Technological processes to decrease the allergenicity of peach juice and nectar

Relevance of the recombinant lipid transfer protein of Hevea brasiliensis: IgE-binding reactivity in fruit-allergic adults

BACKGROUND

Lipid transfer proteins (LTPs) are relevant allergens in certain plants. The role of the LTP of Hevea brasiliensis in the latex-fruit syndrome is widely unknown.

OBJECTIVE

To study IgE reactivity with recombinant Hevea LTP in sera of fruit-allergic adults with and without natural rubber latex (NRL) allergy.

METHODS

An LTP-specific complementary DNA of H brasiliensis leaves was amplified, subcloned into the pMAL expression system, and analyzed. The recombinant protein was coupled to ImmunoCAP, and the IgE-binding properties were studied in sera of 10 NRL-allergic patients without symptoms to fruit and 48 atopic patients with fruit allergy. Eleven of these 48 patients were also allergic to NRL, 14 displayed sensitization to NRL without symptoms on NRL exposure so far, and 23 had neither symptoms nor IgE antibodies to NRL.

RESULTS

After expression in Escherichia coli, a soluble maltose-binding protein-rHev b 12 fusion protein was isolated and coupled to ImmunoCAP to determine rHev b 12 specific IgE reactivity. rHev b 12 specific IgE binding was found in 3 fruit-allergic patients with NRL sensitization (0.68, 0.88, and 0.96 kU/L) and in 3 fruit-allergic patients without NRL sensitization (1.58, 2.25, and 2.27 kU/L). The remaining 52 serum samples and all maltose-binding protein control test results were negative (< 0.35 kU/L).

CONCLUSIONS

In these patients, rHev b 12 specific IgE reactivity seems to result from common cross-reactive epitopes with some of the fruit LTPs tested and underscores only an involvement in co-recognition. No clinical relevance of IgE binding to the LTP of H brasiliensis in association with NRL allergy was detected.

Plant non-specific lipid transfer proteins: an interface between plant defence and human allergy

Plant non-specific LTPs (lipid transfer proteins) form a protein family of basic polypeptides of 9 kDa ubiquitously distributed throughout the plant kingdom. The members of this family are located extracellularly, usually associated with plant cell walls, and possess a broad lipid-binding specificity closely related to their three-dimensional structure. The nsLTP fold is characterized by a compact domain composed of 4 alpha-helices, firmly held by a network of 4 conserved disulphide bridges. This fold presents a large internal tunnel-like cavity, which can accommodate different types of lipids. nsLTPs are involved in plant defence mechanisms against phytopathogenic bacteria and fungi, and, possibly, in the assembly of hydrophobic protective layers of surface polymers, such as cutin. In addition, several members of the nsLTP family have been identified as relevant allergens in plant foods and pollens. Their high resistance to both heat treatment and digestive proteolytic attack has been related with the induction by these allergens of severe symptoms in many patients. Therefore, they are probably primary sensitizers by the oral route. nsLTP sensitization shows an unexpected pattern throughout Europe, with a high prevalence in the Mediterranean area, but a low incidence in Northern and Central European countries.

Rice: Another Potential Cause of Food Allergy in Patients Sensitized to Lipid Transfer Protein

Recent studies show that the lipid transfer protein (LTP), the major Rosaceae allergen in patients not sensitized to birch pollen, is a largely cross-reacting allergen. Moreover, it is a potentially hazardous allergen due to its stability upon thermal treatment and pepsin digestion. The present study reports 3 cases of rice-induced anaphylaxis in LTP-allergic patients. In vitro inhibition studies, carried out using LTP purified from both rice and apple as well as whole peach extract, show that LTP was the relevant allergen in these patients and demonstrate the cross-reactivity between rice LTP and peach/apple LTP.

Influence of cultivar and processing on cherry (Prunus avium) allergenicity

Oral allergy syndrome is an immediate food allergic event that affects lips, mouth, and pharynx, is often triggered by fruits and vegetables, and may be associated with pollinosis. Here, we report on the allergenic pattern of different varieties of cherry (Prunus avium) and results obtained by applying several technological processes to the selected varieties. Whole cherries were submitted to chemical peeling, thermal treatment, and syruping processes, and the relative protein extracts were analyzed by in vitro (sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting analysis) and in vivo tests (skin prick test). Electrophoretic analyses demonstrated that there was no marked difference among cherry cultivars. Chemical peeling successfully removed Pru av 3, a lipid transfer protein (LTP) responsible for oral allergy syndrome in patients without pollinosis, leading to the industrial production of cherry hypoallergenic derivatives. Furthermore, the syruping process removed almost all allergenic proteins to whom patients with pollinosis are responsive. In vivo tests confirmed electrophoretic results.

The effect of thermal processing on the IgE reactivity of the non-specific lipid transfer protein from apple, Mal d 3

BACKGROUND

Non-specific lipid transfer proteins (LTPs) are involved in allergy to fresh and processed fruits. We have investigated the effect of thermal treatment and glycation on the physico-chemical and IgE-binding properties of the LTP from apple (Mal d 3).

METHODS

Mal d 3 was purified from apple peel and the effect of heating in the absence and presence of glucose investigated by CD spectroscopy, electrospray and MALDI-TOF mass spectrometry. IgE reactivity was determined by RAST and immunoblot inhibition, SPT and basophil histamine release test.

RESULTS

The identity and IgE reactivity of purified Mal d 3 was confirmed. Mild heat treatment (90 degrees C, 20 min) in the absence or presence of glucose did not alter its IgE reactivity. More severe heat treatment (100 degrees C, 2 h) induced minor changes in protein structure, but a significant decrease in IgE-binding (30-fold) and biological activity (100- to 1000-fold). Addition of glucose resulted in up to four glucose residues attached to Mal d 3 and only a 2- and 10-fold decrease of IgE-binding and biological activity, respectively.

CONCLUSIONS

Only severe heat treatment caused a significant decrease in the allergenicity of Mal d 3 but glycation had a protective effect. The presence of sugars in fruits may contribute to the thermostability of the allergenic activity of LTP in heat-processed foods.

Effects of food processing on the stability of food allergens

The ubiquitous presence of allergens in the human food supply coupled with increased awareness of food allergies warrants undertaking appropriate preventive measures to protect sensitive consumers from unwanted exposure to offending food allergens. Attempts to reduce or eliminate food allergenicity through food processing have met with mixed results. The rationale for using food processing to reduce/eliminate allergenicity and limitations to using this approach are discussed.

Plant food allergies: a suggested approach to allergen-resolved diagnosis in the clinical practice by identifying easily available sensitization markers

BACKGROUND

Molecular biology techniques have led to the identification of a number of allergens in vegetable foods, but due to the lack of purified food proteins for routine diagnostic use, the detection of sensitizing allergens remains a nearly impossible task in most clinical settings. The allergen-resolved diagnosis of food allergy is essential because each plant-derived food may contain a number of different allergens showing different physical/chemical characteristics that strongly influence the clinical expression of allergy; moreover, many allergens may cross-react with homologue proteins present in botanically unrelated vegetable foods.

OBJECTIVE

Through a review of the available literature, this study aimed to detect "markers" of sensitization to specific plant food allergens that are easily accessible in the clinical practice.

RESULTS

There are several "markers" of sensitization to different allergenic proteins in vegetable foods that can be helpful in the clinical practice. Specific algorithms for patients allergic to Rosaceae and to tree nuts were built.

CONCLUSION

Clinical allergologists lacking the assistance of an advanced molecular biology lab may take advantage of some specific clinical data as well as of some "markers" in the difficult task of correctly diagnosing patients with plant food allergy and to provide them the best preventive advice.

Nonspecific lipid-transfer proteins in plant foods and pollens: an important allergen class

PURPOSE OF REVIEW

Here we focus our attention on the structural stability and physicochemical properties of plant nonspecific lipid-transfer proteins (nsLTPs) as keys to their allergenicity. We further present the current opinions on the route of sensitization and include the latest additions to the nsLTP allergen family.

RECENT FINDINGS

Plant nsLTPs are small cysteine-rich lipid-binding proteins that play a key role in plant resistance to biotic and abiotic stress. Besides their relevance for plant-pathogen interactions, nsLTPs have attracted interest as true food allergens which are of high importance to atopics in Mediterranean countries. It is now becoming clear that their molecular properties such as the remarkable stability to proteolysis and thermal denaturation are intrinsically linked to their allergenicity. These properties also facilitate sensitization via the gastrointestinal tract which allows these molecules to act as allergens independently of prior exposure to pollen. In addition, a group of allergenic pollen nsLTPs exists which seem to be only partially linked to the food nsLTPs by cross-reactivity.

SUMMARY

Research into the family of nsLTPs will continue to provide insights about the particular molecular properties that make an nsLTP an allergen and how primary sensitization occurs.

Why do lipid transfer protein-hypersensitive patients tolerate bean (and other legumes)?

BACKGROUND

Patients allergic to nonspecific lipid transfer protein (LTP) frequently score positive on SPT with legumes but virtually never report adverse reactions eating these foods.

OBJECTIVE

This study investigated the IgE reactivity to legumes of LTP-allergic patients and aimed to establish whether legumes can be considered safe in LTP-allergic patients.

METHODS

Skin reactivity as well as clinical allergy to bean and pea were evaluated in a large cohort of LTP-hypersensitive patients. Sera from 12 patients showing clinical allergy to a number of botanically unrelated plant-derived foods and high levels of IgE to peach LTP were employed in in vitro studies (ELISA, ELISA inhibition, SDS-PAGE/immunoblot) aiming to investigate IgE reactivity to bean.

RESULTS

Preabsorption of patients' sera with boiled bean extract did not cause any loss of IgE reactivity to peach LTP (whereas boiled apple totally abolished it). Immunoblot analysis did not show any IgE reactivity to bean proteins at about 10 kDa, and the SDS profile of bean showed little or no staining at 10 kDa.

CONCLUSION

Sera from LTP-allergic patients do not seem to show any IgE reactivity to 10-kDa proteins in bean. Whether this is caused by epitopic differences between Rosaceae and bean LTPs or by the fact that LTP is not expressed in bean remains to be established. This study explains why virtually all LTP-allergic patients tolerate legumes and suggests that these foods should be considered safe for patients sensitized to this protein.

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.

Structural, biological, and evolutionary relationships of plant food allergens sensitizing via the gastrointestinal tract

The recently completed genome sequence of the model plant species Arabidopsis has been estimated to encode over 25,000 proteins, which, on the basis of their function, can be classified into structural and metabolic (the vast majority of plant proteins), protective proteins, which defend a plant against invasion by pathogens or feeding by pests, and storage proteins, which proved a nutrient store to support germination in seeds. It is now clear that almost all plant food allergens are either protective or storage proteins. It is also becoming evident that those proteins that trigger the development of an allergic response through the gastrointestinal tract belong primarily to two large protein superfamilies: (1) The cereal prolamin superfamily, comprising three major groups of plant food allergens, the 2S albumins, lipid transfer proteins, and cereal alpha-amylase/trypsin inhibitors, which have related structures, and are stable to thermal processing and proteolysis. They include major allergens from Brazil nut, peanuts, fruits, such as peaches, and cereals, such as rice and wheat; (2) The cupin superfamily, comprising the major globulin storage proteins from a number of plant species. The globulins have been found to be allergens in plant foods, such as peanuts, soya bean, and walnut; (3) The cyteine protease C1 family, comprising the papain-like proteases from microbes, plants, and animals. This family contains two notable allergens that sensitize via the GI tract, namely actinidin from kiwi fruit and the soybean allergen, Gly m Bd 30k/P34. This study describes the properties, structures, and evolutionary relationships of these protein families, the allergens that belong to them, and discusses them in relation to the role protein structure may play in determining protein allergenicity.

Presence of allergenic proteins in different peach (Prunus persica) cultivars and dependence of their content on fruit ripening

It has been reported that various cultivars of fruits and vegetables may present a different pattern for the contained allergens. Here, we report on the different content in allergenic proteins for different peach (Prunus persica) cultivars, sampled during two consecutive harvest seasons. Fruits from six cultivars of peaches were harvested fully ripe, and the proteins extracted from whole or chemically peeled fruits were analyzed by SDS-PAGE and immunoblotting. All the protein extracts from whole fruit contained a 9 kDa protein. This protein proved to be absent in the extracts taken from chemically peeled fruit. In four cultivars, this protein corresponds to the allergen Pru p3, a lipid transfer protein that causes the oral allergy syndrome (OAS) in sensitized people. In the following year, fruits from four of the six cultivars of peaches studied previously were harvested at different times, at one and two weeks before the commercial ripening time and when fully ripe, to ascertain whether the presence of the 9 kDa allergen might be related to the ripening process. Two cultivars out of four produced an intense allergenic band corresponding to a 9 kDa protein already two weeks before the commercial ripening date, while the others showed a progressive increment of the 9 kDa allergen during ripening.

Plant non-specific lipid transfer proteins as food and pollen allergens

Several members of the plant non-specific lipid transfer protein (LTP) family have been identified as relevant allergens in foods and pollens. These allergens are highly resistant to both heat treatment and proteolytic digestion. These characteristics have been related with the induction of severe systemic reactions in many patients, and with the possibility of being primary sensitizers by the oral route. A specific geographical distribution pattern of sensitization to LTP allergens has been uncovered. This allergen family is particularly important in the Mediterranean area, but shows a very limited incidence in Central and Northern Europe. The potential role in the plant, as well as the biochemical and allergenic properties of the LTP family, are reviewed here.

Effect of technological processing on the allergenicity of mangoes (Mangifera indica L.)

In parallel with the rising popularity of exotic fruits in Europe, allergy against mango is of increasing importance. Because mangoes are also consumed as processed products such as chutneys or beverages, the influences of different process conditions on their allergenicity were investigated. Mango purees and nectars were manufactured at small pilot-plant scale, and the allergenic potencies of the resulting intermediate and final products were determined by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting and inhibitive enzyme allergosorbent tests (EAST-inhibition), using a pool serum of 9 individuals with manifest mango allergy. The mango allergens were shown to be very stable during technological processing. Irrespective of enzymatic matrix decomposition, mechanical tissue disintegration and heating during peeling, mash treatment, and pasteurization, significant loss of allergenicity could not be observed in the extracts of mango purees and nectars derived thereof. These results were confirmed by analogous investigation of commercial mango drinks and nectars. Hence, conventional mango processing into pulp-containing products typical for this species obviously does not allow complete elimination of the allergenic potency.

New Trends in Food Processing

In this work some of the newest trends in food processing are reviewed. This revision intends to provide an updated overview (including works published until February 2001) on the newest food processes, including food manufacturing, preservation, and control. Modern processes for food and food ingredients manufacturing based on membrane technology, super-critical fluid technology, and some applications of biotechnology are presented, mainly applied to obtain functional foods, "all-natural" enriched foods, probiotics and prebiotics. Also included is a critical assessment concerning non-thermal preservation techniques used for food preservation, such as high hydrostatic pressure, pulsed electric fields, ultrasound, pulsed light, hurdle systems, etc. Finally, a group of new analytical techniques (i.e., molecular techniques such as Polymerase Chain Reaction (PCR), food image analysis, and biosensors) and their use for food and process control is reviewed.

Detection of clinical markers of sensitization to profilin in patients allergic to plant-derived foods

BACKGROUND

A proper classification of patients allergic to plant-derived foods is of pivotal importance because the clinical features of allergic reactions to fruits and vegetables depend on the nature and characteristics of proteins responsible for sensitization. However, in normal clinical settings this is presently impossible.

OBJECTIVE

We sought to detect clinical markers of sensitization to profilin.

METHODS

Seventy-one patients allergic to fruits and vegetables but not sensitized to lipid transfer protein or natural rubber latex were studied. Food allergy was ascertained on the basis of clinical history and positive skin prick test responses with fresh foods, commercial extracts, or both. Allergies to foods that had caused less than 2 adverse reactions were confirmed by means of open oral challenge. IgE reactivity to rBet v 1/rBet v 2 and to natural Phleum species profilin were detected. Moreover, IgE to the 30- to 40-kd and 60- to 90-kd birch pollen-enriched fractions, which also can be involved in cross-reactivity phenomena, were measured in sera from 52 patients by means of ELISA.

RESULTS

On the basis of in vitro tests, 24, 18, and 25 patients turned out to be sensitized to Bet v 1, Bet v 2, or both, respectively. Four patients had negative test results for both allergens. Hypersensitivity to Bet v 2 was strongly associated with clinical allergy to citrus fruits (39% in patients monosensitized to Bet v 2 vs 4% in patients monosensitized to Bet v 1, P <.025), melon or watermelon (67% vs 0%, P <.001), banana (66% vs 8%, P <.001), and tomato (33% vs 0%, P <.05), whereas Bet v 1 sensitivity was associated with clinical allergy to apple (100% vs 39%, P <.001) and hazelnut (56% vs 0%, P <.001). The sensitivity of a history of allergy to gourd fruits, citrus fruits, tomato, banana, or a combination thereof as a means to detect profilin-hypersensitive patients was 85% (41/48). The specificity of an allergy to any of these fruits exceeded 85%, with positive predictive values ranging between 68% and 91%.

CONCLUSION

In clinical settings in which laboratory investigations are not easily accessible, allergy to melon, watermelon, citrus fruits, tomato, and banana can be used as a marker of profilin hypersensitivity once a sensitization to natural rubber latex and lipid transfer protein is ruled out.

[Cross-reactivity between fruit and vegetables]

Vegetable foods are the most frequent cause of food allergy after the age of 5 years. The most commonly implicated foods are fruit and dried fruits, followed in Spain by legumes and fresh garden produce. In patients allergic to fruit and garden produce, multiple sensitizations to other vegetable products, whether from the same family or taxonomically unrelated, are frequent, although they do not always share the same clinical expression. Furthermore, more than 75 % of these patients are allergic to pollen, the type of pollen varying in relation to the aerobiology of the area. The basis of these associations among vegetable foods and with pollens lies in the existence of IgE antibodies against "panallergens", which determines cross-reactivity. Panallergens are proteins that are spread throughout the vegetable kingdom and are implicated in important biological functions (generally defense) and consequently their sequences and structures are highly conserved. The three best-known groups are allergens homologous to Bet v 1, profilins, and lipid transfer proteins (LTP). Allergens homologous to Bet v 1 (major birch pollen allergen) constitute a group of defense proteins (PR-10), with a molecular weight of 17 kDa, which behave as major allergens in patients from northern and central Europe with allergy to vegetables associated with birch pollen allergy. In these patients, the primary sensitization seems to be produced through the inhalation route on exposure to birch pollen. The symptomatology characteristically associated with sensitization to this family of allergens is oral allergy syndrome (OAS). Profilins are highly conserved proteins in all eukaryotic organisms and are present in pollen and a wide variety of vegetable foods. They have a molecular weight of 14 kDa and present a high degree of structural homology as well as marked cross-reactivity among one another. The presence of anti-profilin IgE broadens the spectrum of sensitizations to vegetable foods detected through skin tests and/or in vitro tests but whether it correlates with the clinical expression of food allergy is unclear.LTPs are the most commonly implicated allergens in allergy to Rosaceae fruits in patients from the Mediterranean area without birch pollen sensitization. LTPs are a family of 9kDA polypeptides, widely found in the vegetable kingdom and implicated in cuticle formation and defense against pathogens (PR-14). They are thermostable and resistant to pepsin digestion, which makes them potent food allergens and explains the frequent development of systemic symptoms (urticaria, anaphylaxis) in patients allergic to Rosaceae fruits in Spain. LTPs have also been identified in other vegetable foods and in pollens and a marked degree of cross-reactivity among them has been demonstrated, which may explain (together with profilin) the frequency of individuals sensitized to vegetable foods in the Mediterranean area.

Roasted hazelnuts--allergenic activity evaluated by double-blind, placebo-controlled food challenge

BACKGROUND

Allergy to hazelnuts is a common example of birch pollen related food allergy. Symptoms upon ingestion are often confined to the mouth and throat, but severe systemic reactions have been described in some patients. The aim of the study was to evaluate the reduction in allergenicity by roasting of the nuts.

METHODS

Double-blind, placebo-controlled food challenges (DBPCFC) with roasted hazelnuts (140 degrees C, 40 min) were performed in 17 birch pollen allergic patients with DBPCFC-confirmed food allergy to raw hazelnuts. The effect of roasting was further evaluated by skin prick test (SPT), histamine release (HR), measurement of specific IgE, and IgE-inhibition experiments.

RESULTS

In 5/17 patients the DBPCFC with the roasted nuts were positive. The symptoms were generally mild and included OAS (oral allergy syndrome) in all patients. Roasting of the nuts significantly reduced the allergenic activity evaluated by SPT, HR, specific IgE, and IgE-inhibition. Immunoblotting experiments with recombinant hazelnut allergens showed sensitization against Cor a 1.04 in 16/17 patients and against Cor a 2 in 7/17 patients. None of the patients were sensitized to Cor a 8. Challenge-positive patients did not differ from the rest in IgE-binding pattern.

CONCLUSIONS

All the applied methods indicated that roasting of hazelnuts reduces the allergenicity, but since 5/17 birch pollen allergic patients were DBPCFC-positive to the roasted nuts, ingestion of roasted hazelnuts or products containing roasted hazelnuts can not be considered safe for a number of hazelnut allergic consumers. For patients with a history of severe allergic symptoms upon ingestion of hazelnuts, thorough and conscientious food labelling of hazelnuts and hazelnut residues is essential.

Stability of bovine allergens during food processing

OBJECTIVE

The primary objective of this review was to summarize reported findings about the influence of various food manufacturing processes on the potential alteration of bovine allergens in cow's milk, beef, and related food products.

DATA SOURCES

This review was based on literature research in two German databases.

STUDY SELECTION

The expert opinion of the authors was used to select the relevant data for the review.

RESULTS

Changes in allergenic activity during food processing are attributable to inactivation or destruction of epitope structures, formation of new epitopes, or improved access of previously hidden epitopes. The allergenic potency of food could be altered by several food manufacturing procedures--such as mechanical, purification, thermal, biochemical, and chemical processes. The main processing steps studied by investigators were heating (dry heating, boiling, or cooking) and enzymatic digestion. A review of the available literature on the alteration of bovine allergens in cow's milk, meat, and related food products revealed reduction (but not elimination) of allergenicity by heating of cow's milk for 10 minutes. Although homogenization did not change the allergenic potency of cow's milk, it decreased the allergenicity of beef, as did freeze-drying. Digestion studies showed varied results.

CONCLUSIONS

The allergenicity of some food products decreased during certain processing steps, but the results of other investigations differed. Therefore, more systematic research on the influence of food processing on allergenicity should be undertaken.

Characterization of asparagus allergens: a relevant role of lipid transfer proteins

BACKGROUND

No asparagus allergen has been characterized to date. Lipid transfer proteins (LTPs) have an ubiquitous distribution in plant foods and have been identified as relevant allergens in some fruits, seeds, and pollens.

OBJECTIVE

We sought to identify asparagus allergens and to evaluate the potential involvement of the panallergen LTP family in asparagus allergy.

METHODS

Eighteen patients with asthma, anaphylaxis, and/or contact urticaria after asparagus ingestion or exposure and positive skin prick test (SPT) responses and serum-specific IgE levels to asparagus were selected. Two LTPs were isolated from crude asparagus extract by using chromatographic methods and characterized by means of N-terminal amino acid sequencing. Both isolated proteins were tested by means of immunodetection, CAP inhibition assays, and SPTs. Additional asparagus allergens were located by using immunodetection with a pool of sera from patients allergic to asparagus and with rabbit polyclonal antibodies to sunflower pollen profilin and anti-complex asparagine-linked glycans antibodies.

RESULTS

The purified LTPs showed an N-terminal amino acid sequence similar to that of Pru p 3 and a strong reaction to anti-Pru p 3 antibodies. Each isolated protein reached inhibition values of up to 60% in CAP inhibition assays against asparagus extracts and elicited positive SPT responses in 9 of 18 patients with asparagus allergy. Immunodetection assays allowed us to identify profilin and cross-reacting carbohydrate determinants as asparagus IgE-binding components.

CONCLUSION

Asparagus LTPs are relevant allergens. In addition, profilin and glycoproteins harboring complex asparagine-linked glycans can also be involved in asparagus allergy.

Immunological cross-reactivity between lipid transfer proteins from botanically unrelated plant-derived foods: a clinical study

BACKGROUND

Lipid transfer proteins (LTP) are highly conserved and widely distributed throughout the plant kingdom. Recent studies demonstrated immunological cross-reactivity between LTP from many botanically unrelated fruits and vegetables and concluded that LTP are pan-allergens. This study aimed to evaluate the clinical relevance of such cross-reactivity in a group of subjects monosensitized to LTP.

METHODS

Twenty LTP-hypersensitive patients were selected from a population of about 600 subjects with history of Rosaceae allergy by means of: 1) negative skin prick test (SPT) with a commercial birch pollen extract; 2) positive SPT with a commercial plum extract, rich in LTP but virtually lacking both Bet v 1-like proteins and profilin; 3) in-vitro IgE reactivity to the 9-10 kDa fraction of peach peel or immunoblot with peach peel showing a single band at 10 kDa; and 4) total inhibition of reactivity to whole peach extract (containing Bet v 1-related allergen, profilin, and LTP) by purified peach LTP on enzyme-linked immunoassay (ELISA). Allergy to foods other than Rosaceae was ascertained by careful interview and analysis of medical recordings. SPT with a large series of plant-derived foods were carried out as well. The cross reactivity between LTPs from botanically unrelated plant-derived foods was assessed by ELISA inhibition tests using walnut and peanut extracts as substrate, and peach LTP as inhibitor.

RESULTS

All patients reported allergic reactions after the ingestion of at least one from a large number of vegetable foods other than Rosaceae, and in several cases clinical reactions were very severe (anaphylaxis, asthma, urticaria/angioedema). Nuts and peanuts were the most frequently reported causes of allergic reactions (80% and 40% of patients, respectively). All patients showed positive SPT to several non-Rosaceae food extracts. SPT with nuts, peanut, legumes, celery, rice, and corn were positive in the majority of patients. In ELISA inhibition studies, absorption of sera with peach LTP caused complete inhibition of IgE reactivity to walnut and peanut in all cases.

CONCLUSION

LTP is a clinically relevant pan-allergen. Most Rosaceae-allergic, LTP-hypersensitive patients experience adverse reactions after ingestion of botanically unrelated plant-derived foods as well. In view of the high prevalence and severity of the allergic reactions induced, hazelnut, walnut, and peanut should be regarded as potentially hazardous for these patients.

Patterns of reactivity to lipid transfer proteins of plant foods and Artemisia pollen: an in vivo study

BACKGROUND

Lipid transfer proteins (LTPs) are major allergens of Rosaceae fruits in the Mediterranean area. IgE-cross-reactivity has been demonstrated in vitro among LTPs from peach, apple, chestnut and Artemisia pollen. The aim of this study was to evaluate the reactivity to LTPs from peach, apple, chestnut and Artemisia pollen by means of skin prick tests (SPTs).

METHODS

Forty-seven patients allergic to peach (peach group), 20 patients sensitized to Artemisia pollen with no food allergies (Artemisia group), and 12 control subjects were skin tested with fresh peach, as well as with whole extracts and purified LTPs of peach, apple, chestnut and Artemisia pollen.

RESULTS

The rates of positive SPTs for peach, apple, chestnut and Artemisia LTPs were, respectively, 91, 77, 23, and 36% in the peach group, and 30, 5, 15 and 40% in the Artemisia group. No response was observed in the control subjects. SPTs with peach LTP strongly correlated with SPTs conducted with fresh peach. In the peach group, the most frequent pattern of reactivity to LTPs was the combination peach-apple (45%), followed by peach-apple-Artemisia-chestnut (21%). Significant correlations were found between peach and apple LTPs, and between Artemisia and chestnut LTPs. Positive SPTs to chestnut LTP were only observed in patients with positive SPTs to Artemisia LTP. All the patients with positive case histories to chestnut reacted to chestnut LTP.

CONCLUSIONS

LTPs are plant panallergens with different patterns of cross-reactivity. They are major allergens of Rosaceae fruits and seem to be involved in allergic reactions to unrelated foodstuffs such as chestnut, probably through sensitization to the cross-reactive Artemisia LTP. Rosaceae LTPs could be useful tools for in vivo diagnosis of Rosaceae fruit allergy.

Identification of hazelnut major allergens in sensitive patients with positive double-blind, placebo-controlled food challenge results

BACKGROUND

The hazelnut major allergens identified to date are an 18-kd protein homologous to Bet v 1 and a 14-kd allergen homologous to Bet v 2. No studies have reported hazelnut allergens recognized in patients with positive double-blind, placebo-controlled food challenge (DBPCFC) results or in patients allergic to hazelnut but not to birch.

OBJECTIVE

We characterized the hazelnut allergens by studying the IgE reactivity of 65 patients with positive DBPCFC results and 7 patients with severe anaphylaxis to hazelnut.

METHODS

Hazelnut allergens were identified by means of SDS-PAGE and IgE immunoblotting. Further characterization was done with amino acid sequencing, evaluation of the IgE-binding properties of raw and roasted hazelnut with enzyme allergosorbent test inhibition, assessment of cross-reactivity with different allergens by means of immunoblotting inhibition, and purification by means of HPLC.

RESULTS

All the sera from the patients with positive DBPCFC results recognized an 18- and a 47-kd allergen; other major allergens were at molecular weights of 32 and 35 kd. Binding to the 18-kd band was inhibited by birch extract, indicating its homology with the birch major allergen, and abolished in roasted hazelnut. The 47-kd allergen is a sucrose-binding protein, the 35-kd allergen is a legumin, and the 32-kd allergen is a 2S albumin. Patients with severe anaphylactic reactions to hazelnut showed specific IgE reactivity to a 9-kd allergen, totally inhibited by purified peach lipid-transfer protein (LTP), which was heat stable and, when purified, corresponded to an LTP.

CONCLUSIONS

The major allergen of hazelnut is an 18-kd protein homologous to Bet v 1, and the 9-kd allergen is presumably an LTP. Other major allergens have molecular weights of 47, 32, and 35 kd.

cDNA cloning and heterologous expression of the major allergens from peach and apple belonging to the lipid-transfer protein family

BACKGROUND

Lipid-transfer proteins (LTPs) have been identified as major allergens of Rosaceae fruits in populations living in areas virtually free of Fagales trees, such as several Mediterranean communities. Pru p 3 and Mal d 3, the allergens from peach and apple, respectively, have a main clinical relevance in these areas.

OBJECTIVE

To isolate and characterize cDNAs for Pru p 3 and Mal d 3, and to produce recombinant Pru p 3 in the yeast Pichiapastoris.

METHODS

cDNAs for both allergens were isolated by polymerase chain reaction using nondegenerated primers. Expression of Pru p 3 was performed in P. pastoris using the pPIC 9 vector. The recombinant product was purified by gel-filtration chromatography followed by RP-HPLC. Immunodetection and immunoblot inhibition assays were carried out with sera from peach-allergic patients.

RESULTS

The cDNAs for both Pru p 3 and Mal d 3 showed a 273 open reading frame coding for the 91 amino acid mature polypeptides. The deduced amino acid sequences exhibited N-terminal regions fully identical to those previously determined for the natural peach and apple allergens. Pru p 3 was expressed in P. pastoris at 20 mg/L of culture medium. The recombinant allergen showed the same N-terminal sequence (plus a glutamic acid added for proper extracellular expression) and apparent molecular size as natural Pru p 3. Both the recombinant and natural forms of Pru p 3 displayed similar immunoglobulin (Ig)E-binding capacity in immunodetection and immunoblot inhibition assays.

CONCLUSIONS

Comparison of the complete primary structures of mature Pru p 3 and Mal d 3 deduced from their corresponding cDNA clones supports the close relationship between both allergens. Recombinant Pru p 3 binds IgE in vitro like its natural counterpart. Therefore, it can be a useful tool for specific diagnosis and structural studies.

Impact of (bio)chemical and physical procedures on food allergen stability

A variety of methods have been used to attempt to decrease the allergenicity of food products, with highly variable success. Limited knowledge of allergen and epitope structures and the factors governing their stability may explain this, and the ensuing need for an empirical approach. A combined effort from a processing and genomics-based approach may open up new ways to improve the quality of foods from an allergenic perspective. Based on structural knowledge, a suitable approach can be chosen that is, for instance, heat stable but protease sensitive; protease resistant but not heat stable; easy to extract; easy to mask because the epitope is exactly on a crosslink site; a molecular probe design that allows screening of germplasm collections.

Lipid transfer proteins and 2S albumins as allergens

Plant lipid transfer proteins, a widespread family of proteins, have been recently identified as important food allergens. Their common structural features, such as eight conserved cysteines forming disulfide bridges, basic isoelectric point and high similarity in amino acid sequence, are the basis of allergic clinical cross-reactivity. This has been demonstrated for the LTP allergens of the Prunoideae subfamily, whose similarity is about 95% as demonstrated for the purified allergens of peach, apricot, plum and apple. A relevant aspect is the existence of sequence homology of LTPs of botanically unrelated foods, as demonstrated for LTPs of maize and peach. A class of food allergens of well recognized clinical importance is that of seed storage 2S albumins. They have been identified in the most diffused edible seeds and nuts, such as mustard, sesame, Brazil nut, walnut and peanut. In particular, a strong correlation between IgE-binding to these proteins and food-induced anaphylaxis has been demonstrated for Brazil nut and sesame seeds.

Stability of food allergens and allergenicity of processed foods

The allergenicity of food could be altered by several processing procedures. For various foods of animal and plant origin the available literature on this alteration is described. Investigations on hidden allergens in food products are also dealt with.

Double-blind, placebo-controlled food challenge with apple

The aim of the study was to develop and evaluate different methods of double-blind, placebo-controlled food challenge (DBPCFC) with apple. Three different DBPCFC models were evaluated: fresh apple juice, freshly grated apple, and freeze-dried apple powder. All challenges were performed outside the pollen season and took place from 1997 to 1999. The freeze-dried apple material was characterized by means of leukocyte histamine release (HR), skin prick test (SPT), and immunoblotting experiments. The study population consisted of birch pollen-allergic patients with a history of rhinitis in the birch-pollen season and positive specific IgE to birch. For comparison of the DBPCFC models, 65 patients with a positive open oral challenge with apple were selected. In the characterization of the freeze-dried apple material, 46 birch pollen-allergic patients were included. The IgE reactivity to apple was evaluated by measurement of specific IgE, HR, and SPT. Golden Delicious apples were used in all experiments. The results of this study showed that it was possible to perform DBPCFC with apple in birch pollen-allergic individuals. The model with freshly squeezed apple juice had a low sensitivity and displayed a high frequency of reactions to placebo, probably due to the ingredients used for blinding. The sensitivity of the models with freshly grated apple and freeze-dried apple powder was 0.74/0.60. An increase in sensitivity is desirable. The freeze-dried apple powder proved to be useful for SPT, HR, and oral challenges, but further investigation of the stability and the allergenic profile of the material is needed.