Clinical implications of cross-reactive food allergens

Recombinant Pru p 3 and natural Pru p 3, a major peach allergen, show equivalent immunologic reactivity: a new tool for the diagnosis of fruit allergy

BACKGROUND

The peach lipid transfer protein Pru p 3 has been identified as a major allergen from this fruit. Homologous cross-reactive allergens have been found in several plant foods and pollens. Recombinant Pru p 3 has been recently produced in the yeast Pichia pastoris.

OBJECTIVE

We sought to evaluate the potential role of recombinant Pru p 3 as a novel tool for the diagnosis of fruit allergy.

METHODS

Circular dichroism analysis was used to compare the protein folding of natural Pru p 3 and recombinant Pru p 3. IgE binding by both molecular forms was quantified by means of ELISA and ELISA inhibition assays, and their biologic activity was estimated by using basophil activation, histamine release, and sulphidoleukotriene production tests. Individual sera or blood samples from patients with peach allergy (up to 17) were used in the assays.

RESULTS

A nearly identical circular dichroism spectra was shown by using natural Pru p 3 and recombinant Pru p 3, indicating that both protein forms are similarly folded. No difference was detected in the IgE-binding capacity of the 2 mo-lecular versions. Basophil activation and induction of sulphidoleukotriene production were positive in 9 of 10 patients, and histamine release was induced in at least half of the patients, with similar effects of the natural and recombinant forms in the 3 assays.

CONCLUSION

Recombinant Pru p 3 shows a strong immunologic activity equivalent to that of its natural counterpart, and therefore it can be a useful tool for diagnosis (and future immunotherapy) of fruit allergy.

9. Food allergy

Food allergies affect as many as 6% of young children, most of whom "outgrow" the sensitivity, and about 2% of the general population. Although any food may provoke a reaction, relatively few foods are responsible for the vast majority of food allergic reactions: milk, egg, peanuts, tree nuts, fish, and shellfish. Many of these food allergens have been characterized at a molecular level, which has increased our understanding of the immunopathogenesis of many responses and may soon lead to novel immunotherapeutic approaches. Food allergic reactions are responsible for a variety of symptoms involving the skin, gastrointestinal tract, and respiratory tract and may be due to IgE-mediated and non-IgE-mediated mechanisms. A systematic approach including history, laboratory studies, elimination diets, and often food challenges will lead to the correct diagnosis. Currently, management of food allergies consists of educating the patient to avoid ingesting the responsible allergen and to initiate therapy in case of an unintended ingestion.

[Cross-reactive allergen clusters in pollen-associated food allergy]

Immediate symptoms caused by allergens without previous primary sensitization are commonly based on cross-reactive IgE antibodies. They are responsible for pollen-associated food allergies, i.e., fruit allergy in cases of birch pollen allergy or allergy to celery and spices in cases of mugwort pollen allergy. Similar structures between the major allergen of birch pollen (Bet v 1) and a variety of pathogenesis-related proteins from the same family (PR-10), abundant in hazelnuts, fruits, and vegetables, have been well established. Other candidates are profilins, ubiquitous panallergens with little clinical relevance, and stable lipid transfer proteins, responsible for systemic reactions predominantly in Mediterranean countries. Depending on stability, dose, and resorption of these proteins, clinical symptoms are limited to the oro-pharyngeal cavity or develop systemically far from the site of allergen exposure. Clinical diagnosis is based on a positive case history with corresponding allergic sensitization to pollen allergens. Targeted skin testing with native products (i.e., prick to prick test with fresh fruits) appears to be superior for unstable allergens compared to commercial extracts. Individuals should be familiar with cross-reactive patterns; however, allergen avoidance is only recommended in cases of clinical symptoms.

SDAP: database and computational tools for allergenic proteins

SDAP (Structural Database of Allergenic Proteins) is a web server that provides rapid, cross-referenced access to the sequences, structures and IgE epitopes of allergenic proteins. The SDAP core is a series of CGI scripts that process the user queries, interrogate the database, perform various computations related to protein allergenic determinants and prepare the output HTML pages. The database component of SDAP contains information about the allergen name, source, sequence, structure, IgE epitopes and literature references and easy links to the major protein (PDB, SWISS-PROT/TrEMBL, PIR-ALN, NCBI Taxonomy Browser) and literature (PubMed, MEDLINE) on-line servers. The computational component in SDAP uses an original algorithm based on conserved properties of amino acid side chains to identify regions of known allergens similar to user-supplied peptides or selected from the SDAP database of IgE epitopes. This and other bioinformatics tools can be used to rapidly determine potential cross-reactivities between allergens and to screen novel proteins for the presence of IgE epitopes they may share with known allergens. SDAP is available via the World Wide Web at http://fermi.utmb.edu/SDAP/.

Latex-fruit syndrome

Natural rubber latex immunoglobulin E-mediated hypersensitivity is probably one of the most relevant challenges that has been faced in the treatment of allergies during recent years. Additionally, allergen cross-reactivity has arisen as another very important problem, in the difficulty in diagnosing it and in its clinical implications. It is clear that some latex allergens cross-react with plant-derived food allergens, the so-called latex-fruit syndrome, with evident clinical consequences. Although the foods most frequently involved are banana, avocado, kiwi, and chestnut, several others are also implicated. Investigations point to a group of defense-related plant proteins, class I chitinases, which cross-react with a major latex allergen, hevein, as the panallergens responsible for the syndrome. This review focuses on our current understanding of the latex-fruit syndrome.

Characterization of asparagus allergens: a relevant role of lipid transfer proteins

BACKGROUND

No asparagus allergen has been characterized to date. Lipid transfer proteins (LTPs) have an ubiquitous distribution in plant foods and have been identified as relevant allergens in some fruits, seeds, and pollens.

OBJECTIVE

We sought to identify asparagus allergens and to evaluate the potential involvement of the panallergen LTP family in asparagus allergy.

METHODS

Eighteen patients with asthma, anaphylaxis, and/or contact urticaria after asparagus ingestion or exposure and positive skin prick test (SPT) responses and serum-specific IgE levels to asparagus were selected. Two LTPs were isolated from crude asparagus extract by using chromatographic methods and characterized by means of N-terminal amino acid sequencing. Both isolated proteins were tested by means of immunodetection, CAP inhibition assays, and SPTs. Additional asparagus allergens were located by using immunodetection with a pool of sera from patients allergic to asparagus and with rabbit polyclonal antibodies to sunflower pollen profilin and anti-complex asparagine-linked glycans antibodies.

RESULTS

The purified LTPs showed an N-terminal amino acid sequence similar to that of Pru p 3 and a strong reaction to anti-Pru p 3 antibodies. Each isolated protein reached inhibition values of up to 60% in CAP inhibition assays against asparagus extracts and elicited positive SPT responses in 9 of 18 patients with asparagus allergy. Immunodetection assays allowed us to identify profilin and cross-reacting carbohydrate determinants as asparagus IgE-binding components.

CONCLUSION

Asparagus LTPs are relevant allergens. In addition, profilin and glycoproteins harboring complex asparagine-linked glycans can also be involved in asparagus allergy.

Oral allergy syndrome induced by tomato in a dog with Japanese cedar (Cryptomeria japonica) pollinosis

A dog with Japanese cedar (Cryptomeria japonica, CJ) pollinosis had oral allergy syndrome (OAS) after ingesting fresh tomato. The dog showed specific IgE to both CJ and tomato allergens. As a negative control, twenty dogs without atopic dermatitis that had no exposure to tomato and no specific IgE to CJ allergen were used. They had no specific IgE to tomato allergen. Furthermore, IgE cross-reactivity was observed between CJ and tomato allergens in the dog. We found that OAS induced by tomato exists in the dog and there is a relationship between CJ and tomato allergens.

Food allergies

Adverse reactions to foods are commonly implicated in the causation of ill health. However, foreign antigens, including food proteins and commensal microbes encountered in the gastrointestinal tract, are usually well tolerated. True food allergies, implying immune-mediated adverse responses to food antigens, do exist, however, and are especially common in infants and young children. Allergic reactions to food manifest clinically in a variety of presentations involving the gastrointestinal, cutaneous, and respiratory systems and in generalized reactions such as anaphylaxis. Both IgE-mediated and non-IgE-mediated immune mechanisms are recognized. Important advances in the clinical features underlying specific food hypersensitivity disorders are reviewed.

Recent developments in latex allergy

PURPOSE OF REVIEW

Immediate allergic reactions to natural rubber latex continue to be an important medical and occupational health problem. In this review we focus on progress made in understanding the significance of occupational exposure and epidemiology, risk groups, diagnosis and prevention of natural rubber latex allergy. We also discuss methods aimed at quantification of clinically relevant natural rubber latex allergens and studies on B-cell epitopes of major natural rubber latex allergens.

RECENT FINDINGS

Prospective studies have been published focusing on the prevention of natural rubber latex allergy. Efforts to identify and characterize new natural rubber latex allergens were continued in several research groups. The use of purified allergens or proteins produced by recombinant DNA technology was assessed in studies aimed at improving the diagnosis of natural rubber latex allergy as well as in developing quantitative methods for the measurement of specific natural rubber latex allergens. For the first time, conformational immunoglobulin E epitopes were identified in a major natural rubber latex allergen, hevein, using a novel chimera-based allergen epitope mapping strategy.

SUMMARY

Measures taken in health care to reduce exposure to natural rubber latex products seem to be effective in reducing the number of new sensitizations. A few new minor natural rubber latex allergens, probably important in allergen cross reactions, were identified, and some nonmedical natural rubber latex products were found to be potentially dangerous to natural rubber latex-allergic patients. Sensitive and specific immunoassays for quantification of clinically relevant natural rubber latex allergens in manufactured products were developed in some laboratories. These assays may eventually replace the nonspecific total protein measurement, currently advocated by health authorities in the indirect estimation of allergen amounts in natural rubber latex products. Knowledge about conformational immunoglobulin-binding B-cell epitopes of major allergens is expected to be helpful in designing optimal reagents to specific immunotherapy.

Food allergy

Food allergy encompasses a range of disorders that result from adverse immune responses to dietary antigens. This group of conditions includes acute, potentially fatal reactions, and a host of chronic diseases that mainly affect the skin and gastrointestinal tract. Tools for diagnosis and management have not changed much in the past two decades, and include the clinical history, physical examination, tests for specific IgE antibody to suspected foods, elimination diets, oral food challenges, and provision of medications such as epinephrine for emergency treatment. However, much research in the past few years has enhanced our understanding of the clinical, epidemiological, and immunological aspects of these disorders. In this review I will discuss these advances and incorporate them into an improved diagnostic and management scheme. Additionally, emergent diagnostic, treatment, and prevention strategies are reviewed.

Allergies to cross-reactive plant proteins. Latex-fruit syndrome is comparable with pollen-food allergy syndrome

Both latex-fruit syndrome and oral allergy syndrome concomitant with pollinosis (pollen-food allergy syndrome) are considered to be caused by cross-reactivity between sensitizers and symptom elicitors. The cross-reactive food allergens relevant to these syndromes are mostly sensitive to heat and digestive enzymes. Such a vulnerable antigen cannot sensitize people perorally but provokes allergic reactions in already sensitized patients based on its cross-reactivity to the corresponding sensitizer. These types of food allergens are often called incomplete food allergens or nonsensitizing elicitors. Their features contrast with those of complete food allergens that have the capacity for peroral sensitization as well as symptom elicitation. Although highly antigenic and cross-reactive, carbohydrate epitopes do not generally elicit allergic reactions and often disturb in vitro IgE tests. Recent research has revealed that some of the cross-reactive allergens responsible for the two syndromes are proteins related to the defense responses of higher plants. Plant defense-related proteins are relatively conserved in the course of evolution and can supply cross-reactive epitopes. It is important to note that various stresses can stimulate the expression of these proteins, which implies that allergens increase in plants under stressful conditions like severe growing situations and exposure to some kinds of chemicals. Because defense-related proteins usually provide a plant with resistance to stresses, varieties that are apt to intensively induce such proteins are agriculturally valuable. Less toxic substances that cause crops to express defensive proteins are being investigated as a new type of agrochemical. Moreover, some defense-related proteins are going to be constantly produced in genetically modified plants. Even though these proteins can be useful agriculturally, their allergenicity should be evaluated carefully.

Clinical features of cross-reactivity of food allergy caused by fruits

Fruits are increasingly recognized as a cause of food allergy. The wide cross-reactivity among these foods has been extensively studied. In this review we will focus on studies addressing the clinical relevance of cross-reactivity among fruits, the diagnostic management of patients complaining of reactions to multiple fruits, and adequate dietary recommendations.