Treatment of murine interferon-alpha/beta-sensitive and -resistant friend leukemia cells with tumor necrosis factor in combination with murine interferon-alpha/beta or -gamma.

Interferon-alpha/beta (IFN-alpha/beta)-sensitive (FLC 745) and -resistant (FLC 3Cl8) Friend leukemia cells (FLC) were fairly refractory to the cytotoxicity of murine tumor necrosis factor (MuTNF) in vitro. Both lines became highly sensitive to mTNF when treated in combination with murine IFN-gamma; when treated with IFN-alpha/beta, only the FLC 745 became sensitive to MuTNF. Romeo et al. have reported previously that an antiviral state was induced in both FLC lines by IFN-gamma, but only in FLC 745 by IFN-alpha/beta. The present results suggest that the sensitivity to the synergistic cytotoxic effect of IFN and TNF in these cells is correlated with the ability to be induced into an antiviral state.