Lipid-transfer protein is the major maize allergen maintaining IgE-binding activity after cooking at 100 degrees C, as demonstrated in anaphylactic patients and patients with positive double-blind, placebo-controlled food challenge results.

BACKGROUND: In a previous study a 9-kd lipid-transfer protein (LTP) was identified as the major allergen of raw maize in a population of 22 anaphylactic patients. However, the stability of this protein in cooked maize is unknown. OBJECTIVE: We investigated the allergenicity of 5 maize hybrids and its modification after different thermal treatments by using sera from anaphylactic patients and patients with positive double-blind, placebo-controlled food challenges. METHODS: Five maize hybrids were extracted by using different methods, obtaining the water-soluble, zein, total zein, glutelin, and total protein fractions. The IgE-binding capacity of the different extracts, both raw and after thermal treatment, was investigated by means of SDS-PAGE immunoblotting. A 9-kd heat-stable allergen was purified by means of HPLC and sequenced. Changes in its secondary structure during and after heating from 25 degrees C to 100 degrees C were monitored by means of circular dichroism. RESULTS: All raw maize hybrids showed similar protein and IgE-binding profiles. The SDS-PAGE of all the heat-treated hybrids demonstrated a decreased number of stained bands in respect to the raw samples. The IgE immunoblotting demonstrated that the major allergen of the water-soluble, total zein, total protein, and glutelin fractions was a 9-kd protein identified by means of amino acid sequence as an LTP and a sub-tilisin-chymotrypsin inhibitor (in total zein fraction). The IgE-binding capacity of this 9-kd protein remained unchanged after thermal treatments, even though circular dichroism demonstrated an altered secondary structure. CONCLUSIONS: Maize LTP maintains its IgE-binding capacity after heat treatment, thus being the most eligible candidate for a causative role in severe anaphylactic reactions to both raw and cooked maize.

Identification of hazelnut major allergens in sensitive patients with positive double-blind, placebo-controlled food challenge results.

BACKGROUND: The hazelnut major allergens identified to date are an 18-kd protein homologous to Bet v 1 and a 14-kd allergen homologous to Bet v 2. No studies have reported hazelnut allergens recognized in patients with positive double-blind, placebo-controlled food challenge (DBPCFC) results or in patients allergic to hazelnut but not to birch. OBJECTIVE: We characterized the hazelnut allergens by studying the IgE reactivity of 65 patients with positive DBPCFC results and 7 patients with severe anaphylaxis to hazelnut. METHODS: Hazelnut allergens were identified by means of SDS-PAGE and IgE immunoblotting. Further characterization was done with amino acid sequencing, evaluation of the IgE-binding properties of raw and roasted hazelnut with enzyme allergosorbent test inhibition, assessment of cross-reactivity with different allergens by means of immunoblotting inhibition, and purification by means of HPLC. RESULTS: All the sera from the patients with positive DBPCFC results recognized an 18- and a 47-kd allergen; other major allergens were at molecular weights of 32 and 35 kd. Binding to the 18-kd band was inhibited by birch extract, indicating its homology with the birch major allergen, and abolished in roasted hazelnut. The 47-kd allergen is a sucrose-binding protein, the 35-kd allergen is a legumin, and the 32-kd allergen is a 2S albumin. Patients with severe anaphylactic reactions to hazelnut showed specific IgE reactivity to a 9-kd allergen, totally inhibited by purified peach lipid-transfer protein (LTP), which was heat stable and, when purified, corresponded to an LTP. CONCLUSIONS: The major allergen of hazelnut is an 18-kd protein homologous to Bet v 1, and the 9-kd allergen is presumably an LTP. Other major allergens have molecular weights of 47, 32, and 35 kd.