The distribution of individual threshold doses eliciting allergic reactions in a population with peanut allergy

BACKGROUND

Hidden peanut in consumer products can endanger patients with peanut allergy. Individual threshold doses for eliciting allergic reactions need to be elucidated to assess the risks for development of allergic reactions after accidental ingestion of peanut in a population with peanut allergy.

OBJECTIVE

We sought to determine the distribution of individual threshold doses in a population with peanut allergy and to correlate these thresholds to the severity of peanut-induced symptoms.

METHODS

Twenty-six adult patients with a convincing history of peanut-related symptoms, a specific IgE level of 0.7 kU/L or greater, or a positive skin prick test response of 2+ or greater to peanut were included. These patients underwent double-blind, placebo-controlled food challenges with increasing doses of peanut. A threshold dose could be established when objective or repetitive subjective reactions occurred after active doses.

RESULTS

All patients had subjective oral symptoms (n = 26), prior subjective gastrointestinal symptoms (n = 14), or objective symptoms (n = 5). Reactions started within 30 minutes after ingestion of peanut, but in 2 patients additional symptoms were delayed by 1 to 2 hours. Threshold doses for allergic reactions ranged from a dose as low as 100 microg up to 1 g of peanut protein. Fifty percent of the study population (95% CI, 30%-70%) already had an allergic reaction after ingestion of 3 mg of peanut protein. Patients with severe symptoms had lower threshold doses compared with those of patients with mild symptoms (P =.027).

CONCLUSIONS

A substantial part of a population with peanut allergy will react to very low amounts of peanut, requiring accurate declaration of peanut content in consumer products. This is even more important because patients with severe reactions react to lower doses than patients with mild symptoms.

The range of minimum provoking doses in hazelnut-allergic patients as determined by double-blind, placebo-controlled food challenges

BACKGROUND

The risk for allergic reactions depends on the sensitivity of individuals and the quantities of offending food ingested. The sensitivity varies among allergic individuals, as does the threshold dose of a food allergen capable of inducing an allergic reaction.

OBJECTIVE

This study aimed at determining the distribution of minimum provoking doses of hazelnut in a hazelnut-allergic population.

METHODS

Thirty-one patients with a history of hazelnut-related allergic symptoms, a positive skin prick test to hazelnut and/or an elevated specific IgE level, were included. Double-blind, placebo-controlled food challenges (DBPCFC) were performed with seven increasing doses of dried hazelnut (1 mg to 1 g hazelnut protein) randomly interspersed with seven placebo doses.

RESULTS

Twenty-nine patients had a positive challenge. Itching of the oral cavity and/or lips was the first symptom in all cases. Additional gastrointestinal symptoms were reported in five patients and difficulty in swallowing in one patient. Lip swelling was observed in two patients, followed by generalized urticaria in one of these. Threshold doses for eliciting subjective reactions varied from a dose of 1 mg up to 100 mg hazelnut protein (equivalent to 6.4-640 mg hazelnut meal). Extrapolation of the dose-response curve showed that 50% of our hazelnut-allergic population will suffer from an allergic reaction after ingestion of 6 mg (95% CI, 2-11 mg) of hazelnut protein. Objective symptoms were observed in two patients after 1 and 1,000 mg, respectively.

CONCLUSION

DBPCFCs demonstrated threshold doses in half of the hazelnut-allergic patients similar to doses previously described to be hidden in consumer products. This stresses the need for careful labelling and strategies to prevent and detect contamination of food products with hazelnut residues.

Bioinformatic methods for allergenicity assessment using a comprehensive allergen database

BACKGROUND

A principal aim of the safety assessment of genetically modified crops is to prevent the introduction of known or clinically cross-reactive allergens. Current bioinformatic tools and a database of allergens and gliadins were tested for the ability to identify potential allergens by analyzing 6 Bacillus thuringiensis insecticidal proteins, 3 common non-allergenic food proteins and 50 randomly selected corn (Zea mays) proteins.

METHODS

Protein sequences were compared to allergens using the FASTA algorithm and by searching for matches of 6, 7 or 8 contiguous identical amino acids.

RESULTS

No significant sequence similarities or matches of 8 contiguous amino acids were found with the B. thuringiensis or food proteins. Surprisingly, 41 of 50 corn proteins matched at least one allergen with 6 contiguous identical amino acids. Only 7 of 50 corn proteins matched an allergen with 8 contiguous identical amino acids. When assessed for overall structural similarity to allergens, these 7 plus 2 additional corn proteins shared >or=35% identity in an overlap of >or=80 amino acids, but only 6 of the 7 were similar across the length of the protein, or shared >50% identity to an allergen.

CONCLUSIONS

An evaluation of a protein by the FASTA algorithm is the most predictive of a clinically relevant cross-reactive allergen. An additional search for matches of 8 amino acids may provide an added margin of safety when assessing the potential allergenicity of a protein, but a search with a 6-amino-acid window produces many random, irrelevant matches.

Genetically engineered foods: implications for food allergy

The products of agricultural biotechnology, including such common foods as corn and soybeans, are already reaching the consumer marketplace. Consumer exposure to such foods is already fairly significant, particularly in the USA. Thus far, no reports exist regarding allergic reactions to the crops that have been approved for introduction into the food supply. These crops have been modified to only a minor extent by comparison with their traditional counterparts, and the level of expression of new and novel proteins is quite low. Thus, consumer exposure to these novel proteins is very low and unlikely to result in allergic sensitization. Nevertheless, foods produced through agricultural biotechnology must be assessed for safety, including their potential allergenicity, before they may be approved by worldwide regulatory agencies for entry into the food supply. However, the adequacy of the current approach to the assessment of the potential allergenicity of foods produced through agricultural biotechnology has been the subject of considerable scientific and regulatory debate.

Factors affecting the determination of threshold doses for allergenic foods: how much is too much?

BACKGROUND

Ingestion of small amounts of an offending food can elicit adverse reactions in individuals with IgE-mediated food allergies. The threshold dose for provocation of such reactions is often considered to be zero. However, because of various practical limitations in food production and processing, foods may occasionally contain trace residues of the offending food. Are these very low, residual quantities hazardous to allergic consumers? How much of the offending food is too much? Very little quantitative information exists to allow any risk assessments to be conducted by the food industry.

OBJECTIVE

We sought to determine whether the quality and quantity of existing clinical data on threshold doses for commonly allergenic foods were sufficient to allow consensus to be reached on establishment of threshold doses for specific foods.

METHODS

In September 1999, 12 clinical allergists and other interested parties were invited to participate in a roundtable conference to share existing data on threshold doses and to discuss clinical approaches that would allow the acquisition of that information.

RESULTS

Considerable data were identified in clinical files relating to the threshold doses for peanut, cows' milk, and egg; limited data were available for other foods, such as fish and mustard.

CONCLUSIONS

Because these data were often obtained by means of different protocols, the estimation of a threshold dose was very difficult. Development of a standardized protocol for clinical experiments to allow determination of the threshold dose is needed.

How much food is too much? Threshold doses for allergenic foods

This review summarizes recent findings and controversies in the area of threshold doses for allergenic foods. Over the years, there have been many clinical reports that ingestion of small amounts of food can elicit IgE-mediated allergic reactions. In exquisitely allergic individuals, the threshold dose for elicitation of such reactions is often considered to be zero. However, some food-allergic patients report that they can tolerate small quantities of allergenic food. Are very low quantities hazardous to food-allergic consumers? How much of the offending food is too much? Why is the concept of a threshold level important? There have been very few studies to date on threshold doses for allergenic foods, and more research is needed in this important area.

Development of a sandwich enzyme-linked immunosorbent assay for the detection of egg residues in processed foodst

Chicken eggs are used extensively as an excellent source of dietary proteins. These proteins have many functional properties, making them valuable food ingredients. However, eggs are a frequent cause of food hypersensitivity, especially in children. Of major concern to food processors is the inadvertent cross-contact of food products with allergenic residues, which could result in potentially life-threatening reactions in those with a food allergy. The aim of the present study was to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of undeclared egg residues in foods. Commercially purified ovalbumin (OVA) and dehydrated egg white solids were used as antigens to induce antibodies in rabbits and goats. Reference pasta standards and various food samples were extracted, then clarified by centrifugation. Goat anti-egg white antibodies were used as the capture reagent, nonspecific sites were blocked with gelatin, then standard and sample extracts were added. Rabbit anti-OVA antibodies were used as detector antibodies, followed by addition of commercial goat anti-rabbit IgG antibody labeled with alkaline phosphatase and subsequent substrate addition. Twenty brands of egg-free pasta (two lots each) were analyzed using the ELISA. Fourteen common pasta ingredients were also evaluated for cross-reactivity problems in the method. The detection limit of the assay was 1 ppm spray-dried whole egg. Fifty-five percent (22 samples) of the egg-free pasta samples tested positive for the presence of undeclared egg residues, with values ranging from 1 to >100,000 ppm. Minimal cross-reactivity was encountered in general, but portobello mushrooms and basil caused some minor matrix effects. This sandwich-type ELISA method can be used to detect undeclared egg residues in processed foods and to evaluate industrial clean-up operations.

Ingredient and labeling issues associated with allergenic foods

Foods contain a wide range of food ingredients that serve numerous technical functions. Per capita consumer exposure to most of these food ingredients is rather low with a few notable exceptions such as sugar and starch. Some food ingredients including edible oils, hydrolyzed proteins, lecithin, starch, lactose, flavors and gelatin may, at least in some products, be derived from sources commonly involved in IgE-mediated food allergies. These ingredients should be avoided by consumers with allergies to the source material if the ingredient contains detectable protein residues. Other food ingredients, including starch, malt, alcohol and vinegar, may be derived in some cases from wheat, rye or barley, the grains that are implicated in the causation of celiac disease. If these ingredients contain gluten residues, then they should be avoided by celiac sufferers. A few food ingredients are capable of eliciting allergic sensitization, although these ingredients would be classified as rarely allergenic. These ingredients include carmine, cochineal extract, annatto, tragacanth gum and papain. Food manufacturers should declare the presence of allergenic food ingredients in the ingredient listings on product labels so that allergic consumers can know to avoid these potentially hazardous products.

Hidden food allergens

This review summarizes recent advances and findings in the area of 'hidden' food allergens, i.e. allergenic foods that can either contaminate other foods, or be 'disguised' as part of a food, and cause allergic reactions. Newly emerging allergenic foods of increasing importance, recently developed methods for the detection of allergenic residues, the potential allergenicity of genetically engineered foods, and some unexpected sources of food allergens are described.

Will genetically modified foods be allergenic?

Foods produced through agricultural biotechnology, including such staples as corn, soybeans, canola, and potatoes, are already reaching the consumer marketplace. Agricultural biotechnology offers the promise to produce crops with improved agronomic characteristics (eg, insect resistance, herbicide tolerance, disease resistance, and climatic tolerance) and enhanced consumer benefits (eg, better taste and texture, longer shelf life, and more nutritious). Certainly, the products of agricultural biotechnology should be subjected to a careful and complete safety assessment before commercialization. Because the genetic modification ultimately results in the introduction of new proteins into the food plant, the safety, including the potential allergenicity, of the newly introduced proteins must be assessed. Although most allergens are proteins, only a few of the many proteins found in foods are allergenic under the typical circumstances of exposure. The potential allergenicity of the introduced proteins can be evaluated by focusing on the source of the gene, the sequence homology of the newly introduced protein to known allergens, the expression level of the novel protein in the modified crop, the functional classification of the novel protein, the reactivity of the novel protein with IgE from the serum of individuals with known allergies to the source of the transferred genetic material, and various physicochemical properties of the newly introduced protein, such as heat stability and digestive stability. Few products of agricultural biotechnology (and none of the current products) will involve the transfer of genes from known allergenic sources. Applying such criteria provides reasonable assurance that the newly introduced protein has limited capability to become an allergen.

Effect of ICAM-1 blockade on lung inflammation and physiology during acute viral bronchiolitis in rats

Viral respiratory infections cause acute bronchiolitis and physiologic dysfunction in human infants and in animals. It is possible that the pulmonary dysfunction is a consequence of the inflammatory cells that are recruited during viral illness. We hypothesized that blockade of intercellular adhesion molecule-1 (ICAM-1), a major cell adhesion molecule, would impede the ingress of leukocytes during viral infection and attenuate virus-induced pulmonary dysfunction. Adult male rats were inoculated with parainfluenza type 1 (Sendai) virus or sterile vehicle, and treated with blocking or nonblocking MAb specific for rat ICAM-1. Respiratory system resistance, oxygenation (PaO2), methacholine responsiveness, and bronchoalveolar lavage (BAL) leukocyte counts were measured in anesthetized, paralyzed, ventilated rats. Treatment with the blocking ICAM-1 antibody reduced virus-induced increases in BAL neutrophils and lymphocytes by 70% (p < 0.001), but did not affect BAL monocytes/macrophages. Peripheral blood leukocyte counts were elevated in anti-ICAM-1 blocking antibody-treated rats (p = 0.0003). Although virus-induced increases in resistance and decreases in PaO2 were not affected by anti-ICAM-1 treatment, there was a small but significant attenuation of virus-induced methacholine hyperresponsiveness (p = 0.02). We conclude that ICAM-1 has an important role in neutrophil and lymphocyte infiltration during respiratory viral illness, and that virus-induced changes in pulmonary physiology are not related directly to the numbers of neutrophils and lymphocytes that migrate to the air spaces during infection.

2S methionine-rich protein (SSA) from sunflower seed is an IgE-binding protein

BACKGROUND

Sunflower seed contains 2S albumins that in other crops have been associated with allergenicity. The sunflower seed methionine-rich 2S albumin (SSA) may be an IgE-binding protein responsible for anaphylactic reactions in some sunflower seed-sensitive subjects. The objective was to demonstrate that SSA is an IgE-binding protein.

METHODS

SSA was purified and the amino-acid sequence determined. The degree of purity of SSA was evaluated by silver staining, and its IgE-binding capacity by immunoblotting with serum from a subject with a convincing clinical history of anaphylaxis to sunflower seed.

RESULTS

The amino-acid sequence confirmed that the purified protein was the mature form of the methionine-rich storage protein SSA from sunflower seed (Helianthus annuus). The SSA was specifically recognized by IgE from the serum of the sunflower seed-allergic subject.

CONCLUSIONS

SSA is an IgE-binding protein, and subjects allergic to sunflower seed whose IgE binds to SSA are at risk of developing allergic reactions if they consume SSA.

A sandwich enzyme-linked immunosorbent assay for the detection of almonds in foods

An enzyme-linked immunosorbent assay was developed to detect almonds as potential allergenic contaminants in food. Polyclonal antibodies directed against roasted almonds were partially purified from immunized sheep and rabbits and used as capture and secondary antibodies, respectively, in a sandwich-type, 96-well plate format. Food samples and almond-spiked samples were extracted 1:10 in phosphate-buffered saline at 60 degrees C for 2 h, centrifuged, and applied to wells coated with sheep anti-almond antibody. After incubation, washing, and the addition of rabbit anti-almond antibody, the amount of almond present was detected with the subsequent addition of goat anti-rabbit immunoglobulin G-alkaline phosphatase conjugate and p-nitrophenyl phosphate substrate. Plate absorbances were read at 410 nm, and standard curves were developed in all matrices to quantify unknowns. Antibodies developed were specific for almond; however, some cross-reactivity was observed with extracts of some tree nuts and sesame seeds. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western immunoblotting indicated that sheep anti-almond antibody recognized proteins extracted from black walnuts, Brazil nuts, cashews, hazelnuts, macadamia nuts, pistachios, and sesame seeds in addition to those from almond. The assay was optimized to detect less than 1 ppm of almond and was used successfully to determine almond residues in cereal and chocolate without cross-reacting interferences. A retail survey of 20 brands of cereal demonstrated that the assay produced statistically consistent results. This assay provides a useful quality control tool for the food industry for the protection of consumers allergic to almonds.

Identification of sunflower seed IgE-binding proteins

BACKGROUND

Sunflower seed can cause severe anaphylactic reactions in some susceptible individuals. It is conceivable that the 2S sunflower seed protein is an allergen based on its high degree of homology (34%) with the allergenic mature 2S albumin protein of the Brazil nut. The first step in determining the allergenicity of sunflower seed proteins is to identify IgE-binding proteins.

METHODS

Sera from sunflower seed-sensitive individuals were evaluated by radioallergosorbent test (RAST), isoelectric focusing (IEF) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting with sunflower seed proteins.

RESULTS

Positive RAST scores (>2) were observed in 3 individuals and immunoblotting demonstrated IgE-binding to 2-7 distinct proteins ranging in size from 10 to 50 kD. Two out of 3 sera recognized two proteins between 16 and 17 kD. The lower molecular weight protein (16 kD) approximates to the prepo region of the precursor methionine-rich 2S albumin protein found in sunflower seed (SFA-8/SSA). IEF followed by immunoblotting demonstrated several IgE-binding proteins, including two proteins with isoelectric points of 5.97 and 5.3, respectively, which are consistent with the mature and immature forms of the SFA-8/SSA region.

CONCLUSIONS

Sunflower seed contains several IgE-binding proteins, including regions of the high-methionine 2S albumin SFA-8/SSA.

Impact of processing on food allergens

In general, allergenic foods are resistant to processes commonly used in food manufacturing. Nearly all the causative proteins (allergens) retain their allergenicity after treatment by heat and/or proteolysis. Notable exceptions exist; for example, the allergenicity of many fresh fruits and vegetables is decreased or removed by relatively mild processes such as gentle heating or mashing. The use of proteolytic enzymes to remove allergenicity is successfully used in the production of hypoallergenic infant formulas, but this approach with other allergenic foods has resulted in only limited success. Processing effects can result in decreased or complete removal of allergenic qualities of a food, such as the removal of proteins in oilseed processing, which renders the oils hypoallergenic and safe for consumption by allergic individuals. This discussion will address the different allergenic foods and processes which can affect or decrease their allergenicity.

Anaphylaxis in a milk-allergic child following ingestion of lemon sorbet containing trace quantities of milk

Although allergic persons can react to foods containing trace quantities of unlabeled or unintended food allergens, there are few data available on the quantities of these allergens required to evoke allergic symptoms. We report a milk-allergic 3-year-old boy who experienced throat itching, facial angioedema, and vomiting within 20 min of ingesting 4 to 6 oz (ca. 113.4 to 170.1 g) of lemon sorbet. Subsequent analysis of two sorbet samples provided by the parents and a third sample purchased locally by the investigators revealed trace quantities of milk allergens, whey protein (8.8 micrograms/ml), or lactose (200 ppm). The quantity of whey protein ingested was estimated to be 120 to 180 micrograms (equivalent to 23 to 24 microliters of milk). All three sorbet samples had been manufactured in the same plant within a 4-month period; the equipment used to produce and package the sorbet was also used to produce and package ice cream. No milk allergen or whey protein was detected in 38 other marketplace sorbet samples submitted by the manufacturer for testing. We concluded that trace quantities of whey proteins (< 200 micrograms) can elicit systemic reactions in exquisitely milk-allergic individuals. Such individuals should avoid eating frozen desserts prepared using equipment also used for producing or packaging ice cream, unless manufacturers can demonstrate unequivocally that their cleaning practices are sufficient to prevent milk contamination. Adequate tests are not currently available to food manufacturers but are under development.

An evaluation of the sensitivity of subjects with peanut allergy to very low doses of peanut protein: a randomized, double-blind, placebo-controlled food challenge study

BACKGROUND

The minimum dose of food protein to which subjects with food allergy have reacted in double-blind, placebo-controlled food challenges is between 50 and 100 mg. However, subjects with peanut allergy often report severe reactions after minimal contact with peanuts, even through intact skin.

OBJECTIVE

We sought to determine whether adults previously proven by challenge to be allergic to peanut react to very low doses of peanut protein.

METHODS

We used a randomized, double-blind, placebo-controlled food challenge of 14 subjects allergic to peanuts with doses of peanut ranging from 10 microg to 50 mg, administered in the form of a commercially available peanut flour.

RESULTS

One subject had a systemic reaction to 5 mg of peanut protein, and two subjects had mild objective reactions to 2 mg and 50 mg of peanut protein, respectively. Five subjects had mild subjective reactions (1 to 5 mg and 4 to 50 mg). All subjects with convincing objective reactions had short-lived subjective reactions to preceding doses, as low as 100 microg in two cases. Five subjects did not react to any dose up to 50 mg.

CONCLUSION

Even in a group of well-characterized, highly sensitive subjects with peanut allergy, the threshold dose of peanut protein varies. As little as 100 microg of peanut protein provokes symptoms in some subjects with peanut allergy.