Fast ω-gliadin is a major allergen in wheat-dependent exercise-induced anaphylaxis (1)
An immediate-type hypersensitivity to water/salt-insoluble fraction of wheat proteins (gluten), has been considered to underlie in wheat-dependent exercise-induced anaphylaxis.
In skin prick test all patients reacted with gluten and at least two types of gliadins or glutenins. Four of five patients reacted with fast v-gliadin, three reacted with g- gliadin or slow v-gliadin, however, a-gliadin and b- gliadin were found to be less allergenic.
The patients’ sera reacted with these proteins almost parallel to the skin-reaction with a few exceptions. In this dot- blotting test high titer of IgE reacting to gluten was detected in all patients’ sera, and fast v-gliadin was the most potent allergen among these water/ salt-insoluble proteins.
The v-gliadins and g-gliadin caused dose-dependent inhibition of the patients’ serum IgE-binding to solid-phase gluten proteins in all three patients. Almost 100% inhibition was ob- tained at 100 ug/ml of fast w-gliadin (final concentration), however, more of 60% inhibition and somewhat less inhibition were seen with slow w-gliadin as well as g-gliadin.
The incubation with fast v-gliadin of the patient’s serum caused dose-dependent inhibition in the IgE-binding to g-gliadin and slow w-gliadin
The wheat gluten is categorized as gliadins and glutenins. The former consists of a-gliadin, b- gliadin, g-gliadin and w-gliadins, and the latter divided into HMW and LMW. a- gliadin and g-gliadin-like protein (later this was found to be identical to w-5 gliadin) as major allergen for the anaphylaxis. w-gliadins (slow w- gliadin) contain about 40 mol.% glutamine and 30 mol.% proline, whereas w-gliadins (fast w-gliadin) contain higher levels of glutamine (approximately 50 mol.%) and less proline (approximately 20 mol.%). Amino acid sequences of these proteins are largely repetitive, consisting mainly of octapeptides (consensus PQQPFPQQ) flanked by unique short sequences. Repeats of QQXP, QQQXP or QQQQXP for w-gliadins (fast w-gliadin), where X is phenylalanine, isoleucine or leucine in order of predominance, being distinct from the repeat type of the slow v-gliadin. This might account for the strongest allergenicity of the fast v-gliadin.