Food allergies in children

Genetics of Food Allergy

The risk factors for food allergy (FA) include both genetic variants and environmental factors. Advances using both candidate-gene association studies and genome-wide approaches have led to the identification of FA-associated genes involved in immune responses and skin barrier functions. Epigenetic changes have also been associated with the risk of FA. In this chapter, we outline current understanding of the genetics, epigenetics and the interplay with environmental risk factors associated with FA. Future studies of gene-environment interactions, gene-gene interactions, and multi-omics integration may help shed light on the mechanisms of FA, and lead to improved diagnostic and treatment strategies.

Natural history of food allergy in infants and children in Israel

BACKGROUND

Knowledge about the natural history of food allergy, especially sesame, is scarce.

OBJECTIVE

To follow the natural history of food allergies in Israel, particularly of sesame allergy.

METHODS

The survey was conducted based on clinical records and a detailed questionnaire of children diagnosed as having food allergy.

RESULTS

We found 234 children with suspected food allergy. Testing detected 283 allergies in 180 patients (77%) with confirmed diagnosis. The most common allergies were to cow's milk (n = 125), eggs (n = 71), sesame (n = 30), and soy (n = 23). Of those with milk allergy, 69% were IgE mediated (group 1) and 31% were non-IgE mediated (group 2). Group 1 was more likely to have an atopic background than was group 2 (P = .003), whereas group 2 was more likely to have resolution of the allergy (35 of 39 [90%] in group 2 compared with only 32 of 86 [37%] in group 1, P < .001). Allergy to soy was found in 23 children, of whom 87% manifested with gastrointestinal symptoms and 21 (91%) were also allergic to cow's milk. In 19 children (83%), the allergy resolved. Thirty children had allergy to sesame, and 73% of them had an atopic background. The allergy resolved in only 9 of these patients (30%) at a mean age of 2.8 years.

CONCLUSIONS

The distribution of food allergens in Israel differs from that in other countries. Non-IgE-mediated food allergy and particularly milk and soy allergy were likely to resolve completely with time. Sesame allergy was 1 of the most frequent in this cohort, was usually IgE mediated, and tended to resolve in only a few patients.

Clinical features of legume allergy in children from a Mediterranean area

BACKGROUND

Lentils, chickpeas, beans, and peas are the most common consumed legumes in the Mediterranean area. However, there is little information about allergy to these legumes.

OBJECTIVES

To describe the clinical features of a Spanish pediatric population allergic to legumes (lentils, chickpeas, peas, white beans, and peanuts), to evaluate the clinical allergy to several legumes, and to determine which legume extract is most appropriate to use in the diagnosis of legume allergy by skin tests.

METHODS

Fifty-four children with allergic reactions after exposure to legumes were studied. The diagnosis of legume allergy was confirmed by positive skin prick test results with legume extracts and food challenges or a recent convincing history of severe reactions.

RESULTS

The onset of allergic reactions was at approximately the age of 2 years (median, 22 months). Skin prick test results were positive for at least 3 legumes in 38 children (70%). Positive results were more frequent to boiled extracts than to raw extracts in children with a positive oral challenge. Allergy to lentil was the most frequently diagnosed legume allergy (43 children [80%]), followed by allergy to chickpea (32 children [59%]). Oral challenges with more than 1 legume (median, 3 legumes) were positive in 37 children (69%). The most frequent induced symptoms on challenge were respiratory (rhinitis and/or asthma) and cutaneous.

CONCLUSION

In this population, lentils and chickpeas are the legumes that cause most allergic reactions, clinical allergy to more than 1 legume is common, and boiled legume extracts are most appropriate to discriminate between allergic and tolerant sensitized children.

Increased number of CCR4-positive cells in the duodenum of ovalbumin-induced food allergy model Nc/jic mice and antiallergic activity of fructooligosaccharides

BACKGROUND

Fructooligosaccharides (FOS) in prebiotic foods can alter intestinal immune responses. The combination of probiotics with oligosaccharides has been reported to alter intestinal flora and suggested to be beneficial against food allergy in humans.

METHODS

All male Nc/jic mice used in this 8-week study were 6 weeks of age and were allotted to the following three groups: (1) the nonsensitization group; (2) the ovalbumin (OVA) sensitization +5% fructose-containing control food administration group; and (3) the OVA sensitization +5% FOS-containing food administration group. Duodenal tissues were collected and then immunohistochemically stained with monoclonal antibodies to CCR4 and CCR5. The number of mast cells and the villus edema formation rate in the duodenum were determined by image analysis.

RESULTS

The number of CCR4-positive cells increased significantly in Group 2 as compared with Group 1 and tended to decrease in Group 3 as compared with Group 2. Relatively few CCR5-positive cells were observed in the duodenum. FOS tended to reduce the number of CCR4-positive cells but significantly reduced the number of mast cells and the edema formation rate in the duodenum.

CONCLUSIONS

This study demonstrated a correlation between the number of CCR4-positive cells and villus edema formation rate. Therefore, FOS, which we inferred to show antiallergic activity for food allergy in this study and which has already been established to be safe for use as food in humans, can be considered to be potentially useful for the prevention of food allergy in pediatric patients with allergy.

Paediatric emergency department anaphylaxis: different patterns from adults

BACKGROUND AND AIMS

Data on acute paediatric anaphylaxis presentations to the emergency department (ED) are limited. All allergic presentations to one Australian paediatric ED were studied to determine epidemiological, clinical, and outcome data.

METHODS

Retrospective, case based study of patients under 16 years attending one metropolitan, paediatric teaching hospital ED in Australia over three years. The medical records of patients presenting with generalised allergic reactions and anaphylaxis satisfying relevant ICD-9-CM diagnostic codes were studied. The incidence, age, sex ratio, co-morbidities, likely aetiology, clinical features, management, and disposal were determined.

RESULTS

A total of 526 children with generalised allergic reactions, and 57 with anaphylaxis were included in the study. This represented incidences of 9.3:1000 ED presentations for generalised allergic reactions and 1:1000 for anaphylaxis. There were no fatalities. In anaphylaxis cases, a cause was recognised in 68.4%. Cutaneous features were present in 82.5%. A past history of asthma was reported in 36.8%. Adrenaline was used in 39.3% of severe anaphylaxis cases. The ED alone definitively cared for 97.8% of all patients. Follow up was inadequate in cases of anaphylaxis.

CONCLUSIONS

This is the first reported incidence figure for paediatric anaphylaxis ED presentations in Australia, and is less than that reported in adults in the same local population. However, the incidence of generalised allergic reactions of 9.3:1000 was greater than in the adults. Virtually all paediatric allergic cases may be managed in the ED alone, provided that the importance of specialist follow up, particularly for severe anaphylaxis, is recognised.

Allergenic characteristics of a modified peanut allergen

Attempts to treat peanut allergy using traditional methods of allergen desensitization are accompanied by a high risk of anaphylaxis. The aim of this study was to determine if modifications to the IgE-binding epitopes of a major peanut allergen would result in a safer immunotherapeutic agent for the treatment of peanut-allergic patients. IgE-binding epitopes on the Ara h 2 allergen were modified, and modified Ara h 2 (mAra h 2) protein was produced. Wild-type (wAra h 2) and mAra h 2 proteins were analyzed for their ability to interact with T-cells, their ability to bind IgE, and their ability to release mediators from a passively sensitized RBL-2H3 cell line. Multiple T-cell epitopes were identified on the major peanut allergen, Ara h 2. Ara h 2 amino acid regions 11-35, 86-125, and 121-155 contained the majority of peptides that interact with T-cells from most patients. The wAra h 2 and mAra h 2 proteins stimulated proliferation of T-cells from peanut-allergic patients to similar levels. In contrast, the mAra h 2 protein exhibited greatly reduced IgE-binding capacity compared to the wild-type allergen. In addition, the modified allergen released significantly lower amounts of beta-hexosaminidase, a marker for IgE-mediated RBL-2H3 degranulation, compared to the wild-type allergen.

Seafood allergy: lessons from clinical symptoms, immunological mechanisms and molecular biology

Food allergy consists of a wide range of disorders that result from adverse immune responses to dietary antigens. Manifestations of allergic response includes acute, potentially fatal anaphylactic reactions and a variety of chronic diseases that mainly affect the gastrointestinal tract, skin, and respiratory tract. Tools for clinical diagnosis and management, which have not changed much in the past two decades, include the clinical history, tests for specific IgE antibody to suspected foods, elimination diets, oral food challenges, and provision of medications such as epinephrine for emergency treatment. On the other hand, recent immunological and molecular biological research have enhanced our understanding of the mechanisms of these disorders and revealed the identities of many food allergens. Here, we will discuss seafood allergies with respect to the clinical manifestations, diagnosis, immunological mechanisms, and molecular biology of seafood allergens. Furthermore, potential applications and future directions in the clinical management of seafood allergies are discussed.

Assessing Genetically Modified Crops to Minimize the Risk of Increased Food Allergy: A Review

The first genetically modified (GM) crops approved for food use (tomato and soybean) were evaluated for safety by the United States Food and Drug Administration prior to commercial production. Among other factors, those products and all additional GM crops that have been grown commercially have been evaluated for potential increases in allergenic properties using methods that are consistent with the current understanding of food allergens and knowledge regarding the prediction of allergenic activity. Although there have been refinements, the key aspects of the evaluation have not changed. The allergenic properties of the gene donor and the host (recipient) organisms are considered in determining the appropriate testing strategy. The amino acid sequence of the encoded protein is compared to all known allergens to determine whether the protein is a known allergen or is sufficiently similar to any known allergen to indicate an increased probability of allergic cross-reactivity. Stability of the protein in the presence of acid with the stomach protease pepsin is tested as a risk factor for food allergenicity. In vitro or in vivo human IgE binding are tested when appropriate, if the gene donor is an allergen or the sequence of the protein is similar to an allergen. Serum donors and skin test subjects are selected based on their proven allergic responses to the gene donor or to material containing the allergen that was matched in sequence. While some scientists and regulators have suggested using animal models, performing broadly targeted serum IgE testing or extensive pre- or post-market clinical tests, current evidence does not support these tests as being predictive or practical. Based on the evidence to date, the current assessment process has worked well to prevent the unintended introduction of allergens in commercial GM crops.

Risks of allergic reactions to biotech proteins in foods: perception and reality

In recent years, significant attention has been paid to the use of biotechnology to improve the quality and quantity of the food supply due in part to the projected growth in the world population, plus limited options available for increasing the amount of land under cultivation. Alterations in the food supply induced by classical breeding and selection methods typically involve the movement of large portions of genomic DNA between different plant varieties to obtain the desired trait. This is in contrast to techniques of genetic engineering which allows the selection and transfers specific genes from one species to another. The primary allergy risk to consumers from genetically modified crops may be placed into one of three categories. The first represents the highest risk to the allergic consumer is the transfer of known allergen or cross-reacting allergen into a food crop. The second category, representing an intermediate risk to the consumer, is the potential for replacing the endogenous allergenicity of a genetically-modified crop. The last category involves expression of novel proteins that may become allergens in man and generally represents a relatively low risk to the consumer, although this possibility has received attention of late. In order to mitigate the three categories of potential allergy risk associated with biotech crops, all genes introduced into food crops undergo a series of tests designed to determine if the biotech protein exhibits properties of known food allergens. The result of this risk assessment process to date is that no biotech proteins in foods have been documented to cause allergic reactions. These results indicate that the current assessment process is robust, although as science of allergy and allergens evolves, new information and new technology should help further the assessment process for potential allergenicity.

Food Allergy in Children

Food allergic reactions have generated increasing concern in the United States, with approximately one fourth of American households altering their dietary habits because a member of the family is perceived to suffer from food allergies. IgE-mediated (type I) hypersensitivity accounts for most well-characterized food allergic reactions, although non-IgE-mediated immune mechanisms are believed to be responsible for a variety of hypersensitivity disorders. This article examines adverse food reactions that are IgE-mediated, non-IgE-mediated, and those entities that have characteristics of both.

Genetic modification of food allergens

OBJECTIVE

To review allergen risk evaluation for genetically modified foods and our ability to predict protein allergenicity, methods that are being used to develop foods with reduced allergenic activity, and clinical aspects relative to assessing potentially allergic patients.

DATA SOURCES

Information was identified using the MEDLINE database for governmental, international, and industry organizations that have considered possible unintended health effects such as food allergy and how they can be avoided.

DATA SELECTION

The author's knowledge of the field was used to select articles for inclusion in this review.

RESULTS

Organizations have created a decision process that has generally been successful in avoiding development of products that cause allergic reactions. Since some proteins expressed do not have any history of human exposure, risk evaluation may be more of a challenge for them. Biotechnology has also been used to try to develop foods with reduced allergenicity, and in future years such products should yield safer foods.

CONCLUSIONS

Allergy risk evaluation for known allergens and genetically modified foods appears to be reasonable and provides assurance of food safety. Allergenicity evaluation of novel proteins is a more complicated process that needs to be and will be improved as our knowledge of food allergens increases. Biotechnology can be used to produce safer and healthier foods; for example, allergenicity of some foods may be reduced through biotechnology. The role of the health care professional in assessing allergic reactions to genetically modified foods is essential and should play a greater role in the interaction of consumers, industry, and regulators.

Early infant multivitamin supplementation is associated with increased risk for food allergy and asthma

OBJECTIVE

Dietary vitamins have potent immunomodulating effects in vitro. Individual vitamins have been shown to skew T cells toward either T-helper 1 or T-helper 2 phenotypic classes, suggesting that they may participate in inflammatory or allergic disease. With the exception of antioxidant protection, there has been little study on the effect of early vitamin supplementation on the subsequent risk for asthma and allergic disease. The objective of this study was to determine whether early vitamin supplementation during infancy affects the risk for asthma and allergic disease during early childhood.

METHODS

Cohort data were analyzed from the National Center for Health Statistics 1988 National Maternal-Infant Health Survey, which followed pregnant women and their newborns, and the 1991 Longitudinal Follow-up of the same patients, which measured health and disease outcomes. Patients were stratified by race and breastfeeding status. Factors that are known to be associated with alteration of risk for asthma or food allergies were identified using univariate logistic regression. Those factors were then analyzed in multivariate logistic regression models. Early vitamin supplementation was defined as vitamin use within the first 6 months.

RESULTS

There were >8000 total patients in the study. The overall incidence of asthma was 10.5% and of food allergy was 4.9%. In univariate analysis, male gender, smoker in the household, child care, prematurity (<37 weeks), being black, no history of breastfeeding, lower income, and lower education were associated with higher risk for asthma. Child care, higher levels of education, income, and history of breastfeeding were associated with a higher risk for food allergies. In multivariate logistic analyses, a history of vitamin use within the first 6 months of life was associated with a higher risk for asthma in black infants (odds ratio [OR]: 1.27; 95% confidence interval [CI]: 1.04-1.56). Early vitamin use was also associated with a higher risk for food allergies in the exclusively formula-fed population (OR: 1.63; 95% CI: 1.21-2.20). Vitamin use at 3 years of age was associated with increased risk for food allergies but not asthma in both breastfed (OR: 1.62; 95% CI: 1.19-2.21) and exclusively formula-fed infants (OR: 1.39; 95% CI: 1.03-1.88).

CONCLUSIONS

Early vitamin supplementation is associated with increased risk for asthma in black children and food allergies in exclusively formula-fed children. Additional study is warranted to examine which components most strongly contribute to this risk.

What makes a food protein an allergen?

Food allergens are almost always proteins, but not all food proteins are allergens. This one statement sums up the purpose of this article, defining the difference between an innocuous food protein and a food allergen. The simplest answer is that a food allergen has the ability to first elicit an IgE response, and then, on subsequent exposures, to elicit a clinical response to the same or similar protein. However, this simplistic answer avoids the more complex issues of defining the biochemical characteristics that allow a food protein to survive the extremes of food processing, escape the digestive enzymes of the human gastrointestinal tract, and interact with the immune system. More than 700 allergen sequences have been identified from food and nonfood sources. However, despite increasing knowledge of the structure and amino acid sequences of the identified allergens, only a few biochemical characteristics can be associated with food allergens. Food allergen characteristics, including abundance of the protein in the food; multiple, linear IgE binding epitopes; resistance of the protein to digestion and processing; and allergen structure are discussed, and the possible reasons they predispose some food proteins to become allergens are suggested.

Effect of exclusive breast-feeding and early solid food avoidance on the incidence of atopic dermatitis in high-risk infants at 1 year of age

The aim of this study was to assess the preventive effect of exclusive breast-feeding and early solid food avoidance on atopic dermatitis (AD) in infancy. This study is part of a dietary clinical trial in a prospective cohort of healthy term newborns at risk of atopy. It was recommended to breast-feed for at least 4 months and to avoid solid food in the same time-period. Eight hundred and sixty-five infants exclusively breast-fed, and 256 infants partially or exclusively formula-fed, were followed-up until the end of the first year following birth. AD and sensitization to milk and egg were considered as study end-points. The 1-year incidence of AD was compared between the two study groups. Adjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated by multiple logistic regression. The incidence of AD was calculated in relation to age at introduction of solid food and amount of food given. In the breast-fed group, the adjusted OR for AD was 0.47 (95% CI 0.30-0.74). The strongest risk factor was the occurrence of AD in the subject's core family. The risk of infants with AD to be sensitized to milk was four times higher, and to egg eight times higher, than in infants without AD. Age at first introduction of solid food and diversity of solid food showed no effect on AD incidence. We conclude that in infants at atopic risk, exclusive breast-feeding for at least 4 months is effective in preventing AD in the first year of life.

Current understanding of food allergens

Food allergies are IgE-mediated immunological reactions; this distinguishes them from other adverse reactions to foods. Most (>90%) of the recognized food allergies are generally thought to be caused by eight foods or food groups. A number of factors can affect food allergy development, including diet and culture, route of exposure, processing, cooking, and digestion. In addition, it is thought that the properties of certain food proteins render them more likely to be allergenic than other proteins. Most food allergens are major proteins, polyvalent molecules with at least two or more IgE-binding sites, and are recognized as foreign molecules (hence immunogenic). A number of major food allergens have been recently characterized, and amino acid sequences determined. Tropomyosin is the only major allergen of shrimp. A number of IgE-binding epitopes have been identified in this molecule, though they may vary from one shrimp-allergic individual to another. Single amino acid substitutions within epitopes based on that of homologous, nonreactive tropomyosins can substantially enhance or abolish IgE antibody binding. Using the accumulated knowledge of food allergen protein structure, the allergenicity of novel proteins to which there has been no prior human exposure has been assessed. This has been based primarily on the lability or resistance of a protein to enzymatic degradation. Clearly, further criteria must be developed to refine this process. In this regard, the development of animal models that have been sufficiently validated as surrogates of human IgE antibody responses is needed for more precise assessment of the allergenic potential of proteins.

Comparative studies on antigenicity and allergenicity of native and denatured egg white proteins

The binding activities of IgG and IgE antibodies from egg-allergic patients to physically or chemically treated egg white proteins were examined and compared with those of rabbit anti-egg white IgG antibodies. The sera from eight patients and four rabbit antibodies were used in this study. The binding activities of human IgG antibody to partially denatured ovotransferrin (Tf), ovalbumin (OA), and lysozyme (Lys) forms were increased, whereas carboxymethylation (RCM) and heat treatment caused a dramatic decrease in the antigenicity of Tf and ovomucoid (OVM). Tf and OVM were major immunogenic antigens for the rabbit IgG response. Urea also caused Tf to exhibit greater rabbit IgG binding activity. In contrast, human and rabbit antibodies did not react with ovomucin. Partially denatured Tf and Lys also induced strong IgE binding activities. The allergenicity of Tf, OVM, and Lys was decreased by RCM, whereas OA retained its binding capacity. These results suggested that anti-OA IgE recognizes more sequential epitopes and that anti-OVM and Lys antibodies recognize both conformational and sequential epitopes. Tf and OVM were dominant allergens for the IgE antibodies of anaphylaxis patients, whereas IgE from atopic patients bound more strongly with OA and OVM.

Food allergy is a matter of geography after all: sesame as a major cause of severe IgE-mediated food allergic reactions among infants and young children in Israel

OBJECTIVE

To determine the prevalence, importance, and the order of frequency of IgE-mediated food allergens among infants and young children in Israel.

STUDY DESIGN AND PATIENTS

In a cross-sectional study, the prevalence of IgE-mediated food allergy was investigated in 9070 infants and young children (0-2 years) who were followed-up at 23 Family Health Centers (FHCs) in central Israel. Patients with suspected IgE-mediated food allergic reactions, were recruited for further evaluation (detailed questionnaire and skin-prick test (SPT)).

RESULTS

We identified 150 out of 9070 (1.7%) patients with suspected IgE-mediated food allergy. Among them, 102/150 (67%) [59 males, 43 females; mean age 10.3 months] completed a detailed questionnaire and underwent SPT. Evaluation revealed 131 positive SPTs in 78/102 (76.5%) patients. Twenty-seven positive SPTs in 18 patients were considered clinically irrelevant based on previous consumption of the relevant foods without clinical symptoms. Thus, there were 104 relevant positive SPTs in 78 patients. The overall prevalence of clinically relevant IgE-mediated food allergic reactions among these patients is estimated to be 1.2% (104/9070). The most common food allergens were egg, cow's milk, and sesame. Anaphylaxis was the presenting symptom in 14/78 (18%) including six sesame-induced cases. A history of other atopic diseases was reported in 27 (35%) patients. In addition, 22 (28%) had a history of atopy in first-degree family members.

CONCLUSIONS

We found sesame to be a major cause of IgE-mediated food allergy in Israel. In fact, it is second only to cow's milk as a cause of anaphylaxis. We recommend that testing for food allergens be tailored to each community based on local experience and should include sesame in appropriate populations.

Early life exposure to dietary and inhalant allergens

Increasing evidence points to early life, including fetal life, as being a critical time period during which the infant's allergic fate may be determined. However, initial antigen priming in utero necessitates fetal exposure to maternally derived allergen. This article reviews our current knowledge regarding materno-fetal allergen transfer in vivo and reflects on mechanisms by which this exposure might exert immunomodulatory influences on the developing immune system.

Criteria to determine food allergen priority

The emergent health issue of food allergens presents an important challenge to the food industry. More than 170 foods have been reported in the scientific literature as causing allergic reactions. Clearly, it would be impossible to deal with the presence of trace amounts of all these in the context of food labeling. If the decision to classify major allergens is based solely on the knowledge and experience of allergists and food scientists in the field, without scientifically defined criteria, it is likely to lead to a proliferation of lists. Such practices may lead to an unnecessary elimination of foods containing important nutrients. This paper defines food allergy, food intolerance, and food anaphylaxis and identifies criteria for classifying food allergens associated with frequent allergic reactions. A practical list of food allergens that may result in potentially life-threatening allergic reactions is provided. A mechanism-based (i.e., immunoglobulin E mediated), acute life-threatening anaphylaxis that is standardized and measurable and reflects the severity of health risk is proposed as the principal inclusion criterion for food allergen labeling. Where available, prevalence in the population and threshold levels of allergens should be used as an additional guide to identify possible future labeling needs.

Parent reported allergy and anaphylaxis in 4173 South Australian children

OBJECTIVES

To determine the prevalence of parent reported allergy and anaphylaxis in a sample of children and to investigate the first aid management of anaphylaxis in the schools and preschools that these children attend.

METHODS

The study sample comprised 4173 South Australian children aged 3-17 years. Information was collected regarding parent-reported allergy and anaphylaxis. All children with known anaphylaxis were contacted and an attempt was made to contact those with reports of allergy to ascertain if these children had anaphylaxis. A telephone questionnaire was used to verify reports of anaphylaxis and determine the cause, severity and school first aid management of anaphylaxis.

RESULTS

The rate of parent reported allergy and anaphylaxis was 7.3 and 0.59 per 100 children, respectively. Two-thirds of children with anaphylaxis did not have emergency medication available at school, an emergency action plan, or a teacher on site able to administer adrenaline for first aid use.

CONCLUSIONS

Children attending preschool or school may have had a past history of anaphylaxis. Arrangements for first aid management of these children while in this environment are often inadequate.

Molecular cloning and epitope analysis of the peanut allergen Ara h 3

Peanut allergy is a significant IgE-mediated health problem because of the increased prevalence, potential severity, and chronicity of the reaction. Following our characterization of the two peanut allergens Ara h 1 and Ara h 2, we have isolated a cDNA clone encoding a third peanut allergen, Ara h 3. The deduced amino acid sequence of Ara h 3 shows homology to 11S seed-storage proteins. The recombinant form of this protein was expressed in a bacterial system and was recognized by serum IgE from approximately 45% of our peanut-allergic patient population. Serum IgE from these patients and overlapping, synthetic peptides were used to map the linear, IgE-binding epitopes of Ara h 3. Four epitopes, between 10 and 15 amino acids in length, were found within the primary sequence, with no obvious sequence motif shared by the peptides. One epitope is recognized by all Ara h 3-allergic patients. Mutational analysis of the epitopes revealed that single amino acid changes within these peptides could lead to a reduction or loss of IgE binding. By determining which amino acids are critical for IgE binding, it might be possible to alter the Ara h 3 cDNA to encode a protein with a reduced IgE-binding capacity. These results will enable the design of improved diagnostic and therapeutic approaches for food-hypersensitivity reactions.

In vitro testing in pediatric food allergy

Food allergies are an important cause of morbidity in the pediatric population. We used a questionnaire to assess the value of in vitro testing in evaluating children for food allergy. The patient population was divided into two groups: those who tested positive (Class I or greater) for food allergy (combined food/inhalant allergy or food allergy alone) and those who tested negative for food allergy (inhalant only or negative test). Although we recognize that a significant proportion of food allergies may not be IgE-mediated, for the purposes of this study we considered a patient food allergy--positive if in vitro testing was positive and food allergy--negative if testing was negative. Thirty-eight of 77 patients tested (49%) were positive for food allergies. Those with food allergies did not have pretreatment scores significantly different from those of patients negative for food allergies (55 vs. 65, p = 0.11). Similarly, we detected no statistically significant difference between the symptom-improvement scores of the two groups (37 vs. 40, p = 0.57). We conclude that in vitro testing for food allergies is warranted in children with allergic symptoms, for several reasons: The prevalence of IgE-mediated food allergy in children may be higher than previously thought, and children with food allergies experience the same severity of symptoms as those without. It must be remembered that in vitro testing only detects IgE levels, and therefore a negative test does not mean that the patient does not have food allergies. However, when positive, in vitro testing gives the physician the opportunity to modify the treatment plan, helping avoid time-consuming and demanding oral food challenges. Our questionnaire also showed that food allergy and non-food allergy patients had similar pretreatment and posttreatment symptom scores.

Biochemical and structural analysis of the IgE binding sites on ara h1, an abundant and highly allergenic peanut protein

Allergy to peanut is a significant IgE-mediated health problem because of the high prevalence, potential severity, and chronicity of the reaction. Ara h1, an abundant peanut protein, is recognized by serum IgE from >90% of peanut-sensitive individuals. It has been shown to belong to the vicilin family of seed storage proteins and to contain 23 linear IgE binding epitopes. In this communication, we have determined the critical amino acids within each of the IgE binding epitopes of Ara h1 that are important for immunoglobulin binding. Surprisingly, substitution of a single amino acid within each of the epitopes led to loss of IgE binding. In addition, hydrophobic residues appeared to be most critical for IgE binding. The position of each of the IgE binding epitopes on a homology-based molecular model of Ara h1 showed that they were clustered into two main regions, despite their more even distribution in the primary sequence. Finally, we have shown that Ara h1 forms a stable trimer by the use of a reproducible fluorescence assay. This information will be important in studies designed to reduce the risk of peanut-induced anaphylaxis by lowering the IgE binding capacity of the allergen.

Identification and mutational analysis of the immunodominant IgE binding epitopes of the major peanut allergen Ara h 2

A major peanut allergen, Ara h 2, is recognized by serum IgE from > 90% of patients with peanut hypersensitivity. Biochemical characterization of this allergen indicates that it is a glycoprotein of approximately 17.5 kDa. Using N-terminal amino acid sequence data from purified Ara h 2, oligonucleotide primers were synthesized and used to identify a clone (741 bp) from a peanut cDNA library. This clone was capable of encoding a 17.5-kDa protein with homology to the conglutin family of seed storage proteins. The major linear immunoglobulin E (IgE)-binding epitopes of this allergen were mapped using overlapping peptides synthesized on an activated cellulose membrane and pooled serum IgE from 15 peanut-sensitive patients. Ten IgE-binding epitopes were identified, distributed throughout the length of the Ara h 2 protein. Sixty-three percent of the amino acids represented in the epitopes were either polar uncharged or apolar residues. In an effort to determine which, if any, of the 10 epitopes were recognized by the majority of patients with peanut hypersensitivity, each set of 10 peptides was probed individually with serum IgE from 10 different patients. All of the patient sera tested recognized multiple epitopes. Three epitopes (aa27-36, aa57-66, and aa65-74) were recognized by all patients tested. In addition, these three peptides bound more IgE than all the other epitopes combined, indicating that they are the immunodominant epitopes of the Ara h 2 protein. Mutational analysis of the Ara h 2 epitopes indicate that single amino acid changes result in loss of IgE binding. Two epitopes in region aa57-74 contained the amino acid sequence DPYSP that appears to be necessary for IgE binding. These results may allow for the design of improved diagnostic and therapeutic approaches to peanut hypersensitivity.

Food allergy in children

The diagnosis of hypersensitivity reactions to foods in infancy and childhood requires the use of clinical skills and laboratory diagnostic methods to identify suspect foods. Patients and parents occasionally may need to keep food/symptom diaries to explore the association of foods and adverse reaction. Skin testing or RAST may shorten the list of potential allergens because of their excellent negative predictive value. Except for obvious serious allergic reactions after ingestion of a single food, confirmation of the reaction may be ideally confirmed by a DBPCFC, especially if the reported symptoms are subjective in nature. Equivocal responses should be repeated. Although many in vitro and in vivo diagnostic methods have been developed to potentially improve the diagnosis of food allergy in children, no test has been able to predict the results of the DBPCFC with any greater accuracy than skin tests or RAST. The "perfect" test with excellent positive and negative predictive values has yet to be developed.