Background: Cereal grains are recognized as the cause of adverse reactions in some patients exposed to grain or flour by either inhalation or ingestion. Cereal-related diseases, such as celiac disease and baker's asthma, have been well studied and the causative cereal proteins have been characterized. Although cereals form an essential part of daily nutrition, the allergenic proteins causing symptoms on ingestion in atopic dermatitis (AD) have remained obscure. In this study, we have investigated the allergenic fraction of wheat in AD.
Methods: Skin prick tests (SPT) with a NaCl wheat suspension and the ethanol-soluble wheat gliadin were performed on 18 wheat-challenge-positive or -negative children with AD, six adult AD patients with suspected cereal allergy, and one adult with wheat-dependent exercise-induced urticaria/anaphylaxis. Serum total IgE and specific IgE-antibody levels to wheat and gluten were measured with the radioallergosorbent test (RAST) simultaneously. In addition serum samples of all 25 patients were analyzed by IgE immunoblotting with the ethanol-soluble wheat-protein extract.
Results: Thirteen of the AD children were wheat-challenge-positive, 11/12 of them appeared to be positive with gliadin SPT, and all had an elevated gluten RAST value. Those challenge-negative were negative with both gliadin SPT and gluten RAST. Positive wheat SPT and RAST alone were not associated with positive challenges. Four of the adult patients responded to a cereal-free diet, although only two of them appeared to be positive with gliadin SPT and gluten RAST. A broad and intensive staining of gliadin peptides in IgE-immunoblotting studies was seen in challenge-positive children with positive gliadin SPT and/or gluten RAST. Besides staining of peptides in the main gliadin area of 30–46 kDa, a characteristic finding was the staining of small, <14-kDa proteins with sera of challenge- and gliadin-SPT-positive patients.
Conclusions: We found that wheat-allergic AD patients have IgE antibodies against gliadin that can be detected by both SPT and the sensitive immunoblotting method. This suggests that gliadin peptides are important allergens, and ingestion of wheat causes symptoms of AD. A broad and intensive IgE staining was seen of gliadin peptides against both the previously characterized peptides in the main gliadin area and small, previously uncharacterized peptides of less than 14 kDa. The gliadin SPT and gluten RAST are good screening methods. Further characterization of the IgE-stained gliadin proteins is needed.