Cross-reactivity among non-specific lipid-transfer proteins from food and pollen allergenic sources

Improving In Vitro Detection of Sensitization to Lipid Transfer Proteins: A New Molecular Multiplex IgE Assay

SCOPE

LTP-syndrome is characterized by sensitization (IgE) to multiple non-specific lipid transfer proteins (nsLTPs) with a variable clinical outcome. The treatment is primarily based on offending food avoidance. However, the determination of Pru p 3-specific IgE is currently the main diagnostic tool to assess sensitization to nsLTPs. Herein, the study evaluates improvement of LTP-syndrome diagnosis and clinical management using a new IgE multiplex-immunoblot assay with a high diversity of food nsLTPs.

METHODS AND RESULTS

An EUROLINE-LTP strip with 28 recombinant nsLTPs from 18 allergenic sources is designed. In total the study investigates 38 patients with LTP-syndrome and compares results from the nsLTPs (LTP-strip) with the respective food extracts of Prick-by-prick (PbP) testing. The agreement exceeds 70% for most nsLTPs, e.g., Pru p 3 (100%), Mal d 3 (97%), Pru av 3 (89%), Pha v 3 isoforms (87%/84%), Ara h 9 (82%), Cor a 8 (82%), and Jug r 3 (82%). The functionality and allergenic relevance of nine recombinant nsLTPs are proven by Basophil activation testing (BAT).

CONCLUSIONS

The new IgE multiplex-immunoblot nsLTP assay shows a good diagnostic performance allowing culprit food assessment. Negative results from LTP-strip may indicate potentially tolerable foods, improving diet intervention and patients' quality of life.

Herbivory-inducible lipid-transfer proteins (LTPs) of Cicer arietinum as potential human allergens

Lipid-transfer proteins (LTPs) are lipid-binding small proteins, ubiquitously distributed amongst plant kingdom. Apart from their involvement in plant defense, it has also been discovered that they induce allergic reactions in humans. A plethora of LTPs have been identified in vegetables, fruits, pollens, nuts, and latex, among which Pru p 3, a LTP allergen from peach fruit, is extensively studied and exhibits cross-reactivity with potential allergens from different species. In Cicer arietinum, a family of LTPs (CaLTPs) has been identified and their importance in plant defense during Helicoverpa armigera-infestation has been recognized. However, the determination of the allergenicity potential of CaLTPs has not been attempted. In this study, we aim to decipher the allergenicity potential of defense-related CaLTPs. The allergenicity potential prediction, and identification of B-cell epitope binding regions showed that the CaLTPs had conserved domains and B-cell epitopes in the same regions as Prup3 (a marker allergen for LTPs). Using molecular docking and simulations, we observed that the CaLTPs successfully interacted with the Immunoglobin E(IgE)with docking energies ranging from -315.5 to -268.4 and the structures were stabilized within 10 ns of simulation. Through this study, we intend to embellish our present knowledge and understanding of the sensitization and allergenicity potential of CaLTPs.Communicated by Ramaswamy H. Sarma.

BSACI guideline for the diagnosis and management of pollen food syndrome in the UK

Pollen food syndrome (PFS) is a highly prevalent food allergy affecting pollen-sensitized children and adults. Sufferers experience allergic symptoms when consuming raw plant foods, due to the homology between the pollen allergens and unstable proteins in these foods. The triggers involved can vary depending on the pollen sensitization, which in turn is affected by geographical location. The British Society of Allergy and Clinical Immunology (BSACI) Standards of Care Committee (SOCC) identified a need to develop a guideline for the diagnosis and management of PFS in the United Kingdom (UK). Guidelines produced by the BSACI use either the GRADE or SIGN methodology; due to a lack of high-quality evidence these recommendations were formulated using the SIGN guidelines, which is acknowledged to be less robust than the GRADE approach. The correct diagnosis of PFS ensures the avoidance of a misdiagnosis of a primary peanut or tree nut allergy or confusion with another plant food allergy to non-specific lipid transfer proteins. The characteristic foods involved, and rapid-onset oropharyngeal symptoms, mean PFS can often be diagnosed from the clinical history alone. However, reactions involving tree nuts, peanuts and soya milk or severe/atypical reactions to fruits and vegetables may require additional diagnostic tests. Management is through the exclusion of known trigger foods, which may appear to be simple, but is highly problematic if coupled with a pre-existing food allergy or for individuals following a vegetarian/vegan diet. Immunotherapy to pollens is not an effective treatment for PFS, and although oral or sublingual immunotherapy to foods seems more promising, large, controlled studies are needed. The typically mild symptoms of PFS can lead to an erroneous perception that this condition is always easily managed, but severe reactions can occur, and anxiety about the onset of symptoms to new foods can have a profound effect on quality of life.

From Allergen Molecules to Molecular Immunotherapy of Nut Allergy: A Hard Nut to Crack

Peanuts and tree nuts are two of the most common elicitors of immunoglobulin E (IgE)-mediated food allergy. Nut allergy is frequently associated with systemic reactions and can lead to potentially life-threatening respiratory and circulatory symptoms. Furthermore, nut allergy usually persists throughout life. Whether sensitized patients exhibit severe and life-threatening reactions (e.g., anaphylaxis), mild and/or local reactions (e.g., pollen-food allergy syndrome) or no relevant symptoms depends much on IgE recognition of digestion-resistant class I food allergens, IgE cross-reactivity of class II food allergens with respiratory allergens and clinically not relevant plant-derived carbohydrate epitopes, respectively. Accordingly, molecular allergy diagnosis based on the measurement of allergen-specific IgE levels to allergen molecules provides important information in addition to provocation testing in the diagnosis of food allergy. Molecular allergy diagnosis helps identifying the genuinely sensitizing nuts, it determines IgE sensitization to class I and II food allergen molecules and hence provides a basis for personalized forms of treatment such as precise prescription of diet and allergen-specific immunotherapy (AIT). Currently available forms of nut-specific AIT are based only on allergen extracts, have been mainly developed for peanut but not for other nuts and, unlike AIT for respiratory allergies which utilize often subcutaneous administration, are given preferentially by the oral route. Here we review prevalence of allergy to peanut and tree nuts in different populations of the world, summarize knowledge regarding the involved nut allergen molecules and current AIT approaches for nut allergy. We argue that nut-specific AIT may benefit from molecular subcutaneous AIT (SCIT) approaches but identify also possible hurdles for such an approach and explain why molecular SCIT may be a hard nut to crack.

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.

The diagnosis and management of allergic reactions in patients sensitized to non-specific lipid transfer proteins

Sensitization to one or more non-specific lipid transfer proteins (nsLTPs), initially thought to exist mainly in southern Europe, is becoming accepted as a cause of allergic reactions to plant foods across Europe and beyond. The peach nsLTP allergen Pru p 3 is a dominant sensitizing allergen and peaches a common food trigger, although multiple foods can be involved. A frequent feature of reactions is the requirement for a cofactor (exercise, alcohol, non-steroidal anti-inflammatory drugs, Cannabis sativa) to be present for a food to elicit a reaction. The variability in the food and cofactor triggers makes it essential to include an allergy-focused diet and clinical history in the diagnostic workup. Testing on suspected food triggers should also establish whether sensitization to nsLTP is present, using purified or recombinant nsLTP allergens such as Pru p 3. The avoidance of known trigger foods and advice on cofactors is currently the main management for this condition. Studies on immunotherapy are promising, but it is unknown whether such treatments will be useful in populations where Pru p 3 is not the primary sensitizing allergen. Future research should focus on the mechanisms of cofactors, improving diagnostic accuracy and establishing the efficacy of immunotherapy.

New insights into the sensitization to nonspecific lipid transfer proteins from pollen and food: New role of allergen Ole e 7

BACKGROUND

Ole e 7 is a nonspecific lipid transfer protein (nsLTP) from olive pollen, one of the main allergenic pollens worldwide. This allergenic nsLTP is responsible for severe symptoms in regions with high olive pollen exposure, where many Ole e 7-sensitized patients exhibit a co-sensitization to the peach nsLTP, Pru p 3. However, there is no evidence of cross-reactivity, which explains this observed co-sensitization. Therefore, the purpose of this study was to explore the relationship between Ole e 7 and Pru p 3.

METHODS

A total of 48 patients sensitized to Ole e 7 and/or Pru p 3 were included in the study. Specific IgE serum levels were measured by ImmunoCAP 250 and ELISA. Inhibition assays were performed to determine the existence of cross-reactivity between both nsLTPs. Allergic response was analyzed ex vivo (basophil activation test) and in vitro (RBL-2H3 mast cell model).

RESULTS

Common IgG and IgE epitopes were identified between both allergens. IgE-binding inhibition was detected in Ole e 7-monosensitized patients using rPru p 3 as inhibitor, reaching inhibition values of 25 and 100%. Ex vivo and in vitro assays revealed a response against rPru p 3 in four (31%) Ole e 7-monosensitized patients.

CONCLUSIONS

Our results suggest that Ole e 7 could play a new role as primary sensitizer in regions with high olive pollen exposure, leading to the peach nsLTP sensitization. This co-sensitization process would occur because of the cross-reactivity between Ole e 7 and Pru p 3 observed in some allergic patients.

2S albumins and nsLTP are involved in anaphylaxis to pizza sauce: IgE recognition before and after allergen processing

Although pizza is one of the most popular foods in the world, allergic responses after ingesting pizza are relatively uncommon. However, precisely identifying the allergens responsible for these allergic reactions is challenging because of the high and diverse number of ingredients used in pizza preparation. In this report, we aim to identify the allergens responsible for systemic allergic reactions following ingestion of pizza in two patients. Using a skin prick by prick test (SPPT) and in vitro techniques, with natural and recombinant purified allergens from tomato and mustard seeds, we identified 2S albumin and non-specific lipid transfer proteins (nsLTP) as the proteins involved. However, IgE responses to the four nsLTPs differed before and after denaturation and reduction, thus suggesting additional complexity around nsLTP in food processing.

A robust method for the estimation and visualization of IgE cross-reactivity likelihood between allergens belonging to the same protein family

Among the vast number of identified protein families, allergens emanate from relatively few families which translates to only a small fraction of identified protein families. In allergy diagnostics and immunotherapy, interactions between immunoglobulin E and allergens are crucial because the formation of an allergen-antibody complex is necessary for triggering an allergic reaction. In allergic diseases, there is a phenomenon known as cross-reactivity. Cross-reactivity describes a situation where an individual has produced antibodies against a particular allergenic protein, but said antibodies fail to discriminate between the original sensitizer and other similar proteins that usually belong to the same family. To expound the concept of cross-reactivity, this study examines ten protein families that include allergens selected specifically for the analysis of cross-reactivity. The selected allergen families had at least 13 representative proteins, overall folds that differ significantly between families, and include relevant allergens with various potencies. The selected allergens were analyzed using information on sequence similarities and identities between members of the families as well as reports on clinically relevant cross-reactivities. Based on our analysis, we propose to introduce a new A-RISC index (Allergens’–Relative Identity, Similarity and Cross-reactivity) which describes homology between two allergens belonging to the same protein family and is used to predict the likelihood of cross-reactivity between them. Information on sequence similarities and identities, as well as on the values of the proposed A-RISC index is used to introduce four categories describing a risk of a cross-reactive reaction, namely: high, medium-high, medium-low and low. The proposed approach can facilitate analysis in component-resolved allergy diagnostics, generation of avoidance guidelines for allergic individuals, and help with the design of immunotherapy.

Ragweed Pollen Allergy: Burden, Characteristics, and Management of an Imported Allergen Source in Europe

Ambrosia artemisiifolia, also known as common or short ragweed, is an invasive annual flowering herbaceous plant that has its origin in North America. Nowadays, ragweed can be found in many areas worldwide. Ragweed pollen is known for its high potential to cause type I allergic reactions in late summer and autumn and represents a major health problem in America and several countries in Europe. Climate change and urbanization, as well as long distance transport capacity, enhance the spread of ragweed pollen. Therefore ragweed is becoming domestic in non-invaded areas which in turn will increase the sensitization rate. So far 11 ragweed allergens have been described and, according to IgE reactivity, Amb a 1 and Amb a 11 seem to be major allergens. Sensitization rates of the other allergens vary between 10 and 50%. Most of the allergens have already been recombinantly produced, but most of them have not been characterized regarding their allergenic activity, therefore no conclusion on the clinical relevance of all the allergens can be made, which is important and necessary for an accurate diagnosis. Pharmacotherapy is the most common treatment for ragweed pollen allergy but fails to impact on the course of allergy. Allergen-specific immunotherapy (AIT) is the only causative and disease-modifying treatment of allergy with long-lasting effects, but currently it is based on the administration of ragweed pollen extract or Amb a 1 only. In order to improve ragweed pollen AIT, new strategies are required with higher efficacy and safety.

Assessment of Natural Variability of Maize Lipid Transfer Protein Using a Validated Sandwich ELISA

Lipid transfer protein (LTP) is the main causative agent for rare food allergic reactions to maize. This paper describes a new, validated ELISA that accurately measures maize LTP concentrations from 0.2 to 6.4 ng/mL. The levels of LTP ranged from 171 to 865 μg/g of grain, a 5.1-fold difference, across a set of 49 samples of maize B73 hybrids derived from the Nested Association Mapping (NAM) founder lines and a diverse collection of landrace accessions from North and South America. A second set of 107 unique samples from 18 commercial hybrids grown over two years across 10 U.S. states showed a comparable range of LTP level (212-751 μg/g of grain). Statistical analysis showed that genetic and environmental factors contributed 63 and 6%, respectively, to the variance in LTP levels. Therefore, the natural variation of maize LTP is up to 5-fold different across a diverse collection of varieties that have a history of safe cultivation and consumption.

Asymptomatic LTP sensitisation is common in plant-food allergic children from the Northeast of Spain

BACKGROUND

The sensitisation profile at molecular level in plant-food allergy is complex. Several allergens may be involved, with different potential for severe reactions. lipid transfer proteins (LTP) are considered the most relevant plant-food allergens in adults in Mediterranean countries, but less is known in children.

AIM

To describe the clinical pattern and sensitisation profile of children with plant-food allergy and LTP sensitisation from Northeast Spain.

METHODS

Children with history of immediate reaction to plant-food(s), positive skin-prick-test to the culprit plant-food(s) and specific-IgE to plant-food LTPs were analysed.

RESULTS

130 children were included. 69.2% (90/130) had reacted to ≥2 taxonomically unrelated plant-foods. Peach, walnut, hazelnut and peanut were most frequently involved. Reactions severity ranged from anaphylaxis (45.4%, 59/130) to oral symptoms only. Sensitisation to a particular plant-food LTP not always caused clinical symptoms with that plant-food; 69% (40/58) and 63% (17/27) of peach- and walnut-tolerant subjects had positive rPru p 3 and nJug r 3 specific IgE, respectively. 65.4% (85/130) of children were also sensitised to storage proteins, which was associated to anaphylaxis and nut allergy. However, 60% of patients without nuts/seeds allergy were sensitised to storage proteins. Specific-IgE levels to LTPs and/or storage proteins were not useful to predict allergy (vs. tolerance) to peach, walnut, peanut or hazelnut.

CONCLUSIONS

Sensitisation to LTP and/or storage proteins without clear clinical significance is relatively common. Prospective longitudinal studies are required to evaluate the relevance of these silent sensitisations over time. Caution is required when interpreting the results of molecular-based diagnostic tools in clinical practice.

Lipid Transfer Protein Syndrome in a Non-Mediterranean Area

BACKGROUND

Plant food allergies associated with lipid transfer protein (LTP) have been widely described in the Mediterranean Basin.

OBJECTIVE

The aim of this work was to describe the clinical profile and pollen sensitization of plant food- allergic patients sensitized to LTP in a non-Mediterranean area.

METHODS

Patients with clear IgE-mediated symptoms associated with plant foods and a positive skin prick test (SPT) to Pru p 3 were included in a prospective study in the north of Spain. Reported symptoms were analyzed together with a battery of food and pollen SPTs and specific IgE components by ISAC microarray. Cross-inhibition studies were performed by ImmunoCAP with plane tree, mugwort and rPru p 3.

RESULTS

Among the 72 patients included, the most frequent food allergy reported was to peaches (69%) followed by nuts (walnuts 55%, peanuts 54% and hazelnuts 43%). Most patients suffered from symptoms with multiple plant foods (a median of 6 foods per patient). Regarding the patients' pollen sensitization, 36% were sensitized to mugwort pollen (72% showing sIgE to Art v 3), 33% to grass pollen and 24% to plane tree pollen (94% with sIgE to Pla a 3). Inhibition studies showed that specific IgEs against mugwort and plane tree pollen are inhibited by Pru p 3 in a strong manner, whereas Pru p 3 was less inhibited by pollen extracts.

CONCLUSIONS

LTP syndrome occurs in a non-Mediterranean area and is related to multiple sensitizations to foods and pollens such as plane tree and mugwort. In these pollen sensitizations, Pru p 3 seems to be the primary sensitizer.

Bioanalytical methods for food allergy diagnosis, allergen detection and new allergen discovery

For effective monitoring and prevention of the food allergy, one of the emerging health problems nowadays, existing diagnostic procedures and allergen detection techniques are constantly improved. Meanwhile, new methods are also developed, and more and more putative allergens are discovered. This review describes traditional methods and summarizes recent advances in the fast evolving field of the in vitro food allergy diagnosis, allergen detection in food products and discovery of the new allergenic molecules. A special attention is paid to the new diagnostic methods under laboratory development like various immuno- and aptamer-based assays, including immunoaffinity capillary electrophoresis. The latter technique shows the importance of MS application not only for the allergen detection but also for the allergy diagnosis.

In silico allergenicity prediction of several lipid transfer proteins

Non-specific lipid transfer proteins (nsLTPs) are common allergens and they are particularly widespread within the plant kingdom. They have a highly conserved three-dimensional structure that generate a strong cross-reactivity among the members of this family. In the last years several web tools for the prediction of allergenicity of new molecules based on their homology with known allergens have been released, and guidelines to assess potential allergenicity of proteins through bioinformatics have been established. Even if such tools are only partially reliable yet, they can provide important indications when other kinds of molecular characterization are lacking. The potential allergenicity of 28 amino acid sequences of LTPs homologs, either retrieved from the UniProt database or in silico deduced from the corresponding EST coding sequence, was predicted using 7 publicly available web tools. Moreover, their similarity degree to their closest known LTP allergens was calculated, in order to evaluate their potential cross-reactivity. Finally, all sequences were studied for their identity degree with the peach allergen Pru p 3, considering the regions involved in the formation of its known conformational IgE-binding epitope. Most of the analyzed sequences displayed a high probability to be allergenic according to all the software employed. The analyzed LTPs from bell pepper, cassava, mango, mungbean and soybean showed high homology (>70%) with some known allergenic LTPs, suggesting a potential risk of cross-reactivity for sensitized individuals. Other LTPs, like for example those from canola, cassava, mango, mungbean, papaya or persimmon, displayed a high degree of identity with Pru p 3 within the consensus sequence responsible for the formation, at three-dimensional level, of its major conformational epitope. Since recent studies highlighted how in patients mono-sensitized to peach LTP the levels of IgE seem directly proportional to the chance of developing cross-reactivity to LTPs from non-Rosaceae foods, and these chances increase the more similar the protein is to Pru p 3, these proteins should be taken into special account for future studies aimed at evaluating the risk of cross-allergenicity in highly sensitized individuals.

Structural and Functional Characterization of the Hazelnut Allergen Cor a 8

Nonspecific lipid transfer proteins (nsLTPs) are basic proteins, stabilized by four disulfide bonds, and are expressed throughout the plant kingdom. These proteins are also known as important allergens in fruits and tree nuts. In this study, the nsLTP from hazelnuts, Cor a 8, was purified and its crystal structure determined. The protein is stable at low pH and refolds after thermal denaturation. Molecular dynamics simulations were used to provide an insight into conformational changes of Cor a 8 upon ligand binding. When known epitope areas from Pru p 3 were compared to those of Cor a 8, differences were obvious, which may contribute to limited cross-reactivity between peach and hazelnut allergens. Differences in epitope regions may contribute to limited cross-reactivity between Cor a 8 and nsLTPs from other plant sources. The structure of Cor a 8 represents the first resolved structure of a hazelnut allergen.