Intestinal processing of soluble protein antigen

Abstract

Food and environmental antigens entering the intestine are processed at several levels before interacting with class II molecules and, ultimately, with the antigen receptors of T cells which will regulate the appropriate immune response. Thus: intraluminal digestive enzymes; epithelial transcytosis mechanisms; lysosomal activity of lamina propria macrophages; and mechanisms acting downstream of the mucosa may all have a modifying effect.

In experiments in which pigs were weaned onto a diet containing ovalbumin as the protein source, the survival of the antigen in the intestine was found to be dependent on stomach emptying time and efficiency of intraluminal enzyme activity (both of which were age-dependent). In in vitro experiments, using isolated rat cells, ovalbumin was not degraded by enterocytes as assessed by SDS-PAGE and leupeptin did not suppress effective enterocyte processing mechanisms. However, chloroquine, ammonium chloride and monensin all inhibited “processing” by enterocytes.

The results indicate that the processing changes which take place in the ovalbumin molecule during absorption are dependent on functional endocytic pathways in the enterocyte and are more subtle than the degradative mechanisms characteristic of systemic systems.