Oral immunization specifically inhibits intestinal protein uptake in the common carp Cyprinus carpio L.

It is well established that a part of orally administered protein is absorbed as macromolecules in the intestine of fish, and is transported into the blood circulation. These protein molecules can induce immune responses including antibody production in fish. In this study, human gammaglobulin (HGG) was orally administered to the common carp immunized previously with a repeated oral dosage of HGG, to clarify the effect of oral immunization on intestinal protein uptake in fish. After intubation, plasma HGG concentration is significantly lower in immunized fish than in the control. HGG was also injected intravascularly for analysis using pharmacokinetic calculations to obtain blood resident time and enteric absorption rate of HGG. Intestinal absorption of orally administered HGG decreased antigen-specifically in immunized fish, while clearance from the blood did not augment significantly. This indicates that an intestinal immunological barrier developed after oral immunization inhibited protein uptake via the alimentary canal in carp.