Gastrointestinal stability of baker's yeast allergens: an in vitro study

An in vitro model was established to study the stability of baker's yeast (Saccharomyces cerevisiae) allergens in conditions simulating the gastrointestinal tract. The protocol consisted of 2 hr incubation under gastric conditions (pH 1.2, +37 degrees C and gastric enzymes) and 2 hr incubation under duodenal conditions (pH 6.8, +37 degrees C and duodenal enzymes). These were studied together and separately, as well as under pure acidic conditions without gastric enzymes. The yeast extracts contained equal amounts of allergen and were analyzed by IgE-immunoblotting. The acidic conditions had partly an enhancing and slightly degrading effect on the yeast allergens, whereas the gastric enzymes destroyed several allergens, including the important intermediate allergens of 31 and 45 kD. After treatment under both gastric and duodenal conditions most of the yeast allergens were destroyed, except mannan and a 10 kD protein component. The findings suggest that the allergen exposure caused by baker's yeast takes place mainly on the mucosal surfaces orally and oesophageally and through viable baker's yeast organisms that manage to pass the stomach and duodenum and possibly lead to intestinal growth of the organism. Patients with IgE production against the 10 kD allergen and mannan are, however, moderately exposed to allergens consisting of soluble antigenic material only.