THE KINETICS OF ⁵¹,Cr RELEASE FROM TARGET CELLS IN CELL MEDIATED CYTOTOXICITY AND THE RELATIONSHIP TO THE KINETICS OF KILLING

The kinetics of T‐cell mediated cytotoxicity (CMC) have been re‐examined. It is clear that per cent 51 Cr release is linearly related to effector cell number and not to its log as often suggested. Data are presented showing that killing can occur within 1 min of lymphocyte‐target cell contact and that 51 Cr is released rapidly from killed cells. Inactivation experiments aimed to stop ongoing cytolysis indicate that all target cells are brought into contact with effector lymphocytes within 45 min. At a ratio of 50:1 the kinetics of contact resemble saturation kinetics, indicating a number of effector cells similar to or in excess of the number of target cells (that is, at least 2 % of total lymphocytes). Although CMC is causally related to cell contact, it is chronometrically unrelated and occurs as a random reaction (that is it can occur immediately or up to hours later than contact). The mean time depends on the number of effector cells. The killing reaction is temperature dependent and proportional to the number of effector cells but does not depend on the intact effector cell. An intact effector cell is only required to bring about contact. It is suggested that this final cytolytic event is brought about by the target cell itself, perhaps as a result of attempts to free itself from the attached lymphocyte.