Lipid-transfer protein is the major maize allergen maintaining IgE-binding activity after cooking at 100°C, as demonstrated in anaphylactic patients and patients with positive double-blind, placebo-controlled food challenge results

Stability of barley and malt lipid transfer protein 1 (LTP1) toward heating and reducing agents: relationships with the brewing process

Barley lipid transfer protein (LTP1) is a heat-stable and protease-resistant albumin that concentrates in beer, where it participates in the formation and stability of beer foam. Whereas the barley LTP1 does not display any foaming properties, the corresponding beer protein is surface-active. Such an improvement is related to glycation by Maillard reactions on malting, acylation on mashing, and structural unfolding on brewing. The structural stability of purified barley and glycated malt LTP1 toward heating has been analyzed. Whatever the modification, lipid adduction or glycation, barley LTP1s are highly stable proteins that resisted temperatures up to 100 degrees C. Unfolding of LTP1 occurred only when heating was conducted in the presence of a reducing agent. In the presence of sodium sulfite, the lipid-adducted barley and malt LTP1 displayed higher heat stability than the nonadducted protein. Glycation had no or weak effect on heat-induced unfolding. Finally, it was shown that unfolding occurred on wort boiling before fermentation and that the reducing conditions are provided by malt extract.

Purification and characterization of non-specific lipid transfer proteins from the leaves of Pandanus amaryllifolius (Pandanaceae)

Two proteins were isolated from the saline extract of mature leaves of Pandanus amaryllifolius, using affinity chromatography on fetuin-agarose and Affi-gel Blue gel, anion exchange chromatography as well as gel filtration. The proteins were demonstrated as non-glycoproteins, with molecular mass of 18 and 13 kDa, respectively, comprising of peptide subunits from 6.5 to 9 kDa in the forms of heterodimer and homodimer. All of them have similar N-terminal amino acid sequences with only minor variations and are matched to non-specific lipid transfer proteins (nsLTPs) of the other plants such as wheat LTP using NCBI Blast searching for short, nearly exact matches. Furthermore, they explicated each other as isoforms originated putatively from a multigene family with various molecular weight, binding affinity, ionic strength, and subunits. However, the potencies for antiproliferation of HL-60 cell line and inhibition of the growth of the bacteria Pseudomonas aeruginosa are different in that those of the fetuin-binding protein are greater than non-fetuin binding proteins. The non-specific lipid transfer proteins of P. amaryllifolius exhibit weak to moderate hemagglutinating activity toward rabbit erythrocytes, but, this activity could not be reversed by mannose. They thus could be easily differentiated from the previously reported mannose-binding lectin isolated from this plant, which has subunits with similar molecular weight.

Screening the allergenic repertoires of wheat and maize with sera from double-blind, placebo-controlled food challenge positive patients

BACKGROUND

Food allergy to wheat and maize is an increasing factor of deterioration of life quality, especially childhood and can, in rare cases, even induce anaphylaxis. Although omega-5 gliadin from wheat and maize lipid transfer protein have been characterized as major cereal allergens on the molecular level, the list of food allergens is far to be complete.

METHODS

To identify the IgE-binding repertoires of wheat and maize we screened respective cDNA libraries displayed on phage surface with sera from patients with a confirmed food allergy. The study included six patients with a positive double-blind, placebo-controlled food challenge (DBPCFC) to wheat, nine patients with a positive DBPCFC to maize, and six patients with anaphylactic reactions after ingestion of wheat.

RESULTS

The enriched sequences encoding IgE-binding proteins showed heterogeneous repertoires for both, wheat and maize. The selected wheat repertoire yielded 12, the maize repertoire 11 open reading frames. Among these we identified allergens belonging to already characterized allergens families, such as gliadin, profilin and beta-expansin. Besides, we found novel proteins with high cross-reactive potential, such as thioredoxins, as well as sequences that had so far not been related to cereal allergy at all. The IgE-binding capacity of some selected proteins was evaluated in vitro and cross-reactivity was demonstrated by competition ELISA.

CONCLUSION

With regard to the heterogeneity of the characterized sequences as well as to the biochemical nature of the new allergens detected we conclude that wheat and maize-related food allergy is more complex than so far anticipated.

The effect of thermal processing on the IgE reactivity of the non-specific lipid transfer protein from apple, Mal d 3

BACKGROUND

Non-specific lipid transfer proteins (LTPs) are involved in allergy to fresh and processed fruits. We have investigated the effect of thermal treatment and glycation on the physico-chemical and IgE-binding properties of the LTP from apple (Mal d 3).

METHODS

Mal d 3 was purified from apple peel and the effect of heating in the absence and presence of glucose investigated by CD spectroscopy, electrospray and MALDI-TOF mass spectrometry. IgE reactivity was determined by RAST and immunoblot inhibition, SPT and basophil histamine release test.

RESULTS

The identity and IgE reactivity of purified Mal d 3 was confirmed. Mild heat treatment (90 degrees C, 20 min) in the absence or presence of glucose did not alter its IgE reactivity. More severe heat treatment (100 degrees C, 2 h) induced minor changes in protein structure, but a significant decrease in IgE-binding (30-fold) and biological activity (100- to 1000-fold). Addition of glucose resulted in up to four glucose residues attached to Mal d 3 and only a 2- and 10-fold decrease of IgE-binding and biological activity, respectively.

CONCLUSIONS

Only severe heat treatment caused a significant decrease in the allergenicity of Mal d 3 but glycation had a protective effect. The presence of sugars in fruits may contribute to the thermostability of the allergenic activity of LTP in heat-processed foods.

Plant food allergies: a suggested approach to allergen-resolved diagnosis in the clinical practice by identifying easily available sensitization markers

BACKGROUND

Molecular biology techniques have led to the identification of a number of allergens in vegetable foods, but due to the lack of purified food proteins for routine diagnostic use, the detection of sensitizing allergens remains a nearly impossible task in most clinical settings. The allergen-resolved diagnosis of food allergy is essential because each plant-derived food may contain a number of different allergens showing different physical/chemical characteristics that strongly influence the clinical expression of allergy; moreover, many allergens may cross-react with homologue proteins present in botanically unrelated vegetable foods.

OBJECTIVE

Through a review of the available literature, this study aimed to detect "markers" of sensitization to specific plant food allergens that are easily accessible in the clinical practice.

RESULTS

There are several "markers" of sensitization to different allergenic proteins in vegetable foods that can be helpful in the clinical practice. Specific algorithms for patients allergic to Rosaceae and to tree nuts were built.

CONCLUSION

Clinical allergologists lacking the assistance of an advanced molecular biology lab may take advantage of some specific clinical data as well as of some "markers" in the difficult task of correctly diagnosing patients with plant food allergy and to provide them the best preventive advice.

Nonspecific lipid-transfer proteins in plant foods and pollens: an important allergen class

PURPOSE OF REVIEW

Here we focus our attention on the structural stability and physicochemical properties of plant nonspecific lipid-transfer proteins (nsLTPs) as keys to their allergenicity. We further present the current opinions on the route of sensitization and include the latest additions to the nsLTP allergen family.

RECENT FINDINGS

Plant nsLTPs are small cysteine-rich lipid-binding proteins that play a key role in plant resistance to biotic and abiotic stress. Besides their relevance for plant-pathogen interactions, nsLTPs have attracted interest as true food allergens which are of high importance to atopics in Mediterranean countries. It is now becoming clear that their molecular properties such as the remarkable stability to proteolysis and thermal denaturation are intrinsically linked to their allergenicity. These properties also facilitate sensitization via the gastrointestinal tract which allows these molecules to act as allergens independently of prior exposure to pollen. In addition, a group of allergenic pollen nsLTPs exists which seem to be only partially linked to the food nsLTPs by cross-reactivity.

SUMMARY

Research into the family of nsLTPs will continue to provide insights about the particular molecular properties that make an nsLTP an allergen and how primary sensitization occurs.

Why do lipid transfer protein-hypersensitive patients tolerate bean (and other legumes)?

BACKGROUND

Patients allergic to nonspecific lipid transfer protein (LTP) frequently score positive on SPT with legumes but virtually never report adverse reactions eating these foods.

OBJECTIVE

This study investigated the IgE reactivity to legumes of LTP-allergic patients and aimed to establish whether legumes can be considered safe in LTP-allergic patients.

METHODS

Skin reactivity as well as clinical allergy to bean and pea were evaluated in a large cohort of LTP-hypersensitive patients. Sera from 12 patients showing clinical allergy to a number of botanically unrelated plant-derived foods and high levels of IgE to peach LTP were employed in in vitro studies (ELISA, ELISA inhibition, SDS-PAGE/immunoblot) aiming to investigate IgE reactivity to bean.

RESULTS

Preabsorption of patients' sera with boiled bean extract did not cause any loss of IgE reactivity to peach LTP (whereas boiled apple totally abolished it). Immunoblot analysis did not show any IgE reactivity to bean proteins at about 10 kDa, and the SDS profile of bean showed little or no staining at 10 kDa.

CONCLUSION

Sera from LTP-allergic patients do not seem to show any IgE reactivity to 10-kDa proteins in bean. Whether this is caused by epitopic differences between Rosaceae and bean LTPs or by the fact that LTP is not expressed in bean remains to be established. This study explains why virtually all LTP-allergic patients tolerate legumes and suggests that these foods should be considered safe for patients sensitized to this protein.

Influence of thermal processing on the allergenicity of peanut proteins

Peanuts are one of the most common and severe food allergens. Nevertheless, the occurrence of peanut allergy varies between countries and depends on both the exposure and the way peanuts are consumed. Processing is known to influence the allergenicity of peanut proteins. The aim of this study was to assess the effect of thermal processing on the IgE-binding capacity of whole peanut protein extracts and of the major peanut allergens Ara h 1 and Ara h 2. Whole proteins, Ara h 1, and Ara h 2 were extracted and purified from raw, roasted and boiled peanuts using selective precipitation and multiple chromatographic steps, and were then characterized by electrophoresis and mass spectrometry. The immunoreactivity of whole peanut extracts and purified proteins was analyzed by the enzyme allergosorbent test (EAST) and EAST inhibition using the sera of 37 peanut-allergic patients. The composition of the whole protein extracts was modified after heat processing, especially after boiling. The electrophoretic pattern showed protein bands of low molecular weight that were less marked in boiled than in raw and roasted peanuts. The same low-molecular-weight proteins were found in the cooking water of peanuts. Whole peanut protein extracts obtained after the different processes were all recognized by the IgE of the 37 patients. The IgE-binding capacity of the whole peanut protein extracts prepared from boiled peanuts was 2-fold lower than that of the extracts prepared from raw and roasted peanuts. No significant difference was observed between protein extracts from raw and roasted peanuts. It is noteworthy that the proteins present in the cooking water were also recognized by the IgE of peanut-allergic patients. IgE immunoreactivity of purified Ara h 1 and Ara h 2 prepared from roasted peanuts was higher than that of their counterparts prepared from raw and boiled peanuts. The IgE-binding capacity of purified Ara h 1 and Ara h 2 was altered by heat treatment and in particular was increased by roasting. However, no significant difference in IgE immunoreactivity was observed between whole protein extracts from raw and roasted peanuts. The decrease in allergenicity of boiled peanuts results mainly from a transfer of low-molecular-weight allergens into the water during cooking.

Large scale purification of rapeseed proteins (Brassica napus L.)

Rapeseed (Brassica napus L.) cruciferin (12S globulin), napin (2S albumin) and lipid transfer proteins (LTP) were purified at a multi-g scale. The procedure developed was simple, rather fast and resolutive; it permitted the recovery of these proteins with a good yield, such as 40% for cruciferin and 18% for napin. Nanofiltration eliminated the major phenolic compounds. The remaining protein fraction was fractionated by cation exchange chromatography (CEC) on a streamline SP-XL column in alkaline conditions. The unbound neutral cruciferin was polished by size exclusion chromatography. The alkaline napin isoforms and LTP, adsorbed on the beads, were eluted as a whole fraction and further separated by an other CEC step at acidic pH. Napins were polished by hydrophobic interaction chromatography (HIC). The fractions were characterized by reverse phase HPLC, electrophoresis, N-terminal sequencing and mass spectrometry. All the fractions contained less than 5% of impurities.

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.

Contact urticaria and protein contact dermatitis from corn in a patient with serum IgE specific for a salt-soluble corn protein of low molecular weight

Among the cereals, wheat, rye, barley and oats, have been reported to cause protein contact dermatitis. However, in these cases neither the involvement of an immunological mechanism nor the role of specific protein(s) has been demonstrated. We present a case of protein contact dermatitis from corn. The patient presented with a Type I sensitization to corn, as shown by the presence of specific immunoglobulin (Ig)E and positivity to prick tests with both a flour suspension and the salt-soluble protein fraction of this cereal. The same corn preparations induced a strong urticarial reaction on scratch testing. This reaction was followed several days later by the appearance of erythema and then eczema at the site of application. When boiled, these preparations became inactive on both prick and scratch testing. Patch tests were negative in all cases. Immunoblotting performed with the patient's serum showed the presence of a unique IgE-binding protein band with a molecular weight of around 14 kDa, belonging to the salt-soluble corn protein fraction. Our results give the first clear evidence that cornflour can induce protein contact dermatitis. The IgE-binding 14-kDa protein has characteristics identical to those of the trypsin/alpha-amylase inhibitors from cereals.

Food processing: effects on allergenicity

PURPOSE OF REVIEW

There has been an increase in the prevalence of food allergy, asthma and severe reactions to foods in the past decade. The reason for this increase is unknown and despite the potential for a lethal outcome, no treatments or therapies are available. Many areas are being explored to understand the increase in food allergy and the role of modern processing techniques is one of them.

RECENT FINDINGS

The fact that processing influences allergenicity is not a new concept, but due to some definitive studies in the last few years the topic has been revitalized. Not only is the processed form of a particular allergen important in assessment of allergenicity, but the role of the food matrix in which an allergen is processed must also be evaluated. The issue of allergenicity of particular foods is therefore highly complex, and even with our existing knowledge we have just begun to understand some of the contributions of processing to allergenic properties of proteins and foods.

SUMMARY

Researchers and medical personnel have begun to weigh the benefits and potential disadvantages of assessing the allergenicity of foods in unprocessed forms. In this review, the known effects of processing on the allergenicity of various foods will be discussed along with the implications of the most recent studies on the future direction of research in this area.

Plant non-specific lipid transfer proteins as food and pollen allergens

Several members of the plant non-specific lipid transfer protein (LTP) family have been identified as relevant allergens in foods and pollens. These allergens are highly resistant to both heat treatment and proteolytic digestion. These characteristics have been related with the induction of severe systemic reactions in many patients, and with the possibility of being primary sensitizers by the oral route. A specific geographical distribution pattern of sensitization to LTP allergens has been uncovered. This allergen family is particularly important in the Mediterranean area, but shows a very limited incidence in Central and Northern Europe. The potential role in the plant, as well as the biochemical and allergenic properties of the LTP family, are reviewed here.

Clinical importance of cross-reactivity in food allergy

PURPOSE OF REVIEW

Review of recent developments in the field of cross-reactivity in food allergy and the clinical relevance of these developments.

RECENT FINDINGS

New foods have been added to the list of Bet v 1 and profilin-related food allergies. Clinical relevance of cross-reactions based on recognition of carbohydrate determinants and profilin is limited for the population of pollen-allergic patients as a whole. For selected food allergic patients, however, N-glycans and particularly profilin are potentially of clinical relevance. Lipid transfer proteins have further been established as clinically more severe allergens in several foods. This severity is attributed to their stability to proteolysis and processing. Storage proteins of several nuts and seeds have been identified as important allergens, but cross-reactivity between storage proteins of different foods appears to be limited. Using cross-reactivity as the basis for immunotherapy in food allergy seems promising but needs confirmation by double-blind, placebo-controlled trials.

SUMMARY

The continued identification and characterization of cross-reactive allergens facilitates the study of factors determining clinical relevance of cross-reactivity and of possible efficacy of immunotherapy in food allergy.

Do we have suitable in-vitro diagnostic tests for the diagnosis of food allergy?

PURPOSE OF REVIEW

Positive standardized food challenges represent the gold standard of diagnostic procedures in food-related reactions suspected to be of allergic nature. Skin prick testing and in-vitro diagnosis is helpful in most cases and can help to avoid cumbersome food challenges. This review considers recent progress in the use of in-vitro tests in the diagnosis of food allergy.

RECENT FINDINGS

Recent studies have addressed the characterization of 'new' food allergens which might now be used more accurately in the in-vitro diagnosis of food allergy. Additionally, while in-vitro tests must always be interpreted in line with the allergen tested and the clinical history, levels of food-specific immunoglobulin E can be correlated with the outcome of challenges to foods such as tree nuts as well as egg, according to two recent studies. Finally, epitope binding patterns of specific food allergens might help to predict which patients will most likely outgrow their food allergy, or which patients are clinically tolerant. This might help to avoid food challenges, which carry a risk for a potentially severe outcome.

SUMMARY

Recent studies of in-vitro diagnosis of food allergy have helped to provide safer and more accurate tests in the diagnosis and prognosis of food allergy.