Apple allergy manifests as two main groups of clinical entities reflecting different patterns of allergen sensitization: oral allergy syndrome (OAS) and generalized symptoms (GS).
We analysed the sensitization profile to a wide panel of different components of food allergens (rMal d 1, Mal d 2, rMal d 3, rMal d 4, rPru p 3, rBet v 1 and Pho d 2) for a population of Mediterranean patients with OAS and GS to apple.
Patients (N = 81) with a history of apple allergy that could be confirmed by positive prick-prick test and/or double-blind-placebo-controlled food challenge (DBPCFC), were included. Skin prick test (SPT) and ELISA were performed using a panel of inhalant, fruit and nut allergens. ELISA and ELISA inhibition studies were performed in order to analyse the sensitization patterns.
Thirty-five cases (43.2%) had OAS and 46 (56.8%) GS. SPT showed a significantly higher number of positive results with peach, cherry and hazelnut in those with GS. ELISA showed a significantly high percentage of positive cases to rMal d 3, rMal d 4, rPru p 3 and Pho d 2 in patients with OAS and GS compared to controls, and to rBet v 1 in patients with OAS vs controls and between OAS and GS patients. Three different patterns of recognition were detected: positive to LTP (rMal d 3 or rPru p 3), positive to profilin (rMal d 4 and Pho d 2), or positive to both. There were also patients with rMal d 1 recognition who showed cross-reactivity to rBet v 1.
Citation: Gomez F, Aranda A, Campo P, Diaz-Perales A, Blanca-Lopez N, Perkins J, et al. (2014) High Prevalence of Lipid Transfer Protein Sensitization in Apple Allergic Patients with Systemic Symptoms. PLoS ONE 9(9): e107304. https://doi.org/10.1371/journal.pone.0107304
Editor: Simon Patrick Hogan, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, United States of America
Received: February 12, 2014; Accepted: August 12, 2014; Published: September 11, 2014
Copyright: © 2014 Gomez et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The study was funded by the FIS-Thematic Networks and Co-operative Research Centres: RIRAAF (RD07/0064) and ISCIII PI12/02481. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
In adults and older children Rosacea fruits are the plant foods most often responsible for allergic reactions –. Of these, apple allergy is a prevalent entity in Central and Northern Europe and the sensitization pattern has been studied in detail , . Although also important in Southern Europe, it is less frequent and has thus received less attention , , . Four apple allergens have been identified so far: Mal d 1, a pathogenesis-related protein (PR-10) ; Mal d 2, a thaumatin-like protein (TLP) ; Mal d 3, a lipid transfer protein (LTP) ; and Mal d 4, a profilin .
Two major groups of entities have been described according to the patterns of allergen sensitization , –: oral allergy syndrome (OAS) and generalized symptoms (GS) that include urticaria and anaphylaxis. In Central and Northern Europe, apple sensitization has been associated with initial sensitization to an aeroallergen, with Betula pollen allergen the most often involved , , . Patients sensitized to Bet v 1 also respond to Mal d 1 because of the structural homology , , . In fact, over 60% of Betula sensitized patients have mild symptoms after apple ingestion, usually OAS , , . By contrast, in Southern European countries, apple allergic patients more frequently have GS, no association with Betula sensitization and cross-reactions to other fruits, especially peach , , , . In this situation peach LTP, Pru p 3, is the strongest candidate for these sensitizations , , , . Moreover, atopic patients allergic to peach and apple may have OAS in an environment where the prevalence of Betula pollen sensitization is low. In this situation, profilin is an important sensitizer –.
As mentioned earlier, in the Mediterranean area, the origin of apple allergy is generally attributed to LTP sensitization , , , , although the relevance of sensitization to other allergens has not yet been fully established, particularly for patients with pollen allergy. Therefore OAS can be caused both by labile (such as PR-10 and profilins), as well as stable allergens (such as LTPs), whereas systemic symptoms are associated with the latter and seldom with labile allergens. The aim of this study was to undertake a detailed analysis of allergen sensitization profiles in an important number of patients diagnosed as allergic to apple from a Mediterranean population. A clinical questionnaire was used to record the allergic response or tolerance to other fruits and vegetables. Inhibition ELISA was performed using the four apple allergens identified, as well as other important related allergens such as rBet v 1, rPru p 3 and Pho d 2 (equivalent to rMal d 1, rMal d 3 and rMal d 4, respectively).
Materials and Methods
Patients and controls
Patients referred to the Allergy Unit of Malaga Hospital (south of Spain area) with a history of apple allergy that could be confirmed by positive prick-prick test and/or double-blind-placebo-controlled food challenge (DBPCFC), were included. Patients were classified according to symptoms: OAS when they were restricted to the skin or mucosal sites of direct contact with the allergen (itching of the oral mucosa and lips with or without angioedema immediately after eating apple), and GS when reactions involved organs far from the site of initial contact with the food (urticaria, with or without angioedema, and anaphylaxis) accompanied or not to OAS. A control group, from the same geographical area, comprised 25 non-allergic subjects with tolerance to apple. All participants completed a written informed consent and the ethical committee of our institution approved the study (CEI Provincial of Malaga).
The allergological evaluation included an examination of the patient's clinical history, a detailed questionnaire, skin test, specific IgE determination and DBPCFC.
The skin test was performed according to European guidelines  using Golden Delicious apples for the prick-prick technique with peel and pulp tested separately, and by SPT using commercialized extract from Phleum, Olea, Betula, Platanus, Cupressus, Parietaria and Artemisia pollen and apple, peach, cherry and hazelnut from ALK-Abelló (Madrid, Spain). The SPT response was considered positive if the diameter of the wheal area was 3 mm greater than that induced by the negative control.
Specific IgE antibodies to apple were measured by ImmunoCAP following the manufactureŕs recommendations (Phadia, Uppsala, Sweden). A positive result was defined as a value >0.35 kUA/l.
DBPCFC was performed as described , except in cases with a recent history (<1 year) of anaphylaxis after apple ingestion and SPT positive to apple. Briefly, meals containing 5, 40, and 120 g of fresh ground apple with a mixture of yogurt, orange juice, coffee dried, and oatmeal flakes were freshly prepared 5 minutes before administration to prevent the loss of allergenicity. Placebo meals consisted of the same ingredients, without fresh apple. If cutaneous and/or respiratory symptoms or alterations in vital signs appeared, the procedure was stopped and the symptoms were evaluated and treated.
Purification and quality controls
The LTPs was purified following the method previous published by Diaz-Perales . Briefly, LTP was purified from defatted peel peach or apple fruit by RP-HPLC on a Vydac-C4 column (22×250 mm; particle size 10 mm; The Separations Group, Hesperia, CA, USA), followed by RP-HPLC Nucleosil 300-C4 column (8×250 mm; particle size 5 mm; Sugelabor, Madrid, Spain). Finally, proteins were analyzed by mass spectrometry, SDS-PAGE and immunoblotting.
Mal d 2 was purified from apple fruit by cation-exchange chromatography on a Bio-ScaleTM Mini Macro-Preps High S column (BioRad, Hercules,CA, USA). Following this, its purity and reactivity was analyzed by mass spectrometry, SDS-PAGE and immunoblotting.
rMal d 1 and Pho d 2 was obtained from Biomay (Vienna, Austria) and ALK-Abello (Madrid, Spain), respectively.
rMal d 4 was prepared using the protocol described by Scheurer S . Briefly, the protein was cloned by polymerase chain reaction and produced in Escherichia coli BL21. The profilin was purified as non-fusion proteins by affinity chromatography on poly-(L-proline)-Sepharose and its purity and IgE reactivity was analyzed by SDS-PAGE and immunoblotting.
rBet v 1 was produced in Escherichia coli BL21 (DE3). This protein was purified under denaturing conditions from inclusion bodies and subsequently subjected to Immobilized Metal Affinity Chromatography (IMAC) followed by ion-exchange chromatography (IEC). Finally, His-Tagged rBet v 1 was analyzed by SDS PAGE and Immunoblotting using an anti-His-Tag antibody, anti-Bet v 1 monoclonal antibody and sera from patients with IgE-reactivity to Bet v 1.
Specific IgE and inhibition studies by ELISA
ELISA assays were performed as described . Costar plates (Corning, NY, USA) were coated with 5 µg/mL of rMal d 1 (Biomay, Vienna, Austria), Mal d 2, rMal d 3 and rPru p 3 (Dra Díaz-Perales, Polytechnical University of Madrid), rMal d 4 and rBet v 1 (Dr Vieths, Paul-Ehrlich Institut) and Pho d 2 (ALK-Abelló). After, the plates were blocked with blocking solution (Sigma, St. Louis,USA) for 1 h. Individual serum from patients and controls at 1∶5 dilution was added to each well. We used two negative controls, a pool of sera from non-allergic subjects and blocking buffer, and as positive controls we used patients sera with known specific IgE to proteins. The assay was completed with rabbit anti-human IgE antibody (1∶3000, DAKO, Denmark) conjugated to horseradish peroxidase (HRP). IgE binding was detected using o-phenylenediamine (OPD, DAKO). Results are expressed as absorbance units, measured at 490 nm. They were considered positive when >0.18 (mean OD + 3xSD to blocking).
For ELISA inhibition, sera were pre-incubated with different inhibitors (rMal d 3, rMal d 4, rPru p 3, Pho d 2) at final concentrations of 20, 2, and 0.2 µg/mL or with phosphate buffer for the non-inhibited serum for 3 h at room temperature. Subsequently, the inhibitor mixtures were added to plates coated with rMal d 3, rMal d 4, rPru p 3 or Pho d 2, followed by the ELISA protocol described above.
To analyse the sensitization of patients positive to rMal d 1 and rBet v 1, sera from specific IgE positive patients were pre-incubated with rMal d 1, Mal d 2, rMal d 3, rMal d 4 and rBet v 1 and added in solid phases with rMal d 1 and rBet v 1.
Percentage inhibition of IgE binding was calculated as follows: % Inhibition = (serum not inhibited-serum inhibited/serum not inhibited) x100.
Quantitative variables are shown as medians and interquartile ranges (IR), while qualitative variables are shown as frequencies. Medians between groups were compared using Mann-Whitney or Kruskal-Wallis tests, while χ2 was used to compare proportions. Differences with a p<0.05 were considered significant.
The study included 81 patients with a diagnosis of hypersensitivity to apple. Their median age was 31 (IR:25–38) years and 62 (76.44%) were female. Thirty-five patients (43.20%) had OAS and 46 (56.79%) had GS (22 anaphylaxis (47.82%) and 24 (52.12%) urticaria). Sixty-eight cases (83.95%) showed positive prick by prick skin tests with apple peel and pulp and 55 (67.90%) positive skin test with the commercial extract for 77.14% of cases tested using prick by prick and for 57.14% with skin test. In GS patients we found that 76.08% showed skin test positivity with commercial extract and 89.13% with prick by prick. Moreover, we did not find any patient who was positive with commercial extracts and negative with prick by prick. In addition, 65 (80.24%) had serum specific IgE to apple and 62 a positive DBPCFC to apple. DBPCFC was not performed in 19 cases who had recent apple-related anaphylaxis (<1 year) and a positive skin test to apple.
Seventy-one (87.65%) were sensitized to pollen and from these 54 (76.05%) had clinical symptoms consisting of rhinitis and/or asthma; 77 (95.06%) presented symptoms with peach and 31 (38.27%) with hazelnut. The median age at symptom onset was 15 (IR:10–25) years to peach, 17 (IR:11–27) to apple, 17.5 (IR:7.75–25) to pollen and 18 (IR:13–25) to hazelnut.
Comparisons between patients with OAS and GS (Table 1) showed that although the percentage of cases with a positive SPT and specific IgE to apple was higher in those with GS, there were no significant differences between the groups in any of the variables evaluated.
Comparisons of clinical symptoms between patients with (N = 54, 66.66%) and without pollen allergy (N = 27, 33.33%) showed that in those with pollen allergy 24 (44.44%) developed GS and 30 (55.55%) OAS, whereas in those without pollen allergy, 18 (66.66%) developed GS and 9 (33.33%) OAS (Data not shown).
Skin prick test results
Analysis of the SPT showed that 49 (60.49%) cases were positive to Phleum, 54 (66.67%) to Olea, 30 (65.22%) to Betula, 44 (54.32%) to Platanus, 41 (50.62%) to Cupressus, 38 (46.91%) to Parietaria, 35 (43.21%) to Artemisa, 46 (56.79%) to peach, 34 (41.97%) to cherry and 32 (39.51%) to hazelnut. Comparison between patients with OAS and those with GS showed a significantly higher percentage of positive results only with peach, cherry and hazelnut in those with GS (Table 2).
Specific IgE results by ELISA
Comparisons of specific IgE determinations (Figure 1A) in OAS, GS, and controls showed significant differences between the three groups for rMal d 3 (p<0.001), rMal d 4 (p<0.001), rPru p 3 (p = 0.015) and rBet v 1 (p = 0.02). In more detail, there was an increase in levels of IgE to four allergens in OAS when compared to controls (rMal d 3: p<0.001, rMal d 4: p<0.001, rPru p 3: p = 0.007, and rBet v 1: 0.010) and in GS compared to controls (rMal d 3: p<0.001, rMal d 4: p = 0.001, rPru p 3: p = 0.013, and rBet v 1: p = 0.041), with no differences between OAS and GS. Comparisons in terms of positive percentage (Figure 1B) showed significant differences between OAS and controls for rMal d 3 (p = 0.036), rMal d 4 (p = 0.042), rPru p 3 (p = 0.009), rBet v 1 (p = 0.038) and Pho d 2 (p = 0.021) and between GS and controls for rMal d 3 (p = 0.005), rMal d 4 (p = 0.009), rPru p 3 (p = 0.007) and Pho d 2 (p = 0.045). Moreover, rBet v 1 was higher in OAS compared to GS (p = 0.011).
Sensitization frequencies to apple allergens
We detected that 27% of the patients recognized Mal d 1, 5% to Mal d 2, 37% to Mal d 3 and 30% to Mal d 4. When we analyzed the sensitization percentages taking into account symptoms we observed no significant differences between OAS and GS. In patients with OAS, 31% of them had specific IgE to Mal d 1, 2% to Mal d 2, 38% to Mal d 3 and 28% to Mal d 4. In patients with GS, 23% had specific IgE to Mal d 1, 9% to Mal d 2, 37.50% to Mal d 3 and 35% to Mal d 4.
Based on the IgE response to allergens from LTP and profillin families, the patients were classified in three groups (Table 3): Group 1 (LTP pattern), positive to rMal d 3 and/or rPru p 3; Group 2 (Profilin pattern), positive to rMal d 4 and/or Pho d 2; and Group 3 (LTP-Profilin pattern), positive to both. We found a significant increase in the percentage of patients positive to LTP-profilin in the group with GS. Moreover, if we consider all those with an LTP response, regardless of the profilin results, there were 11 (31.42%) positive cases in the OAS group and 27 (58.69%) in the GS (p = 0.024). On the other hand, considering all those who were positive to profilin, regardless of the LTP results, 9 (25.71%) were positive in the OAS group and 18 (39.13%) in the GS group (p = 0.240).
IgE recognition pattern to different allergens
ELISA inhibition was performed for all cases showing a sIgE level greater than 0.5 of O.D. Figure 2 shows the ELISA inhibition pattern for representative cases from each group of patients. Results from the Group 1, patients with GS, showed that using either rMal d 3 or rPru p 3 in the solid phase the strongest inhibitor was rPru p 3, followed by rMal d 3, with no inhibition by the other allergens (Figure 2A).
Sera were preincubated with decreasing concentrations (20–0.2 µg/ml) of rMal d 3, rMal d 4, rPru p 3, and Pho d 2, before they were added to the solid phase. Results are expressed as percentage inhibition.
In Group 2, patients with either OAS or GS, using rMal d 4 in the solid phase, the highest inhibition was found with itself followed by Pho d 2; similar results were seen using Pho d 2 in the solid phase (Figure 2B and C).
Figures 2D and 2E show sera from Group 3 for patients with OAS or GS, respectively. In both cases, when using rMal d 3 in the solid phase the highest inhibition was found with rMal d 3 followed by rPru p 3. Using Pho d 2 in the solid phase we detected the highest inhibition with itself and rMal d 4.
In order to further analyse sensitization to Bet v 1 observed in the patients allergic to apple, ELISA inhibition studies were performed by analyzing the IgE recognition to the PR-10 proteins, rMal d 1 and rBet v 1 (Figure 3). Data showed that rMal d 1 was the most potent inhibitor regardless of the solid phase used (rMal d 1 or rBet v 1). However, rBet v 1 only showed high inhibition when the same allergen was used in the solid phase. Moreover, no inhibition was detected with Mal d 2, rMal d 3 or rMal d 4.
In this study we compared the sensitization pattern and IgE recognition for a wide panel of relevant purified proteins from inhalant and fruit allergens in a population of Mediterranean patients allergic to apple. Patients were selected based on a consistent clinical history, skin test, specific IgE and/or DBPCFC. Considering the clinical symptoms, in our population over 50% of patients developed GS, with almost half developing anaphylaxis. This is contrary to what occurs in Central and Northern European countries, where OAS is the most frequent clinical entity , , , . This case series differs from a previously published study of a Spanish population, which reported a lower percentage of patients with GS (35%) .
For patients with GS we found that 58.69% of cases had IgE antibodies to LTP (rMal d 3 or rPru p 3), independently of profilin sensitization; thus confirming previous data showing that proteins from the LTP family are the most relevant sensitizers in apple allergy in southern Europe , , . Moreover, these patients had higher sensitization to peach, cherry and hazelnut, where LTPs are also relevant allergens , , therefore confirming that in apple allergic patients, LTP sensitization is related with more severe symptoms .
Considering profilin sensitization (rMal d 4 and Pho d 2), we found that 38.06% of cases were positive to these allergens only, with no differences between patients with OAS and GS (22.85% and 15.21% of cases respectively). These results indicate that when all patients with apple allergy are analysed together the picture is more complex than previously thought , , and that in some cases profilin may be the sole agent responsible for the symptoms. Nevertheless, our results are in agreement with some studies detecting a high association between profilin sensitization and OAS in peach and/or apple allergic patients , , .
Importantly, this study confirmed different patterns of IgE recognition through the use of detailed inhibition studies. Our data indicate the recognition of Mal d 3 with high cross-reactivity with Pru p 3 in those with LTP sensitization and of Mal d 4 with high cross-reactivity with Pho d 2 in those sensitized to profilin.
Another important point is that in our population 87.65% of all cases were sensitized to pollen with 76.05% of all cases having clinical symptoms of asthma or rhinitis. When we consider apple allergy in the context of pollen sensitization we found that those positive to these inhalant allergens had less severe symptoms as have been described by Pastorello in peach allergy where patients positive to Pru p 3 were significantly less likely to develop severe symptoms when also sensitised to Pru p 1 and Pru p 4 . More specifically, among those with GS, 66.7% did not have pollen allergy compared to 44.6% who did have pollen allergy.
Although Betula is not normally encountered in our area we detected positive SPT to Betula pollen and specific IgE antibodies to Bet v 1 in 43.41% and 20.29% of cases, respectively, with no differences between patients with OAS and with GS. Differences were also observed between the Betula major allergen Bet v 1 and the homologous Mal d 1, with higher percentages of specific IgE antibodies in patients with OAS (33.32% and 31%, respectively) compared with GS (3% and 23.14%, respectively). These figures, although lower than those detected in central and northern Europe , , are nevertheless higher than those previously detected in a Spanish population allergic to apple . In our geographical area, people are not exposed to Betula and the clinical expression of this sensitization is not relevant. Other, Betula related species, such as such as hazel and oak from the Fagales order, have been shown to cause cross-reactivity in Betula-free areas , . However, in our study the inhibition results indicate that Betula recognition in our population could be due to cross-reactivity with Mal d 1, the latter being the primary sensitizer.
Summarizing, we have analysed a population of patients with apple allergy and a high percentage of pollinosis. Within this population we have seen various patterns of sensitization, with LTP being the most prevalent sensitizer for patients with GS while profilin, though more prevalent for those with OAS, is an important sensitizer for patients with both type of symptoms. Moreover, Mal d 1 was also detected and associated with mild symptoms. All these results indicate that, given the different recognition patterns, it would be desirable to include profillin, LTP and also PR-10 allergens in routine diagnosis of apple allergic patients.
We thank to Stefan Vieths (Paul-Ehrlich-Institut, Federal Institute for Vaccines and Biomedicines, Division of Allergology, Langen, Germany) for the provision of different allergens necessary for the study. We also thank Ian Johnstone for help with the English language version of the manuscript and Luisa Galindo for the technical assistance in the diagnostic studies.
Conceived and designed the experiments: MJT CM MB. Performed the experiments: AA CM ADP MG. Analyzed the data: AA CM. Contributed reagents/materials/analysis tools: MJT CM MB. Wrote the paper: MJT FG AA CM. Collected patients' sera: MJT FG NBL PC MB. Corrected the manuscript and suggested important contributions to define the final version: MJT CM JP MB.
- 1. Cuesta Herranz J, Lazaro M, Figueredo E, Igea JM, Umpierrez A, et al. (2000) Allergy to plant derived fresh foods in a birch and ragweed free area. Clin Exp Allergy 30: 1411–1416.
- 2. Kanny G, Moneret-Vautrin DA, Flabee J, Beaudouin E, Morisset M, et al. (2001) Population study of food allergy in France. J Allergy Clin Immunol 108: 133–140.
- 3. Kivity S, Dunner K, Marian Y (1994) The pattern of food hypersensitivity in patients with onset after 10 years of age. Clin Exp Allergy 24: 19–22.
- 4. Eriksson NE, Formgren H, Svenonius E (1982) Food hypersensitivity in patients with pollen allergy. Allergy 37: 437–443.
- 5. Ortolani C, Ispano M, Pastorello EA, Bigi A, Ansaloni R (1988) The oral allergy syndrome. Ann Allergy 61: 47–52.
- 6. Fernandez Rivas M, van Ree R, Cuevas M (1997) Allergy to Rosaceae fruits without related pollinosis. J Allergy Clin Immunol 100: 728–733.
- 7. Fernandez Rivas M, Bolhaar S, Gonzalez-Mancebo E, Asero R, van Leeuwen A, et al. (2006) Apple allergy across Europe: How allergen sensitization profiles determine the clinical expression of allergies to plant foods. J Allergy Clin Immunol 118: 481–488.
- 8. Vanek-Krebitz M, Hoffmann-Sommergruber K, Laimer da Camara Machado M, Susani M, Ebner C, et al. (1995) Cloning and sequencing of Mal d 1, the major allergen from apple (Malus domestica), and its immunological relationship to Bet v 1, the major birch pollen allergen. Biochem Biophys Res Commun 214: 538–551.
- 9. Krebitz M, Wagner B, Ferreira F, Peterbauer C, Campillo N, et al. (2003) Plant-based heterologous expression of Mal d 2, a thaumatin-like protein and allergen of apple (Malus domestica), and its characterization as an antifungal protein. J Mol Biol 329: 721–730.
- 10. Garcia-Selles FJ, Diaz-Perales A, Sanchez-Monge R, Alcántara M, Lombardero M, et al. (2002) Patterns of reactivity to lipid transfer proteins of plant foods and Artemisia pollen: an in vivo study. Int Arch Allergy Immunol 128: 115–122.
- 11. Ma Y, Zuidmeerw L, Bohle B, Bolhaar ST, Gadermaier G, et al. (2006) Characterization of recombinant Mal d 4 and its application for component resolved diagnosis of apple allergy. Clin Exp Allergy 36: 1087–1096.
- 12. González-Mancebo E, Fernández-Rivas M (2008) Outcome and safety of double-blind, placebo-controlled food challenges in 111 patients sensitized to lipid transfer proteins. J Allergy Clin Immunol 121: 1507–1508.
- 13. Cuesta-Herranz J, Barber D, Blanco C, Cistero-Bahíma A, Crespo JF, et al. (2010) Differences among pollen-allergic patients with and without plant food allergy. Int Arch Allergy Immunol 153: 182–192.
- 14. Asero R, Monsalve R, Barber D (2008) Profilin sensitization detected in the office by skin prick test: a study of prevalence and clinical relevance of profilin as a plant food allergen. Clin Exp Allergy 38: 1033–1037.
- 15. Andersen MB, Hall S, Dragsted LO (2011) Identification of european allergy patterns to the allergen families PR-10, LTP, and profilin from Rosaceae fruits. Clin Rev Allergy Immunol 41: 4–19.
- 16. Dreborg S, Frew A (1993) Allergen Standardization and skin tests. Allergy 48: 49–54.
- 17. Bolhaar STHP, van de Weg WE, van Ree R, Gonzalez-Mancebo E, Zuidmeer L, et al. (2005) In vivo assessment with prick-to-prick testing and double-blind, placebo-controlled food challenge of allergenicity of apple cultivars. J Allergy Clin Immunol 116: 1080–1086.
- 18. Perales Diaz, Lombardero M, Sánchez-Monge R, García-Selles FJ, Pernas M, et al. (2000) Lipid-transfer proteins as potential plant panallergens: cross-reactivity among proteins of Artemisia pollen, Castanea nut and Rosaceae fruits, with different IgE-binding capacities. Clin Exp Allergy 30: 1403–1410.
- 19. Scheurer S, Wangorsch A, Nerkamp J, Skov PS, Ballmer-Weber B, et al. (2001) Cross-reactivity within the profilin panallergen family investigated by comparison of recombinant profilins from pear (Pyr c 4), cherry (Pru av 4) and celery (Api g 4) with birch pollen profilin Bet v 2. J Chromatogr B Biomed Sci Appl. 756(1–2): 315–25.
- 20. Pastorello EA, Pravettoni V, Farioli L, Gonzalez-Mancebo E, Zuidmeer L, et al. (1999) Clinical role of a lipid transfer protein that acts as a new apple-specific allergen. J Allergy Clin Immunol 104: 1099–1106.
- 21. Barber D, de la Torre F, Feo F, Florido F, Guardia P, et al. (2008) Understanding patient sensitization profiles in complex pollen areas: a molecular epidemiological study. Allergy 63: 1550–1558.
- 22. Asero R, Mistrello G, Roncarolo D, de Vries SC, Gautier MF, et al. (2000) Lipid transfer protein: a pan-allergen in plant-derived foods that is highly resistant to pepsin digestion. Int Arch Allergy Immunol 122: 20–32.
- 23. Pastorello EA, Farioli L, Pravettoni V, Scibilia J, Mascheri A, et al. (2011) Pru p 3-sensitised Italian peach-allergic patients are less likely to develop severe symptoms when also presenting IgE antibodies to Pru p 1 and Pru p 4. Int Arch Allergy Immunol 156: 362–372.
- 24. Ebner C, Hirschwehr R, Bauer L, Breiteneder H, Valenta R, et al. (1995) Identification of allergens in fruits and vegetables: IgE cross-reactivities with the important birch pollen allergens Bet v 1 and Bet v 2 (birch profilin). J Allergy Clin Immunol 95: 962–969.
- 25. Mari A, Wallner M, Ferreira F (2003) Fagales pollen sensitization in a birch-free area: a respiratory cohort survey using Fagales pollen extracts and birch recombinant allergens (rBet v 1, rBet v 2, rBet v 4). Clin Exp Allergy 33: 1419–28.
- 26. Mari A (2001) Multiple pollen sensitization: a molecular approach to the diagnosis. Int Arch Allergy Immunol 125: 57–65.
- 27. Palacin A, Tordesillas L, Gamboa P, Sanchez-Monge R, Cuesta-Herranz J, et al. (2010) Characterization of peach thaumatin-like proteins. Clin Exp Allergy 40: 1422–1430.
- 28. Palacín A, Rivas LA, Gómez-Casado C, Aguirre J, Tordesillas L, et al. (2012) The involvement of thaumatin-like proteins in plant food cross-reactivity: a multicenter study using a specific protein microarray. PLoS One (9): e44088.