A novel wheat gliadin as a cause of exercise-induced anaphylaxis.
BACKGROUND
Food-dependent, exercise-induced anaphylaxis is a severe form of allergy; the reaction is caused by ingestion of a specific food before exercise. This disorder often escapes diagnosis because neither the ingested food nor the exercise alone induces the symptoms.


OBJECTIVE
The aim of the study was to characterize the allergens involved in wheat-dependent, exercise-induced anaphylaxis and to describe the clinical outcome in a series of 18 adult patients.


METHODS
All 18 patients had experienced recurrent episodes of generalized urticaria during exercise, 17 patients in association with collapse and 15 patients with an anaphylactic reaction. The symptoms appeared only when the patients had eaten food containing wheat before exercise. Wheat allergens were detected by immunoblotting, purified by gel filtration and reversed-phase chromatography, and subjected to N-terminal sequencing. The IgE-binding ability of the purified proteins was studied by ELISA, and their in vivo reactivity was studied by skin prick testing.


RESULTS
IgE antibodies from pooled patient sera were bound to 65-kd and 40-kd wheat proteins in immunoblotting. The 65-kd allergen was a previously undescribed wheat protein, showing 61% sequence identity to gamma-gliadin, whereas the 40-kd allergen had 100% identity to alpha-gliadin. In ELISA, all 18 patients showed elevated IgE levels to the novel gamma-like gliadin, and 13 of the patients showed elevated IgE levels to the alpha-gliadin. None of the 54 control subjects with wheat allergy, urticaria, or coeliac disease had IgE antibodies to the gamma-like gliadin. The in vivo reactivity of the gamma-like gliadin was verified by positive skin prick test responses in all of the 15 patients who were tested. During the follow-up on a gluten-free or wheat-free diet, 3 patients experienced reactions after having unknowingly eaten wheat before exercise, but all the other patients who were adhering to the diet remained symptom-free.


CONCLUSIONS
This study shows that wheat is a frequent cause of food-dependent, exercise-induced anaphylaxis and suggests that the major allergen is a previously undescribed gamma-like gliadin. For screening of this life-threatening allergy, we recommend skin prick testing with crude gliadin and we recommend a gluten-free diet for treatment.
D000293:Adolescent; D000328:Adult; D000485:Allergens / Q000737:chemistry; D000595:Amino Acid Sequence; D000707:Anaphylaxis / Q000209:etiology*; D002352:Carrier Proteins / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay; D015444:Exercise; D005512:Food Hypersensitivity / Q000209:etiology / Q000276:immunology; D005903:Gliadin / Q000009:adverse effects*; D006801:Humans; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000097:blood / Q000378:metabolism; D008875:Middle Aged; D010940:Plant Proteins / Q000097:blood / Q000276:immunology; D014581:Urticaria / Q000178:diet therapy / Q000517:prevention & control