The immunological synapse of CTL contains a secretory domain and membrane bridges

Cytotoxic T lymphocytes (CTL) rapidly destroy their targets. Here we show t hat although target cell death occurs within 5 min of CTL-target cell conta ct, an immunological synapse similar to that seen in CD4 cells rapidly form s in CTL, with a ring of adhesion proteins surrounding an inner signaling m olecule domain. Lytic granule secretion occurs in a separate domain within the adhesion ring, maintaining signaling protein organization during exocyt osis. Live and fixed cell studies show target cell plasma membrane markers are transferred to the CTL as the cells separate. Electron microscopy revea ls continuities forming membrane bridges between the CTL and target cell me mbranes, suggesting a possible mechanism for this transfer.