Immunochemical Characterization of Tomato Peel and Pulp Extracts

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RATIONALE: Tomatoes (Lycopersicum esculentum) are consumed worldwide and several allergens have been described, including Lyc e 1 (profilin), Lyc e 2 (b-fructofuranosidase) and Lyc e 3 (LTP). The aim of this study was to analyze the in vitro characteristics of peel and pulp tomato extracts in a Spanish population.

METHODS: Tomatoes of the Canary variety were purchased at a local market. Peel and pulp extracts were prepared, separately. Forty-three patients, residing in the Mediterranean Coast of Spain, with a positive skin prick test to peel extract (10 mg of freeze dried material/ml) were enrolled in the study. Specific IgE to peel and pulp extracts was measured by ELISA. The antigenic and allergenic profiles of the extracts were evaluated by SDS-PAGE, 2-D electrophoresis, IEF and immunoblots.

RESULTS: SDS-PAGE of the peel extract showed 7 prominent bands in a molecular weigh range of 8 to 50 kDa. The pulp extract had 2 main bands at 8 and 9 kDa. The protein content of the peel extract was 85 mcg/mg and of the pulp extract 37.5 mcg/mg of freeze-dried material. Twenty two patients had detectable specific IgE against the peel extract and 4 against the pulp. Thirteen sera were used for immunoblots. Five patients (38%) recognized a 45 kDa band (probably polygalacturonase 2A, or Lyc c 2), 4 (30.8%) a 31 kDa band (probably pectinesterase) and 4 (30.8%) a band of 9 kDa (probably LTP).

CONCLUSIONS: Several proteins seem to be implicated in tomato allergy. Most tomato allergic patients are sensitized to peel proteins.