Transfer of functional immunoglobulin G (IgG) antibody into the gastrointestinal tract accounts for IgG clearance in calves.

The transfer of circulating immunoglobulin G1 (IgG1) antibody to the gastrointestinal tract in young calves was quantified by using bovine anti-dinitrophenol IgG1 antibody labeled with 125I. The antibody was administered to newborn calves by intravenous injection, and transfer of the labeled IgG1 to the gastrointestinal tract occurred as demonstrated by excretion of protein-bound label in the feces and by the presence of the labeled IgG1 antibody in the gastrointestinal tract lumen at necropsy. Sixty-eight percent of the [125I]IgG1 clearance occurred by transfer to the gastrointestinal tract. Protein-bound 125I in the gastrointestinal tract lumen retained 65% of the specific dinitrophenol-binding ability of the labeled antibody originally administered. These results show that (i) transfer to the intestinal lumen is the major means of IgG1 clearance in calves, and (ii) this transfer results in antigen-binding antibody in the intestinal tract lumen. The potential contribution to enteric immunity of IgG1 reaching the intestinal lumen from circulation remains to be determined.