Kinetic analysis of lymphokine-activated killer (LAK) cells: lytic parameters and determination of LAK cell frequency

Kinetic analysis was used to define lytic events in murine lymphokine-activated killer (LAK) cell-mediated tumour cell lysis. The maximum rate of target cell lysis (Vmax) and Km (target cell number resulting in 1/2 Vmax) were determined. Single cell lytic assays demonstrated that only LAK effector cells bound to target cells (i.e. non-lytic, bystander lymphocytes did not influence the determination of kinetic parameters) in contrast to natural killer (NK) cell lysis. This finding allowed for LAK cell frequency determinations where Km approximates the concentration of lytic LAK effector cells within a given number of lymphocytes. Frequencies determined in this manner were not significantly different from those obtained using the more cumbersome single cell lytic assay. Furthermore, frequencies determined for the same lymphocyte population against four different NK-resistant tumour targets, that varied in their sensitivity to LAK cell lysis, were not significantly different. In addition, LAK cell lytic programming of target cells was found to be the rate limiting lytic event. This study provides a means of determining reliable estimates of LAK cell frequencies within a lymphocyte population, which will be useful in studies evaluating LAK cytolytic mechanisms and the effects of drugs, biological response modifiers, or disease states on LAK cell lytic activity.