Figure 1.

Current models of perforin granzyme synergy to induce apoptosis. There are two models to explain the synergistic effect between granzymes and perforin to induce apoptosis in a target cell. Both models are similar in regards to the process by which cytotoxic granules are produced by the effector cell. The difference lies at the target cell membrane surface. In Model 1, perforin forms a pore on the plasma membrane of the target cell allowing granzyme to be delivered to induce apoptosis (A). In model 2, granzyme and perforin are released from the cytotoxic granule, enter the target cell, and are then repackaged within the endosome. Perforin then forms a pore within the endosome, disrupting the membrane integrity, allowing granzyme to escape and induce apoptosis (B).