Identification and characterization of DC-SIGN-binding glycoproteins in allergenic foods

C-Type Lectin Receptor Mediated Modulation of T2 Immune Responses to Allergens

PURPOSE OF REVIEW

Allergic diseases represent a major health problem of increasing prevalence worldwide. In allergy, dendritic cells (DCs) contribute to both the pathophysiology and the induction of healthy immune responses to the allergens. Different studies have reported that some common allergens contain glycans in their structure. C-type lectin receptors (CLRs) expressed by DCs recognize carbohydrate structures and are crucial in allergen uptake, presentation, and polarization of T cell responses. This review summarizes the recent literature regarding the role of CLRs in the regulation of type 2 immune responses to allergens.

RECENT FINDINGS

In this review, we highlight the capacity of CLRs to recognize carbohydrates in common allergens triggering different signaling pathways involved in the polarization of CD4⁺ T cells towards specific Th2 responses. Under certain conditions, specific CLRs could also promote tolerogenic responses to allergens, which might well be exploited to develop novel therapeutic approaches of allergen-specific immunotherapy (AIT), the single treatment with potential disease-modifying capacity for allergic disease. At this regard, polymerized allergens conjugated to non-oxidized mannan (allergoid-mannan conjugated) are next-generation vaccines targeting DCs via CLRs that promote regulatory T cells, thus favoring allergen tolerance both in preclinical models and clinical trials. A better understanding of the role of CLRs in the development of allergy and in the induction of allergen tolerance might well pave the way for the design of novel strategies for allergic diseases.

Methylation changes induced by a glycodendropeptide immunotherapy and associated to tolerance in mice

Introduction

Allergen-specific immunotherapy (AIT) is applied as treatment to rise tolerance in patients with food allergies. Although AIT is thoroughly used, the underlying epigenetic events related to tolerant induction are still unknown. Thus, we aim to investigate epigenetic changes that could be related to tolerance in dendritic cells (DCs) from anaphylactic mice to lipid transfer proteins, Pru p 3, in the context of a sublingual immunotherapy (SLIT) with a glycodendropeptide (D1ManPrup3) that has demonstrated tolerant or desensitization responses depending on the treatment dose.

Methods

Changes in DNA methylation in CpG context were determined comparing Sensitized (Antigen-only) animals and two groups receiving SLIT with the D1ManPrup3 nanostructure (D1ManPrup3-SLIT): Tolerant (2nM D1ManPrup3) and Desensitized (5nM D1ManPrup3), against anaphylactic animals. DNA from lymph nodes-DCs were isolated and then, Whole Genome Bisulphite Sequencing was performed to analyze methylation.

Results

Most differentially methylated regions were found on the area of influence of gene promoters (DMPRs). Compared to the Anaphylactic group, the highest value was found in Desensitized mice (n = 7,713 DMPRs), followed by Tolerant (n = 4,091 DMPRs) and Sensitized (n = 3,931 DMPRs) mice. Moreover, many of these epigenetic changes were found in genes involved in immune and tolerance responses (Il1b, Il12b, Il1a, Ifng, and Tnf) as shown by functional enrichment (DCs regulation, B cell-mediated immunity, and effector mechanisms).

Discussion

In conclusion, different doses of D1ManPrup3-SLIT induce different DNA methylation changes, which are reflected in the induction of distinct responses, tolerance, or desensitization.

Scientific Opinion on development needs for the allergenicity and protein safety assessment of food and feed products derived from biotechnology

This Scientific Opinion addresses the formulation of specific development needs, including research requirements for allergenicity assessment and protein safety, in general, which is urgently needed in a world that demands more sustainable food systems. Current allergenicity risk assessment strategies are based on the principles and guidelines of the Codex Alimentarius for the safety assessment of foods derived from 'modern' biotechnology initially published in 2003. The core approach for the safety assessment is based on a 'weight-of-evidence' approach because no single piece of information or experimental method provides sufficient evidence to predict allergenicity. Although the Codex Alimentarius and EFSA guidance documents successfully addressed allergenicity assessments of single/stacked event GM applications, experience gained and new developments in the field call for a modernisation of some key elements of the risk assessment. These should include the consideration of clinical relevance, route of exposure and potential threshold values of food allergens, the update of in silico tools used with more targeted databases and better integration and standardisation of test materials and in vitro/in vivo protocols. Furthermore, more complex future products will likely challenge the overall practical implementation of current guidelines, which were mainly targeted to assess a few newly expressed proteins. Therefore, it is timely to review and clarify the main purpose of the allergenicity risk assessment and the vital role it plays in protecting consumers' health. A roadmap to (re)define the allergenicity safety objectives and risk assessment needs will be required to inform a series of key questions for risk assessors and risk managers such as 'what is the purpose of the allergenicity risk assessment?' or 'what level of confidence is necessary for the predictions?'.

A positive feedback loop reinforces the allergic immune response in human peanut allergy

Food allergies are a leading cause of anaphylaxis, and cellular mechanisms involving antigen presentation likely play key roles in their pathogenesis. However, little is known about the response of specific antigen-presenting cell (APC) subsets to food allergens in the setting of food allergies. Here, we show that in peanut-allergic humans, peanut allergen drives the differentiation of CD209+ monocyte-derived dendritic cells (DCs) and CD23+ (FcєRII) myeloid dendritic cells through the action of allergen-specific CD4+ T cells. CD209+ DCs act reciprocally on the same peanut-specific CD4+ T cell population to reinforce Th2 cytokine expression in a positive feedback loop, which may explain the persistence of established food allergy. In support of this novel model, we show clinically that the initiation of oral immunotherapy (OIT) in peanut-allergic patients is associated with a decrease in CD209+ DCs, suggesting that breaking the cycle of positive feedback is associated with therapeutic effect.

Immunomodulation by Human Milk Oligosaccharides: The Potential Role in Prevention of Allergic Diseases

The prevalence and incidence of allergic diseases is rising and these diseases have become the most common chronic diseases during childhood in Westernized countries. Early life forms a critical window predisposing for health or disease. Therefore, this can also be a window of opportunity for allergy prevention. Postnatally the gut needs to mature, and the microbiome is built which further drives the training of infant's immune system. Immunomodulatory components in breastmilk protect the infant in this crucial period by; providing nutrients that contain substrates for the microbiome, supporting intestinal barrier function, protecting against pathogenic infections, enhancing immune development and facilitating immune tolerance. The presence of a diverse human milk oligosaccharide (HMOS) mixture, containing several types of functional groups, points to engagement in several mechanisms related to immune and microbiome maturation in the infant's gastrointestinal tract. In recent years, several pathways impacted by HMOS have been elucidated, including their capacity to; fortify the microbiome composition, enhance production of short chain fatty acids, bind directly to pathogens and interact directly with the intestinal epithelium and immune cells. The exact mechanisms underlying the immune protective effects have not been fully elucidated yet. We hypothesize that HMOS may be involved in and can be utilized to provide protection from developing allergic diseases at a young age. In this review, we highlight several pathways involved in the immunomodulatory effects of HMOS and the potential role in prevention of allergic diseases. Recent studies have proposed possible mechanisms through which HMOS may contribute, either directly or indirectly, via microbiome modification, to induce oral tolerance. Future research should focus on the identification of specific pathways by which individual HMOS structures exert protective actions and thereby contribute to the capacity of the authentic HMOS mixture in early life allergy prevention.

C-type lectins in immunity and homeostasis

The C-type lectins are a superfamily of proteins that recognize a broad repertoire of ligands and that regulate a diverse range of physiological functions. Most research attention has focused on the ability of C-type lectins to function in innate and adaptive antimicrobial immune responses, but these proteins are increasingly being recognized to have a major role in autoimmune diseases and to contribute to many other aspects of multicellular existence. Defects in these molecules lead to developmental and physiological abnormalities, as well as altered susceptibility to infectious and non-infectious diseases. In this Review, we present an overview of the roles of C-type lectins in immunity and homeostasis, with an emphasis on the most exciting recent discoveries.

Polyphenol-enriched berry extracts naturally modulate reactive proteins in model foods

Healthy foods like polyphenol-rich berries and high quality edible proteins are in demand in today's functional food marketplace, but it can be difficult to formulate convenient food products with physiologically-relevant amounts of these ingredients and still maintain product quality. In part, this is because proteins can interact with other food ingredients and precipitate destabilizing events, which can disrupt food structure and diminish shelf life. Proteins in foods can also interact with human receptors to provoke adverse consequences such as allergies. When proteins and polyphenols were pre-aggregated into stable colloidal particles prior to use as ingredients, highly palatable food formulations (with reduced astringency of polyphenols) could be prepared, and the overall structural properties of food formulations were significantly improved. All of the nutritive and phytoactive benefits of the proteins and concentrated polyphenols remained highly bioavailable, but the protein molecules in the particle matrix did not self-aggregate into networks or react with other food ingredients. Both the drainage half-life (a marker of structural stability) and the yield stress (resistance to flow) of model foams made with the protein-polyphenol particles were increased in a dose-dependent manner. Of high significance in this complexation process, the reactive allergenic epitopes of certain proteins were effectively blunted by binding with polyphenols, attenuating the allergenicity of the food proteins. Porcine macrophages produced TNF-α proinflammatory cytokine when provoked with whey protein, but, this response was blocked completely when the cells were stimulated with particles that complexed whey protein with cinnamon-derived polyphenols. Cytokine and chemokine production characteristic of allergic reactions were blocked by the polyphenols, allowing for the potential creation of hypoallergenic protein-berry polyphenol enriched foods.

Role of dendritic cells in peanut allergy

INTRODUCTION

The prevalence of peanut allergy (PA) has increased, affecting approximately 1.1% of children in Western countries. PA causes life-threatening anaphylaxis and frequently persists for life. There are no standardized curative therapies for PA, and avoidance of peanuts remains the main therapeutic option. A better understanding of the pathogenesis of PA is essential to identify new treatment strategies. Intestinal dendritic cells (DCs) are essential in the induction and maintenance of food tolerance because they present dietary allergens to T cells, thereby directing subsequent immune responses. Areas covered: In this review, we discuss the factors related to the acquisition of oral tolerance to peanut proteins. We focus on intestinal DC-related aspects, including the latest advances in the biology of intestinal DC subtypes, effect of tolerance-inducing factors on DCs, effect of dietary components on oral tolerance, and role of DCs in peanut sensitization. Expert commentary: Given the increasing prevalence of PA, difficulty of avoiding peanut products, and the potentially serious accidental reactions, the development of novel therapies for PA is needed. The ability of DCs to trigger tolerance or immunity makes them an interesting target for new treatment strategies against PA.

The Skin as a Route of Allergen Exposure: Part II. Allergens and Role of the Microbiome and Environmental Exposures

PURPOSE OF REVIEW

This second part of the article aims to highlight recent contributions in the literature that enhance our understanding of the cutaneous immune response to allergen.

RECENT FINDINGS

Several properties of allergens facilitate barrier disruption and cutaneous sensitization. There is a strong epidemiologic relationship between the microbiome, both the gut and skin, and atopic dermatitis (AD). The mechanisms connecting these two entities remain enigmatic; however, recent murine models show that commensal skin bacteria play an active role in supporting skin barrier homeostasis and defense against microbial penetration. Likewise, the association between the lack of colonization with Staph species and AD development suggests a potentially functional role for these organisms in regulating the skin barrier and response to environmental allergens. In undisrupted skin, evidence suggests that the cutaneous route may promote allergen tolerance. Properties of environmental allergens and commensal bacteria add to the complex landscape of skin immunity. Further investigation is needed to elucidate how these properties regulate the cutaneous immune response to allergen.

Application of the adverse outcome pathway (AOP) concept to structure the available in vivo and in vitro mechanistic data for allergic sensitization to food proteins

BACKGROUND

The introduction of whole new foods in a population may lead to sensitization and food allergy. This constitutes a potential public health problem and a challenge to risk assessors and managers as the existing understanding of the pathophysiological processes and the currently available biological tools for prediction of the risk for food allergy development and the severity of the reaction are not sufficient. There is a substantial body of in vivo and in vitro data describing molecular and cellular events potentially involved in food sensitization. However, these events have not been organized in a sequence of related events that is plausible to result in sensitization, and useful to challenge current hypotheses. The aim of this manuscript was to collect and structure the current mechanistic understanding of sensitization induction to food proteins by applying the concept of adverse outcome pathway (AOP).

MAIN BODY

The proposed AOP for food sensitization is based on information on molecular and cellular mechanisms and pathways evidenced to be involved in sensitization by food and food proteins and uses the AOPs for chemical skin sensitization and respiratory sensitization induction as templates. Available mechanistic data on protein respiratory sensitization were included to fill out gaps in the understanding of how proteins may affect cells, cell-cell interactions and tissue homeostasis. Analysis revealed several key events (KE) and biomarkers that may have potential use in testing and assessment of proteins for their sensitizing potential.

CONCLUSION

The application of the AOP concept to structure mechanistic in vivo and in vitro knowledge has made it possible to identify a number of methods, each addressing a specific KE, that provide information about the food allergenic potential of new proteins. When applied in the context of an integrated strategy these methods may reduce, if not replace, current animal testing approaches. The proposed AOP will be shared at the www.aopwiki.org platform to expand the mechanistic data, improve the confidence in each of the proposed KE and key event relations (KERs), and allow for the identification of new, or refinement of established KE and KERs.