events. Ozone causes greater release of IL-33 into bronchoalveolar lavage fluid in obese than in lean mice. Furthermore, an antibody blocking the IL-33 receptor, ST2, attenuates ozone-induced airway hyperresponsiveness in obese but not in lean mice. Our data also indicate a complex role for tumor necrosis factor (TNF)-α in obesity-related effects on the response to ozone. In obese mice, genetic deficiency in either TNF-α or TNF-α receptor 2 augments ozone-induced airway hyperresponsiveness, whereas TNF-α receptor 2 deficiency virtually abolishes ozone-induced airway hyperresponsiveness in lean mice. Finally, obesity is known to alter the gut microbiome. In female mice, antibiotics attenuate obesity-related increases in the effect of ozone on airway hyperresponsiveness, possibly by altering microbial production of short-chain fatty acids. Asthma control is often difficult to achieve in obese patients with asthma. Our data suggest that therapeutics directed against IL-33 may ultimately prove effective in these patients. The data also suggest that dietary manipulations and other strategies (prebiotics, probiotics) that alter the microbiome and/or its metabolic products may represent a new frontier for treating asthma in obese individuals.

Neonatal Immunity, Respiratory Virus Infections, and the Development of Asthma

Infants are exposed to a wide range of potential pathogens in the first months of life. Although maternal antibodies acquired transplacentally protect full-term neonates from many systemic pathogens, infections at mucosal surfaces still occur with great frequency, causing significant morbidity and mortality. At least part of this elevated risk is attributable to the neonatal immune system that tends to favor T regulatory and Th2 type responses when microbes are first encountered. Early-life infection with respiratory viruses is of particular interest because such exposures can disrupt normal lung development and increase the risk of chronic respiratory conditions, such as asthma. The immunologic mechanisms that underlie neonatal host-virus interactions that contribute to the subsequent development of asthma have not yet been fully defined. The goals of this review are (1) to outline the differences between the neonatal and adult immune systems and (2) to present murine and human data that support the hypothesis that early-life interactions between the immune system and respiratory viruses can create a lung environment conducive to the development of asthma.

A Guide to IL-1 family cytokines in adjuvanticity

Growing awareness of the multiplicity of roles for the IL-1 family in immune regulation has prompted research exploring these cytokines in the context of vaccine-induced immunity. While tightly regulated, cytokines of the IL-1 family are normally released in response to cellular stress and in combination with other danger-/damage-associated molecular patterns (DAMPs), triggering potent local and systemic immune responses. In the context of infection or autoimmunity, engagement of IL-1 family receptors links robust innate responses to adaptive immunity. Clinical and experimental evidence has revealed that many vaccine adjuvants induce the release of one or multiple IL-1 family cytokines. The coordinated release of IL-1 family members in response to adjuvant-induced damage or cell death may be a determining factor in the transition from local inflammation to the induction of an adaptive response. Here, we analyse the effects of IL-1 family cytokines on innate and adaptive immunity with a particular emphasis on activation of antigen-presenting cells and induction of T cell-mediated immunity, and we address in detail the contribution of these cytokines to the modes of action of vaccine adjuvants including those currently approved for human use.

IL-33: biological properties, functions, and roles in airway disease

Interleukin (IL)-33 is a key cytokine involved in type 2 immunity and allergic airway diseases. Abundantly expressed in lung epithelial cells, IL-33 plays critical roles in both innate and adaptive immune responses in mucosal organs. In innate immunity, IL-33 and group 2 innate lymphoid cells (ILC2s) provide an essential axis for rapid immune responses and tissue homeostasis. In adaptive immunity, IL-33 interacts with dendritic cells, Th2 cells, follicular T cells, and regulatory T cells, where IL-33 influences the development of chronic airway inflammation and tissue remodeling. The clinical findings that both the IL-33 and ILC2 levels are elevated in patients with allergic airway diseases suggest that IL-33 plays an important role in the pathogenesis of these diseases. IL-33 and ILC2 may also serve as biomarkers for disease classification and to monitor the progression of diseases. In this article, we reviewed the current knowledge of the biology of IL-33 and discussed the roles of the IL-33 in regulating airway immune responses and allergic airway diseases.

IL-33/ST2 axis affects the polarization and efferocytosis of decidual macrophages in early pregnancy

PROBLEM

To explore whether IL-33/ST2 axis modulates the polarization and efferocytosis of decidual macrophages (dMφs).

METHOD OF STUDY

The phenotype characteristics of dMφs from both normal pregnant women and recurrent spontaneous abortion (RSA) patients were determined by real-time polymerase chain reaction (RT-PCR) and flow cytometry (FCM). Then, the efferocytosis and expression of IL-33 and its receptor (ST2) in dMφs were analyzed by FCM. Finally, the effects of sST2, a decoy receptor for IL-33 that inhibits the IL-33/ST2 signaling pathway, on the polarization and efferocytosis of dMφs and human macrophage cell line U937 were investigated.

RESULTS

Compared with normal pregnancy, dMφs from RSA patients presented a M1 phenotype with high secretion of IL-33, whereas the expression of ST2 decreased. However, dMφs from RSA patients possessed a more powerful efferocytosis ability to clear the apoptotic decidual stromal cells (DSCs) compared with dMφs from normal pregnancy patients. Treatment with recombinant human sST2 led to the up-regulation of M1 bias and efferocytosis ability of both normal dMφs and U937.

CONCLUSION

This study indicates that IL-33 secreted by dMφs promotes M2 bias at the feto-maternal interface, and as a result, RSA might attribute to the disturbance of IL-33/ST2 axis and the enhancement of efferocytosis of dMφs subsequently.

Adenosine receptors differentially regulate type 2 cytokine production by IL-33-activated bone marrow cells, ILC2s, and macrophages

Group 2 innate lymphoid cells (ILC2s) represent a rapid source of type 2 cytokines, such as IL-5 and IL-13, and play an important role in orchestrating type 2 immune response. Adenosine is an endogenous purine nucleoside, a catabolite of ATP that binds and activates ≥1 of 4 transmembrane G protein-coupled cell-surface adenosine receptors (ARs)-A1, A2A, A2B, and A3. Here, we studied the role of ARs in the regulation of cytokine production by ILC2s. We found that A2BARs suppress the production of both IL-5 and IL-13 by ILC2s, whereas A2AARs augment IL-5 production and fail to affect IL-13 release. Combined stimulation of all ARs led to the suppression of both IL-5 and IL-13 production, which indicated that A2BARs dominate A2AARs. Both pre- and post-transcriptional processes may be involved in the AR modulation of ILC2 IL-5 and IL-13 production. Thus, we identify adenosine as a novel negative regulator of ILC2 activation.-Csóka, B., Németh, Z. H., Duerr, C. U., Fritz, J. H., Pacher, P., Haskó, G. Adenosine receptors differentially regulate type 2 cytokine production by IL-33-activated bone marrow cells, ILC2s, and macrophages.

Potentiating Tissue-Resident Type 2 Innate Lymphoid Cells by IL-33 to Prevent Renal Ischemia-Reperfusion Injury

The IL-33-type 2 innate lymphoid cell (ILC2) axis has an important role in tissue homeostasis, inflammation, and wound healing. However, the relative importance of this innate immune pathway for immunotherapy against inflammation and tissue damage remains unclear. Here, we show that treatment with recombinant mouse IL-33 prevented renal structural and functional injury and reduced mortality in mice subjected to ischemia-reperfusion injury (IRI). Compared with control-treated IRI mice, IL-33-treated IRI mice had increased levels of IL-4 and IL-13 in serum and kidney and more ILC2, regulatory T cells (Tregs), and anti-inflammatory (M2) macrophages. Depletion of ILC2, but not Tregs, substantially abolished the protective effect of IL-33 on renal IRI. Adoptive transfer of ex vivo-expanded ILC2 prevented renal injury in mice subjected to IRI. This protective effect associated with induction of M2 macrophages in kidney and required ILC2 production of amphiregulin. Treatment of mice with IL-33 or ILC2 after IRI was also renoprotective. Furthermore, in a humanized mouse model of renal IRI, treatment with human IL-33 or transfer of ex vivo-expanded human ILC2 ameliorated renal IRI. This study has uncovered a major protective role of the IL-33-ILC2 axis in renal IRI that could be potentiated as a therapeutic strategy.

Novel protective mechanism for interleukin-33 at the mucosal barrier during influenza-associated bacterial superinfection

Influenza A is a highly contagious respiratory virus that causes seasonal epidemics and occasional worldwide pandemics. The primary cause of influenza-related mortality is bacterial superinfection. There are numerous mechanisms by which preceding influenza infection attenuates host defense, allowing for increased susceptibility to bacterial pneumonia. Herein, we demonstrate that influenza inhibits Staphylococcus aureus-induced production of interleukin-33 (IL-33). Restoration of IL-33 during influenza A and methicillin-resistant S. aureus superinfection enhanced bacterial clearance and improved mortality. Innate lymphoid Type 2 cells and alternatively activated macrophages are not required for IL-33-mediated protection during superinfection. We show that IL-33 treatment resulted in neutrophil recruitment to the lung, associated with improved bacterial clearance. These findings identify a novel role for IL-33 in antibacterial host defense at the mucosal barrier.

HpARI Protein Secreted by a Helminth Parasite Suppresses Interleukin-33

Infection by helminth parasites is associated with amelioration of allergic reactivity, but mechanistic insights into this association are lacking. Products secreted by the mouse parasite Heligmosomoides polygyrus suppress type 2 (allergic) immune responses through interference in the interleukin-33 (IL-33) pathway. Here, we identified H. polygyrus Alarmin Release Inhibitor (HpARI), an IL-33-suppressive 26-kDa protein, containing three predicted complement control protein (CCP) modules. In vivo, recombinant HpARI abrogated IL-33, group 2 innate lymphoid cell (ILC2) and eosinophilic responses to Alternaria allergen administration, and diminished eosinophilic responses to Nippostrongylus brasiliensis, increasing parasite burden. HpARI bound directly to both mouse and human IL-33 (in the cytokine’s activated state) and also to nuclear DNA via its N-terminal CCP module pair (CCP1/2), tethering active IL-33 within necrotic cells, preventing its release, and forestalling initiation of type 2 allergic responses. Thus, HpARI employs a novel molecular strategy to suppress type 2 immunity in both infection and allergy.

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HpARI is a suppressor of IL-33 release and consequent allergic sensitization

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HpARI binds active IL-33 and nuclear DNA, tethering IL-33 within necrotic cells

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HpARI is active against both human and murine IL-33

Myeloid Cell Phenotypes in Susceptibility and Resistance to Helminth Parasite Infections

Many major tropical diseases are caused by long-lived helminth parasites that are able to survive by modulation of the host immune system, including the innate compartment of myeloid cells. In particular, dendritic cells and macrophages show markedly altered phenotypes during parasite infections. In addition, many specialized subsets such as eosinophils and basophils expand dramatically in response to these pathogens. The changes in phenotype and function, and their effects on both immunity to infection and reactivity to bystander antigens such as allergens, are discussed.