Inflammatory cytokine signalling in vulvovaginal candidiasis: a hot mess driving immunopathology

Protective immunity to opportunistic fungal infections consists of tightly regulated innate and adaptive immune responses that clear the infection. Immune responses to infections of the vaginal mucosa by Candida species are, however, an exception. In the case of vulvovaginal candidiasis (VVC), the inflammatory response is associated with symptomatic disease, rather than that it results in pathogen clearance. As such VVC can be considered an inflammatory disease, which is a significant public health problem due to its predominance as a female-specific fungal infection. Particularly, women with recurrent VVC (RVVC) suffer from a significant negative impact on their quality of life and mental health. Knowledge of the inflammatory pathogenesis of (R)VVC may guide more effective diagnostic and therapeutic options to improve the quality of life of women with (R)VVC. Here, we review the immunopathogenesis of (R)VVC describing several elements that induce an inflammatory arson, starting with the activation threshold established by vaginal epithelial cells that prevent unnecessary ignition of inflammatory responses, epithelial and inflammasome-dependent immune responses. These inflammatory responses will drive neutrophil recruitment and dysfunctional neutrophil-mediated inflammation. We also review the, sometimes controversial, findings on the involvement of adaptive and systemic responses. Finally, we provide future perspectives on the potential of some unexplored cytokine axes and discuss whether VVC needs to be subdivided into subgroups to improve diagnosis and treatment.

Cathelicidin boosts the antifungal activity of neutrophils and improves prognosis during Aspergillus fumigatus keratitis

Aspergillus fumigatus (A. fumigatus) is one of the common pathogens of fungal keratitis. Fungal growth and invasion cause excessive inflammation and corneal damage, leading to severe vision loss. Neutrophils are the primary infiltrating cells critical for fungal clearance. Cathelicidin [LL-37 in humans and cathelicidin-related antimicrobial peptide (CRAMP) in mice], a natural antimicrobial peptide, can directly inhibit the growth of many pathogens and regulate immune responses. However, the role of cathelicidin and its effect on neutrophils in A. fumigatus keratitis remain unclear. By establishing A. fumigatus keratitis mouse models, we found that cathelicidin was increased in A. fumigatus keratitis. It could reduce fungal loads, lower clinical scores, and improve corneal transparency. Restriction of CRAMP on fungal proliferation was largely counteracted in CD18-/- mice, in which neutrophils cannot migrate into infected sites. When WT neutrophils were transferred into CD18-/- mice, corneal fungal loads were distinctly reduced, indicating that neutrophils are vital for CRAMP-mediated resistance. Furthermore, cathelicidin promoted neutrophils to phagocytose and degrade conidia both in vitro and in vivo. CXC chemokine receptor 2 (CXCR2) was reported to be a functional receptor of LL-37 on neutrophils. CXCR2 antagonist SB225002 or phospholipase C (PLC) inhibitor U73122 weakened LL-37-induced phagocytosis. Meanwhile, LL-37 induced PLC γ phosphorylation, which was attenuated by SB225002. SB225002 or the autophagy inhibitors Bafilomycin-A1 and 3-Methyladenine weakened LL-37-induced degradation of conidia. Transmission electron microscopy (TEM) observed that LL-37 increased autophagosomes in Aspergillus-infected neutrophils. Consistently, LL-37 elevated autophagy-associated protein expressions (Beclin-1 and LC3-II), but this effect was weakened by SB225002. Collectively, cathelicidin reduces fungal loads and improves the prognosis of A. fumigatus keratitis. Both in vitro and in vivo, cathelicidin promotes neutrophils to phagocytose and degrade conidia. LL-37/CXCR2 activates PLC γ to amplify neutrophils' phagocytosis and induces autophagy to eliminate intracellular conidia.

ST2-Mediated Neutrophilic Airway Inflammation: A Therapeutic Target for Patients With Uncontrolled Asthma

PURPOSE

Suppression of tumorigenicity 2 (ST2) has been proposed as the receptor contributing to neutrophilic inflammation in patients with type 2-low asthma. However, the exact role of ST2 in neutrophil activation remains poorly understood.

METHODS

A total of 105 asthmatic patients (classified into 3 groups according to control status: the controlled asthma [CA], partly-controlled asthma [PA], and uncontrolled asthma [UA] groups), and 104 healthy controls were enrolled to compare serum levels of soluble ST2 (sST2) and interleukin (IL)-33. Moreover, the functions of ST2 in neutrophils and macrophages (Mϕ) were evaluated ex vivo and in vivo.

RESULTS

Serum sST2 levels were significantly higher in the UA group than in the CA or PA groups (P < 0.05 for all) with a negative correlation between serum sST2 and forced expiratory volume in 1 second % (r = -0.203, P = 0.038). Significantly higher expression of ST2 receptors on peripheral neutrophils was noted in the UA group than in the PA or CA groups. IL-33 exerted its effects on the production of reactive oxygen species, the formation of extracellular traps from neutrophils, and Mϕ polarization/activation. In neutrophilic asthmatic mice, treatment with anti-ST2 antibody significantly suppressed proinflammatory cytokines (tumor necrosis factor-alpha and IL-17A) as well as the numbers of immune cells (neutrophils, Mϕ, and group 3 innate lymphoid cells) in the lungs.

CONCLUSIONS

These results suggest that IL-33 induces the activation of neutrophils and Mϕ via ST2 receptors, leading to neutrophilic airway inflammation and poor control status of asthma. ST2 could be a therapeutic target for neutrophilic airway inflammation in patients with UA.

IL-33 priming and antigenic stimulation synergistically promote the transcription of proinflammatory cytokine and chemokine genes in human skin mast cells

BACKGROUND

Antigenic stimulation through cross-linking the IgE receptor and epithelial cell-derived cytokine IL-33 are potent stimuli of mast cell (MC) activation. Moreover, IL-33 primes a variety of cell types, including MCs to respond more vigorously to external stimuli. However, target genes induced by the combined IL-33 priming and antigenic stimulation have not been investigated in human skin mast cells (HSMCs) in a genome-wide manner. Furthermore, epigenetic changes induced by the combined IL-33 priming and antigenic stimulation have not been evaluated.

RESULTS

We found that IL-33 priming of HSMCs enhanced their capacity to promote transcriptional synergy of the IL1B and CXCL8 genes by 16- and 3-fold, respectively, in response to combined IL-33 and antigen stimulation compared to without IL-33 priming. We identified the target genes in IL-33-primed HSMCs in response to the combined IL-33 and antigenic stimulation using RNA sequencing (RNA-seq). We found that the majority of genes synergistically upregulated in the IL-33-primed HSMCs in response to the combined IL-33 and antigenic stimulation were predominantly proinflammatory cytokine and chemokine genes. Moreover, the combined IL-33 priming and antigenic stimulation increase chromatin accessibility in the synergy target genes but not synergistically. Transcription factor binding motif analysis revealed more binding sites for NF-κB, AP-1, GABPA, and RAP1 in the induced or increased chromatin accessible regions of the synergy target genes.

CONCLUSIONS

Our study demonstrates that IL-33 priming greatly potentiates MCs' ability to transcribe proinflammatory cytokine and chemokine genes in response to antigenic stimulation, shining light on how epithelial cell-derived cytokine IL-33 can cause exacerbation of skin MC-mediated allergic inflammation.

Cytokines and their role as immunotherapeutics and vaccine Adjuvants: The emerging concepts

Cytokines are a protein family comprising interleukins, lymphokines, chemokines, monokines and interferons. They are significant constituents of the immune system, and they act in accordance with specific cytokine inhibiting compounds and receptors for the regulation of immune responses. Cytokine studies have resulted in the establishment of newer therapies which are being utilized for the treatment of several malignant diseases. The advancement of these therapies has occurred from two distinct strategies. The first strategy involves administrating the recombinant and purified cytokines, and the second strategy involves administrating the therapeutics which inhibits harmful effects of endogenous and overexpressed cytokines. Colony stimulating factors and interferons are two exemplary therapeutics of cytokines. An important effect of cytokine receptor antagonist is that they can serve as anti-inflammatory agents by altering the treatments of inflammation disorder, therefore inhibiting the effects of tumour necrosis factor. In this article, we have highlighted the research behind the establishment of cytokines as therapeutics and vaccine adjuvants, their role of immunotolerance, and their limitations.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

The role of G protein-coupled receptor in neutrophil dysfunction during sepsis-induced acute respiratory distress syndrome

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.

Knowledge mapping and research trends of IL-33 from 2004 to 2022: a bibliometric analysis

Background

IL-33 has been studied widely but its comprehensive and systematic bibliometric analysis is yet available. The present study is to summarize the research progress of IL-33 through bibliometric analysis.

Methods

The publications related to IL-33 were identified and selected from the Web of Science Core Collection (WoSCC) database on 7 December 2022. The downloaded data was analyzed with bibliometric package in R software. CiteSpace and VOSviewer were used to conduct IL-33 bibliometric and knowledge mapping analysis.

Results

From 1 January 2004 to 7 December 2022, 4711 articles on IL-33 research published in 1009 academic journals by 24652 authors in 483 institutions from 89 countries were identified. The number of articles had grown steadily over this period. The United States of America(USA) and China are the major contributors in the field of research while University of Tokyo and University of Glasgow are the most active institutions. The most prolific journal is Frontiers in Immunology, while the Journal of Immunity is the top 1 co-cited journal. Andrew N. J. Mckenzie published the most significant number of articles and Jochen Schmitz was co-cited most. The major fields of these publications are immunology, cell biology, and biochemistry & molecular biology. After analysis, the high-frequency keywords of IL-33 research related to molecular biology (sST2, IL-1), immunological effects (type 2 immunity, Th2 cells), and diseases (asthma, cancer, cardiovascular diseases). Among these, the involvement of IL-33 in the regulation of type 2 inflammation has strong research potential and is a current research hotspot.

Conclusion

The present study quantifies and identifies the current research status and trends of IL-33 using bibliometric and knowledge mapping analysis. This study may offer the direction of IL-33-related research for scholars.

A Fun-Guide to Innate Immune Responses to Fungal Infections

Immunocompromised individuals are at high risk of developing severe fungal infections with high mortality rates, while fungal pathogens pose little risk to most healthy people. Poor therapeutic outcomes and growing antifungal resistance pose further challenges for treatments. Identifying specific immunomodulatory mechanisms exploited by fungal pathogens is critical for our understanding of fungal diseases and development of new therapies. A gap currently exists between the large body of literature concerning the innate immune response to fungal infections and the potential manipulation of host immune responses to aid clearance of infection. This review considers the innate immune mechanisms the host deploys to prevent fungal infection and how these mechanisms fail in immunocompromised hosts. Three clinically relevant fungal pathogens (Candida albicans, Cryptococcus spp. and Aspergillus spp.) will be explored. This review will also examine potential mechanisms of targeting the host therapeutically to improve outcomes of fungal infection.

The Interactions Between Autoinflammation and Type 2 Immunity: From Mechanistic Studies to Epidemiologic Associations

Autoinflammatory diseases are a group of clinical syndromes characterized by constitutive overactivation of innate immune pathways. This results in increased production of or responses to monocyte- and neutrophil-derived cytokines such as interleukin-1β (IL-1β), Tumor Necrosis Factor-α (TNF-α), and Type 1 interferon (IFN). By contrast, clinical allergy is caused by dysregulated type 2 immunity, which is characterized by expansion of T helper 2 (Th2) cells and eosinophils, as well as overproduction of the associated cytokines IL-4, IL-5, IL-9, and IL-13. Traditionally, type 2 immune cells and autoinflammatory effectors were thought to counter-regulate each other. However, an expanding body of evidence suggests that, in some contexts, autoinflammatory pathways and cytokines may potentiate type 2 immune responses. Conversely, type 2 immune cells and cytokines can regulate autoinflammatory responses in complex and context-dependent manners. Here, we introduce the concepts of autoinflammation and type 2 immunity. We proceed to review the mechanisms by which autoinflammatory and type 2 immune responses can modulate each other. Finally, we discuss the epidemiology of type 2 immunity and clinical allergy in several monogenic and complex autoinflammatory diseases. In the future, these interactions between type 2 immunity and autoinflammation may help to expand the spectrum of autoinflammation and to guide the management of patients with various autoinflammatory and allergic diseases.

Pathogen size alters C-type lectin receptor signaling in dendritic cells to influence CD4 Th9 cell differentiation

Dectin-1 recognizes β-glucan in fungal cell walls, and activation of Dectin-1 in dendritic cells (DCs) influences immune responses against fungi. Although many studies have shown that DCs activated via Dectin-1 induce different subsets of T helper cells according to different cytokine milieus, the mechanisms underlying such differences remain unknown. By harnessing polymorphic Candida albicans and polystyrene beads of different sizes, we find that target size influences production of cytokines that control differentiation of T helper cell subsets. Hyphal C. albicans and large beads activate DCs but cannot be phagocytosed due to their sizes, which prolongs the duration of Dectin-1 signaling. Transcriptomic analysis reveals that expression of Il33 is significantly increased by larger targets, and increased IL-33 expression promotes T_H9 responses. Expression of IL-33 is regulated by the Dectin-1-SYK-PLCγ-CARD9-ERK pathway. Altogether, our study demonstrates that size of fungi can be a determining factor in how DCs induce context-appropriate adaptive immune responses.

Oh et al. show that dendritic cells exposed to C. albicans hyphae more strongly induce IL-9-producing T cells compared with cells exposed to yeast. They find that this T_H9 response is driven in large part by Dectin-1 sensing microbe size, leading to elevated production of IL-33.

LncRNA: A Potential Target for Host-Directed Therapy of Candida Infection

Despite various drugs work against Candida, candidiasis represents clinical management challenges worldwide due to the rising incidence and recurrence rate, as well as epidemics, of new drug-resistant pathogens. Recent insights into interactions between Candida and hosts contribute to exploring novel therapeutic strategies, termed host-directed therapies (HDTs). HDTs are viable adjuncts with good efficacy for the existing standard antifungal regimens. However, HDTs induce other response unintendedly, thus requiring molecular targets with highly specificity. Long noncoding RNAs (lncRNAs) with highly specific expression patterns could affect biological processes, including the immune response. Herein, this review will summarize recent advances of HDTs based on the Candida–host interaction. Especially, the findings and application strategies of lncRNAs related to the host response are emphasized. We propose it is feasible to target lncRNAs to modulate the host defense during Candida infection, which provides a new perspective in identifying options of HDTs for candidiasis.

IL-33 Coordinates Innate Defense to Systemic Candida albicans Infection by Regulating IL-23 and IL-10 in an Opposite Way

Invasive candidiasis has high mortality rates in immunocompromised patients, causing serious health problems. In mouse models, innate immunity protects the host by rapidly mobilizing a variety of resistance and tolerance mechanisms to systemic Candida albicans infection. We have previously demonstrated that exogenous IL-33 regulates multiple steps of innate immunity involving resistance and tolerance processes. In this study, we systematically analyzed the in vivo functions of endogenous IL-33 using Il33 ^-/- mice and in vitro immune cell culture. Tubular epithelial cells mainly secreted IL-33 in response to systemic C. albicans infection. Il33 ^-/- mice showed increased mortality and morbidity, which were due to impaired fungal clearance. IL-33 initiated an innate defense mechanism by costimulating dendritic cells to produce IL-23 after systemic C. albicans infection, which in turn promoted the phagocytosis of neutrophils through secretion of GM-CSF by NK cells. The susceptibility of Il33 ^-/- mice was also associated with increased levels of IL-10, and neutralization of IL-10 resulted in enhanced fungal clearance in Il33 ^-/- mice. However, depletion of IL-10 overrode the effect of IL-33 on fungal clearance. In Il10 ^-/- mouse kidneys, MHC class II⁺F4/80⁺ macrophages were massively differentiated after C. albicans infection, and these cells were superior to MHC class II^-F4/80⁺ macrophages that were preferentially differentiated in wild-type mouse kidneys in killing of extracellular hyphal C. albicans Taken together, our results identify IL-33 as critical early regulator controlling a serial downstream signaling events of innate defense to C. albicans infection.

Emerging Functions of IL-33 in Homeostasis and Immunity

Our understanding of the functions of the IL-1 superfamily cytokine and damage-associated molecular pattern IL-33 continues to evolve with our understanding of homeostasis and immunity. The early findings that IL-33 is a potent driver of type 2 immune responses promoting parasite expulsion, but also inflammatory diseases like allergy and asthma, have been further supported. Yet, as the importance of a type 2 response in tissue repair and homeostasis has emerged, so has the fundamental importance of IL-33 to these processes. In this review, we outline an evolving understanding of IL-33 immunobiology, paying particular attention to how IL-33 directs a network of ST2+ regulatory T cells, reparative and regulatory macrophages, and type 2 innate lymphoid cells that are fundamental to tissue development, homeostasis, and repair.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

CD137 Signaling Is Critical in Fungal Clearance during Systemic Candida albicans Infection

Invasive fungal infections by Candida albicans frequently cause mortality in immunocompromised patients. Neutrophils are particularly important for fungal clearance during systemic C. albican infection, yet little has been known regarding which surface receptor controls neutrophils’ antifungal activities. CD137, which is encoded by Tnfrsf9, belongs to the tumor necrosis receptor superfamily and has been shown to regulate neutrophils in Gram-positive bacterial infection. Here, we used genetic and immunological tools to probe the involvement of neutrophil CD137 signaling in innate defense mechanisms against systemic C. albicans infection. We first found that Tnfrsf9^−/− mice were susceptible to C. albicans infection, whereas injection of anti-CD137 agonistic antibody protected the host from infection, suggesting that CD137 signaling is indispensable for innate immunity against C. albicans infection. Priming of isolated neutrophils with anti-CD137 antibody promoted their phagocytic and fungicidal activities through phospholipase C. In addition, injection of anti-CD137 antibody significantly augmented restriction of fungal growth in Tnfrsf9^−/− mice that received wild-type (WT) neutrophils. In conclusion, our results demonstrate that CD137 signaling contributes to defense mechanisms against systemic C. albicans infection by promoting rapid fungal clearance.

Role for IL-1 Family Cytokines in Fungal Infections

Fungal pathogens kill approximately 1.5 million individuals per year and represent a severe disease burden worldwide. It is estimated over 150 million people have serious fungal disease such as recurrent mucosal infections or life-threatening systemic infections. Disease can ensue from commensal fungi or new infection and involves different fungal morphologies and the expression of virulence factors. Therefore, anti-fungal immunity is complex and requires coordination between multiple facets of the immune system. IL-1 family cytokines are associated with acute and chronic inflammation and are essential for the innate response to infection. Recent research indicates IL-1 cytokines play a key role mediating immunity against different fungal infections. During mucosal disease, IL-1R and IL-36R are required for neutrophil recruitment and protective Th17 responses, but function through different mechanisms. During systemic disease, IL-18 drives protective Th1 responses, while IL-33 promotes Th2 and suppresses Th1 immunity. The IL-1 family represents an attractive anti-fungal immunotherapy target. There is a need for novel anti-fungal therapeutics, as current therapies are ineffective, toxic and encounter resistance, and no anti-fungal vaccine exists. Furthering our understanding of the IL-1 family cytokines and their complex role during fungal infection may aid the development of novel therapies. As such, this review will discuss the role for IL-1 family cytokines in fungal infections.

Circulating levels of IL-33 are elevated by obesity and positively correlated with metabolic disorders in Chinese adults

BACKGROUND

Interleukin-33 (IL-33) plays a pivotal role in regulating innate immune response and metabolic homeostasis. However, whether its circulating level is correlated with obesity and metabolic disorders in humans remains largely unknown. We aimed to address this gap by determining IL-33 serum level and its downstream type 2 inflammatory cytokines interleukin-5 (IL-5) and interleukin-13 (IL-13) in overweight/obese population, and analyzing the specific associations between IL-33 and obesity metabolic phenotypes.

METHODS

217 subjects were enrolled and divided into three groups: healthy control (HC) subjects, metabolically healthy overweight/obese (MHOO) subjects and metabolically unhealthy overweight/obese (MUOO) subjects. Circulating levels of IL-33, IL-5 and IL-13 were measured using ELISA analyses. Multivariate regression analyses were further performed to determine the independent association between IL-33 and obesity metabolic phenotypes.

RESULTS

Circulating levels of IL-33 were significantly elevated in subjects of MUOO group compared with HC group and MHOO group, while no significant difference was observed between the latter two groups in IL-33 levels. Consistent with this, serum levels of IL-5/13 were higher in the MUOO group compared with HC and MHOO groups. After adjusted for all confounders, MUOO phenotype was significantly associated with increased IL-33 serum levels (OR = 1.70; 95% CI 1.09-2.64; p = 0.019). With the MHOO group as the reference population, higher circulating level of IL-33 was also positively associated with MUOO phenotype after adjusting for confounders (OR = 1.50; 95% CI 1.20-1.88; p = 2.91E-4). However, there was no significant association between MHOO phenotype and IL-33 levels (p = 0.942). Trend analysis further confirmed the positive correlation between MUOO phenotype and IL-33 level (p for trend = 0.019). Additionally, IL-33 was significantly and positively correlated with diastolic blood pressure (DBP), total cholesterol (TC), alanine aminotransferase (ALT), aspartate aminotransferase (AST), white blood cell (WBC), neutrophil and IL-5 only in MUOO group, while inversely correlated with high density lipoprotein cholesterol (HDL-C) in MHOO subjects.

CONCLUSION

Circulating levels of IL-33 were significantly elevated in overweight/obese Chinese adults with metabolic disorders. Increased levels of IL-33 were positively associated with metabolically unhealthy overweight/obese phenotype and several metabolic syndrome risk factors.

Inhibition of Aerobic Glycolysis Promotes Neutrophil to Influx to the Infectious Site Via CXCR2 in Sepsis

Recent evidences suggest that metabolic reprogramming plays an important role in the regulation of innate inflammatory response; however, the specific mechanism is unclear. In this study, we found that glycolytic inhibitor 2-deoxyglucose (2-DG) significantly improved the survival rate in cecal ligation and puncture (CLP)-induced septic mice. 2-DG-treated mice developed increased neutrophil migration to the infectious site and more efficient bacterial clearance than untreated mice. 2-DG reversed the down-regulation of chemokine receptor 2 (CXCR2) and the impaired chemotaxis induced by CLP in mice or lipopolysaccharides (LPS) in human neutrophils. Furthermore, 2-DG reversed the down-regulation of CXCR2 in neutrophils by decreasing the expression of G protein-coupled receptor kinase-2 (GRK2), a serin-threonine protein kinase that mediated the internalization of chemokine receptors, which was induced via the inhibition of extracellular regulated protein kinases (ERK) phosphorylation and the promotion of P38 phosphorylation. Finally, SB225002, a CXCR2 antagonist, partially blocked the protective effects of 2-DG in sepsis. Together, we found a novel mechanism for the migration of neutrophils regulated by metabolism and suggested that aerobic glycolysis might be a potential target of intervention in sepsis.

CCR5-mediated Recruitment of NK Cells to the Kidney Is a Critical Step for Host Defense to Systemic Candida albicans Infection

C-C chemokine receptor type 5 (CCR5) regulates the trafficking of various immune cells to sites of infection. In this study, we showed that expression of CCR5 and its ligands was rapidly increased in the kidney after systemic Candida albicans infection, and infected CCR5^−/− mice exhibited increased mortality and morbidity, indicating that CCR5 contributes to an effective defense mechanism against systemic C. albicans infection. The susceptibility of CCR5^−/− mice to C. albicans infection was due to impaired fungal clearance, which in turn resulted in exacerbated renal inflammation and damage. CCR5-mediated recruitment of NK cells to the kidney in response to C. albicans infection was necessary for the anti-microbial activity of neutrophils, the main fungicidal effector cells. Mechanistically, C. albicans induced expression of IL-23 by CD11c⁺ dendritic cells (DCs). IL-23 in turn augmented the fungicidal activity of neutrophils through GM-CSF production by NK cells. As GM-CSF potentiated production of IL-23 in response to C. albicans, a positive feedback loop formed between NK cells and DCs seemed to function as an amplification point for host defense. Taken together, our results suggest that CCR5-mediated recruitment of NK cells to the site of fungal infection is an important step that underlies innate resistance to systemic C. albicans infection.

Cellular context of IL-33 expression dictates impact on anti-helminth immunity

Interleukin-33 (IL-33) is a pleiotropic cytokine that can promote type 2 inflammation but also drives immunoregulation through Foxp3⁺T_reg expansion. How IL-33 is exported from cells to serve this dual role in immunosuppression and inflammation remains unclear. Here, we demonstrate that the biological consequences of IL-33 activity are dictated by its cellular source. Whereas IL-33 derived from epithelial cells stimulates group 2 innate lymphoid cell (ILC2)-driven type 2 immunity and parasite clearance, we report that IL-33 derived from myeloid antigen-presenting cells (APCs) suppresses host-protective inflammatory responses. Conditional deletion of IL-33 in CD11c-expressing cells resulted in lowered numbers of intestinal Foxp3⁺T_reg cells that express the transcription factor GATA3 and the IL-33 receptor ST2, causing elevated IL-5 and IL-13 production and accelerated anti-helminth immunity. We demonstrate that cell-intrinsic IL-33 promoted mouse dendritic cells (DCs) to express the pore-forming protein perforin-2, which may function as a conduit on the plasma membrane facilitating IL-33 export. Lack of perforin-2 in DCs blocked the proliferative expansion of the ST2⁺Foxp3⁺T_reg subset. We propose that perforin-2 can provide a plasma membrane conduit in DCs that promotes the export of IL-33, contributing to mucosal immunoregulation under steady-state and infectious conditions.

Soluble suppression of tumorigenicity-2 predicts pneumonia in patients with inhalation injury: Results of a pilot study

INTRODUCTION

Several mechanisms play a role in the development of pneumonia after inhalation injury. Our aim was to analyze whether higher concentrations of inflammatory markers or of biomarkers of epithelial injury are associated with a higher incidence of pneumonia in patients with inhalation injury.

MATERIAL AND METHODS

Secondary analysis of a single-center prospective observational cohort pilot study, performed over a two-year period (2015-2017) at the Burns Unit of the Plastic and Reconstructive Surgery Department of Vall d'Hebron University Hospital. All patients aged 18 with suspected inhalation injury undergoing admission to the Burns Unit were included. Plasma biomarkers of the lung epithelium (RAGE and SP-D), inflammation markers (IL6, IL8), and IL33, as well as soluble suppression of tumorigenicity-2 (sST2) levels, were measured within the first 24 h of admission.

RESULTS

Twenty-four patients with inhalation injury were included. Eight (33.3%) developed pneumonia after a median of 7 (4-8) days of hospital stay. Patients with pneumonia presented higher plasma concentrations of sST2 (2853 [2356-3351] ng/mL vs 1352 [865-1839] ng/mL; p < 0.001), IL33 (1.95 [1.31-2.59] pg/mL vs 1.26 [1.07-1.45] pg/mL; p = 0.002) and IL8 (325.7 [221.6-430.0] pg/mL vs 174.1 [95.2-253.0] pg/mL; p = 0.017) on day 1 of inclusion. Plasma sST2 concentration in the first 24 h demonstrated excellent diagnostic accuracy for predicting the occurrence of pneumonia in patients with smoke inhalation (AUROC 0.929 [95%CI 0.818-1.000]). A cutoff point of ≥2825 ng/mL for sST2 had a sensitivity of 75% and a specificity of 100%. The risk ratio of pneumonia in patients with sST2 ≥ 2825 ng/mL was 7.14 ([95% CI 1.56-32.61]; p = 0.016).

CONCLUSIONS

Plasma sST2 in the first 24 h of admission predicts the occurrence of pneumonia in patients with inhalation injury.

IL-33 enhances macrophage release of IL-1β and promotes pain and inflammation in gouty arthritis

OBJECTIVE

To investigate the role of IL-33 in gouty arthritis.

MATERIAL

174 Balb/c (wild-type) and 54 ST2^-/- mice were used in this study. In vitro experiments were conducted in bone marrow-derived macrophages (BMDMs). Synovial fluid samples from gouty arthritis (n = 7) and osteoarthritis (n = 8) hospital patients were used to measure IL-33 and sST2 levels.

METHODS

Gout was induced by injection of monosodium urate (MSU) crystals in the knee joint of mice. Pain was determined using the electronic von Frey and static weight bearing. Neutrophil recruitment was determined by H&E staining, Rosenfeld staining slides, and MPO activity. ELISA was used for cytokine and sST2 measurement. The priming effect of IL-33 was determined in BMDM.

RESULTS

Synovial fluid of gout patients showed higher IL-33 levels and neutrophil counts than osteoarthritis patients. In mice, the absence of ST2 prevented mechanical pain, knee joint edema, neutrophil recruitment to the knee joint, and lowered IL-1β and superoxide anion levels. In macrophages, IL-33 enhanced the release of IL-1β and TNF-α, and BMDMs from ST2^-/- showed reduced levels of these cytokines after stimulus with MSU crystals.

CONCLUSION

IL-33 mediates gout pain and inflammation by boosting macrophages production of cytokines upon MSU crystals stimulus.

IL-33/ST2 pathway regulates neutrophil migration and predicts outcome in patients with severe alcoholic hepatitis

BACKGROUND & AIMS

Severe alcoholic hepatitis (SAH) is associated with a high risk of infection. The IL-33/ST2 pathway is involved in sepsis control but data regarding its role in alcohol-related liver disease (ALD) are lacking. We aimed to characterize the role of IL-33/ST2 in the polymorphonuclear neutrophils (PMNs) of patients with ALD and SAH.

METHODS

Serum and circulating neutrophils were collected from patients with SAH, alcoholic cirrhosis and healthy controls. We quantified IL-33/ST2 pathway activity and CXCR2 at baseline and after exposure to IL-33. We also determined the migration capacity of PMNs.

RESULTS

The decoy receptor of IL-33 (soluble ST2 [sST2]) was increased in SAH vs. cirrhosis and controls, demonstrating the defect in this pathway during ALD. The sST2 level was associated with response to treatment, 2-month survival, infection-free survival and probability of infection in SAH. Endotoxemia was weakly correlated with sST2. GRK2, a negative regulator of CXCR2, was overexpressed in PMNs of patients with SAH and cirrhosis and was decreased by IL-33. CXCR2 levels on PMNs were lower in SAH vs. cirrhosis and controls. Treatment with IL-33 partially restored CXCR2 expression in SAH and cirrhosis. PMN migration upon IL-8 was lower in patients with SAH and cirrhosis vs. controls. Treatment with IL-33 partially restored migration in those with SAH and cirrhosis. Interestingly, the migration capacity of PMNs and the response to IL-33 were enhanced in responders to corticosteroids (Lille <0.45) compared to non-responders.

CONCLUSION

The IL33/ST2 pathway is defective in SAH and predicts outcome. This defect is associated with decreased CXCR2 expression on the surface of PMNs and lower migration capacity, which can be corrected by IL-33, especially in patients responding to steroids. These results suggest that IL-33 has therapeutic potential for SAH and its infectious complications.

LAY SUMMARY

The neutrophils of patients with severe alcoholic hepatitis are associated with a defect in the IL-33/ST2 pathway. This defect is associated with lower migration capacities in neutrophils and a higher probability of getting infected. Administration of IL-33 to the neutrophils at least partly restores this defect and may be effective at reducing the risk of infection in patients with severe alcoholic hepatitis.

New Host-Directed Therapeutics for the Treatment of Clostridioides difficile Infection

Frequent and excessive use of antibiotics primes patients to Clostridioides difficile infection (CDI), which leads to fatal pseudomembranous colitis, with limited treatment options. In earlier reports, we used a drug repurposing strategy and identified amoxapine (an antidepressant), doxapram (a breathing stimulant), and trifluoperazine (an antipsychotic), which provided significant protection to mice against lethal infections with several pathogens, including C. difficile However, the mechanisms of action of these drugs were not known. Here, we provide evidence that all three drugs offered protection against experimental CDI by reducing bacterial burden and toxin levels, although the drugs were neither bacteriostatic nor bactericidal in nature and had minimal impact on the composition of the microbiota. Drug-mediated protection was dependent on the presence of the microbiota, implicating its role in evoking host defenses that promoted protective immunity. By utilizing transcriptome sequencing (RNA-seq), we identified that each drug increased expression of several innate immune response-related genes, including those involved in the recruitment of neutrophils, the production of interleukin 33 (IL-33), and the IL-22 signaling pathway. The RNA-seq data on selected genes were confirmed by quantitative real-time PCR (qRT-PCR) and protein assays. Focusing on amoxapine, which had the best anti-CDI outcome, we demonstrated that neutralization of IL-33 or depletion of neutrophils resulted in loss of drug efficacy. Overall, our lead drugs promote disease alleviation and survival in the murine model through activation of IL-33 and by clearing the pathogen through host defense mechanisms that critically include an early influx of neutrophils.IMPORTANCEClostridioides difficile is a spore-forming anaerobic bacterium and the leading cause of antibiotic-associated colitis. With few therapeutic options and high rates of disease recurrence, the need to develop new treatment options is urgent. Prior studies utilizing a repurposing approach identified three nonantibiotic Food and Drug Administration-approved drugs, amoxapine, doxapram, and trifluoperazine, with efficacy against a broad range of human pathogens; however, the protective mechanisms remained unknown. Here, we identified mechanisms leading to drug efficacy in a murine model of lethal C. difficile infection (CDI), advancing our understanding of the role of these drugs in infectious disease pathogenesis that center on host immune responses to C. difficile Overall, these studies highlight the crucial involvement of innate immune responses, as well as the importance of immunomodulation as a potential therapeutic option to combat CDI.

IL-33 induces immunosuppressive neutrophils via a type 2 innate lymphoid cell/IL-13/STAT6 axis and protects the liver against injury in LCMV infection-induced viral hepatitis

Viral hepatitis is still a public health problem affecting several million people around the world. Neutrophils are polymorphonuclear cells that have a critical role in antibacterial infection. However, the role of neutrophils in viral infection is not fully understood. By using a mouse model of lymphocytic choriomeningitis virus infection-induced viral hepatitis, we observed increased neutrophil recruitment in the liver accompanied by enhanced CD8+ T-cell responses. Liver neutrophils expressed high levels of immunomodulatory cytokines, such as C-X-C chemokine ligand 2, arginase-1, inducible nitric oxide synthase and interleukin (IL)-10, demonstrating immunosuppressive properties. Depletion of neutrophils in vivo by a neutralizing antibody resulted in the exacerbation of liver injury and the promotion of T-cell responses at the immune contraction stage. IL-33 significantly induced neutrophil recruitment in the liver and attenuated liver injury by limiting effector T-cell accumulation. Mechanistically, we found that IL-33 promoted the expression of arginase-1 in neutrophils through the type 2 innate lymphoid cell (ILC2)-derived IL-13. Additionally, IL-13 increased the inhibitory effect of neutrophils on CD8+ T-cell proliferation in vitro, partially through arginase-1. Finally, we found that IL-13 induced arginase-1 expression, depending on signal transducer and activator of transcription factor 6 (STAT6) signaling. Therefore, IL-33 induced immunosuppressive neutrophils via an ILC2/IL-13/STAT6 axis. Collectively, our findings shed new light on the mechanisms associated with IL-33-triggered neutrophils in the liver and suggest potential targets for therapeutic investigation in viral hepatitis.

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.

IL-33 Treatment Attenuates the Systemic Inflammation Reaction in Acinetobacter baumannii Pneumonia by Suppressing TLR4/NF-κB Signaling

Interleukin (IL)-33 treatment has been reported to reduce mortality in a rat model of sepsis, and the present study aimed to determine whether this effect of IL-33 is achieved through a reduction in the systemic inflammatory response in Acinetobacter baumannii pneumonia. After induction of pneumonia, rats were treated with normal saline or IL-33, and mortality over 5 days was recorded. Inflammation within lung tissues was evaluated by hematoxylin and eosin staining as well as measurement of the concentrations of IL-8 and tumor necrosis factor alpha (TNF-α) in the bronchoalveolar lavage fluid (BALF) and plasma by enzyme-linked immunosorbent assay. In addition, the expression of Toll-like receptor 4 (TLR4), ST2, and nuclear factor kappa B (NF-κB) in rat lung tissues was assessed by western blotting. The result showed that the mortality rate and systemic inflammation were significantly increased in rats upon infection with A. baumannii, as evidenced by significant increases in the IL-8 and TNF-α levels in BALF and plasma as well as increased NF-κB activity and TLR4 expression in rat lung tissues. Importantly, IL-33 (1 μg/kg) treatment significantly decreased mortality and pulmonary inflammation in A. baumannii-infected rats. Moreover, IL-33 treatment suppressed the elevation of IL-8 and TNF-α levels and inhibited TLR4 expression and NF-κB activation. Overall, these results suggest that IL-33 may decrease the mortality and inhibit the systematic inflammatory response associated with A. baumannii pneumonia by suppressing TLR4/NF-κB signaling.

Recent advances in understanding the roles of blood platelets in the pathogenesis of allergic inflammation and bronchial asthma

Platelets play an essential role in hemostasis to minimize blood loss due to traumatic injury. In addition, they contain various immune-associated molecules and contribute to immunological barrier formation at sites of vascular injury, thereby protecting against invading pathogens. Platelets are also crucially involved in development of allergic diseases, including bronchial asthma. Platelets in asthmatics are more activated than those in healthy individuals. By using a murine asthma model, platelets were shown to be actively involved in progression of the disease, including in airway eosinophilia and airway remodeling. In the asthmatic airway, pathological microvascular angiogenesis, a component of airway remodeling, is commonly observed, and the degree of abnormality is significantly associated with disease severity. Therefore, in order to repair the newly formed and structurally fragile blood vessels under inflammatory conditions, platelets may be continuously activated in asthmatics. Importantly, platelets constitutively express IL-33 protein, an alarmin cytokine that is essential for development of bronchial asthma. Meanwhile, the concept of development of allergic diseases has recently changed dramatically, and allergy researchers now share a belief in the centrality of epithelial barrier functions. In particular, IL-33 released from epithelial barrier tissue at sites of eczema can activate the antigen-non-specific innate immune system as an alarmin that is believed to be necessary for subsequent antigen-specific acquired immunological responses. From this perspective, we propose in this review a possible mechanism for how activated platelets act as an alarmin in development of bronchial asthma.

The Interaction of Human Pathogenic Fungi With C-Type Lectin Receptors

Fungi, usually present as commensals, are a major cause of opportunistic infections in immunocompromised patients. Such infections, if not diagnosed or treated properly, can prove fatal. However, in most cases healthy individuals are able to avert the fungal attacks by mounting proper antifungal immune responses. Among the pattern recognition receptors (PRRs), C-type lectin receptors (CLRs) are the major players in antifungal immunity. CLRs can recognize carbohydrate ligands, such as β-glucans and mannans, which are mainly found on fungal cell surfaces. They induce proinflammatory immune reactions, including phagocytosis, oxidative burst, cytokine, and chemokine production from innate effector cells, as well as activation of adaptive immunity via Th17 responses. CLRs such as Dectin-1, Dectin-2, Mincle, mannose receptor (MR), and DC-SIGN can recognize many disease-causing fungi and also collaborate with each other as well as other PRRs in mounting a fungi-specific immune response. Mutations in these receptors affect the host response and have been linked to a higher risk in contracting fungal infections. This review focuses on how CLRs on various immune cells orchestrate the antifungal response and on the contribution of single nucleotide polymorphisms in these receptors toward the risk of developing such infections.

Targeting IL-33/ST2 signaling: regulation of immune function and analgesia

INTRODUCTION

IL-33 signals through ST2 receptor and promotes inflammation by activating downstream pathways culminating in the production of pro-inflammatory mediators such as IL-1β, TNF-α, and IL-6 in an NF-κB-dependent manner. In fact, compelling evidence has demonstrated the importance of IL-33/ST2 in both innate and adaptive immune responses in diseases presenting pain as an important clinical symptom. Areas covered: IL-33 is a pleiotropic cytokine with varied immune functions. Dysregulation of this pathway has been described as a key step in varied immune responses. Further, IL-33 contributes to peripheral and spinal cord nociceptor neuron sensitization in innate and adaptive inflammatory immune responses as well as in neuropathic and cancer pain. In this sense, targeting IL-33/ST2 signaling is a promising therapeutic approach. Expert opinion: The modulation of IL-33/ST2 signaling represents a possible approach in regulating immune functions. In addition to immune function, strategies targeting IL-33/ST2 signaling pathway display a favorable preclinical analgesic profile in both acute and chronic models of pain. Therefore, IL-33-targeting therapies represent a potential target for the development of novel analgesic drugs given that IL-33 activates, for instance, neutrophils, mast cells, macrophages, astrocytes, and microglia that are important cells in the induction and maintenance of chronic pain states.

IL-33 Signaling Regulates Innate IL-17A and IL-22 Production via Suppression of Prostaglandin E2 during Lung Fungal Infection

Members of the IL-1 family play protective and regulatory roles in immune defense against the opportunistic mold Aspergillus fumigatus In this study, we investigated the IL-1 family member IL-33 in lung defense against A. fumigatus IL-33 was detected in the naive lung, which further increased after exposure to A. fumigatus in a dectin-1-independent manner. Mice deficient in the receptor for IL-33 (Il1rl1-/-) unexpectedly demonstrated enhanced lung clearance of A. fumigatus IL-33 functioned as a negative regulator of multiple inflammatory cytokines, as IL-1α, IL-1β, IL-6, IL-17A, and IL-22 were significantly elevated in fungal-exposed Il1rl1-/- mice. Subsequently, IL-33 administration to normal mice attenuated fungal-induced IL-17A and IL-22, but not IL-1α, IL-1β, or IL-6, production. IL-33-mediated regulation of IL-17A and IL-22 did not involve the modulation of IL-23 but rather PGE2; PGE2 was significantly increased in fungal-exposed Il1rl1-/- mice, and normal mice produced less PGE2 after fungal exposure when administered IL-33, suggesting that IL-33-mediated regulation of IL-17A and IL-22 occurred at the level of PGE2 This was confirmed by in vivo cyclooxygenase 2 inhibition, which attenuated fungal-induced IL-17A and IL-22, as well as IL-1α, IL-1β, and IL-6, production in Il1rl1-/- mice, resulting in impaired fungal clearance. We also show that a PGE2 receptor agonist increased, whereas a PGE2 synthase inhibitor decreased, the levels of IL-17A and IL-22 but not IL-1α, IL-1β, or IL-6. This study establishes novel mechanisms of innate IL-17A/IL-22 production via PGE2 and regulation of the PGE2/IL-17A/IL-22 axis via IL-33 signaling during lung fungal exposure.

Multiple Phenotypic Changes Define Neutrophil Priming

Exposure to pro-inflammatory cytokines, chemokines, mitochondrial contents, and bacterial and viral products induces neutrophils to transition from a basal state into a primed one, which is currently defined as an enhanced response to activating stimuli. Although, typically associated with enhanced generation of reactive oxygen species (ROS) by the NADPH oxidase, primed neutrophils show enhanced responsiveness of exocytosis, NET formation, and chemotaxis. Phenotypic changes associated with priming also include activation of a subset of functions, including adhesion, transcription, metabolism, and rate of apoptosis. This review summarizes the breadth of phenotypic changes associated with priming and reviews current knowledge of the molecular mechanisms behind those changes. We conclude that the current definition of priming is too restrictive. Priming represents a combination of enhanced responsiveness and activated functions that regulate both adaptive and innate immune responses.

Endogenous IL-33 Deficiency Exacerbates Liver Injury and Increases Hepatic Influx of Neutrophils in Acute Murine Viral Hepatitis

The alarmin IL-33 has been described to be upregulated in human and murine viral hepatitis. However, the role of endogenous IL-33 in viral hepatitis remains obscure. We aimed to decipher its function by infecting IL-33-deficient mice (IL-33 KO) and their wild-type (WT) littermates with pathogenic mouse hepatitis virus (L2-MHV3). The IL-33 KO mice were more sensitive to L2-MHV3 infection exhibiting higher levels of AST/ALT, higher tissue damage, significant weight loss, and earlier death. An increased depletion of B and T lymphocytes, NKT cells, dendritic cells, and macrophages was observed 48 h postinfection (PI) in IL-33 KO mice than that in WT mice. In contrast, a massive influx of neutrophils was observed in IL-33 KO mice at 48 h PI. A transcriptomic study of inflammatory and cell-signaling genes revealed the overexpression of IL-6, TNFα, and several chemokines involved in recruitment/activation of neutrophils (CXCL2, CXCL5, CCL2, and CCL6) at 72 h PI in IL-33 KO mice. However, the IFNγ was strongly induced in WT mice with less profound expression in IL-33 KO mice demonstrating that endogenous IL-33 regulated IFNγ expression during L2-MHV3 hepatitis. In conclusion, we demonstrated that endogenous IL-33 had multifaceted immunoregulatory effect during viral hepatitis via induction of IFNγ, survival effect on immune cells, and infiltration of neutrophils in the liver.

Emerging Roles of IL-33/ST2 Axis in Renal Diseases

Renal diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), have a great impact on health care systems worldwide. Similar to cardiovascular diseases, renal diseases are inflammatory diseases involving a variety of cytokines. Primary causes of renal injury include ischemia, uremic toxins, bacteremia, or nephrotoxicity. Inflammation represents an important component following kidney injury. Interleukin (IL)-33 is a member of the IL-1 cytokine family, which is widely expressed in epithelial barrier tissues and endothelial cells, and mediates both tissue inflammation and repair responses. IL-33 is released as a nuclear alarmin in response to tissue damage and triggers innate and adaptive immune responses by binding to its receptor, suppression of tumorigenicity 2 (ST2). Recent evidence from clinical and experimental animal studies indicates that the IL-33/ST2 axis is involved in the pathogenesis of CKD, renal graft injury, systemic lupus nephritis, and AKI. In this review, we discuss the pathological and tissue reparative roles of the IL-33/ST2 pathway in different types of renal diseases.

The Correlation of CD206, CD209, and Disease Severity in Behçet's Disease with Arthritis

The purpose of this study was to clarify the role of pattern recognition receptors in Behçet's disease (BD). The frequencies of several pattern recognition receptors (CD11b, CD11c, CD32, CD206, CD209, and dectin-1) were analyzed in patients with BD by flow cytometry, and cytokine levels, interleukin- (IL-) 18, IL-23, and IL-17A, were compared in plasma. The analysis was performed in active (n = 13) and inactive (n = 13) stages of BD patients. Rheumatoid arthritis patients (n = 19), as a disease control, and healthy control (HC) (n = 19) were enrolled. The frequencies of CD11b+ and CD32+ cells were significantly increased in active BD patients compared to HC. Disease severity score was correlated to CD11c+, CD206+, and CD209+ in whole leukocytes and CD11b+, CD11c+, CD206+, CD209+, and Dectin-1+ in granulocytes. The plasma levels of IL-17A were significantly different between HC and active BD. IL-18 showed significant difference between active and inactive BD patients. From this study, we concluded the expressions of several pattern recognition receptors were correlated to the joint symptoms of BD.

Interleukin-33 in health and disease

Interleukin-33 (IL-33) - a member of the IL-1 family - was originally described as an inducer of type 2 immune responses, activating T helper 2 (T_H2) cells and mast cells. Now, evidence is accumulating that IL-33 also potently stimulates group 2 innate lymphoid cells (ILC2s), regulatory T (T_reg) cells, T_H1 cells, CD8⁺ T cells and natural killer (NK) cells. This pleiotropic nature is reflected in the role of IL-33 in tissue and metabolic homeostasis, infection, inflammation, cancer and diseases of the central nervous system. In this Review, we highlight the molecular and cellular characteristics of IL-33, together with its major role in health and disease and the potential therapeutic implications of these findings in humans.

Roles of IL-33 in Resistance and Tolerance to Systemic Candida albicans Infections

IL-33 is a multifunctional cytokine that is released in response to a variety of intrinsic and extrinsic stimuli. The role of IL-33 in Candida albicans infections is just beginning to be revealed. This cytokine has beneficial effects on host defense against systemic C. albicans infections, and it promotes resistance mechanisms by which the immune system eliminates the invading fungal pathogens; and it also elevates host tolerance by reducing the inflammatory response and thereby, potentially, tissue damage. Thus, IL-33 is classified as a cytokine that has evolved functionally to protect the host from damage by pathogens and immunopathology.

Paradoxical Roles of the Neutrophil in Sepsis: Protective and Deleterious

Sepsis, an overwhelming inflammatory response syndrome secondary to infection, is one of the costliest and deadliest medical conditions worldwide. Neutrophils are classically considered to be essential players in the host defense against invading pathogens. However, several investigations have shown that impairment of neutrophil migration to the site of infection, also referred to as neutrophil paralysis, occurs during severe sepsis, resulting in an inability of the host to contain and eliminate the infection. On the other hand, the neutrophil antibacterial arsenal contributes to tissue damage and the development of organ dysfunction during sepsis. In this review, we provide an overview of the main events in which neutrophils play a beneficial or deleterious role in the outcome of sepsis.

Interleukin-33 facilitates neutrophil recruitment and bacterial clearance in S. aureus-caused peritonitis

Interleukin (IL)-33, a newly recognized member of IL-1 family of cytokines, plays an important role in polarizing Th2-associated immunity. Recently growing evidence indicates that IL-33 also represents a crucial mediator of antimicrobial infection. In this study, we investigated the effect of IL-33 on antibacterial response using an acute Staphylococcus aureus peritoneal infection model. Our results showed that IL-33 administration induced a rapid bacterial clearance and markedly reduced the S. aureus infection-related mortality. IL-33-treated mice displayed increased neutrophil influx into the focus of infection and higher concentrations of chemokine CXCL2 in the peritoneum than untreated mice. The beneficial effect of IL-33 priming was related to reversal of the S. aureus-induced reduction of CXCR2 expression on the surface of neutrophils. Furthermore, conditioning of neutrophils by IL-33 led to the enhancement of complement receptor 3 expression induced by S. aureus, which in turn facilitates the phagocytosis of opsonized S. aureus. Finally, neutrophils primed by IL-33 upregulated the production of reactive oxygen species and the subsequent killing activity for S. aureus. All together, these findings suggest that IL-33, through regulating multiple steps of neutrophil-mediated bactericidal function, provides a profound effect in host antimicrobial defense response.

Potential Therapeutic Aspects of Alarmin Cytokine Interleukin 33 or Its Inhibitors in Various Diseases

PURPOSE

The purpose of this review was to examine the comprehensively accumulated data regarding potential therapeutic aspects of exogenous administration of interleukin 33 (IL-33) or its antagonists in allergic, cancerous, infectious, and inflammatory diseases.

METHODS

A selected review was undertaken of publications that examined the protective and exacerbating effects of IL-33 or its inhibitors in different diseases. Mechanisms of action are summarized to examine the putative role of IL-33 in various diseases.

FINDINGS

IL-33 promoted antibacterial, antiviral, anti-inflammatory, and vaccine adjuvant functions. However, in TH2-biased respiratory, allergic, parasitic, and inflammatory conditions, IL-33 exhibited disease-sensitizing effects. The alarmin cytokine IL-33 induced protective effects in diseases via recruitment of regulatory T cells; antiviral CD8(+) cells, natural killer cells, γδ T cells, and nuocytes; antibacterial and antifungal neutrophils or macrophages; vaccine-associated B/T cells; and inhibition of nuclear factor-κB-mediated gene transcription. In contrast, IL-33 exacerbated the disease process by increasing TH2 cytokines, IgE and eosinophilic immune responses, and inhibition of leukocyte recruitment in various diseases.

IMPLICATIONS

The protective or exacerbated aspects of use of IL-33 or its inhibitors are dependent on the type of infection or inflammatory condition, duration of disease (acute or chronic), organ involved, cytokine microenvironment, dose or kinetics of IL-33, and genetic predisposition. The alarmin cytokine IL-33 acts at cellular, molecular, and transcriptional levels to mediate pluripotent functions in various diseases and has potential therapeutic value to mitigate the disease process.

Intratumorally Establishing Type 2 Innate Lymphoid Cells Blocks Tumor Growth

A long-standing question in the field of tumor immunotherapy is how Th2 cytokines block tumor growth. Their antitumor effects are particularly prominent when they are secreted continuously in tumors, suggesting that Th2 cytokines may create a tumor microenvironment unfavorable for tumor growth independently of adaptive immunity. In this study, we show that local production of IL-33 establishes a high number of type 2 innate lymphoid cells (ILC2s) with potent antitumor activity. IL-33 promotes secretion of a massive amount of CXCR2 ligands from ILC2s but creates a tumor microenvironment where tumor cells express CXCR2 through a dysfunctional angiogenesis/hypoxia/reactive oxygen species axis. These two signaling events converge to reinforce tumor cell-specific apoptosis through CXCR2. Our results identify a previously unrecognized antitumor therapeutic pathway wherein ILC2s play a central role.

Effects of Il-33/St2 pathway on alteration of iron and hematological parameters in acute inflammation

AIM

The aim of this study was to examine the role of the IL-33/ST2 pathway in pathogenesis of acute inflammation by investigating its possible role in alteration of iron and hematological parameters in experimental model of acute inflammation.

MATERIAL AND METHODS

Wild-type and ST2 knockout BALB/c mice were divided into four groups: wild-type control group, ST2-/- control group, wild-type inflammatory group, and ST2-/- inflammatory group. Acute inflammation was induced by intramuscular injection of turpentine oil, while control groups were injected with saline. After 12h animals were anesthetized, and the treated tissue, blood and spleen were collected. Iron concentration in the treated tissue, hemoglobin blood concentration, mean corpuscular hemoglobin (MCH), hematocrit, erythrocyte, neutrophil and lymphocyte blood count, and erythrocytes percentage in spleen were determined.

RESULTS

Iron concentration in the treated tissue was significantly higher in wild-type inflammatory group (WT-I) when compared to both, the wild-type control group (WT-C) and ST2-/- inflammatory group (KO-I). There was no significant difference in iron concentration between ST2-/- control group (KO-C) and the KO-I. MCH had significantly decreased in WT-I when compared to WT-C, while there was no significant difference between KO-C and KO-I. Hemoglobin blood concentration significantly increased in KO-I in comparison to KO-C, while it did not significantly differ between WT-I and KO-I. Erythrocyte count and hematocrit had significantly increased, while the percentage of erythrocytes in spleen decreased in both inflammatory groups when compared to their controls. Neutrophil count significantly decreased in WT-I, when compared to WT-C. Lymphocyte count decreased in both inflammatory groups when compared to their controls.

CONCLUSION

Results of this study indicate that the IL-33/ST2 axis could have a role in the alteration of iron in acute inflammation, namely in an increase of iron concentration at the site of acute inflammation and a decrease of blood mean corpuscular hemoglobin.

Thymic stromal lymphopoietin-induced interleukin-17A is involved in the development of IgE-mediated atopic dermatitis-like skin lesions in mice

Atopic dermatitis (AD) is a chronic inflammatory skin disease associated with elevated levels of allergen-specific IgE. Although thymic stromal lymphopoietin (TSLP) and interleukin-17A (IL-17A) have been considered as important factors in allergic diseases, their relationships in AD have not been fully defined. Here, we show the contribution of TSLP-induced IL-17A responses to IgE-mediated AD-like skin lesions. BALB/c mice passively sensitized by intraperitoneal injections of ovalbumin (OVA)-specific IgE monoclonal antibody (mAb) were challenged with OVA applied to the skin six times. Treatment with anti-TSLP mAb during the second to sixth challenges inhibited IgE-mediated AD-like skin lesions and IL-17A production in lymph nodes. Furthermore, the increased number of IL-17A-producing CD4(+) and γδ T cells in lymph nodes and neutrophilic inflammation in the skin were reduced by anti-TSLP mAb. These findings prompted us to examine the roles of IL-17A. Treatment with anti-IL-17A mAb suppressed the AD-like skin lesions and neutrophilic inflammation; anti-Gr-1 mAb also inhibited them. Furthermore, treatment with CXCR2 antagonist reduced the AD-like skin lesions and neutrophilic inflammation accompanied by the reduction of IL-17A production; the increased CXCR2 expression in the epidermal cells was suppressed by anti-TSLP mAb. Meanwhile, these treatments, except for anti-Gr-1 mAb, inhibited the increased mast cell accumulation in the skin. Collectively, the mechanism of IgE mediating IL-17A-producing CD4(+) and γδ T cells through TSLP by repeated antigen challenges is involved in AD-like skin lesions associated with skin inflammation, such as neutrophil and mast cell accumulation; TSLP may regulate CXCR2 signalling-induced IL-17A production.

TLR-4 cooperates with Dectin-1 and mannose receptor to expand Th17 and Tc17 cells induced by Paracoccidioides brasiliensis stimulated dendritic cells

The concomitant use of diverse pattern recognition receptors (PRRs) by innate immune cells can result in synergistic or inhibitory activities that profoundly influence anti-microbial immunity. Dectin-1 and the mannose receptor (MR) are C-type lectin receptors (CLRs) previously reported to cooperate with toll-like receptors (TLRs) signaling in the initial inflammatory response and in the induction of adaptive Th17 and Tc17 immunity mediated by CD4(+) and CD8(+) T cells, respectively. The protective immunity against paracoccidioidomycosis, the most prevalent fungal infection of Latin America, was previously shown to be influenced by these T cell subsets motivating us to study the contribution of TLRs, Dectin-1, and MR to the development of Th17/Tc17 immunity. First, curdlan a specific Dectin-1 agonist was used to characterize the influence of this receptor in the proliferative response and Th17/Tc17 differentiation of naïve lymphocytes induced by Paracoccidioides brasiliensis activated dendritic cells (DCs) from C57BL/6 mice. Then, wild type (WT), Dectin-1(-/-), TLR-2(-/-), and TLR-4(-/-) DCs treated or untreated with anti-Dectin-1 and anti-MR antibodies were used to investigate the contribution of these receptors in lymphocyte activation and differentiation. We verified that curdlan induces an enhanced lymphocyte proliferation and development of IL-17 producing CD4(+) and CD8(+) T cells. In addition, treatment of WT, TLR-2(-/-), and TLR-4(-/-) DCs by anti-Dectin-1 antibodies or antigen presentation by Dectin-1(-/-) DCs led to decreased lymphoproliferation and impaired Th17 and Tc17 expansion. These responses were also inhibited by anti-MR treatment of DCs, but a synergistic action on Th17/Tc17 differentiation was mediated by TLR-4 and MR. Taken together, our results indicate that diverse TLRs and CLRs are involved in the induction of lymphocyte proliferation and Th17/Tc17 differentiation mediated by P. brasiliensis activated DCs, but a synergist action was restricted to Dectin-1, TLR-4, and MR.

Host response to Candida albicans bloodstream infection and sepsis

Candida albicans is a major cause of bloodstream infection which may present as sepsis and septic shock - major causes of morbidity and mortality world-wide. After invasion of the pathogen, innate mechanisms govern the early response. Here, we outline the models used to study these mechanisms and summarize our current understanding of innate immune responses during Candida bloodstream infection. This includes protective immunity as well as harmful responses resulting in Candida induced sepsis. Neutrophilic granulocytes are considered principal effector cells conferring protection and recognize C. albicans mainly via complement receptor 3. They possess a range of effector mechanisms, contributing to elimination of the pathogen. Neutrophil activation is closely linked to complement and modulated by activated mononuclear cells. A thorough understanding of these mechanisms will help in creating an individualized approach to patients suffering from systemic candidiasis and aid in optimizing clinical management.

Pediatric severe asthma with fungal sensitization is mediated by steroid-resistant IL-33

Background

The mechanism underlying severe asthma with fungal sensitization (SAFS) is unknown. IL-33 is important in fungus-induced asthma exacerbations, but its role in fungal sensitization is unexplored.

Objective

We sought to determine whether fungal sensitization in children with severe therapy-resistant asthma is mediated by IL-33.

Methods

Eighty-two children (median age, 11.7 years; 63% male) with severe therapy-resistant asthma were included. SAFS (n = 38) was defined as specific IgE or skin prick test response positivity to Aspergillus fumigatus, Alternaria alternata, or Cladosporium herbarum. Clinical features and airway immunopathology were assessed. Chronic exposure to house dust mite and A alternata were compared in a neonatal mouse model.

Results

Children with SAFS had earlier symptom onset (0.5 vs 1.5 years, P = .006), higher total IgE levels (637 vs 177 IU/mL, P = .002), and nonfungal inhalant allergen-specific IgE. Significantly more children with SAFS were prescribed maintenance oral steroids (42% vs 14%, P = .02). SAFS was associated with higher airway IL-33 levels. In neonatal mice A alternata exposure induced higher serum IgE levels, pulmonary IL-33 levels, and IL-13⁺ innate lymphoid cell (ILC) and T_H2 cell numbers but similar airway hyperresponsiveness (AHR) compared with those after house dust mite exposure. Lung IL-33 levels, IL-13⁺ ILC numbers, T_H2 cell numbers, IL-13 levels, and AHR remained increased with inhaled budesonide during A alternata exposure, but all features were significantly reduced in ST2^−/− mice lacking a functional receptor for IL-33.

Conclusion

Pediatric SAFS was associated with more oral steroid therapy and higher IL-33 levels. A alternata exposure resulted in increased IL-33–mediated ILC2 numbers, T_H2 cell numbers, and steroid-resistant AHR. IL-33 might be a novel therapeutic target for SAFS.

Crucial and diverse role of the interleukin-33/ST2 axis in infectious diseases

Interleukin-33 (IL-33) has now emerged as a cytokine with diverse and pleiotropic functions in various infectious and inflammatory diseases. IL-33 is expressed by epithelial cells, endothelial cells, fibroblasts, and hepatocytes. The target cells of IL-33 are Th2 cells, basophils, dendritic cells, mast cells, macrophages, NKT cells, and nuocytes, newly discovered natural helper cells/innate lymphoid cells bearing the ST2 receptor. IL-33 has dual functions, both as a traditional cytokine and as a nuclear factor that regulates gene transcription. IL-33 functions as an "alarmin" released following cell death, as a biomarker, and as a vaccine adjuvant, with proinflammatory and protective effects during various infections. The exacerbated or protective role of the IL-33/ST2 axis during different infections is dependent upon the organ involved, type of infectious agent, whether the infection is acute or chronic, the invasiveness of the infectious agent, the host immune compartment, and cellular and cytokine microenvironments. In this review, we focus on recent advances in the understanding of the role of the IL-33/ST2 axis in various viral, bacterial, fungal, helminth, and protozoal infectious diseases gained from animal models and studies in human patients. The functional role of IL-33 and ST2 during experimentally induced infections has been summarized by accumulating the data for IL-33- and ST2-deficient mice or for mice exogenously administered IL-33. In summary, exploring the crucial and diverse roles of the IL-33/ST2 axis during infections may help in the development of therapeutic interventions for a wide range of infectious diseases.