Allergen Exposure

A plum is a stone fruit tree in the genus Prunus, family Rosaceae.

There are more than 2 000 varieties of plum cultivated throughout the world. The round, smooth-skinned fruits can be red, yellow, blue or green; P. domestica is usually a purple-black colour, and P. salicina, Japanese plum, tends to be yellow to crimson. In Canada and the US, plums are widely cultivated and dried into prunes. Botanically, all prunes are plums.

Plums are popular as a dessert fruit and are often eaten out of hand, as well as in pastries and preserves. However, the fruit is most readily available dried, under the name ‘prunes’, which are legendary as a laxative.

Allergen Description

The following allergens have been characterised:

Pru d 1, a Bet v 1 homologue. (1)

Pru d 2, a Thaumatin-like protein (TLP). (2)

Pru d 3, a 9 kDa lipid transfer protein. (3, 4, 5, 6, 7)

Pru d 4, a profilin. (8)

The lipid transfer protein tends to concentrate in the skin of Rosaceae fruits; in plum, it predominates as a cell-surface-exposed allergen. (3)

Potential Cross Reactivity

Extensive cross-reactivity between the fruit of the different individual members of the Rosaceae family occurs. (9) However, as judged from reports on the prevalence of allergic reactions (10) and studies on this cross-reactivity, plum, cherry, apricot and peach allergens show overlapping but far from identical specificity. (11, 12, 13) This is illustrated by examples below.

Plum contains a non-specific lipid transfer protein (LTP), Pru d 3, which is highly homologous to the major allergen of peach (4) and may result in cross-reactivity with other LTP-containing foods such as the LTPs of Rosaceae fruits (peach, apricot, cherry, plum and apple), which are major allergens for Mediterranean atopic populations. (14, 15) LTPs may result in cross-reactivity between botanically unrelated foods, as demonstrated for LTPs of maize and peach. (13) However, IgE-binding cross-reactivity due to fruit LTP has varying degrees of clinical relevance. This cross-reactivity is not necessarily accompanied by cross-allergenicity to the corresponding fruits; (2) and elimination diets that rely on total avoidance of a group of foods, or only on the results of allergy testing, may result in unnecessary restriction of foods such as plum. (16) For example, Mal d 3, the apple LTP, has been shown to have significant cross-reactivity to peach, cherry and nectarine, and to a lesser extent to hazelnut and plum. (17) Cowpea LTP has been shown to have high homology to plant LTPs of mung bean (94%), plum (82%), and maize (72%). (5)

Birch pollen-allergic individuals have a high prevalence of oral allergy syndrome (OAS) to fruits and vegetables. In a Japanese study of 843 patients with birch pollen allergy, 378 patients (37%) reported episodes of oral allergy syndrome. The most frequent foods causing OAS were apple, peach and cherry, followed by kiwi, pear, plum and melon. (18) A second study in the same region, investigating spring pollen allergy and OAS, found that the most common allergen was birch tree pollen, affecting 54 of 87 patients (62%). Of this group, 61% reported adverse reactions to fruit and vegetable: apple in 97%, peach in 67%, cherry in 58%, pear in 40%, plum in 40%, and melon in 33%. (19)

Allergy to plum has occasionally been reported to be associated with latex allergy. (20, 21)

Clinical Experience

IgE-mediated reactions

Plum may induce symptoms of food allergy in sensitised individuals. (8, 9, 14, 22, 23, 24, 25, 26, 27, 28) Oral allergy syndrome (OAS) is the most often reported symptom to plum. OAS to fruits from the genus Prunus (plum, cherry, apricot, and peach) has been described as a cluster of hypersensitivities and occurs mostly as a result of the presence of a profilin. (8, 9, 19, 20, 22) As a result of the presence of profilin and lipid transfer proteins, adverse reactions to plum will vary according to geographical locality; for example, severe reactions from lipid transfer protein being more common in Southern Europe, and milder symptoms as a result of profilin being more common in Northern Europe.

In a study conducted at 17 clinics in 15 European cities to evaluate the differences between some northern countries regarding what foods elicit hypersensitivity symptoms, it was reported, according to food-allergic individuals surveyed concerning 86 different foods, that the foods most often eliciting symptoms in Russia, Estonia, and Lithuania were citrus fruits, chocolate, honey, apple, hazelnut, strawberry, fish, tomato, hen’s egg, and cow’s milk; this profile differed from that of Sweden and Denmark, where birch pollen-related foods, such as nuts, apple, pear, kiwi, stone fruits and carrot were the most common causes. The most common symptoms reported were oral allergy syndrome and urticaria. Birch pollen-related foods dominate in Scandinavia, whereas some mugwort-related foods were of more importance in Russia and the Baltic States. Among 1 139 individuals, plum was the 20th-most-reported food, resulting in adverse effects in 21%. (25)

The prevalence of plum allergy varies widely. In a cross-sectional, descriptive, questionnaire-based survey conducted in Toulouse schools to determine the prevalence of food allergies among schoolchildren, with 192 questionnaires reporting a food allergy, allergy to plum was self-reported in 1 individual. (29) However, among patients (mainly adult) with birch pollen allergy, the prevalence of oral allergy syndrome (OAS) to plum varied from 21% in Northern Europe (30) to 37% - 62% in Japan. (16, 17) Authors have suggested that skin-prick tests with commercial extracts of plum and walnut may be usefully employed to detect patients with OAS reacting against allergens. (19)

Anaphylaxis to plum has been reported. (31) Severe adverse reactions to plum may commonly occur as a result of the presence of a lipid transfer protein (LTP). LTPs are the major allergens in patients sensitive to Rosaceae who are not also allergic to birch pollen. (32)

A 32-year-old nurse with latex allergy experienced anaphylactic reactions following the ingestion of several members of the stone fruit family (plum, peach, and nectarine). Within 30 minutes of ingestion of fresh plum, she began to experience vaginal pruritus, generalised erythema, facial swelling, shortness of breath, and the sensation of tightening in her throat. Skin tests were strongly positive to freshly prepared fruit extracts, but serum-specific IgE tests were equivocal or very weakly positive. In vitro latex-specific IgE tests were strongly positive. (18)

Similarly, a 53-year-old man experienced severe dyspnoea and pruritus of both hands 30 minutes after drinking a milkshake containing peach, banana, and grapefruit. A similar episode occurred after eating plum. He subsequently noted itching and urticaria of his hands when wearing natural rubber latex gloves. He was found to be latex-allergic and shown to be sensitised to uncharacterised high-molecular-weight latex proteins that cross-reacted with proteins in plant-derived foods. (19)

A 21-year-old woman began having severe perennial rhinitis 6 months after starting to work in a wholesale fruit storehouse in Southern Italy where large amounts of fruit, including peaches, were handled. Symptoms subsided when she left the workplace for more than 5 days, and relapsed as soon as she was back at work. She subsequently developed severe food allergy to peach, hazelnut, peanut, apricot, plum and tomato. Sensitisation to an LTP was demonstrated. The authors concluded that LTP may induce sensitisation via the respiratory tract due to inhalation of air-dispersed food particles, and that this may precede the onset of food allergy; they suggested that individuals are at risk where high levels of airborne LTP exposure may occur, e.g. from peach fuzz. (33)

Last reviewed: June 2022