Intestinal uptake of macromolecules. Differences in distribution and degradation of protein antigen in control and immunised rats.

The present study examined intraluminal events in the in vivo processing of a protein antigen by the intestine of normal and orally immunised rats. One hour after the administration of 125I-bovine serum albumin (125I-BSA) and unlabelled BSA by gavage, the majority of the radioactivity was found in the distal small intestine of control and immunised rats but there was a difference in the distribution of radioactivity. In contrast with controls, immunised rats retained a lesser percentage of radioactivity in the proximal small intestine and a greater percentage of radioactivity in the distal small intestine. Radioactive substances present in intestinal rinse fluids and mucosal extracts were characterised by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), density gradient ultracentrifugation, and by immunochemical methods. Rinse fluids and mucosal extracts from immunised rats fed 125I-BSA by gavage contained high molecular weight components with characteristics of antigen-antibody complexes. Rinse fluids and extracts of normal rats contained more intact BSA and less fragments of BSA than did rinse fluids and extracts from immunised animals. These findings suggest that oral immunisation alters the distribution of antigen administered into the gut and that immunisation enhances the intraluminal degradation of antigen.