The effect of immunization with protein-hapten conjugate on the intestinal uptake of p-aminobenzoic acid as a hapten.

Intestinal uptake of p-aminobenzoic acid was examined by means of an in vitro everted sac technique in rats immunized with ovalbumin-p-aminobenzoic acid conjugate. A dose-dependent and antigen-specific decrease in the serosal transfer of p-aminobenzoic acid was observed in rats immunized 6 times with protein-hapten conjugate compared with the control. There was a significant increase in the recovery of p-acetamidobenzoic acid, a metabolite of p-aminobenzoic acid, in mucosal fluid, tissue, and serosal fluid in the jejunum. In the case of ileum, increase of p-acetamidobenzoic acid was observed in mucosal fluid. However, there was no significant effect in the ileal p-acetamidobenzoic acid in tissue and serosal fluid between immunized and non-immunized rats. To examine the increased metabolism of immunized rats, N-acetyltransferase activity of the small intestinal mucosa was examined. There was a significant increase in mucosal N-acetyltransferase activity in immunized rats compared with the control animals. These observations suggested that the mucosal immune system may play an important role in regulating the intestinal uptake of the low molecular weight compounds.