transendocytosis

Transendocytosis is a form of endocytosis in which membrane components such as receptors or ligands are removed from one cell and internalized into a neighboring cell at a cell–cell contact site. The process often results in the transfer of surface proteins between cells and can influence the availability of receptors and ligands on both the donor and recipient cells. Transendocytosis is distinct from trogocytosis in indicating active internalization of membrane proteins by the opposing cell rather than mere transfer of membrane patches.

In immunology and developmental biology, transendocytosis is most prominently described in two contexts. In Notch signaling, ligands such as Delta-like or Jagged are presented by a signal-sending cell and engage Notch receptors on a neighboring signal-receiving cell. The ligand-expressing cell endocytoses the ligand, pulling on the receptor and enabling proteolytic events that activate Notch in the receiving cell. In CTLA-4–mediated regulation, T cells expressing CTLA-4 can capture and internalize CD80 and CD86 from antigen-presenting cells, reducing the costimulatory capacity of the APC surface and dampening T cell activation.

Mechanistically, transendocytosis requires direct cell contact and engagement of membrane proteins, with endocytic and cytoskeletal machinery facilitating internalization. The direction of internalization and the cellular context can vary between systems, influencing downstream signaling or immune regulation. Transendocytosis is of interest for understanding intercellular communication and has implications for developmental signaling and immune modulation.