MADRID—Does melon allergy result from pollen exposure? This hypothesis comes from a Spanish study that has provided new details on the clinical characteristics of melon (Cucumis melo) allergy.[1] Among the conditions linked to melon sensitization were pollen allergy, allergy to other nonrelated fruits, and latex sensitivity. Perhaps most clinically interesting was the finding that the pollinosis in the melon allergy patients often occured in association with asthma.

Javier Cuesta-Herranz, MD, one of the lead investigators, said that the association suggests the novel possibility that the higher frequency of asthma among pollen-allergic patients might be linked to melon allergy. If confirmed, he speculated, one could infer that “fruit allergy in general, and melon allergy in particular, would be a risk factor for asthma among pollen-allergic patients.”

ASSESSING FOR SENSITIVITY

The researchers evaluated 66 patients with melon allergy and 95 control patients with pollen allergy (to compare pollen allergy between the two groups). Participants provided a detailed clinical history and completed an extensive de-mographic and allergy questionnaire.

Diagnosis of melon allergy was based on a convincing clinical history, a positive result on skin prick testing (SPT) with fresh melon pulp, and a positive result on oral challenge. The oral challenge test involved chewing, then swallowing, a portion of melon pulp until a positive response was obtained or the sample was eaten without symptoms; all patients as well as controls with evidence of melon allergy completed this test. SPT was also performed to test for allergy to other fresh fruits and a range of common allergens.

CHARACTERISTICS OF MELON ALLERGY

All of the patients in the melon allergy group (mean age, 27) had both a positive SPT result and oral symptoms. Of the 13 patients (19.7%) who also had extraoral symptoms, five reported gastrointestinal complaints, three reported conjunctivitis, three reported contact urticaria, one reported rhinitis, and one reported contact urticaria and conjunctivitis. Oral symptoms always preceded extraoral symptoms, and no one with melon allergy experienced generalized urticaria or anaphylaxis. Most of the patients had begun to experience symptoms before age 20.

Almost 14% of the control patients had a positive SPT to fresh melon pulp, but only 7.4% of this subset had melon allergy based on both this test and oral challenge.

POLLINOSIS AND MELON ALLERGY

All of the patients with melon allergy were sensitized to pollens and had symptoms of pollen allergy. Sensitization frequency to grass, tree, and weed pollens was especially high in these patients—the lowest sensitization frequency was a robust 65.6% for Artemisia allergen. In comparison to the controls, the patients with melon allergy were markedly more likely to be sensitized to Ulmus glaba, Ambrosia trifida, and Chonopodium album. Another important difference between the two groups was that the patients with melon allergy were more than twice as likely to have asthma as were the controls.

The biology behind the melon allergy/asthma association might begin with sensitization to a panallergen common to melon and several taxonomically nonrelated fruits, Dr. Cuesta-Herranz said. “In patients sensitized to a panallergen, any pollen in the atmosphere would be an allergen for the patient, eliciting higher levels of antigenic exposition, [and in turn] eliciting a higher frequency of asthma.”

A temporal pattern in the presentation of allergy was also identified. Most patients with melon allergy exhibited pollen allergy first (67%). Fewer individuals with melon allergy actually had a melon allergy first (23%), and still fewer developed both types of allergy within the same year (11%).

MELON ALLERGY AND OTHER FOODS

To some extent, most of the fresh fruits and nuts tested caused skin reactions in the patients with melon allergy. The most notable allergy was to kiwis, which elicited a positive SPT result in 92% of the patients. Other frequent elicitors of an allergy response on SPT were figs, peaches, pears, apples, and grapes. However, many of these positive skin test reactions were not matched by oral symptoms when the food was eaten. This discrepancy, Dr. Cuesta-Herranz emphasized, should be kept in mind when evaluating food allergy in these patients.

Consumed foods other than melon that most often caused oral manifestations were peaches (62% had symptoms), figs (48%), and kiwis (42%). Nearly 50% of melon-allergic patients were also sensitized to nuts, walnuts and hazelnuts being the most frequently implicated (in 35% and 18% of patients, respectively). Dr. Cuesta-Herranz said that these data probably indicate immunologic and clinical cross-reactivity. “We are now investigating these findings, but it is clear that profilin, carbohydrate–cross-reactive determinant, and other antigens might be involved in these reactions.”

LATEX SENSITIVITY

SPT also revealed that 23% of the melon-allergic patients were sensitized to latex, though only 13% of them exhibited clinical latex allergy. This so-called latex-fruit syndrome, Dr. Cuesta-Herranz said, is common in persons with latex sensitivity but typically involves other fruits, mainly bananas, avocados, and chestnuts. In patients who are allergic to latex, concomitant pollen allergy seems to be a key factor in sensitivity to other foods, including melon, he suggested.

The mechanism linking fruit and latex allergy has been attributed to cross-reactivity of the class I chitinases. “Chitinases are proteins that hydrolytically degrade chitin from within the polymer,” he explained. “Class I chitinases in plant-derived foods have high structural homology with Hev b6, or hevein, a major latex allergen.”

—Verna L. Schwartz, MS