Tumor cell killing by macrophages activated in vitro with lymphocyte mediators: I. Development of a short term in vitro microcytotoxicity assay

We describe a short term in vitro microcytotoxicity assay to study the killing by macrophages of adhering tumor cells prelabeled with [³H]proline. With this assay, killing of line 1 hepatoma cells can be demonstrated within 6 hr of cocultivation with normal macrophages activated in vitro with the lymphocyte mediator macrophage activating factor (MAF).The data show that the decrease in residual adhering radioactivity, on which the calculations of percent kill are based, results from the lysis as well as from the detachment of tumor cells. However, detached tumor cells fail to exclude trypan blue and are no longer capable of DNA and protein synthesis. This suggests that the detachment of intact but nonviable tumor cells precedes actual target cell lysis in this system.