In Vitrostudy of the gastrointestinal stability of celery allergens

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Abstract
The gastrointestinal stability of proteins and allergens from native celery roots was studied by a simple two‐step in vitro procedure. Commercial enzyme tablets that contained peptic and pancreatic enzymes were used to simulate gastric and duodenal conditions respectively. The influence on the whole protein pattern was monitored by SDS‐PAGE. The antigenicity and allergenicity of the three known important allergenic structures of celery were investigated with IgG from two rabbit antisera, IgE from sera of allergic patients with known specificity for individual allergens, and by a mediator release assay utilizing allergen‐specific polyclonal murine IgE. The following allergens were studied: (i) Api g 1, a 16‐kDa celery protein which shares high sequence identity with the major birch pollen allergen. Bet v 1, (ii) celery profilin that belongs to a group of ubiquitous ‘plant pan allergens’ and (Hi) ubiquitous carbohydrate determinants present in many glycans of plant proteins in the mass range of 35–90 kDa. SDS‐PAGE indicated degradation of many proteins under gastric conditions, but immunoblotting showed only a weak influence on the antigenicity and IgE reactivity of the allergens. The protein degradation was clearly enhanced after 45 min of pancreatic digestion. To a weaker degree, all allergens were again recognized on immunoblots. The presence of a considerable residual allergenic activity which seems to resist even duodenal conditions was confirmed by the determination of human IgE specific for the digests using an Enzyme Allergosorbent Test. In addition, competitive IgE inhibition assays and measuring the celery‐induced mediator release of permanently growing RBL‐2H3 cells that had been passively sensitized with celery‐specific murine IgE showed similar results. The generation of small IgE binding peptides (≤ 3 kDa) was tested by ultrafiltration experiments. The whole IgE binding capacity was present in the retentates even after duodenal digestion. We concluded that, like many other allergens from foods and other sources, the allergens of native celery are relatively stable under gastrointestinal conditions and that the residual allergenic activity is mainly due to undigested allergens.