The role of monocyte cytotoxic factor in monocyte-mediated lysis of tumour cells.

The role of a monocyte cytotoxic factor (CF) in monocyte-mediated lysis of leukaemia cells (K562) has been investigated using a polyclonal rabbit antiserum raised against purified CF. The CF antiserum inhibited K562 cell lysis mediated by interferon gamma (IFN-gamma)-activated monocytes. CF antiserum also inhibited monocyte-mediated lysis of antibody-coated K562 cells (AbK562). Preimmune serum at the same concentration as CF antiserum did not affect monocyte-mediated lysis, and the CF antiserum did not inhibit binding between effector and target cells, indicating that inhibition of monocyte-mediated lysis by CF antiserum was not merely a result of toxic components present in the rabbit serum, or a result of a decrease in monocyte-target cell binding. Taken together, the data suggest that CF is involved in monocyte-mediated lysis of uncoated as well as antibody-coated K562 cells.