Characterization of cross-reactive bell pepper allergens involved in the latex-fruit syndrome

Latex Allergy in Children

Notwithstanding the efforts made in the last decades to mitigate the consequences of natural rubber latex allergy, this disease continues to be a major health problem, especially in developing countries. The categories of patients with greater and frequent exposure to latex (such as health care professionals and, in the pediatric field, subjects who undergo repeated surgery, e.g., those suffering from spina bifida and urogenital malformations) have an increased risk of developing sensitization and allergy to latex. Herein we provide an overview of the current knowledge and practical recommendations with a focus on epidemiology, diagnostics, and management (including both prevention and therapy) in order to guide a correct recognition and containment of this potentially fatal condition.

Immunoreactive proteins of Capsicum-based spices as a threat to human health: mass spectrometry analysis and in silico mapping

Dietary patterns are changing severely, especially the consumption of highly processed foods with lots of spices is increasing, carrying an increased risk of immediate hypersensitivity (type I), in sensitised individuals, due to the possible presence of allergens, especially the hidden ones. Paprika is a fruit of the Capsicum genus, which belongs to the Solanaceae family and is commonly consumed fresh or as a spice. Despite recorded cases of anaphylaxis, its allergenicity has yet to be clearly investigated. In this study, we research to identify proteins that could trigger a severe allergic reaction in patients with an equivocal clinical picture. Two types of protein extracts extracted from 3 different paprika spices were immunoblotted with sera from patients with severe allergic symptoms, presumably to paprika. Proteins from the IgE reactive bands obtained were subjected to LC-MS/MS identification and then in silico analysis to assess their possible sensitising capacity and proinflammatory potential using online tools. The spices were shown to contain a number of incompletely investigated highly immunoreactive allergenic proteins, including proteins of foreign origin (contaminants), the presence of which can stimulate inflammatory mechanisms and cross-reactivity with other food allergens, which can threaten life and health and should be investigated in detail.

Capsicum Allergy: Involvement of Cap a 7, a New Clinically Relevant Gibberellin-Regulated Protein Cross-Reactive With Cry j 7, the Gibberellin-Regulated Protein From Japanese Cedar Pollen

The Capsicum genus belongs to the Solanaceae family. Bell or chili peppers are consumed worldwide, but allergy to Capsicum is rare. It is involved in the celery-birch-mugwort-spice syndrome and cross-reactivities were reported with latex. Several allergens have been described, but only 2 are referenced in the World Health Organization/International Union of Immunological Societies allergen data bank, a thaumatin-like protein and a profilin. A patient allergic to bell/chili pepper, peach, orange and Japanese cedar pollen was clinically and biologically analyzed including direct and competitive immunoblots and basophil activation tests (BATs) with allergenic source extracts and recombinant gibberellin-regulated proteins (GRPs). The patient was shown to be sensitized to Cap a 7, the GRP of Capsicum annuum newly described herein. Cross-reactivities were demonstrated between various GRPs from bell/chili pepper, peach, orange and Japanese cedar pollen either in native form in the different extracts or as recombinant allergens. A similar immunoglobulin E reactivity was found also in Capsicum chinense and against snakin-1, the GRP from potato. The patient showed a positive BAT with recombinant Cry j 7, Pru p 7 and Cap a 7, but not with recombinant snakin-1. Despite the ubiquitous nature of GRPs in plants and the immunochemical cross-reactivity observed between different GRPs, clinically relevant sensitization to this protein family seems restricted to some allergenic sources, often associated with Cupressaceae pollen allergy, and to some patients, therefore reflecting very specific and peculiar mechanisms of conditional sensitization.

Update on pollen-food allergy syndrome

INTRODUCTION

Allergies affect 20-30% of the population and respiratory allergies are mostly due to pollen grains from anemophilous plants. One to 5% of people suffer from food allergies and clinicians report increasing numbers of pollen-food allergy syndrome (PFAS), such that the symptoms have broadened from respiratory to gastrointestinal, and even to anaphylactic shock in the presence of cofactors. Thirty to 60% of food allergies are associated with pollen allergy while the percentage of pollen allergies associated to food allergy varies according to local environment and dietary habits.

AREAS COVERED

Articles published in peer-reviewed journals, covered by PubMed databank, clinical data are discussed including symptoms, diagnosis, and management. A chapter emphasizes the role of six well-known allergen families involved in PFAS: PR10 proteins, profilins, lipid transfer proteins, thaumatin-like proteins, isoflavone reductases, and β-1,3 glucanases. The relevance in PFAS of three supplementary allergen families is presented: oleosins, polygalacturonases, and gibberellin-regulated proteins. To support the discussion a few original relevant results were added.

EXPERT OPINION

Both allergenic sources, pollen and food, are submitted to the same stressful environmental changes resulting in an increase of pathogenesis-related proteins in which numerous allergens are found. This might be responsible for the potential increase of PFAS.

Search for New Allergens in Lolium perenne Pollen Growing under Different Air Pollution Conditions by Comparative Transcriptome Study

The relationship between air pollution and the allergenic capacity of pollen is widely accepted, with allergenicity being directly related to air pollution. To our knowledge, this is the first study comparing the differential expression of Lolium perenne pollen genes by RNAseq, in two wild populations with different levels of air pollution. The objective is to search for proteins that are expressed differentially in both situations and to establish a relationship with increased allergenic capacity. Two populations of L. perenne (Madrid and Ciudad Real) have been studied in two consecutive years, under the rationale that overexpressed genes in Madrid, with higher levels of NO₂ and SO₂, could be a cause for their greater allergenic capacity. Heat shock proteins (HSP), glycoside hydrolases, proteins with leucin-rich repeat motifs, and proteins with EF-HAND motifs were consistently overexpressed in Madrid pollen in the two years studied. Interestingly, some genes were overexpressed only in one of the years studied, such as pectinesterases in the first year, and lipid transfer proteins (LTPs) and thaumatin in the second. Despite the fact that the potential of all these proteins in relation to possible allergies has been reported, this is the first time they are cited as possible allergens of L. perenne. The results found can contribute decisively to the knowledge of the allergens of L. perenne and their relationship with atmospheric pollution, and to the development of much more effective vaccines.

Molecular approach to a patient's tailored diagnosis of the oral allergy syndrome

Oral allergy syndrome (OAS) is one of the most common IgE-mediated allergic reactions. It is characterized by a number of symptoms induced by the exposure of the oral and pharyngeal mucosa to allergenic proteins belonging to class 1 or to class 2 food allergens. OAS occurring when patients sensitized to pollens are exposed to some fresh plant foods has been called pollen food allergy syndrome (PFAS). In the wake of PFAS, several different associations of allergenic sources have been progressively proposed and called syndromes. Molecular allergology has shown that these associations are based on IgE co-recognition taking place between homologous allergens present in different allergenic sources. In addition, the molecular approach reveals that some allergens involved in OAS are also responsible for systemic reactions, as in the case of some food Bet v 1-related proteins, lipid transfer proteins and gibberellin regulated proteins. Therefore, in the presence of a convincing history of OAS, it becomes crucial to perform a patient's tailored molecule-based diagnosis in order to identify the individual IgE sensitization profile. This information allows the prediction of possible cross-reactions with homologous molecules contained in other sources. In addition, it allows the assessment of the risk of developing more severe symptoms on the basis of the features of the allergenic proteins to which the patient is sensitized. In this context, we aimed to provide an overview of the features of relevant plant allergenic molecules and their involvement in the clinical onset of OAS. The value of a personalized molecule-based approach to OAS diagnosis is also analyzed and discussed.

ENEA, a peach and apricot IgE-binding protein cross-reacting with the latex major allergen Hev b 5

Peach and apricot can cause allergic reactions with symptoms ranging from mild to very severe, including anaphylaxis. Sometimes subjects allergic to fruits of the Prunus genus have been reported to be also allergic to rubber latex products. The objective of this study is the characterization of a newly identified peach and apricot protein showing similarities with the allergens Hev b 5 from rubber latex and Man e 5 from manioc. This protein has been named ENEA on the basis of the single letter amino acid code of the first four N-terminal residues of the isolated molecule. It has been found in very variable amounts in different peach cultivars and batches. ENEA was isolated from peach pulp extracts by chromatographic separations and identified by direct protein sequencing. At that time, the full length sequence was available only for the homologous protein of the taxonomically closely related apricot, which was produced as a recombinant molecule in Escherichia coli. The following availability of the full length sequence of peach ENEA revealed a very high identity (97%) with the apricot homolog. Similarly to Hev b 5 and to Man e 5, the structural characterization indicated that ENEA is an intrinsically disordered protein. The immunological properties, investigated by dot blotting, the ABA system and the FABER test, showed that ENEA is recognized by specific IgE of allergic patients. In a selected population of 31 patients reporting allergic reactions to peach fruit and/or IgE positive to Hev b 5, 28 and 27 subjects resulted co-sensitized to rENEA and Hev b 5 in the ABA and ISAC test, respectively. In a random population of 3305 suspected allergic patients, analyzed with the FABER test, 17 of them were sensitized to rENEA and 10 of them were also positive to Hev b 5. In addition, both the natural molecule from peach and the recombinant protein of apricot partially inhibited the IgE binding to Hev b 5. In conclusion, a new peach and apricot IgE-binding protein, cross-reacting with the major latex allergen Hev b 5, has been identified. Its variable concentration in the fruit might explain some occasionally occurring allergic reactions. The apricot molecule has recently been registered by the WHO/IUIS Allergen Nomenclature Sub-Committee with the allergen name Pru ar 5. The recombinant form of apricot ENEA, now available, will contribute to allergy diagnosis.

Cross-Reactive Aeroallergens: Which Need to Cross Our Mind in Food Allergy Diagnosis?

Secondary food allergies due to cross-reactivity between inhalant and food allergens are a significant and increasing global health issue. Cross-reactive food allergies predominantly involve plant-derived foods resulting from a prior sensitization to cross-reactive components present in pollen (grass, tree, weeds) and natural rubber latex. Also, primary sensitization to allergens present in fungi, insects, and both nonmammalian and mammalian meat might induce cross-reactive food allergic syndromes. Correct diagnosis of these associated food allergies is not always straightforward and can pose a difficult challenge. As a matter of fact, cross-reactive allergens might hamper food allergy diagnosis, as they can cause clinically irrelevant positive tests to cross-reacting foods that are safely consumed. This review summarizes the most relevant cross-reactivity syndromes between inhalant and food allergens. Particular focus is paid to the potential and limitations of confirmatory testing such as skin testing, specific IgE assays, molecular diagnosis, and basophil activation test.

Bioinformatics analysis to assess potential risks of allergenicity and toxicity of HRAP and PFLP proteins in genetically modified bananas resistant to Xanthomonas wilt disease

Banana Xanthomonas wilt (BXW) disease threatens banana production and food security throughout East Africa. Natural resistance is lacking among common cultivars. Genetically modified (GM) bananas resistant to BXW disease were developed by inserting the hypersensitive response-assisting protein (Hrap) or/and the plant ferredoxin-like protein (Pflp) gene(s) from sweet pepper (Capsicum annuum). Several of these GM banana events showed 100% resistance to BXW disease under field conditions in Uganda. The current study evaluated the potential allergenicity and toxicity of the expressed proteins HRAP and PFLP based on evaluation of published information on the history of safe use of the natural source of the proteins as well as established bioinformatics sequence comparison methods to known allergens (www.AllergenOnline.org and NCBI Protein) and toxins (NCBI Protein). The results did not identify potential risks of allergy and toxicity to either HRAP or PFLP proteins expressed in the GM bananas that might suggest potential health risks to humans. We recognize that additional tests including stability of these proteins in pepsin assay, nutrient analysis and possibly an acute rodent toxicity assay may be required by national regulatory authorities.

Mining Novel Allergens from Coconut Pollen Employing Manual De Novo Sequencing and Homology-Driven Proteomics

Coconut pollen, one of the major palm pollen grains is an important constituent among vectors of inhalant allergens in India and a major sensitizer for respiratory allergy in susceptible patients. To gain insight into its allergenic components, pollen proteins were analyzed by two-dimensional electrophoresis, immunoblotted with coconut pollen sensitive patient sera, followed by mass spectrometry of IgE reactive proteins. Coconut being largely unsequenced, a proteomic workflow has been devised that combines the conventional database-dependent analysis of tandem mass spectral data and manual de novo sequencing followed by a homology-based search for identifying the allergenic proteins. N-terminal acetylation helped to distinguish "b" ions from others, facilitating reliable sequencing. This led to the identification of 12 allergenic proteins. Cluster analysis with individual patient sera recognized vicilin-like protein as a major allergen, which was purified to assess its in vitro allergenicity and then partially sequenced. Other IgE-sensitive spots showed significant homology with well-known allergenic proteins such as 11S globulin, enolase, and isoflavone reductase along with a few which are reported as novel allergens. The allergens identified can be used as potential candidates to develop hypoallergenic vaccines, to design specific immunotherapy trials, and to enrich the repertoire of existing IgE reactive proteins.

An Enzymatically Active β-1,3-Glucanase from Ash Pollen with Allergenic Properties: A Particular Member in the Oleaceae Family

Endo-β-1,3-glucanases are widespread enzymes with glycosyl hydrolitic activity involved in carbohydrate remodelling during the germination and pollen tube growth. Although members of this protein family with allergenic activity have been reported, their effective contribution to allergy is little known. In this work, we identified Fra e 9 as a novel allergenic β-1,3-glucanase from ash pollen. We produced the catalytic and carbohydrate-binding domains as two independent recombinant proteins and characterized them from structural, biochemical and immunological point of view in comparison to their counterparts from olive pollen. We showed that despite having significant differences in biochemical activity Fra e 9 and Ole e 9 display similar IgE-binding capacity, suggesting that β-1,3-glucanases represent an heterogeneous family that could display intrinsic allergenic capacity. Specific cDNA encoding Fra e 9 was cloned and sequenced. The full-length cDNA encoded a polypeptide chain of 461 amino acids containing a signal peptide of 29 residues, leading to a mature protein of 47760.2 Da and a pI of 8.66. An N-terminal catalytic domain and a C-terminal carbohydrate-binding module are the components of this enzyme. Despite the phylogenetic proximity to the olive pollen β-1,3-glucanase, Ole e 9, there is only a 39% identity between both sequences. The N- and C-terminal domains have been produced as independent recombinant proteins in Escherichia coli and Pichia pastoris, respectively. Although a low or null enzymatic activity has been associated to long β-1,3-glucanases, the recombinant N-terminal domain has 200-fold higher hydrolytic activity on laminarin than reported for Ole e 9. The C-terminal domain of Fra e 9, a cysteine-rich compact structure, is able to bind laminarin. Both molecules retain comparable IgE-binding capacity when assayed with allergic sera. In summary, the structural and functional comparison between these two closely phylogenetic related enzymes provides novel insights into the complexity of β-1,3-glucanases, representing a heterogeneous protein family with intrinsic allergenic capacity.

Review article: the diagnosis and management of food allergy and food intolerances

BACKGROUND

Adverse reactions to food include immune mediated food allergies and non-immune mediated food intolerances. Food allergies and intolerances are often confused by health professionals, patients and the public.

AIM

To critically review the data relating to diagnosis and management of food allergy and food intolerance in adults and children.

METHODS

MEDLINE, EMBASE and the Cochrane Database were searched up until May 2014, using search terms related to food allergy and intolerance.

RESULTS

An estimated one-fifth of the population believe that they have adverse reactions to food. Estimates of true IgE-mediated food allergy vary, but in some countries it may be as prevalent as 4-7% of preschool children. The most common food allergens are cow's milk, egg, peanut, tree nuts, soy, shellfish and finned fish. Reactions vary from urticaria to anaphylaxis and death. Tolerance for many foods including milk and egg develops with age, but is far less likely with peanut allergy. Estimates of IgE-mediated food allergy in adults are closer to 1-2%. Non-IgE-mediated food allergies such as Food Protein-Induced Enterocolitis Syndrome are rarer and predominantly recognised in childhood. Eosinophilic gastrointestinal disorders including eosinophilic oesophagitis are mixed IgE- and non-IgE-mediated food allergic conditions, and are improved by dietary exclusions. By contrast food intolerances are nonspecific, and the resultant symptoms resemble other common medically unexplained complaints, often overlapping with symptoms found in functional disorders such as irritable bowel syndrome. Improved dietary treatments for the irritable bowel syndrome have recently been described.

CONCLUSIONS

Food allergies are more common in children, can be life-threatening and are distinct from food intolerances. Food intolerances may pose little risk but since functional disorders are so prevalent, greater efforts to understand adverse effects of foods in functional disorders are warranted.

Current overview of allergens of plant pathogenesis related protein families

Pathogenesis related (PR) proteins are one of the major sources of plant derived allergens. These proteins are induced by the plants as a defense response system in stress conditions like microbial and insect infections, wounding, exposure to harsh chemicals, and atmospheric conditions. However, some plant tissues that are more exposed to environmental conditions like UV irradiation and insect or fungal attacks express these proteins constitutively. These proteins are mostly resistant to proteases and most of them show considerable stability at low pH. Many of these plant pathogenesis related proteins are found to act as food allergens, latex allergens, and pollen allergens. Proteins having similar amino acid sequences among the members of PR proteins may be responsible for cross-reactivity among allergens from diverse plants. This review analyzes the different pathogenesis related protein families that have been reported as allergens. Proteins of these families have been characterized in regard to their biological functions, amino acid sequence, and cross-reactivity. The three-dimensional structures of some of these allergens have also been evaluated to elucidate the antigenic determinants of these molecules and to explain the cross-reactivity among the various allergens.

Clinico-Immunological Analysis of Eggplant (Solanum melongena) Allergy Indicates Preponderance of Allergens in the Peel

Background

Eggplant (Solanum melongena L.) is known to cause food allergy in some Asian countries but detailed studies on eggplant allergy are lacking.

Objective

The objective is to investigate sensitization to different parts of eggplant fruit, and detection of the allergens.

Methods

Six eggplant-allergic subjects were assessed for sensitization to eggplant (peel/pulp, and raw/cooked) by skin prick test, allergen-specific IgE, and immunoblots. Allergens were analyzed for glycoprotein nature by staining/lectinoblots, and in vitro stability in simulated gastric fluid.

Results

All the eggplant-sensitized subjects showed positive skin prick test with peel, pulp, raw, and cooked eggplant extracts; allergen-specific IgE to all these was positive. Raw eggplant contains 5 allergens in the range 36-71 kD. Most allergens are localized in the eggplant peel (9 allergens; 26-71 kD range) than the pulp (3 allergens; 52-71 kD); among these, the 26, 28, 36, and 71 kD allergens seem to be heat-stable. The 43, 45, 64, and 71 kD allergens are detected as glycoproteins; the 26, 64, and 71 kD allergens are stable displaying retention of IgE-binding ability in simulated gastric fluid digestion.

Conclusions

Eggplant is a multiallergenic vegetable in the context of presence of allergens in all edible parts of eggplant having preponderance in the peel.

Structures of an active-site mutant of a plant 1,3-β-glucanase in complex with oligosaccharide products of hydrolysis

Plant endo-1,3-β-glucanases are involved in important physiological processes such as defence mechanisms, cell division and flowering. They hydrolyze (1→3)-β-glucans, with very limited activity towards mixed (1→3,1→4)-β-glucans and branched (1→3,1→6)-β-glucans. Here, crystal structures of the potato (Solanum tuberosum) endo-1,3-β-glucanase GLUB20-2 with the nucleophilic Glu259 residue substituted by alanine (E259A) are reported. Despite this active-site mutation, the protein retained residual endoglucanase activity and when incubated in the crystallization buffer with a linear hexameric substrate derived from (1→3)-β-glucan (laminarahexose) cleaved it in two different ways, generating trisaccharides and tetrasaccharides, as confirmed by mass spectrometry. The trisaccharide (laminaratriose) shows higher binding affinity and was found to fully occupy the -1, -2 and -3 sites of the active-site cleft, even at a low molar excess of the substrate. At elevated substrate concentration the tetrasaccharide molecule (laminaratetrose) also occupies the active site, spanning the opposite sites +1, +2, +3 and +4 of the cleft. These are the first crystal structures of a plant glycoside hydrolase family 17 (GH17) member to reveal the protein-saccharide interactions and were determined at resolutions of 1.68 and 1.55 Å, respectively. The geometry of the active-site cleft clearly precludes any (1→4)-β-glucan topology at the subsites from -3 to +4 and could possibly accommodate β-1,6-branching only at subsites +1 and +2. The glucose units at subsites -1 and -2 interact with highly conserved protein residues. In contrast, subsites -3, +3 and +4 are variable, suggesting that the mode of glucose binding at these sites may vary between different plant endo-1,3-β-glucanases. Low substrate affinity is observed at subsites +1 and +2, as manifested by disorder of the glycosyl units there.

Two high-resolution structures of potato endo-1,3-β-glucanase reveal subdomain flexibility with implications for substrate binding

Endo-1,3-β-glucanases are widely distributed among bacteria, fungi and higher plants. They are responsible for hydrolysis of the glycosidic bond in specific polysaccharides with tracts of unsubstituted β-1,3-linked glucosyl residues. The plant enzymes belong to glycoside hydrolase family 17 (GH17) and are also members of class 2 of pathogenesis-related (PR) proteins. X-ray diffraction data were collected to 1.40 and 1.26 Å resolution from two crystals of endo-1,3-β-glucanase from Solanum tuberosum (potato, cultivar Désirée) which, despite having a similar packing framework, represented two separate crystal forms. In particular, they differed in the Matthews coefficient and are consequently referred to as higher density (HD; 1.40 Å resolution) and lower density (LD; 1.26 Å resolution) forms. The general fold of the protein resembles that of other known plant endo-1,3-β-glucanases and is defined by a (β/α)(8)-barrel with an additional subdomain built around the C-terminal half of the barrel. The structures revealed high flexibility of the subdomain, which forms part of the catalytic cleft. Comparison with structures of other GH17 endo-1,3-β-glucanases revealed differences in the arrangement of the secondary-structure elements in this region, which can be correlated with sequence variability and may suggest distinct substrate-binding patterns. The crystal structures revealed an unusual packing mode, clearly visible in the LD structure, caused by the presence of the C-terminal His(6) tag, which extends from the compact fold of the enzyme molecule and docks in the catalytic cleft of a neighbouring molecule. In this way, an infinite chain of His-tag-linked protein molecules is formed along the c direction.

Molecular and immunological characterization of Mus a 5 allergen from banana fruit

SCOPE

Banana fruit has become an important cause of fruit allergy in the recent years. Among the five registered IUIS allergens, Mus a 1 and Mus a 2 have been characterized in detail. In this study, molecular characterization and evaluation of the allergenic properties of β-1,3-glucanase from banana (Musa acuminata), denoted as Mus a 5, were performed.

METHODS AND RESULTS

The gene of Mus a 5 was cloned and sequenced. The obtained cDNA revealed a novel Mus a 5 isoform with an open reading frame encoding a protein of 340 amino acids comprising a putative signal peptide of 28 amino acid residues. By MALDI-TOF analysis Mus a 5 isolated from banana fruit revealed a molecular mass of 33451±67 Da. Two Mus a 5 isoforms (pI 7.7 and 8.0) were detected by 2D immunoblot with an identical N-terminal sequence. By mass fingerprint, 76 and 83% of the primary structure was confirmed for the two mature Mus a 5 isoforms, respectively. IgE reactivity to Mus a 5 was found in 74% of patients sensitized to banana fruit. Upregulation of basophil activation markers CD63 and CD203c was achieved with Mus a 5 in a concentration-dependent manner.

CONCLUSION

Mus a 5 is a functional allergen and a candidate for the component-resolved allergy diagnosis of banana allergy.

Assessment of allergenicity of diploid and hexaploid wheat genotypes: identification of allergens in the albumin/globulin fraction

Wheat is an important part of the daily diet of millions of people. However, this staple food is also responsible for food allergies. Ancient cultivars of wheat are gaining interest today but nothing is known about their allergenicity. Many wheat proteins have been reported as causative food allergens, including some prolamin-type gluten proteins, and salt soluble proteins of the albumin/globulin (A/G) type. The objective of this work is to obtain information about the allergenicity of the salt soluble A/G fraction of an ancient diploid cultivar compared with a standard hexaploid bread wheat cultivar using 20 sera from patients with wheat allergy. Differences in the IgE reactivity of sera towards the two genotypes were quantified by ELISA. Qualitative differences in IgE-binding proteins were searched after 1D or 2D electrophoresis. For most of the sera, the concentration in A/G specific IgE was higher for the hexaploid T. aestivum (cv Récital) than for the diploid T. monococcum (cv Engrain). The analysis of 2D spots revealed by immunoblotting leads to the identification by mass spectrometry of 39 IgE-binding proteins, some of them unknown until now as wheat allergens. Numerous allergens were identified, differences observed between Engrain and Récital will be discussed.

Latex-allergic patients sensitized to the major allergen hevein and hevein-like domains of class I chitinases show no increased frequency of latex-associated plant food allergy

Allergies to certain fruits such as banana, avocado, chestnut and kiwi are described in 30–70% of latex-allergic patients. This association is attributed to the cross-reactivity between the major latex allergen hevein and hevein-like domains (HLDs) from fruit class I chitinases. We aimed to assess the extent of cross-reactivity between hevein and HLDs using sera from latex-allergic patients with and without plant food allergy. Hevein and HLDs of latex, banana, and avocado chitinases were expressed in Escherichia coli as fusion proteins with the maltose-binding protein and purified by affinity chromatography. IgE binding to these proteins was studied in sera from 59 latex-allergic patients and 20 banana-allergic patients without latex allergy by ELISA and ELISA inhibition. Additionally, 16,408 allergic patients’ sera were tested for IgE binding to hevein, latex chitinase, and wheat germ agglutinin using an allergen microarray. Hevein-specific IgE was detected in 34/59 (58%) latex-allergic patients’ sera. HLDs of latex, banana, and avocado chitinases were recognized by 21 (36%), 20 (34%), and 9 (15%) sera, respectively. In contrast, only one of 20 banana-allergic patients without latex allergy was sensitized to chitinase HLDs. In most tested latex-allergic patients’ sera, IgE binding to hevein was only partially reduced by preincubation with HLDs. Among hevein-sensitized, latex-allergic patients, the percentage of plant food allergy (15/34 = 44%) was equal to latex-allergic patients without hevein sensitization (11/25 = 44%). In the general allergic population, 230 of 16,408 sera (1.4%) reacted to hevein and/or a hevein-like allergen. Of these, 128 sera showed an isolated sensitization to hevein, whereas only 17 bound to latex chitinase or wheat germ agglutinin without hevein sensitization. In conclusion, the IgE response to HLDs is elicited by hevein as sensitizing allergen in most cases. Despite considerable cross-reactivity between these allergens, no correlation between latex-associated plant food allergy and sensitization to hevein or HLDs was found.

Mapping of IgE-binding epitopes on the major latex allergen Hev b 2 and the cross-reacting 1,3beta-glucanase fruit allergens as a molecular basis for the latex-fruit syndrome

Nine distinct IgE-binding epitopes were identified along the entire amino acid sequence of the major latex allergen Hev b 2 (1,3beta-glucanase) using a set of synthetic 15-mer peptides frameshifted by 3 residues immobilized on cellulose membrane (Spot technique). Most of the amino acid residues building these IgE-binding epitopic regions are nicely exposed on the surface and the epitopes usually correspond to charged regions on the molecular surface of the protein. A smaller number of 5 IgE-binding epitopic areas was identified on the banana 1,3beta-glucanase, which exhibits a very similar overall conformation and charge distribution. The latter epitopes might be responsible for the IgE-binding cross-reactivity currently observed in the latex-fruit syndrome. Using rabbit polyclonal IgG anti-BanGluc as a probe instead of IgE from allergic patients the same epitopic regions were identified in both Hev b 2 and BanGluc. Additionally, surface-exposed regions with a very close conformation were predicted to occur on Ole e 9, the 1,3beta-glucanase allergen identified in olive pollen.

Latex allergy: a model for therapy

Allergy to natural rubber latex products emerged as an important clinical condition following an increase in the use of latex gloves for barrier protection in the early 1980s. In addition to latex glove users, other high-risk groups with different latex exposure include spina bifida patients and others with multiple surgical procedures. Subjects with fruit and vegetable allergy are also at risk due to cross-reactive allergens. Following the significant advances in the identification and characterization of common aeroallergens, latex allergy was well placed to become an excellent model of therapy. Awareness of latex allergy and modes of sensitization enabled epidemiological studies to inform allergen avoidance initiatives, substantially reducing inadvertent exposure in major hospitals in Western countries. Spina bifida is often identified in utero or soon after birth, allowing vigorous latex allergen avoidance with enhanced efficacy of primary prevention. However, changing demographics of latex allergy and technological revolution in countries such as China and India are predicted to unleash a second wave of latex allergy reemphasizing the incentive for improved manufacturing procedures for latex products. The desirable high tensile strength and elasticity of natural rubber latex have made the commercial identification of good alternatives very difficult but this would also be attractive for primary prevention. In addition, an effective specific immunotherapy regimen would be valuable for selected high-risk atopic individuals. Current subcutaneous and sublingual immunotherapy schedules have been tested for treatment of latex allergy with evidence of efficacy but the risks of adverse events are high. For such potent allergens as latex, hypoallergenic but T cell-reactive preparations are required for clinical use. Identification of allergenic components of latex products, with generation of monoclonal antibodies and recombinant allergens, allowed sequence determination and mapping of T cell and B cell epitopes. Together, these reagents and data facilitated improved diagnostics and investigation of novel-specific therapeutics. Potential hypoallergenic latex preparations identified include modified non-IgE-reactive allergen molecules and short T cell epitope peptides. The co-administration of adjunct therapies such as anti-IgE or corticosteroids and of appropriate adjuvants for induction of regulatory T cell response offers promise for clinically effective, safe latex-specific vaccines.

Latex allergy: low prevalence of immunoglobulin E to highly purified proteins Hev b 2 and Hev b 13

BACKGROUND

Hevea brasiliensis (Hev b) 2 and Hev b 13 have recently been identified as major latex allergens by detecting specific IgE antibodies in >50% of sera from Hev b latex-allergic individuals.

OBJECTIVE

We assessed the prevalence rates for sensitization to extensively purified latex allergens in patients from three diverse geographical areas.

METHODS

Native Hev b 2, Hev b 5, Hev b 6.01 and Hev b 13 were purified by non-denaturating chromatography and were used in ELISAs to assess sera from 215 latex-allergic patients and 172 atopic non-sensitized controls from Finland, Spain and the United States to detect allergen-specific IgE antibodies.

RESULTS

Unexpectedly, even highly purified Hev b 13 contained epitope(s) to which Hev b 6-specific human IgE antibodies bound effectively. Further purification, however, reduced the prevalence of IgE antibody reactivity to low levels: 15%, 5% and 11% for Hev b 2, and 18%, 30% and 27% for Hev b 13 among latex-allergic Finnish, Spanish and American patients, respectively. Interestingly, Finnish patients had a lower prevalence of Hev b 5-specific IgE antibody (28%) as compared with Spanish (49%) and American (71%) patients. The prevalence of Hev b 6.01-specific IgE reactivity was uniformly >50% in all three populations.

CONCLUSION

Neither Hev b 2 nor Hev b 13 appear to be major latex allergens when evaluated in serological assays using highly purified allergens. The reason(s) for the observed differences in published sensitization rates in various geographic regions requires further study. The purity of the allergen preparations has a marked impact on the accuracy of latex-specific IgE antibody detection in epidemiological studies and in the serological diagnosis of latex allergy.

Latex allergy within a cohort of not-at-risk subjects with respiratory symptoms: prevalence of latex sensitization and assessment of diagnostic tools

BACKGROUND

Immunoglobluin E (IgE)-mediated hypersensitivity to natural rubber latex (NRL) is a major problem in allergy practice. Currently, the use of skin prick tests (SPTs) with latex extracts and specific IgE detection for the diagnosis of NRL allergy in suspected patients is directed to identification of risk factors. Many cases of NRL allergy remain undiagnosed due to misreporting of symptoms by the patients or lack of proper questions asked by the physician.

MATERIALS AND METHODS

A total of 6,126 subjects referred for respiratory symptoms underwent SPTs with NRL. Positive subjects were resurveyed for exposure to NRL, and specific IgE for NRL extracts and recombinant molecules was determined. Immunoblots of NRL extracts were performed to identify IgE patterns.

RESULTS

Forty-six of 3,930 sensitized subjects had a positive SPT with NRL, displaying a prevalence of NRL sensitization of 0.75% for the general and 1.2% for the sensitized population. Eleven out of 46 (23.9%) subjects could be defined as NRL asymptomatic, whereas 35 (76.1%) developed symptoms upon exposure to NRL. Specific IgE to NRL was detected for 22 (75.86%) of 29 tested sera. Seventeen out of 22 (77%) sera displayed specific IgE to recombinant allergens with most reactions to Hev b 5, Hev b 6.01 and Hev b 6.02. Immunoblots of NRL extract fractions with patients' sera showed heterogeneous patterns.

CONCLUSIONS

SPTs with NRL extract should be routinely performed in patients with respiratory symptoms. Hev b 5, Hev b 6.01 and Hev b 6.02 are the most important allergens, but further characterization of NRL extracts is needed to identify novel allergens and to clarify the role of crossreactive carbohydrate determinants.

Advances in development of hypoallergenic latex immunotherapy

PURPOSE OF REVIEW

The characterization of clinically relevant latex allergens and the production of recombinant allergens is now well advanced, but this knowledge needs to be translated into new strategies for the safe and effective specific treatment of latex allergic diseases including asthma and anaphylaxis.

RECENT FINDINGS

The current status of latex allergy is discussed indicating a changing demographic paradigm. A new wave of latex allergy is emerging outside the healthcare setting with the widespread use of latex products. An increased prevalence in developing countries is also reported. Limited studies on current specific immunotherapy for latex allergy are reviewed, confirming the feasibility but demonstrating an unacceptable risk of adverse events. The characterization of latex allergens and the identification of B and T-cell epitopes point to rational strategies for the generation of hypoallergenic preparations for specific immunotherapy. Results to date for latex allergens are reviewed, including recombinant, chemical modification and synthetic peptide approaches. Candidate hypoallergenic preparations for targeting sensitization to the major allergens Hev b 1, Hev b 3, Hev b 5 and Hev b 6.01 have been identified. Further investigations of optimal regimens for the delivery of specific immunotherapy to induce regulatory T-cell function are warranted.

SUMMARY

The findings point to the selection of suitable hypoallergenic preparations for clinical trials of effective and safe latex allergy immunotherapy.

Hevea brasiliensis latex allergens: current panel and clinical relevance

Latex allergy has been studied in detail in Europe and the US over the past two decades, resulting in specific guidelines that succeeded in reducing its incidence in high-risk populations within the medical field. How these developments have affected high-risk populations outside the health care scenario is an important unanswered question. In addition, a second wave of latex allergy may occur in nations that are striving to attain higher economic and technologic standards, including population-dense countries such as China. Therefore, the application of Hevea allergens in novel diagnostic assays and the development of specific latex immunotherapy will provide new opportunities for latex allergy research. In this review, we summarize current knowledge on the immunological properties of the 13 officially accepted Hevea brasiliensis latex allergens.