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Updated: Aug 21, 2026

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability
Published on: June 7, 2022
Functional and morphological studies of protein transcytosis in continuous endothelia
Dan Predescu1, Stephen M Vogel, Asrar B Malik
1Department of Pharmacology, The University of Illinois College of Medicine, Chicago, Illinois 60612, USA.
Abstract:
Continuous microvascular endothelium constitutively transfers protein from vessel lumen to interstitial space. Compelling recent biochemical, ultrastructural, and physiological evidence reviewed herein demonstrates that protein transport is not the result of barrier "leakiness" but, rather, is an active process occurring primarily in a transendothelial vesicular pathway. Protein accesses the vesicular pathway by means of caveolae open to the vessel lumen. Vascular tracer proteins appear in free cytoplasmic vesicles within minutes; contents of transport vesicles are rapidly deposited into the subendothelial matrix by exocytosis. Caveolin-1 deficiency eliminates caveolae and abolishes vesicular protein transport; interestingly, exchange vessels develop a compensatory transport mode through the opening of a paracellular permeability pathway. The evidence supports the transcytosis hypothesis and the concept that transcytosis is a fundamental component of transendothelial permeability of macromolecules.
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