Peanut allergen Ara h 3: isolation from peanuts and biochemical characterization

Probiotic VSL#3-induced TGF-β ameliorates food allergy inflammation in a mouse model of peanut sensitization through the induction of regulatory T cells in the gut mucosa

SCOPE

Among food allergies, peanut allergy is frequently associated with severe anaphylactic reactions. In the need for safe and effective therapeutic strategies, probiotics may be considered on the basis of their immunomodulatory properties. The aim of the present study was to investigate the immunological mediators involved in the effects of probiotic VSL#3 oral supplementation on Th2 inflammation and anaphylaxis in a mouse model of peanut allergy.

METHODS AND RESULTS

VSL#3 supplementation to peanut-sensitized mice was effective in ameliorating anaphylaxis and Th2-mediated inflammation, by promoting regulatory responses in the jejunum mucosa and in the mesenteric lymph node, as evaluated by ELISA, real-time PCR, histologic, and immunohistochemical analysis. Probiotic-induced TGF-β mediates its protective effects through the induction of regulatory T cells expressing FOXP3 and/or latency-associated peptide, as proven by in vivo blockade of TGF-β in VSL#3-treated mice with a neutralizing monoclonal antibody one day before challenge.

CONCLUSION

TGF-β, induced in the gut by VSL#3 supplementation, is capable of reducing the Th2 inflammation associated with food anaphylaxis in a mouse model of peanut sensitization. TGF-β acts through the induction/maintenance of regulatory T cells expressing FOXP3 and/or latency-associated peptide. Probiotics supplementation may represent an effective and safe strategy for treating food allergies in adult population.

Peanut Allergy, Allergen Composition, and Methods of Reducing Allergenicity: A Review

Peanut allergy affects 1-2% of the world's population. It is dangerous, and usually lifelong, and it greatly decreases the life quality of peanut-allergic individuals and their families. In a word, peanut allergy has become a major health concern worldwide. Thirteen peanut allergens are identified, and they are briefly introduced in this paper. Although there is no feasible solution to peanut allergy at present, many methods have shown great promise. This paper reviews methods of reducing peanut allergenicity, including physical methods (heat and pressure, PUV), chemical methods (tannic acid and magnetic beads), and biological methods (conventional breeding, irradiation breeding, genetic engineering, enzymatic treatment, and fermentation).

Moving from peanut extract to peanut components: towards validation of component-resolved IgE tests

BACKGROUND

Replacement of peanut extracts by recombinant peanut components is an important step in allergy serologic testing. Criteria are needed for the unbiased inclusion of patients into a study to validate such a replacement.

METHODS

Plasma samples from 64 peanut-positive children (42 reactors, 22 nonreactors in a double-blind, placebo-controlled food challenge) were used to compare IgE reactivity to six recombinant peanut allergens with reactivity to natural peanut proteins extracted at neutral or low pH. We tested the hypothesis that poor extractability of Ara h 9 and other basic allergens at neutral pH leads to under-representation of patients with such sensitization.

RESULTS

IgE reactivity to the components did not fully explain IgE reactivity to peanut extract in 5 of 32 reactors with IgE to peanut extract ≤100 kUA /l. IgE reactivity to components was stronger than to the extract in 11 plasma samples, which was largely due to a low Ara h 8 reactivity of the extract. IgE reactivity to Ara h 9 was much lower than reactivity to other basic proteins, some of which bound IgE well in the RAST, but lost IgE reactivity upon immunoblotting.

CONCLUSIONS

Conventional peanut extracts are deficient in significant IgE-binding components. The inclusion of patients for a validation study should be based on serology performed with improved peanut reagents to avoid a bias against these under-represented, potentially important allergens. To judge clinical relevance of an allergen, the reagent used for inclusion of patients needs to be efficient in detecting IgE to this component.

Comparative proteomic analysis and IgE binding properties of peanut seed and testa (skin)

To investigate the protein composition and potential allergenicity of peanut testae or skins, proteome analysis was conducted using nanoLC-MS/MS sequencing. Initial amino acid analysis suggested differences in protein compositions between the blanched seed (skins removed) and skin. Phenolic compounds hindered analysis of proteins in skins when the conventional extraction method was used; therefore, phenol extraction of proteins was necessary. A total of 123 proteins were identified in blanched seed and skins, and 83 of the proteins were common between the two structures. The skins contained all of the known peanut allergens in addition to 38 proteins not identified in the seed. Multiple defense proteins with antifungal activity were identified in the skins. Western blotting using sera from peanut-allergic patients revealed that proteins extracted from both the blanched seed and skin bound significant levels of IgE. However, when phenolic compounds were present in the skin protein extract, no IgE binding was observed. These findings indicate that peanut skins contain potentially allergenic proteins; however, the presence of phenolic compounds may attenuate this effect.

Analysis of crude protein and allergen abundance in peanuts (Arachis hypogaea cv. Walter) from three growing regions in Australia

The effects of plant growth conditions on concentrations of proteins, including allergens, in peanut ( Arachis hypogaea L.) kernels are largely unknown. Peanuts (cv. Walter) were grown at five sites (Taabinga, Redvale, Childers, Bundaberg, and Kairi) covering three commercial growing regions in Queensland, Australia. Differences in temperature, rainfall, and solar radiation during the growing season were evaluated. Kernel yield varied from 2.3 t/ha (Kairi) to 3.9 t/ha (Childers), probably due to differences in solar radiation. Crude protein appeared to vary only between Kairi and Childers, whereas Ara h 1 and 2 concentrations were similar in all locations. 2D-DIGE revealed significant differences in spot volumes for only two minor protein spots from peanuts grown in the five locations. Western blotting using peanut-allergic serum revealed no qualitative differences in recognition of antigens. It was concluded that peanuts grown in different growing regions in Queensland, Australia, had similar protein compositions and therefore were unlikely to show differences in allergenicity.

Redefining the major peanut allergens

Food allergy has become a major public health concern in westernized countries, and allergic reactions to peanuts are particularly common and severe. Allergens are defined as antigens that elicit an IgE response, and most allergenic materials (e.g., pollens, danders, and foods) contain multiple allergenic proteins. This has led to the concept that there are "major" allergens and allergens of less importance. "Major allergens" have been defined as allergens that bind a large amount of IgE from the majority of patients and have biologic activity. However, the ability of an allergen to cross-link complexes of IgE and its high-affinity receptor FcεRI (IgE/FcεRI), which we have termed its allergic effector activity, does not correlate well with assays of IgE binding. To identify the proteins that are the most active allergens in peanuts, we and others have employed in vitro model assays of allergen-mediated cross-linking of IgE/FcεRI complexes and have demonstrated that the most potent allergens are not necessarily those that bind the most IgE. The importance of a specific allergen can be determined by measuring the allergic effector activity of that allergen following purification under non-denaturing conditions and by specifically removing the allergen from a complex allergenic extract either by chromatography or by specific immunodepletion. In our studies of peanut allergens, our laboratory has found that two related allergens, Ara h 2 and Ara h 6, together account for the majority of the effector activity in a crude peanut extract. Furthermore, murine studies demonstrated that Ara h 2 and Ara h 6 are not only the major elicitors of anaphylaxis in this system, but also can effectively desensitize peanut-allergic mice. As a result of these observations, we propose that the definition of a major allergen should be based on the potency of that allergen in assays of allergic effector activity and demonstration that removal of that allergen from an extract results in loss of potency. Using these criteria, Ara h 2 and Ara h 6 are the major peanut allergens.

The 11S globulin Sin a 2 from yellow mustard seeds shows IgE cross-reactivity with homologous counterparts from tree nuts and peanut

Background

The 11S globulin Sin a 2 is a marker to predict severity of symptoms in mustard allergic patients. The potential implication of Sin a 2 in cross-reactivity with tree nuts and peanut has not been investigated so far. In this work, we studied at the IgG and IgE level the involvement of the 11S globulin Sin a 2 in cross-reactivity among mustard, tree nuts and peanut.

Methods

Eleven well-characterized mustard-allergic patients sensitized to Sin a 2 were included in the study. A specific anti-Sin a 2 serum was obtained in rabbit. Skin prick tests (SPT), enzyme-linked immunosorbent assay (ELISA), immunoblotting and IgG or IgE-inhibition immunoblotting experiments using purified Sin a 2, Sin a 1, Sin a 3, mustard, almond, hazelnut, pistachio, walnut or peanut extracts were performed.

Results

The rabbit anti-Sin a 2 serum showed high affinity and specificity to Sin a 2, which allowed us to demonstrate that Sin a 2 shares IgG epitopes with allergenic 11S globulins from tree nuts (almond, hazelnut, pistachio and walnut) but not from peanut. All the patients included in the study had positive skin prick test to tree nuts and/or peanut and we subdivided them into two different groups according to their clinical symptoms after ingestion of such allergenic sources. We showed that 11S globulins contain conserved IgE epitopes involved in cross-reactivity among mustard, tree nuts and peanut as well as species-specific IgE epitopes.

Conclusions

The allergenic 11S globulin Sin a 2 from mustard is involved in cross-reactivity at the IgE level with tree nuts and peanut. Although the clinical relevance of the cross-reactive IgE epitopes present in 11S globulins needs to be investigated in further detail, our results contribute to improve the diagnosis and management of mustard allergic patients sensitized to Sin a 2.

Significance of Ara h 2 in clinical reactivity and effect of cooking methods on allergenicity

BACKGROUND

The prevalence and clinical severity of peanut allergy vary between Western countries and Asia. It has been suggested that cooking methods are responsible for this discrepancy.

OBJECTIVES

To evaluate the specific IgE responses to major peanut allergens in peanut allergic Korean children and to examine the influence of different cooking methods on peanut proteins.

METHODS

Raw peanut protein extracts were immunolabeled with serum samples from 42 children with a level of peanut specific IgE of 15 kUA/L or higher to detect specific binding to Ara h 1, Ara h 2, and Ara h 3. Clinical severity scores were assessed on a scale of 0 to 5. Protein extracts from boiled, roasted, fried, and pickled peanuts were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with pooled serum samples from 7 patients.

RESULTS

Most patients' serum samples reacted with Ara h 1 (76.2%) and Ara h 3 (78.6%) from raw peanuts, whereas only 53.0% of patients had specific IgE against Ara h 2. IgE binding to Ara h 2 was more prevalent in patients with more severe reaction than in those with mild reactions. IgE binding to Ara h 2 was increased by roasting, but there was significantly less IgE binding after vinegar treatment.

CONCLUSION

Our results suggest that Ara h 2 is an important allergen to predict clinical symptoms but less prevalent in Korean children than in Western children. This finding may be attributed in part to different cooking methods and dietary habits among regions.

Size-selective fractionation and visual mapping of allergen protein chemistry in Arachis hypogaea

Peanuts (Arachis hypogaea) in addition to milk, eggs, fish, crustaceans, wheat, tree nuts, and soybean are commonly referred to as the "big eight" foods that contribute to the majority of food allergies worldwide. Despite the severity of allergic reactions and growing prevalence in children and adults, there is no cure for peanut allergy, leaving avoidance as the primary mode of treatment. To improve analytical methods for peanut allergen detection, researchers must overcome obstacles involved in handling complex food matrices while attempting to decipher the chemistry that underlies allergen protein interactions. To address such challenges, we conducted a global proteome characterization of raw peanuts using a sophisticated GELFrEE-PAGE-LC-MS/MS platform consisting of gel-based protein fractionation followed by mass spectrometric identification. The in-solution mass-selective protein fractionation: (1) enhances the number of unique peptide identifications, (2) provides a visual map of protein isoforms, and (3) aids in the identification of disulfide-linked protein complexes. GELFrEE-PAGE-LC-MS/MS not only overcomes many of the challenges involved in the study of plant proteomics, but enriches the understanding of peanut protein chemistry, which is typically unattainable in a traditional bottom-up proteomic analysis. A global understanding of protein chemistry in Arachis hypogaea ultimately will aid the development of improved methods for allergen detection in food.

Purification and characterization of Ara h1 and Ara h3 from four peanut market types revealed higher order oligomeric structures

This study aimed to purify and characterize the peanut allergens Ara h1 and Ara h3 from four cultivars that represent the four major market types to provide better understanding of the molecular organization of oligomers in different market types. The chromatographic profiles of Ara h1 and Ara h3 from the four cultivars obtained from anion exchange chromatography were similar. However, they differed in the distribution of trimeric and hexameric structures of Ara h3 isolated by size exclusion chromatography. The Menzies (Runner market type) and Walter (Spanish market type) cultivars, wherein Ara h3 proteins consist of two acidic subunits, exhibited trimeric and hexameric conformations proportionally. However, the Middleton (Virginia market type) and Kelinci (Valencia market type) cultivars, wherein Ara h3 proteins consist of three acidic subunits, showed predominantly a hexameric structure. The oligomeric structures of the purified Ara h1 demonstrated strong IgE binding properties, whereas the allergenic property of the oligomeric Ara h3 could not be performed due to lack of availability of specific IgE. In addition, the polyclonal antibodies raised against the purified Ara h1 and Ara h3 showed highly specific binding to their respective antigens.

Measurement of Ara h 1-, 2-, and 3-specific IgE antibodies is useful in diagnosis of peanut allergy in Japanese children

BACKGROUND

Food challenges are time-consuming, expensive, and not always possible to perform. Therefore, new tools to diagnose food allergy are desired. The aim was to evaluate IgE antibodies to peanut allergens in the diagnosis of peanut allergy in Japanese children using ImmunoCAP(®) and IgE immunoblotting.

METHODS

The study included 2-13-yr-old consecutive patients (n = 57) referred to our specialist clinic for investigation of current peanut allergy using food challenge. All children had a previous doctor's diagnosis of peanut allergy and were on elimination diet. Serum samples were analyzed for IgE reactivity to peanut, recombinant (r) Ara h 1, 2, 3, 5, 8, and 9. IgE immunoblotting (n = 23) was performed using extracts from raw and roasted peanut.

RESULTS

Twenty-six of the children failed (allergic group), and 31 passed the peanut challenge (tolerant group). The rAra h 2 ImmunoCAP test was superior in its ability to differentiate between children in the allergic and tolerant groups with a sensitivity and specificity of 88% and 84%, respectively (cutoff, 0.35 kU(A)/l). The combination of rAra h 1, 2, and 3 resulted in a higher specificity (94%) when IgE to all of them was the criteria for positivity. ImmunoCAP generally showed a good agreement with immunoblotting using both raw and roasted peanut for IgE reactivity to Ara h 1, 2, and 3.

CONCLUSIONS

Measurement of IgE antibodies to rAra h 1, 2, and 3 is useful in the diagnosis of peanut allergy and in the investigation of reactions to raw and roasted peanut.

Identification of a new IgE-binding epitope of peanut oleosin that cross-reacts with buckwheat

Peanut and buckwheat induce a severe allergic reaction, anaphylaxis, which is considered to be mediated by immunoglobulin E (IgE). We identified in this study a new IgE-binding epitope of the peanut allergen that cross-reacted with buckwheat. The phosphate-buffered saline-soluble fraction of buckwheat inhibited the binding between IgE and the peanut allergen. A cross-reactive peptide was isolated from the α-chymotrypsin hydrolysate of peanut. Based on the amino acid sequence and mass spectrometric analysis data, the peptide was identified as Ser-Asp-Gln-Thr-Arg-Thr-Gly-Tyr (SDQTRTGY); this sequence is identical to amino acids 2-9 in the N-terminal hydrophilic domain of oleosin 3 which is located on the surface of the lipid storage body. Synthetic SDQTRTGY was found to bind with IgE in the sera of all eight peanut-allergic patients tested. Since many foods of plant origin contain oleosin, the possibility of an anaphylactic cross-reaction in allergic patients should always be considered.

Patterns of sensitization to peanut allergen components in Taiwanese Preschool children

BACKGROUND/PURPOSE

Peanut allergy is very common in Western countries, although it is seldom encountered in Eastern countries. Peanuts are comprised of at least 11 components, but the contribution to clinical symptoms by each component in each individual is not known. This study investigated the distributions of sensitivity to peanut allergen components among Taiwanese children who were sensitized to peanuts and followed the evolution of sensitization patterns to these components.

METHODS

We enrolled 29 preschool children (age=2.11±1.36 years) who were sensitized to peanuts above class 3. Serum was analyzed for specific immunoglobulin E (IgE) antibodies to recombinant Ara h 1, Ara h 2, Ara h 3, Ara h 8, and Ara h 9. Allergen component-specific IgE ≥0.35 kU(A)/L was defined as positive. Eighteen children were retested 22.64±5.1 months later. Peanut allergy symptoms were recorded from detailed questionnaires.

RESULTS

The percentages of children sensitized to Ara h 1, 2, 3, 8, and 9 were, respectively, 51.8%, 65.5%, 62.1%, 13.8%, and 24.1%. Regarding changing patterns of peanut component sensitization at follow-up, children with clinical symptoms to peanuts had persistent elevations of Ara h 2-specific IgE: 12.6±1.01 up to 34.15±19.4 kU(A)/L; p=0.144. In contrast, Ara h 2 concentrations decreased significantly in children without clinical symptoms. Ara h 8 and 9 were nonspecific for children with or without symptoms.

CONCLUSION

Ara h 1, Ara h 2, and Ara h 3 were major components contributing to peanut sensitization in Taiwanese children. Ara h 2 was probably the most important component that contributed to clinical symptoms and remained steady in children who had peanut allergy.

Antigen-fixed leukocytes tolerize Th2 responses in mouse models of allergy

Allergic diseases, including asthma and food allergies, are an increasing health concern. Immunotherapy is an effective therapeutic approach for many allergic diseases but requires long dose escalation periods and has a high risk of adverse reactions, particularly in food allergy. New methods to safely induce Ag-specific tolerance could improve the clinical approach to allergic disease. We hypothesized that Ag-specific tolerance induced by the i.v. injection of Ags attached to the surface of syngeneic splenic leukocytes (Ag-coupled splenocytes [Ag-SPs]) with the chemical cross-linking agent ethylene-carbodiimide, which effectively modulate Th1/Th17 diseases, may also safely and efficiently induce tolerance in Th2-mediated mouse models of allergic asthma and food allergy. Mice were tolerized with Ag-SP before or after initiation of OVA/alum-induced allergic airway inflammation or peanut-induced food allergy. The effects on disease pathology and Th2-directed cytokine and Ab responses were studied. Ag-SP tolerance prevented disease development in both models and safely tolerized T cell responses in an Ag-specific manner in presensitized animals. Prophylactically, Ag-SP efficiently decreased local and systemic Th2 responses, eosinophilia, and Ag-specific IgE. Interestingly, Ag-SP induced Th2 tolerance was found to be partially dependent on the function of CD25(+) regulatory T cells in the food allergy model, but was regulatory T cell independent in the model of allergic airway inflammation. We demonstrate that Ag-SP tolerance can be rapidly, safely, and efficiently induced in murine models of allergic disease, highlighting a potential new Ag-specific tolerance immunotherapy for Th2-associated allergic diseases.

Influence of enzymatic hydrolysis on the allergenicity of roasted peanut protein extract

BACKGROUND

Peanut allergy is recognized as one of the most severe food allergies. Some studies have investigated the effects of enzymatic treatments on the in vitro immunological reactivity of members of the Leguminosae family, such as the soybean, chickpea and lentil. Nevertheless, there are only a few studies carried out with sera from patients with a well-documented allergy.

METHODS

Roasted peanut protein extract was hydrolyzed by the sequential and individual action of 2 food-grade enzymes, an endoprotease (Alcalase) and an exoprotease (Flavourzyme). Immunoreactivity to roasted peanut extract and hydrolyzed samples was evaluated by means of IgE immunoblot, ELISA and 2-dimensional electrophoresis using sera from 5 patients with a clinical allergy to peanuts and anti-Ara h 1, anti-Ara h 2 and anti-Ara h 3 immunoblots.

RESULTS

Immunoblot and ELISA assays showed an important decrease of IgE reactivity and Ara h 1, Ara h 2 and Ara h 3 levels in the first 30 min of hydrolyzation with Alcalase. In contrast, individual treatment with Flavourzyme caused an increase in IgE reactivity detected by ELISA at 30 min and led to a 65% inhibition of IgE reactivity at the end of the assay (300 min). Ara h 1 and the basic subunit of Ara h 3 were still recognized after treatment with Flavourzyme for 300 min.

CONCLUSION

Hydrolysis with the endoprotease Alcalase decreases IgE reactivity in the soluble protein fraction of roasted peanut better than hydrolysis with the exoprotease Flavourzyme.

Digestion of peanut allergens Ara h 1, Ara h 2, Ara h 3, and Ara h 6: a comparative in vitro study and partial characterization of digestion-resistant peptides

SCOPE

There are differences in stability to pepsin between the major allergens in peanut; however, data are from different reports using different digestion models. This study provides a comprehensive comparison of the digestibility of the major peanut allergens.

METHODS AND RESULTS

Peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 were incubated with pepsin to mimic the effect of gastric digestion. Samples were analyzed using SDS-PAGE. To further investigate resistance to digestion, Ara h 2 was additionally subjected to digestion with trypsin and residual peptides were characterized. Ara h 1 and Ara h 3 were rapidly hydrolyzed by pepsin. On the contrary, Ara h 2 and Ara h 6 were resistant to pepsin digestion, even at very high concentrations of pepsin. In fact, limited proteolysis could only be demonstrated by SDS-PAGE performed under reducing conditions, indicating an important role for the disulfide bridges in maintaining the quaternary structure of Ara h 2 and Ara h 6. Trypsin digestion of Ara h 2 similarly resulted in large residual peptides and these were identified.

CONCLUSION

Ara h 2 and Ara h 6 are considerably more stable towards digestion than Ara h 1 and Ara h 3.

Anti-acid medication as a risk factor for food allergy

An important feature for oral allergens is their digestion-resistance during gastrointestinal transit. For some oral allergens, digestion stability is an innate feature, whereas digestion-labile antigens may only persist in times of impairment of the digestive system. In this review, we collect evidence from mouse and human studies that besides the inherent molecular characteristics of a food protein, the stomach function is decisive for the allergenic potential. Gastric acid levels determine the activation of gastric pepsin and also the release of pancreatic enzymes. When anti-ulcer drugs inhibit or neutralize gastric acid, they allow persistence of intact food allergens and protein-bound oral drugs with enhanced capacity to sensitize and elicit allergic reactions via the oral route. Mouse studies further suggest that maternal food allergy arising from co-application of a food protein with anti-acid drugs results in a Th2-biased immune response in the offspring. Especially, anti-ulcer drugs containing aluminum compounds act as Th2 adjuvants. Proton pump inhibitors act on proton secretion but also on expression of the morphogen Sonic hedgehog, which has been related to the development of atrophic gastritis. On the other hand, atrophic gastritis and resulting hypoacidity have previously been correlated with enhanced sensitization risk to food allergens in elderly patients. In summary, impairment of gastric function is a documented risk factor for sensitization against oral proteins and drugs.

Liquid chromatography and mass spectrometry in food allergen detection

Food allergy is an important issue in the field of food safety because of the hazards for affected persons and the hygiene requirements and legal regulations imposed on the food industry. Consumer protection and law enforcement require suitable analytical techniques for the detection of allergens in foods. Immunological methods are currently preferred; however, confirmatory alternatives are needed. The determination of allergenic proteins by liquid chromatography and mass spectrometry has greatly advanced in recent years, and gel-free allergenomics is becoming a routinely used approach for the identification and quantitation of food allergens. The present review provides a brief overview of the principles of proteomic procedures, various chromatographic set ups, and mass spectrometry instrumentation used in allergenomics. A compendium of published liquid chromatography methods, proteomic analyses, typical marker peptides, and quantitative assays for 14 main allergy-causing foods is also included.

Partial characterization of red gram (Cajanus cajan L. Millsp) polypeptides recognized by patients exhibiting rhinitis and bronchial asthma

We sought to assess the allergenic potential of red gram by identifying and characterizing the responsible proteins. Immunoblotting was performed to detect IgE binding proteins. Identities of these proteins were confirmed by mass spectrometry. To evaluate allergenic potential, BALB/c mice were sensitized with red gram proteins and levels of specific immunoglobulins, histamine, Th2 cytokines were measured. Allergenic response was evident by significant increase in specific IgE, IgG1, histamine and Th2 cytokine levels. Prominent anaphylactic symptoms, discernible histopathological responses and down regulation of IFN-gamma levels give strong support towards allergenicity of red gram proteins. IgE immunoblot detected five proteins; one of 66 kDa, three of 45 kDa (pI of approximately 5.3, 5.9 and 6.6) and one of 30 kDa. All these proteins showed homology to known allergens of soybean (different subunits of beta-conglycinin), lentil (Len c1 and Len c2), peanut (Ara h1) and pea (vicilin). In conclusion, five novel IgE binding proteins (namely Caj c1, Caj c2, Caj c3, Caj c4 and Caj c5) were identified as putative clinically relevant allergens.

T cell responses to major peanut allergens in children with and without peanut allergy

BACKGROUND

T cell responses involved in peanut allergy are poorly understood.

OBJECTIVE

To investigate T cell responses towards major peanut allergens in peanut-allergic (PA) subjects compared with peanut-sensitized (PS) non-allergic children and non-atopic (NA) controls.

METHODS

Eighteen PA children, seven non-allergic PS children and 11 NA adults were included. Peripheral blood mononuclear cells were stimulated with a crude peanut extract (CPE). Short-term T cell lines were generated and subsequently stimulated with CPE and purified Ara h 1, Ara h 2, Ara h 3 and Ara h 6. The proliferation and production of IL-13, IFN-gamma, IL-10 and TNF-alpha were analysed.

RESULTS

Proliferation to CPE and major allergens was enhanced in PA subjects. The primary response to CPE was comparable with PS subjects, with increased production of IL-13 and IFN-gamma compared with NA. Production of IL-10 was not observed. In short-term T cell lines, the response to CPE was stronger in PA than in PS and NA subjects. Only PA children had a detectable response to major peanut allergens, characterized by IL-13 production. The response was the highest after Ara h 3 stimulation, and the lowest after Ara h 2 stimulation. No significant correlation was observed between peanut-specific IgE levels and T cell responses to CPE.

CONCLUSION

T cell responses to CPE in PA and PS children were characterized by Th1 and Th2 cytokines. Only PA children showed enhanced Th2 responses to Ara h 1, Ara h 3 and Ara h 6.

The non-specific lipid transfer protein, Ara h 9, is an important allergen in peanut

BACKGROUND

Plant food allergy in the Mediterranean area is mainly caused by non-specific lipid transfer proteins (nsLTP). The aim of this study was to characterize peanut nsLTP in comparison with peach nsLTP, Pru p 3, and assess its importance in peanut allergy.

METHODS

Peanut-allergic patients from Spain (n=32) were included on the basis of a positive case history and either a positive skin prick test or specific IgE to peanut. For comparison, sera of 41 peanut-allergic subjects from outside the Mediterranean area were used. Natural Ara h 9 and two isoforms of recombinant Ara h 9, expressed in Pichia pastoris, were purified using a two-step chromatographic procedure. Allergen characterization was carried out by N-terminal sequencing, circular dichroism (CD) spectroscopy, immunoblotting, IgE inhibition tests and basophil histamine release assays.

RESULTS

Compared with natural peanut nsLTP, the recombinant proteins could be purified in high amounts from yeast supernatant (> or =45 mg/L). The identity of the proteins was verified by N-terminal amino acid sequencing and with rabbit nsLTP-specific antibodies. CD spectroscopy revealed similar secondary structures for all preparations and Pru p 3. The Ara h 9 isoforms showed 62-68% amino acid sequence identity with Pru p 3. IgE antibody reactivity to rAra h 9 was present in 29/32 Spanish and 6/41 non-Mediterranean subjects. Recombinant Ara h 9 showed strong cross-reactivity to nPru p 3 and similar IgE-binding capacity as nAra h 9. The two Ara h 9 isoforms displayed similar IgE reactivity. In peanut-allergic patients with concomitant peach allergy, Ara h 9 showed a weaker allergenic potency than Pru p 3 in histamine release assays.

CONCLUSIONS

Ara h 9 is a major allergen in peanut-allergic patients from the Mediterranean area. Ara h 9 is capable of inducing histamine release from basophils, but to a lesser extent than Pru p 3.

Capacity of purified peanut allergens to induce degranulation in a functional in vitro assay: Ara h 2 and Ara h 6 are the most efficient elicitors

BACKGROUND

Peanut is a most common and potent food allergen. Many peanut allergens have been characterized using, in particular, IgE-binding studies.

OBJECTIVES

We optimized an in vitro functional assay to assess the capacity of peanut allergens to degranulate humanized rat basophilic leukaemia cells, RBL SX-38 cells, after sensitization by serum IgE from peanut-allergic patients. We thus compared the activity of the main peanut allergens, i.e. Ara h 1, Ara h 2, Ara h 3 and Ara h 6, purified from roasted peanut.

METHODS

Sera of 12 peanut-allergic patients were collected and total and peanut-specific IgE were measured. They were used to sensitize RBL SX-38 cells and the degranulation was induced by incubation with ranging concentrations of a whole peanut protein extract or of purified peanut allergens. The mediator release was quantified by the determination of beta-hexosaminidase activity in the supernatant. The intensity of the degranulation was expressed as maximum release and as EC50, corresponding to the dose of allergen that induced 50% of the maximum release.

RESULTS

For each serum, only 10 IU/mL of human IgE was necessary to sensitize the cells and obtain an optimal degranulation. With all the allergens, the release was positively correlated with the concentration of allergen-specific IgE in the serum used to sensitize the cells. The medians of EC50 obtained for Ara h 2 and Ara h 6 were 2.1 and 2.8 pm, respectively, while they were much higher for Ara h 3 and Ara h 1 (65 and 150 pm, respectively).

CONCLUSION

The RBL SX-38 release assay proved to be sensitive, specific and reproducible. It allowed the comparison of the degranulation potential of different peanut allergens. For all the sera tested, Ara h 2 and Ara h 6 were more potent than Ara h 1 or Ara h 3.

Effector activity of peanut allergens: a critical role for Ara h 2, Ara h 6, and their variants

RATIONALE

An important property of allergens is their ability to cross-link IgE and activate mast cells and basophils. The effector activity of peanut allergens has not been well characterized.

METHODS

Crude extracts of fresh peanut flour were fractionated by gel filtration. Effector function was assayed by measuring degranulation of RBL SX-38 cells sensitized with IgE from individual sera and from pools of sera of peanut-allergic donors.

RESULTS

Following gel filtration, 75 +/- 7% of the applied protein and 76 +/- 16% (n=3) of the applied activity (assayed with a pool of 11 sera) were recovered in the resultant fractions. The majority (85 +/- 2%; n=3) of the recovered activity resided in a fraction with a theoretical average molecular weight of approximately 20 kDa and a range of 13-25 kDa. When all the individual fractions were recombined, the measured activity was similar to that of the original extract [140 +/- 43% when measured with a pool of serum (n=2) and 66 +/- 7% when measured with individual sera (n=4)]; when all individual fractions excluding the 20 kDa fraction were recombined, the measured activity was only 8 +/- 2% (n=2) of the original extract when assayed with the serum pool and 10 +/- 4% (n=3) when assayed with the individual sera. Two-dimensional gel electrophoresis of this biologically active fraction revealed >60 protein spots. Analysis of 50 of the most prominent spots by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry and of the full mixture by automated tandem mass spectrometry coupled to online capillary liquid chromatography revealed that >97% of the protein mass consisted of Ara h 2.0101, Ara h 2.0201, Ara h 6 isoforms, and variants of these proteins.

CONCLUSIONS

Ara h 2 and Ara h 6 account for the majority of the effector activity found in a crude peanut extract.

Resolution and identification of major peanut allergens using a combination of fluorescence two-dimensional differential gel electrophoresis, Western blotting and Q-TOF mass spectrometry

Peanut allergy is triggered by several proteins known as allergens. In this study, the complexity the peanut allergome is investigated with proteomic tools. The strength of this investigation resides in combining the high-resolving power and reproducibility of fluorescence two-dimensional differential gel electrophoresis with specific immunological detection as well as polypeptide sequencing by high-resolution mass spectrometry. Matching of the peanut proteins in 2D gels was achieved by differential labelling whereby peanut proteins and purified allergens (Ara h 1, Ara h 2 or Ara h 3/4) were run on the same gel. Ten protein spots on a mass line of ca. 63-68 kDa were likely to correspond to Ara h 1. Two doublets on two different mass lines at ca. 16 and 18 kDa matched with purified allergen Ara h 2. The basic and acidic sub-units of Ara h 3/4 were observed at masses of ca. 25 kDa and 40-45 kDa, respectively. Subsequently the antibody-binding capacity of spots corresponding to peanut allergens was investigated by Western blotting of 2D gels using antibodies (IgY) raised against Ara h 1, Ara h 2 and the recombinant 40 kDa sub-unit of Ara h 3/4. Final confirmation of the identity of the protein spots matched after 2D electrophoresis and identified by Western blotting was obtained by in-gel digestion of protein spots and analysis by quadrupole time-of-flight mass spectrometry. By using the method developed in our work, the location and identification of two different isoforms of the allergen Ara h 1, the allergen Ara h 2 and six isoforms of the allergen Ara h 3/4 in 2D peanut protein maps was established.

Two cases of pollen-food allergy syndrome to soy milk diagnosed by skin prick test, specific serum immunoglobulin E and microarray analysis

Oral allergy syndrome to soy milk is classified as a phenotype of pollen-food allergy syndrome (PFAS). As causative antigens, Gly m 4 (Bet v 1 homolog, 17 kD) and oleosin (23 kD), have been reported. In this study, we report two cases of PFAS to soy milk. Both cases showed positive reactions to soy milk in skin prick tests (SPT) and to Gly m 4 in specific serum immunoglobulin (Ig)E antibody. When we measured specific serum IgE antibody of soy-related proteins using a new laboratory testing method, microarray analysis, both cases showed a positive reaction for Bet v 1. One case was weakly positive for a soybean protein, beta-conglycinin. Other results for reactivity to soy, peanut, cross-reactive carbohydrate determinants and profilin were negative. Based on these results, we diagnosed the two cases as PFAS to Gly m 4. We also performed protein microarray analysis and found it useful as a screening test for immediate allergy, such as PFAS.

Effects of transglutaminase catalysis on the functional and immunoglobulin binding properties of peanut flour dispersions containing casein

The functionality of light roasted peanut flour (PF) dispersions containing supplemental casein (CN) was altered after polymerization with microbial transglutaminase (TGase). The formation of high molecular weight covalent cross-links was observed with likely development of PF-PF, PF-CN, and CN-CN polymers based on Western blotting patterns visualized using antiserum directed against Ara h 1, Ara h 2, Ara h 3, or casein. The gelling temperature of TGase-treated PF dispersions containing 2.5% CN was significantly raised compared to the nontreated PF-CN control solutions. Furthermore, the gel strength and water holding capacity of cross-linked PF-CN test samples containing 5% CN was increased, while the yield stress and apparent viscosity were lowered compared to control dispersions. The immunological staining patterns were also changed where, in some cases, IgE binding to TGase-treated PF-CN fractions appeared less reactive compared to equivalent polymeric PF dispersions lacking supplemental CN and non-cross-linked PF-CN samples. Perhaps, covalent modification masked IgE peanut protein binding epitopes, at least to some degree, on an individual patient basis. Casein proved to be an effective cosubstrate with PF for creating Tgase modified PF-CN dispersions for use as a novel high protein food ingredient.

Impairing oral tolerance promotes allergy and anaphylaxis: a new murine food allergy model

BACKGROUND

Food allergy is a disorder in which antigenic food proteins elicit immune responses. Animal models of food allergy have several limitations that influence their utility, including failure to recapitulate several key immunologic hallmarks. Consequently, little is known regarding the pathogenesis and mechanisms leading to food allergy. Staphylococcus aureus-derived enterotoxins, a common cause of food contamination, are associated with antigen responses in atopic dermatitis.

OBJECTIVE

We hypothesized that S aureus-derived enterotoxins might influence the development of food allergy. We examined the influence of administration of staphylococcal enterotoxin B (SEB) with food allergens on immunologic responses and compared these responses with those elicited by a cholera toxin-driven food allergy model.

METHODS

Oral administration of ovalbumin or whole peanut extract with or without SEB was performed once weekly. After 8 weeks, mice were challenged with oral antigen alone, and the physiologic and immunologic responses to antigen were studied.

RESULTS

SEB administered with antigen resulted in immune responses to the antigen. Responses were highly T(H)2 polarized, and oral challenge with antigen triggered anaphylaxis and local and systemic mast cell degranulation. SEB-driven sensitization induced eosinophilia in the blood and intestinal tissues not observed with cholera toxin sensitization. SEB impaired tolerance specifically by impairing expression of TGF-beta and regulatory T cells, and tolerance was restored with high-dose antigen.

CONCLUSIONS

We demonstrate a new model of food allergy to oral antigen in common laboratory strains of mice that recapitulates many features of clinical food allergy that are not seen in other models. We demonstrate that SEB impairs oral tolerance and permits allergic responses.

Purification and characterization of the 7S vicilin from Korean pine (Pinus koraiensis)

Pine nuts are economically important as a source of human food. They are also of medical importance because numerous pine nut allergy cases have been recently reported. However, little is known about the proteins in pine nuts. The purpose of this study was to purify and characterize pine nut storage proteins. Reported here is the first detailed purification protocol of the 7S vicilin-type globulin from Korean pine (Pinus koraiensis) by gel filtration, anion exchange, and hydrophobic interaction chromatography. Reducing SDS-PAGE analysis indicated that purified vicilin consists of four major bands, reminiscent of post-translational protease cleavage of storage proteins during protein body packing in other species. The N-terminal ends of vicilin peptides were sequenced by Edman degradation. Circular dichroism (CD) and differential scanning calorimetry (DSC) analyses revealed that pine nut vicilin is stable up to 80 degrees C and its folding-unfolding equilibrium monitored by intrinsic fluorescence can be interpreted in terms of a two-state model.

Legumin allergens from peanuts and soybeans: effects of denaturation and aggregation on allergenicity

Legumin proteins Ara h 3 from peanuts and glycinin from soybeans are increasingly described as important allergens. The stability of an allergen's IgE binding capacity towards heating and digestion is considered an important characteristic for food allergens. We investigated the effects of heating and digestion on the IgE binding of Ara h 3 and glycinin. Both proteins are relatively stable to denaturation, having denaturation temperatures ranging from 70 to 92 degrees C, depending on their quaternary structure and the ionic strength. Aggregates were formed upon heating, which were partly soluble for glycinin. Heating slightly decreased the pepsin digestion rate of both allergens. However, heating did not affect the IgE binding capacity of the hydrolyzates, as after only 10 min of hydrolysis no IgE binding could be detected any more in all samples. Peanut allergen Ara h 1, when digested under equal conditions, still showed IgE binding after 2 h of hydrolysis. Our results indicate that the IgE binding capacity of legumin allergens from peanuts and soybeans does not withstand peptic digestion. Consequently, these allergens are likely unable to sensitize via the gastro-intestinal tract and cause systemic food allergy symptoms. These proteins might thus be less important allergens than was previously assumed.

Peanut allergy

Peanut allergy has become a major health concern worldwide, especially in developed countries. However, the reasons for this increasing prevalence over the past several decades are not well understood. Because of the potentially severe health consequences of peanut allergy, those suspected of having had an allergic reaction to peanuts deserve a thorough evaluation. All patients with peanut allergy should be given an emergency management plan, as well as epinephrine and antihistamines to have on hand at all times. Patients and families should be taught to recognise early allergic reactions to peanuts and how to implement appropriate peanut-avoidance strategies. It is imperative that severe, or potentially severe, reactions be treated promptly with intramuscular epinephrine and oral antihistamines. Patients who have had such a reaction should be kept under observation in a hospital emergency department or equivalent for up to 4 h because of the possible development of the late-phase allergic response. This Seminar looks at the changing epidemiology of this allergy--and theories as to the rise in prevalence, diagnosis, and management of the allergy, and potential new treatments and prevention strategies under development.

Assessment of three human FcepsilonRI-transfected RBL cell-lines for identifying IgE induced degranulation utilizing peanut-allergic patient sera and peanut protein extract

Specific IgE sera screening studies are employed to investigate protein cross-reactivity. Such nonfunctional immunochemical methods cannot measure the biological activity of proteins. Therefore, an assay using RBL cells transfected with human FcepsilonRI was developed. Our objective was to evaluate the degranulation of three cell-lines expressing either the alpha-(RBL-hEI(a)-2B12 and RBL-30/25cells) or alpha-, beta-, and gamma-subunits (RBL SX-38) of the human FcepsilonRI by beta-hexosaminidase release. Purified human IgE and serum-derived polyclonal IgE from peanut-allergic subjects following challenge with anti-IgE or peanut protein extract, respectively, were utilized. Robust degranulation was induced in all three: RBL-30/25 (84%), -hEI(a)-2B12 (54%), SX-38 (94%), respectively, using purified IgE+anti-human IgE. Good release (18%, 40-45%, and 65%, respectively) occurred for one peanut-allergic subject+peanut extract with all cell-lines. With serum from three other peanut-allergic subjects, no beta-hexosaminidase release occurred with RBL-hEI(a)-2B12 cells+peanut extract, while only serum from one subject induced good degranulation, 30% and 60%, respectively, with RBL-30/25 and RBL SX 38 cells. Consistent degranulation with a potent food allergen (peanuts) was not observed. The assay's utility in safety assessment, predictive value and reproducibility for evaluating the cross-reactivity of proteins with allergens needs further investigation with additional proteins and well-characterized sera.

Identification of a new natural Ara h 6 isoform and of its proteolytic product as major allergens in peanut

Numerous food allergens of plant origin belong to the 2S albumin family, including peanut Ara h 2. In addition to Ara h 2, several other conglutins related to 2S albumins are present in peanut seeds. We evaluated the allergenicity of different peanut conglutins as compared with Ara h 2. Several conglutins were isolated from the kernel, i.e. Ara h 2, a new isoform of Ara h 6 and its derived product, which is likely to be naturally formed during seed processing. Enzyme allergosorbent tests performed on sera of peanut allergic patients showed that more than 94% of 47 analyzed patients had positive IgE responses to Ara h 6 isoform and to its degradation product. Skin prick tests with the new isoform of Ara h 6 led to a positive response in seven out of the eight tested patients. Both enzyme allergosorbent tests and skin prick tests showed that the reactivity of Ara h 6 was similar to, or even higher than, that of Ara h 2, suggesting that the present isoform of Ara h 6 is as allergenic as Ara h 2. In addition the IgE response to the plant processed (i.e., hydrolyzed) Ara h 6 new isoform is equivalent to the IgE response to the native isoform. The IgE immunoreactivity is mostly abrogated by chemical reduction and denaturation of Ara h 6 isoforms, which underlined the importance of tertiary structure in Ara h 6 immunoreactivity. These results, and particularly the high correlation between anti-Ara h 2 and anti-Ara h 6 IgE responses, emphasise the major role of 2S albumins in peanut allergenicity.

Ses i 6, the sesame 11S globulin, can activate basophils and shows cross-reactivity with walnut in vitro

BACKGROUND

Sesame allergy is increasingly being reported, and multi-sensitization to peanut and tree nuts has been described. The clinical relevance and cross-reactivity of many sesame proteins, such as Ses i 6, are unknown.

OBJECTIVE

The aims of this study were to perform a preliminary examination of the cross-reactivity of Ses i 6 in vitro, examine the ability of Ses i 6 to activate basophils in a modified basophil activation test (mBAT), and assess whether such an assay may help to distinguish between potentially relevant and irrelevant IgE reactivity towards 11S globulin proteins.

METHODS

Inhibition immunoblotting and chicken anti-rJug r 4 antibodies were used to determine the cross-reactivity of rSes i 6. Basophils from atopic donors were stripped of resident IgE before passive sensitization with food-allergic sera and challenged with protein extracts or recombinant protein. Basophil activation was measured using two activation markers, CD203c and CD63, via flow cytometry.

RESULTS

IgE immunoblotting showed cross-reactivity between rJug r 4 and rSes i 6 using sera from two human donors and chicken IgY. Additionally, rSes i 6 activated basophils passively sensitized with sesame-allergic sera. Cross-reactive serum from a sesame-allergic but walnut-tolerant donor was not able to activate basophils when challenged by walnut extract despite IgE reactivity to walnut determined by immunoblotting.

CONCLUSIONS

The sesame 11S globulin shows partial immunological cross-reactivity with walnut, and although it is classified as a minor allergen, activated basophils sensitized with serum from seven out of eleven sesame-allergic donors. Additionally, the mBAT may help distinguish between clinically relevant and irrelevant in vitro IgE cross-reactivity of seed storage proteins in nuts and seeds and thus warrants use in further studies.

Does skin prick test reactivity to purified allergens correlate with clinical severity of peanut allergy?

BACKGROUND

Recognition of specific peanut allergens or the diversity of IgE binding to peanut allergens may play a role in the elicitation of severe allergic reactions.

OBJECTIVE

To investigate whether sensitization to individual allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 is correlated with clinical severity.

METHODS

The reactivity of purified peanut allergens was measured by skin prick test (SPT) and by IgE immunoblot in 30 patients. The results were related to the clinical reactivity by history, and in 25 of them to the eliciting dose (ED).

RESULTS

The majority of patients recognized Ara h 2 and Ara h 6. Patients with severe symptoms had a higher SPT response to Ara h 2 and Ara h 6 at low concentrations (0.1 micro g/mL) and to Ara h 1 and Ara h 3 at higher concentrations (100 micro g/mL), compared with patients with mild symptoms. They also recognized a greater number of allergens and showed a higher cumulative SPT response compared with patients with mild symptoms. No significant differences were observed between patients with a low or high ED.

CONCLUSIONS

Ara h 2 and Ara h 6 appeared to be more potent than Ara h 1 and Ara h 3. Both SPT reactivity to low concentrations of Ara h 2 and Ara h 6 and to higher concentrations of Ara h 1 and Ara h 3 were shown to be indicative of severe symptoms.

Purification, crystallization and initial crystallographic characterization of peanut major allergen Ara h 3

The peanut is a significant food source, but is responsible for many cases of anaphylaxis. The peanut 11S legumin-like seed storage protein Ara h 3 is one of the best characterized allergens. In this study, Ara h 3 was extracted from peanut kernels and purified by sequential anion-exchange, hydrophobic interaction and gel-filtration chromatography to very high purity to facilitate crystallization and structural studies. Well diffracting single crystals were obtained by the vapor-diffusion method. A molecular-replacement structural solution has been obtained and refinement of the structure is currently under way.

Peanut allergy: Emerging concepts and approaches for an apparent epidemic

Peanut allergy is typically lifelong, often severe, and potentially fatal. Because reactions can occur from small amounts, the allergy presents patients with significant obstacles to avoid allergic reactions. In North America and the United Kingdom, prevalence rates among schoolchildren are now in excess of 1%, framing an increasing public health concern and raising research questions about environmental, immunologic, and genetic factors that may influence outcomes of peanut allergy. This review focuses on recent observations that continue to question the influences of maternal and infant diet on outcomes of peanut allergy, and explore how peanut may be uniquely suited to induce an allergic response. We highlight studies that affect current diagnosis, management, and the nature of advice that can be provided to patients, including the utility of diagnostic tests, doses that elicit reactions, characteristics of reactions from exposure, issues of cross-reactivity, concerns about peanut contamination of manufactured goods, and the natural course of the allergy. Clinical, molecular, and immunologic advances are reviewed, highlighting research discoveries that influence strategies for improved diagnosis, prevention, and treatment. Among the therapeutic strategies reviewed are sublingual and oral immunotherapy, anti-IgE, Chinese herbal medicine, and vaccine strategies.