The Reactions of Pepsin and Pepsin-Trypsin Digestion Products of Bovine Serum Albumin with Antisera from Rabbits Ingesting This Protein

Abstract The effect of digestion by alimentary enzymes on the antigenicity of bovine serum albumin (BSA) was studied by the sequential exposure of this food antigen to pepsin and trypsin under conditions simulating mammalian digestion. The physical degradation was assessed by G-100 chromatography which demonstrated three different molecular weight groups. The first peak of the pepsin digest eluted in the same area as undigested BSA and the last peak was composed mainly of dialyzable peptides. The major alteration caused by trypsin digestion was a decrease in the amount of peak 1. A comparison of the antigenicity of these digests with that of BSA demonstrated that they contained all the antigenic sites of BSA, but in concentrations approximately 1/100 that in the intact molecule. Peak 1 also appeared to have all these sites in an unaltered form whereas the sites in peak 2 appeared to be altered by the digestion. New antigenic sites were demonstrated in peaks 1 and 2 by using antisera from rabbits parenterally immunized with the pepsin digest. However, antisera from animals orally immunized to BSA reacted with the intact protein and the digestion products in a manner identical to antisera from rabbits subcutaneously immunized with BSA. These data suggest that enough surface antigenic sites survive alimentary digestion to sensitize the lamina propria of rabbits. In addition, the recognition of only surface antigenic sites by antisera from orally immunized rabbits implies that these animals are not immunized to the internal determinants uncovered by alimentary digestion.