Molecular characterization of contact urticaria in patients with melon allergy.

BACKGROUND: The relevance of contact allergy to plant-related food has recently emerged. Oral allergy syndrome is one of the most characteristic symptoms of fruit allergy, although it also causes systemic reactions. Plant-food allergy is increasing at the same time as pollen allergy, and fruit-induced allergic contact urticaria could be rising as well.

OBJECTIVES: The present study was carried out in order to investigate whether one particular primary melon-peel allergen is responsible for contact urticaria.

METHODS: Fourteen patients presenting with contact urticaria after touching melon peel were evaluated. A melon-peel extract was prepared and analysed by immunoblotting using the patients' sera. Molecular characterization of IgE-binding bands was performed using mass spectrometry. Melon-peel lipid transfer protein (LTP) was purified. Inhibition studies and contact challenge with the protein were performed to confirm IgE reactivity to the purified allergen.

RESULTS: An IgE-binding band of ~8-9 kDa was observed in an immunoblotting assay with all the patients' sera and was identified as an LTP. The melon-peel LTP was purified in two chromatography steps. Inhibition studies confirmed LTP as a major allergen in patients with melon-peel contact urticaria. Contact challenge with melon-peel LTP was performed in five patients, all of whom had positive results, exhibiting itchy erythema and hives in the area of contact.

CONCLUSIONS: This study confirmed our previous findings that melon-peel LTP is a major allergen and is responsible for contact allergy. This knowledge may be used to improve both diagnosis and treatment of patients allergic to melon.