Abnormal thymic stromal lymphopoietin expression in the duodenal mucosa of patients with coeliac disease

TSLP is localized in and released from human lung macrophages activated by T2-high and T2-low stimuli: relevance in asthma and COPD

BACKGROUND

Macrophages are the predominant immune cells in the human lung and play a central role in airway inflammation, including asthma and chronic obstructive pulmonary disease (COPD). Thymic stromal lymphopoietin (TSLP), a pleiotropic cytokine mainly expressed by bronchial epithelial cells, plays a key role in asthma and COPD pathobiology. TSLP exists in two variants: the long form (lfTSLP) and a shorter TSLP isoform (sfTSLP). We aimed to localize TSLP in human lung macrophages (HLMs) and investigate the mechanisms of its release from these cells. We also evaluated the effects of the two variants of TSLP on the release of angiogenic factor from HLMs.

METHODS

We employed immunofluorescence and Western blot to localize intracellular TSLP in HLMs purified from human lung parenchyma. HLMs were activated by T2-high (IL-4, IL-13) and T2-low (lipopolysaccharide: LPS) immunological stimuli.

RESULTS

TSLP was detected in HLMs and subcellularly localized in the cytoplasm. IL-4 and LPS induced TSLP release from HLMs. Preincubation of macrophages with brefeldin A, known to disrupt the Golgi apparatus, inhibited TSLP release induced by LPS and IL-4. lfTSLP concentration-dependently induced the release of vascular endothelial growth factor-A (VEGF-A), the most potent angiogenic factor, from HLMs. sfTSLP neither activated nor interfered with the activating property of lfTSLP on macrophages.

CONCLUSIONS

Our results highlight a novel immunologic circuit between HLMs and TSLP. Given the central role of macrophages in airway inflammation, this autocrine loop holds potential translational relevance in understanding innovative aspects of the pathobiology of asthma and chronic inflammatory lung disorders.

Thymic stromal lymphopoietin (TSLP) is a substrate for tryptase in patients with mastocytosis

Mastocytosis is a heterogeneous disease associated to uncontrolled proliferation and increased density of mast cells in different organs. This clonal disorder is related to gain-of-function pathogenic variants of the c-kit gene that encodes for KIT (CD117) expressed on mast cell membrane. Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine, which plays a key role in allergic disorders and several cancers. TSLP is a survival and activating factor for human mast cells through the engagement of the TSLP receptor. Activated human mast cells release several preformed mediators, including tryptase. Increased mast cell-derived tryptase is a diagnostic biomarker of mastocytosis. In this study, we found that in these patients serum concentrations of TSLP were lower than healthy donors. There was an inverse correlation between TSLP and tryptase concentrations in mastocytosis. Incubation of human recombinant TSLP with sera from patients with mastocytosis, containing increasing concentrations of tryptase, concentration-dependently decreased TSLP immunoreactivity. Similarly, recombinant β-tryptase reduced the immunoreactivity of recombinant TSLP, inducing the formation of a cleavage product of approximately 10 kDa. Collectively, these results indicate that TSLP is a substrate for human mast cell tryptase and highlight a novel loop involving these mediators in mastocytosis.

The Emerging Role of Innate Lymphoid Cells (ILCs) and Alarmins in Celiac Disease: An Update on Pathophysiological Insights, Potential Use as Disease Biomarkers, and Therapeutic Implications

Celiac disease (CD) is an intestinal disease that develops in genetically predisposed individuals and is triggered by the ingestion of gluten. CD was considered a Th1-disease. Today, the role of Th17, IL-21, and IL-17A lymphocytes is well known. Inflammation is regulated by the activity of gluten-specific CD4+ T lymphocytes that produce pro-inflammatory cytokines, including IFN-γ, TNF-α, and IL-21, perpetuating the Th1 response. These cytokines determine an inflammatory state of the small intestine, with consequent epithelial infiltration of lymphocytes and an alteration of the architecture of the duodenal mucosa. B cells produce antibodies against tissue transglutaminase and against deamidated gliadin. Although the role of the adaptive immune response is currently known, the evidence about the role of innate immunity cells is still poorly understood. Epithelial damage determines the release of damage-associated molecular patterns (DAMPs), also known as alarmins. Together with the intestinal epithelial cells and the type 1 innate lymphoid cells (ILC1s), alarmins like TSLP, IL-33, and HMGB1 could have a fundamental role in the genesis and maintenance of inflammation. Our study aims to evaluate the evidence in the literature about the role of ILCs and alarmins in celiac disease, evaluating the possible future diagnostic and therapeutic implications.

Development of an inhaled anti-TSLP therapy for asthma

Thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine, acts as a key mediator in airway inflammation and modulates the function of multiple cell types, including dendritic cells and group 2 innate lymphoid cells. TSLP plays a role in asthma pathogenesis as an upstream cytokine, and data suggest that TSLP blockade with the anti-TSLP monoclonal antibody, tezepelumab, could be efficacious in a broad asthma population. Currently approved asthma biologic therapies target allergic or eosinophilic disease and require phenotyping; therefore, an unmet need exists for a therapy that can address Type 2 (T2)-high and T2-low inflammation in asthma. All currently approved biologic treatments are delivered intravenously or subcutaneously; an inhaled therapy route that allows direct targeting of the lung with reduced systemic impact may offer advantages. Currently in development, ecleralimab (CSJ117) represents the first inhaled anti-TSLP antibody fragment that binds soluble TSLP and prevents TSLP receptor activation, thereby inhibiting further inflammatory signalling cascades. This anti-TSLP antibody fragment is being developed for patients with severe uncontrolled asthma despite standard of care inhaled therapy. A Phase IIa proof of concept study, using allergen bronchoprovocation as a model for asthma exacerbations, found that ecleralimab was well-tolerated and reduced allergen-induced bronchoconstriction in adult patients with mild asthma. These results suggest ecleralimab may be a promising, new therapeutic class for asthma treatment.

Increased expression of long-isoform thymic stromal lymphopoietin is associated with rheumatoid arthritis and fosters inflammatory responses

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine that is involved in the pathogenesis of inflammatory diseases and asthma, but the expression and biological implications of the existence of two isoforms, long TSLP (lTSLP) and short TSLP (sTSLP), in RA have yet to be elucidated. Here we report that lTSLP is the predominant TSLP isoform in RA and active RA, whereas sTSLP is the major TSLP isoform in inactive RA and healthy controls. lTSLP expression is associated with disease activity, including 28-joint Disease Activity Score (DAS28) and erythrocyte sedimentation rate (ESR), as well as proinflammatory cytokine expression, irrespective of other laboratory parameters. Importantly, lTSLP alone or combined with LPS promotes the expression of proinflammatory cytokines IL-1β, IL-6, and IL-8 in PBMCs of RA, but restrains anti-inflammatory cytokine IL-10 expression in PBMCs of RA. Furthermore, we found that STAT5 signaling is involved in lTSLP-induced inflammatory accumulation in PBMCs of RA. Therefore, these results highlight the clinical significance of lTSLP in RA pathology and inflammatory response in acute-phase disease, which may provide a therapeutic target for RA.

Furin inhibits epithelial cell injury and alleviates experimental colitis by activating the Nrf2-Gpx4 signaling pathway

BACKGROUND AND AIM

Furin is a proprotein convertase reported to have protective effects in several autoimmune diseases. However, the role of furin in ulcerative colitis (UC) remains unclear. We aimed to clarify this role.

METHODS

Furin expression was measured in UC and dextran sulfate sodium (DSS)-induced colitis. Gain- and loss-of-function experiments were conducted to evaluate the effect of furin in UC using DSS-treated NCM460 cells. Several ferroptotic parameters, including cell viability, cell death rate, lipid reactive oxygen species level, mitochondrial membrane damage and glutathione peroxidase 4 (Gpx4) expression, were measured. Exogenous furin was used to treat the DSS-induced colitis in mice to confirm the results in vivo. Finally, the activation of nuclear factor erythroid 2-like 2 (Nrf2) was detected to explore the mechanism.

RESULTS

Furin expression was aberrant in UC. Furin overexpression attenuated DSS-induced ferroptosis-like injury and upregulated Gpx4 in NCM460 cells, whereas silencing furin had the opposite effects. Exogenous furin treatment alleviated DSS-induced colitis in mice by upregulating Gpx4. Mechanistic experiments revealed that furin activated Nrf2 both in vitro and in vivo.

CONCLUSIONS

Furin protects epithelial cells from DSS-induced ferroptosis-like cell injury and alleviates experimental colitis by activating the Nrf2-Gpx4 signaling pathway.

Gut Microbiome and Common Variable Immunodeficiency: Few Certainties and Many Outstanding Questions

Common variable immunodeficiency (CVID) is the most common symptomatic primary antibody immunodeficiency, characterized by reduced serum levels of IgG, IgA, and/or IgM. The vast majority of CVID patients have polygenic inheritance. Immune dysfunction in CVID can frequently involve the gastrointestinal tract and lung. Few studies have started to investigate the gut microbiota profile in CVID patients. Overall, the results suggest that in CVID patients there is a reduction of alpha and beta diversity compared to controls. In addition, these patients can exhibit increased plasma levels of lipopolysaccharide (LPS) and markers (sCD14 and sCD25) of systemic immune cell activation. CVID patients with enteropathy exhibit decreased IgA expression in duodenal tissue. Mouse models for CVID unsatisfactorily recapitulate the polygenic causes of human CVID. The molecular pathways by which gut microbiota contribute to systemic inflammation and possibly tumorigenesis in CVID patients remain poorly understood. Several fundamental questions concerning the relationships between gut microbiota and the development of chronic inflammatory conditions, autoimmune disorders or cancer in CVID patients remain unanswered. Moreover, it is unknown whether it is possible to modify the microbiome and the outcome of CVID patients through specific therapeutic interventions.

Human Lung-Resident Macrophages Express and Are Targets of Thymic Stromal Lymphopoietin in the Tumor Microenvironment

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine highly expressed by epithelial cells and several innate and adaptive immune cells. TSLP exerts its biological effects by binding to a heterodimeric complex composed of TSLP receptor (TSLPR) and IL-7Rα. In humans, there are two TSLP isoforms: the short form (sfTSLP), constitutively expressed, and the long form (lfTSLP), which is upregulated in inflammation. TSLP has been implicated in the induction and progression of several experimental and human cancers. Primary human lung macrophages (HLMs), monocyte-derived macrophages (MDMs), and peripheral blood monocytes consitutively expressed sfTSLP mRNA. Incubation of HLMs, MDMs, and monocytes with lipopolysaccharide (LPS) or IL-4, but not with IL-13, induced TSLP release from HLMs. LPS, but not IL-4 or IL-13, induced CXCL8 release from HLMs. LPS, IL-4 alone or in combination with IL-13, induced the expression of lfTSLP, but not of sfTSLP from HLMs. Preincubation of HLMs with IL-4, alone or in combination with IL-13, but not IL-13 alone, synergistically enhanced TSLP release from LPS-activated macrophages. By contrast, IL-4, alone or in combination with IL-13, inhibited LPS-induced CXCL8 release from HLMs. Immunoreactive TSLP was detected in lysates of HLMs, MDMs, and monocytes. Incubation of HLMs with TSLP induced the release of proinflammatory (TNF-α), angiogenic (VEGF-A, angiopoietin 2), and lymphangiogenic (VEGF-C) factors. TSLP, TSLPR, and IL-7Rα were expressed in intratumoral and peritumoral areas of human lung cancer. sfTSLP and lfTSLP mRNAs were differentially expressed in peritumoral and intratumoral lung cancer tissues. The TSLP system, expressed in HLMs, MDMs, and monocytes, could play a role in chronic inflammatory disorders including lung cancer.

Short-Form Thymic Stromal Lymphopoietin (sfTSLP) Is the Predominant Isoform Expressed by Gynaecologic Cancers and Promotes Tumour Growth

Simple Summary

Cytokines are a group of small proteins in the body that play an important part in boosting the immune system. Thymic stromal lymphopoietin (TSLP) is a cytokine that plays an important role in the maturation of T cells. Two variants of TSLP, long-form (lfTSLP) and short-form (sfTSLP), have been found, however their roles in cancers are not known. In this study, we discovered that sfTSLP, but not lfTSLP, is predominantly expressed in ovarian and endometrial cancers. The switch that turns the sfTSLP gene on or off is controlled by external modifications of DNA. Our results also found that sfTSLP promotes tumour growth through activating several signal pathways in cancer cells.

Abstract

Thymic stromal lymphopoietin (TSLP) is an epithelial cell derived cytokine belonging to the IL-7 family and a key initiator of allergic inflammation. Two main isoforms of TSLP, classified as long- (lfTSLP) and short-form (sfTSLP), have been reported in human, but their expression patterns and role(s) in cancers are not yet clear. mRNA expression was examined by isoform-specific RT-PCR and RNA in situ hybridisation. Epigenetic regulation was investigated by chromatin immunoprecipitation-PCR and bisulfite sequencing. Tumour progression was investigated by gene overexpression, cell viability assay, cancer organoid culture and transwell invasion. Signals were investigated by proteome profiler protein array and RNA-sequencing. With the use of isoform-specific primers and probes, we uncovered that only sfTSLP was expressed in the cell lines and tumour tissues of human ovarian and endometrial cancers. We also showed the epigenetic regulation of sfTSLP: sfTSLP transcription was regulated by histone acetylation at promoters in ovarian cancer cells, whereas silencing of the sfTSLP transcripts was regulated by promoter DNA methylation in endometrial cancer cells. In vitro study showed that ectopically overexpressing sfTSLP promoted tumour growth but not invasion. Human phosphokinase array application demonstrated that the sfTSLP overexpression activated phosphorylation of multiple intracellular kinases (including GSK3α/β, AMPKα1, p53, AKT1/2, ERK1/2 and Src) in ovarian cancer cells in a context-dependent manner. We further investigated the impact of sfTSLP overexpression on transcriptome by RNA-sequencing and found that EFNB2 and PBX1 were downregulated in ovarian and endometrial cancer cells, suggesting their role in sfTSLP-mediated tumour growth. In conclusion, sfTSLP is predominantly expressed in ovarian and endometrial cancers and promotes tumour growth.

Evaluation of an O2-Substituted (1-3)-β-D-Glucan, Produced by Pediococcus parvulus 2.6, in ex vivo Models of Crohn's Disease

1,3-β-glucans are extracellular polysaccharides synthesized by microorganisms and plants, with therapeutic potential. Among them, the O2-substituted-(1–3)-β-D-glucan, synthesized by some lactic acid bacteria (LAB), has a prebiotic effect on probiotic strains, an immunomodulatory effect on monocyte-derived macrophages, and potentiates the ability of the producer strain to adhere to Caco-2 cells differentiated to enterocytes. In this work, the O2-substituted-(1–3)-β-D-glucan polymers produced by GTF glycoyltransferase in the natural host Pediococcus parvulus 2.6 and in the recombinant strain Lactococcus lactis NZ9000[pNGTF] were tested. Their immunomodulatory activity was investigated in an ex vivo model using human biopsies from patients affected by Crohn’s disease (CD). Both polymers had an anti-inflammatory effect including, a reduction of Interleukine 8 both at the level of its gene expression and its secreted levels. The overall data indicate that the O2-substituted-(1–3)-β-D-glucan have a potential role in ameliorating inflammation via the gut immune system cell modulation.

TSLP as druggable target - a silver-lining for atopic diseases?

Atopic diseases refer to common allergic inflammatory diseases such as atopic dermatitis (AD), allergic rhinitis (AR), and allergic asthma (AA). AD often develops in early childhood and may herald the onset of other allergic disorders such as food allergy (FA), AR, and AA. This progression of the disease is also known as the atopic march, and it goes hand in hand with a significantly impaired quality of life as well as a significant economic burden. Atopic diseases usually are considered as T helper type 2 (Th2) cell-mediated inflammatory diseases. Thymic stromal lymphopoietin (TSLP), an epithelium-derived pro-inflammatory cytokine, activates distinct immune and non-immune cells. It has been shown to be a master regulator of type 2 immune responses and atopic diseases. In experimental settings, the inhibition or knockout of TSLP signaling has shown great therapeutic potential. This, in conjunction with the increasing knowledge about the central role of TSLP in the pathogenesis of atopic diseases, has sparked an interest in TSLP as a druggable target. In this review, we will discuss the autocrine and paracrine effects of TSLP, how it regulates the tissue microenvironment and drives atopic diseases, which provide the rationale for the increasing interest in TSLP as a druggable target.

Modulation of Signaling Mediated by TSLP and IL-7 in Inflammation, Autoimmune Diseases, and Cancer

Thymic Stromal Lymphopoietin (TSLP) and Interleukin-7 (IL-7) are widely studied cytokines within distinct branches of immunology. On one hand, TSLP is crucially important for mediating type 2 immunity at barrier surfaces and has been linked to widespread allergic and inflammatory diseases of the airways, skin, and gut. On the other hand, IL-7 operates at the foundations of T-cell and innate lymphoid cell (ILC) development and homeostasis and has been associated with cancer. Yet, TSLP and IL-7 are united by key commonalities in their structure and the structural basis of the receptor assemblies they mediate to initiate cellular signaling, in particular their cross-utilization of IL-7Rα. As therapeutic targeting of TSLP and IL-7 via diverse approaches is reaching advanced stages and in light of the plethora of mechanistic and structural data on receptor signaling mediated by the two cytokines, the time is ripe to provide integrated views of such knowledge. Here, we first discuss the major pathophysiological roles of TSLP and IL-7 in autoimmune diseases, inflammation and cancer. Subsequently, we curate structural and mechanistic knowledge about receptor assemblies mediated by the two cytokines. Finally, we review therapeutic avenues targeting TSLP and IL-7 signaling. We envision that such integrated view of the mechanism, structure, and modulation of signaling assemblies mediated by TSLP and IL-7 will enhance and fine-tune the development of more effective and selective approaches to further interrogate the role of TSLP and IL-7 in physiology and disease.

Abnormal thymic stromal lymphopoietin expression in the gastrointestinal mucosa of patients with eosinophilic gastroenteritis

OBJECTIVE

To investigate the differential expression of the thymic stromal lymphopoietin isoforms, short and long, and discern their biological implications under eosinophilic gastroenteritis.

METHODS

The expression of thymic stromal lymphopoietin and its two isoforms in tissues was assessed by quantitative RT-PCR in healthy controls (n=24) and patients with eosinophilic gastroenteritis (n=17).

RESULTS

Thymic stromal lymphopoietin mRNA was significantly reduced in eosinophilic gastroenteritis when compared with healthy controls (p<0.0001). A significantly lower amount of short thymic stromal lymphopoietin mRNA was observed in eosinophilic gastroenteritis when compared with controls (p<0.05), while a significantly higher amount of long thymic stromal lymphopoietin mRNA was observed in eosinophilic gastroenteritis when compared with controls (p<0.05). Peak eosinophilic count is significantly positively correlated with the expression of long thymic stromal lymphopoietin mRNA in the gastrointestinal mucosal of patients with eosinophilic gastroenteritis (r_s=0.623, p<0.005), while peak eosinophilic count is significantly negatively correlated with the expression of short thymic stromal lymphopoietin mRNA in the gastrointestinal mucosal of patients with eosinophilic gastroenteritis (r_s=-0.4474, p<0.05).

CONCLUSIONS

Abnormal mucosal thymic stromal lymphopoietin expression may contribute to gastrointestinal mucosa damage in eosinophilic gastroenteritis.

Anti-TSLP antibodies: Targeting a master regulator of type 2 immune responses

TSLP is an epithelial cell-derived cytokine synthesized in response to various stimuli, including protease allergens and microorganisms like viruses and bacteria. Biological functions of TSLP require heterodimer formation between the TSLP receptor (TSLPR) and IL-7 receptor-α, which polarize dendritic cells to induce type 2 inflammation and directly expand and/or activate Th2 cells, group 2 innate lymphoid cells, basophils, and other immune cells. TSLP is thus considered a master regulator of type 2 immune responses at the barrier surfaces of skin and the respiratory/gastrointestinal tract. Indeed, genetic, experimental, and clinical evidence suggests that the TSLP-TSLPR pathway is associated with the pathogenesis of allergic diseases such as atopic dermatitis (AD) and asthma. Tezepelumab (AMG-157/MEDI9929) is a human anti-TSLP antibody that prevents TSLP-TSLPR interactions. A phase 2 trial for moderate to severe AD showed that a greater but not statistically significant percentage of tezepelumab-treated patients showed clinical improvements compared to the placebo group. A phase 2 trial for uncontrolled, severe asthma showed significant decreases in asthma exacerbation rate and improved pulmonary function and asthma control for tezepelumab-treated patients. Levels of biomarkers of type 2 inflammation, such as blood/sputum eosinophil counts and fraction of exhaled nitric oxide decreased, however, clinical efficacy was observed irrespective of the baseline levels of these biomarkers. A blockade of the TSLP-TSLPR pathway likely will exert significant clinical effects on AD, asthma, and other allergic diseases. The efficacy of anti-TSLP antibodies compared to other biologics needs to be further examined.

Tezepelumab: a novel biological therapy for the treatment of severe uncontrolled asthma

Introduction: Thymic stromal lymphopoietin (TSLP) is overexpressed in the airways of severe asthmatics and is an upstream cytokine that orchestrates inflammatory responses in asthma. TSLP exerts its effects by binding to a high affinity heteromeric receptor complex composed of TSLPR and IL-7Rα. An association of polymorphisms in TSLP with airway hyperresponsiveness, IgE, eosinophilia and asthma has been documented. TSLP has been implicated in asthma pathophysiology. Tezepelumab is a first-in-class human monoclonal antibody that binds to TSLP, thus inhibiting its interaction with TSLP receptor complex. Tezepelumab given as an add-on-therapy to patients with severe uncontrolled asthma has shown safety, tolerability and efficacy. Several trials are evaluating the long-term safety and the efficacy of tezepelumab in adults and adolescents with severe uncontrolled asthma.Areas covered: We provide an overview of the monoclonal antibody therapeutics market for severe uncontrolled asthma, examine the underlying pathophysiology that drives TSLP and discuss the use of tezepelumab for the treatment of severe uncontrolled asthma,Expert opinion: TSLP is a promising target for T2-high and perhaps some patients with T2-low asthma. The results of preliminary clinical trials are encouraging. Several unanswered questions concerning basic pathophysiological aspects of TSLP variants, the long-term safety and efficacy of tezepelumab with different phenotypes/endotypes of asthma should be addressed.

Thymic stromal lymphopoietin levels are increased in patients with celiac disease

Thymic stromal lymphopoietin (TSLP) is a cytokine produced by epithelial cells in the lungs, skin, and intestinal mucosa and is involved in several physiological and pathological processes. In this study, we evaluated serum TSLP levels in patients with celiac disease (CD). The prospective study was conducted at a gastroenterology outpatient clinic between March 2018 and August 2018. Eighty-nine participants aged between 18 and 75 years were classified into following groups: 22 patients with newly diagnosed CD; 20 patients with CD who were compliant with a gluten-free diet (GFD); 32 patients with CD who were not compliant with a GFD; and 15 healthy controls. Demographic characteristics, disease duration, and selected biochemical and hematologic parameters were recorded and compared between groups. Median serum TSLP levels were 1193.65 pg/mL (range: 480.1-1547.1) in newly diagnosed CD patients, 110.25 pg/mL (range: 60.3-216.7) in CD patients who were compliant with a GFD, 113.1 pg/mL (range: 76.3-303.4) in CD patients who were not compliant with a GFD, and 57 pg/mL (range: 49-67.8) in healthy controls. Overall, there was a significant difference in serum TSLP levels between groups (p = 0.001). Patients with newly diagnosed CD had the highest serum TSLP levels. There was no significant difference in serum TSLP levels between patients with CD who were and were not compliant with a GFD. TSLP appears to be involved in the pathogenesis of CD. Further studies are required to determine if the TSLP signaling pathway can be used in the treatment of CD.

Constitutive alterations in vesicular trafficking increase the sensitivity of cells from celiac disease patients to gliadin

Celiac Disease (CD) is an autoimmune disease characterized by inflammation of the intestinal mucosa due to an immune response to wheat gliadins. Some gliadin peptides (e.g., A-gliadin P57-68) induce an adaptive Th1 pro-inflammatory response. Other gliadin peptides (e.g., A-gliadin P31-43) induce a stress/innate immune response involving interleukin 15 (IL15) and interferon α (IFN-α). In the present study, we describe a stressed/inflamed celiac cellular phenotype in enterocytes and fibroblasts probably due to an alteration in the early-recycling endosomal system. Celiac cells are more sensitive to the gliadin peptide P31-43 and IL15 than controls. This phenotype is reproduced in control cells by inducing a delay in early vesicular trafficking. This constitutive lesion might mediate the stress/innate immune response to gliadin, which can be one of the triggers of the gliadin-specific T-cell response.

Epithelial cell-derived cytokines: more than just signaling the alarm

The epithelial cell-derived cytokines thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 are central regulators of type 2 immunity, which drives a broad array of allergic responses. Often characterized as "alarmins" that are released by the barrier epithelium in response to external insults, these epithelial cell-derived cytokines were initially thought to act only early in allergic inflammation. Indeed, TSLP can condition dendritic cells to initiate type 2 responses, and IL-33 may influence susceptibility to asthma through its role in establishing the immune environment in the perinatal lungs. However, TSLP, IL-33, and IL-25 all regulate a broad spectrum of innate immune cell populations and are particularly potent in eliciting and activating type 2 innate lymphoid cells (ILC2s) that may act throughout allergic inflammation. Recent data suggest that a TSLP/ILC axis may mediate steroid resistance in asthma. Recent identification of memory Th2 cell subsets that are characterized by high receptor expression for TSLP, IL-33, and IL-25 further supports a role for these cytokines in allergic exacerbations. There is therefore growing interest in developing biologics that target TSLP, IL-33, and IL-25. This Review provides an overview of TSLP, IL-33, and IL-25 and the development of blocking antibodies that target these epithelial cell-derived cytokines.

MicroRNA-31 Targets Thymic Stromal Lymphopoietin in Mucosal Infiltrated CD4+ T Cells: A Role in Achieving Mucosal Healing in Ulcerative Colitis?

BACKGROUND

Ulcerative colitis (UC) is characterized by disruption of the mucosal intestinal barrier. MicroRNAs, single-stranded noncoding RNAs of approximately 22nt, are dysregulated in UC. MicroRNAs targeting thymic stromal lymphopoietin (TSLP), a cytokine involved in T-cell maturation and polarization, may be involved in regulating UC inflammation and mucosal healing.

METHODS

Biopsy samples from non-UC (n = 38), inactive UC (n = 18), and active UC (n = 23) patients were analyzed for mRNA (real-time quantitative polymerase chain reaction) or TSLP protein expression (enzyme-linked immunosorbent assay). Flow cytometry was used to isolate CD4+ T cells from biopsies. The functional mechanism was shown using luciferase assays and antago-miR transfections. The TSLP/miR-31 association was analyzed on 196 subjects from a previous clinical trial that tested the anti-IL-13 drug tralokinumab, whereas mucosal healing effects were studied on a subset of patients (n = 13) from this trial.

RESULTS

We found that TSLP is reduced at both mRNA and protein levels in inflamed UC patients when compared with healthy subjects, in both whole biopsies and biopsy-isolated CD4+ CD25+ T cells. The expression of miR-31, predicted to target TSLP, inversely co-related to the levels of TSLP mRNA in T cells. Blocking miR-31 in vitro in T cells increased both TSLP mRNA expression and protein secretion. Luciferase assays showed that miR-31 directly targeted TSLP mRNA, suggesting a direct mechanistic link. We also found that TSLP is increased in patients who achieve mucosal healing, comparing biopsies before and after treatment from the tralokinumab trial.

CONCLUSIONS

Our data suggest a role for TSLP in promoting mucosal healing and regulating inflammation in UC, whereas miR-31 can directly block this effect.

Thymic Stromal Lymphopoietin Isoforms, Inflammatory Disorders, and Cancer

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine originally isolated from a murine thymic stromal cell line. TSLP exerts its biological effects by binding to a high-affinity heteromeric complex composed of thymic stromal lymphopoietin receptor chain and IL-7Rα. TSLP is primarily expressed by activated lung and intestinal epithelial cells, keratinocytes, and fibroblasts. However, dendritic cells (DCs), mast cells, and presumably other immune cells can also produce TSLP. Different groups of investigators have demonstrated the existence of two variants for TSLP in human tissues: the main isoform expressed in steady state is the short form (sf TSLP), which plays a homeostatic role, whereas the long form (lfTSLP) is upregulated in inflammatory conditions. In addition, there is evidence that in pathological conditions, TSLP can be cleaved by several endogenous proteases. Several cellular targets for TSLP have been identified, including immune (DCs, ILC2, T and B cells, NKT and Treg cells, eosinophils, neutrophils, basophils, monocytes, mast cells, and macrophages) and non-immune cells (platelets and sensory neurons). TSLP has been originally implicated in a variety of allergic diseases (e.g., atopic dermatitis, bronchial asthma, eosinophilic esophagitis). Emerging evidence indicates that TSLP is also involved in chronic inflammatory (i.e., chronic obstructive pulmonary disease and celiac disease) and autoimmune (e.g., psoriasis, rheumatoid arthritis) disorders and several cancers. These emerging observations greatly widen the role of TSLP in different human diseases. Most of these studies have not used tools to analyze the expression of the two TSLP isoforms. The broad pathophysiologic profile of TSLP has motivated therapeutic targeting of this cytokine. Tezepelumab is a first-in-class human monoclonal antibody (1) that binds to TSLP inhibiting its interaction with TSLP receptor complex. Tezepelumab given as an add-on-therapy to patients with severe uncontrolled asthma has shown safety and efficacy. Several clinical trials are evaluating the safety and the efficacy of tezepelumab in different inflammatory disorders. Monoclonal antibodies used to neutralize TSLP should not interact or hamper the homeostatic effects of sf TSLP.

Vaccine Immunotherapy for Celiac Disease

Autoimmune and allergic disorders are highly prevalent conditions in which an altered or abnormal immune response is mounted against self- or environmental antigens, respectively. Antigen-based immunotherapy is a therapeutic option aimed at restoring the specific immune tolerance toward pathogenic antigens while leaving the rest of the immune system unaffected. This strategy proved efficacy especially in allergic diseases, including asthma, allergic rhinitis, and food allergies, but still has shortcomings for the treatment of autoimmune diseases. However, there are no available therapies, currently, in clinical practice for restoring the physiological tolerance that is typically lost in autoimmune diseases. In celiac disease, which is a common immune-mediated enteropathy triggered by the ingestion of gluten in genetically susceptible individuals, antigen-based immunotherapy could be a feasible option thanks to our deep understanding of the pathogenic mechanisms underpinning this condition. In fact, the immunodominant gluten epitopes are well-characterized and are recognized by pathogenic CD4+ T-cells that could be desensitized with immunotherapy. Moreover, the intestinal damage occurring in celiac disease (i.e., villous atrophy) is reversible upon gluten withdrawal. Only recently the results of a phase I trial of an intradermal, adjuvant-free, formulation of three specific gluten peptides (Nexvax2) showed a good safety profile, albeit its efficacy still needs to be demonstrated. More results are awaited, as they may radically change patients' quality of life that is constrained by the lifelong gluten-free diet and by the potential onset of life-threatening complications.

Structure and antagonism of the receptor complex mediated by human TSLP in allergy and asthma

The pro-inflammatory cytokine thymic stromal lymphopoietin (TSLP) is pivotal to the pathophysiology of widespread allergic diseases mediated by type 2 helper T cell (Th2) responses, including asthma and atopic dermatitis. The emergence of human TSLP as a clinical target against asthma calls for maximally harnessing its therapeutic potential via structural and mechanistic considerations. Here we employ an integrative experimental approach focusing on productive and antagonized TSLP complexes and free cytokine. We reveal how cognate receptor TSLPR allosterically activates TSLP to potentiate the recruitment of the shared interleukin 7 receptor α-chain (IL-7Rα) by leveraging the flexibility, conformational heterogeneity and electrostatics of the cytokine. We further show that the monoclonal antibody Tezepelumab partly exploits these principles to neutralize TSLP activity. Finally, we introduce a fusion protein comprising a tandem of the TSLPR and IL-7Rα extracellular domains, which harnesses the mechanistic intricacies of the TSLP-driven receptor complex to manifest high antagonistic potency.

The pro-inflammatory cytokine thymic stromal lymphopoietin (TSLP) is a promising therapeutic target. Here the authors characterize the assembly mechanism of the receptor complex driven by human TSLP, and its antagonism by the monoclonal antibody Tezepelumab and a fusion protein comprising the TSLP receptors.

Thymic Stromal Lymphopoietin: To Cut a Long Story Short

Thymic stromal lymphopoietin (TSLP) was identified more than 20 years ago as a secreted factor of a mouse thymic stromal cell line; later, a human orthologue was also identified. The signaling pathway triggered by TSLP has been extensively studied, and upregulation of the cytokine itself is linked to the pathogenesis of numerous Th2-related diseases, including atopic dermatitis, asthma, allergic responses, as well as certain types of cancers. On the other hand, TSLP mediates several immune homeostatic functions in both the gut and the thymus. Thus, a paradox occurs; why is TSLP homeostatic in certain tissues and a hallmark of exacerbated Th2 responses in the aforementioned pathologies? We and others have recently shown that in humans a novel isoform exists; this is a shorter isoform of TSLP whose expression is constitutive and controlled by a separate promoter. Short TSLP isoform mediates the homeostatic functions, whereas the long isoform is expressed at low/undetectable level at steady state and upregulated during inflammation in several tissues. Here we review the most recent data concerning the differential expression of the 2 isoforms and provide a potential explanation to the paradox. TSLP is regarded as a promising target for treatment of relevant pathologies, with a number of clinical trials already underway. It is important to design new strategies aimed at leaving intact the homeostatic effects of the short isoform while targeting the inflammatory effects of the long isoform.

Innate and adaptive immunity in self-reported nonceliac gluten sensitivity versus celiac disease

BACKGROUND

Immune mechanisms have been implicated in nonceliac gluten sensitivity (NCGS), a condition characterized by intestinal and/or extraintestinal symptoms caused by the ingestion of gluten in non-celiac/non-wheat allergic individuals.

AIMS

We investigated innate and adaptive immunity in self-reported NCGS versus celiac disease (CD).

METHODS

In the supernatants of ex vivo-cultured duodenal biopsies from 14 self-reported NCGS patients, 9 untreated and 10 treated CD patients, and 12 controls we detected innate cytokines - interleukin (IL)-15, tumor necrosis factor-α, IL-1β, IL-6, IL-12p70, IL-23, IL-27, IL-32α, thymic stromal lymphopoietin (TSLP), IFN-α-, adaptive cytokines - interferon (IFN)-γ, IL-17A, IL-4, IL-5, IL-10, IL-13-, chemokines - IL-8, CCL1, CCL2, CCL3, CCL4, CCL5, CXCL1, CXCL10-, granulocyte colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF).

RESULTS

Mucosal innate and adaptive cytokines, chemokines and growth factors did not differ between self-reported NCGS, treated CD and controls. On the contrary, IL-6, IL-15, IL-27, IFN-α, IFN-γ, IL-17A, IL-23, G-CSF, GM-CSF, IL-8, CCL1 and CCL4 were significantly higher in untreated CD than in self-reported NCGS, treated CD and controls, while TSLP was significantly lower in untreated CD than in self-reported NCGS, treated CD and controls.

CONCLUSION

In our hands, patients with self-reported NCGS showed no abnormalities of the mucosal immune response.

Preferential Secretion of Thymic Stromal Lymphopoietin (TSLP) by Terminally Differentiated Esophageal Epithelial Cells: Relevance to Eosinophilic Esophagitis (EoE)

Eosinophilic esophagitis (EoE) is a chronic Th2 and food antigen-mediated disease characterized by esophageal eosinophilic infiltration. Thymic stromal lymphopoetin (TSLP), an epithelial derived cytokine which bridges innate and Th2-type adaptive immune responses in other allergic conditions, is overexpressed in esophageal biopsies of EoE subjects. However, the triggers of TSLP expression in the esophageal epithelium are unknown. The objective of the current study was to characterize TSLP expression in human esophageal epithelium in EoE in vivo and to determine the role of food antigens upon epithelial TSLP expression in vitro. Using immunohistochemistry (IHC), we localized TSLP in esophageal biopsies of active EoE (≥15 eos/hpf), inactive EoE (<15 eos/hpf) and non-EoE control subjects, and found that TSLP expression was restricted to the differentiated suprabasal layer of the epithelium in actively inflamed EoE biopsies. Consistent with these results in vivo, inducible TSLP protein secretion was higher in CaCl₂ differentiated telomerase-immortalized esophageal epithelial cells (EPC2-hTERT) compared to undifferentiated cells of the basal phenotype, following stimulation with the TLR3 ligand poly(I:C). To determine whether food antigens could directly induce epithelial TSLP secretion, differentiated and undifferentiated primary esophageal epithelial cells from EoE and non-EoE subjects were challenged with food antigens clinically relevant to EoE: Chicken egg ovalbumin (OVA), wheat, and milk proteins beta-lactoglobulin (blg) and beta-casein. Food antigens failed to induce TSLP secretion by undifferentiated cells; in contrast, only OVA induced TSLP secretion in differentiated epithelial cells from both EoE and control cell lines, an effect abolished by budesonide and NF-κb inhibition. Together, our study shows that specific food antigens can trigger innate immune mediated esophageal TSLP secretion, suggesting that esophageal epithelial cells at the barrier surface may play a significant role in the pathogenesis of EoE by regulating TSLP expression.