Permeability properties of the postcapillary high-endothelial venules in lymph nodes of the mouse.

The permeability of the postcapillary high-endothelial venules in mice was investigated by light and electron microscopy. Experiments with intravenously injected horseradish peroxidase demonstrated a pronounced intercellular passage of this tracer. Vesicular transport was not observed. Additional experiments with lanthanum and tannic acid showed that no continous tight junctions sealed the intercellular spaces. However, some focal membrane appositions were observed.