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.