Transcytos

Transcytos is a term used in cell biology to describe a vesicle-mediated transcellular transport process in which cargo is moved from one plasma membrane domain to another across a polarized cell, such as an epithelial or endothelial cell. In transcytosis, the cargo is typically contained within membrane-bound vesicles throughout its journey, allowing passage from the basolateral to the apical surface or in the reverse direction without diffusing into the cytosol.

Mechanistically, transcytos begins with endocytosis at the entry surface, followed by vesicular trafficking through the cytoplasm, often along microtubules powered by motor proteins. Endosomal sorting directs the cargo toward the opposite membrane, where exocytosis occurs. The process relies on a coordinated set of molecular players, including Rab GTPases and SNARE proteins, to ensure vesicle docking and fusion at the appropriate membrane domain and to maintain cargo integrity during transit.

Biological contexts discussed in the literature include transport across intestinal and placental barriers, vascular endothelium, and the blood–brain barrier. Physiological examples include receptor-mediated transcytosis of antibodies and albumin, as well as engineered cargoes such as nanoparticles designed to cross epithelial or endothelial barriers. Transcytos can also be exploited by pathogens to traverse barriers and by the immune system to survey tissues.

Regulation and open questions remain. Cargo selectivity, directionality, and the relative contribution of transcytosis versus alternative transport routes vary by cell type and physiological state. The term transcytos is used variably and is not universally standardized, reflecting ongoing research into the fundamental mechanisms of transcellular transport. Related concepts include transcytosis, endocytosis, and exocytosis.