Transcytosis

Transcytosis carries material through a biological cell from one surface to another by combining endocytosis, intracellular vesicle transport and exocytosis. In an epithelial sheet, cargo can enter at the apical surface facing a cavity and leave at the basal or lateral surface facing underlying tissue. This route crosses the cell rather than passing through the gap between neighbouring cells.

An illuminating example is transfer of maternal antibodies across the intestine of a newborn rat. Richard Rodewald followed antibodies carrying an electron-dense ferritin label, and independently followed antibodies recognizable by a peroxidase reaction. Electron microscopy located tracer at the apical surface, in internal tubular vesicles and near release sites at the opposite surface. Experiments used isolated, ligated intestinal segments and control tracers to distinguish selective transport from leakage between cells. The observations establish a route across the epithelial cell, not merely disappearance from the intestinal cavity.^[ref]