Cross-reactive Plant Allergens Research Articles

Eosinophilic esophagitis is characterized by a non-IgE-mediated food hypersensitivity.

Eosinophilic esophagitis (EoE) is a chronic disease characterized clinically by symptoms of esophageal dysfunction and histologically by eosinophil-predominant inflammation. EoE is frequently associated with concomitant atopic diseases and immunoglobulin E (IgE) sensitization to food allergens in children as well as to aeroallergens and cross-reactive plant allergen components in adults. Patients with EoE respond well to elemental and empirical food elimination diets. Recent research has, however, indicated that the pathogenesis of EoE is distinct from IgE-mediated food allergy. In this review, we discuss the individual roles of epithelial barrier defects, dysregulated innate and adaptive immune responses, and of microbiota in the pathogenesis of EoE. Although food has been recognized as a trigger factor of EoE, the mechanism by which it initiates or facilitates eosinophilic inflammation appears to be largely independent of IgE and needs to be further investigated. Understanding the pathogenic role of food in EoE is a prerequisite for the development of specific diagnostic tools and targeted therapeutic procedures.

Identification and characterization of a basic thaumatin‐like protein (TLP 2) as an allergen in sapodilla plum (Manilkara zapota)

Cases of oral allergy syndrome following the ingestion of sapodilla plum (Manilkara zapota) have been reported rarely. As the causative allergens are not known, the main objective of this study was to identify and characterize the important allergens in sapodilla. Allergy to sapodilla was diagnosed by case history, skin prick test, and serum allergen-specific IgE. The allergen was detected by IgE immunoblotting, purified on SP-Sepharose and characterized by native/SDS-PAGE, IEF, MS, and amino acid composition. Several cases of allergy to sapodilla fruit were identified; majority of the sapodilla-allergic subjects (6/7) experienced typical oral allergy syndrome symptoms, and allergen-specific IgE to the purified protein was positive. The allergen has a pI ≥9.5 and high contents of arginine, threonine, glycine, and cysteine. Circular dichroism revealed a secondary structure rich in beta sheets/turns. Based on its N-terminal sequence of A-T-F-D-I-Q-N-N-C-X-Y-, the allergen (21 578 Da) was identified as a thaumatin-like protein by homology. The causative allergen in sapodilla plum has been identified and characterized as a highly basic thaumatin-like protein belonging to the pathogenesis-related protein (PR-5) family, which has been recognized as a new family of conserved, cross-reactive plant allergens.

Frequent sensitization to Candida albicans and profilins in adult eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is often associated with atopic airway and skin diseases. More than 80% of EoE patients are sensitized to aero- and/or food allergens. Immunoglobulin (Ig)E-mediated immune responses to microbes have been reported to be deleterious in connection with atopic diseases. The aim of this study was to obtain a comprehensive overview about the sensitization spectrum of adult EoE patients. IgE in sera of 35 patients with active EoE were analyzed for reactivity to Candida albicans, as well as to a panel of recombinant and purified natural allergen components, using a microarray. IgE sensitization to Candida albicans was found in 43% of EoE patients. More than 80% of EoE patients were sensitized to aeroallergens and 22% to food-specific allergen components, whereas 69% of the patients exhibited specific IgE to cross-reactive allergens. Among the latter, profilins were identified as most frequent IgE cross-reactive allergen components. Interestingly, dysphagia, the main symptom of adult EoE patients following rice and/or bread ingestion, was associated with sensitization to cross-reactive allergens such as profilins, pathogenesis-related (PR) 10 and lipid transfer proteins (LTP). Intolerance toward meat rarely correlated with sensitization to animal food allergens. Candida albicans and cross-reactive plant allergen components, in particular profilins, were identified as frequent sensitizers in adult EoE patients. Specific elimination therapies are suggested to reveal their actual roles in the pathogenesis of EoE.

Cross‐reactive and species‐specific immunoglobulin E epitopes of plant profilins: an experimental and structure‐based analysis

Profilins are cross-reactive plant allergens responsible for multiple pollen sensitization and pollen-associated food allergy. While it is assumed that profilins from different species are immunologically equivalent, some studies suggest partial or even lacking IgE cross-reactivity between certain profilins. We aimed to obtain a semi-quantitative assessment of the contributions of conserved and species-specific epitopes to IgE binding of plant profilins. We compared model structures of profilins from timothy, mugwort, celery and bell pepper with crystal structures of birch and latex profilins. We predicted potential conformational epitopes that consisted of contiguous patches of at least 20% surface-exposed residues. Celery and timothy profilins were purified from their natural sources, and profilins from birch, mugwort, bell pepper and latex were expressed in Escherichia coli. The structural integrity of all purified proteins was confirmed by circular dichroism spectroscopy. IgE ELISAs and ELISA inhibitions using sera from 22 profilin-sensitized allergic patients were carried out. Peptide backbone conformations of all six profilins were highly similar. Nine variable epitopes and two containing high proportions of conserved residues were predicted. IgE from all sera bound to all tested profilins and the amounts were highly correlated. However, IgE inhibition experiments revealed that up to 60% of total IgE binding was mediated by species-specific epitopes. The extent of cross-reactivity among profilins from timothy, birch, latex and celery was greater than cross-reactivity to mugwort and bell pepper profilins. This pattern was mirrored by sequence similarities among one of the predicted variable epitopes. Patients with IgE to cross-reactive epitopes displayed allergic reactions to a greater number of plant foods than patients having IgE directed to species-specific epitopes. The large extent of cross-reactivity among plant profilins justifies using a single profilin for diagnosis. However, the fine specificity of IgE directed to variable epitopes may influence the clinical manifestation of profilin sensitization.

Identification of a villin-related tobacco protein as a novel cross-reactive plant allergen

In a paradigmatic approach we identified cross-reactive plant allergens for allergy diagnosis and treatment by screening of a tobacco leaf complementary DNA (cDNA) library with serum IgE from a polysensitized allergic patient. Two IgE-reactive cDNA clones were isolated which code for proteins with significant sequence similarity to the actin-binding protein, villin. Northern- and Western-blotting demonstrate expression of the villin-related allergens in pollen and somatic plant tissues. In addition, villin-related proteins were detected in several plant allergen sources (tree-, grass-, weed pollen, fruits, vegetables, nuts). A recombinant C-terminal fragment of the villin-related protein was expressed in Escherichia coli, purified and shown to react specifically with allergic patients IgE. After profilin, villin-related proteins represent another family of cytoskeletal proteins, which has been identified as cross-reactive plant allergens. They may be used for the diagnosis and treatment of patients suffering from multivalent plant allergies.

Molecular Cloning and Characterization of Hazel Pollen Protein (70 kD) as a Luminal Binding Protein (BiP): A Novel Cross-Reactive Plant Allergen

Background: Tree pollen contains many allergens showing cross-reactivity to proteins from pollen, seeds, and fruits of different plant species. Amongst Fagales, responsible for several allergenic responses, hazel provides the best material to study pollen as well as food allergens in one species. The aim of this study was to identify and characterize the physiological function of an allergen from hazel pollen and to determine possible cross-reactivity to proteins from hazelnut. Methods: Monoclonal antibodies (mAbs) against hazel pollen crude extract were produced. On the basis of IgE binding, demonstrated by sera from patients allergic to hazel pollen, one mAb indicating the best correlation has been selected, and the putative allergen was purified by preparative gel electrophoresis. Isoforms were investigated by two-dimensional PAGE, and for molecular identification a hazel pollen cDNA library was constructed. In situ localization of the allergen during pollen development was performed by immunofluorescence labelling. Results: Immunological staining of crude hazel pollen extract with specific IgE and mAb revealed a 70-kD protein. Immunoblot studies with mAb showed cross-reactive proteins of 70–72 kD in different plant tissues and species. After protein purification, the IgE-binding reactivity of the allergen has been reconfirmed, and two isoforms were detected. Molecular cloning identified the allergen as a luminal binding protein (BiP) of the Hsp70 family with 88–92% sequence identity in various plants. Further immunocytological studies indicated involvement of BiP during pollen development. Conclusions: Chaperons like BiP play an important role in protein synthesis and in the protection of cellular structures during stress-related processes. Because of their highly conserved protein sequences, we propose that such allergens could be responsible for at least a part of the allergenic cross-reactivity between proteins from different pollens and plant foods.

Features and Mode of Action of Cross-reactive Plant Allergens Relevant to Latex-fruit Syndrome

Immediate-type reactions to articles made from natural rubber latex are collectively referred to as latex allergy. Some latex-sensitized patients also experience allergic reactions to various fruits and vegetables. This phenomenon is called latex-fruit syndrome. Recent research revealed that several proteins related to the defense mechanisms of plants are responsible for latex allergy and the accompanying cross-reactivity. Protective systems of higher plants are relatively conserved in the course of evolution, and therefore homologous defense-related proteins are produced regardless of the species. Once sensitized by such a conserved protein, the patient is expected to cross-react to taxonomically unrelated plants. Remarkably, cross-reactive antigens in the causative foods are generally sensitive to heat and digestive enzymes. Per-oral sensitization is not commonly established by such food antigens. They are instead considered to elicit allergic reactions in latex-sensitized patients based on their cross-reactivity to the corresponding sensitizers. Defense-related proteins in higher plants are agriculturally useful, and various environmental stresses up-regulate their production. These proteins are also suspected to be relevant to the increasing allergies to plants.

Human monoclonal IgG antibodies derived from a patient allergic to birch pollen as tools to study the in situ localization of the major birch pollen allergen, Bet v 1, by immunogold electron microscopy

Background: Bet v 1, the major birch pollen allergen, and related allergens present in various tree pollens, fruits, and vegetables represent a family of important cross-reactive allergens. Although the DNA, deduced amino–acid sequence, and structure of Bet v 1 have been determined, little is known regarding its biologic functions. Objective: Human monoclonal antibodies derived from an individual allergic to birch pollen were used for refined ultrastructural localization of Bet v 1 in birch pollen grains to gain information regarding the allergen distribution and its possible biologic function. These data were to be supplemented by sequence analyses. Methods: Ultrathin sections of anhydrously prepared birch pollen grains were incubated with human monoclonal antibodies (BAB1, BAB2, and BAB4). The binding sites were visualized in the transmission electron microscope by gold-conjugated anti-human IgG antibodies. Results: In the cytoplasm of the birch pollen grain, human monoclonal antibodies bound to ribosome-rich areas and to pollen nuclei. Sequence analysis of Bet v 1 and homologous allergens identified a highly conserved p-loop motif in these proteins, which is typically found in nucleotide-binding proteins. Conclusions: Immunolocalization of Bet v 1 to ribosome-rich areas and the nucleus would be consistent with a highly conserved biologic function of Bet v 1 and homologous proteins as nucleotide binding proteins and explains why this group of plant proteins represents highly cross-reactive plant allergens against which many type I patients are sensitized. (J Allergy Clin Immunol 1998;101:60-6.)

Molecular Characterization, Expression inEscherichia coli,and Epitope Analysis of a Two EF-Hand Calcium-Binding Birch Pollen Allergen, Bet v 4

Birch pollen belongs to the most potent elicitors of Type I allergic reactions in early spring. Using serum IgE from a birch pollen allergic patient, two cDNA clones (clone 6 and clone 13) were isolated from a birch pollen expression cDNA library constructed in phage λgt11. Clone 6 encoded a 9.3 kD two EF-hand calcium-binding protein, designated Bet v 4, with significant end to end sequence homology to EF-hand calcium-binding allergens from weed and grass pollen. Recombinant Bet v 4, expressed as β-galactosidase fusion protein, reacted with serum IgE from approximately 20% of pollen allergic individuals. Depletion of allergen-bound calcium by EGTA treatment lead to a substantial reduction of IgE-binding to Bet v 4, indicating that protein-bound calcium is necessary for the maintenance of IgE-epitopes. The greatly reduced IgE-binding capacity of clone 13, a Bet v 4 fragment that lacked the 16 N-terminal amino acids, indicated that the N-terminus contributes significantly to the proteins IgE-binding capacity. By IgE-inhibition experiments it was demonstrated that recombinant Bet v 4 shared IgE-epitopes with natural Bet v 4 and a homologous timothy grass pollen allergen. Recombinant Bet v 4 may therefore be considered as a relevant crossreactive plant allergen, which may be used for diagnosis and treatment of patients suffering from multivalent plant allergies.

Identification of a 60 kd cross-reactive allergen in pollen and plant-derived food

Background: Cross-reactive IgE antibodies were found to be responsible for allergic reactions in patients allergic to pollen on ingestion of food (oral allergy syndrome). So far, the major birch pollen allergen Bet v 1 and birch profilin (Bet v 2) were identified as relevant cross-reactive allergens. Objective: In this study we attempted to identify additional cross-reactive plant allergens, which could be responsible for food intolerance in patients allergic to pollen. Methods: Monoclonal antibodies specific for the major mugwort pollen allergen, Art v 1, representing a 60 kd glycoprotein, were used to detect cross-reactive allergens in other pollens and plant-derived food. The amino acid compositions of the cross-reactive structures were determined, and their resistance against trypsin treatment was investigated. In addition, IgE immunoblot inhibitions were done with the 60 kd mugwort pollen allergen. Results: Monoclonal antibodies specific for the major mugwort pollen allergen, Art v 1, cross-reacted with proteins of comparable molecular weight in fruit and vegetables. Preadsorption of patients’ sera with the 60 kd mugwort allergen led to a reduction of IgE binding to components of a similar molecular weight present in different pollen (birch, timothy grass), fruit (apple, peanuts), and vegetable (celery) extracts and reduced IgE binding to apple, kiwi, and celery as determined by RAST inhibitions. Conclusion: A cross-reactive plant panallergen, possibly identical to the major mugwort pollen allergen, Art v 1, is described. The allergen represents a protein of approximately 60 kd present in various pollen and plant foods, which is distinct from Bet v 1 and profilin and hence may represent a novel cross-reactive allergen in the oral allergy syndrome. (J A LLERGY C LIN I MMUNOL 1996;98:938-47.)

Immunological and structural similarities among allergens: prerequisite for a specific and component-based therapy of allergy.

It is known that allergic patients are frequently co-sensitized against different allergen sources. Progress made in the field of allergen characterization by molecular biological techniques has now revealed that sensitization against different allergen sources can be explained as cross-reactivity of IgE antibodies with structurally and immunologically related components present in these allergen sources. This review defines groups of cross-reactive plant allergens with significant sequence homology. The similarities among allergens may facilitate allergy diagnosis by using a few representative cross-reactive allergens to determine the patient's IgE reactivity profile (allergogram). According to that typing, a few cross-reactive allergens, carrying most of the relevant IgE epitopes, may then be selected for patient-tailored specific therapy.