The role of monocyte cytotoxic factor (CF) in cytostasis mediated by IFN-gamma-activated monocytes

The role of monocyte cytotoxic factor (CF) in cytostasis mediated by lymphokine- and interferon gamma (IFN-gamma)-activated monocytes was investigated. Recombinant IFN-gamma as well as lymphokines enhanced monocyte-mediated cytostasis concomitantly with an increase in monocyte CF content. The incubation of lymphokines with monoclonal antibody against human IFN-gamma inhibited cytostasis mediated by lymphokine-exposed monocytes, indicating that the main monocyte-activating factor in the lymphokine supernatant was IFN-gamma. A neutralizing antiserum raised against purified CF inhibited monocyte-mediated cytostasis in a dose-dependent manner. When CF antiserum was added to monocytes previously exposed to lymphokines treated with a monoclonal antibody against IFN-gamma, all cytostatic activity was completely abrogated. No inhibitory effect on cytostasis was observed with preimmune serum. The results indicate that CF is an effector molecule in cytostasis mediated by lymphokine- or IFN-gamma-activated monocytes.