The biochemical basis and clinical evidence of food allergy due to lipid transfer proteins: a comprehensive review

Tolerance of peanuts and tree nuts in Spanish children with exclusive sensitization to lipid transfer proteins

BACKGROUND

Allergy to peanuts and tree nuts is a common cause of food allergy in Spain, with lipid transfer proteins (LTP) being the most frequently recognized panallergen. LTP sensitization often leads to multiple food group sensitivities, resulting in overly restrictive diets that hinder patient's quality of life. This study aimed to assess the tolerance of peanuts and tree nuts (hazelnuts and walnuts) in children sensitized to LTP, potentially mitigating the need for such diets.

METHODS

This prospective study enrolled individuals diagnosed with allergy to peanuts, hazelnuts, or walnuts. Data were collected from medical records, including demographics and clinical history. Allergological assessment comprised skin prick tests using commercial extracts and the nuts in question, alongside measurements of total and specific IgE to nuts and their primary molecular components. Participants showing positive LTP sensitization without sensitization to seed storage proteins underwent open oral nut challenges.

RESULTS

A total of 75 individuals labeled as allergic to peanuts, 44 to hazelnuts, and 51 to walnuts were included. All of them underwent an open oral provocation test with the incriminated nut, showing a high tolerance rate. Peanut was tolerated by 98.6% of patients, 97.72% tolerated hazelnut, and 84.3% tolerated walnut.

CONCLUSION

The findings suggest that the majority of patients allergic to peanuts, hazelnuts, or walnuts, due to LTP sensitization and lacking IgE reactivity to seed storage proteins, can tolerate these nuts. This supports the need for personalized nut tolerance assessments to avoid unnecessary dietary restrictions.

Worldwide Heterogeneity of Food Allergy: Focus on Peach Allergy in Southern Italy

Food allergy (FA) has shown an increasing prevalence in the last decades, becoming a major public health problem. However, data on the prevalence of FA across the world are heterogeneous because they are influenced by several factors. Among IgE-mediated FA, an important role is played by FA related to plant-derived food which can result from the sensitization to a single protein (specific FA) or to homologous proteins present in different foods (cross-reactive FA) including non-specific lipid transfer proteins (nsLTPs), profilins, and pathogenesis-related class 10 (PR-10). In addition, the clinical presentation of FA is widely heterogeneous ranging from mild symptoms to severe reactions up to anaphylaxis, most frequently associated with nsLTP-related FA (LTP syndrome). Considering the potential life-threatening nature of nsLTP-related FA, the patient's geographical setting should always be taken into account; thereby, it is highly recommended to build a personalized approach for managing FA across the world in the precision medicine era. For this reason, in this review, we aim to provide an overview of the prevalence of nsLTP-mediated allergies in the Mediterranean area and to point out the potential reasons for the different geographical significance of LTP-driven allergies with a particular focus on the allergenic properties of food allergens and their cross reactivity.

Reference proteomes of five wheat species as starting point for future design of cultivars with lower allergenic potential

Wheat is an important staple food and its processing quality is largely driven by proteins. However, there is a sizable number of people with inflammatory reactions to wheat proteins, namely celiac disease, wheat allergy and the syndrome of non-celiac wheat sensitivity. Thus, proteome profiles should be of high importance for stakeholders along the wheat supply chain. We applied liquid chromatography-tandem mass spectrometry-based proteomics to establish the flour reference proteome for five wheat species, ancient to modern, each based on 10 cultivars grown in three diverse environments. We identified at least 2540 proteins in each species and a cluster analyses clearly separated the species based on their proteome profiles. Even more, >50% of proteins significantly differed between species - many of them implicated in products' quality, grain-starch synthesis, plant stress regulation and proven or potential allergic reactions in humans. Notably, the expression of several important wheat proteins was found to be mainly driven by genetics vs. environmental factors, which enables selection and refinement of improved cultivars for the wheat supply chain as long as rapid test methods will be developed. Especially einkorn expressed 5.4 and 7.2-fold lower quantities of potential allergens and immunogenic amylase trypsin inhibitors, respectively, than common wheat, whereas potential allergen content was intermediate in tetraploid wheat species. This urgently warrants well-targeted clinical studies, where the developed reference proteomes will help to design representative test diets.

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.

Biotechnological applications of versatile plant lipid transfer proteins (LTPs)

Plant AMPs are usually cysteine-rich, and can be classified in several classes, including lipid transfer proteins (LTPs). LTPs are small plant cationic peptides, and can be classified in two subclasses, LTP₁ (9-10 kDa) and LTP₂ (7 kDa). They have been identified and isolated from various plant species and can be involved in a number of processes, including responses against several phytopathogens. LTP₁ presents 4 parallel α- helices and a 3₁₀-helix fragment. These structures form a tunnel with large and small entrances. LTP₂ presents 3 parallel α- helices, which form a cavity with triangular structure. Both LTP subclasses present a hydrophobic cavity, which makes interaction with different lipids and general hydrophobic molecules possible. Several studies report a broad spectrum of activity of plant LTPs, including antibacterial, antifungal, antiviral, antitumoral, and insecticidal activity. Thus, these molecules can be employed in human and animal health as an alternative to the conventional treatment of disease, well as providing the source of novel drugs. However, employing peptides in human health can present challenges, such as the toxicity of peptides, the difference between the results found in in vitro assays and in pre-clinical or clinical tests and their low efficiency against Gram-negative bacteria. In this context, plant LTPs can be an interesting alternative means by which to bypass such challenges. This review addresses the versatility of plant LTPs, their broad spectrum of activities and their potential applications in human and animal health and in agricultural production, and examines challenges in their biotechnological application.

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.

Identification and Purification of Novel Low-Molecular-Weight Lupine Allergens as Components for Personalized Diagnostics

Lupine flour is a valuable food due to its favorable nutritional properties. In spite of its allergenic potential, its use is increasing. Three lupine species, Lupinus angustifolius, L. luteus, and L. albus are relevant for human nutrition. The aim of this study is to clarify whether the species differ with regard to their allergen composition and whether anaphylaxis marker allergens could be identified in lupine. Patients with the following characteristics were included: lupine allergy, suspected lupine allergy, lupine sensitization only, and peanut allergy. Lupine sensitization was detected via CAP-FEIA (ImmunoCAP) and skin prick test. Protein, DNA and expressed sequence tag (EST) databases were queried for lupine proteins homologous to already known legume allergens. Different extraction methods applied on seeds from all species were examined by SDS-PAGE and screened by immunoblotting for IgE-binding proteins. The extracts underwent different and successive chromatography methods. Low-molecular-weight components were purified and investigated for IgE-reactivity. Proteomics revealed a molecular diversity of the three species, which was confirmed when investigated for IgE-reactivity. Three new allergens, L. albus profilin, L. angustifolius and L. luteus lipid transfer protein (LTP), were identified. LTP as a potential marker allergen for severity is a valuable additional candidate for molecular allergy diagnostic tests.

Lipid Transfer Protein Sensitization: Risk of Anaphylaxis and Molecular Sensitization Profile in Pru p 3-Sensitized Patients

BACKGROUND

Component-resolved diagnosis reveals the IgE response to many inhaled, food, and other allergens, improving the understanding and diagnosis of allergic diseases.

OBJECTIVE

The aims of the study are to study the recognition of different lipid transfer proteins (LTPs) and other allergen families in a large group of people sensitized to Pru p 3 and to analyze the relationship between the clinical entities and the allergens.

METHODS

This cross-sectional study included a large cohort of patients with positive skin tests to peach fruit and Pru p 3 specific IgE antibodies. Respiratory and food allergy symptoms were collected, and we performed prick tests with pollen, plant food, and other allergens plus the ImmunoCAP ISAC assay.

RESULTS

Our sample consisted of 421 people with a mean age of 33.25 years (range 16-68); 54.6% were women. Clinical entities included anaphylaxis (37.1%), urticaria (67.9%), and oral allergy syndrome (59.1%). Rhinitis, rhinoconjunctivitis, and/or asthma were diagnosed in 71.8% of the participants. The most pronounced correlation existed between sensitization to Pru p 3 and to Jug r 3, Pla a 3, Ara h 9, and Cor a 8. We found a higher incidence of anaphylaxis in people with 5 or more recognized LTPs. No association was observed between inhaled and food allergies.

CONCLUSION

Most Pru p 3-sensitized participants were sensitized to additional allergens from the same family and, to a lesser extent, to other allergens, mainly in the profilin and PR-10 protein families. Anaphylaxis occurred in more than a third of the cases evaluated, and almost three-quarters of them had respiratory symptoms. Respiratory and food allergies involving LTPs do not seem to be associated.

Phenotyping peach-allergic patients sensitized to lipid transfer protein and analysing severity biomarkers

BACKGROUND

Patients with peach allergy due to nsLTP sensitization constitute a heterogeneous group in terms of sensitization profile and severity. This could be due to the presence of additional allergies to pollens. The aim of this study was to analyse the clinical characteristics, sensitization profile and severity of reactions in peach-allergic patients sensitized to nsLTP from two Mediterranean areas with different pollen exposure.

METHODS

Patients with diagnosis of LTP allergy from the Allergy Unit of Hospital Regional Universitario de Malaga (HRUM) and Hospital Clinic de Barcelona (HCB) were prospectively included and classified into two groups; (a) LTP-monoallergic: those that presented reaction only with peach and (b) LTP-Allergy: those that presented reaction with peach and at least another plant-food containing LTP.

RESULTS

A total of 252 patients were included, 235 (93.2%) had LTP-syndrome and 17 (6.8%) were LTP-monoallergic. We found a higher percentage of anaphylaxis and delayed onset of symptoms in the LTP-monoallergic group (P = .02 and P = .04, respectively). Moreover, anaphylaxis was less frequent in patients with profilin sensitization (P = .03). The comparison of patients' data from HRUM with data from HCB showed differences in sensitization to olive tree pollen and profilin (P = .01 and P = .001, respectively).

CONCLUSION

This study was undertaken to characterize two large group of subjects from to two regions with differing exposures to pollen. We found that more than 90% of peach-allergic patients in both populations evolved to LTP-Allergy and showed an early onset. Profilin sensitization could be more useful as a severity biomarker than the number of nsLTP, aeroallergen sensitizations or sIgE levels. This could provide clues regarding sensitization and severity patterns that might be relevant in other geographical areas.

An Arabidopsis DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 is required for resistance against various phytopathogens and tolerance to salt stress

Synchronous and timely regulation of multiple genes results in an effective defense response that decides the fate of the host when challenged with pathogens or unexpected changes in environmental conditions. One such gene, which is downregulated in response to multiple bacterial pathogens, is a putative nonspecific lipid transfer protein (nsLTP) of unknown function that we have named DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 (DRN1). We show that upon pathogen challenge, DRN1 is strongly downregulated, while a putative DRN1-targeting novel microRNA (miRNA) named DRN1 Regulating miRNA (DmiR) is reciprocally upregulated. Furthermore, we provide evidence that DRN1 is required for defense against bacterial and fungal pathogens as well as for normal seedling growth under salinity stress. Although nsLTP family members from different plant species are known to be a significant source of food allergens and are often associated with antimicrobial properties, our knowledge on the biological functions and regulation of this gene family is limited. Our current work not only sheds light on the mechanism of regulation but also helps in the functional characterization of DRN1, a putative nsLTP family member of hitherto unknown function.

Lipid transfer proteins: the lipid commute via shuttles, bridges and tubes

Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of lipid traffic is mediated by a large group of lipid transfer proteins (LTPs), which move small numbers of lipids at a time using hydrophobic cavities that stabilize lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with lipid transport and distribution, opening up the possibility of developing therapies that specifically target lipid transfer.

Component-Resolved Diagnosis in Food Allergies

Component-resolved diagnostics (CRD) in food allergies is an approach utilized to characterize the molecular components of each allergen involved in a specific IgE (sIgE)-mediated response. In the clinical practice, CRD can improve diagnostic accuracy and assist the physician in many aspects of the allergy work-up. CRD allows for discriminatory co-sensitization versus cross-sensitization phenomena and can be useful to stratify the clinical risk associated with a specific sensitization pattern, in addition to the oral food challenge (OFC). Despite this, there are still some unmet needs, such as the risk of over-prescribing unnecessary elimination diets and adrenaline auto-injectors. Moreover, up until now, none of the identified sIgE cutoff have shown a specificity and sensitivity profile as accurate as the OFC, which is the gold standard in diagnosing food allergies. In light of this, the aim of this review is to summarize the most relevant concepts in the field of CRD in food allergy and to provide a practical approach useful in clinical practice.

Lipid Transfer Protein allergy in the United Kingdom: Characterization and comparison with a matched Italian cohort

BACKGROUND

Although pollen-related food allergy occurs in all European populations, lipid transfer protein (LTP) allergy is considered to manifest mainly in Mediterranean countries. We aimed to characterize adults presenting with LTP allergy in a northern European country.

METHOD

The clinical history and sensitization patterns of subjects born and residing in the United Kingdom (UK), with a prior diagnosis of LTP allergy and sensitization to the peach LTP allergen Pru p 3, were compared to UK subjects with pollen food syndrome (PFS). The sensitization patterns were also evaluated against a matched cohort of Italian subjects diagnosed with LTP allergy.

RESULTS

None of the 15 UK PFS subjects had a positive SPT to LTP-enriched peach reagent, compared to 91% of the 35 UK LTP subjects. The UK LTP cohort were also more likely to have positive skin prick tests to cabbage, lettuce and mustard and sensitization to the LTP allergens in peach, walnut, mugwort and plane tree These sensitization patterns to individual allergens were not significantly different to those obtained from the Italian LTP subjects, with significant correlations between Pru p 3 and the LTP allergens in peanuts, walnuts, plane tree and mugwort in both groups.

CONCLUSION

Native UK subjects with LTP allergy are not dissimilar to those with LTP allergy in southern Europe. Testing to LTP-enriched peach SPT reagent and/or LTP allergens in peach, walnut, mugwort and plane tree may enhance diagnostic accuracy.

Purification and Characterization of a Nonspecific Lipid Transfer Protein 1 (nsLTP1) from Ajwain (Trachyspermum ammi) Seeds

Ajwain (Trachyspermum ammi) belongs to the family Umbelliferae, is commonly used in traditional, and folk medicine due to its carminative, stimulant, antiseptic, diuretic, antihypertensive, and hepatoprotective activities. Non-specific lipid transfer proteins (nsLTPs) reported from various plants are known to be involved in transferring lipids between membranes and in plants defense response. Here, we describe the complete primary structure of a monomeric non-specific lipid transfer protein 1 (nsLTP1), with molecular weight of 9.66 kDa, from ajwain seeds. The nsLTP1 has been purified by combination of chromatographic techniques, and further characterized by mass spectrometry, and Edman degradation. The ajwain nsLTP1 is comprised of 91 amino acids, with eight conserved cysteine residues. The amino acid sequence based predicted three dimensional (3D) structure is composed of four α-helices stabilized by four disulfide bonds, and a long C-terminal tail. The predicted model was verified by using different computational tools; i.e. ERRAT, verify 3D web server, and PROCHECK. The docking of ajwain nsLTP1 with ligands; myristic acid (MYR), and oleic acid (OLE) was performed, and molecular dynamics (MD) simulation was used to validate the docking results. The findings suggested that amino acids; Leu11, Leu12, Ala55, Ala56, Val15, Tyr59, and Leu62 are pivotal for the binding of lipid molecules with ajwain nsLTP1.

Identification of non-specific Lipid Transfer Protein gene family members in Solanum lycopersicum and insights into the features of Sola l 3 protein

Non-specific lipid transfer proteins (nsLTPs) are characterized by an eight-cysteine motif backbone that is stabilized by four disulphide bonds. The strong interest towards this protein family is mainly due to the fact that nsLTPs are involved in many biological processes and have been identified as major human allergens. Since tomato (Solanum lycopersicum L.) is one of the most consumed and allergenic vegetables, a full characterization of this family is needed. In this study, hidden Markov model profiles were used to identify nsLTPs within the tomato protein complement. Following manual curation, 64 nsLTP genes were classified into six sub-families. Furthermore, nsLTP gene structure, distribution and arrangement along tomato chromosomes were investigated. Available RNA-seq expression profile data and Real-Time PCR analyses were used to derive expression patterns of tomato nsLTPs in different tissues/organs. Non-specific LTP genes with high level of expression in tomato fruits were filtered out since they could play a key role in tomato allergenicity. Among these genes was Solyc10g075090 that encodes the allergen Sola l 3. Finally, cloning, heterologous expression, purification and biochemical characterization of the recombinant protein Sola l 3 was performed.

Anaphylaxis caused by lipid transfer proteins: an unpredictable clinical syndrome

INTRODUCTION

Lipid transfer proteins (LTPs) are panallergens found in many plant foods. They are a common cause of food-induced anaphylaxis (FIA) in adults living in the Mediterranean area. LTPs have also been proposed as a main cause of food-dependent exercise-induced anaphylaxis (FDEIA).

OBJECTIVES

Describe clinical characteristics and allergen sensitization profiles in patients with FIA related to LTP.

MATERIALS AND METHODS

Forty-three patients were included, aged 3-52 years with a clinical history of FIA and proven sensitization to LTP. Patients were tested with a multiple plant food and pollen panel and specific IgE to LTP allergens. LTP sensitization was assessed by in vivo (Pru p 3, LTP extract) and/or by in vitro tests (specific IgE, ImmunoCAP/ISAC^®).

RESULTS

Median age of first anaphylactic episode was 24 years (range 2-51), 44% had asthma, 74% were atopic and 42% had pollinosis (olive, mugwort, plane tree, wall pellitory and cypress). Co-sensitization to profilins was found in 22%. Overall in our center, LTP-induced anaphylaxis represents 17% of all causes of FIA. Foods implicated in anaphylactic reactions were: fresh fruits 51%, tree nuts 42%, vegetables (including peanut) 40% and seeds 14%. Seven patients had FDEIA.

CONCLUSIONS

LTPs are important allergens of FIA in Portugal. Clinical reactivity to several taxonomically unrelated plant foods may raise suspicion toward LTP sensitization. The association of LTP-induced anaphylaxis with pollinosis is relevant in our country. The unpredictable clinical expression depends on the effect of cofactors such as exercise. The management of avoidance plans can be challenging due to LTP being a widely cross-reacting allergen in plant foods.

Plant lipid transfer proteins: are we finally closing in on the roles of these enigmatic proteins?

The nonspecific lipid transfer proteins (LTPs) are small compact proteins folded around a tunnel-like hydrophobic cavity, making them suitable for lipid binding and transport. LTPs are encoded by large gene families in all land plants, but they have not been identified in algae or any other organisms. Thus, LTPs are considered key proteins for plant survival on and colonization of land. LTPs are abundantly expressed in most plant tissues, both above and below ground. They are usually localized to extracellular spaces outside the plasma membrane. Although the in vivo functions of LTPs remain unclear, accumulating evidence suggests a role for LTPs in the transfer and deposition of monomers required for assembly of the waterproof lipid barriers, such as cutin and cuticular wax, suberin, and sporopollenin, formed on many plant surfaces. Some LTPs may be involved in other processes, such as signaling during pathogen attacks. Here, we present the current status of LTP research with a focus on the role of these proteins in lipid barrier deposition and cell expansion. We suggest that LTPs facilitate extracellular transfer of barrier materials and adhesion between barriers and extracellular materials. A growing body of research may uncover the true role of LTPs in plants.

Component-resolved diagnosis in anaphylaxis

PURPOSE OF REVIEW

Component-resolved diagnosis (CRD) is an advanced tool capable of aiding the clinician in fine tuning the diagnosis of the causal allergens of a reaction with the added value of providing information of severity risk, potential cross-reactivity, and subsequently, guiding management measures. This review will focus on the advantages of CRD of anaphylaxis in clinical practice.

RECENT FINDINGS

Research is continuously providing insight to which molecules are associated with genuine sensitization and/or potential severity risk for hymenoptera venom (Api m1, Ves v 1, Ves v 5, and Pol d 5), food allergy (seed storage proteins and nonspecific lipid transfer proteins), cofactor-enhanced food allergy (ω-5-gliadine, nonspecific lipid transfer proteins), red meat delayed anaphylaxis (α-gal), latex allergy (Hev b 1, Hev b 3, Hev b 5, and Hev b 6), and Anisakis allergy (Ani s 1, Ani s 4, Ani s 7, and Ani s 13); other molecules are primary associated with nonclinically relevant sensitizations, cross-reactivity, or mild reactions (carbohydrate determinants and profilins). New molecules, some minor allergens, are being identified as new potential biomarkers of severity.

SUMMARY

The usefulness of CRD in anaphylaxis is self-evident, since it improves the recognition of sensitization profiles associated with specific clinical outcomes and provides information to guide further management.

Multifactorial Modulation of Food-Induced Anaphylaxis

Prevalence of food-induced anaphylaxis increases progressively and occurs in an unpredictable manner, seriously affecting the quality of life of patients. Intrinsic factors including age, physiological, and genetic features of the patient as well as extrinsic factors such as the intake of drugs and exposure to environmental agents modulate this disorder. It has been proven that diseases, such as mastocytosis, defects in HLA, or filaggrin genes, increase the risk of severe allergic episodes. Certain allergen families such as storage proteins, lipid transfer proteins, or parvalbumins have also been linked to anaphylaxis. Environmental factors such as inhaled allergens or sensitization through the skin can exacerbate or trigger acute anaphylaxis. Moreover, the effect of dietary habits such as the early introduction of certain foods in the diet, and the advantage of the breastfeeding remain as yet unresolved. Interaction of allergens with the intestinal cell barrier together with a set of effector cells represents the primary pathways of food-induced anaphylaxis. After an antigen cross-links the IgEs on the membrane of effector cells, a complex intracellular signaling cascade is initiated, which leads cells to release preformed mediators stored in their granules that are responsible for the acute symptoms of anaphylaxis. Afterward, they can also rapidly synthesize lipid compounds such as prostaglandins or leukotrienes. Cytokines or chemokines are also released, leading to the recruitment and activation of immune cells in the inflammatory microenvironment. Multiple factors that affect food-induced anaphylaxis are discussed in this review, paying special attention to dietary habits and environmental and genetic conditions.

Lipid transfer proteins: classification, nomenclature, structure, and function

The non-specific lipid transfer proteins (LTPs) constitute a large protein family found in all land plants. They are small proteins characterized by a tunnel-like hydrophobic cavity, which makes them suitable for binding and transporting various lipids. The LTPs are abundantly expressed in most tissues. In general, they are synthesized with an N-terminal signal peptide that localizes the protein to spaces exterior to the plasma membrane. The in vivo functions of LTPs are still disputed, although evidence has accumulated for a role in the synthesis of lipid barrier polymers, such as cuticular waxes, suberin, and sporopollenin. There are also reports suggesting that LTPs are involved in signaling during pathogen attacks. LTPs are considered as key proteins for the plant's survival and colonization of land. In this review, we aim to present an overview of the current status of LTP research and also to discuss potential future applications of these proteins. We update the knowledge on 3D structures and lipid binding and review the most recent data from functional investigations, such as from knockout or overexpressing experiments. We also propose and argument for a novel system for the classification and naming of the LTPs.

Can we identify patients at risk of life-threatening allergic reactions to food?

Anaphylaxis has been defined as a 'severe, life-threatening generalized or systemic hypersensitivity reaction'. However, data indicate that the vast majority of food-triggered anaphylactic reactions are not life-threatening. Nonetheless, severe life-threatening reactions do occur and are unpredictable. We discuss the concepts surrounding perceptions of severe, life-threatening allergic reactions to food by different stakeholders, with particular reference to the inclusion of clinical severity as a factor in allergy and allergen risk management. We review the evidence regarding factors that might be used to identify those at most risk of severe allergic reactions to food, and the consequences of misinformation in this regard. For example, a significant proportion of food-allergic children also have asthma, yet almost none will experience a fatal food-allergic reaction; asthma is not, in itself, a strong predictor for fatal anaphylaxis. The relationship between dose of allergen exposure and symptom severity is unclear. While dose appears to be a risk factor in at least a subgroup of patients, studies report that individuals with prior anaphylaxis do not have a lower eliciting dose than those reporting previous mild reactions. It is therefore important to consider severity and sensitivity as separate factors, as a highly sensitive individual will not necessarily experience severe symptoms during an allergic reaction. We identify the knowledge gaps that need to be addressed to improve our ability to better identify those most at risk of severe food-induced allergic reactions.

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.

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.

Expression and characterization of a new isoform of the 9 kDa allergenic lipid transfer protein from tomato (variety San Marzano)

Lipid transfer proteins (LTPs) are food allergens found first in fruits of the Rosaceae family and later identified in other food plants. Their high structural stability causes them to behave as allergens in cooked and processed foods. Allergenic LTPs have been identified in tomato fruits as well, but studies of their thermal stability and structural characteristics are limited. In this article we report the identification of the coding region for a novel 9 kDa LTP isoform in the tomato variety San Marzano, together with the expression of the recombinant mature protein. The purified recombinant protein was further characterized for its thermal stability and was found to bind 1-palmitoil-2-lysophosphatidylcholine (Lyso-C16) after thermal treatments up to 105 °C. Analysis of a modeling derived structure of the protein allowed the identification of possible epitope regions on the molecular surface.

The challenge of treating orphan disease

Uncommon or orphan diseases are less frequently addressed in mainstream medical journals and, as a consequence, their understanding and clinical recognition may rely on case series or anecdotal data with limited guidelines and management directions. The study of selected underrepresented autoimmune and allergy conditions is the subject of the present issue of Clinical Reviews in Allergy and Immunology to provide peculiar perspectives on common and rare themes. First, allergy remains a major concern for physicians worldwide despite the limited developments over the past years, particularly for antigens such as mite or Alternaria alternata, and due to the increasing incidence of drug hypersensitivity. Second, the female predominance of autoimmune diseases such as systemic sclerosis is well recognized but enigmatic, and a unifying hypothesis remains elusive. Third, the management of conditions triggered by infectious agents as in Guillain-Barre syndrome or mixed cryoglobulinemia is challenging, and clinical guidelines are needed in the setting of infections and autoimmunity. Fourth, gamma-delta T cells represent major players in innate immunity and are the subject of extensive studies in autoimmune diseases to provide new therapeutic targets for disease prevention or modulation in the near future. Ultimately, we acknowledge the major developments in the broad fields of rheumatology and immunology and expect that microbiota definition, epigenetics studies, and microRNA analysis will provide new exciting avenues toward the understanding and treatment of chronic and acute inflammation.

The changing geoepidemiology of food allergies

The science of food allergy has been rapidly evolving before our eyes in the past half century. Like other allergic disorders, the prevalence of food allergies has dramatically increased, and coupled with the increased public awareness of anaphylaxis due to food allergy, this has driven an explosion in basic and clinical research in this extremely broad subject. Treatment of food allergies has evolved and practices such as food challenges have become an integral part of an allergy practice. The impact of the increase of food allergy has driven package labeling laws, legislation on emergency treatment availability in schools and other public places, and school policy. But to this day, our knowledge of the pathogenesis of food allergy is still incomplete. There are the most obvious IgE-mediated immediate hypersensitivity reactions, but then multiple previously unidentified conditions such as eosinophilic esophagitis, food protein-induced enterocolitis syndrome, milk protein allergy, food-induced atopic dermatitis, oral allergy syndrome, and others have complicated the diagnosis and management of many of our patients who are unable to tolerate certain foods. Many of these conditions are not IgE-mediated, but may be T cell-driven diseases. The role of T regulatory cells and immune tolerance and the newly discovered immunological role of vitamin D have shed light on the variable clinical presentation of food allergy and the development of new methods of immunotherapy in an example of bench-to-bedside research. Component-resolved diagnostic techniques have already begun to allow us to more precisely define the epitopes that are targeted in food allergic patients. The development of biological modulators, research on genomics and proteomics, and epigenetic techniques all offer promising avenues for new modes of therapy of food allergy in the twenty-first century.