Signal transduction during antibody-dependent cellular cytotoxicity mediated by U937 cells

Stimulation of the human promonocytic cell line U937 with antibody-coated chicken red blood cells (Ab-CRBC), leads to inositol phosphate (IP) release in the effector cells. Neomycin (5 x 10(-4) M) completely inhibits activation of phosphoinositide breakdown, while ADCC is suppressed in a dose-dependent manner. Bordetella pertussis toxin (PT) (0.5 micrograms/ml), entirely inhibits IP release, while ADCC activity is markedly suppressed. The PKC inhibitors H-7 and propranolol also suppress ADCC. HA-1004, which has far lower PKC inhibitory activity than H-7, has a minimal effect on ADCC. The calmodulin antagonists W-7 and TFP are strongly inhibitory. These results indicate that stimulation of U937 cells for ADCC is associated to an increase in IP levels, which may provide positive transduction signals for the activation of this lytic mechanism.