Resistance to natural killer cell-mediated cytolysis by a pleiotropic drug-resistant human erythroleukemia (K562-R) cell line.

K562-R, a pleiotropic drug-resistant cell line established in vitro, and K562-S, the chemotherapy-sensitive parent line, were used as targets in the natural killer cell (NK) system. At each of the effector:target ratios studied, the K562-R demonstrated a decrease in their susceptibility to both unstimulated and interferon-activated NK cells, as compared to the K562-S line. This difference did not appear to be related to a variable expression of NK target structures, as the number of effector:target conjugates was similar, and both lines competed equally well in cold target inhibition experiments. The K562-R cells were not resistant to complement or monocyte-mediated killing, suggesting a relatively specific resistance to cell-mediated killing. These results are compatible with an NK postbinding defect in the K562-R cells and suggest that greater tumorigenicity for pleiotropic drug-resistant cells may in part be due to altered susceptibility to host defense.