Effects of Chloroquine, Mefloquine and Quinine on Natural Killer Cell Activity in vitro An Analysis of the Inhibitory Mechanism

Natural killer (NK) cell activity against K 562 target cells was inhibited by pharmacological concentrations of chloroquine, mefloquine and quinine. The most potent were mefloquine and quinine. The drug‐induced inhibition of the NK cell activity was abolished by addition of α interferon (IF) or interleukin 2 (II‐2); preincubation of mononuclear cells with IF or II‐2 followed by addition of anti‐malarial drugs decreased the inhibitory effects of the drugs. The drug‐induced inhibition of the NK cell activity was not dependent on the presence of monocytes. Using monocyte depleted Percoll fractionated NK cell enriched populations in a single cell agarose assay, it was shown that the inhibitory effects of mefloquine, but not of chloroquine and quinine were due to an inhibition of the formation of effector/target cell conjugates.