Human Monocyte-mediated Cytotoxicity to K-562 Cells: Activation by Lymphokines

Abstract

Human monocytes purified by adherence and prolonged in vitro monolayer cullure were activated by supernatants of autoiogous lymphocytes stimulated with live bacillus Calmelte-Guérin or killed Corynebacterium Corynebacterium parvum. Activated monocytes expressed increased ability to lyse K-562 cells prelabelled with methyl-³H-thymidine in a 48 h assay. Activation could be detected at a 1:64 dilution of lymphokine supernatants. Target cell killing by activated monocytes was strongly influenced by the density of the monocyte monolayer. Monocytes at an intermediate stage of in vitro differentiation seemed to be most responsive to lymphokine activation. Morphological studies indicated that a considerable number of K-562 cells attach firmly to monocytes, The monocyte-mediated lysis of K-562 seems to be extracellular, as phagocytosis was not observed. Freshly isolated adherent blood mononuclear cells (>90% monocytes) were strongly cytostatic to K-562 cells, as determined by inhibition of methyl-³H-thymidine uptake. Considerable cytolytic activity was also found with freshly isolated adherent cells, strong enhancement being produced by performing the assay in the presence of newborn calf serum, as opposed to human AB serum.