Antigens of Euparipha pisana (Snail)

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Abstract
The data obtained in this study suggest that eating Euparipha pisana (snail), a common food in Mediterranean countries, could give serious allergic reaction such as asthma. We describe here the identification and partial characterization of allergenic molecules form this new source. An aqueous extract of snail was obtained by homogenization in distilled water, centrifugation, dialysis and defatting with ethyl ether. Skin prick test (SPT) performed with the snail extract on 70 subjects allergic to the more common allergens of the Mediterranean area gave a SPT positivity in 61% of the subjects tested, with a mean value of histamine-equivalent prick (HEP) equal to 0.81 ± 0.25 (n = 43), while no SPT-snail-positive reactions were obtained by using the same extract on 30 not allergic subjects. To ascertain if such a sensitivity was IgE-mediated, sera from SPT-snail-positive subjects were analyzed by RAST, coupling the snail extract to polystyrene balls and to paper discs. 19% of the sera tested were RAST-positive, mean value of binding 4.8 ± 2.8% (n = 13), while when using sera from SPT-snail-negative subjects, the RAST mean value was 0.49 ± 0.18% (n = 27). Histamine release (HR) was also performed. Basophils prepared from SPT-snail-positive subjects were incubated with a snail extract. All of the SPT-snail-positive subjects gave a significant value of HR, mean value 21.8 ± 7% using 1 μg of snail extract (n = 16), while 1.41 ± 1.1% (n = 10) was the mean value obtained when SPT-snail-negative subjects were analyzed. The components of the snail extract, fractionated by sodium dodecylsulfate polyacryl-amide gel electrophoresis and then transferred to nitrocellulose membrane, were studied by electroblotting using 10 sera collected from SPT- and RAST-snail-positive subjects. After a reaction with 125I-antihuman IgE and autoradiography, 6 bands were capable of binding human IgE, ranging in molecular weight value from 12,000 to over 66,000 daltons. Finally, a strong cross-reactivity was detected by means of RAST inhibition, between the snail and the Parietaria judaica, Dermatophagoides pharinae and Poa pratensis allergens. The results obtained with four different methods provide evidence that the snail is a new source of allergenic molecules, and leads us to more extensive studies of this type of food allergy.