Abstract
Transepithelial transport of proteins is an important step in the immune response to food allergens. Mammalian meat allergy is characterized by an IgE response against the carbohydrate moiety galactosyl-α-1,3-galactose (α-Gal) present on mammalian glycoproteins and glycolipids, which causes severe allergic reactions several hours after red meat consumption. The delayed reaction may be related to the processing of α-Gal carrying proteins in the gastrointestinal tract. The aim of this study was to investigate how protein glycosylation by α-Gal affects the susceptibility to gastric digestion and transport through the Caco-2 cell monolayer. We found that α-Gal glycosylation altered protein susceptibility to gastric digestion, where large protein fragments bearing the α-Gal epitope remained for up to 2 h of digestion. Furthermore, α-Gal glycosylation of the protein hampered transcytosis of the protein through the Caco-2 monolayer. α-Gal epitope on the intact protein could be detected in the endosomal fraction obtained by differential centrifugation of Caco-2 cell lysates. Furthermore, the level of galectin-3 in Caco-2 cells was not affected by the presence of α-Gal glycosylated BSA (bovine serum albumin) (BSA-α-Gal). Taken together, our data add new knowledge and shed light on the digestion and transport of α-Gal glycosylated proteins.
Highlights
Most glycan antigens do not cause allergic symptoms, during the last decade, the mammalian carbohydrate epitope galactosyl-α-1,3-galactose (α-Gal) has been shown to cause severe allergic reactions [1]
The α-Gal epitope is expressed on non-primate mammalian proteins [2], and patients with mammalian meat allergy have IgE antibodies to α-Gal and report symptoms of anaphylaxis, angioedema, or urticaria 3 to 6 h after red meat consumption [3,4,5]
When cultured on permeable supports, the cells differentiate into a monolayer that is similar to the small intestinal villus epithelium and this monolayer expresses brush border proteins, tight junctions between cells, and is highly polarized [7,8]
Summary
Most glycan antigens do not cause allergic symptoms, during the last decade, the mammalian carbohydrate epitope galactosyl-α-1,3-galactose (α-Gal) has been shown to cause severe allergic reactions [1]. The timing of the symptoms has been confirmed in food challenges where the patients’ basophils were activated in the same timeframe [6]. There is a lack of literature dealing with the fate of α-Gal carrying proteins in the gastrointestinal tract, including processing, uptake and transport of α-Gal carrying proteins by the intestinal epithelium. Enterocytes of the intestinal epithelium are the most important cells for absorbing nutrients from food and at the same time excluding antigenic macromolecules and microbes from crossing the barrier. We investigated the impact of α-Gal glycosylation on protein susceptibility to gastric digestion and whether the α-Gal epitope influences protein transcytosis through the Caco-2 cell monolayer
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