Trogocytosis

Trogocytosis (trogo; gnaw) is when a cell nibbles another cell. It is a process whereby lymphocytes (B, T and NK cells) conjugated to antigen-presenting cells extract surface molecules from these cells and express them on their own surface. The molecular reorganization occurring at the interface between the lymphocyte and the antigen-presenting cell during conjugation is also called "immunological synapse". First indication for the existence of this process dates back late 70s when several research groups reported on the presence of unexpected molecules such as Major Histocompatibility complex molecules (MHC) on T cells. The notion that membrane fragments, and not isolated molecules, could be captured by T cells on antigen-presenting cells was suggested by the capture of MHC molecules fused to the green fluorescent protein (GFP) in their intracellular portion. The demonstration that membrane fragments were involved in this transfer process came when fluorescent probes incorporated in the plasma membrane of the antigen-presenting cell as well as non-MHC molecules were found to be captured by T cells together with the antigen. Trogocytosis has been initially documented in T, B, and NK cells both in vivo and in vitro. On T cells and B cells, trogocytosis is triggered when the T cell receptor (TCR) on T cells or B cell receptor (BCR) on B cells interacts with the antigen recognized on antigen-presenting cells. Like in lymphocytes, trogocytosis occurs with PMN (polymorphonuclear leukocytes, also known as granulocytes) and is associated with effective ADCC (Antibody dependent cell mediated cytotoxicity). It was shown that in order to initiate ADCC in vitro, PMN's have to adhere to their target cells and form tight junctions with antibody opsonized tumor cells. This cell clustering precedes mutual membrane lipid exchange between effector and target cell during ADCC and does not happen in the absence of opsonizing antibodies. Trogocytosis also occurs in monocytes, and dendritic cells.