Food allergy in mice is modulated through the thymic stromal lymphopoietin pathway

Thymic Stromal Lymphopoietin (TSLP), Its Isoforms and the Interplay with the Epithelium in Allergy and Asthma

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine that has emerged as a critical player in the development and progression of allergy and asthma. It is primarily produced by epithelial cells and functions as a potent immune system activator. TSLP acts through interaction with its receptor complex, composed of the TSLP receptor (TSLPR) and interleukin-7 receptor alpha chain (IL-7Rα), activating downstream complex signalling pathways. The TSLP major isoform, known as long-form TSLP (lfTSLP), is upregulated in the airway epithelium of patients with allergic diseases. More research is warranted to explore the precise mechanisms by which short-form TSLP (sfTSLP) regulates immune responses. Understanding the dynamic interplay between TSLP and the dysfunctional epithelium provides insights into the mechanisms underlying allergy and asthma pathogenesis. Targeting TSLP represents an important therapeutic strategy, as it may upstream disrupt the inflammatory cascade and alleviate symptoms associated with allergic inflammation.

Emerging Role of Alarmins in Food Allergy: An Update on Pathophysiological Insights, Potential Use as Disease Biomarkers, and Therapeutic Implications

Food allergies are immuno-mediated adverse reactions to ingestion or contact with foods, representing a widespread health problem. The immune response can be IgE-mediated, non-IgE-mediated, or with a mixed mechanism. The role of innate immunity and alarmins in the pathogenesis of diseases such as asthma and atopic dermatitis is well known. Some authors have investigated the correlation between alarmins and food allergies, often obtaining interesting results. We analyzed articles published in English from the last 22 years present on PubMed concerning the role of alarmins in the pathogenesis of food allergies and their potential use as disease biomarkers, response biomarkers to therapy, or potential therapeutic targets. Nuclear alarmins (TSLP, IL-33, IL-25) appear to have a critical role in IgE-mediated allergies but are also implicated in entities such as eosinophilic esophagitis. Calprotectin and defensins may play a role as disease biomarkers and could help predict response to therapy, although results in the literature are often conflicting. Despite the promising results, more studies on humans still need to be conducted. Deepening our knowledge regarding alarmins and their involvement in food allergies could lead to the development of new biological therapies, significantly impacting patients' quality of life.

Suspected gut barrier disruptors and development of food allergy: Adjuvant effects and early immune responses

Food allergy is an increasing public health challenge worldwide. It has recently been hypothesized that the increase in exposure to intestinal epithelial barrier-damaging biological and chemical agents contribute to this development. In animal models, exposure to adjuvants with a food allergen has been shown to promote sensitization and development of food allergy, and barrier disrupting capacities have been suggested to be one mechanism of adjuvant action. Here, we investigated how gut barrier disrupting compounds affected food allergy development in a mouse model of peanut allergy. Sensitization and clinical peanut allergy in C3H/HEOuJ mice were assessed after repeated oral exposure to peanut extract together with cholera toxin (CT; positive control), the mycotoxin deoxynivalenol (DON), house dust mite (HDM) or the pesticide glyphosate (GLY). In addition, we investigated early effects 4 to 48 h after a single exposure to the compounds by assessing markers of intestinal barrier permeability, alarmin production, intestinal epithelial responses, and local immune responses. CT and DON exerted adjuvant effects on peanut allergy development assessed as clinical anaphylaxis in mice. Early markers were affected only by DON, observed as increased IL-33 (interleukin 33) and thymic stromal lymphopoietin (TSLP) alarmin production in intestines and IL-33 receptor ST2 in serum. DON also induced an inflammatory immune response in lymph node cells stimulated with lipopolysaccharide (LPS). HDM and GLY did not clearly promote clinical food allergy and affected few of the early markers at the doses tested. In conclusion, oral exposure to CT and DON promoted development of clinical anaphylaxis in the peanut allergy mouse model. DON, but not CT, affected the early markers measured in this study, indicating that DON and CT have different modes of action at the early stages of peanut sensitization.

Molecular and Immunomodulatory Actions of New Antiasthmatic Agents: Exploring the Diversity of Biologics in Th2 Endotype Asthma

Asthma is a major respiratory disorder characterised by chronic inflammation and airway remodelling. It affects about 1-8% of the global population and is responsible for over 461,000 deaths annually. Until recently, the pharmacotherapy of severe asthma involved high doses of inhaled corticosteroids in combination with β-agonist for prolonged action, including theophylline, leukotriene antagonist or anticholinergic yielding limited benefit. Although the use of newer agents to target Th2 asthma endotypes has improved therapeutic outcomes in severe asthmatic conditions, there seems to be a paucity of understanding the diverse mechanisms through which these classes of drugs act. This article delineates the molecular and immunomodulatory mechanisms of action of new antiasthmatic agents currently being trialled in preclinical and clinical studies to remit asthmatic conditions. The ultimate goal in developing antiasthmatic agents is based on two types of approaches: either anti-inflammatory or bronchodilators. Biologic and most small molecules have been shown to modulate specific asthma endotypes, targeting thymic stromal lymphopoietin, tryptase, spleen tyrosine kinase (Syk), Janus kinase, PD-L1/PD-L2, GATA-3, and CD38 for the treatment and management of Th2 endotype asthma.

Role of the Intestinal Epithelium and Its Interaction With the Microbiota in Food Allergy

The intestinal epithelial tract forms a dynamic lining of the digestive system consisting of a range of epithelial cell sub-types with diverse functions fulfilling specific niches. The intestinal epithelium is more than just a physical barrier regulating nutrient uptake, rather it plays a critical role in homeostasis through its intrinsic innate immune function, pivotal regulation of antigen sensitization, and a bi-directional interplay with the microbiota that evolves with age. In this review we will discuss these functions of the epithelium in the context of food allergy.

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.

Overview of in vivo and ex vivo endpoints in murine food allergy models: Suitable for evaluation of the sensitizing capacity of novel proteins?

Significant efforts are necessary to introduce new dietary protein sources to feed a growing world population while maintaining food supply chain sustainability. Such a sustainable protein transition includes the use of highly modified proteins from side streams or the introduction of new protein sources that may lead to increased clinically relevant allergic sensitization. With food allergy being a major health problem of increasing concern, understanding the potential allergenicity of new or modified proteins is crucial to ensure public health protection. The best predictive risk assessment methods currently relied on are in vivo models, making the choice of endpoint parameters a key element in evaluating the sensitizing capacity of novel proteins. Here, we provide a comprehensive overview of the most frequently used in vivo and ex vivo endpoints in murine food allergy models, addressing their strengths and limitations for assessing sensitization risks. For optimal laboratory‐to‐laboratory reproducibility and reliable use of predictive tests for protein risk assessment, it is important that researchers maintain and apply the same relevant parameters and procedures. Thus, there is an urgent need for a consensus on key food allergy parameters to be applied in future food allergy research in synergy between both knowledge institutes and clinicians.

New Developments in Non-allergen-specific Therapy for the Treatment of Food Allergy

PURPOSE OF REVIEW

The prevalence of food allergy is increasing. At the current time, there are no approved treatments for food allergy. Major limitations of immunotherapy are long treatment periods (months or years), frequent clinic visits, high costs, increased risk of adverse events during treatment, and lack of durability of desensitization. Additionally, it is allergen-specific, and in those allergic to multiple allergens, the length and cost of treatment are further increased. In this review, we summarize recent developments in novel non-allergen-specific treatments for food allergy.

RECENT FINDINGS

A number of monoclonal antibodies that block IgE or specific pro-allergenic cytokines or their receptors have shown promise in clinical trials for food allergy. The insight we have gained through the use of one drug for the treatment of an atopic disease is quickly being translated to other atopic diseases, including food allergy. The future for food allergy treatment with biologics looks bright.

Combined Exposure of Activated Intestinal Epithelial Cells to Nondigestible Oligosaccharides and CpG-ODN Suppresses Th2-Associated CCL22 Release While Enhancing Galectin-9, TGFβ, and Th1 Polarization

Background

Short-chain galacto- and long-chain fructo-oligosaccharides (scGOS/lcFOS) and CpG-ODN affect intestinal epithelial cells (IEC). Epithelial IL1α may contribute to allergic sensitization via autocrine mediator release affecting dendritic cells (DC). We studied whether IL1α contributes to Th2-associated mediator release by activated IEC and IEC/DC cocultures and possible modulation by scGOS/lcFOS±CpG-ODN.

Methods

Solid phase or transwell cultured IEC were preincubated with IL1α and/or IFNγ/TNFα for 6 h. The transwell IEC were also apically exposed to scGOS/lcFOS±CpG-ODN for 6 h, washed, and re-exposed, while cocultured with immature moDC (ccDC) for 48 h. These ccDC were subsequently added to allogeneic naïve T cells (MLR). IEC- and/or DC-derived mediators and T cell cytokines were measured.

Results

IL1α tended to enhance IL25 and enhanced IL33 and CCL20 release by IEC, while IL1α or TNFα or IFNγ enhanced CCL22. These were all further increased upon combined exposure of IFNγ/TNFα±IL1α coinciding with increased IL33 secretion in the solid phase culture. In the transwell, IL25 and IL33 remained under detection, while CCL20 and CCL22 were induced by IL1α or IFNγ/TNFα, respectively, and a synergistic increase was observed upon combined exposure of IFNγ/TNFα and IL1α. Furthermore, IFNγ was found to enhance galectin-9 secretion, which was more pronounced in IFNγ/TNFα±IL1α-exposed IEC and coincided with TGFβ increase. Epithelial CpG-ODN exposure further increased CCL20, while reducing CCL22 release by IFNγ/TNFα/IL1α-activated IEC; however, scGOS/lcFOS suppressed both. Combined scGOS/lcFOS and CpG-ODN reduced CCL22, while CCL20 and regulatory galectin-9 and TGFβ remained high in the supernatant of IFNγ/TNFα/IL1α-activated IEC and the following IEC/DC coculture. ccDC of scGOS/lcFOS- and CpG-ODN-exposed IFNγ/TNFα/IL1α-activated IEC increased IFNγ, IL10, TGFβ, and galectin-9 secretion in the MLR compared to ccDC exposed to control-activated IEC.

Conclusion

IL1α enhanced CCL20 and Th2-associated CCL22 release by IFNγ/TNFα-activated IEC. Combined scGOS/lcFOS and CpG-ODN exposure suppressed CCL22, while maintaining high CCL20, TGFβ, and galectin-9 concentrations. In addition, ccDC derived from this IEC/DC coculture enhanced Th1 and regulatory mediator secretion mimicking known in vivo effects.

Mechanism for initiation of food allergy: Dependence on skin barrier mutations and environmental allergen costimulation

BACKGROUND

Mechanisms for the development of food allergy in neonates are unknown but clearly linked in patient populations to a genetic predisposition to skin barrier defects. Whether skin barrier defects contribute functionally to development of food allergy is unknown.

OBJECTIVE

The purpose of the study was to determine whether skin barrier mutations, which are primarily heterozygous in patient populations, contribute to the development of food allergy.

METHODS

Mice heterozygous for the filaggrin (Flg)ft and Tmem79ma mutations were skin sensitized with environmental and food allergens. After sensitization, mice received oral challenge with food allergen, and then inflammation, inflammatory mediators, and anaphylaxis were measured.

RESULTS

We define development of inflammation, inflammatory mediators, and food allergen-induced anaphylaxis in neonatal mice with skin barrier mutations after brief concurrent cutaneous exposure to food and environmental allergens. Moreover, neonates of allergic mothers have increased responses to suboptimal sensitization with food allergens. Importantly, responses to food allergens by these neonatal mice were dependent on genetic defects in skin barrier function and on exposure to environmental allergens. ST2 blockade during skin sensitization inhibited the development of anaphylaxis, antigen-specific IgE, and inflammatory mediators. Neonatal anaphylactic responses and antigen-specific IgE were also inhibited by oral pre-exposure to food allergen, but interestingly, this was blunted by concurrent pre-exposure of the skin to environmental allergen.

CONCLUSION

These studies uncover mechanisms for food allergy sensitization and anaphylaxis in neonatal mice that are consistent with features of human early-life exposures and genetics in patients with clinical food allergy and demonstrate that changes in barrier function drive development of anaphylaxis to food allergen.

Oral sensitization to whey proteins induces age- and sex-dependent behavioral abnormality and neuroinflammatory responses in a mouse model of food allergy: a potential role of mast cells

BACKGROUND

Growing evidence has strengthened the association of food allergy with neuropsychiatric symptoms such as depression, anxiety, and autism. However, underlying mechanisms by which peripheral allergic responses lead to behavioral dysfunction are yet to be determined. Allergen-activated mast cells may serve as mediators by releasing histamine and other inflammatory factors that could adversely affect brain function. We hypothesized that eliciting food allergy in experimental animals would result in behavioral changes accompanied by mast cell accumulation in the brain. Our hypothesis was tested in a mouse model of milk allergy using bovine milk whey proteins (WP) as the allergen.

METHODS

Male and female C57BL/6 mice at 4 weeks (young) and 10 months (old) of age underwent 5-week WP sensitization with weekly intragastric administration of 20 mg WP and 10 μg cholera toxin as an adjuvant. Age-matched sham animals were given the vehicle containing only the adjuvant. All animals were orally challenged with 50 mg WP in week 6 and their intrinsic digging behavior was assessed the next day. Animals were sacrificed 3 days after the challenge, and WP-specific serum IgE, intestinal and brain mast cells, glial activation, and epigenetic DNA modification in the brain were examined.

RESULTS

WP-sensitized males showed significantly less digging activity than the sham males in both age groups while no apparent difference was observed in females. Mast cells and their activities were evident in the intestines in an age- and sex-dependent manner. Brain mast cells were predominantly located in the region between the lateral midbrain and medial hippocampus, and their number increased in the WP-sensitized young, but not old, male brains. Noticeable differences in for 5-hydroxymethylcytosine immunoreactivity were observed in WP mice of both age groups in the amygdala, suggesting epigenetic regulation. Increased microglial Iba1 immunoreactivity and perivascular astrocytes hypertrophy were also observed in the WP-sensitized old male mice.

CONCLUSIONS

Our results demonstrated that food allergy induced behavioral abnormality, increases in the number of mast cells, epigenetic DNA modification in the brain, microgliosis, and astrocyte hypertrophy in a sex- and age-dependent manner, providing a potential mechanism by which peripheral allergic responses evoke behavioral dysfunction.

Regulation of Allergic Immune Responses by Microbial Metabolites

Emerging evidence demonstrates that the microbiota plays an essential role in shaping the development and function of host immune responses. A variety of environmental stimuli, including foods and commensals, are recognized by the host through the epithelium, acting as a physical barrier. Two allergic diseases, atopic dermatitis and food allergy, are closely linked to the microbiota, because inflammatory responses occur on the epidermal border. The microbiota generates metabolites such as short-chain fatty acids and poly-γ-glutamic acid (γPGA), which can modulate host immune responses. Here, we review how microbial metabolites can regulate allergic immune responses. Furthermore, we focus on the effect of γPGA on allergic T helper (Th) 2 responses and its therapeutic application.

Thymic Stromal Lymphopoietin Is Critical for Regulation of Proinflammatory Cytokine Response and Resistance to Experimental Trypanosoma congolense Infection

African trypanosomiasis (sleeping sickness) poses serious threat to human and animal health in sub-Saharan Africa. Because there is currently no vaccine for preventing this disease and available drugs are not safe, understanding the mechanisms that regulate resistance and/or susceptibility to the disease could reveal novel targets for effective disease therapy and prevention. Thymic stromal lymphopoietin (TSLP) plays a critical role in driving Th2 immune response. Although susceptibility to experimental Trypanosoma congolense infection in mice is associated with excessive proinflammatory responses due in part to impaired Th2 response, the role of TSLP in resistance to African trypanosomiasis has not been well studied. Here, we investigated whether TSLP is critical for maintaining Th2 environment necessary for survival of T. congolense-infected mice. We observed an increased TSLP level in mice after infection with T. congolense, suggesting a role for this cytokine in resistance to the infection. Indeed, TSLPR^-/- mice were more susceptible to T. congolense infection and died significantly earlier than their wild-type (WT) controls. Interestingly, serum levels of IFN-γ and TNF-α and the frequency of IFN-γ- and TNF-α-producing CD4⁺ T cells in the spleens and liver were significantly higher in infected TSLPR^-/- mice than in the WT control mice. Susceptibility was also associated with excessive M1 macrophage activation. Treatment of TSLPR^-/- mice with anti-IFN-γ mAb during infection abolished their enhanced susceptibility to T. congolense infection. Collectively, our study shows that TSLP plays a critical role in resistance to T. congolense infection by dampening the production of proinflammatory cytokines and its associated M1 macrophage activation.

A mutually beneficial collaboration between the European Academy of Allergy and Clinical Immunology Junior Members and Clinical and Translational Allergy

The European Academy of Allergy and Clinical Immunology (EAACI) Junior Members (JM) comprise the largest EAACI section with around 4000 clinicians and scientists under 35 years of age working in the field of allergy and clinical immunology. The Junior Member collaboration with Clinical and Translational Allergy Journal is a mutually beneficial relationship providing Junior Members of EAACI with excellent opportunities to publish their work in the Journal, enhance their visibility in their respective field, and get involved with Journal-related activities and processes. In the future, this collaboration will grow, not only by the consolidation of these activities, but also by the implementation of new initiatives, such as a platform for discussing and/or publishing Junior Members’ dissertations in the Journal. From the CTA perspective, the collaboration presents an opportunity to promote a new generation of allergists with experience of conducting and presenting research, with improved skills in critical review.