Direct Analysis of Individual Killer T Cells: Susceptibility of Target Cells to Lysis and Secretion of Hydrolytic Enzymes by CTL

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Abstract
T cell mediated lysis has been extensively studied using the standard chromium release test (1) which measures semi-quantitatively the activity of cytotoxic T lyphocyte (CTL) suspensions from in vivo (2, 3) and in vitro (4) experimental systems. As reviewed by Berke (5) and more recently by Henney (6, 7), biological conditions required for T cell mediated cytotoxicity (T CMC) were well defined and the lytic process was dissected into three succesive stages: A) Binding, which is dependent upon the specific recognition by effector cells (E) of sensitizing antigens carried by targets (T). E-T cell contact is a necessary step for target lysis. B) Lethal hit during which stage a lesion occurs on the target cell. This process is at once “the most interesting and most enigmatic,” (7) since we do not know yet the nature of the “hit.” One hypothesis indeed proposed that target cell destruction is caused by a soluble mediator secreted by the killer lymphocytes (8). C) Cytolysis which does not require the continuous presence of the effector cell. The target cell undergoes a series of membrane permeability alterations leading to cell destruction (5–7).