Inhibition of mouse natural killer cytotoxicity by heparin

The effect of heparin on mouse natural killer (NK) cytotoxicity was investigated. Heparin greatly inhibited NK activity at a concentration of more than 10 units/ml. Inhibition of NK cytotoxicity was observed only when heparin was present in the reaction mixture of the cytotoxicity assay. The results of kinetic study of NK inhibition and target-effector binding assay proposed the possibility that heparin inhibits NK cytotoxicity after the binding of effector cells to target cells. Dextran sulfate, the heparin analog, which has potent negative charge also had an inhibitory effect on NK activity. Fractionation of heparin on Sephadex A-25 column revealed the parallelism of the negative charge and the inhibitory effect of heparin on NK cytotoxicity. These results demonstrated that polyanion could modulate NK cytotoxicity.