f329 Watermelon

Allergenic molecules

Table adapted: (7-12)

Seven trypsin inhibitors were isolated from the seeds of Cucurbitaceae plants: 2 from cucumber (Cucumis sativus) and red bryony (Bryonia diotica) and 1 from figleaf gourd (Cucurbita ficifolia), spaghetti squash (Cucurbita pepo var. vegetable spaghetti), and watermelon (Citrullus vulgaris). (13) Evaluation for allergenic potential was not conducted.

Cross-reactivity

Extensive cross-reactivity betwen the different individual species of the genus could be expected and has been reported. (14) Cross-reactivity was demonstrated between pumpkin, pumpkin seed, musk melon, watermelon, cucumber and zucchini. (15)

Cit la 2, a profilin, may result in cross-reactivity with other foods containing profilin. Profilins are cross-reactive allergens that bind IgE antibodies of almost 20% of plant-allergic patients. (12) Profilin has been identified as a major IgE-binding component of melon. Amino acid sequences of melon profilin compared with other profilins showed the most identity in the case of watermelon profilin. The melon profilin showed substantial cross-reactivity with profilin from tomato, peach, grape and Bermuda grass pollen. However, cantaloupe, watermelon, banana and Kentucky blue grass displayed no notable cross-inhibition. The study suggests that IgE reactivity to melon profilin strongly depends on the highly conserved conformational structure of the epitope, rather than on a high degree of amino acid sequence identity or even linear epitope identity. (12) An earlier study reported that, as in melon, the profilin of zucchini, cucumber, and watermelon extracts were strongly recognised by the IgE antibodies of the patients with melon allergy. (11)

Hypersensitivity to Bet v 2, a profilin, has been reported to be strongly associated with clinical allergy to citrus fruits (which occurs in 39% of patients monosensitised to Bet v 2, vs 4% of patients monosensitised to Bet v 1), melon or watermelon (67% vs 0%), banana (66% vs 8%), and tomato (33% vs 0%); whereas Bet v 1 sensitivity was associated with clinical allergy to apple (100% vs 39%) and hazelnut (56% vs 0%). A history of allergy to gourd fruits, citrus fruits, tomato, banana, or a combination thereof as a means to predict profilin-hypersensitive patients was 85% (41/48). The specificity of an allergy to any of these fruits exceeded 85%, with positive predictive values ranging between 68% and 91%. The conclusion drawn was that in clinical settings in which laboratory investigations are not easily accessible, allergy to melon, watermelon, citrus fruits, tomato, or banana can be used as a marker of profilin hypersensitivity once a sensitisation to natural rubber latex and lipid transfer protein is ruled out.(16)

In a subsequent study, 200 consecutive patients with pollen allergy underwent skin-prick tests with purified natural date palm profilin (Pho d 2). Sixty patients (30%) showed reactivity to this profilin. Thirty-four of 60 (57%) profilin reactors had food allergy; 21 of these were monosensitised to profilin, 11 were sensitised to both profilin and Bet v 1-homologous protein, 1 to both profilin and LTP, and 1 to all 3 allergens. The large majority of profilin-allergic patients reported oral allergy syndrome as the only food-induced symptom and were able to tolerate the offending foods if they were cooked or otherwise processed. Twenty-eight of 34 reported reactivity to 2 or more plant-derived foods. Rosaceae, tree nuts, melon and watermelon, tomato, pineapple, citrus fruits and banana were the most frequently offending foods. The authors re-iterated that allergy to melon, watermelon, tomato, banana, pineapple or orange may be considered a marker of profilin hypersensitivity. (17)

In a study of the prevalence of and risk factors for latex hypersensitivity among healthcare workers (HCW) in an Italian general hospital, 24 of 672 who responded to the questionnaire, out of a potential total of 1 747 healthcare workers, reported oral allergy syndrome. It was most commonly related to kiwi, tomato, peach and melon/watermelon. Latex-specific IgE was found in 62 out of 1 747 HCW (3.6%). (18)

ELISA inhibition assays demonstrated allergenic similarity among celery, cucumber, carrot, and watermelon. Immunoblots of individual sera showed a 15 kDa protein band common to all 4 foods. The authors conclude that these foods possess shared antigens that may account for the clustering of allergies to them in patients. (19) Cit la 2, a profilin, may have been the allergen responsible.

Allergy to watermelon has been associated with other allergies, e.g. to melon and latex. In a study, the most common foods associated with melon allergy were avocado (n = 7), banana (n = 7), kiwi (n = 6), watermelon (n = 6), and peach (n = 5). (20)

An increased prevalence of food allergies in patients with latex allergy occurs. Among a group of these patients, foods responsible for reactions included banana (9, or 18.3%), avocado (8, or 16.3%), shellfish (6, or 12.2%), fish (4, or 8.1%), kiwi (6, or 12.2%), tomato (3, or 6.1%), watermelon, peach, carrot (2, or 4.1% each), and apple, chestnut, cherry, coconut, apricot, strawberry, and loquat (1, or 2.0% each). (21)

Over the last 3 decades, several authors have described an association between sensitivity to diverse pollens and sensitivity to diverse plant foods. An association between ragweed pollinosis and hypersensitivity to Cucurbitaceae foods (e.g. watermelon, melon, cucumber) and banana has been reported. (22) An association between grass pollinosis and sensitisation to tomato, potato, green pea, peanut, watermelon, melon, apple, orange and kiwi has been reported. (23)

Watermelon and ragweed have been proposed as having similar allergens. Between 28% and 50% of 120 patients whose sera contained specific IgE to ragweed also had specific IgE to 1 or more members of the gourd family studied (watermelon, cantaloupe, honeydew melon, zucchini, and cucumber). In an ELISA system, the extracts of watermelon and ragweed inhibited each other in a dose-dependent manner. (24)