Latin name: Pyrus communis
Source material: Peel from fresh fruit
A food, which may result in allergy symptoms in sensitised individuals.
Pear is a pomaceous fruit produced by a tree of the genus Pyrus, classified within Maloideae, a subfamily of Rosaceae. Apple is also a member of this subfamily. Peach and apricot are also members of the Rosaceae family. Pears are thought to have originated in China. The pear tree grows wild in western Asia and eastern Europe, but many varieties are under cultivation. Pears are now found in coastal and mildly temperate regions, from Western Europe to North Africa and clear across Asia. There are about 30 primary species, major subspecies, and naturally occurring interspecific hybrids of pear. Several thousand varieties are known. (1)
The enormous number of varieties of the cultivated European pear (Pyrus communis), are probably derived from 1 or 2 wild species (P. pyraster and P. caucasica), widely distributed throughout Europe. These sometimes form part of the natural vegetation of forests in Europe. Asian species with medium to large edible fruit include P. pyrifolia, P. ussuriensis, P. x bretschneideri, P. x sinkiangensis, and P. pashia.
Pear trees are medium-sized, reaching 10–17 m, often with a tall, narrow crown. A few species are shrubby. The leaves are alternately arranged, simple, 2 to 12 cm long, glossy green for some species, densely silver-haired in some others; leaf shape varies from broad oval to narrow lanceolate. Most pear trees are deciduous, but 1 or 2 species in south-east Asia are evergreen.
Pear tree flowers are white, rarely tinted yellow or pink, 2 to 4 cm in diameter, and have 5 petals. Like apple, pear fruit is a pome. In most wild species it is 1 to 4 cm in diameter. In some cultivated forms it may be up to 18 cm long and 8 cm broad; the shape varies from oblate to globose to the classic pyriform ‘pear shape’ of the European pear, with an elongated basal portion and a bulbous end.
The pear is very similar to the apple in cultivation, propagation and pollination.
The fruit is composed of the receptacle or upper end of the flower-stalk (the calyx tube) which is greatly dilated, and encloses within its cellular flesh the 5 cartilaginous carpels, which constitute the ‘core’ and are really the true fruit. From the upper rim of the receptacle are the 5 sepals, the 5 petals, and the very numerous stamens. Quince and apple are major relatives of the pear.
Pears may be eaten raw or cooked, or may be used for the manufacture of alcoholic beverages such as Perry (a cider).
The following allergens have been characterised:
Pyr c 1, a major allergen, a Bet v 1 homologue, a Group 1 Fagales-related protein. (2, 3, 4, 5)
Pyr c 3, a lipid transfer protein. (2, 6)
Pyr c 4, a 14 kDa protein, a major allergen, a profilin. (2, 5, 7, 8)
Pyr c 5, a 30-35 kDa protein, an isoflavone reductase (IFR). (2, 9, 10, 11)
A study reported that peels of Rosaceae fruits such as apple, peach, and pear have a higher allergenicity than the pulps. In 33 patients allergic to these fruits, adverse reactions were reported to appear more frequently and to be more severe when the whole fruit was eaten. More than 40% of patients allergic to apple and pear tolerated the ingestion of the pulp of these fruits, and reactions were elicited only by the intake of the whole fruit. (12)
Foods belonging to the order Rosacea – which includes apple, pear, peach and almond – most commonly cause symptoms in birch-allergic patients. Bet v 1, the major birch tree pollen allergen, accounts for most of the pollen’s cross-reactivity. (13) In areas where birch pollen is an important aeroallergen, there is an association between spring pollen allergy and allergy to pear and apple. (5, 14, 15, 16) However, studies have shown that although the related major allergens Bet v 1 (from birch pollen) and Mal d 1 (from apple) inhibit to a high degree the binding of IgE to pear Pyr c 1, Api g 1 from celery – also belonging to this family – had little effect, indicating epitope differences between Bet v 1-related food allergens. (3) A number of other factors also influence cross-reactivity between foods and plants containing a Bet v 1-homologous protein. For example, the prevalence of birch-fruit syndrome varies depending on geographic location. The primary sensitisation in birch-fruit syndrome is to birch pollen, and the symptoms elicited by foods are a secondary phenomenon. (17) The primary allergen responsible for these phenomena is a Bet v 1 homologue.
However, pear allergens detectable by birch pollen-sensitised patients were shown to be closely related to and to cross-react not only with Bet v 1, but also with Bet v 2. (5) For example, 18 of 20 pollen-allergic patients studied had IgE antibodies against pear allergens; 14 of them reacted to a Bet v 1 homologue, and 4 to the Bet v 2 homologue (profilin). In addition, a 35 kDa birch pollen allergen was shown to be related to a pear allergen. (14) The 35 kDa protein was subsequently identified as Bet v 5. (18)
In Mediterranean areas like central Spain (and probably other areas), where Betulaceae pollens are not important, allergy against Rosaceae fruits may be completey unrelated to pollen allergy. In such cases the disease is often severe, generally with systemic reactions and with a high frequency of anaphylaxis. (19) The causative allergen is most probably a lipid transfer protein that not only results in severe allergy but also cross-reacts with other lipid transfer protein-containing foods. (20) Patients with clinical reactivity to pear had IgE antibodies to pear and related Rosaceae fruits, but not to pollens, Bet v 1 or Bet v 2. Possible allergenic relations between pear and latex have been discussed but have not been confirmed by data. (21)
The influence of lipid transfer proteins is similarly indicated in a Spanish study of 134 patients with allergy to olive pollen and also allergy to foods. Twenty-one patients were classified as Group A based on symptoms of OAS, and 19 as Group B based on symptoms of anaphylaxis. Patients in Group B were more frequently sensitised to Ole e 7, a lipid transfer protein. Oral challenges confirmed approximately 50% of positive skin-prick tests, with the following positive results: peach (68.4%), pear (50%), melon (71.4%) and kiwi (53.8%). In patients from Group B, there was a significant association between positive skin-prick tests to Rosaceae fruits and to Ole e 3 and Ole e 7. (22)
Pear profilin (Pyr c 4) and cherry profilin (Pru av 4) have a high amino acid sequence identity with birch pollen profilin, Bet v 2 (76-83%), as well as with other allergenic plant profilins. Eighty-eight per cent of 49 patients pre-selected for IgE-reactivity with Bet v 2 showed specific IgE-antibodies to recombinant pear protein; 92% of the sera were positive with the recombinant cherry allergen, and 80% of the sera were reactive with the celery protein. Strong IgE cross-reactivity with profilins from plant foods and birch pollen was shown. However, IgE binding profiles also indicated the presence of epitope differences between related profilins. The authors concluded that cross-reactivity among related profilins may explain pollen-related allergy to food in a minority of patients. (6) A mango profilin isoform, Man I 3.02, was shown to be closely related to the profilin of pear (80%), peach (90%) and apple (80%). (23)
In a Japanese study that investigated spring pollen allergy and OAS, the most common allergen was found to be birch, affecting 62% of 87 patients. Among the patients with birch allergy, apple was the most prevalent allergen (97%), followed by peach (67%), cherry (58%), pear (40%), plum (40%) and melon (33%). (24) Similar results were reported in a recent Japanese study of 843 patients with birch pollen allergy, of whom 37% reported OAS. (25)
Pyr c 5, an isoflavone reductase (IFR), may result in cross-reactivity with other foods containing a similar IFR, e.g. pea, orange, and banana. (9)
In a study of 59 subjects 2 to 40 years old with spina bifida, latex sensitisation was present in 25%. Allergy to pear and kiwi were significantly associated with latex sensitisation. (26)
Pear may result in symptoms of food allergy, anaphylaxis, and (in particular) oral allergy syndrome (OAS), in sensitised individuals. (18, 27, 28, 29) In an Italian study of OAS in patients suffering from pollen allergy and allergic reactions after eating fruits and/or vegetables, allergy to pear was detected in 22%. (18)
Allergy to Rosaceae fruits in patients with a related pollen allergy, usually to birch pollen, is often expressed as OAS. However, allergy to Rosaceae fruits in patients without a related pollen allergy tends to be a severe clinical entity. Profilin- and Bet v 1-related structures are not involved. (18) In Mediterranean areas like central Spain, and probably in other areas where Betulaceae pollens are not important, allergy against Rosaceae fruits may be totally unrelated to pollen allergy. In such cases, the disease is often severe, generally with systemic reactions and a high frequency of anaphylaxis. (18)(See ‘Potential Cross-Reactivity’, above.)
The aim of a study conducted at 17 clinics in 15 European cities was to describe the differences among between northern countries regarding self-reported food hypersensitivity symptoms. Patients with a history of food hypersensitivity were asked to fill in a questionnaire in which 86 different foodstuffs were listed. ‘Slight symptoms’ were most commonly reported. This was the case with pear, which was the 10th-most-often-reported culprit in adverse effects, purportedly affecting 28% of 1 139 individuals. The foods that were most often reported as eliciting symptoms in Russia, Estonia, and Lithuania were citrus fruits, chocolate, honey, apple, hazelnut, strawberry, fish, tomato, hen’s egg, and cow’s milk; which differed from the situation in Sweden and Denmark, where birch pollen-related foods, such as nuts, apple, pear, kiwi, stone fruits, and carrot were the most common causes. (30)
Anaphylaxis and food-dependent, exercise-induced anaphylaxis to pear has been reported. (26, 27) In 2002, 107 cases of severe allergic reactions were reported to the French Allergy Vigilance Network, of which 59.8% were cases of anaphylactic shock (1 being fatal), 18.7% of systemic reaction, 15.9% of laryngeal angioedema, and 5.6% of serious acute asthma (1 fatal). Pear was implicated in only 1 instance. (27)
A 20-year-old women who experienced anaphylaxis to string bean also reported urticaria from ingesting fresh fennel, boiled cabbage, mustard, hazelnut cream and commercial pear juice. (31)
Occupational contact urticaria and contact dermatitis to pear have been reported. (32)
Ingestion of pear fruit juice may result in chronic, non-specific diarrhoea in infancy and childhood. (33)
Pear and Japanese pear (P. pyrifolia) pollen may result in asthma and rhinoconjunctivitis in sensitised individuals. (34, 35)
Compiled by Dr Harris Steinman, email@example.com
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- Scheurer S, Wangorsch A, Nerkamp J, Skov PS, Ballmer-Weber B, Wuthrich B, Haustein D, Vieths S. Cross-reactivity within the profilin panallergen family investigated by comparison of recombinant profilins from pear (Pyr c 4), cherry (Pru av 4) and celery (Api g 4) with birch pollen profilin Bet v 2. J Chromatogr B Biomed Sci Appl 2001;756(1-2):315-25.
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