Identification and molecular characterization of allergenic non-specific lipid-transfer protein from durum wheat (Triticum turgidum)

Allergenic Biomarkers in the Molecular Diagnosis of IgE-Mediated Wheat Allergy

IgE-mediated wheat allergy can take on various forms, including childhood food allergy to wheat, wheat-dependent exercise-induced anaphylaxis in young adults, baker's respiratory allergy/asthma in workers exposed to wheat flour inhalation, and contact urticaria that is caused by hydrolyzed wheat proteins in some cosmetics, and that is sometimes associated with a food allergy. Singleplex and multiplex immunoassays detect specific IgE antibodies to wheat allergenic molecular biomarkers such as omega-5 gliadin Tri a 19, lipid transfer protein Tri a 14, and alpha-amylase inhibitors. The fluorescence enzyme immunoassay with capsulated cellulose polymer solid-phase coupled allergens is a commonly used singleplex assay. Multiplex methods include the ELISA-based macroarray immunoassay using nano-bead technology and a microarray immunoassay on polymer-coated slides. Another promising diagnostic tool is the basophil activation test performed with omega-5 gliadin and other wheat protein types. Detailed comprehension of the structural and immunological features of the numerous wheat allergens significant in clinical settings is imperative for advancing diagnostic biomarkers for IgE-mediated wheat allergies.

A systematic review of allergen cross-reactivity: Translating basic concepts into clinical relevance

Access to the molecular culprits of allergic reactions allows for the leveraging of molecular allergology as a new precision medicine approach-one built on interdisciplinary, basic, and clinical knowledge. Molecular allergology relies on the use of allergen molecules as in vitro tools for the diagnosis and management of allergic patients. It complements the conventional approach based on skin and in vitro allergen extract testing. Major applications of molecular allergology comprise accurate identification of the offending allergen thanks to discrimination between genuine sensitization and allergen cross-reactivity, evaluation of potential severity, patient-tailored choice of the adequate allergen immunotherapy, and prediction of its expected efficacy and safety. Allergen cross-reactivity, defined as the recognition of 2 or more allergen molecules by antibodies or T cells of the same specificity, frequently interferes with allergen extract testing. At the mechanistic level, allergen cross-reactivity depends on the allergen, the host's immune response, and the context of their interaction. The multiplicity of allergen molecules and families adds further difficulty. Understanding allergen cross-reactivity at the immunologic level and translating it into a daily tool for the management of allergic patients is further complicated by the ever-increasing number of characterized allergenic molecules, the lack of dedicated resources, and the need for a personalized, patient-centered approach. Conversely, knowledge sharing paves the way for improved clinical use, innovative diagnostic tools, and further interdisciplinary research. Here, we aimed to provide a comprehensive and unbiased state-of-the art systematic review on allergen cross-reactivity. To optimize learning, we enhanced the review with basic, translational, and clinical definitions, clinical vignettes, and an overview of online allergen databases.

Understanding of lipid transfer protein sensitization patterns and its clinical significance in children

Background: Lipid transfer proteins (LTP) are the most common food allergens in the Mediterranean region. Objective: The study aimed to investigate co-sensitization patterns and cluster relationships between LTP allergen molecules across a broad range of allergen-specific sensitization patterns, and clinical outcomes in eastern Mediterranean children. Methods: Among 496 children evaluated for multiple sensitizations with multiplex testing, 105 children (21%) with 16 different LTP sensitizations were analyzed. Clinical reactivity was examined based on clear-cut history of immunoglobulin E mediated symptoms (oral allergy syndrome [OAS], systemic reactions, and anaphylaxis). Results: All children included were sensitive to food LTPs, but 56% were sensitive to pollen LTPs. The number of children with OAS and clinical reactivity was 12 and 59, respectively, and no cofactors were reported. The most common sensitizations were Pru p 3 (74%) and Cor a 8 (66%). Significant correlations were observed in the heatmap between the LTP molecules other than Par j 2 and Tri a 14. Overall, clinical reactivity was associated with increased age and number of LTP molecule positivity. Conclusion: In the eastern Mediterranean region, 21% of children with multiple food and/or pollen sensitizations were found to have LTP sensitization; however, almost half reported clinical reactivity. The hierarchical pathway highlights that distinct LTP allergen molecules can act as primary sensitizers. Clinical reactivity is linked to increasing numbers of LTP molecule positivity and increasing age.

Factors and co-factors influencing clinical manifestations in nsLTPs allergy: between the good and the bad

Non-specific lipid transfer proteins (nsLTPs) are a family of plant pan-allergens that represent the primary cause of food allergies in the Mediterranean area, characterized by a wide range of clinical manifestations, ranging from the total absence of symptoms up to anaphylaxis. This wide variety of symptoms is related to the intrinsic capacity of nsLTPs to cause an allergic reaction in a specific subject, but also to the presence of co-factors exacerbating (i.e., exercise, NSAIDs, PPIs, alcohol, cannabis, prolonged fasting, menstruation, acute infections, sleep deprivation, chronic urticaria) or protecting from (i.e., co-sensitization to PR10, profilin or polcalcin) severe reactions. In this picture, recognizing some nsLTPs-related peculiarities (i.e., route, type and number of sensitizations, concentration of the allergen, cross-reactions) and eventual co-factors may help the allergist to define the risk profile of the single patient, in order to promote the appropriate management of the allergy from dietary advices up to the prescription of life-saving epinephrine autoinjector.

Allergenicity of wheat protein in diet: Mechanisms, modifications and challenges

Wheat is widely available in people's daily diets. However, some people are currently experiencing IgE-mediated allergic reactions to wheat-based foods, which seriously impact their quality of life. Thus, it is imperative to provide comprehensive knowledge and effective methods to reduce the risk of wheat allergy (WA) in food. In the present review, recent advances in WA symptoms, the major allergens, detection methods, opportunities and challenges in establishing animal models of WA are summarized and discussed. Furthermore, an updated overview of the different modification methods that are currently being applied to wheat-based foods is provided. This study concludes that future approaches to food allergen detection will focus on combining multiple tools to rapidly and accurately quantify individual allergens in complex food matrices. Besides, biological modification has many advantages over physical or chemical modification methods in the development of hypoallergenic wheat products, such as enzymatic hydrolysis and fermentation. It is worth noting that using biotechnology to edit wheat allergen genes to produce allergen-free food may be a promising method in the future which could improve the safety of wheat foods and the health of allergy sufferers.

Genome-wide characterization, chromosome localization, and expression profile analysis of poplar non-specific lipid transfer proteins

Plant non-specific lipid transfer proteins (nsLTPs) are small and have a broad biological function involved in reproductive development and abiotic stress resistance. Although a small part of plant nsLTPs have been identified, these proteins have not been characterized in poplar at the genomic level. A genome-wide characterization and expression identification of poplar nsLTP members were performed in this study. A total of 42 poplar nsLTP genes were identified from the poplar genome. A comprehensive analysis of poplar nsLTPs was conducted by a phylogenetic tree, duplication events, gene structures, and conserved motifs. The cis-elements of poplar nsLTPs were predicted to respond to light, hormone, and abiotic stress. Many transcription factors (TFs) were identified to interact with poplar nsLTP cis-elements. The tested poplar nsLTPs were expressed in leaves, stems, and roots, but their expression levels differed among tested tissues. Most poplar nsLTP expression levels were changed by abiotic stress, implying that poplar nsLTP may be involved in abiotic stress resistance. Network analysis showed that poplar nsLTPs are putative genes involved in fatty acid (FA) metabolism. This research provides sight into the further study to explain the regulatory mechanism of the poplar nsLTPs.

Cofactors, age at onset, allergic comorbidities and gender are different in patients sensitized to omega-5 gliadin and Pru p 3

Aim of this study is to clarify the impact of cofactors on allergic reactions in patients sensitized to LTP and ω-5-gliadin. We retrospectively examined the charts of our outpatients from January 2015 to July 2019 and identified 157 patients seen for urticaria/angioedema or anaphylaxis after a meal, in presence or absence of cofactors and sensitized to LTPs (Pru p 3 and/or Tri a 14) and/or ω-5-gliadin (Tri a 19). we compared LTPs-positive patients and those sensitized to Tri a 19 in order to assess the difference in cofactors involved and in frequency of clinical presentation. Our data show that exercise is the most frequent cofactor in FDEIAn and the involvement of exercise, alcohol and multiple cofactors was more frequently found in males than in females. We found that exercise, pollen counts peaks and multiple cofactors were more often related to anaphylaxis than mild reactions. Finally, we performed a comparison between patients LTPs+ and Tri a 19+ that showed in the latter group a lower frequency of allergic comorbidities, a higher median age at the onset of symptoms and frequency of alcohol exposure. Our data show that the search for possible cofactors involved in food allergy is essential not only for diagnostic purposes, but also for risk assessment strategies.

Identification and molecular characterization of a novel non-specific lipid transfer protein (TdLTP2) from durum wheat

Non-specific lipid transfer proteins (nsLTPs) are small, cysteine-rich proteins, a part of the pathogenesis-related protein family, and numerous of them act as positive regulators during plant disease resistance, growth, and reproduction. These proteins are involved also in the intracellular transfer of lipids, as well as in plant immune responses. Besides their differences in sequences, they show similar features in their structure. However, they show distinct lipid-binding specificities signifying their various biological roles that dictate further structural study. This study reports the identification, in silico characterization and purification of a novel member of the nsLTP2 protein family from durum wheat, TdLTP2. It was generated and purified using the combination of gel filtration chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC). Its identity was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MALDI-TOF). TdLTP2 had been expressed in different stress to detect its localization; therefore, fluor-immunolocalization studies accomplished this data. In this approach, to assess the allergenicity of TdLTP2, thirty patients with baker’s asthma were enrolled and ELISA to detect the presence of specific IgE antibodies tested their sera. Moreover, the lipid-binding properties of TdLTP2 were examined in vitro and validated using a molecular docking study. In summary, our results demonstrate a new addition of member in plant nsLTPs family, TdLTP2, which can develop a better understanding about its biological functions and shed light on future applications.

Plant non-specific lipid transfer proteins: An overview

Plant non-specific lipid transfer proteins (nsLTPs) are usually defined as small, basic proteins, with a wide distribution in all orders of higher plants. Structurally, nsLTPs contain a conserved motif of eight cysteines, linked by four disulphide bonds, and a hydrophobic cavity in which the ligand is housed. This structure confers stability and enhances the ability to bind and transport a variety of hydrophobic molecules. Their highly conserved structural resemblance but low sequence identity reflects the wide variety of ligands they can carry, as well as the broad biological functions to which they are linked to, such as membrane stabilization, cell wall organization and signal transduction. In addition, they have also been described as essential in resistance to biotic and abiotic stresses, plant growth and development, seed development, and germination. Hence, there is growing interest in this family of proteins for their critical roles in plant development and for the many unresolved questions that need to be clarified, regarding their subcellular localization, transfer capacity, expression profile, biological function, and evolution.

Lipid transfer protein allergy: A review of current controversies

Sensitization to lipid transfer protein (LTP), the most frequent cause of food allergy in southern Europe, still shows several controversial, but also intriguing, aspects. Some of these include the degree of cross-reactivity between LTPs from botanically distant sources, the definition of risk factors, the role of some cofactors, clinical outcomes, geographical differences and the identification of the primary sensitizer in different areas. This review article tries to analyse and comment on these aspects point by point suggesting some explanatory hypotheses with the final scope to stimulate critical thoughts and elicit the scientific discussion about this issue in the readership.

Non-specific lipid-transfer proteins: Allergen structure and function, cross-reactivity, sensitization, and epidemiology

Background

Discovered and described 40 years ago, non‐specific lipid transfer proteins (nsLTP) are present in many plant species and play an important role protecting plants from stressors such as heat or drought. In the last 20 years, sensitization to nsLTP and consequent reactions to plant foods has become an increasing concern.

Aim

The aim of this paper is to review the evidence for the structure and function of nsLTP allergens, and cross‐reactivity, sensitization, and epidemiology of nsLTP allergy.

Materials and Methods

A Task Force, supported by the European Academy of Allergy & Clinical Immunology (EAACI), reviewed current evidence and provide a signpost for future research. The search terms for this paper were “Non‐specific Lipid Transfer Proteins”, “LTP syndrome”, “Pru p 3”, “plant food allergy”, “pollen‐food syndrome”.

Results

Most nsLTP allergens have a highly conserved structure stabilised by 4‐disulphide bridges. Studies on the peach nsLTP, Pru p 3, demonstrate that nsLTPs are very cross‐reactive, with the four major IgE epitopes of Pru p 3 being shared by nsLTP from other botanically related fruits. These nsLTP allergens are to varying degrees resistant to heat and digestion, and sensitization may occur through the oral, inhaled or cutaneous routes. In some populations, Pru p 3 is the primary and sole sensitizing allergen, but many are poly‐sensitised both to botanically un‐related nsLTP in foods, and non‐food sources of nsLTP such as Cannabis sativa, Platanus acerifolia, (plane tree), Ambrosia artemisiifolia (ragweed) and Artemisia vulgaris (mugwort). Initially, nsLTP sensitization appeared to be limited to Mediterranean countries, however more recent studies suggest clinically relevant sensitization occurs in North Atlantic regions and also countries in Northern Europe, with nsLTP sensitisation profiles being broadly similar.

Discussion

These robust allergens have the potential to sensitize and provoke symptoms to a large number of plant foods, including those which are raw, cooked or processed. It is unknown why some sensitized individuals develop clinical symptoms to foods whereas others do not, or indeed what other allergens besides Pru p 3 may be primary sensitising allergens. It is clear that these allergens are also relevant in non‐Mediterranean populations and there needs to be more recognition of this.

Conclusion

Non‐specific LTP allergens, present in a wide variety of plant foods and pollens, are structurally robust and so may be present in both raw and cooked foods. More studies are needed to understand routes of sensitization and the world‐wide prevalence of clinical symptoms associated with sensitization to these complex allergens.

Developments allergy in 2019 through the eyes of clinical and experimental allergy, part I mechanisms

In the first of two linked articles, we describe the development in the mechanisms underlying allergy as described by Clinical & Experimental Allergy and other journals in 2019. Experimental models of allergic disease, basic mechanisms, clinical mechanisms and allergens are all covered.

A WAO - ARIA - GA2LEN consensus document on molecular-based allergy diagnosis (PAMD@): Update 2020

Precision allergy molecular diagnostic applications (PAMD@) is increasingly entering routine care. Currently, more than 130 allergenic molecules from more than 50 allergy sources are commercially available for in vitro specific immunoglobulin E (sIgE) testing. Since the last publication of this consensus document, a great deal of new information has become available regarding this topic, with over 100 publications in the last year alone. It thus seems quite reasonable to publish an update. It is imperative that clinicians and immunologists specifically trained in allergology keep abreast of the new and rapidly evolving evidence available for PAMD@.

PAMD@ may initially appear complex to interpret; however, with increasing experience, the information gained provides relevant information for the allergist. This is especially true for food allergy, Hymenoptera allergy, and for the selection of allergen immunotherapy. Nevertheless, all sIgE tests, including PAMD@, should be evaluated within the framework of a patient's clinical history, because allergen sensitization does not necessarily imply clinical relevant allergies.