Digestibility in the gastrointestinal tract and migration to blood of β′-component (Onk k 5), a major salmon roe IgE-binding protein

•Salmon roe allergen (β′-c) orally administered to mice was detected by ELISA.•β′-c passed through the digestive tract without marked degradation.•β′-c was absorbed in the small intestine and circulated in blood stream.•The absorbed β′-c migrated through cytoplasm of the intestinal epithelial cells. The major allergen of chum salmon (Oncorhynchus keta) roe is the β′-component (Onc k 5, β′-c), which is a yolk protein and a fragment of vitellogenin. When yolk content containing β′-c was orally administered to mice, β′-c passed through the gastrointestinal tract and was excreted in feces without marked degradation. The direct administration of β′-c to ligated jejunal and ileal loops showed that β′-c was absorbed through the small intestine and transferred into the blood. Immunohistochemical staining showed that orally administered β′-c was distributed from the apical side to the basal side of intestinal epithelial cells, suggesting that endocytosis may be involved in the intestinal absorption of β′-c. In conclusion, β′-c is absorbed along a large portion of the small intestine and circulates in the blood stream without significant digestion. The resistance of β′-c to gastrointestinal digestion seems to contribute to its strong allergenicity.