Received: 18 December 2020 DOI: 10.1002/clt2.12010 REVIEW - Accepted: 8 January 2021 Non‐specific lipid‐transfer proteins: Allergen structure and function, cross‐reactivity, sensitization, and epidemiology Isabel J. Skypala1 | Ricardo Asero2 | Domingo Barber3,4 | Lorenzo Cecchi5 | 6 7 8 Arazeli Diaz Perales | Karin Hoffmann‐Sommergruber | Elide A. Pastorello | 9 10 11 Ines Swoboda | Joan Bartra | Didier G. Ebo | Margaretha A. Faber11 | Montserrat Fernández‐Rivas12 | Francesca Gomez13 | Anastasios. P. Konstantinopoulos14 | Olga Luengo15 | Ronald van Ree16 | Enrico Scala17 | Stephen J. Till18,19 | European Academy of Allergy Clinical Immunology (EAACI) Task Force: Non‐specific Lipid Transfer Protein Allergy Across Europe 1 Department of Allergy & Clinical Immunology, Royal Brompton & Harefield NHS Foundation Trust, Imperial College, London, UK 2 Ambulatorio di Allergologia, Clinica San Carlo, Milan, Italy 3 IMMA, School of Medicine, Universidad San Pablo CEU, CEU Universities, Madrid, Spain 4 RETIC ARADYAL RD16/0006/0015, Instituto de Salud Carlos III, Madrid, Spain 5 SOS Allergy and Clinical Immunology, USL Toscana Centro, Prato, Italy 6 Departamento de Biotecnología‐Biología Vegetal, Centro de Biotecnología y Genómica de Plantas (CBGP, UPM‐INIA), Universidad Politécnica de Madrid, Madrid, Spain 7 Department of Pathophysiology and Allergy Research, Medical University of Vienna, Austria 8 Unit of Allergology and Immunology, ASST Grande Ospedale Metropolitano Niguarda, University of Milan, Milan, Italy 9 Biotechnology Section, FH Campus Wien, University of Applied Sciences, Vienna, Austria 10 Hospital Clinic de Barcelona, IDIBAPS, Universitat de Barcelona, ARADyAL, Barcelona, Spain 11 Department of Immunology, Allergology, Rheumatology and Infla‐Med Centre of Excellence, Faculty of Medicine and Health Sciences, University of Antwerp and Antwerp University Hospital, Ghent, Belgium 12 Department of Allergy, Hospital Clínico San Carlos, Universidad Complutense de Madrid, IdISSC, ARADyAL, Madrid, Spain 13 Allergy Unit, IBIMA‐ Hospital Regional Universitario de Malaga, Malaga, and Spanish Network for Allergy ‐ RETICS de Asma, Reacciones adversas y Alérgicas (ARADyAL), Madrid, Spain 14 Allergy Department, 2nd Paediatric Clinic, University of Athens, Athens, Greece 15 Allergy Unit, Internal Medicine Department, Vall d'Hebron University Hospital, Universitat Autònoma de Barcelona, ARADyAL, Barcelona, Spain 16 Department of Experimental Immunology and Department of Otorhinolaryngology, Amsterdam University Medical Centers, location AMC, Amsterdam, The Netherlands 17 Experimental Allergy Unit, Istituto Dermopatico Dell’immacolata, IRCCS, FLMM, Rome, Italy 18 Peter Gorer Department of Immunobiology, King’s College London, London, UK 19 Department of Allergy, Guy’s & St Thomas’ NHS Foundation Trust, London, UK - This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. © 2021 The Authors. Clinical and Translational Allergy published by John Wiley and Sons Ltd on behalf of European Academy of Allergy and Clinical Immunology. Clin Transl Allergy. 2021;1–13. wileyonlinelibrary.com/journal/clt2 1 2 - SKYPALA ET AL. Correspondence Isabel Skypala, Department of Allergy & Clinical Abstract Immunology, Royal Brompton Hospital, Sydney Background: Discovered and described 40 years ago, non‐specific lipid transfer Street, London SW3 6NP, UK. Email: proteins (nsLTP) are present in many plant species and play an important role pro- tecting 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. KEYWORDS allergy, epidemiology, food, lipid transfer protein, LTP, sensitization 1 | BACKGROUND Kader, whose numerous and fundamental studies advanced the botanical knowledge regarding this family of proteins.2 The biological Non‐specific lipid‐transfer proteins (nsLTPs) are a ubiquitous multi- longevity of nsLTPs throughout time is probably also due to their gene family of molecules expressed in the Plant kingdom, starting life important role in defence of plants against biotic and abiotic stress and 470 million years ago in Marchantiophyta, the first plants grown on their expression in different plant tissues under different environ- land after red and green algae.1 Despite their longevity, nsLTPs were mental conditions.3 Their immunoglobulin E (IgE)‐binding capacity first discovered in plants only about 40 years ago, by Jean‐Claude was first demonstrated in peach fruits and Parietaria pollen, and then SKYPALA ET AL. - 3 was detected by IgE immunoblotting in peach, cherry, apricot and Proteins’, ‘LTP syndrome’, ‘Pru p 3’, ‘plant food allergy’, ‘pollen‐food plum. It was found not to be birch (Betula verrucosa) cross‐reactive, syndrome’. unlike the Bet v 1 homologues, which at the time were considered to be the main trigger of allergic symptoms to fruits. The novel nsLTP allergens seemed initially to be an important cause of symptoms only 2 | MOLECULAR STRUCTURE AND BIOLOGICAL in southern Europe. 4 The peach nsLTP, Pru p 3, was first fully FUNCTION OF nsLTPs sequenced and characterized simultaneously in Italy and Spain, iden- tifying a 9 kDa protein, of 91–93 amino acids long, with a high p nsLTPs form a large protein family, known to occur in land plants, (isoelectric point) and a conserved 8 cysteine motif, now considered as where they are abundantly expressed in most tissues.1,17 These the major structural characteristic shared by all members of the nsLTP nsLTPs are small, non‐glycosylated proteins of 6–9 kDa and basic protein family.5,6 isoelectric points of 9.2 They are encoded by multigene families and Many further studies have demonstrated that nsLTPs are rele- occur in many flowering plants.18 Currently, 46 nsLTPs have been vant allergens of several pollens and plant foods belonging to both listed by the WHO/IUIS Allergen Nomenclature Sub‐Committee the widespread Rosaceae family and many other distantly related (Table 1). Most nsLTPs are synthesized with an N‐terminal signal species and can elicit systemic reactions in nsLTP sensitized sub- peptide, which directs the proteins to the extracellular, apoplastic jects.7 Unlike Bet v 1‐related or profilin‐related food allergy, re- space. Several nsLTPs also contain a C‐terminal sequence motif for actions involving LTP allergens have also been demonstrated to occur post‐translational addition of a glycosylphosphatidylinositol (GPI)‐ with cereals.8 It has also been observed that nsLTP sensitization anchor, such GPI‐anchors that target the nsLTPs to the plasma could induce other food‐related allergic conditions, including membrane surfaces.19,20 Based on their molecular mass, nsLTPs are ‘Baker’s’ asthma and food‐dependent, exercise‐induced anaphylaxis grouped into two types, LTP1 (9–10 kDa; around 90 amino acids) and (FDEIA).9,10 Sensitization to nsLTP and the elicited clinical reactions LTP2 (6‐7 kDa; around 70 amino acids).21 However, the majority of were initially mostly reported to affect subjects living in the Medi- allergenic nsLTPs belong to the nsLTP1 type. terranean area, with those who were not pollen‐sensitized typically Structural studies on nsLTPs from wheat, maize, barley and rice experiencing more severe reactions.11,12 were performed by x‐ray and / or nuclear magnetic resonance ana- In some countries (notably Italy and Spain), y Pru p 3, the nsLTP lyses22–26 and the crystal structure of Pru p 3 was described in 2005 by from peach (Prunus persica), is the first sensitizing allergen in children Pasquato and colleagues27 (see Figure 1). These studies confirmed the who may subsequently develop sensitization to a larger number of overall highly conserved structure of nsLTPs, consisting of four alpha‐ nsLTP‐containing foods.13 According to the data published from a helices, which are stabilized by four highly conserved disulphide number of different countries, Pru p 3 is also a marker allergen in bridges and connected by flexible loops. The characteristic of the adult‐onset symptoms attributed to nsLTP allergens. However, nsLTP structure is an internal, tunnel‐like, hydrophobic cavity, which nsLTPs present in different sources also seem to be able to initiate allows binding and transportation of various lipids2,17 (see Figure 2). sensitization via different routes of exposure and contact and The major biological role of nsLTPs seems to be the transfer and different climate zones.14,15 The mechanism underlying the induction deposition of lipids for the assembly of complex barrier polymers on of sensitization to Pru p 3 has recently been demonstrated, identi- the surface of plant tissues and organs, such as waxes on leaves28, fying the role of the ligand in the allergic immune response which suberin in seeds and roots, and sporopollenin in pollen grains.29 Such may lead to further insights into how nsLTP sensitization may barriers are required to control the fluxes of gases and liquids, but are develop.16 also important for the protection of the plants from biotic and abiotic Over the last 30 years, many researchers have contributed to stress. Indeed, the involvement of nsLTPs in signalling during pathogen our understanding of the structure, function and IgE‐binding attack30,31 and in the defence against temperature extremes or properties of nsLTPs, providing evidence of the clinical entity of drought has been shown.32 nsLTP syndrome(s), now well recognized by the entire International Structural studies of liganded nsLTPs provided evidence that the Scientific Community. However, the challenging nature of this hydrophobic internal cavity can bind to a range of different ligands condition, the characterization of an increasing number of nsLTP including fatty acids, acyl‐coenzyme A and phospholipids, thus proteins in different foods and the complexities surrounding showing great flexibility of the cavity. Furthermore, ligand binding sensitization mechanisms led to the formation of a Task Force, affects the orientation of certain conserved amino acid residues at the supported by the European Academy of Allergy & Clinical Immu- C‐terminal region and induces a conformational change as shown for nology (EAACI). The Task Force’s aim was to produce a summary Pru p 3, Jug r 3 and Mal d 3.33–35 These structural modifications can of the current evidence and provide a signpost for future research also modify the IgE‐binding capacity of nsLTPs.33–35 Moreover, evi- needs to ensure that this fascinating condition can be more dence has accumulated that the lipid–ligand bound to Pru p 3 can act effectively managed in the future. This paper is the first of the two as an adjuvant to promote sensitization to Pru p 3 via CD1d‐mediated papers, with the second one reviewing the evidence for the diag- activation of invariant natural killer T‐cells (iNKTs).16 These findings nosis and management of symptoms linked to nsLTP sensitization. show that nsLTP–lipid interaction can increase the allergenic prop- The search terms for this paper were ‘Non‐specific Lipid Transfer erties of nsLTPs and might promote sensitization to these proteins.36 4 - SKYPALA ET AL. TABLE 1 Allergen nomenclature as agreed by the WHO/IUIS Allergen Nomenclature Sub Committee Species Allergen Biochemical name MW UniProt 1 Ambrosia artemisiifolia (Short ragweed) Amb a 6 nsLTP 1 10 kDa O04004 2 Apium graveolens (Celery) Api g 2 nsLTP 1 9 kDa E6Y8S8 3 Apium graveolens (Celery) Api g 6 nsLTP 2 7 kDa P86809 4 Arachis hypogaea (Peanut, groundnut) Ara h 9 nsLTP 1 9.8 kDa B6CEX8 5 Arachis hypogaea (Peanut, groundnut) Ara h 16 nsLTP 2 8.5 kDa ‐ 6 Arachis hypogaea (Peanut, groundnut) Ara h 17 nsLTP 1 11 kDa ‐ 7 Artemisia vulgaris (Mugwort, wormwood) Art v 3 nsLTP 1 12 kDa P0C088 8 Asparagus officinalis (Asparagus) Aspa o 1 nsLTP 1 9 kDa ‐ 9 Brassica oleracea (Cabbage and others) Bra o 3 nsLTP 1 9 kDa ‐ 10 Cannabis sativa (Indian hemp) Can s 3 nsLTP 1 9 kDa W0U0V5 11 Castanea sativa (Chestnut) Cas s 8 nsLTP 1 9 kDa (red) ‐ 12 Citrus limon (Lemon) Cit l 3 nsLTP 1 9.6 kDa P84160 13 Citrus reticulata (Tangerine) Cit r 3 nsLTP 1 9 kDa P84161 14 Citrus sinensis (Sweet orange) Cit s 3 nsLTP 1 9.46 kDa P84161 15 Corylus avellana (Hazelnut) Cor a 8 nsLTP 1 9 kDa Q9ATH2 16 Fragaria ananassa (Strawberry) Fra a 3 nsLTP 1 9 kDa Q8VX12 17 Helianthus annuus (Sunflower) Hel a 3 nsLTP 1 9 kDa Q7X9Q5 18 Hevea brasiliensis (Para rubber tree (latex)) Hev b 12 nsLTP 1 9 kDa Q8RYA8 19 Juglans regia (English walnut) Jug r 3 nsLTP 1 9 kDa C5H617 20 Lactuca sativa (Cultivated lettuce) Lac s 1 nsLTP 1 9 kDa ‐ 21 Lens culinaris (Lentil) Len c 3 nsLTP 1 9 kDa A0AT29 22 Lupinus angustifolius (Narrow‐leaved blue lupin) Lup an 3 nsLTP 1 11 kDa ‐ 23 Malus domestica (Apple) Mal d 3 nsLTP 1 9 kDa Q5J026 24 Morus nigra (Mulberry) Mor n 3 nsLTP 1 10 kDa P85894 25 Musa acuminata (Banana) Mus a 3 nsLTP 1 9 kDa P86333 26 Olea europaea (Olive) Ole e 7 nsLTP 1 9.5 kDa P81430 27 Parietaria judaica (Wall Pellitory) Par j 1 PhosphoLTP 15 kDa P43217 28 Parietaria judaica (Wall Pellitory) Par j 2 PhosphoLTP 10‐14 kDa P55958 29 Parietaria officinalis (Pellitory) Par o 1 PhosphoLTP 15 kDa ‐ 30 Phaseolus vulgaris (Green bean, French bean) Pha v 3 nsLTP 1 8.8‐9.0 kDa D3W146 31 Platanus acerifolia (London plane tree) Pla a 3 nsLTP 1 10 kDa ‐ 32 Prunus armeniaca (Apricot) Pru ar 3 nsLTP 1 9 kDa P81651 33 Prunus avium (Sweet cherry) Pru av 3 nsLTP 1 10 kDa Q9M5X8 34 Prunus domestica (European plum) Pru d 3 nsLTP 1 9 kDa P82534 35 Prunus dulcis (Almond) Pru du 3 nsLTP 1 9 kDa C0L0I5 36 Prunus persica (Peach) Pru p 3 nsLTP 1 10 kDa P81402 37 Punica granatum (Pomegranate) Pun g 1 nsLTP 1 9 kDa A0A059STC4 38 Pyrus communis (Pear) Pyr c 3 nsLTP 1 9 kDa Q9M5X6 39 Rubus idaeus (Red raspberry) Rub i 3 nsLTP 1 11 kDa Q0Z8V0 40 Sinapis alba (Yellow mustard) Sin a 3 nsLTP 1 12.3 kDa E6Y2L9 SKYPALA ET AL. - 5 TABLE 1 (Continued) Species Allergen Biochemical name MW UniProt 41 Solanum lycopersicum (Lycopersicon sculentum) (Tomato) Sola l 3 nsLTP 1 9 kDa P93224 42 Solanum lycopersicum (Lycopersicon sculentum) (Tomato) Sola l 6 nsLTP 2 7 kDa K4BBD9 43 Triticum aestivum (Wheat) Tri a 14 nsLTP 1 9 kDa D2T2K2 44 Triticum turgidum ssp durum (Durum wheat) Tri tu 14 nsLTP 1 9.2 kDa ‐ 45 Vitis vinifera (Grape) Vit v 1 nsLTP 1 9 kDa Q850K5 46 Zea mays (Maize) Zea m 14 nsLTP 1 9 kDa P19656‐1 BOX 1. Definitions nsLTP sensitization—sensitization to one or more nsLTPs nsLTP allergy—clinically relevant sensitization to one or more nsLTPs nsLTP syndrome—multiple plant food allergies attributed to nsLTP sensitization binding of lipids or the structural differences among individual mem- FIGURE 1 Structure of lipid‐transfer protein allergens bers of the nsLTP family might cause this selective resistance 44 The abundancy of allergenic nsLTPs in the culprit food can also So far, it has been shown that four major (immunodominant) contribute to the allergenic risk. While the concentration of Pru p 3 IgE epitopes of Pru p 3 are shared by LTPs of fruits from the in peach peel is comparatively high (approx. 6 mg/g peach peel; it is Rosaceae family.37,38 In a cohort of Spanish and Italian peach allergic less in apple peel (approx. 66 μg/g tissue).45,46 Regarding tree nuts, patients, a Th2‐dominated response was identified, and among nsLTPs from walnut and hazelnut are accumulated in the brown skin several T‐cell epitopes, immunodominant T‐cell‐activating regions of of the embryo and the concentration per nut is comparatively low 39 Pru p 3 were detected. In contrast, other nsLTPs from more compared to peach.47 distantly related species, such as Cor a 8 in hazelnut (Corylus avel- lane) and Hel a 3s in sunflower seed (Helianthus annuus), do not contain these conserved epitope sequences. In a study on patients 3 | HIERARCHY OF CROSS‐REACTIVITY allergic to hazelnut and peach, the immunodominant role of Pru p 3 was confirmed, but no Cor a 8‐specific T‐cell epitopes were Patients suffering from an ‘nsLTP syndrome’ frequently display detected suggesting cross‐reactivity rather than genuine primary symptoms with multiple plant‐derived foods due to the ubiquitous sensitization to Cor a 8.40 These molecular data suggest that Pru p distribution of these pan‐allergens.48,49 The clinical relevance of 3 could be the primary sensitizer behind nsLTP‐driven food allergy these allergens, as well as the primary sensitizer, varies greatly in some populations. depending on the patient's age and geographic area.50 Initial The disulphide bridges contribute to the folding of nsLTPs into a epidemiological studies on nsLTP sensitization have mainly been compact structure with high thermal and proteolytic stability, which conducted in southern Europe on adult or adolescent pop- might explain the high allergenicity of nsLTPs.41,42 In vitro experiments ulations.49 In this region, most allergists agree that peach is the confirmed the stability of Pru p 3 and its resistance to digestion and primary driving source behind nsLTP sensitization, although nsLTPs heat treatment in an acidic environment by circular dichroism (CD) of some pollen, particularly plane tree and mugwort, have been spectroscopy . However, when performing these experiments under proposed as contributing to sensitization.51 According to Palacin’s neutral pH conditions, the stability of these proteins is reduced as study, where the IgE‐binding capacity of a number of purified LTPs shown for Pru p 3 and Cor a 8 which might be due to the cleavage of was analysed using sera from nsLTP syndrome patients; Pru p 3 disulphide bonds at neutral pH and high temperature.43–45 Interest- (peach) was the most frequently recognized, followed by Mal d 3 ingly, stability to endolysosomal degradation also seems to differ (apple), Cit r 3 (orange), Bra o 3 (cabbage) Sin a 3 (mustard) and within the nsLTP protein family, since Pru p 3 showed higher resis- the tree nut LTPs, Jug r 3 (walnut) and Cas s 8 (chestnut). In 40 tance as compared to Cor a 8. These data point towards a selective contrast, Tri a 14, the wheat nsLTP, was seldom recognized in the resistance of individual nsLTPs. It remains to be shown, whether the population studied.52 6 - SKYPALA ET AL. Furthermore, IgE binding frequently does not predict clinical contribute to the progression from respiratory to food allergy in Bet cross‐reactivity; most patients did not report any clinical reaction to v 1 homologues, profilin and nsLTP allergic syndromes. lentil, soybean, maize and sesame, despite specific IgE levels to the Respiratory exposure and subsequent clinical reactivity to nsLTP nsLTPs in these foods. This might suggest either that in these foods, can also occur due to inhalation of Cannabis sativa. The first nsLTPs are less abundant or thermal processing reduces allerge- description of a case of a patient sensitized to Pru p 3, with nsLTP 53,54 nicity. So, patients with an ‘nsLTP syndrome’ are usually poly- sensitization mediated by smoking marijuana, was published by sensitized to multiple foods, to some extent, influenced by the Gamboa in 2007 and has been followed by other publications sup- amount of allergen present in the sources, the route of sensitization, porting the relevance of C. sativa as a potential source of nsLTP geographical patterns and the sensitizing agent. Primary sensitization sensitization and cannabis‐related allergy.14,72–74 Research from through Can s 3 exposure might, for example, result in a different northern/central Europe suggests marijuana inhalation is an effective array of hierarchical order of food nsLTP reactivity.55 entry route to nsLTP sensitization in the absence of Pru p 3‐mediated allergy.75–77 Decuyper and colleagues reported that 45% of 120 patients allergic to C. sativa and sensitized to Can s 3, and the nsLTP 4 | ROUTES OF SENSITIZATION TO nsLTP in C. sativa had severe and generalized allergy to plant foods.78 Passive inhalation of smoke from C. sativa can also lead to sensiti- Sensitization to nsLTP can occur in several different ways. The char- zation to Can s 3, and other nsLTP allergens.79 However, sensitiza- acterization of lipid ligands bound to nsLTPs has shed light on the tion to Can s 3 may not be universal; a publication from the United potential innate stimulatory properties of nsLTPs, which might ac- States, reporting on the sequencing of allergens from 23 patients 16,56 count for their high sensitization potential. In early life, sensiti- with a positive skin prick test to a crude extract of C. sativa, did not zation to foods such as milk, egg and peanut may occur through find anything sensitized to Can s 3.80 cutaneous exposure due to skin barrier disruption and exposure via the epi‐cutaneous route, with IgG1+ B‐cell immunity preceding the initiation of IgE responses.57,58 Sensitization to nsLTP may also occur 5 | SENSITIZATION TO POLLEN nsLTP ALLERGENS through the cutaneous route; is reported that peach‐induced contact urticaria has been linked to nsLTP sensitization.59 Sensitization to Sensitization to nsLTP in plant foods via the inhaled route may also foods via the gastrointestinal tract is a common cause of food‐allergic involve nsLTP in pollens. reactions, and this is also true of nsLTP allergens. Tordesillas et al. The existence of pollen food syndrome mediated by nsLTPs was demonstrated that Pru p 3 has a high capacity to cross the gastric first described by García‐Sellés in 2002.81 Pollen nsLTPs such as Art barrier, a factor that could be relevant to the capacity for sensitization v 3 from Artemisia vulgaris (mugwort) and Pla a 3 from Platanus by the gastric route.60 acerifolia (plane tree) share partial cross‐reactivity with Rosaceae Just as reactions to plant foods also frequently occur through nsLTPs, and could thus initiate the sensitization process and/or sensitization to inhaled pollen aeroallergens provoking cross‐reac- contribute to the progressive recognition of multiple nsLTPs.82 In tivity to plant foods, sensitization to nsLTP in foods via inhalation some areas, high exposure to nsLTP‐containing pollens could result in may also occur.61 Case reports describe a patient who developed the development of allergic respiratory symptoms, with a proportion respiratory symptoms when exposed to peach tree crops, and of individuals also affected by nsLTP‐driven food allergy.15,83–85 For a second patient who developed rhinitis after working in a example, the pollen allergen Pla a 3 was first noted to play a clinically wholesale fruit warehouse, both of whom subsequently developed relevant role by clinicians in Barcelona, an area with high Platanus severe reactions to eating peaches and other foods.62,63 Garcia and pollen exposure where a significant percentage of pollen‐allergic colleagues subsequently showed that peach leaves contain Pru p 3, patients (12%) are mono‐sensitized to Platanus.86,87 Thus, Pla a 3 which might explain up to 10% of residents in an area with sensitization is associated with nsLTP food sensitization, and in in- extensive orchard‐tree crops were mono‐sensitized to Pru p 3, and hibition assays plane pollen extracts inhibited IgE binding to food the finding that Pru p 3 is an occupational respiratory allergen in nsLTPs by between 50% and 100%.88 peach crop workers.19,64 nsLTP in a variety of foods has also been Likewise, some with nsLTP sensitization to foods are also affected shown to be relevant in occupational allergy in those involved in by respiratory symptoms due to nsLTP allergens in the pollen, with processing other plant food crops including asparagus, wheat and cross‐sectional studies suggesting that in some cases the nsLTP within maize.9,65–69 the pollen is the primary sensitizer.84–86 Studies suggest that Art v 3 Rodriguez and colleagues generated animal models of anaphy- could also act as a primary sensitizer, demonstrating the clinical laxis to Pru p 3 following sensitization via the nasal route in combi- relevance of pollen nsLTPs in areas of high exposure to Artemisia nation with lipopolysaccharide (LPS).70 Recently, Rosace et al. have pollen.85,89 For example, Artemisia is the dominant allergenic pollen in described a progressive remodelling process of the oral mucosa, China, and studies have demonstrated that this might be a mechanism along with respiratory allergy progression, using profilin as an of sensitization to Pru p 3, and the cause of peach allergy in the 71 allergen. Co‐localization of CD11+ and CD4+ cells demonstrates Chinese population.83 In areas with high exposure to either Artemisia that the oral mucosa is an immunocompetent organ and can pollen as Gran Canaria Island4 or to Platanus pollen as Barcelona, SKYPALA ET AL. - 7 Italian subjects.90. A study performed in patients with a clinical history of peach anaphylaxis demonstrated dual sensitization to both Pru p 3 and Art v 3, and therefore, even in the absence of atmospheric mugwort pollen, there is a possibility that these patients could still develop a respiratory allergy if exposed to mugwort.88,91 The presence of nsLTP sensitization in the United Kingdom, and other parts of more northerly European latitudes suggests the primary sensitizing nsLTP might be from a pollen rather than from a food.90,92 Allergenic pollen nsLTPs have also been described from other sources including Parietaria judaica (Par j 2) and olive tree (Oleum Europea) (Ole e 7). Sensitization to Parietaria has been reported in subjects from northern European countries free from this weed, suggesting this is another expression of cross‐reactivity and probably to relevant.90,92 A study by Tordesillas and colleagues in 2011 re- ported that there was no cross‐reactivity between nsLTP allergens from olive and parietaria, or between the pollen nsLTP and nsLTP allergens from foods.93 However, a more recent study from Ciprandi and colleagues reported that in a group of children with allergic rhinitis due to Parietaria pollen allergy and sensitization to Pru p 3, 50% reported a food allergy or oral allergy symptoms, and 25% reported anaphylaxis after ingesting nsLTP‐containing foods.94 It is also unclear how pertinent Ole e 7 is in terms of diagnostic relevance. Although it has less than 20% amino acid sequence identity with Pru p 3, recognition of Ole e 7 is associated with reactions to plant‐ derived food (mainly peach, walnut and peanut), and 80% of Ole e 7 reactors are sensitized to food nsLTPs versus only 30% of Ole e 1 reactors.95 A recent study reported that common IgG and IgE epitopes were identified in Ole e 7 and Pru p 3, with inhibition studies suggesting that primary sensitization to Ole e 7 could lead to sensi- tization to Pru p 3.96 There has been some suggestion that the greater the atmo- spheric burden of birch pollen, the lower the incidence of nsLTP sensitization, leading to a hypothesis that high levels of birch pollen protect against nsLTP allergy.97 It is suggested one potential expla- nation could be lower reactivity of effector cells exposed to the nsLTPs, as described by Christensen et al., on the basis of interfer- ence by other IgE molecules bound to the high‐affinity IgE receptors on effector cells.98 However, a recent study from Belgium demon- strate that many subjects are sensitized to both nsLTP allergens in foods and pollens.92 A study on nsLTP sensitized adults in the UK study reported that co‐sensitization to birch pollen allergens did not seem to be protective against severe reactions, with the use of F I G U R E 2 Structure of Pru p 3: (A) surface model, (B) ribbon adrenaline and subsequent hospital attendance being significantly model, (C) internal cavity with ligand binding reported.90 epidemiological studies have also demonstrated a broader recognition pattern to nsLTPs in sensitized and symptomatic patients.52 6 | EPIDEMIOLOGY It has also been demonstrated that patients sensitized to Pru p 3 can show sensitization to Art v 3 and/or Pla a 3 even in geographical Epidemiological data have most often involved the reporting of the areas lacking Artemisia/plane tree pollen, presumably due to IgE cross‐ rates of sensitization to the peach nsLTP Pru p 3. Using ISAC reactivity.84,85 Despite a lack of Artemisia pollen, a recent UK study microarray, Scala et al. reported that 9% of 23,000 patients living in reported a strong correlation between Pru p 3 and both Pla a 3 and Art central and southern Italy were sensitized to Pru p 3.99 In Spain, v 3, with the r‐value being greater than that for a matched group of Barber et al. detected Pru p 3 sensitization in 12% of 2000 Spanish 8 - SKYPALA ET AL. FIGURE 3 World‐wide reported lipid‐transfer protein sensitization patients with pollen allergy.100,101 This proportion was confirmed by population are lacking, there is little doubt that sensitization to Gonzalez‐Mancebo et al. who reported that 53/430 (12.3%) of out- nsLTPs is a significant cause of primary food allergy in adults living patients seen in their allergy unit for any reason were sensitized in the Mediterranean basin12,109 where it accounts for a large—if 102 to Pru p 3. Those sensitized to Pru p 3 may not always be not the largest—proportion of food‐induced anaphylaxis.8 Inter- symptomatic and the symptom severity may vary. A study on nsLTP estingly, there are marked geographic variations in the prevalence syndrome reported that in a group of 87 subjects sensitized to Pru p of LTP hypersensitivity within single countries. This has been best 3, 44% experienced anaphylaxis, 43% skin or oropharyngeal re- shown for Italy due to its very different climate zones, that is, 103 actions, and 13% were asymptomatic. It is generally accepted that northern (continental climate) and central southern (Mediterranean nsLTP sensitization often occurs early in life.104,105 Pru p 3 sensiti- climate), with nsLTP sensitization dominating in the latter.12,110 zation among children in a Spanish cohort was twice as high as that Similar observations have been seen in two Spanish studies, where in adults.100 Another study reported that the level of Pru p 3 sensi- nsLTP‐sensitization prevalence among patients with seasonal allergy in tization in a large population of Italian subjects peaks around the different areas was 2% and 40%, respectively.52,101 However, a Medi- 106 start of the third decade of life. Further, a study in LTP‐allergic terranean climate on its own is not the only factor in the development of adults suggested that the younger the age of onset, the higher the sensitization to nsLTP. A high prevalence of nsLTP sensitization is also titres of specific IgE to Pru p 3 that are detected in patients.13 found in Portugal, which, despite being part of the Iberian Peninsula, is In addition to those who are mono‐sensitized to Pru p 3, studies an Atlantic country.111 In addition, those living in areas of Spain and Italy have also investigated subjects with sensitization to multiple nsLTP characterized either by a continental or Atlantic climate may also be and usually have clinically relevant allergy to different plant foods. sensitized to nsLTP.12,112 107 These individuals have the so‐called LTP syndrome. Rosaceae The geographic variability of nsLTP sensitization can be best fruits and nuts are the main plant food allergens involved in this appreciated in multinational studies, where the differences between syndrome.108 In a nationwide review of 17 Italian allergy clinics, 210 northern and southern European countries are evident.113 However, subjects sensitized to nsLTP reported reactions to multiple food the presence of nsLTP sensitization in European countries other than triggers including peach (85%), apple (35%) and tree nuts (20%). the traditional ‘endemic’ Mediterranean areas is also emerging—see Offending foods included also other Rosaceae (apricot, plum, pear, Figure 3. A study from Belgium reported nsLTP sensitization rates in almond, strawberry), cereals (maize, beer, rice), kiwifruit, grapes, selected pollen and/or plant food allergic children and adults to lettuce, cauliflower and broccoli.12 exceed 20% (albeit clinically irrelevant in most cases).92 Other re- Following initial identification around 20 years ago, nsLTP ports have been published from Austria,114,115 France,75 Belgium,116 sensitization appears to be most prevalent in the ‘Mediterranean Germany,117,118 Poland119 and the United Kingdom.90,120. Outside basin’, a climate area which is defined by a southern European Europe, nsLTP hypersensitivity and allergy seem relevant in certain latitude. Although precise epidemiologic data from the general areas of China.83,121 A single report has been published from SKYPALA ET AL. - 9 Australia.122 Remarkably, nsLTP sensitization has not yet been re- studies into such mechanisms that may ameliorate severe nsLTP ported in the Americas or Africa. reactions. Evaluation of sensitization profiles to pollen and food in different regions of Europe might contribute to the identification of primary sensitizers, whether they be from plant foods, pollens or 7 | FUTURE RESEARCH NEEDS other inhalants such as cannabis, thus paving the way for prevention and control measures. Although experimental and clinical studies of nsLTP sensitization have increased significantly in the last decade, there are still several issues not fully understood. Although some definitions have 8 | CONCLUSION been agreed by the Task Force, it is important to develop inter- nationally agreed criteria and definitions for nsLTP sensitization Investigating the structure and function of nsLTP has led to an and nsLTP syndromes, especially when determining the prevalence understanding of their allergenic potential, which is exacerbated of nsLTP sensitization. In paediatric populations, nsLTP sensitiza- due to the high degree of cross‐reactivity between nsLTP from tion has some peculiarities: the lower risk of severe reactions different plant species. These allergens are present in fruits, vege- compared to adults and the common occurrence of subclinical tables, nuts, seeds, legumes and cereals, and food nsLTPs have been sensitization. Continent‐wide epidemiological prevalence studies in shown to be able to sensitize through the oral, respiratory and both adults and children are urgently needed to evaluate the cutaneous routes. Exposure to peaches has been linked to the prevalence of nsLTP sensitization, its geographical distribution, development of primary sensitization to the peach nsLTP, Pru p 3, risk/protective factors, genetic predisposition, clinical features and which dominates in the Mediterranean areas of Europe. However, natural history. the sensitization process might depend on both individual (dietary/ The variation in the severity of symptoms also warrants inves- occupational) and/or geographical factors. Although data suggest it tigation. It has already been demonstrated in one study that there is a is an important cause of primary food allergy in the southern 92 link between multiple nsLTP sensitizations and systemic reactions. European countries, the extent of nsLTP sensitization could also be It is possible that patients sensitized to multiple nsLTPs, with strong significant in the rest of Europe. In this context, the role of expo- concomitant exposure to pollen‐derived nsLTP allergens, could sure to pollen needs further study, with some pollens, such as those display a broad T‐cell stimulatory repertoire, similar to that reported of mugwort and plane tree, potentially playing a major role in 123,124 for profilin allergy. The reports of more severe reactions in sensitization to food nsLTPs. Despite high levels of sensitization to those with nsLTP sensitization but without pollinosis confirms the Pru p 3, many children remain asymptomatic or experience only complex nature of food‐allergic mechanisms and identifies a need for mild skin symptoms. Moderate or severe clinical symptoms are much more likely to present in teenage years or in adults, despite levels of Pru p 3 falling. Sensitization to nsLTP is common and likely to be much more widespread than has been previously thought. It is therefore likely to be an important cause of plant food allergy in Key Messages many adults in Europe and beyond. 1. nsLTPs are a large group of allergens found in land plants; the majority of allergenic nsLTPs belong to LTP AC K NO W L E DG E M E NT (type )1 (9–10 kDa; around 90 amino acids). Not applicable. 2. nsLTPs are highly cross‐reactive with particular hierar- chies of sensitization depending on the primary CO N F L I C T S O F I N T E R E S T sensitizer. The following authors declare that they have competing interests: 3. In Italy and Spain, sensitization frequently occurs in K. Hoffmann‐Somergruber has received support from the Austrian childhood, with peach nsLTP (Pru p 3) often being the Science funds (FWF) by SFB Subproject F‐4603, L. Cecchi has sole sensitizing nsLTP. received honoraria from Malseci, Menarini, Mylan and Thermofisher, 4. Sensitization may be both via the oral, inhaled or cuta- D Barber is a scientific advisor to ALK and AIMMUNE, E.Scala has neous route, and may be initiated by a pollen nsLTP. received consultant arrangements and speakers’ bureau participation 5. Although first described in Italy and Spain, nsLTP from Stallergenes and Thermo Fisher Scientific. M. Fernández‐Rivas sensitization occurs in many European countries and has declares grants from Spanish Government (ISCIII; MINECO), Aim- also been reported in China. mune Therapeutics and Diater to her organization; consultancy fees 6. When an allergy to a plant food is suspected, nsLTP al- from Aimmune, DBV, Novartis, SPRIM; lecture fees from Aimmune, lergens should not be ruled out as a trigger, wherever ALK, Diater, GSK, HAL Allergy, Thermofisher Scientific, outside the the geographical location submitted work. R. van Ree undertakes consultancies for HAL Allergy BV, Citeq BV and Angany Inc, has received honoraria from HAL 10 - SKYPALA ET AL. Allergy BV, ThermoFisher Scientific and funding support from the 4. Pastorello EA, Ortolani C, Farioli L, et al. C. Allergenic cross‐ European Commission, Dutch Science Foundation, Health Holland. reactivity among peach, apricot, plum, and cherry in patients with oral allergy syndrome: an in vivo and in vitro study. J Allergy Clin I. Skypala, D. Ebo, M. Faber, A Diaz‐Perales, I Swoboda, F Gomez, Immunol. 1994;94:699‐707. R. Asero, E. Pastorello, O. Luengo, S Till, J Bartra, A Kon- 5. Pastorello EA, Farioli L, Pravettoni V, et al. The major allergen of stantinopoulos have no conflict of interests to declare peach (Prunus persica) is a lipid transfer protein. J Allergy Clin Immunol. 1999;103:520‐526. 6. Sánchez‐Monge R, Lombardero M, García‐Sellés FJ, Barber D, Salcedo G. Lipid‐transfer proteins are relevant allergens in fruit A U TH O R C O N TR IB UT I O N S allergy. J Allergy Clin Immunol. 1999;103:514‐519. Isabel Skypala established the Task Force, set up and chaired the 7. Asero R, Antonicelli L, Arena A, et al. Causes of food‐induced meetings, determined the sections of the manuscript, merged all of anaphylaxis in Italian adults: a multi‐centre study. Int Arch Allergy the sections from individual contributors, added key points, wrote the Immunol. 2009;150:271‐277. abstract, made amendments to the manuscript following both internal 8. Pastorello EA, Farioli L, Stafylaraki C, et al. Wheat‐dependent ex- ercise‐induced anaphylaxis caused by a lipid transfer protein and and external reviews and submitted the manuscript in its final format. not by ω‐5 gliadin. Ann Allergy Asthma Immunol. 2014;112:386‐387. Ricardo Asero, Domingo Barber, Lorenzo Cecchi, Arazeli Diaz Perales, 9. Palacin A, Quirce S, Armentia A, et al. Wheat lipid transfer protein Karin Hoffmann‐Sommergruber, Elide A. Pastorello, and Ines Swoboda is a major allergen associated with baker's asthma. J Allergy Clin attended and contributed to the meetings, wrote individual sections of Immunol. 2007;120:1132‐1138. 10. Romano A, Scala E, Rumi G, et al. Lipid transfer proteins: the most the manuscript, reviewed it once all the sections had been put together frequent sensitizer in Italian subjects with food‐dependent exer- and following internal and external review. Joan Bartra, Didier G. Ebo, cise‐induced anaphylaxis. Clin Exp Allergy. 2012;42:1643‐1653. Margaretha A. Faber, Montserrat Fernández‐Rivas, Francesca Gomez, 11. Pastorello EA, Farioli L, Pravettoni V, et al. Pru p 3‐sensitised A. P. Konstantinopoulos, Olga Luengo, Ronald van Ree, Enrico Scala Italian peach‐allergic patients are less likely to develop severe symptoms when also presenting IgE antibodies to Pru p 1 and Pru p and Stephen J. Till attended and contributed to the meetings and 4. Int Arch Allergy Immunol. 2011;156:362‐372. reviewed the manuscript following review. 12. Asero R, Antonicelli L, Arena A, et al. EpidemAAITO: features of food allergy in Italian adults attending allergy clinics: a multi‐centre O R C ID study. Clin Exp Allergy. 2009;39:547‐555. 13. Pastorello EA, Farioli L, Stafylaraki C, et al. Anti‐rPru p 3 IgE levels Isabel J. Skypala https://orcid.org/0000-0003-3629-4293 are inversely related to the age at onset of peach‐induced severe Ricardo Asero https://orcid.org/0000-0002-8277-1700 symptoms reported by peach‐allergic adults. Int Arch Allergy Domingo Barber https://orcid.org/0000-0002-5488-5700 Immunol. 2013;162:45‐49. Lorenzo Cecchi https://orcid.org/0000-0002-0658-2449 14. Gamboa P, Sanchez‐Monge R, Sanz ML, Palacín A, Salcedo G, Diaz‐Perales A. Sensitization to Cannabis sativa caused by a novel Arazeli Diaz Perales https://orcid.org/0000-0002-1093-3627 allergenic lipid transfer protein, Can s 3. J Allergy Clin Immunol. Karin Hoffmann‐Sommergruber https://orcid.org/0000-0002-8830- 2007;120:1459‐1460. 058X 15. Deng S, Yin J. Mugwort Pollen‐related food allergy: lipid transfer Elide A. Pastorello https://orcid.org/0000-0002-3753-1783 protein sensitization and correlation with the severity of allergic Ines Swoboda https://orcid.org/0000-0002-9164-1721 reactions in a Chinese population. Allergy Asthma Immunol Res. 2019;11:116‐128. Joan Bartra https://orcid.org/0000-0001-7767-4730 16. Tordesillas L, Cubells‐Baeza N, Gómez‐Casado C, et al. Mecha- Didier G. Ebo https://orcid.org/0000-0003-0672-7529 nisms underlying induction of allergic sensitization by Pru p3. Clin Margaretha A. Faber https://orcid.org/0000-0002-1277-5052 Exp Allergy. 2017;47:1398‐1408. Montserrat Fernández‐Rivas https://orcid.org/0000-0003-1748- 17. Salminen TA, Blomqvist K, Edqvist J. Lipid transfer proteins: clas- sification, nomenclature, structure, and function. Planta. 2328 2016;244:971‐997. Francesca Gomez https://orcid.org/0000-0003-1607-6686 18. Boutrot F, Chantret N, Gautier MF. Genome‐wide analysis of the Anastasios. P. Konstantinopoulos https://orcid.org/0000-0002- rice and Arabidopsis non‐specific lipid transfer protein (nsLTPp) 7060-653X gene families and identification of wheat nsLTP genes by EST data mining. BMC Genomics. 2008;9:86. Olga Luengo https://orcid.org/0000-0002-8905-2776 19. Debono A, Yeats TH, Rose JK, et al. Arabidopsis LTPG is a Enrico Scala https://orcid.org/0000-0002-9391-9168 glycosylphosphatidylinositol‐anchored lipid transfer protein Stephen J. Till https://orcid.org/0000-0003-4518-3093 required for export of lipids to the plant surface. Plant Cell. 2009;21:1230‐1238. 20. Lee SB, Go YS, Bae HJ, et al. Disruption of glyco- REFERENCES sylphosphatidylinositol‐anchored lipid transfer protein gene altered 1. Edstam MM, Viitanen L, Salminen TA, Edqvist J. Evolutionary his- cuticular lipid composition, increased plastoglobules, and enhanced tory of the non‐specific lipid transfer proteins. Mol Plant. susceptibility to infection by the fungal pathogen Alternaria brassi- 2011;4:947‐964. cicola. Plant Physiol. 2009;150:42‐54. 2. Kader JC. Lipid transfer proteins in plants. Ann Rev Plant Physiol 21. Lin CH, Li L, Lyu PC, Chang JY. Distinct unfolding and refolding Mol Biol. 1996;47:627‐654. pathways of lipid transfer proteins LTP1 and LTP2. Protein J. 3. Liu F, Zhang X, Lu C, et al. Non‐specific lipid transfer proteins in 2004;23:553‐566. plants: presenting new advances and an integrated functional 22. Gincel E, Simorre JP, Caille A, Marion D, Ptak M, Vovelle F. Three‐ analysis. J Exp Bot. 2015;66:56635681. dimensional structure in solution of a wheat lipid‐transfer protein SKYPALA ET AL. - 11 from multidimensional 1H‐NMR data. A new folding for lipid 42. Lindorff‐Larsen K, Winther JR. Surprisingly high stability of barley carriers. Eur J Biochem. 1994;226:413‐422. lipid transfer protein, LTP1, towards denaturant, heat and pro- 23. Shin DH, Lee JY, Hwang KY, Kim KK, Suh SW. High‐resolution teases. FEBS Lett. 2001;488:145‐148. crystal structure of the non‐specific lipid‐transfer protein from 43. Offermann LR, Bublin M, Perdue ML, et al. Structural and func- maize seedlings. Structure. 1995;3:189‐199. tional characterization of the hazelnut allergen Cor a 8. J Agric Food 24. Gomar J, Petit MC, Sodano P, et al. Solution structure and lipid Chem. 2015;63:9150‐9158. binding of a nonspecific lipid transfer protein extracted from maize 44. Bublin M, Eiwegger T, Breiteneder H. Do lipids influence the seeds. Protein Sci. 1996;5:565‐577. allergic sensitization process? J Allergy Clin Immunol. 25. Lerche MH, Kragelund BB, Bech LM, Poulsen FM. Barley lipid‐ 2014;134:521‐529. transfer protein complexed with palmitoyl CoA: the structure re- 45. Gaier S, Marsh J, Oberhuber C, et al. Purification and structural veals a hydrophobic binding site that can expand to fit both large stability of the peach allergens Pru p 1 and Pru p 3. Mol Nutr Food and small lipid‐like ligands. Structure. 1997;5:291‐306. Res. 2008;52(Suppl 2):S220‐S229. 26. Lee JY, Min K, Cha H, Shin DH, Hwang KY, Suh SW. Rice non‐ 46. Sancho AI, van Ree R, van Leeuwen A. Measurement of lipid specific lipid transfer protein: the 1.6 A crystal structure in the transfer protein in 88 apple cultivars. Int Arch Allergy Immunol. unliganded state reveals a small hydrophobic cavity. J Mol Biol. 2008;146:19‐26. 1998;276:437‐448. 47. Pastorello EA, Farioli L, Pravettoni V, et al. Lipid transfer protein 27. Pasquato N, Berni R, Folli C, et al. Crystal structure of peach Pru p and vicilin are important walnut allergens in patients not allergic to 3, the prototypic member of the family of plant non‐specific lipid pollen. J Allergy Clin Immunol. 2004;114:908‐914. transfer protein pan‐allergens. J Mol Biol. 2006;356:684‐694. 48. Van Winkle RC, Chang C. The biochemical basis and clinical evi- 28. Liu F, Xiong X, Wu L, et al. BraLTP1, a lipid transfer protein gene dence of food allergy due to lipid transfer proteins: a compre- involved in epicuticular wax deposition, cell proliferation and flower hensive review. Clin Rev Allergy Immunol. 2014;46:211‐224. development in Brassica napus. PLoS One. 2014;9(10):e110272. 49. Salcedo G, Sanchez‐Monge R, Diaz‐Perales A, Garcia‐Casado G, 29. Edstam MM, Blomqvist K, Eklöf A, Wennergren U, Edqvist J. Barber D. Plant non‐specific lipid transfer proteins as food and Coexpression patterns indicate that GPI‐anchored non‐specific pollen allergens. Clin Exp Allergy. 2004;34:1336‐1341. lipid transfer proteins are involved in accumulation of cuticular 50. Asero R, Mistrello G, Roncarolo D, et al. Immunological cross‐ wax, suberin and sporopollenin. Plant Mol Biol. 2013;83:625‐649. reactivity between lipid transfer proteins from botanically 30. García‐Olmedo F, Molina A, Segura A, Moreno M. The defensive unrelated plant‐derived foods: a clinical study. Allergy. 2002;57: role of nonspecific lipid‐transfer proteins in plants. Trends Microbiol. 900‐906. 1995;3:72‐74. 51. Pascal M, Muñoz‐Cano R, Reina Z, et al. Lipid transfer protein 31. Sun JY, Gaudet DA, Lu ZX, Frick M, Puchalski B, Laroche A. syndrome: clinical pattern, cofactor effect and profile of molecular Characterization and antifungal properties of wheat nonspecific sensitization to plant‐foods and pollens. Clin Exp Allergy. 2012; lipid transfer proteins. Mol Plant Microbe Interact. 2008;21: 42:1529‐1539. 346‐360. 52. Palacín A, Gómez‐Casado C, Rivas LA, et al. Graph based study of 32. Guo L, Yang H, Zhang X, Yang S. Lipid transfer protein 3 as a target allergen cross‐reactivity of plant lipid transfer proteins (LTPs) using of MYB96 mediates freezing and drought stress in Arabidopsis. microarray in a multicenter study. PLoS One. 2012;7(12):e50799. J Exp Bot. 2013;64:1755‐1767. 53. Asero R. In patients with LTP syndrome food‐specific IgE show a 33. Dubiela P, Aina R, Polak D, et al. Enhanced Pru p 3 IgE‐binding predictable hierarchical order. Eur Ann Allergy Clin Immunol. activity by selective free fatty acid‐interaction. J Allergy Clin 2014;46:142‐146. Immunol. 2017;140:1728‐1731. 54. Asero R, Mistrello G, Roncarolo D, Amato S, Falagiani P. Why do 34. Dubiela P, Del Conte R, Cantini F, et al. Impact of lipid binding lipid transfer protein‐hypersensitive patients tolerate bean (and on the tertiary structure and allergenic potential of Jug r 3, the other legumes)? Int Arch Allergy Immunol. 2005;137:236‐240. non‐specific lipid transfer protein from walnut. Sci Rep. 55. Decuyper, II, Faber MA, Lapeere H, et al. Cannabis allergy: 2019;9:2007. A diagnostic challenge. Allergy. 2018;73:1911‐1914. 35. Aina R, Dubiela P, Geiselhart S, et al. Distinct Lipid Transfer Pro- 56. Cubells‐Baeza N, Gómez‐Casado C, Tordesillas L, et al. Identifica- teins display different IgE‐binding activities that are affected by tion of the ligand of Pru p 3, a peach LTP. Plant Mol Biol. fatty acid binding. Allergy. 2019;74:827‐831. 2017;94:33‐44. 36. Scheurer S, Schülke S. Interaction of non‐specific lipid‐transfer 57. Kong J, Chalcraft K, Mandur TS, et al. Comprehensive metab- proteins with plant‐derived lipids and its impact on allergic sensi- olomics identifies the alarmin uric acid as a critical signal for the tization. Front Immunol. 2018;9:1389. induction of peanut allergy. Allergy. 2015;70:495‐505. 37. Borges JP, Barre A, Culerrier R, Granier C, Didier A, Rougé P. Lipid 58. Jiménez‐Saiz R, Ellenbogen Y, Koenig JFE, et al. IgG1(+) B‐cell transfer proteins from Rosaceae fruits share consensus epitopes immunity predates IgE responses in epicutaneous sensitization to responsible for their IgE‐binding cross‐reactivity. Biochem Biophys foods. Allergy. 2019;74:165‐175. Res Commun. 2008;365:685‐690. 59. Asero R. Peach‐induced contact urticaria is associated with lipid 38. García‐Casado G, Pacios LF, Díaz‐Perales A, et al. Identification of transfer protein sensitization. Int Arch Allergy Immunol. IgE‐binding epitopes of the major peach allergen Pru p 3. J Allergy 2011;154:345‐348. Clin Immunol. 2003;112:599‐605. 60. Tordesillas L, Gómez‐Casado C, Garrido‐Arandia M, et al. Trans- 39. Schulten V, Radakovics A, Hartz C, et al. Characterization of the port of Pru p 3 across gastrointestinal epithelium ‐ an essential allergic T‐cell response to Pru p 3, the nonspecific lipid transfer step towards the induction of food allergy? Clin Exp Allergy. protein in peach. J Allergy Clin Immunol. 2009;124:100‐107. 2013;43:1374‐83. 40. Schulten V, Nagl B, Scala E, et al. Pru p 3, the nonspecific lipid 61. Werfel T, Asero R, Ballmer‐Weber BK, et al. Position paper of the transfer protein from peach, dominates the immune response to its EAACI: food allergy due to immunological cross‐reactions with homolog in hazelnut. Allergy. 2011;66:1005‐1013. common inhalant allergens. Allergy. 2015;70:1079‐1090. 41. Asero R, Mistrello G, Roncarolo D, et al. Lipid transfer protein: a 62. García BE, Lombardero M, Echechipía S, et al. Respiratory allergy pan‐allergen in plant‐derived foods that is highly resistant to to peach leaves and lipid‐transfer proteins. Clin Exp Allergy. pepsin digestion. Int Arch Allergy Immunol. 2000;122:20‐32. 2004;34:291‐295. 12 - SKYPALA ET AL. 63. Borghesan F, Mistrello G, Roncarolo D, Amato S, Plebani M, Asero 84. Lauer I, Miguel‐Moncin MS, Abel T, et al. Identification of a plane R. Respiratory allergy to lipid transfer protein. Int Arch Allergy pollen lipid transfer protein (Pla a 3) and its immunological relation Immunol. 2008;147:161‐165. to the peach lipid‐transfer protein, Pru p 3. Clin Exp Allergy. 64. Pérez‐Calderón R, Gonzalo‐Garijo MÁ, Rodríguez‐Velasco FJ, 2007;37:261‐269. Sánchez‐Vega S, Bartolomé‐Zavala B. Occupational respiratory 85. Lombardero M, García‐Sellés FJ, Polo F, et al. Prevalence of allergy in peach crop workers. Allergy. 2017;72:1556‐1564. sensitization to Artemisia allergens Art v 1, Art v 3 and Art v 65. Tabar AI, Alvarez‐Puebla MJ, Gomez B, et al. Diversity of aspar- 60kDa. Cross‐reactivity among Art v 3 and other relevant lipid‐ agus allergy: clinical and immunological features. Clin Exp Allergy. transfer allergens. Clin Exp Allergy. 2004;34:1415‐1421. 2004;34:131‐136. 86. Wangorsch A, Larsson H, Messmer M, et al. Molecular cloning of 66. Pastorello EA, Farioli L, Robino AM, Trambaioli C, Conti A, plane pollen allergen Pla a 3 and its utility as diagnostic marker for Pravettoni V. A lipid transfer protein involved in occupational peach associated plane pollen allergy. Clin Exp Allergy. sensitization to spelt. J Allergy Clin Immunol. 2001;108:145‐146. 2016;46:764‐774. 67. Guillen D, Barranco P, Palacín A, Quirce S. Occupational rhino- 87. Barber D, Díaz‐Perales A, Villalba M, Chivato T. Challenges for conjunctivitis due to maize in a snack processor: a cross‐reactivity allergy diagnosis in regions with complex pollen exposures. Curr study between lipid transfer proteins from different cereals and Allergy Asthma Rep. 2015;15:496. peach. Allergy Asthma Immunol Res. 2014;6:470‐473. 88. Scala E, Till SJ, Asero R, et al. Lipid transfer protein sensitization: 68. Safi H, Wangorsch A, Lidholm J, et al. Identification and molecular reactivity profiles and clinical risk assessment in an Italian cohort. characterization of allergenic non‐specific lipid‐transfer protein Allergy. 2015;70:933‐943. from durum wheat (Triticum turgidum). Clin Exp Allergy. 89. Scala E, Cecchi L, Abeni D, et al. Pla a 2 and Pla a 3‐reactivity 2019;49:120‐129. identify plane tree‐allergic patients with respiratory symptoms or 69. Díaz‐Perales A, Tabar AI, Sánchez‐Monge R, et al. Characterization food allergy. Allergy. 2017;72:671‐674. of asparagus allergens: A relevant role of lipid transfer proteins. 90. Skypala IJ, Cecchi L, Shamji MH, Scala E, Till S. Lipid Transfer Protein J Allergy Clin Immunol. 2002;110:790‐796. allergy in the United Kingdom: Characterization and comparison 70. Rodriguez MJ, Aranda A, Fernandez TD, et al. LPS promotes Th2 with a matched Italian cohort. Allergy. 2019;74:1340‐1351. dependent sensitisation leading to anaphylaxis in a Pru p 3 mouse 91. Sánchez‐López J, Tordesillas L, Pascal M, et al. J. Role of Art v 3 in model. Sci Rep. 2017;7:40449. pollinosis of patients allergic to Pru p 3. J Allergy Clin Immunol. 71. Rosace D, Gomez‐Casado C, Fernandez P, et al. Profilin‐mediated 2014;133:1018‐1025. food‐induced allergic reactions are associated with oral epithelial 92. Faber MA, Van Gasse AL, Decuyper, II, et al. IgE‐reactivity profiles remodeling. J Allergy Clin Immunol. 2019;143:681‐690. to nonspecific lipid transfer proteins in a north western European 72. Rojas Pérez‐Ezquerra P, Sánchez‐Morillas L, Davila‐Ferandez G, country. J Allergy Clin Immunol. 2017;139:679‐682. et al. Contact urticaria to Cannabis sativa due to a lipid transfer 93. Tordesillas L, Sirvent S, Díaz‐Perales A, et al. Plant lipid transfer protein (LTP). Allergol Immunopathol. 2015;43:231‐233. protein allergens: no cross‐reactivity between those from foods 73. Larramendi CH, López‐Matas MÁ, Ferrer A, et al. Prevalence of and olive and Parietaria pollen. Int Arch Allergy Immunol. sensitization to Cannabis sativa. Lipid‐transfer and thaumatin‐like 2011;156:291‐296. proteins are relevant allergens. Int Arch Allergy Immunol. 94. Ciprandi G, Del Barba P, Silvestri M, Barberi S, Tosca MA. Pru p 3 2013;162:115‐22. sensitization in children with allergy to Parietaria pollens. Acta 74. Decuyper, II, Rihs HP, Van Gasse AL, et al. Cannabis allergy: what Biomed. 2019;90:265268. the clinician needs to know in 2019. Expert Rev Clin Immunol. 95. Scala E, Abeni D, Pomponi D, et al. Ole e 1, Ole e 7, and Ole e 9: 2019;15:599‐606. Identifying distinct clinical subsets of olive tree‐allergic patients. 75. Metz‐Favre C, Pauli G, Bessot JC, De Blay F. Molecular allergology J Allergy Clin Immunol. 2016;137:629‐631. in practice: an unusual case of LTP sensitization. Eur Ann Allergy Clin 96. Oeo‐Santos C, Navas A, Benedé S, et al. New insights into the Immunol. 2011;43:193‐195. sensitization to nonrelated nsLTPs from pollen and food: New role 76. Drouet M, Hoppe A, Moreau AS, Bonneau JC, Leclere JM, Le Sellin of the allergen Ole e 7. Allergy. 2019. J. Cannabis and crossed allergy with food. Rev Pneumol Clin. 97. Rial MJ, Sastre J. Food allergies caused by allergenic lipid transfer 2017;73:290‐293. proteins: what is behind the geographic restriction? Curr Allergy 77. Ebo DG, Swerts S, Sabato V, et al. New food allergies in a European Asthma Rep. 2018;18:56. non‐Mediterranean region: is Cannabis sativa to blame? Int Arch 98. Christensen LH, Holm J, Lund G, Riise E, Lund K. Several distinct Allergy Immunol. 2013;161:220‐228. properties of the IgE repertoire determine effector cell degranula- 78. Decuyper, II, Van Gasse AL, Faber MA, et al. Exploring the diag- tion in response to allergen challenge. J Allergy Clin Immunol. nosis and profile of cannabis allergy. J Clin Immunol. Pract. 2019;7: 2008;122:298‐304. 983‐989. 99. Scala E, Alessandri C, Bernardi ML, et al. Cross‐sectional survey on 79. Decuyper, II, Faber MA, Sabato V, et al. Where there’s smoke, immunoglobulin E reactivity in 23,077 subjects using an allergenic there’s fire: cannabis allergy through passive exposure. J Allergy molecule‐based microarray detection system. Clin Exp Allergy. Clin Immunol Pract. 2017;5:864‐865. 2010;40:911‐921. 80. Nayak AP, Green BJ, Sussman G, et al. Characterization of Cannabis 100. Barber D, de la Torre F, Feo F, et al. Understanding patient sativa allergens. Ann Allergy Asthma Immunol. 2013;111:32‐37. sensitization profiles in complex pollen areas: a molecular 81. García‐Sellés FJ, Díaz‐Perales A, Sánchez‐Monge R, et al. Patterns of epidemiological study. Allergy. 2008;63:1550‐1558. Reactivity to lipid transfer proteins of plant foods and Artemisia 101. Barber D, de la Torre F, Lombardero M, et al. Component‐resolved pollen: an in vivo study. Int Arch of Allergy Immunol. 2002;128. 115‐22. diagnosis of pollen allergy based on skin testing with profilin, 82. Enrique E, Ahrazem O, Bartra J, et al. Lipid transfer protein is polcalcin and lipid transfer protein pan‐allergens. Clin Exp Allergy. involved in rhinoconjunctivitis and asthma produced by rice inha- 2009;39:1764‐1773. lation. J Allergy Clin Immunol. 2005;116:926‐928. 102. González‐Mancebo E, González‐de‐Olano D, Trujillo MJ, et al. 83. Gao ZS, Yang ZW, Wu SD. Peach allergy in China: a dominant role Prevalence of sensitization to lipid transfer proteins and profilins in for mugwort pollen lipid transfer protein as a primary sensitizer. a population of 430 patients in the south of Madrid. J Investig J Allergy Clin Immunol. 2013;131:224‐225. Allergol Clin Immunol. 2011;21:278‐82. SKYPALA ET AL. - 13 103. Basagaña M, Elduque C, Teniente‐Serra A, Casas I, Roger A. 116. Ebo DG, Ahrazem O, Lopez‐Torrejon G, Bridts CH, Salcedo G, Clinical profile of lipid transfer protein syndrome in a Mediterra- Stevens WJ. Anaphylaxis from mandarin (Citrus reticulata): iden- nean area. J Investig Allergol Clin Immunol. 2018;28:58‐60. tification of potential responsible allergens. Int Arch Allergy Immu- 104. Pascal M, Vazquez‐Ortiz M, Folque MM, et al. Asymptomatic nol. 2007;144:39‐43. LTP sensitisation is common in plant‐food allergic children from 117. Schad SG, Trcka J, Vieths S, et al. Wine anaphylaxis in a German the Northeast of Spain. Allergol Immunopathol (Madr). 2016;44: patient: IgE‐mediated allergy against a lipid transfer protein of 351‐358. grapes. Int Arch Allergy Immunol. 2005;136:159‐164. 105. Mastrorilli C, Tripodi S, Caffarelli C, et al. Endotypes of pollen‐food 118. Gülsen A, Jappe U. Lipid transfer protein sensitization in an apple‐ syndrome in children with seasonal allergic rhinoconjunctivitis: a allergic patient: a case report from northern Europe. Eur Ann molecular classification. Allergy. 2016;71:1181‐1191. Allergy Clin Immunol. 2019;51:80‐83. 106. Ciprandi G, De Amici M, Di Martino ML, Barocci F, Comite P. The 119. Ukleja‐Sokołowska N, Gawrońska‐Ukleja E, Żbikowska‐Gotz M, impact of age on Pru p 3 IgE production in Italy. Asia Pac Allergy. Sokołowski Ł, Bartuzi Z. Recurrent anaphylaxis in patient allergic 2017;7:42‐47. to eggplant ‐ a Lipid transfer protein (LTP) syndrome. Asian Pac J 107. Pastorello EA, Robino AM. Clinical role of lipid transfer proteins in Allergy Immunol. 2018;36:109‐112. food allergy. Mol Nutr Food Res. 2004;48:356‐362. 120. Anantharachagan A, Sammour R, Vijayadurai P. Non‐specific lipid 108. Asero R, Pravettoni V. Anaphylaxis to plant‐foods and pollen transfer protein allergy in United Kingdom. Ann Allergy Asthma allergens in patients with lipid transfer protein syndrome. Curr Opin Immunol. 2019;123:618‐620. Allergy Clin Immunol. 2013;13:379‐385. 121. Ma S, Nie L, Li H, Wang R, Yin J. Component‐resolved diagnosis of 109. Cuesta‐Herranz J, Barber D, Blanco C, et al. Differences among peanut allergy and its possible origins of sensitization in China. Int pollen‐allergic patients with and without plant food allergy. Int Arch Arch Allergy Immunol. 2016;169:241‐248. Allergy Immunol. 2010;153:182‐192. 122. Murad A, Katelaris CH, Baumgart K. A case study of apple seed and 110. Scala E, Villalta D, Uasuf CG, et al. An atlas of IgE sensitization grape allergy with sensitization to nonspecific lipid transfer pro- patterns in different Italian areas. A multicenter, cross‐sectional tein. Asia Pac Allergy. 2016;6:129‐132. study. Eur Ann Allergy Clin Immunol. 2018;50:217‐225. 123. Obeso D, Mera‐Berriatua L, Rodríguez‐Coira J, et al. Multi‐omics 111. Rodrigues‐Alves R, Lopez A, Pereira‐Santos MC, et al. Clinical, analysis points to altered platelet functions in severe food‐associated anamnestic and serological features of peach allergy in Portugal. respiratory allergy. Allergy. 2018;73:2137‐2149. Int Arch Allergy Immunol. 2009;149:65‐73. 124. Lund G, Brand S, Ramos T, et al. Strong and frequent T‐cell re- 112. Azofra J, Berroa F, Gastaminza G, et al. Lipid transfer protein sponses to the minor allergen Phl p 12 in Spanish patients IgE‐ syndrome in a non‐Mediterranean area. Int Arch Allergy Immunol. sensitized to profilins. Allergy. 2018;73:1013‐1021. 2016;169:181‐188. 113. Fernández‐Rivas M, Bolhaar S, González‐Mancebo E, et al. Apple allergy across Europe: how allergen sensitization profiles deter- mine the clinical expression of allergies to plant foods. J Allergy Clin Immunol. 2006;118:481‐488. 114. Gaier S, Oberhuber C, Hemmer W, et al. Pru p 3 as a marker for How to cite this article: Skypala IJ, Asero R, Barber D, et al. symptom severity for patients with peach allergy in a birch pollen Non‐specific lipid‐transfer proteins: Allergen structure and environment. J Allergy Clin Immunol. 2009;124:166‐167. function, cross‐reactivity, sensitization, and epidemiology. Clin 115. Mothes‐Luksch N, Raith M, Stingl G, et al. Pru p 3, a marker allergen for lipid transfer protein sensitization also in Central Transl Allergy. 2021;1–13. https://doi.org/10.1002/clt2.12010 Europe. Allergy. 2017;72:1415‐1418.