Incomplete elimination of the ABBOS epitope of bovine serum albumin under simulated gastrointestinal conditions of infants

OBJECTIVE - Because the bovine serum albumin residues 126-144 (ABBOS) have been reported to be responsible for the autoimmune reaction directed against pancreatic islet cells, it was our aim to study the potential survival of the ABBOS epitope during digestion in the gastrointestinal tract. RESEARCH DESIGN AND METHODS - Either nontreated (commercially available) or heat-treated bovine serum albumin (BSA) was hydrolyzed in vitro with pepsin at a pH of 2.0, 3.0, and 4.0 and subsequently with pancreatic enzymes at a pH of 7.5. Cross-reactivity between the ABBOS peptide and the BSA hydrolysates was determined by competitive enzyme-linked immunosorbent assay (ELISA) using a rabbit polyclonal antibody raised against the ABBOS peptide in BSA. RESULTS - Biochemical findings clearly showed that the degradation of BSA during simulated physiological digestion depended on its conformation and on the pH of its pepsin-catalyzed hydrolysis. Raising the pH of the pepsin-catalyzed hydrolysis from 2.0 to 4.0 decreased the efficiency of the process, especially when BSA had first been denatured by heat treatment. As a consequence, a large proportion of the cross-reactive anti-ABBOS antibody-binding sites was still intact in the final hydrolysates. CONCLUSIONS - The present results suggest that the ABBOS epitope of BSA will not be completely eliminated during digestion under conditions that prevail in the stomach of infants (pH 3-4).