Simultaneous Determination of the Concentration and Lytic Activity of Effector Cells that Mediate Natural and Antibody‐Dependent Cytotoxicity

Cellular cytotoxicity reactions can be studied in a manner analogous to that used to measure enzyme activity. This approach yields two parameters; V_max the maximal rate of target cell lysis that can be achieved by the lymphocyte preparation tested, and K_M^app, the apparent Michaelis constant. By analogy to many enzyme‐catalysed reactions, K_M^app values for cytotoxicity reactions have generally been interpreted in terms of dissociation constants for the interaction of receptor sites on effector cells with antigens on the target cells, In this paper we demonstrate that experimentally determined K_M^app values for natural or antibody‐dependent cytotoxicity reactions are approximately equal to the concentration of NK or K. effector cells in the lymphocyte preparation tested. This result makes possible the simultaneous determination of both effector cell frequency and lytic activity in a given lymphocyte preparation.