Introduction
Barley, a member of the grass family, is a major cereal grain rich in dietary fiber. It has been recognized as a health food because barley beta-glucan lowers cholesterol in the blood1 and is consumed as alcoholic beverages (for example, beer), soups, and cereals worldwide. There are many opportunities to eat cooked barley with rice in childhood in Japan, including school lunch.
Several barley allergies have been reported as cross-reactions to wheat, the third most common cause of immediate food allergy in children in Japan.2 Poupark et al. reported that the percentage of patients with wheat-allergy who were also allergic to barley was 55%, which was higher than that for rye and oats.3Moreover, it has also been reported that 75% of children who showed positivity in the barley oral food challenge test (OFC) were allergic to wheat.4
Immunological cross-antigenicity between wheat and barley has been reported in several studies. Srisuwatchari et al. reported that barley extracts inhibited serum-specific immunoglobulin E (sIgE) bound to wheat gliadin or glutenin by 66% and 53%, respectively, in patients with a wheat allergy, including one defined barley allergy.6In addition, Palsou et al. showed that ω-5 gliadin of wheat has cross-antigenicity with γ-3 hordein, a prolamin of barley, by using the sera of patients with wheat-dependent exercise-induced anaphylaxis (WDEIA).7 Although these two studies showed cross-reactivity between wheat and barley allergen components, neither were examined in sera from patients with a defined barley allergy. No studies have shown clinical cross-reactivity or immunological cross-antigenicity between wheat and barley in patients with barley and wheat allergy. In other words, it is unclear whether allergic reactions to barley in patients with an immediate allergy to wheat are due to individual sensitization or cross-reactivity between both allergens.
Therefore, our study sought to determine the clinical cross-reactivity and immunological cross-antigenicity of wheat and barley. First, to estimate the clinical cross-reactivity of wheat and barley, we compared the results of barley OFCs before oral immunotherapy (OIT) for wheat with those after OIT in patients with a wheat allergy. Next, we evaluated immunological cross-antigenicity by performing enzyme-linked immunosorbent assay (ELISA) inhibition and immunoblotting inhibition using sera from patients allergic to both allergens.