Biochemical and clinical studies in a case of contact urticaria to potato.

Contact urticaria to potato was confirmed by skin testing in a 26-year-old male with atopic dermatitis, birch-pollen rhinoconjunctivitis and a history of immediate finger itching upon handling raw potato. The potato peel was non-reactive. The urticarial reactivity to potato could be transferred by the patient's serum in a Prausnitz-Küstner test, indicating an immunological etiology. Electrophoretic and chromatographic examination of extracts from homogenized potatoes (unexposed to synthetic fertilizers and insecticides) revealed allergenic activity in a heat-labile macromolecular fraction with a mass of 20-30 kdalton migrating towards the anode during agarose gel electrophoresis at pH 8.6 with a mobility similar to that of human alpha 1-antitrypsin. The technique used for preliminary fractionation of the allergenic activity in a potato extract, similar to crossed immunoelectrophoresis, appears to be a simple and widely applicable technique for the characterization of proteins with this biological activity. A partially purified fraction with allergenic activity, seemingly more stable than the activity in crude homogenates, was obtained by gel filtration and preparative agarose gel electrophoresis. When an antihistamine was also injected, the urticarial reaction to the protein fraction was less pronounced. Pretreatment of the skin with compound 48/80, a histamine releaser, blocked the reaction. Histamine thus seems to be the major vasoactive substance mediating the contact urticarial response to potato antigen in this patient.