Hydrolysed ovalbumin offers more effective preventive and therapeutic protection against egg allergy than the intact protein

Intestinal factors promoting the development of RORγt+ cells and oral tolerance

The gastrointestinal tract has to harmonize the two seemingly opposite functions of fulfilling nutritional needs and avoiding the entry of pathogens, toxins and agents that can cause physical damage. This balance requires a constant adjustment of absorptive and defending functions by sensing environmental changes or noxious substances and initiating adaptive or protective mechanisms against them through a complex network of receptors integrated with the central nervous system that communicate with cells of the innate and adaptive immune system. Effective homeostatic processes at barrier sites take the responsibility for oral tolerance, which protects from adverse reactions to food that cause allergic diseases. During a very specific time interval in early life, the establishment of a stable microbiota in the large intestine is sufficient to prevent pathological events in adulthood towards a much larger bacterial community and provide tolerance towards diverse food antigens encountered later in life. The beneficial effects of the microbiome are mainly exerted by innate and adaptive cells that express the transcription factor RORγt, in whose generation, mediated by different bacterial metabolites, retinoic acid signalling plays a predominant role. In addition, recent investigations indicate that food antigens also contribute, analogously to microbial-derived signals, to educating innate immune cells and instructing the development and function of RORγt+ cells in the small intestine, complementing and expanding the tolerogenic effect of the microbiome in the colon. This review addresses the mechanisms through which microbiota-produced metabolites and dietary antigens maintain intestinal homeostasis, highlighting the complementarity and redundancy between their functions.

Allergenicity, assembly and applications of ovalbumin in egg white: a review

Ovalbumin (OVA), the most abundant protein in egg whites, has been widely used in various industries. Currently, the structure of OVA has been clearly established, and the extraction of high-purified OVA has become feasible. However, the allergenicity of OVA is still a serious problem because it can cause severe allergic reactions and may even be life-threatening. The structure and allergenicity of the OVA can be altered by many processing methods. In this article, a detailed description on the structure and a comprehensive overview on the extraction protocols and the allergenicity of OVA was documented. Additionally, the information on assembly and potential applications of OVA was summarized and discussed in detail. Physical treatment, chemical modification, and microbial processing can be applied to alter the IgE-binding capacity of OVA by changing its structure and linear/sequential epitopes. Furthermore, research indicated that OVA could assemble with itself or other biomolecules into various forms (particles, fibers, gels, and nanosheets), which expanded its application in the food field. OVA also shows excellent application prospects, including food preservation, functional food ingredients and nutrient delivery. Therefore, OVA demonstrates significant investigation value as a food grade ingredient.

A review on the immobilization of pepsin: A Lys-poor enzyme that is unstable at alkaline pH values

Pepsin is a protease used in many different applications, and in many instances, it is utilized in an immobilized form to prevent contamination of the reaction product. This enzyme has two peculiarities that make its immobilization complex. The first one is related to the poor presence of primary amino groups on its surface (just one Lys and the terminal amino group). The second one is its poor stability at alkaline pH values. Both features make the immobilization of this enzyme to be considered a complicated goal, as most of the immobilization protocols utilize primary amino groups for immobilization. This review presents some of the attempts to get immobilized pepsin biocatalyst and their applications. The high density of anionic groups (Asp and Glu) make the anion exchange of the enzyme simpler, but this makes many of the strategies utilized to immobilize the enzyme (e.g., amino-glutaraldehyde supports) more related to a mixed ion exchange/hydrophobic adsorption than to real covalent immobilization. Finally, we propose some possibilities that can permit not only the covalent immobilization of this enzyme, but also their stabilization via multipoint covalent attachment.

Protease-digested egg-white products induce oral tolerance in mice but elicit little IgE production upon epicutaneous exposure

BACKGROUND

Early food introduction induces tolerance, but epicutaneous exposure, especially via eczema lesions, promotes IgE sensitization. Aiming for safe and effective primary prevention of egg allergy, we examined several protease-digested egg-white (EW) products for three properties: 1) induction of oral tolerance that prevents IgE sensitization, 2) weak IgE binding that can prevent allergic reactions even in IgE-sensitized mice, and 3) minimal epicutaneous IgE sensitization even when in contact with inflamed skin.

METHODS

Heated EW was digested with several proteases under optimal conditions. First, three-week-old BALB/c female mice were intragastrically administered EW or each protease-digested EW product, followed by intraperitoneal ovalbumin (OVA) or ovomucoid (OVM) injection with alum. Serum OVA- and OVM-specific IgE titers were measured. Second, six-week-old mice were sensitized with OVA/OVM, and the rectal temperature was measured after intraperitoneal administration of EW or each protease-digested EW. Third, EW or each protease-digested EW product was applied to the tape-stripped skin for 3 days/week for 3 weeks. Serum OVA- and OVM-specific IgE titers were measured.

RESULTS

Orally administered pepsin-digested EW product (PDEW) and Thermoase PC10F-digested EW product (TDEW) significantly suppressed OVA-/OVM-specific IgE production. Neither product elicited a body temperature decline (anaphylaxis) in OVA-/OVM-sensitized mice. Serum OVA-/OVM-specific IgE levels were significantly lower in mice epicutaneously exposed to PDEW or TDEW than in EW-exposed mice.

CONCLUSIONS

Two protease-digested EWs showed potential as optimal EW products for early introduction for primary prevention of egg allergy.

Recent Advances in Applications of Bioactive Egg Compounds in Nonfood Sectors

Egg, a highly nutritious food, contains high-quality proteins, vitamins, and minerals. This food has been reported for its potential pharmacological properties, including antibacterial, anti-cancer, anti-inflammatory, angiotensin-converting enzyme (ACE) inhibition, immunomodulatory effects, and use in tissue engineering applications. The significance of eggs and their components in disease prevention and treatment is worth more attention. Eggs not only have been known as a "functional food" to combat diseases and facilitate the promotion of optimal health, but also have numerous industrial applications. The current review focuses on different perceptions and non-food applications of eggs, including cosmetics. The versatility of eggs from an industrial perspective makes them a potential candidate for further exploration of several novel components.

Retinoic Acid Induces Functionally Suppressive Foxp3+RORγt+ T Cells In Vitro

Introduction

CD4⁺ T cells with regulatory function co-expressing Foxp3 and RORγt are linked to the development of oral tolerance towards innocuous food antigens in mice. This study aimed to discern the role played by IL-6 and retinoic acid (RA) in the in vitro generation of Foxp3⁺RORγt⁺ T cells and to investigate whether such cells have suppressive properties.

Methods

CD4⁺CD25^- T cells isolated from the spleen of BALB/c mice, were stimulated in the presence of IL-2 alone or together with TFG-β and different concentrations of IL-6 and/or RA. Percentage of Foxp3⁺, RORγt⁺, IL-17⁺, Foxp3⁺RORγt^-, Foxp3⁺RORγt⁺, and Foxp3^-RORγt⁺ T cells within the total CD4⁺ T cell population, production of cytokines (IL-10 and IL-17A) and gene expression (Foxp3, Rorc, Tgfb1, Il6, Il10, and Il17) were assessed at different time points. The phenotype and ability of cells generated from CD4⁺CD44^-CD62L⁺ cells in the presence of RA to suppress effector T cell proliferation was assessed.

Results

TGF-β plus IL-6 induced the generation of Foxp3⁺ and double positive Foxp3⁺RORγt⁺ T cells to a higher extent than TGF-β alone at the beginning of the incubation period, although expression of Foxp3 subsequently declined. RA, added to TGF-β, increased Foxp3 and Rorc expression and Foxp3 and RORγt transcription and promoted the differentiation of Foxp3⁺RORγt^- and Foxp3⁺RORγt⁺ cells that expressed and secreted IL-17. Foxp3⁺ T cells generated in vitro in presence of RA were functionally suppressive.

Conclusions

Under the influence of IL-2 and TGF-β, suppressive Foxp3⁺RORγt⁺ T cells that express and secrete IL-17 can be produced in vitro and RA further contributes to stabilize this phenotype.

A Mouse Model of Oral Sensitization to Hen's Egg White

Egg allergy is one of the most common food allergies in children, being the most important allergenic proteins found in the egg white (EW). Allergy to EW shows a complex phenotype that involves a multifaceted reaction that can only be assessed in vivo. Although other routes of sensitization have been described, oral exposure to food antigens is one of the most suitable in humans. In mice, oral administration of allergenic proteins results in the development of tolerance, and the use of adjuvants, such as cholera toxin (CT), is required to promote Th2-biased immune responses over tolerogenic responses. In this regard, among the mouse strains that readily display Th2 responses, Balb/c has been widely used. Here, we describe a frequently used protocol of oral EW sensitization by using CT as an adjuvant and we explain in detail the methods that we have developed to analyze the sensitizing and eliciting capacity of EW proteins including evaluation of signs, measurement of serum levels of specific immunoglobulins, mast cell degranulation, cytokine secretion profile of allergen-reactive T cells, phenotyping of mesenteric lymph node- and spleen-derived dendritic and T cells by flow cytometry, and quantification of intestinal gene expression.

Ovalbumin-Derived Peptides Activate Retinoic Acid Signalling Pathways and Induce Regulatory Responses Through Toll-Like Receptor Interactions

This study investigates the potential of a hydrolysate of ovalbumin with pepsin (OP) to preclude Th2-type immunity by the enhancement of tolerogenic dendritic cells (DCs) and regulatory T (Treg) cells. Through Toll-like receptor (TLR) stimulation, OP enhances the retinoic acid pathway on DCs by means of the induction of aldehyde dehydrogenase enzymes and transforming growth factor beta (TGF-β), and it confers upon DC the ability to upregulate interleukin 10 (IL-10) as well as other tolerance-promoting mediators downstream of TRL signalling, such as IL-27, IL-33, Notch ligands, OX40L, and the transcription factors IRF4 and IRF8. OP-conditioned DCs induce the expansion of Foxp3+ and Tr1 cells in co-culture with CD4+ T cells. Furthermore, OP directly conditions CD4+ T cells from naïve mice, without the mediation of DCs, to express aldehyde dehydrogenase (ALDH) enzymes and, in the presence of the Th2 cytokine IL-4 and exogenous TGF-β, it enhances Foxp3 expression. It is noteworthy that, on CD4+ T cells isolated from egg-allergic mice, OP significantly enriches the levels of Foxp3+ and Foxp3+ RORγt+ CD4+ T cells. In conclusion, we show that food peptides may work, analogously to microbial-driven signals, through TLRs, to promote a tolerogenic phenotype on cells of the innate and adaptive immune system, a property that is further enhanced in the context of a Th2 cytokine-rich environment.

Egg yolk augments type 2 immunity by activating innate cells

PURPOSE

Egg yolk (EY) may play a role during the sensitizing phase of egg allergy by exerting intestinal type 2-biasing effects. We aimed to identify the mechanism and role of EY in the induction of allergy to egg white (EW).

METHODS

BALB/c mice were exposed intragastrically to EW, EY, or the mixture of EW:EY. In addition in vitro experiments were conducted with intestinal epithelial cells (IECs), dendritic cells (DCs), and T cells from naïve mice. Inflammatory and type 2 responses were evaluated.

RESULTS

Administration of EW upregulated duodenal expression of factors that influence epithelial barrier integrity and function, such as Muc2 and Cldn2, type 2-promoting epithelial cytokines Il33 and Il25, DC genes Irf4 and Tnfsf4, and Th2-cytokines Il14 and Il13. EW:EY further increased the expression of Il25 and Tslp in the duodenum, Il33 and Tslp in the jejunum, and the proportion of lamina propria group 2 innate immune cells (ILC2s) over EW alone. Moreover, it distinctively enhanced the expression of Irf4 and Cd1d1 in the Peyer's patches (PPs), and of Il6, Il33, Gata3, and Il13, both in PPs and mesenteric lymph nodes. In co-cultures of DCs and T cells, EW:EY induced a higher expression of Gata3, Il4, and Il13, secretion of IL-13 and expansion of CD4⁺ T cells expressing ST2, the IL-33 receptor, than EW or EY added individually.

CONCLUSION

Co-administration of EY may promote sensitization to EW through activation of innate immune cells, such as IECs, DCs and ILC2s, that are central to the progress of allergies.

Developments in the field of allergy in 2017 through the eyes of Clinical and Experimental Allergy

In this article, we described the development in the field of allergy as described by Clinical and Experimental Allergy in 2017. Experimental models of allergic disease, basic mechanisms, clinical mechanisms, allergens, asthma and rhinitis and clinical allergy are all covered.

Comparison of two techniques for a comprehensive gut histopathological analysis: Swiss Roll versus Intestine Strips

Assessing the gut mucosa milieu is important to grade the inflammatory process in conditions such as food hypersensitivity, allergy, gut parasitosis, etc. However, the gastrointestinal tract comprises a challenging system to evaluate, due to its thin tubular structure and mucosa, which suffer fast autolysis after death. Irrespective of the preferred inflammatory score system, it is important to choose the technique that will render the best tissue analysis. Thus, our aim was to compare two of the most frequently used methods to collect, process and analyze gut segments, the Swiss Roll and the Intestinal Strips. Normal C57Bl/6 mice were randomly assigned to Rolls or Strips group. After an overdose of anesthetics, segments of the duodenum, jejunum and ileum were collected and prepared accordingly for histological processing and analysis. Our results show the villi in the Rolls tend to be shorter and wider than those in the Strips in the duodenum and jejunum but not the ileum. No significant differences were observed in intra-epithelial lymphocytes and goblet cells counts. Finally, we staged each segment using our histomorphometric classification system, which revealed that although all animals presented a normal intestinal mucosa, those assigned to the Rolls group had their mucosa staged in the Infiltrative Stage while the Strips group had their mucosa staged as Normal. In conclusion, Swiss Rolls might be desirable for a wider assessment of the intestine, as it allows large segments to be analyzed at once, while Strips are better suited when detailed evaluation of each villus is intended.

Egg Yolk Provides Th2 Adjuvant Stimuli and Promotes Sensitization to Egg White Allergens in BALB/c Mice

SCOPE

Egg is the second most frequent source of allergic reactions in children. Egg yolk (EY) amounts to one-third in weight of a fresh whole egg, but its contribution to egg allergy has not been investigated in depth. This study assesses whether EY influences the capacity of egg white (EW) to sensitize and trigger allergic responses.

METHODS AND RESULTS

BALB/c mice were exposed to EW, EY, and their mixture, using models of orally (with and without adjuvant) and adjuvant-free intraperitoneally induced allergy. In vitro assays were also conducted to examine epithelial and dendritic cell (DC) functions. Results showed that EY played a role during the sensitizing phase of allergy. EY exerted local Th2-biasing effects through the upregulation of intestinal IL-33 expression and it also favored Th2 polarization directly during DC presentation of allergens to T cells.

CONCLUSION

The results obtained reveal that EY provides Th2-adjuvant stimuli to the immune system that may increase the susceptibility to develop egg allergy. The joint administration of EW and EY may be a trigger for initiation or maintenance of egg allergy with implications in prevention strategies regarding egg introduction in the diet of susceptible children.

Assessment of the Allergenic Potential of the Main Egg White Proteins in BALB/c Mice

This work aimed to assess the contribution of the major egg white proteins, ovalbumin, ovomucoid, and lysozyme, to the induction and elicitation of allergenic responses. For this purpose, BALB/c mice were orally administered either the individual egg allergens or a mixture of the three proteins in the same proportion, to evaluate their relative allergenicity avoiding their different abundance in egg white. Cholera toxin was used as a T helper 2 (Th2)-polarizing adjuvant. Ovomucoid and lysozyme triggered the most severe anaphylaxis reactions upon oral challenge. In comparison to ovalbumin and ovomucoid, lysozyme was a more active promotor of early immunoglobulin E and immunoglobulin G1 production and stimulated stronger Th2-biased responses from both mesenteric lymph node and spleen cells. These results indicate that lysozyme is highly immunogenic and should be considered as a major allergen, whose clinical usefulness in the diagnosis, prognosis, and therapeutic approaches of egg allergy deserves further consideration.