Immunoelectron microscopical demonstration of the absorption of colostral IgG by small intestinal enterocytes in newborn rats.

The protein A-gold technique was used in the cranial, transitional and caudal segments of the small intestine of 12 newborn rats to demonstrate the process of absorption of gold-labelled IgG through the enterocytes. The observation of the attachment of labelled IgG molecules to the wall of coated vesicles suggested a receptor-mediated transport of colostral IgG in the cranial segment of the small intestine. However, intracellular micropinocytotic transport predominated in the transitional and caudal segments of the small intestine. There was no evidence for paracellular transport. Lysosomal structures in the enterocytes did not appear to impede the absorptive activity during the absorption period, which lasted 20 days.