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.
Pastorello
Elide A
EA
1st Division of General Medicine Ospedale Maggiore IRCCS, Department of Internal Medicine, University of Milan, Italy.
Pompei
Carlo
C
Pravettoni
Valerio
V
Farioli
Laura
L
Calamari
Ambra Marianna
AM
Scibilia
Joseph
J
Robino
Anna Maria
AM
Conti
Amedeo
A
Iametti
Stefania
S
Fortunato
Donatella
D
Bonomi
Simona
S
Ortolani
Claudio
C
D000328:Adult; D000485:Allergens / Q000276:immunology*; D000595:Amino Acid Sequence / Q000235:genetics; D000707:Anaphylaxis / Q000276:immunology*; D052179:Antigens, Plant; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D003296:Cooking; D004311:Double-Blind Method; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005512:Food Hypersensitivity / Q000276:immunology*; D006801:Humans; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000276:immunology*; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D010940:Plant Proteins; D011487:Protein Conformation; D013696:Temperature; D003313:Zea mays / Q000276:immunology*
D000485:Allergens; D052179:Antigens, Plant; D002352:Carrier Proteins; D010940:Plant Proteins; C511920:lipid transfer proteins, plant; D007073:Immunoglobulin E