Inhibition of neutrophil-mediated cytotoxicity by exogenous adenosine 5'-triphosphate

Human polymorphonuclear leukocytes (PMNs) obtained from normal donors kill human tumor cells in vitro. However, if adenosine 5'-triphosphate (ATP) is added to the neutrophil tumor cell suspensions in micromolar concentrations (10-100 microM), there is marked inhibition of neutrophil-mediated cytotoxicity. The inhibitory activity resulted from an effect of ATP on both the effector cells as well as the target cells. When either the effector cells or target cells were preincubated with ATP they became resistant to the effects of the cytotoxic neutrophils. In addition, inhibitory activity was specific to ATP; as it was not demonstrated with GTP, UTP, or CTP. However, when the other adenosine compounds (AMP and ADP) were tested, both AMP and ADP had some inhibitory activity. Cytotoxicity was also inhibited when 100 microM of ATP were added to the neutrophil monolayers either at the time of addition of the tumor cells or 15-60 min after addition of the tumor cells whereas no inhibition of cytotoxicity occurred when ATP was added more than 1 hr after the initiation of the cytotoxic reaction.