The effect of a new antirheumatic drug, triethylphosphine gold (auranofin), on in vitro lymphocyte and monocyte cytotoxicity.

Therapeutic serum concentrations of auranofin, expressed as elemental gold, range from 0.25 - 1.0 micrograms/ml. Monocyte antibody dependent cellular cytotoxicity (ADCC) could be reduced by up to 50% at a gold concentration of 0.125 micrograms/ml. Lymphocyte ADCC was much less dramatically affected although 2.5 micrograms/ml produced virtually complete inhibition. The most surprising finding is a marked stimulation of natural killer (NK) cell activity using a variety of targets. NK activity was markedly enhanced by concentrations of 0.125 to 0.5 micrograms/ml (range 2-500%). This is a biphasic dose dependent response. 1.0 micrograms/ml was depressive and 2.5 micrograms/ml completely abolished NK cell activity. Whether these selected in vitro responses play a role in modulating tissue damage in vivo is yet to be determined.