Transcytosed

Transcytosed refers to molecules or particles that have undergone transcytosis, a cellular transport process that moves cargo across the interior of a cell from one plasma membrane domain to another. In polarized cells such as endothelia and epithelia, cargo is taken up at one surface by endocytosis, trafficked through endosomal compartments across the cytoplasm, and released by exocytosis at the opposite surface. This enables transfer between tissue compartments while maintaining the integrity of barriers like the intestinal lining or the vascular endothelium.

Cargo may reach the opposite surface via receptor-mediated transcytosis, in which binding to a specific receptor triggers uptake and directed vesicular routing, or through non-receptor pathways such as caveolae- or clathrin-mediated endocytosis and macropinocytosis. Well-known examples include maternal IgG antibodies transported across the placenta through the neonatal Fc receptor (FcRn) and the transport of nutrients or proteins across epithelial barriers. In medicine and biotechnology, transcytosis is exploited to deliver drugs or biologics across difficult barriers, such as the intestinal epithelium or the blood–brain barrier, by engineering cargos to engage transcytotic pathways.

Clinical relevance and research focus include understanding how transcytosis contributes to immune protection, nutrient absorption, and barrier function, as well as how pathogens may hijack the pathway. The term transcytosed thus denotes substances that have completed this vesicle-mediated, transcellular transport.