Antioxidant defense of children and adolescents with atopic dermatitis: Association with disease severity

Background: Atopic dermatitis (AD) is a relapsing, chronic cutaneous inflammatory disease with onset, in general, in early childhood. Chronic skin inflammation is associated with overproduction of reactive oxygen species (ROS) such as superoxide and hydrogen peroxide. Oxidative stress, an imbalance between the production of free radicals and antioxidant defense, results in tissue inflammation due to the upregulation of genes that encode inflammatory cytokines. This condition plays an important role in the pathogenesis of AD. Objective: To compare the antioxidant defense in children and adolescents with AD with that of healthy individuals and to verify the association of antioxidant defense with disease severity and nutritional status. Methods: Cross-sectional study that evaluated 48 children and adolescents with AD and 25 controls for nutritional assessment (body mass index z score [BMIZ] and height for age z score [HAZ]) and levels of vitamins A, C, E, and D, zinc (Zn), copper (Cu), antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx]), high-sensitivity C-reactive protein (CRP) and interleukin 33 (IL-33). Results: There was no significant difference in the comparison between AD and control groups for serum levels of vitamins (A, D, C, and E), copper, and antioxidant enzymes. Serum zinc levels were higher in the AD group (β = 24.20; 95% CI 13.95–34.91; P < 0.001) even after adjusting the BMIZ, HAZ, gender, IL-33, and CRP. Children and adolescents with moderate or severe AD compared to mild AD (SCORAD – 36.7±17.4 vs 11.8 ± 3.9; P < 0.001) had lower values of the vitamin E/total lipid ratio (3.68 [0.29;12.63] vs 5.92 [3.27;17.37]; P = 0.013) (AU)

Probiotics mixture and taurine attenuate L-arginine-induced acute pancreatitis in rats: Impact on transient receptor potential vanilloid-1 (TRPV-1)/IL-33/NF-κB signaling and apoptosis.

Acute pancreatitis (AP) is an inflammatory disorder of acinar cells. It may develop into severe chronic pancreatitis with a significant mortality rate. The current study aimed to assess the therapeutic effect of a Lactobacillus (LAB) mixture against rat AP. Six groups were created including control, taurine (300 mg/kg; i.p.) for 7 days, LAB mixture for 7 days, L-arginine (2.5 g/kg; i.p.) 2 doses with 1 h interval on 1st day, L-arginine+taurine, and L-arginine+LAB. Serum amylase and lipase activities were measured. Pancreatic tissue was used for histopathological examination, oxidative stress biomarkers including malondialdehyde (MDA) and reduced glutathione (GSH), and inflammatory biomarkers including myeloperoxidase (MPO) and interleukin (IL)-33 assessment. qRT-PCR was used for transient receptor potential vanilloid-1 (TRPV-1) investigation and Western blot analysis for measuring nuclear factor kappa-B (NF-κBp65) and the apoptosis biomarker; caspase-3. Taurine and LAB reduced lipase and significantly ameliorated induced oxidative stress by normalizing MDA and GSH contents. They counteracted inflammation by reducing MPO, IL-33, NF-κBp65, and TRPV-1. In addition, taurine and LAB counteracted apoptosis as proved by reduced caspase-3 expression. Taken together, these findings indicate that taurine and the use LAB mixture can mitigate AP by L-arginine via influencing TRPV-1/IL-33/NF-κB signaling together with exhibiting potent antioxidant and anti-inflammatory effects.

IL-33-ILC2 axis promotes anti-tumor CD8+ T cell responses via OX40 signaling.

Group 2 innate lymphoid cells (ILC2s) are resident cells and participate in innate and adaptive immunity. In the tumor microenvironment (TME), ILC2s contribute to both tumorigenesis and inhibition of tumor growth, but the true role of ILC2s in TME construction remains unclear. We show that IL-33 treatment induces an anti-tumor effect in vivo in a mouse model of melanoma in which ILC2s and CD8+ T cells infiltrate into tumor tissue. This anti-tumor effect is dependent on CD8+ T cells, however, IL-33 does not act directly on CD8+ T cells because the cells lack ST2, the receptor for IL-33. ILC2s and CD8+ T cells in tumors of IL-33-treated mice express OX40 ligand (OX40L) and OX40, respectively, and in vivo blockade of OX40L-OX40 interaction canceled the anti-tumor effect of IL-33. Co-culture of CD8+ T cells expressing OX40 with IL-33-stimulated ILC2 expressing OX40L promoted cell activation and proliferation of CD8+ T cells, which was significantly suppressed by administration of anti-OX40L blocking antibody. Thus, the IL-33-ILC2 axis promotes CD8+ T cell responses via OX40/OX40L interaction and exerts an anti-tumor effect.

Maternal IL-33 critically regulates tissue remodeling and type 2 immune responses in the uterus during early pregnancy in mice.

The pregnant uterus is an immunologically rich organ, with dynamic changes in the inflammatory milieu and immune cell function underlying key stages of pregnancy. Recent studies have implicated dysregulated expression of the interleukin-1 (IL-1) family cytokine, IL-33, and its receptor, ST2, in poor pregnancy outcomes in women, including recurrent pregnancy loss, preeclampsia, and preterm labor. How IL-33 supports pregnancy progression in vivo is not well understood. Here, we demonstrate that maternal IL-33 signaling critically regulates uterine tissue remodeling and immune cell function during early pregnancy in mice. IL-33-deficient dams exhibit defects in implantation chamber formation and decidualization, and abnormal vascular remodeling during early pregnancy. These defects coincide with delays in early embryogenesis, increased resorptions, and impaired fetal and placental growth by late pregnancy. At a cellular level, myometrial fibroblasts, and decidual endothelial and stromal cells, are the main IL-33+ cell types in the uterus during decidualization and early placentation, whereas ST2 is expressed by uterine immune populations associated with type 2 immune responses, including ILC2s, Tregs, CD4+ T cells, M2- and cDC2-like myeloid cells, and mast cells. Early pregnancy defects in IL-33-deficient dams are associated with impaired type 2 cytokine responses by uterine lymphocytes and fewer Arginase-1+ macrophages in the uterine microenvironment. Collectively, our data highlight a regulatory network, involving crosstalk between IL-33-producing nonimmune cells and ST2+ immune cells at the maternal-fetal interface, that critically supports pregnancy progression in mice. This work has the potential to advance our understanding of how IL-33 signaling may support optimal pregnancy outcomes in women.

Bacillus Calmette-Guérin-Induced Human Mast Cell Activation Relies on IL-33 Priming.

Bacillus Calmette-Guérin (BCG) vaccine is an attenuated strain of Mycobacterium bovis that provides weak protection against tuberculosis (TB). Mast cells (MCs) are tissue-resident immune cells strategically that serve as the first line of defence against pathogenic threats. In this study, we investigated the response of human MCs (hMCs) to BCG. We found that naïve hMCs exposed to BCG did not secrete cytokines, degranulate, or support the uptake and intracellular growth of bacteria. Since we could show that in hMCs IL-33 promotes the transcription of host-pathogen interaction, cell adhesion and activation genes, we used IL-33 for cell priming. The treatment of hMCs with IL-33, but not IFN-γ, before BCG stimulation increased IL-8, MCP-1 and IL-13 secretion, and induced an enhanced expression of the mycobacteria-binding receptor CD48. These effects were comparable to those caused by the recombinant Mycobacterium tuberculosis (Mtb) 19-KDa lipoprotein. Finally, stimulation of hMCs with IL-33 incremented MC-BCG interactions. Thus, we propose that IL-33 may improve the immunogenicity of BCG vaccine by sensitising hMCs.

Profound Defect of Amphiregulin Secretion by Regulatory T Cells in the Gut of HIV-Treated Patients.

The persistence of a leaky gut in HIV-treated patients leads to chronic inflammation with increased rates of cardiovascular, liver, kidney, and neurological diseases. Tissue regulatory T (tTreg) cells are involved in the maintenance of intestinal homeostasis and wound repair through the IL-33 pathway. In this study, we investigated whether the persistence of gut mucosal injury during HIV infection might be explained in part by a flaw in the mechanisms involved in tissue repair. We observed an increased level of IL-33 in the gut of HIV-infected patients, which is associated with an increased level of fibrosis and a low peripheral reconstitution of CD4+ T cells. Our results showed that intestinal Treg cells from HIV-infected patients were enriched in tTreg cells prone to support tissue repair. However, we observed a functional defect in tTreg cells caused by the lack of amphiregulin secretion, which could contribute to the maintenance of intestinal damage. Our data suggest a mechanism by which the lack of amphiregulin secretion by tTreg may contribute to the lack of repair of the epithelial barrier.

Free fatty acid receptor 4 deletion attenuates colitis by modulating Treg Cells via ZBED6-IL33 pathway.

BACKGROUND: Inflammatory bowel disease (IBD) has complex genetic and environmental aspects, and free fatty acid receptors (FFARs) may bridge genetic and dietary aspects. FFAR4 is highly expressed in the intestine and acts primarily as the receptor of long-chain fatty acids, which are major components of the human diet. It is unclear what role, if any, FFAR4 may play in IBD. METHODS: Mouse and human colitis samples, mice with complete FFAR4 knockout, intestine-specific FFAR4 knockout and FFAR4 overexpression and cell culture were used. RNA-sequencing analysis and flow cytometry were performed to examine the mechanisms. FINDINGS: The results showed that FFAR4 expression was upregulated in colitis tissues and that the loss of intestinal FFAR4 ameliorated colitis, whereas intestinal FFAR4 overexpression exacerbated the disease. We identified intestinal epithelial cell deletion of FFAR4 by upregulating ZBED6, which in turn induced L33 transcription, and L33 elevated Treg cell numbers, ameliorating colitis. INTERPRETATION: FFAR4 deletion attenuates colitis by modulating Treg cells via the ZBED6-IL33 pathway. FUNDING: National Natural Science Foundation of China, Innovation and Application Project of Medical and Public Health Technology of Wuxi Science and Technology, Fundamental Research Funds for the Central Universities and the Fund of Wuxi Healthcare Commission.

Involvement of IL-33 in the Pathophysiology of Systemic Lupus Erythematosus: Review.

IL-33 is a newly discovered cytokine displaying pleiotropic localizations and functions. More specifically, it also functions as an alarmin, following its release from cells undergoing cell death or necrosis, to alert the innate immune system. The role of IL-33 has been underlined in several inflammatory and autoimmune diseases including systemic lupus erythematosus (SLE). The expressions of IL-33 as well as its receptor, ST2, are significantly upregulated in SLE patients and in patients with lupus nephritis. This review discusses the involvement of IL-33 in the pathology of SLE.

Interferon gamma constrains type 2 lymphocyte niche boundaries during mixed inflammation.

Allergic immunity is orchestrated by group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells prominently arrayed at epithelial- and microbial-rich barriers. However, ILC2s and Th2 cells are also present in fibroblast-rich niches within the adventitial layer of larger vessels and similar boundary structures in sterile deep tissues, and it remains unclear whether they undergo dynamic repositioning during immune perturbations. Here, we used thick-section quantitative imaging to show that allergic inflammation drives invasion of lung and liver non-adventitial parenchyma by ILC2s and Th2 cells. However, during concurrent type 1 and type 2 mixed inflammation, IFNγ from broadly distributed type 1 lymphocytes directly blocked both ILC2 parenchymal trafficking and subsequent cell survival. ILC2 and Th2 cell confinement to adventitia limited mortality by the type 1 pathogen Listeria monocytogenes. Our results suggest that the topography of tissue lymphocyte subsets is tightly regulated to promote appropriately timed and balanced immunity.

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.

Neuropilin-1 mediates lung tissue-specific control of ILC2 function in type 2 immunity.

Group 2 innate lymphoid cells (ILC2s) are highly heterogeneous tissue-resident lymphocytes that regulate inflammation and tissue homeostasis in health and disease. However, how these cells integrate into the tissue microenvironment to perform tissue-specific functions is unclear. Here, we show neuropilin-1 (Nrp1), which is induced postnatally and sustained by lung-derived transforming growth factor beta-1 (TGFß1), is a tissue-specific marker of lung ILC2s. Genetic ablation or pharmacological inhibition of Nrp1 suppresses IL-5 and IL-13 production by ILC2s and protects mice from the development of pulmonary fibrosis. Mechanistically, TGFß1-Nrp1 signaling enhances ILC2 function and type 2 immunity by upregulating IL-33 receptor ST2 expression. These findings identify Nrp1 as a tissue-specific regulator of lung-resident ILC2s and highlight Nrp1 as a potential therapeutic target for pulmonary fibrosis.

Siglec-F Promotes IL-33-Induced Cytokine Release from Bone Marrow-Derived Eosinophils Independently of the ITIM and ITIM-like Motif Phosphorylation.

Eosinophils are potent innate effector cells associated mainly with type 2 immune responses elicited by helminths and allergens. Their activity needs to be tightly controlled to prevent severe inflammation and tissue damage. Eosinophil degranulation and secretion of inflammatory effector molecules, including cytokines, chemokines, and lipid mediators, can be regulated by activating and inhibitory receptors on the cell surface. In this study, we investigated the modulation of proliferation, apoptosis, gene expression, and cytokine/chemokine secretion from IL-33-activated Mus musculus eosinophils on cross-linking of the transmembrane receptor Sialic acid-binding Ig-like lectin F (Siglec-F). Siglec-F contains an ITIM plus an ITIM-like motif in its intracellular tail and is mainly regarded as an inhibitory and apoptosis-inducing receptor. In vitro costimulation of bone marrow-derived eosinophils with anti-Siglec-F and IL-33 compared with treatment with either alone led to enhanced STAT6 phosphorylation, stronger induction of hypoxia/glycolysis-related proinflammatory genes, and elevated secretion of type 2 cytokines (IL-4, IL-13) and chemokines (CCL3, CCL4) with only minor effects on proliferation and apoptosis. Using a competitive mixed bone marrow chimera approach with wild-type and Siglec-F-deficient eosinophils, we observed no evidence for Siglec-F-regulated inhibition of Aspergillus fumigatus-elicited lung eosinophilia. Truncation of the Siglec-F cytoplasmic tail, but not mutation of the ITIM and ITIM-like motifs, ablated the effect of enhanced cytokine/chemokine secretion. This provides evidence for an ITIM phosphorylation-independent signaling pathway from the cytoplasmic tail of the Siglec-F receptor that enhances effector molecule release from activated eosinophils.

Expression of Interleukin-33 Gene in Hemodialysis Patients with Chronic Toxoplasmosis in Baghdad, Iraq.

Toxoplasmosis is a protozoan parasite with high distribution, leading to different abnormalities in hosts. The present study aimed to determine the distribution of toxoplasmosis in hemodialysis patients and the expression of the Interleukin (IL)-33 gene in chronic Toxoplasmosis. The present study evaluated 120 subjects, including 60 patients who were undergoing dialysis and 60 healthy samples as the control group, from the 1st February to 1st November 2021. Anti-Toxoplasma gondii IgG was detected by using the enzyme-linked immunosorbent assay (ELISA) technique and the real-time polymerase-chain-reaction (PCR) was used to perform IL-33. The results demonstrated that the highest anti-toxoplasmosis IgG antibody rate was observed in the age group 51-70 years who were undergoing dialysis, in comparison with that in the control group (P<0.05). The male patients who had anti-toxoplasmosis IgG antibodies outnumbered the healthy people (P<0.05), while the female patients did not significantly differ from the healthy group. Chronic toxoplasmosis showed a higher number according to residency (the urban and rural patients), compared to healthy people. The frequency of dialysis times per week in chronic Toxoplasmosis patients was significantly higher among the infected patients. The findings were displayed to be positive in dialysis at 2 weeks (P<0.05). The expression of the IL-33 gene was investigated in patients who were undergoing hemodialysis and in healthy controls by using real-time PCR. The findings demonstrated that there was a high Ct value for patients and controls with a high Ct value of templates, preoperational to the gene concentration. The high prevalence of toxoplasmosis in dialysis patients and the role of IL-33 in cellular immunity in these patients highlight the need to investigate the mechanisms limiting infection with intracellular protozoa.

Adenosine restrains ILC2-driven allergic airway inflammation via A2A receptor.

Although group 2 Innate Lymphoid Cells (ILC2s) play important roles in driving the pathogenesis of allergic airway inflammation, the molecular mechanisms regulating ILC2 responses remain to be fully elucidated. Adenosine signaling is emerging as an important factor to limit excessive inflammation and tissue damage, its role in ILC2-driven airway inflammation remains to be understood. Here we identify adenosine as a negative regulator of ILC2s and allergic airway inflammation. Elevation of adenosine was observed in lungs after protease papain challenge. Adenosine receptor A2A was abundantly expressed in lung ILC2s. The adenosine analog NECA significantly suppress ILC2s responses and relieved airway inflammation induced by IL-33 or papain. Conversely, blockage of adenosine synthesis by CD73 inhibitor APCP or deficiency of A2A aggravated murine airway inflammation. Adoptive transfer of ILC2s into immunodeficiency NCG mice demonstrated that the regulation of ILC2 by adenosine was cell intrinsic. Mechanistic studies showed that the effects of adenosine on ILC2s were associated with changes in transcriptional profiling, and the elevation of intracellular cAMP and resulted NF-κB downregulation. These observations indicate that adenosine-A2A signaling is a negative regulator of ILC2s, which confers protection against airway inflammation and represents a novel therapeutic target for controlling asthma.

Dual blockage of PD-L/PD-1 and IL33/ST2 axes slows tumor growth and improves antitumor immunity by boosting NK cells.

AIMS: Although separate blockage of either IL33/ST2 or PD-L/PD-1 axes has been shown to be beneficial in many tumors, co-blockage of IL33/ST2 and PD-L/PD-1 hasn't been studied yet. MAIN METHODS: 4T1 breast cancer and CT26 colon cancer were inducted in BALB/C wild type (WT) and BALB/C ST2 knockout mice, after which mice underwent anti PD-1 and anti IL-33 treatment. KEY FINDINGS: Co-blockage of IL33/ST2 and PD-L/PD-1 delayed tumor appearance and slowed tumor growth. Enhanced NK cell cytotoxicity against 4T1 tumor cells in ST2 knockout anti-PD-1 treated mice was associated with overexpression of miRNA-150 and miRNA-155, upregulation of NFκB and STAT3, increased expression of activation markers and decreased expression of immunosuppressive markers in splenic and primary tumor derived NK cells. NK cells from ST2 knockout anti-PD-1 treated mice tend to proliferate more and are less prone to apoptosis. Accumulation of immunosuppressive myeloid derived suppressor cells and regulatory T cells was significantly impaired in spleen and primary tumor of ST2 knockout anti-PD-1 treated mice. SIGNIFICANCE: Co-blockage of IL3/ST2 and PD-L/PD-1 axes impedes tumor progression more efficiently than single blockage of either axes, thus offering potential new approach to immunotherapy of tumors.

Targeting androgen signaling in ILC2s protects from IL-33-driven lung inflammation, independently of KLRG1.

BACKGROUND: Allergic asthma is more severe and frequent in women than in men. In male mice, androgens negatively control group 2 innate lymphoid cell (ILC2) development and function by yet unknown mechanisms. OBJECTIVES: We sought to investigate the impact of androgen on ILC2 homeostasis and IL-33-mediated inflammation in female lungs. We evaluated the role of androgen receptor (AR) signaling and the contribution of the putative inhibitory receptor killer cell lectin-like receptor G1 (KLRG1). METHODS: Subcutaneous pellets mimicking physiological levels of androgen were used to treat female mice together with mice expressing a reporter enzyme under the control of androgen response elements and mixed bone marrow chimeras to assess the cell-intrinsic role of AR activation within ILC2s. We generated KLRG1-deficient mice. RESULTS: We established that lung ILC2s express a functionally active AR that can be in vivo targeted with exogenous androgens to negatively control ILC2 homeostasis, proliferation, and function. Androgen signaling upregulated KLRG1 on ILC2s, which inhibited their proliferation on E-cadherin interaction. Despite evidence that KLRG1 impaired the competitive fitness of lung ILC2s during inflammation, KLRG1 deficiency neither alters in vivo ILC2 numbers and functions, nor did it lead to hyperactive ILC2s in either sexes. CONCLUSIONS: AR agonists can be used in vivo to inhibit ILC2 homeostatic numbers and ILC2-dependent lung inflammation through cell-intrinsic AR activation. Although androgen signals in ILC2s to upregulate KLRG1, we demonstrate that KLRG1 is dispensable for androgen-mediated inhibition of pulmonary ILC2s.

The NF-κB Transcription Factor c-Rel Modulates Group 2 Innate Lymphoid Cell Effector Functions and Drives Allergic Airway Inflammation.

Group 2 innate lymphoid cells (ILC2s) play a key role in the initiation and orchestration of early type 2 immune responses. Upon tissue damage, ILC2s are activated by alarmins such as IL-33 and rapidly secrete large amounts of type 2 signature cytokines. ILC2 activation is governed by a network of transcriptional regulators including nuclear factor (NF)-κB family transcription factors. While it is known that activating IL-33 receptor signaling results in downstream NF-κB activation, the underlying molecular mechanisms remain elusive. Here, we found that the NF-κB subunit c-Rel is required to mount effective innate pulmonary type 2 immune responses. IL-33-mediated activation of ILC2s in vitro as well as in vivo was found to induce c-Rel mRNA and protein expression. In addition, we demonstrate that IL-33-mediated activation of ILC2s leads to nuclear translocation of c-Rel in pulmonary ILC2s. Although c-Rel was found to be a critical mediator of innate pulmonary type 2 immune responses, ILC2-intrinsic deficiency of c-Rel did not have an impact on the developmental capacity of ILC2s nor affected homeostatic numbers of lung-resident ILC2s at steady state. Moreover, we demonstrate that ILC2-intrinsic deficiency of c-Rel alters the capacity of ILC2s to upregulate the expression of ICOSL and OX40L, key stimulatory receptors, and the expression of type 2 signature cytokines IL-5, IL-9, IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF). Collectively, our data using Rel-/- mice suggest that c-Rel promotes acute ILC2-driven allergic airway inflammation and suggest that c-Rel may contribute to the pathophysiology of ILC2-mediated allergic airway disease. It thereby represents a promising target for the treatment of allergic asthma, and evaluating the effect of established c-Rel inhibitors in this context would be of great clinical interest.

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.

IL-33/ST2 Axis Plays a Protective Effect in Streptococcus pyogenes Infection through Strengthening of the Innate Immunity.

Group A Streptococcus (GAS) causes invasive human diseases with the cytokine storm. Interleukin-33 (IL-33)/suppression of tumorigenicity 2 (ST2) axis is known to drive TH2 response, while its effect on GAS infection is unclear. We used an air pouch model to examine the effect of the IL-33/ST2 axis on GAS-induced necrotizing fasciitis. GAS infection induced IL-33 expression in wild-type (WT) C57BL/6 mice, whereas the IL-33- and ST2-knockout mice had higher mortality rates, more severe skin lesions and higher bacterial loads in the air pouches than those of WT mice after infection. Surveys of infiltrating cells in the air pouch of GAS-infected mice at the early stage found that the number and cell viability of infiltrating cells in both gene knockout mice were lower than those of WT mice. The predominant effector cells in GAS-infected air pouches were neutrophils. Absence of the IL-33/ST2 axis enhanced the expression of inflammatory cytokines, but not TH1 or TH2 cytokines, in the air pouch after infection. Using in vitro assays, we found that the IL-33/ST2 axis not only enhanced neutrophil migration but also strengthened the bactericidal activity of both sera and neutrophils. These results suggest that the IL-33/ST2 axis provided the protective effect on GAS infection through enhancing the innate immunity.

Endogenous Interleukin-33 Acts as an Alarmin in Liver Ischemia-Reperfusion and Is Associated With Injury After Human Liver Transplantation.

Ischemia and reperfusion injury is an early inflammatory process during liver transplantation that impacts on graft function and clinical outcomes. Interleukin (IL)-33 is a danger-associated molecular pattern involved in kidney ischemia/reperfusion injury and several liver diseases. The aims were to assess whether IL-33 was released as an alarmin responsible for ischemia/reperfusion injury in a mouse model of warm hepatic ischemia, and whether this hypothesis could also apply in the setting of human liver transplantation. First, a model of warm hepatic ischemia/reperfusion was used in wild-type and IL-33-deficient mice. Severity of ischemia/reperfusion injury was assessed with ALT and histological analysis. Then, serum IL-33 was measured in a pilot cohort of 40 liver transplant patients. Hemodynamic postreperfusion syndrome, graft dysfunction (assessed by model for early allograft scoring >6), renal failure, and tissue lesions on time-zero biopsies were assessed. In the mouse model, IL-33 was constitutively expressed in the nucleus of endothelial cells, immediately released in response to hepatic pedicle clamping without neosynthesis, and participated in the recruitment of neutrophils and tissue injury on site. The kinetics of IL-33 in liver transplant patients strikingly matched the ones in the animal model, as attested by serum levels reaching a peak immediately after reperfusion, which correlated to clinical outcomes including postreperfusion syndrome, posttransplant renal failure, graft dysfunction, and histological lesions of ischemia/reperfusion injury. IL-33 was an independent factor of graft dysfunction with a cutoff of IL-33 at 73 pg/ml after reperfusion (73% sensitivity, area under the curve of 0.76). Taken together, these findings establish the immediate implication of IL-33 acting as an alarmin in liver I/R injury and provide evidence of its close association with cardinal features of early liver injury-associated disorders in LT patients.