KINETIC-ANALYSIS OF TARGET-CELL DESTRUCTION BY EFFECTOR T CELLS .1. DELINEATION OF PARAMETERS RELATED TO FREQUENCY AND LYTIC EFFICIENCY OF KILLER CELLS
Murine cytotoxic T [thymus-derived] cell activity was evaluated in analogy with the methods used to characterize enzymes. Concordant with this analogy, the relationship between steady-state lytic rates and target cell (substrate) number was described by a hyperbola, the asymptote of which was the maximum rate of lysis (V) and was directly proportional to the number of killer cells. The number of target cells required to reach a rate of 1/2 V (K) was independent of the number of effector cells, but varied with the total cell concentration in the cultures. The kinetic analogy was extended to analyze this variability by studying the inhibition of cytolysis caused by normal syngeneic lymphocytes. A value for K in the absence of non-killer cells (Kh) was evaluated. This term, which was independent of effector cell frequency, was a measure of lytic efficiency and, as such, was used to compare various effector cell populations. The Kh value for a number of lymphoid cell populations from identically immunized C57BL/6 mice varied considerably, thereby providing direct evidence that effector populations have different lytic efficiencies. Because of this variability, the widely used practice of comparing killer cell populations solely on the basis of their relative lytic activity may often be invalid.