Different patterns of allergen recognition in children allergic to orange☆

[Reduction of Orange Allergen Cit s 2 Levels in Fresh Orange Juice with Pineapple Bromelain Enzymatic Treatment]

Oranges are consumed worldwide; however, they contain Cit s 2, a major profilin allergen. We aimed to reduce Cit s 2 levels by preparing mixed orange fresh juice with pineapple, as a convenient method for any kitchen. Cit s 2 levels in orange extracts digested with pineapple extract and its protease bromelain were evaluated with quantitative enzyme-linked immunosorbent assay. Cit s 2 levels decreased according to reaction temperature and time, which was inhibited by iodoacetic acid. Treatment with pineapple extract diluted 40-fold and 0.1 mg/mL of bromelain at 37℃ for 30 min contributed to reducing residual Cit s 2 levels below the cut-off of 15%, respectively. Since this condition can increase the proportion of orange juice and reduce the risk of ingesting the pineapple allergen bromelain, it is considered to be more practical. Broad utilization of proteases in hypoallergenic food products is expected following clinical studies for verification.

Immunoblotting Quantification Approach for Identifying Potential Hypoallergenic Citrus Cultivars

The inherent allergens of citrus fruits, such as Cit s 1, Cit s 2, Cit s 3 can cause allergic reactions. A better understanding of the genetic factors (cultivar to cultivar) affecting the allergenic potential of citrus fruits would be beneficial for further identification of hypoallergenic genotypes. In the present study, an immunoblotting quantification approach was adopted to assess the potential allergenicity of 21 citrus cultivars, including nine subgroups (tangerine, satsuma, orange, pummelo, grapefruit, lemon, kumquat, tangor, and tangelo). To prepare highly sensitive and specific rabbit polyclonal antibodies, antigenicity of purified rCit s 1.01, rCit s 2.01, and rCit s 3.01 peptides were enhanced with high epitope density in a single protein molecule. The data integration of three citrus allergen quantifications demonstrated that the four pummelo cultivars (Kao Phuang Pummelo, Wanbai Pummelo, Shatian Pummelo, and Guanxi Pummelo) were potential hypoallergenic, compared with other 8 subgroups. Moreover, the immunological analyses with sera of allergic subjects revealed that Shatian Pummelo and Guanxi Pummelo showed the lowest immunoreactivity in 8 representative citrus cultivars. These potential hypoallergenic genotypes are of great significance to not only allergic consumers but also citrus breeders in the genetic improvement of hypoallergenic citrus as breeding resources.

Development of monoclonal antibody-based ELISA for the quantification of orange allergen Cit s 2 in fresh and processed oranges

The aim of this study was to develop a monoclonal antibody (mAb)-based enzyme-linked immunosorbent assay (ELISA) for the quantification of a major allergen (Cit s 2) in fresh and processed oranges. Purified recombinant Cit s 2 (rCit s 2)-small ubiquitin-like modifier (SUMO) was used for the production of mAbs. In the optimized ELISA, the recovery of rCit s 2 from Navel oranges or orange juice was 107-132%, and the intra- and inter-assay coefficients of variation were 3.1-8.8% and 4.4-11%, respectively. The Cit s 2 content in fresh oranges was determined to be 1,800±430ng/g, while this content was much lower in the processed foods. The developed ELISA demonstrated high reproducibility, sensitivity, and accuracy, and this assay may help individuals with orange allergy by determining Cit s 2 quantities in food products and controlling their Cit s 2 intake.

Development and Application of a Multiplex Real-Time PCR Assay as an Indicator of Potential Allergenicity in Citrus Fruits

The effects of tissue type, harvest maturity, and genetic factors on the expression of genes that related to citrus fruit allergies remain poorly understood. In the present study, a multiplex real-time PCR assay was developed to monitor the expression of citrus allergen genes individually with the advantages of much fewer sample requirements and simultaneously multiple target genes detection. Gene specific primer pairs and Taqman probes of three citrus allergen genes Cit s 1.01, Cit s 2.01, and Cit s 3.01 and the house-keeping gene β-actin were designed based on gene sequence differences. The PCR results showed that differential expression patterns were found during the ripening process. The expression levels of Cit s 3.01 were much higher than those of Cit s 1.01 and Cit s 2.01 in both peel and pulp tissues among 10 citrus cultivars. Data suggested that Kao Phuang Pummelo could be safely consumed with a potential low risk in allergenicity. Considering that assessing allergenicity is one of the tests in food safety, this assay might also facilitate the breeding and production of "allergy-friendly" citrus fruits.

Suppression of the TNF-alpha level is mediated by Gan-Lu-Yin (traditional Chinese medicine) in human oral cancer cells through the NF-kappa B, AKT, and ERK-dependent pathways

Oral cancer is one of the major causes of deaths in the male population of Taiwan. Gan-Lu-Yin (GLY) is used for an adjuvant treatment of Traditional Chinese Medicine in clinical patients. In this study, we investigated the molecular mechanisms in oral cancer cell lines after exposure to GLY. The cytometric bead-based array (CBA) method was used for the examining and analyzing of tumor necrosis factor-alpha (TNF-α) secretion level. TNF-α mRNA expression was determined by real-time PCR analysis. Nuclear factor kappa B (NF-κB) activity and other relative proteins were determined by NF-κB promoter assay, Western blotting, electrophoretic mobility shift assay (EMSA), and immuno-staining analyses. GLY decreased the secretion of TNF-α from the oral cancer CAL 27 cells. Furthermore, 2000 μg/mL of GLY significantly suppressed TNF-α mRNA expression of CAL 27 cells in a time-dependent manner. GLY reduced the levels of proteins, including nuclear NF-κB (p65 and p50), p-IKK (ser176), p-IκB, p-AKT, p-ERK, and nuclear Egr-1 in a time and dose-dependent manner. GLY also suppressed the NF-κB activity and translocation in CAL 27 cells. We suggest that GLY might promote the cure of oral cancer through decreasing the level of TNF-α cytokine, and these actions were mediated partially through the NF-κB, AKT, and ERK-dependent pathways in vitro. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1196-1205, 2016.

How relevant is panallergen sensitization in the development of allergies?

Panallergens comprise various protein families of plant as well as animal origin and are responsible for wide IgE cross-reactivity between related and unrelated allergenic sources. Such cross-reactivities include reactions between various pollen sources, pollen and plant-derived foods as well as invertebrate-derived inhalants and foodstuff. Here, we provide an overview on the most clinically relevant panallergens from plants (profilins, polcalcins, non-specific lipid transfer proteins, pathogenesis-related protein family 10 members) and on the prominent animal-derived panallergen family, tropomyosins. In addition, we explore the role of panallergens in the sensitization process and progress of the allergic disease. Emphasis is given on epidemiological aspects of panallergen sensitization and clinical manifestations. Finally, the issues related to diagnosis and therapy of patients sensitized to panallergens are outlined, and the use of panallergens as predictors for cross-reactive allergy and as biomarkers for disease severity is discussed.

The Citrus clementina putative allergens: from proteomic analysis to structural features

Several allergens have been identified and characterized in the genus Citrus, which belongs to the germin-like proteins (GPLs), profilins, and non-specific lipid transfer proteins (nsLTPs). In this work, in silico sequence analysis, protein purification, mass spectrometry identification, and the spectral counting method were integrated to identify new putative allergens of Citrus clementina and their expression level in the fruit peel. The in silico analysis revealed fifteen new sequences belonging to GLPs (Cit cl 1), and two more belonging to nsLTPs (Cit cl 3). No other new sequences were found as regards profilins (Cit cl 2). Each putative allergen from fruit peel was obtained using different protein extraction methods, and the protein sequences of the putative allergens were identified by means of LTQ-Orbitrap XL mass spectrometer. The spectral counting strategy revealed that Cit cl 1 had a higher expression level than Cit cl 2 and Cit cl 3. To predict the quaternary structure and deduced function of Cit cl 1, its primary sequence was used as a template to search a homologous protein structure in the RCSB PDB Database, getting high correspondence with the oxalate oxidase protein in barley.

Citrus allergy from pollen to clinical symptoms

Allergy to citrus fruits is often associated with pollinosis and sensitization to other plants due to a phenomenon of cross-reactivity. The aims of the present study were to highlight the cross-reactivity among citrus and the major allergenic pollens/fruits, throughout clinical and molecular investigations, and to evaluate the sensitization frequency to citrus fruits in a population of children and adults with pollinosis. We found a relevant percentage of sensitisation (39%) to citrus fruits in the patients recruited and in all of them the IgE-mediated mechanism has been confirmed by the positive response to the prick-to-prick test. RT-PCR experiments showed the expression of Cit s 1, Cit s 3 and a profilin isoform, already described in apple, also in Citrus clementine pollen. Data of multiple sequence alignments demonstrated that Citrus allergens shared high percentage identity values with other clinically relevant species (i.e. Triticum aestivum, Malus domestica), confirming the possible cross-allergenicity citrus/grasses and citrus/apple. Finally, a novelty of the present work has been the expression of two phospholipaseA2 isoforms (PLA2 α and β) in Citrus as well as in Triticum pollens; being PLA2 able to generate pro-inflammatory factors, this enzyme could participate in the activation of the allergenic inflammatory cascade.

Identification of Bet v 1-related allergens in fig and other Moraceae fruits

BACKGROUND

Allergy to fig fruit (Ficus carica) has been described in patients allergic to Ficus benjamina or rubber latex but may occur also in pollen-allergic patients.

OBJECTIVE

To study the potential cross-reactivity between fig and taxonomically related fruits with the major birch pollen allergen Bet v 1.

METHODS

One hundred and eighty-eight patients with or without birch pollen allergy were prick-to-prick tested with fig (F. carica), mulberry (Morus alba), jackfruit (Artocarpus heterophyllus; all family Moraceae) and other pollen-associated foods. Moraceae fruit extracts were separated by SDS-PAGE and tested with patient sera and polyclonal antisera against Mal d 1. Western blot inhibition was performed with Moraceae fruit extracts, birch pollen and recombinant Bet v 1. Putative Bet v 1 homologs in Moraceae fruits were analysed by liquid chromatography-ion trap mass spectrometry.

RESULTS

Among 85 patients with isolated birch pollen allergy, 78% had a positive skin test to fresh fig, 10% to dried fig, 91% to mulberry, 91% to jackfruit, 77% to Rosaceae fruits and 83% to hazelnut. Sixty-six per cent of birch pollen-allergic patients positive for fig, reported symptoms after consumption of fresh figs, whereas dried figs were mostly well tolerated. In 60 patients with isolated Ficus benjamina sensitization, the reactivity rates to the same foods were 83-40-0-0-0-0%. None of 32 mugwort pollen-allergic patients reacted to Moraceae fruits. Rabbit anti-Mal d 1 and patient sera reacted to a 17 kDa band in all Moraceae extracts. IgE binding to these proteins was completely inhibited by birch pollen and rBet v 1. Mass spectrometry identified several peptides from the 17 kDa fig, mulberry and jackfruit allergen with respectively 60%, 56% and 76% homology to Bet v 1.

CONCLUSION

Fig and other Moraceae fruits contain allergens homologous to Bet v 1 and represent clinically relevant birch pollen-associated foods.

Proteome from lemon fruit flavedo reveals that this tissue produces high amounts of the Cit s1 germin-like isoforms

A multistep procedure has been developed and applied to extract and purify proteins from lemon fruit flavedo. 2DE, LC-ESI-MS/MS, and bioinformatics were used to detect the high abundance of the germin-like glycoprotein Cit s1, a powerful allergen in humans. Peptide alignments against Citrus EST repositories gave the best scores with the C. sinensis cDNA (gi|188354270/EY710037), annotated as unknown sweet orange fruit protein; additional BLAST of peptides against NCBI databases gave high sequence identities with sequence of orange Cit s1 (gi|52782810/P84159), suggesting that the unknown sweet orange fruit protein is consistent with the Cit s1 protein. Peptides of Cit s1 were detected in 17 spots ranging from 120 to 20 kDa, pointing out that in the flavedo of lemon the Cit s1 may be expressed as several isoforms of which the 120 kDa isoform is the largest monomer and the 20 kDa is the smallest one. This finding adds information about the features of Cit s1, because it has been previously reported as a unique monomeric glycoprotein of 24 kDa.

Anaphylaxis from mandarin (Citrus reticulata): identification of potential responsible allergens

We report on a patient with anaphylaxis from mandarin. Temporal relationship between consumption of the fruit, the presence of positive specific IgE, the positive skin test and the basophil activation test for mandarin strongly supported the diagnosis of an IgE-mediated allergy from mandarin. The lipid transfer protein allergen from mandarin fruit was isolated and characterized. Specific IgE levels and IgE immunodetection data indicated the patient's sensitization to orange (Cit s 3) and mandarin (Cit r 3) lipid transfer protein allergens, as well as to germin-like (Cit s 1) allergen. These results were fully confirmed by skin prick test and basophil activation test (BAT) for lipid transfer proteins, and a BAT for Cit s 1. This case report has several particularities. First, in Central and Northern Europe, it is not widely appreciated that citrus fruits, particularly mandarin, can elicit anaphylaxis. Second, this case report re-emphasizes sensitization from lipid transfer proteins to predispose for severe allergic reactions. Finally, it provides an opportunity to summarize the applications of flow cytometry-assisted analysis and quantification of in vitro activated basophils in the diagnostic approach of anaphylaxis from food.

Molecular and immunological characterization of the glycosylated orange allergen Cit s 1

The IgE of sera from patients with a history of allergy to oranges (Citrus sinensis) binds a number of proteins in orange extract, including Cit s 1, a germin-like protein. In the present study, we have analyzed its immunological cross-reactivity and its molecular nature. Sera from many of the patients examined recognize a range of glycoproteins and neoglycoconjugates containing beta1,2-xylose and core alpha1,3-fucose on their N-glycans. These reagents also inhibited the interaction of Cit s 1 with patients' sera, thus underlining the critical role of glycosylation in the recognition of this protein by patients' IgE and extending previous data showing that deglycosylated Cit s 1 does not possess IgE epitopes. In parallel, we examined the peptide sequence and glycan structure of Cit s 1, using mass spectrometric techniques. Indeed, we achieved complete sequence coverage of the mature protein compared with the translation of an expressed sequence tag cDNA clone and demonstrated that the single N-glycosylation site of this protein carries oligosaccharides with xylose and fucose residues. Owing to the presumed requirement for multivalency for in vivo allergenicity, our molecular data showing that Cit s 1 is monovalent as regards glycosylation and that the single N-glycan is the target of the IgE response to this protein explain the immunological cross-reactive properties of Cit s 1 as well as its equivocal nature as a clinically relevant allergen.

Natural and recombinant molecules of the cherry allergen Pru av 2 show diverse structural and B cell characteristics but similar T cell reactivity

BACKGROUND

Cherry allergy is often reported in the context of allergy to other fruits of the Rosaceae family and pollinosis to trees because of cross-reactive allergens. Allergic reactions to cherry are reported by 19-29% of birch pollen-allergic patients. Pru av 2, identified as a thaumatin-like protein (TLP) from sweet cherry, was recognized by the majority of cherry-allergic patients in immunoblotting.

OBJECTIVES

In order to investigate the structural characteristics and the immunoglobulin (Ig)E- and T cell reactivity of cherry-derived TLP, recombinant Pru av 2 was expressed in Escherichia coli and natural Pru av 2 was purified.

METHODS

Parallel-His and FLAG expression vectors were used for recombinant production of Pru av 2 in the cytoplasm and the periplasm of E. coli. Natural Pru av 2 was purified from fresh cherries and verified by N-terminal sequencing. Structural characterization was performed using circular dichroism (CD) measurements, and the biologic activity was measured in a glucanase assay. Using cherry-specific sera, the IgE-binding ability of recombinant and natural Pru av 2 was investigated in IgE-ELISA and the T cell reactivity was studied in proliferation assays. Results Natural Pru av 2 revealed thaumatin-like structural features and bound IgE of 50% of cherry-allergic patients. It was demonstrated to be enzymatically active. Recombinant Pru av 2 expressed in the cytoplasm of E. coli exhibited a slightly different folding compared with the natural protein. It was not recognized by IgE from cherry-allergic subjects, but retained the ability to stimulate T lymphocytes. Periplasmic recombinant Pru av 2 was able to bind an anti-grape TLP antibody and cherry-specific IgE.

CONCLUSIONS

We prepared two recombinant model TLPs from cherry, and compared their molecular characteristics as well as their IgE-binding activity and T cell interactions in relation to the natural counterpart. The cytoplasmic recombinant Pru av 2 can be used as a hypoallergenic variant in allergen-specific immunotherapy, whereas the periplasmic protein can be included in a component-resolved diagnosis.

Germin-like protein Cit s 1 and profilin Cit s 2 are major allergens in orange (Citrus sinensis) fruits

Oranges are clinically relevant allergenic foods. To date, orange allergens have not been characterized in detail. The study is aimed at analyzing the sensitization profile in orange-sensitized subjects with and without clinical allergy, and to identify orange allergens. Fifty-six sensitized subjects with self-reported reactions to orange were grouped into reactors (anaphylaxis or multiple episodes of immediate reactions and/or positive challenge tests) and non-reactors (negative open food challenge tests). Allergens were characterized by IgE immunoblotting, N-terminal sequencing, IgE-inhibition assays, and mediator release assays were performed to determine the allergenic potency of orange profilin. Of 56 subjects, 23 were classified as orange allergic showing mainly an oral allergy syndrome. Of 23 subjects classified as orange allergic, 22 were sensitized to profilin, Cit s 2. In patients with mono-sensitization to profilin in vitro histamine releases up to 75% from basophils were induced using orange extract and purified plant profilins. Of the allergic patients 78% were sensitized to germin-like protein, Cit s 1. Both allergens showed retained IgE reactivity in heat-processed orange juice. Interestingly, subjects with and without clinical allergy showed a comparable sensitization profile. Profilin and germin-like proteins are major orange allergens. The potential clinical relevance of orange profilin was indicated by its strong capacity to release histamine from basophils. However, a predominant sensitization to both allergens in subjects without symptoms also indicates a high frequency of clinically insignificant sensitization.

Orange Germin-Like Glycoprotein Cit s 1: An Equivocal Allergen

BACKGROUND

Orange allergens are virtually unknown, in spite of the large consumption of this fruit. Germin-like proteins, together with vicilins and legumins, form the cupin superfamily of plant proteins, which includes many seed allergens.

METHODS

Twenty-nine patients with allergy to oranges were studied. A major IgE-binding protein from orange extracts was isolated by means of a two-step cation-exchange chromatographic protocol. The allergen was characterized by N-terminal amino acid sequencing and MALDI analysis, and its reactivity explored by specific IgE determination in individual sera, ELISA inhibition assays and in vivo skin prick tests (SPT). Chemical deglycosylation of the purified allergen was achieved by trifluoromethylsulfonate acid treatment.

RESULTS

The 24-kDa purified allergen, designated Cit s 1, was identified as a germin-like glycoprotein, based on its N-terminal amino acid sequence, molecular size and recognition by rabbit anti-complex N-linked glycan antibodies. Specific IgE to Cit s 1 was detected in 62% of 29 individual sera from orange-allergic patients, whereas positive SPT responses to the purified allergen were obtained in only 10% of such patients. Deglycosylation of Cit s 1 resulted in a loss of its IgE-binding capacity. Moreover, the unrelated plant glycoprotein horseradish peroxidase inhibited over 70% the IgE-binding to Cit s 1.

CONCLUSIONS

Over 60% of patients with allergy to oranges show specific IgE to Cit s 1. However, the purified allergen exerts a low in vivo reactivity. Complex N-linked glycans seem to play a prominent role in the IgE-binding capacity of Cit s 1. This characteristic of Cit s 1, as well as of other orange glycoproteins, could lead to false positives if the diagnosis of allergy to oranges is mainly based on in vitro specific IgE determination.

Isolation, cloning and allergenic reactivity of natural profilin Cit s 2, a major orange allergen

BACKGROUND

Orange is among the most widely consumed fruits, and among the plant food sources causing allergic reactions according to popular perception. However, its relevant allergenic components are virtually unknown. Profilin is a well-defined minor plant panallergen, showing prevalences around 30% in fruits and vegetables.

METHODS

Twenty-three orange-allergic patients were studied. Natural orange profilin, named Cit s 2, was purified by affinity chromatography and characterized by N-terminal amino acid sequencing, matrix-assisted laser desorption/ionization mass spectrometry analysis and isolation of its coding cDNA. Reactivity to Cit s 2 was analyzed in vivo by skin prick tests (SPT) and in vitro by IgE immunodetection, specific IgE determination in individual sera and enzyme-linked immunosorbent assay-inhibition assays.

RESULTS

The N-terminal amino acid sequence and molecular mass of natural Cit s 2, both fully in agreement with the complete amino acid sequence deduced from its coding cDNA, demonstrated its profilin nature. An unexpectedly high reactivity to Cit s 2 was found in vivo (78% of positive SPT responses) and in vitro (87% of sera from orange allergic patients had specific IgE to Cit s 2). The purified allergen inhibited around 50% of the IgE binding to an orange pulp extract.

CONCLUSION

Orange profilin Cit s 2, unlike other plant food profilins, is a major and highly prevalent allergen.

Lipid transfer proteins and allergy to oranges

BACKGROUND

Lipid transfer proteins (LTPs) are relevant fruit allergens, recently proposed as model plant food allergens. No citrus fruit allergen has been characterized to date. We sought to identify and isolate citrus fruit LTPs and to explore their relevance in orange allergy.

METHODS

Twenty-seven patients, showing mainly oral allergy syndrome after orange ingestion, as well as positive prick responses and serum-specific IgE levels to orange, were selected. Natural orange and lemon LTPs, as well as a recombinant orange LTP isoform expressed in Pichia pastoris, were isolated by chromatographic methods and characterized by N-terminal amino acid sequencing and matrix-assisted laser desorption/ionizaion mass spectrometry, and DNA sequencing of the corresponding cDNA in the case of the recombinant allergen. Specific IgE determination, immunodetection, ELISA-inhibition assays and in vivo skin prick tests (SPTs) were performed with all three purified allergens and with the major peach LTP allergen, Pru p 3.

RESULTS

The natural allergens purified from orange (nCit s 3) and lemon (nCit l 3) showed very similar N-terminal amino acid sequences (18 out of 20 identical residues), typical of LTPs, and molecular masses of 9,610 and 9,618 Da, respectively. The recombinant orange isoform (rCit s 3) expressed in P. pastoris (16 out of 20 residues identical to its natural counterpart in the N-terminal region) presented 92 amino acid residues and 9,463 Da, and 67% sequence identity with rPru p 3. Of the 27 sera analyzed, specific IgE to the purified allergens was found in 54% for nCit l 3, 48% for nCit s 3, 46% for rCit s 3 and 37% for rPru p 3. Positive SPT responses were obtained in 7 out of 26 patients tested for nCit s 3, 3 out of 8 for nCit l 3 and 10 out of 26 for nPru p 3. ELISA-inhibition assays showed an equivalent IgE-binding pattern for the natural and recombinant orange LTPs, and IgE cross-reactivity among the purified orange, lemon and peach LTP allergens.

CONCLUSIONS

Members of the LTP allergen family are involved in allergy to oranges, displaying positive in vitro and in vivo reactions in 30-50% of the patients studied. Both orange and lemon allergens show cross-reactivity with the major peach allergen Pru p 3.