Jaap H. Akkerdaas

Lipid Transfer Protein: A Pan-Allergen in Plant-Derived Foods That Is Highly Resistant to Pepsin Digestion

Background: Lipid transfer proteins (LTPs) are small molecules of approximately 10 kD that demonstrate high stability. They have recently been identified as allergens in the Rosaceae subfamilies of the Prunoideae (peach, apricot, plum) and of the Pomoideae (apple). They belong to a family of structurally highly conserved proteins that are also present in non-Rosaceae vegetable foods. Objective: The aim of this study was to investigate the cross-reactivity to non-Rosaceae LTPs, and to study the role of protein stability in allergenicity. Methods: Thirty-eight patients with a positive SPT to Rosaceae fruit extracts enriched for LTP were characterized by interview and SPT. To investigate IgE cross-reactivity between Rosaceae and non-Rosaceae LTPs, RAST and RAST inhibition as well as ELISA and ELISA inhibition were performed, using whole food extracts and purified LTPs. Both purified natural LTPs (peach, carrot and broccoli) and Pichia pastoris recombinant LTPs (carrot and wheat) were included. Pepsin digestion was used to address the role of stability in the allergenicity of LTPs. Results: IgE antibodies to Rosaceae LTPs reacted to a broad range of vegetable foods, including Gramineae (cereals), Leguminosae (peanut), Juglandaceae (walnut), Anacardiaceae (pistachio), Brassicaceae (broccoli), Umbelliferae (carrot, celery), Solanaceae (tomato), Cucurbitaceae (melon), and Actinidiaceae (kiwi). Binding and inhibition studies with purified natural and recombinant LTPs confirmed their role in this cross-reactivity. Many of these cross-reactivities were accompanied by clinical food allergy, frequently including systemic reactions. Antibody binding to LTP was shown to be resistant to pepsin treatment of whole extract or purified LTP. Conclusion: LTP is a pan-allergen with a degree of cross-reactivity comparable to profilin. Due to its extreme resistance to pepsin digestion, LTP is a potentially severe food allergen.

Poor biologic activity of cross-reactive IgE directed to carbohydrate determinants of glycoproteins

BACKGROUND In our outpatient population, approximately one third of patients sensitized to grass pollen were found to have significant serum levels of anti-peanut IgE in the RAST, without positive peanut skin prick test (SPT) response and without peanut-related allergic symptoms. It was suggested earlier that poor biologic activity of IgE antibodies directed to cross-reactive carbohydrate determinants (CCD) of glycoproteins might explain these discrepancies. OBJECTIVE In this study we investigated the biologic activity of IgE directed to CCD. METHODS Sera of 32 patients allergic to grass pollen with significant levels of anti-peanut IgE, a negative response on peanut SPT, and no symptoms of peanut allergy were tested for the presence of anti-CCD IgE. Eleven of these patients with greater than 3.0 IU/ml anti-peanut IgE (patients 1 to 11) were selected together with four control patients allergic to peanut, on the basis of a positive response on peanut SPT and a history of peanut allergy (patients 12 to 15). Inhibition of the peanut RAST was performed by using proteinase K-treated grass pollen extract as a CCD source. Basophil histamine release assays (BHRAs) were performed with peanut extract and the isolated peanut major allergens Ara h 1 and Ara h 2. In addition, intracutaneous tests with peanut extract were performed. RESULTS In 29 (91%) of 32 patients with discrepant peanut RAST and SPT responses, anti-CCD IgE (> or =0.1 IU/ml) was detected. In patients 1 to 11 almost complete inhibition of the peanut RAST with CCD was found (94.3% +/- 5.5%; mean +/- SD). In contrast, in the patients allergic to peanut only partial inhibition (59%) was found in one subject (p = 0.002, Mann-Whitney test). In the BHRAs and the intracutaneous tests of patients with discrepant peanut RAST and SPT results, reactivity was found only at high concentrations of peanut allergens. When related to specific IgE levels, reactivity to peanut allergens in the BHRAs of these patients was found to be at least a factor of 1000 less when compared with reactivity to control inhalant allergens. CONCLUSION We conclude that cross-reactive IgE directed to carbohydrate determinants of glycoproteins, as found in grass pollen-sensitized patients, has poor biologic activity. It can therefore cause positive RAST results without apparent clinical significance.

Cross-reactivity of IgE antibodies to allergens.

The cross‐reactivity of IgE antibodies is of interest for various reasons, three of which are discussed. Firstly, from the clinical view, it is important to know the patterns of cross‐reactivity, because they often (but not always) reflect the pattern of clinical sensitivities. We discuss the cross‐reactivities associated with sensitization to pollen and vegetable foods: PR‐10 (Bet v 1‐related), profilin, the cross‐reactive carbohydrate determinant (CCD), the recently described isoflavone reductase, and the (still elusive) mugwort allergen that is associated with celery anaphylaxis; cross‐reactivities between allergens from invertebrates, particularly tropomyosin, paramyosin, and glutathione S‐transferase (GST); and latex‐associated cross‐reactivities. Clustering cross‐reactive allergens may simplify diagnostic procedures and therapeutic regimens. Secondly, IgE cross‐reactivity is of interest for its immunologic basis, particularly in relation to the regulation of allergic sensitization: are IgE antibodies to allergens more often cross‐reactive than IgG antibodies to “normal” antigens? If so, why? For this discussion, it is relevant to compare not only the structural relation between the two allergens in question, but also the relatedness to the human equivalent (if any) and how the latter influences the immune repertoire. Thirdly, prediction of IgE cross‐reactivity is of interest in relation to allergic reactivity to novel foods. Cross‐reactivity is a property defined by individual antibodies to individual allergens. Quantitative information (including relative affinity) is required on cross‐reactivity in the allergic population and with specific allergens (rather than with whole extracts). Such information is still scarce, but with the increasing availability of purified (usually recombinant) allergens, such quantitative information will soon start to accumulate. It is expected that similarity in short stretches of the linear amino‐acid sequence is unlikely to result in relevant cross‐reactivity between two proteins unless there is similarity in the protein fold.

Possible induction of food allergy during mite immunotherapy

Sera of 17 patients receiving immunotherapy for house‐dust mite allergy were tested for IgE antibodies against snail and shrimp. Serum samples were taken at the start of immunotherapy and 14–20 months later. While the average IgE response to mite, Der p 1, and Der p 2 did not alter significantly, the average response to snail showed a significant increase. This included two conversions from negative to strongly positive. These novel IgE antibodies against snail were shown to be cross‐reactive with mite. Three patients had a positive RAST for shrimp. For one of them, a strong increase of IgE against shrimp (and snail) was observed. In 2/3 snail/shrimp‐positive sera, IgE antibodies against the cross‐reactive allergen tropomyosin from mite, snail, and shrimp were demonstrated. A clear IgE response to snail (> 10% binding in a snail RAST) was confirmed by a positive skin prick test (SPT) for 6/10 patients. The two patients with antitropomyosin IgE also had a positive SPT for shrimp, and demonstrated the oral allergy syndrome (OAS) after eating shrimp. The observations in this study indicate that house‐dust mite immunotherapy is accompanied by the induction of IgE against foods, including tropomyosin‐reactive IgE. Food allergy (OAS) was observed in patients that had IgE antibodies against this cross‐reactive allergen. In conclusion, induction of IgE during mite immunotherapy might occasionally cause allergy to foods of invertebrate animal origin.

Identification of a Cross-Reactive Allergen (Presumably Tropomyosin) in Shrimp, Mite and Insects

A monoclonal antibody to Dermatophagoides pteronyssinus is described that cross-reacts with an IgE-binding antigen present in insects, Crustacea (e.g. shrimp) and other invertebrates. By means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration and immunofluorescence it was shown that this monoclonal antibody presumably recognizes tropomyosin. Tropomyosin was shown to be involved in cross-reactivity between mite, shrimp and insects in shrimp-allergic patients.

Sensitization to Cor a 9 and Cor a 14 is highly specific for a hazelnut allergy with objective symptoms in Dutch children and adults

BACKGROUND Component-resolved diagnosis has been shown to improve the diagnosis of food allergy. OBJECTIVE We sought to evaluate whether component-resolved diagnosis might help to identify patients at risk of objective allergic reactions to hazelnut. METHOD A total of 161 hazelnut-sensitized patients were included: 40 children and 15 adults with objective symptoms on double-blind, placebo-controlled food challenges (DBPCFCs) and 24 adults with a convincing objective history were compared with 41 children and 41 adults with no or subjective symptoms on DBPCFCs (grouped together). IgE levels to hazelnut extract and single components were analyzed with ImmunoCAP. RESULTS IgE levels to hazelnut extract were significantly higher in children with objective than with no or subjective symptoms. In 13% of children and 49% of adults with hazelnut allergy with objective symptoms, only sensitization to rCor a 1.04 was observed and not to other water-soluble allergens. Sensitization to rCor a 8 was rare, which is in contrast to rCor a 1. Sensitization to nCor a 9, rCor a 14, or both was strongly associated with hazelnut allergy with objective symptoms. By using adapted cutoff levels, a diagnostic discrimination between severity groups was obtained. IgE levels to either nCor a 9 of 1 kUA/L or greater or rCor a 14 of 5 kUA/L or greater (children) and IgE levels to either nCor a 9 of 1 kUA/L or greater or rCor a 14 of 1 kUA/L or greater (adults) had a specificity of greater than 90% and accounted for 83% of children and 44% of adults with hazelnut allergy with objective symptoms. CONCLUSION Sensitization to Cor a 9 and Cor a 14 is highly specific for patients with objective symptoms in DBPCFCs as a marker for a more severe hazelnut allergic phenotype.

Asthma after consumption of snails in house‐dust‐mite‐allergic patients: a case of IgE cross‐reactivity

A group of 28 patients from Italy was studied who had asthma after consumption of snail. All patients also had asthma and/or rhinitis caused by house‐dust mite. RAST analyses confirmed the combined sensitization to snail and mite. In a few sera, IgE antibodies reactive with other foods of invertebrate origin (mussel and shrimp) were detected. RAST inhibition showed that most IgE antibodies against snail were cross‐reactive with house‐dust mite. In contrast, the mite RAST was not significantly inhibited by snail. This indicates that house‐dust mite was the sensitizing agent. Immunoblot analyses revealed multiple bands in snail extract recognized by IgE. In contrast to what has been described for cross‐reactivity between shrimp and mite, tropomyosin played only a minor role as a cross‐reactive allergen in these patients. The observations in this study indicate that snail consumption can cause severe asthmatic symptoms in house‐dust‐mite‐allergic patients. It might, therefore, be advisable to screen mite‐allergic asthma patients for allergy to snail and other invertebrate animal foods.

Hazelnut allergy: from pollen-associated mild allergy to severe anaphylactic reactions

Purpose of reviewHazelnut allergy can vary between mild oral symptoms and potentially dangerous anaphylaxis. There is a need to predict which subjects are at risk for severe reactions. In this study, possibilities for ‘component-resolved diagnosis’, based on sensitization to different allergens in hazelnut, are discussed. Recent findingsOne type of hazelnut allergy can be associated with sensitization to homologues of pollen allergens, predominantly birch, in hazelnut: Cor a 1 (Bet v 1) and Cor a 2 (profilin). These allergens account for relatively mild symptoms. However, subjects can also be sensitized to several other allergens in hazelnut that are related to more severe symptoms. These allergens are homologues of allergens in other nuts and peanut: Cor a 8 (lipid transfer protein) and Cor a 9 (11S globulin) and perhaps Cor a 11 (7S globulin). The clinical relevance of these and other potential hazelnut allergens has to be further defined. The diagnosis of hazelnut has to be confirmed by oral double-blind placebo-controlled food challenge. SummarySensitization to hazelnut can either be associated with mild oral symptoms, depending on sensitization to pollen, or with more serious allergic symptoms, related to sensitization to homologues of nut and peanut allergens.

How accurate and safe is the diagnosis of hazelnut allergy by means of commercial skin prick test reagents

Background: Allergy to tree nuts, like hazelnuts, ranks among the most frequently observed food allergies. These allergies can start at early childhood and are, in contrast to other food allergies, not always outgrown by the patient. Tree nut allergy is frequently associated with severe reactions. Diagnosis partially relies on in vivo testing by means of a skin prick test (SPT) using commercially available SPT reagents. Methods: Protein and allergen composition of nine commercial SPT solutions was evaluated using standard protein detection methods and specific immunoassays for measurement of five individual allergens. Diagnostic performance was assessed by SPT in 30 hazelnut-allergic subjects, of which 15 were provocation proven. Results: Protein concentrations ranged from 0.2–14 mg/ml. SDS-PAGE/silver staining revealed clear differences in protein composition. The major allergen Cor a 1 was present in all extracts but concentrations differed up to a factor 50. An allergen associated with severe symptoms, Cor a 8 (lipid transfer protein), was not detected on immunoblot in three products, and concentrations varied by more than a factor 100 as was shown by RAST inhibition. Similar observations were made for profilin, thaumatin-like protein and a not fully characterized 38-kD allergen. Ratios of individual allergens were variable among the nine extracts. SPT showed significant difference, and 6/30 patients displayed false-negative results using 3/9 products. Conclusion: Variability in the composition of products for the diagnosis of hazelnut allergy is extreme. Sometimes, allergens implicated in severe anaphylaxis are not detected by immunoblotting. These shortcomings in standardisation and quality control can potentially cause a false-negative diagnosis in subjects at risk of severe reactions to hazelnuts.

Peanut-specific IgE antibodies in asymptomatic Ghanaian children possibly caused by carbohydrate determinant cross-reactivity

Background The prevalence of peanut allergy has increased in developed countries, but little is known about developing countries with high peanut consumption and widespread parasitic infections. Objective We sought to investigate peanut allergy in Ghana. Methods In a cross-sectional survey among Ghanaian schoolchildren (n = 1604), data were collected on reported adverse reactions to peanut, peanut sensitization (serum specific IgE and skin reactivity), consumption patterns, and parasitic infections. In a subset (n = 43) IgE against Ara h 1, 2, 3, and 9 as well as cross-reactive carbohydrate determinants (CCDs) was measured by using ImmunoCAP. Cross-reactivity and biological activity were investigated by means of ImmunoCAP inhibition and basophil histamine release, respectively. Results Adverse reactions to peanut were reported in 1.5%, skin prick test reactivity in 2.0%, and IgE sensitization (≥0.35 kU/L) in 17.5% of participants. Moreover, 92.4% of those IgE sensitized to peanut (≥0.35 kU/L) had negative peanut skin prick test responses. Schistosoma haematobium infection was positively associated with IgE sensitization (adjusted odds ratio, 2.29; 95% CI, 1.37-3.86). In the subset IgE titers to Ara h 1, 2, 3, and 9 were low (<1.3 kU/L), except for 6 moderately strong reactions to Ara h 9. IgE against peanut was strongly correlated with IgE against CCDs (r = 0.89, P < .0001) and could be almost completely inhibited by CCDs, as well as S haematobium soluble egg antigen. Moreover, IgE to peanut showed poor biological activity. Conclusions Parasite-induced IgE against CCDs might account largely for high IgE levels to peanut in our study population of Ghanaian schoolchildren. No evidence of IgE-mediated peanut allergy was found.