ONTOGENIC DEVELOPMENT AND DISTRIBUTION OF ANTIBODY TRANSPORT AND FC RECEPTOR MESSENGER-RNA EXPRESSION IN RAT INTESTINE

The intestine of the suckling rat has the unique capacity of absorbing immunoglobulins from maternal milk. We investigated intestinal Fc rec eptor mRNA expression and the absorption of orally administered antibo dies to delineate the ontogeny and tissue specificity of this transpor t system, Duodenal expression of Fc receptor mRNA was at maximum level s between 1 and 19 days of age, but was not detectable during fetal li fe and in animals after weaning. Along the horizontal axis of the inte stine, FcRn mRNA expression was maximum in the proximal duodenum and d eclined gradually in distal bowel. Similarly, absorption of orally adm inistered antibody was low shortly after birth, but reached maximum le vels at 14 days of age, By the time of weaning, antibody uptake had al most 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 tra nscriptionally regulated.