Incomplete digestion of codfish represents a risk factor for anaphylaxis in patients with allergy

Background: Fish represents one of the most important allergenic foods causing severe allergic reactions. Nevertheless, it has been shown that gastric digestion significantly reduces its allergenic capacity. Objective: In this study, we assessed the absorption kinetics of fish proteins and investigated the clinical reactivity of patients with fish allergy to codfish digested at physiological or elevated gastric pH. Methods: Healthy individuals were openly challenged with codfish and blood samples were evaluated by histamine release for absorbed fish allergens. Patients with allergy were recruited on the basis of previously diagnosed codfish allergy. Fish extracts were digested with gastric enzymes at pH 2.0 and 3.0 and used for histamine release, skin prick tests, and titrated double-blind placebo-controlled food challenges. Results: Ingestion experiments in subjects without allergy revealed absorption of biologically active fish allergens only 10 minutes after ingestion with maximal serum levels after I to 2 hours. Incubation of fish proteins with digestive enzymes at pH 2.0 resulted in a fragmentation of the proteins leading to a reduced biological activity evidenced by a significantly smaller wheal reaction and reduced histamine release. Fish digested at pH 3.0 revealed comparable reactivity patterns as undigested extracts. Moreover, these test materials triggered reactions at 10-fold to 30-fold lower cumulated challenge doses in patients with allergy. Conclusion: Our data indicate the paramount importance of gastric digestion for fish allergens because the quantitatively significant absorption and elicitation of symptoms seemed to take place in the intestine. Clinical implications: Hindered digestion puts patients with fish allergy at risk to develop severe allergic reactions at minute amounts of allergens.