The major allergen of peach (Prunus persica) is a lipid transfer protein

What establishes a protein as an allergen?

There is little known about the factors that determine the allergenicity of food proteins. Apparently, the ability of a food protein to induce an allergic response requires its presence in substantial amounts in the food supply, its durability during food processing, and its resistance to digestion in the gastrointestinal tract. In addition to the mode and degree of exposure, structural characteristics appear to play an important role for the capacity of a protein to modulate the immune response towards allergic reactions. Until now, however, there has been no indication for common structural characteristics of linear T cell or linear IgE (B cell) epitopes and the knowledge of structural characteristics of conformational IgE binding sites is very limited. Experimental data point only to certain surface areas of allergenic proteins which are important for IgE binding. Therefore, it is not possible to suggest any structural motif or conformational sequence pattern common to all allergenic proteins. Furthermore, glycosylation appears not to be a common critical determinant of allergenicity since food allergens comprise both glycoproteins and nonglycosylated proteins. Based on the few published three-dimensional structures of allergenic proteins including food proteins, one unifying feature of allergens appears to be their spherical shape. The three-dimensional structures of many more allergens have to be determined, however, to allow for a better understanding of the molecular basis of allergenicity. Most recently, new ideas have been introduced as to why certain biochemical or biologic functions such as enzymatic activities may predispose a protein to become an allergen. Proteolytically active allergens have been demonstrated to irritate the human mucosal surface, to enhance their own transmucosal uptake, and to augment IgE production. Therefore, the functional activity of some allergens may play a role among other factors in the process of sensitization and allergic responses.

Recombinant allergens Pru av 1 and Pru av 4 and a newly identified lipid transfer protein in the in vitro diagnosis of cherry allergy

BACKGROUND

In central and northern Europe food allergy to fruits of the Rosaceae family is strongly associated with birch pollinosis because of the existence of IgE cross-reactive homologous allergens in birch pollen and food. By contrast, in the Mediterranean population allergic reactions to these fruits frequently are not related to birch pollen allergy and are predominantly elicited by lipid transfer proteins (LTPs).

OBJECTIVE

We sought to determine the prevalence of IgE sensitization to the recombinant cherry allergens Pru av 1 and Pru av 4 in comparison with cherry extract within a representative group of patients who were allergic to cherries recruited in Germany and to compare the relevance of IgE to cherry LTPs in Italian patients.

METHODS

Recombinant Pru av 1 and rPru av 4 were available from earlier studies. The cDNA of the cherry LTPs was obtained by using a PCR-cloning strategy. The protein was expressed in Escherichia coli and purified by means of metal chelate affinity chromatography. Sera from 101 German patients with birch pollinosis and oral allergy syndrome to cherry and sera from 7 Italian patients with cherry allergy were investigated by using enzyme allergosorbent tests for IgE reactivity with cherry extract, rPru av 1, rPru av 4, and the recombinant cherry LTP. Inhibition experiments were performed to compare the IgE reactivity of natural and recombinant cherry LTPs and to investigate potential cross-reactivity with birch pollen allergens.

RESULTS

The LTP from cherry comprises 91 amino acids and a 26 amino acid signal peptide. The mature cherry LTP shows high amino acid sequence identity with allergenic LTPs from peach (Pru p 3, 88%), apricot (Pru ar 3, 86%), and maize (Zea m 14, 59%) and displays no IgE cross-reactivity with birch pollen. The IgE prevalences in the German patients were as follows: LTP, 3 of 101 (3%); rPru av 1, 97 of 101 (96.0%); rPru av 4, 16 of 101 (16.2%); and cherry extract, 98 of 101 (97%). All 7 Italian patients had IgE against the cherry LTP.

CONCLUSIONS

Recombinant allergens are useful tools for a more accurate in vitro IgE-based diagnosis of cherry allergy. Taken together, they mimic the allergenic activity of cherry extract, having slightly higher biologic activity. Sensitization to the cherry LTP is relevant for a minority of patients recruited in Germany, but our data indicate that it may be a major allergen in Italy.

Cloning and expression in phospholipid containing cultures of the gene encoding the specific phosphatidylglycerol/phosphatidylinositol transfer protein from Aspergillus oryzae: evidence that the pg/pi-tp is tandemly arranged with the putative 3-ketoacyl-CoA thiolase gene

The phosphatidylglycerol/phosphatidylinositol transfer protein (PG/PI-TP) is a new and original phospholipid transfer protein (PLTP) isolated from the Deuteromycete, Aspergillus oryzae. We have isolated a genomic clone of the A. oryzae pg/pi-tp using a probe derived from the corresponding cDNA and sequenced the complete gene. The DNA sequence analysis revealed that pg/pi-tp gene is composed of three exons encoding a 18,823 Da protein of 175 amino acids as previously described and of two introns as deduced by cDNA and genomic sequence alignment. The isolated pg/pi-tp gene do not show similarity with other PLTP genes or the deduced PG/PI-TP protein with proteins already known. Comparison of the encoded PG/PI-TP with other deduced proteins from recent genomic or cDNA sequence from databases revealed that the PG/PI-TP was close to two encoded proteins deduced from the cDNA database of Aspergillus nidulans (54% identity and 68% similarity) and the second from Neurospora crassa (53% identity and 76% similarity). Therefore, we suggested that both proteins might belong to the PLTP family. Southern blot analysis of A. oryzae genomic DNA show that the PG/PI-TP was encoded by a single gene. Expression of pg/pi-tp was performed in phospholipid containing cultures with increasing carbon source concentrations in order to study the regulation of the PLTPs in the filamentous fungus cell. This was done to know if a high density culture could yield a high amount of biomass with high phospholipid transfer activity. Results showed that phospholipids as compared to glucose in standard cultures stimulated mycelial growth and global phospholipid transfer activity, but not the pg/pi-tp transcript accumulation. However, high concentration of both carbon sources yielded an inhibition of the expression of the pg/pi-tp gene and of the global phospholipid transfer activity. In conclusion, both carbon sources are not suitable to increase the PLTP production in high density cultures for biotechnological applications. Finally, using the gene walking sequencing method it is demonstrated that the pg/pi-tp is tandemly arranged on opposite DNA strands in a tail-to-tail orientation with a putative gene encoding the 3-ketoacyl-CoA thiolase (EC 2.3.1.16). Unlike the pg/pi-tp gene, this thiolase gene show a putative 'beta-oxidation box' and encodes a putative 44,150 Da protein of 321 amino acids composed of a putative N-terminal PTS2 (Peroxisomal Targeting Signal) consensus sequence for the peroxisome targeting. Comparison of the amino acid sequence of the A. oryzae thiolase to that of the Yarrowia lipolytica showed a 50% identity and a 69% similarity.

The maize major allergen, which is responsible for food-induced allergic reactions, is a lipid transfer protein

BACKGROUND

Cereals are the most important nutritional component in the human diet. Food-induced allergic reactions to these substances therefore have serious implications, and exhaustive diagnosis is required. Such diagnosis is still difficult because of the incomplete knowledge about major cereal allergens. In particular, few food-induced allergic reactions to maize have been reported, and no information on the allergenic proteins is available.

OBJECTIVE

Having observed several anaphylactic reactions to maize, we planned a study to identify maize major allergens and cross-reactivity with other cereals, as well as to peach because the majority of patients also reacted to Prunoideae fruits.

METHODS

Twenty-two patients with systemic symptoms after maize ingestion and positive skin prick test responses and serum-specific IgE antibodies to maize were selected. The IgE-reactivity pattern was identified by SDS-PAGE and immunoblotting. The major allergen identified was then purified by HPLC and characterized by mass spectrometry, determination of the isoelectric point value, and N-terminal amino acid sequencing.

RESULTS

Sera from 19 (86%) of the 22 patients recognized a 9-kd protein, thus confirming this as the maize major allergen. This protein had an isoelectric point of greater than 9, a molecular mass of 9047.0 d, and no glycosylation. Determination of its N-terminal sequence showed that it was a lipid transfer protein (LTP). By using immunoblotting-inhibition experiments, we demonstrated that the LTP cross-reacts completely with rice and peach LTPs but not with wheat or barley LTPs. N-terminal sequence of the 16-kd allergen (recognized by 36% of patients) showed it to be the maize inhibitor of trypsin. This protein cross-reacts completely with grass, wheat, barley, and rice trypsin inhibitors.

CONCLUSION

The major allergen of maize is an LTP with a molecular weight of 9 kd that is highly homologous with the peach LTP, the major allergen of the Prunoideae subfamily.

Digestibility of allergens extracted from natural rubber latex and vegetable foods

BACKGROUND

Several cross-reactive allergens are now known to be involved in the defense responses of higher plants. Such proteins are drawing the attention of plant breeders because of their antimicrobial or stress-alleviating activities. Plants genetically modified to express defense-related proteins are being developed. The current concern is focused on the allergenicity of these intentionally expressed proteins.

OBJECTIVE

It is believed that food allergens are proteins resistant to digestion. Digestibility tests have been accepted as an appropriate method for evaluating the allergenicity of newly introduced proteins. In this study we investigated the usefulness of this method for detecting allergens from natural rubber latex and vegetable foods.

METHODS

Proteins were extracted from rubber latex, potato, and 5 kinds of fruits. Simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) were used for the digestibility test. An aliquot of each digest was periodically withdrawn and analyzed. Allergens were detected with pooled sera from individuals with latex allergy or patients given a diagnosis of oral allergy syndrome.

RESULTS

Most latex and vegetable food proteins were digested by the SGF within 4 minutes. Numerous allergens were also decomposed by the SGF within 8 minutes. Although vegetable food allergens were relatively stable in the SIF, kiwi allergens were substantially degraded by the SIF within 16 hours.

CONCLUSION

The pronounced lability of the plant-derived allergens was thought to reflect the discrete sensitization and elicitation processes of patients with latex-fruit syndrome or oral allergy syndrome. These results indicate that the allergenicity of a newly expressed protein should be carefully evaluated according to not only its digestibility but also other important properties.

Allergy to plant-derived fresh foods in a birch- and ragweed-free area

BACKGROUND

Allergy to plant-derived fresh foods has often been reported in geographical areas where birch or ragweed pollens are frequent and has been attributed to cross-reactivity to pollens.

OBJECTIVE

The aim of this study has been to evaluate allergy to plant-derived fresh foods among pollen-allergic patients from a birch and ragweed-free area.

METHODS

Ninety-five pollen-allergic patients took part in the study. The study consisted of a questionnaire, skin prick tests and challenge tests. Pollen skin tests to five grasses, eight trees and seven weeds were performed in duplicate. Prick tests (prick by prick) and challenge tests were carried out with the fresh foods.

RESULTS

Most patients allergic to pollens were sensitized to grass (Lolium and Phleum; 97.9%), followed by tree (Olea; 82.1%) and weed pollens (Plantago; 64.2%). 35 of the 95 pollen-allergic patients had positive skin test responses to some plant-derived fresh foods, the highest percentage corresponding to several fruits in the Rosaceae family (peach and pear, 26.3%), followed by Cucurbitacea fruits (melon, 13.7%). The 21. 05% of the pollen-allergic patients were allergic to some type of plant-derived fresh food. Peach was the plant-derived fresh food which most frequently elicited allergy symptoms (12.6%), followed by melon (7.36%). The cluster of positive responses to Rosaceae fruits was higher for skin testing than for challenge testing.

CONCLUSION

Peach was the most important allergy provoking fruit in a birch and ragweed free-area where apples were consumed at a rate of two times more than peaches and the patients allergic to pollen were principally sensitized to grass pollens.

Lipid-transfer proteins as potential plant panallergens: cross-reactivity among proteins of Artemisia pollen, Castanea nut and Rosaceae fruits, with different IgE-binding capacities

BACKGROUND

Lipid-transfer proteins (LTPs), but not Bet v 1 homologues, have been identified as major allergens of apple and peach in the Rosaceae fruit-allergic population in the Mediterranean area. Many of these patients show cosensitization to mugwort pollen. LTPs have an ubiquitous distribution in tissues of many plant species, and have been proposed as a novel type of plant panallergens.

OBJECTIVE

We sought to isolate LTPs from Artemisia pollen and from a plant food not belonging to the Rosaceae family, such as chestnut nut, and to compare their amino acid sequences and IgE-binding capacities with those of apple and peach LTPs.

METHODS

Allergens (LTPs) were isolated by different chromatographic methods (gel-filtration, ion exchange and/or reverse-phase HPLC), and characterized by N-terminal amino acid sequencing and MALDI analysis. Specific IgE-quantification and immunodetection, as well as immunoblot and ELISA inhibition assays, were carried out using sera from patients allergic to both apple and peach.

RESULTS

Purified LTPs from Artemisia pollen and from chestnut seed showed molecular masses about 9 700d, and 43-50% sequence identity with the equivalent allergens of apple and peach in the first 30 N-terminal residues, which comprise about one third of the total amino acid sequence. A similar degree of sequence identity (50%) was found between the Artemisia and chestnut proteins. Both isolated LTPs bound specific IgE of sera from Rosaceae fruits allergic patients. However, substantially lower values of specific IgE-binding and maximum ELISA inhibition percentages were obtained for Artemisia and chestnut LTPs when compared to those from apple and peach.

CONCLUSION

LTPs from Artemisia pollen and chestnut crossreact with allergens (LTPs) of Rosaceae fruits, but significant differences in specific IgE-binding capacities were observed among members of the plant LTP family. Thus, further studies are needed to evaluate the clinical significance of the observed cross-reactivities of plant LTPs.

Clinical cross-reactivity among foods of the Rosaceae family

BACKGROUND

Foods from the Rosaceae botanical family have been increasingly reported as causes of allergic reaction. Patients frequently have positive skin tests or radioallergosorbent test results for multiple members of this botanical family.

OBJECTIVE

Our purpose was to investigate the clinical cross-reactivity assessed by double-blind, placebo-controlled food challenge (DBPCFC) of Rosaceae foods (apricot, almond, plum, strawberry, apple, peach, and pear).

METHODS

Thirty-four consecutive adult patients complaining of adverse reactions to Rosaceae were included in the study. Skin prick tests and CAP System (FEIA) were performed with Rosaceae foods in all patients. Clinical reactivity to Rosaceae was systematically evaluated by open food challenges (OFCs), unless there was a convincing history of a recent severe anaphylaxis. Positive reactions on OFCs were subsequently evaluated by DBPCFCs.

RESULTS

Twenty-six and 24 patients had positive skin prick tests and CAP FEIA with Rosaceae, respectively; from these 88% and 100% had positive tests with >/=2. No evidence of clinical reactivity was found in 66% percent of positive skin prick tests and 63% of positive specific IgE determinations to fruits. A total of 226 food challenges (including OFC and DBPCFC) were performed in the 28 patients with positive skin prick tests or CAP System FEIA. Of 182 initial OFCs carried out, 26 (14%) reactions were confirmed by DBPCFCs. Overall, 40 reactions were considered positive in 22 patients with positive skin tests or CAP FEIA. Thirty-eight reactions had been previously reported, the remaining two were detected by systematic challenges. Most reactions were caused by peach (22 patients), apple (6), and apricot (5). Ten patients (46%) were clinically allergic to peach and other Rosaceae.

CONCLUSION

Positive skin test and CAP System FEIA should not be taken as the only guide for multi-species dietary restrictions. Nevertheless, the potential clinical allergy to other Rosaceae should not be neglected. If the reported reaction is confirmed, current tolerance to other Rosaceae should be precisely established unless there has been ingestion without symptoms after the reaction.

Molecular and biochemical classification of plant-derived food allergens

Molecular biology and biochemical techniques have significantly advanced the knowledge of allergens derived from plant foods. Surprisingly, many of the known plant food allergens are homologous to pathogenesis-related proteins (PRs), proteins that are induced by pathogens, wounding, or certain environmental stresses. PRs have been classified into 14 families. Examples of allergens homologous to PRs include chitinases (PR-3 family) from avocado, banana, and chestnut; antifungal proteins such as the thaumatin-like proteins (PR-5) from cherry and apple; proteins homologous to the major birch pollen allergen Bet v 1 (PR-10) from vegetables and fruits; and lipid transfer proteins (PR-14) from fruits and cereals. Allergens other than PR homologs can be allotted to other well-known protein families such as inhibitors of alpha-amylases and trypsin from cereal seeds, profilins from fruits and vegetables, seed storage proteins from nuts and mustard seeds, and proteases from fruits. As more clinical data and structural information on allergenic molecules becomes available, we may finally be able to answer what characteristics of a molecule are responsible for its allergenicity.

Technological processes to decrease the allergenicity of peach juice and nectar

Among vegetable foods peach (Prunus persica) has been recognized as a significant cause of allergy. The protein, which is considered to be the major peach allergen, has been named Pru p 1. Because peaches are consumed both as fresh fruits and after processing to obtain peach juice, nectar, jam, syrupy peach, etc., research was carried out to identify a technological process for production of hypo- or nonallergenic peach-based products. SDS-PAGE and immunoblotting analysis of extracts prepared from four commercial peach nectars showed that the Pru p 1 was not removed, and neither was its allergenic activity decreased by technological treatments carried out for nectar production. Some treatments oriented toward a removal of or, at least, a decrease in the allergenic power were assumed and verified at laboratory scale. A variable considered was heat treatment at 121 degrees C for 10 and 30 min: this treatment was not able to decrease the allergenicity of the Pru p 1 protein. Furthermore, the protein band was still present even after 60-min reaction with two different acidic proteases. The two technological treatments that were found to decrease the major allergen of peach were chemical lye peeling of fruits and ultrafiltration of juice through membranes with suitable cutoff. On the basis of the results obtained from this research, a processing flow sheet was defined to obtain hypoallergenic or probably nonallergenic limpid juices and nectars. These products may represent, besides finished foods, intermediates to obtain various products after addition of further ingredients such as pectins, sugars, and fiber.

Evidence for a lipid transfer protein as the major allergen of apricot

BACKGROUND

Apricots are widely grown in Europe, and allergic reactions are becoming more common, especially oral allergy syndrome. Apricot belongs to the botanical subfamily of Prunoideae, which includes peach, the major allergen of which was identified as a 9-kd protein, a lipid transfer protein (LTP).

OBJECTIVE

The aim of the study was to evaluate the IgE reactivity pattern to an apricot extract in subjects with allergic reactions to apricot, as demonstrated by a positive oral challenge response.

METHODS

Thirty patients were investigated. All the patients displayed oral allergy syndrome (2 with systemic reactions) to apricot, with positive open food challenge responses, skin prick test responses, and serum-specific IgE antibodies to apricot. The IgE reactivity pattern to apricot extract was identified by using SDS-PAGE and immunoblotting. The major allergen, a 9-kd protein, was then purified by HPLC and characterized by periodic acid-Schiff stain, isoelectric point determination, and N-terminal amino acid sequencing.

RESULTS

The sera from all patients allergic to apricot recognized the 9-kd protein, whereas none of the other allergens, with molecular weights from 15 to 80 kd, acted as a major allergen. The 9-kd allergen has an isoelectric point of 8.7 and is not glycosylated. Determination of the N-terminal 34 amino acid sequence showed that it belongs to the LTP family, with a 94% homology with the LTP from peach. IgE blotting of the apricot extract was completely inhibited by the 9-kd purified LTP from peach.

CONCLUSIONS

The major allergen of apricot is an LTP, which is highly cross-reactive with the LTP from peach.

Detection and clinical characterization of patients with oral allergy syndrome caused by stable allergens in Rosaceae and nuts

BACKGROUND

A minority of patients with oral allergy syndrome (OAS) induced by Rosaceae or nuts are positive on skin prick tests with commercial food extracts. This suggests reactivity against distinct stable allergens.

OBJECTIVES

(1) To define the prevalence of subjects positive on skin prick tests with commercial extracts among patients with OAS caused by Rosaceae and/or nuts and (2) To investigate whether commercial extracts-positive subjects show some peculiar clinical feature and may represent a specific subset with food allergy.

METHODS

Skin prick tests were carried out with a large panel of commercial extracts of airborne allergens (Allergopharma) and of vegetable foods (Dome/Hollister-Stier) in 298 adults with OAS caused by Rosaceae (n = 237) and or nuts (n = 161), positive on skin prick tests with fresh offending foods.

RESULTS

25/237 (11%) patients were positive on prick tests with commercial plum extract. This subgroup showed a higher incidence of systemic symptoms (64% versus 6%; P < .001) and a lower incidence of birch pollen allergy (12% versus 99%; P < .001) than commercial extract-negative patients; moreover, 36% versus 0%, respectively, did not have respiratory allergy (P < .001). Apple and peach were the main offending foods among commercial extract-negative and commercial extract-positive patients, respectively (87% versus 44% for apple, P < .001; and 52% versus 88% for peach, P < .005). Eight of one hundred sixty-one (5%) nuts-sensitive patients were positive on prick test with commercial walnut extract. This subgroup showed a higher proportion of patients who experienced systemic symptoms (63% versus 6%, P < .001), a lower prevalence of birch pollen allergy (13% versus 97%, P < .001), and a higher prevalence of grass pollen allergy (88% versus 41%, P < .05) than commercial extract-negative subjects. Further, reactivity against commercial walnut extract was associated with skin reactivity against commercial extracts of peanut (88% versus 37%, P < .005), tomato (75% versus 5%, P < .001), and plum (63% versus 8%, P < .001), and inversely related with skin reactivity against fresh apple (P < .001). In most cases, high levels of IgE specific for peach, apple, and hazelnut were associated with peanut reactivity rather than with clinical sensitivity to specific foods. In a preliminary investigation, most commercial extract-positive patients reacted against a 10-kDa protein characterized as a lipid transfer protein (LTP).

CONCLUSIONS

Skin prick tests with commercial extracts of plum and walnut may be usefully employed to detect patients with OAS reacting against stable allergens. The high prevalence of systemic symptoms in these patients suggests that allergens' stability is associated with a higher resistance to the gastrointestinal environment and strongly influences the clinical expression of vegetable food allergy. At least some stable allergens, namely lipid transfer protein might be shared by botanically unrelated fruits such as nuts, peanuts, legumes, tomato, and Prunoideae.

Complete amino acid sequence determination of the major allergen of peach (Prunus persica) Pru p 1

The major protein allergen of peach (Prunus persica), Pru p 1, has recently been identified as a lipid transfer protein (LTP). The complete primary structure of Pru p 1, obtained by direct amino acid sequence and liquid chromatography-mass spectrometry (LC-MS) analyses with the purified protein, is described here. The protein consists of 91 amino acids with a calculated molecular mass of 9178 Da. The amino acid sequence contains eight strictly conserved cysteines, as do all known LTPs, but secondary structure predictions failed to classify the peach 9 kDa protein as an 'all-alpha type', due to the high frequency of amino acids (nine prolines) disrupting alpha helices. Although the sequence similarity with maize LTP is only 63%, out of the 25 amino acids forming the inner surface of the tunnel-like hydrophobic cavity in maize ns-LTP 16 are identical and 7 similar in the peach homolog, supporting the hypothesis of a similar function.