Goat's milk allergy without cow's milk allergy: suppression of non-cross-reactive epitopes on caprine β-casein

Cross-reactivity analysis of milk proteins from different goat breeds with cow's milk allergens using a proteomic approach

INTRODUCTION

Goat's milk thought to be a good substitute for cow's milk protein allergic (CMPA) individuals. However, there is growing evidence that their proteins have cross-reactivities with cow's milk allergens. This study aimed to profile and compare milk proteins from different goat breeds that have cross-reactivity to cow's milk allergens.

METHODOLOGY

Proteomics was used to compare protein extracts of skim milk from Saanen, Jamnapari, and Toggenburg. Cow's milk was used as a control. IgE-immunoblotting and mass spectrometry were used to compare and identify proteins that cross-reacted with serum IgE from CMPA patients (n = 10).

RESULTS

The analysis of IgE-reactive proteins revealed that the protein spots identified with high confidence were proteins homologous to common cow's milk allergens such as α-S1-casein (αS1-CN), β-casein (β-CN), κ-casein (κ-CN), and beta-lactoglobulin (β-LG). Jamnapari's milk proteins were found to cross-react with four major milk allergens: α-S1-CN, β-CN, κ-CN, and β-LG. Saanen goat's milk proteins, on the other hand, cross-reacted with two major milk allergens, α-S1-CN and β-LG, whereas Toggenburg goat's milk proteins only react with one of the major milk allergens, κ-CN.

CONCLUSION

These findings may help in the development of hypoallergenic goat milk through cross-breeding strategies of goat breeds with lower allergenic milk protein contents.

Immunodominant conformational and linear IgE epitopes lie in a single segment of Ara h 2

BACKGROUND

Contribution of conformational epitopes to the IgE reactivity of peanut allergens Ara h 2 and Ara h 6 is at least as important as that of the linear epitopes. However, little is known about these conformational IgE-binding epitopes.

OBJECTIVE

We investigated the distribution of conformational epitopes on chimeric 2S-albumins.

METHODS

Recombinant chimeras were generated by exchanging structural segments between Ara h 2 and Ara h 6. Well-refolded chimeras, as verified by circular dichroism analysis, were then used to determine the epitope specificity of mAbs by performing competitive inhibition of IgG binding. Furthermore, we delineated the contribution of each segment to the overall IgE reactivity of both 2S-albumins by measuring the chimeras' IgE-binding capacity with sera from 21 patients allergic to peanut. We finally assessed chimeras' capacity to trigger mast cell degranulation.

RESULTS

Configuration of the conformational epitopes was preserved in the chimeras. Mouse IgG mAbs, raised against natural Ara h 6, and polyclonal human IgE antibodies recognized different conformational epitopes distributed all along Ara h 6. In contrast, we identified human IgG mAbs specific to different Ara h 2 linear or conformational epitopes located in all segments except the C-terminal one. The major conformational IgE-binding epitope of Ara h 2 was located in a segment located between residues 33 and 81 that also contains the major linear hydroxyproline-containing epitope. Accordingly, this segment is critical for the capacity of Ara h 2 to induce mast cell degranulation.

CONCLUSIONS

Chimeric 2S-albumins provide new insights on the conformational IgE-binding epitopes of Ara h 2 and Ara h 6. Proximity of the immunodominant linear and conformational IgE-binding epitopes probably contributes to the high allergenic potency of Ara h 2.

Alternatives to Cow’s Milk-Based Infant Formulas in the Prevention and Management of Cow’s Milk Allergy

Cow’s milk-based infant formulas are the most common substitute to mother’s milk in infancy when breastfeeding is impossible or insufficient, as cow’s milk is a globally available source of mammalian proteins with high nutritional value. However, cow’s milk allergy (CMA) is the most prevalent type of food allergy among infants, affecting up to 3.8% of small children. Hypoallergenic infant formulas based on hydrolysed cow’s milk proteins are commercially available for the management of CMA. Yet, there is a growing demand for more options for infant feeding, both in general but especially for the prevention and management of CMA. Milk from other mammalian sources than the cow, such as goat, sheep, camel, donkey, and horse, has received some attention in the last decade due to the different protein composition profile and protein amino acid sequences, resulting in a potentially low cross-reactivity with cow’s milk proteins. Recently, proteins from plant sources, such as potato, lentil, chickpeas, quinoa, in addition to soy and rice, have gained increased interest due to their climate friendly and vegan status as well as potential lower allergenicity. In this review, we provide an overview of current and potential future infant formulas and their relevance in CMA prevention and management.

Allergen Risk Assessment for Specific Allergy to Small Ruminant's Milk: Development of Sensitive Immunoassays to Detect Goat's and Sheep's Milk Contaminations in Dairy Food Matrices

Despite a high level of sequence identity between cow's, goat's, and sheep's milk (CM, GM, and SM, respectively) proteins, some patients tolerant to CM are allergic to GM and SM. In most cases, this specificity is due to the presence of IgE antibodies that bind only to caprine and ovine caseins. The patients may then develop severe allergic reactions after ingestion of CM products contaminated with low amounts of GM or SM. We thus aimed to develop an assay able to detect traces of caprine/ovine β-caseins in different food matrices, irrespective of the presence of the bovine homolog. We produced monoclonal antibodies (mAbs) specific to caprine caseins in mice tolerized to the bovine whole casein then sensitized to the caprine whole casein. In order to develop a two-site immunometric assay, we selected mAbs that could discriminate the caprine β-casein from its bovine homolog. Characteristics and performances of two tests were determined with various dairy products. Results were analyzed in relation with the IgE-immunoreactivity of the food matrices, thanks to sera from CM, GM/SM allergic patients. Our two-site immunometric assays demonstrated a high sensitivity with a detection limit of 1.6–3.2 ng/mL of caprine and ovine β-caseins. The tests were able to detect contaminations of GM in CM at the ppm level. Heat-treatment, ripening and coagulation processes, usually applied to dairy products that exhibit a very high IgE-immunoreactivity, did not impair the test sensitivity. These quantitative assays could then be useful for the risk assessment of food products potentially contaminated with GM and SM in order to prevent adverse reactions in patients specifically allergic to these milks.

Clinical Relevance of Cross-Reactivity in Food Allergy

The diagnosis and management of food allergy is complicated by an abundance of homologous, cross-reactive proteins in edible foods and aeroallergens. This results in patients having allergic sensitization (positive tests) to many biologically related foods. However, many are sensitized to foods without exhibiting clinical reactivity. Although molecular diagnostics have improved our ability to identify clinically relevant cross-reactivity, the optimal approach to patients requires an understanding of the epidemiology of clinically relevant cross-reactivity, as well as the food-specific (degree of homology, protein stability, abundance) and patient-specific factors (immune response, augmentation factors) that determine clinical relevance. Examples of food families with high rates of cross-reactivity include mammalian milks, eggs, fish, and shellfish. Low rates are noted for grains (wheat, barley, rye), and rates of cross-reactivity are variable for most other foods. This review discusses clinically relevant cross-reactivity related to the aforementioned food groups as well as seeds, legumes (including peanut, soy, chickpea, lentil, and others), tree nuts, meats, fruits and vegetables (including the lipid transfer protein syndrome), and latex. The complicating factor of addressing co-allergy, for example, the risks of allergy to both peanut and tree nuts among atopic patients, is also discussed. Considerations for an approach to individual patient care are highlighted.

Goat Milk Consumption Enhances Innate and Adaptive Immunities and Alleviates Allergen-Induced Airway Inflammation in Offspring Mice

Goat milk (GM), as compared to cow milk (CM), is easier for humans to digest. It also has antioxidant and anti-inflammatory effects and can improve minor digestive disorders and prevent allergic diseases in infants. It is unclear whether GM consumed in pregnant mothers has any protective effects on allergic diseases in infants. In this experimental study with mice, we found GM feeding enhanced immunoglobulin production, antigen-specific (ovalbumin, OVA) immune responses, and phagocytosis activity. The GM-fed mice had an increasing proportion of CD3⁺ T lymphocytes in the spleen. Splenocytes isolated from these animals also showed significantly increased production of cytokines IFN-γ and IL-10. More importantly, GM feeding during pregnancy and lactation periods can confer protective activity onto offspring by alleviating the airway inflammation of allergic asthma induced by mite allergens. There was a remarkably different composition of gut microbiota between offspring of pregnant mice fed with water or with milk (GM or CM). There was a greater proportion of beneficial bacterial species, such as Akkermansia muciniphila, Bacteroides eggerthii, and Parabacteroides goldsteinii in the gut microbiota of offspring from GM- or CM-fed pregnant mice compared to the offspring of water-fed pregnant mice. These results suggested that improving the nutrition of pregnant mice can promote immunological maturation and colonization of gut microbiota in offspring. This mother-to-child biological action may provide a protective effect on atopy development and alleviate allergen-induced airway inflammation in offspring.

Anaphylaxis to goat/sheep's milk in a 4-year-old boy tolerant to cow's milk

Immune-mediated reactions to dairy products may vary depending on the mammalian source. We present a case of anaphylaxis to goat/sheep's milk with tolerance to cow's milk. A 4-year-old boy of Eastern European descent presented with gastrointestinal and respiratory symptoms within minutes after eating a goat/sheep's milk-derived food product. The tryptase level measured 1 hour post initial symptoms and 1 month after the allergic reaction were 14.6 µg/L and 5.1 µg/L, respectively (norm: 0.0-13.5 µg/L), confirming the diagnosis of anaphylaxis. A skin prick test performed 1 month after the reaction was highly positive for goat/sheep's milk, but negative for cow's milk. Skin prick tests may establish a life-threatening goat/sheep's milk allergy. Goat/sheep's milk allergy should always be considered in cow's milk-tolerant patients who present with an allergic reaction to dairy products, or when undergoing/have completed of oral immunotherapy for cow's milk allergy.

Variable IgE cross-reactivity between peanut 2S-albumins: The case for measuring IgE to both Ara h 2 and Ara h 6

BACKGROUND

2S-albumins Ara h 2 and Ara h 6 are the most potent peanut allergens and levels of specific immunoglobulin E (IgE) towards these proteins are good predictors of clinical reactivity. Because of structural homologies, Ara h 6 is generally considered to cross-react extensively with Ara h 2.

OBJECTIVE

We aimed to quantify the IgE cross-reactivity between Ara h 2 and Ara h 6.

METHODS

Peanut 2S-albumins were purified from raw peanuts. The IgE cross-reactivity between Ara h 2 and Ara h 6 was evaluated with 32 sera from French and US peanut-allergic patients by measuring the residual IgE-binding to one 2S-albumin after depletion of IgE antibodies recognizing the other 2S-albumin. The IgE cross-reactivity between Ara h 2 and Ara h 6 was further investigated by competitive inhibition of IgE-binding and by a model of mast cell degranulation.

RESULTS

A highly variable level of IgE cross-reactivity was revealed among the patients. The mean fraction of cross-reactive IgE antibodies represented only 17.1% of 2S-albumins-specific IgE antibodies and was lower than the mean fraction of IgE specific to Ara h 2 (57.4%) or to Ara h 6 (25.5%). The higher level of Ara h 2-specific IgE was principally due to the IgE-binding capacity of an insertion containing the repeated immunodominant linear epitope DPYSP^OH S. The impact of IgE cross-reactivity on diagnostic testing was illustrated with a serum displaying an Ara h 6-specific IgE response of 26 UI/mL that was not associated with the capacity of Ara h 6 to trigger mast cell degranulation.

CONCLUSIONS & CLINICAL RELEVANCE

Immunoglobulin E antibodies specific to peanut 2S-albumins are mainly non-cross-reactive, but low-affinity cross-reactivity can affect diagnostic accuracy. Testing IgE-binding to a mixture of 2S-albumins rather than to each separately may enhance diagnostic performance.

Navigating through the Jungle of Allergens: Features and Applications of Allergen Databases

The increasing number of available data on allergenic proteins demanded the establishment of structured, freely accessible allergen databases. In this review article, features and applications of 6 of the most widely used allergen databases are discussed. The WHO/IUIS Allergen Nomenclature Database is the official resource of allergen designations. Allergome is the most comprehensive collection of data on allergens and allergen sources. AllergenOnline is aimed at providing a peer-reviewed database of allergen sequences for prediction of allergenicity of proteins, such as those planned to be inserted into genetically modified crops. The Structural Database of Allergenic Proteins (SDAP) provides a database of allergen sequences, structures, and epitopes linked to bioinformatics tools for sequence analysis and comparison. The Immune Epitope Database (IEDB) is the largest repository of T-cell, B-cell, and major histocompatibility complex protein epitopes including epitopes of allergens. AllFam classifies allergens into families of evolutionarily related proteins using definitions from the Pfam protein family database. These databases contain mostly overlapping data, but also show differences in terms of their targeted users, the criteria for including allergens, data shown for each allergen, and the availability of bioinformatics tools.

Developments in the field of allergy in 2014 through the eyes of Clinical and Experimental Allergy

The pathogenesis of asthma continues to be a major topic of interest to our authors with reviews and original papers on the role of viruses, mechanisms of inflammation, biomarkers, and phenotypes of asthma being major topics. A number of papers described new treatments for asthma focusing on blocking the Th2 response reflecting the fact that two decades of work in this area is finally bearing fruit. The pathogenesis of chronic rhinosinusitis is a growing area of interest, but there has been less on the genetics of airways disease than in previous years possibly reflecting the degree of rigour (and therefore a smaller body of work), with which these sorts of studies are now being undertaken. There continues to be a wide range of papers dealing with mechanisms of allergic disease ranging from clinical-based studies to basic research and the use of in vivo animal models especially mice. As before, mechanisms and new approaches to immunotherapy are common themes. Several were published in the allergens section investigating modification of allergens to increase their effectiveness and reduce the risk of adverse events. Risk factors for allergic disease was a common theme in the epidemiology section and food allergy a common theme in clinical allergy with papers on the development of protocols to induce tolerance and attempts to find biomarkers to distinguish sensitization from allergic disease. This was another exciting year for the editors, and we hope the readers of the journal.

Current challenges facing the assessment of the allergenic capacity of food allergens in animal models

Food allergy is a major health problem of increasing concern. The insufficiency of protein sources for human nutrition in a world with a growing population is also a significant problem. The introduction of new protein sources into the diet, such as newly developed innovative foods or foods produced using new technologies and production processes, insects, algae, duckweed, or agricultural products from third countries, creates the opportunity for development of new food allergies, and this in turn has driven the need to develop test methods capable of characterizing the allergenic potential of novel food proteins. There is no doubt that robust and reliable animal models for the identification and characterization of food allergens would be valuable tools for safety assessment. However, although various animal models have been proposed for this purpose, to date, none have been formally validated as predictive and none are currently suitable to test the allergenic potential of new foods. Here, the design of various animal models are reviewed, including among others considerations of species and strain, diet, route of administration, dose and formulation of the test protein, relevant controls and endpoints measured.

Baked milk- and egg-containing diet in the management of milk and egg allergy

Cow's milk (CM) and hen's egg allergies are among the most common food allergies in children. With evidence of increasing food allergy prevalence and more persistent disease, it has become vital to improve the management of CM and egg allergies. The ability to tolerate baked milk or egg, such as in a cake or muffin, has been associated with an increased chance of tolerance development. Studies report that about 70% of CM- and egg-allergic children can tolerate baked milk or egg and that incorporating baked milk or egg into the diet is well tolerated. Being able to add baked milk or egg into the diet can also increase quality of life by expanding the diet, boosting nutrition, and promoting inclusion in social activities. There is some debate over how baked milk and egg should be introduced, at home or in a supervised setting. Anaphylaxis and treatment with epinephrine during baked milk or egg challenges have been reported. Study of potential biomarkers to predict tolerability of baked milk and egg, such as serum specific IgE levels and skin prick test wheal diameters, is ongoing. Many parents can reliably report that their CM- or egg-allergic child is already consuming baked goods without symptoms. However, for those who cannot report such tolerance, the most prudent approach is to perform a supervised oral food challenge to determine the tolerability of baked milk and egg. The purpose of this article was to review the pathophysiology, clinical data, and safety of baked milk and egg and provide a practical guide to managing CM allergy and/or egg allergy. Recipes for baked milk and egg challenges and guidance on how to add baked milk and egg if tolerated to the child's regular diet are provided.

Interfaces between allergen structure and diagnosis: know your epitopes

Allergy diagnosis is based on the patient's clinical history and can be strengthened by tests that confirm the origin of sensitization. In the past 25 years, these tests have evolved from the exclusive in vivo or in vitro use of allergen extracts, to complementary molecular-based diagnostics that rely on in vitro measurements of IgE reactivity to individual allergens. For this to occur, an increase in our understanding of the molecular structure of allergens, largely due to the development of technologies such as molecular cloning and expression of recombinant allergens, X-ray crystallography, or nuclear magnetic resonance (NMR), has been essential. New in vitro microarray or multiplex systems are now available to measure IgE against a selected panel of purified natural or recombinant allergens. The determination of the three-dimensional structure of allergens has facilitated detailed molecular studies, including the analysis of antigenic determinants for diagnostic purposes.

100 Years later: Celebrating the contributions of x-ray crystallography to allergy and clinical immunology

Current knowledge of molecules involved in immunology and allergic disease results from the significant contributions of x-ray crystallography, a discipline that just celebrated its 100th anniversary. The histories of allergens and x-ray crystallography are intimately intertwined. The first enzyme structure to be determined was lysozyme, also known as the chicken food allergen Gal d 4. Crystallography determines the exact 3-dimensional positions of atoms in molecules. Structures of molecular complexes in the disciplines of immunology and allergy have revealed the atoms involved in molecular interactions and mechanisms of disease. These complexes include peptides presented by MHC class II molecules, cytokines bound to their receptors, allergen-antibody complexes, and innate immune receptors with their ligands. The information derived from crystallographic studies provides insights into the function of molecules. Allergen function is one of the determinants of environmental exposure, which is essential for IgE sensitization. Proteolytic activity of allergens or their capacity to bind LPSs can also contribute to allergenicity. The atomic positions define the molecular surface that is accessible to antibodies. In turn, this surface determines antibody specificity and cross-reactivity, which are important factors for the selection of allergen panels used for molecular diagnosis and the interpretation of clinical symptoms. This review celebrates the contributions of x-ray crystallography to clinical immunology and allergy, focusing on new molecular perspectives that influence the diagnosis and treatment of allergic diseases.

Use of a rat basophil leukemia (RBL) cell-based immunological assay for allergen identification, clinical diagnosis of allergy, and identification of anti-allergy agents for use in immunotherapy

Food allergy is an important public health problem that affects an estimated 8% of young children and 2% of adults. With an increasing interest in genetically-engineered foods, there is a growing need for development of sensitive and specific tests to evaluate potential allergenicity of foods and novel proteins as well as to determine allergic responses to ensure consumer safety. This review covers progress made in the field of development of cell models, specifically that involving a rat basophil leukemia (RBL) cell-based immunoassay, for use in allergen identification, diagnosis, and immunotherapy. The RBL assay has been extensively employed for determining biologically relevant cross-reactivities of food proteins, assessing the effect of processing on the allergenicity of food proteins, diagnosing allergic responses to whole-food products, and identifying anti-allergy food compounds. From the review of the literature, one might conclude the RBL cell-based assay is a better test system when compared to wild-type mast cell and basophil model systems for use in allergen identification, diagnosis, and analyses of potential immunotherapeutics. However, it is important to emphasize that this assay will only be able to identify those allergens to which the human has already been exposed, but will not identify a truly novel allergen, i.e. one that has never been encountered as in its preferred (humanized) configuration.