Transport of IGF-I across epithelial cell monolayers.
The absorption of beta-lactoglobulin (BLG) by cultured explants of the normal adult duodenal mucosa has been studied in vitro using immunocytochemical techniques. Membrane filters (1 mm2) were soaked in medium containing BLG and placed on the mucosal surface. Explants were cultured for < or = 60 min, and histological sections were immunostained for BLG. Increasing the BLG concentration in the filters and/or the exposure time increased the number and immunoreactivity of the immunopositive epithelial cells present, suggesting increased BLG absorption. Increased BLG penetration of the duodenal mucosa in untreated coeliac disease was also shown using these techniques. In some studies horseradish peroxidase (HRP) was used as an alternative probe and pin-pointed in epithelial cells by ultracytochemical techniques, confirming vesicular uptake of macromolecules. Colocalisation experiments using BLG and HRP and immunofluorocytochemical techniques suggested linkage between the mechanisms of absorption of both proteins into epithelial cells. Short-term organ culture and protein challenge followed by immunolocalisation has been shown to be of value in studying the absorption of BLG and HRP by the upper small intestine and possibly of other protein macromolecules as well.