Natural killing and growth inhibition of K562 cells by subpopulations of mononuclear cells as a function of target cell proliferation.

K562 cells of different proliferative activity were tested for their capability to form lytic and non-lytic conjugates in agarose with peripheral blood mononuclear cells (MNC). Simultaneously, the conjugating MNC were analysed in suspension by monoclonal antibodies (mAb) defining subsets of T cells, natural killer (NK) cells, and monocytes (OKT 8, OKT 4, Leu 7, OKM 1, Mo 2). It is demonstrated that the pattern of conjugating (binding, lysis) is dependent upon the proliferative status of the target cell population. Target cells of intermediate division rate are optimally lysed by MNC of NK phenotype, whereas targets of high and low division rate bind cells predominantly of T cell phenotype, but are not killed. Non-cytolytic conjugating MNC are shown to inhibit significantly the cell cycle progression of their bound tumour target cells. There is evidence of an additional cytostatic effect on non-bound K562 cells in agarose dishes containing effector MNC, possibly mediated by soluble factors released from NK cells. Adherent monocytes contribute only little to cytolysis and cytostasis in our testing system. There is no correlation between the expression of transferrin receptors on target cells as determined by the OKT9 mAb and the extent of killing. Transferrin receptors may, however, be involved in the step of target cell recognition by MNC exhibiting the OKT 8+ phenotype.