Ontogenetic development and distribution of antibody transport and Fc receptor mRNA expression in rat intestine.

The intestine of the suckling rat has the unique capacity of absorbing immunoglobulins from maternal milk. We investigated intestinal Fc receptor mRNA expression and the absorption of orally administered antibodies to delineate the ontogeny and tissue specificity of this transport system. Duodenal expression of Fc receptor mRNA was at maximum levels between 1 and 19 days of age, but was not detectable during fetal life and in animals after weaning. Along the horizontal axis of the intestine, FcRn mRNA expression was maximum in the proximal duodenum and declined gradually in distal bowel. Similarly, absorption of orally administered antibody was low shortly after birth, but reached maximum levels at 14 days of age. By the time of weaning, antibody uptake had almost completely ceased. These data further delineate the temporal and spatial nature of the intestinal immunoglobulin transport system, and represent additional examples of how the intestinal Fc receptor is transcriptionally regulated.