Tumor-derived recognition factor (TDRF) induces production of TNF-alpha by murine macrophages, but requires synergy with IFN-gamma alone or in combination with IL-2 to induce nitric oxide synthase.

A constitutively produced soluble activity, designated tumor-derived recognition factor (TDRF), from L1210, P815 and EL4 tumor targets, was previously shown to synergize with interferon-gamma (IFN-gamma) and subactivating concentrations of interleukin-2 (IL-2) to induce murine macrophage production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) for cytotoxicity of the target of origin. Another study had suggested that TDRF upregulated both TNF-alpha receptor (TNF-alpha R) and IFN-gamma receptor (IFN-gamma R) mRNA synthesis, as well as increased TNF-alpha and IFN-gamma binding to their receptors. In the present study, we have further characterized the concentration-dependent macrophage activating potential of TDRF alone and in synergy with IFN-gamma or IFN-gamma and subactivating concentrations of IL-2. Higher concentrations of TDRF acted independently on inflammatory C3H FeJ mouse macrophage to induce expression of TNF-alpha mRNA and release of TNF-alpha, but failed to induce nitric oxide synthase (NOS) mRNA expression and NO generation. At lower concentrations, TDRF synergized with either IFN-gamma alone or in combination with IL-2 to stimulate a dose-related increase in the expression of TNF-alpha mRNA and secretion of TNF-alpha, as well as increased induction of NOS mRNA and cytotoxic NO generation by macrophage. MCA tumor targets which did not produce TDRF activity were killed by macrophage that had been activated by exogenously added L1210-derived TDRF in synergy with IFN-gamma or in combination with subactivating concentrations of IL-2, but not by TDRF alone. Taken together, our results indicate that TDRF acted independently in a dose-dependent fashion to induce macrophage synthesis and release of TNF-alpha, but in the absence of IFN-gamma or in combination with IL-2 failed to induce the NOS enzyme which was necessary for cytotoxic NO generation. Thus TDRF appears to be a sufficient second signal for IFN-gamma-primed macrophage or alternatively a sufficient third signal for IFN-gamma and IL-2 treated macrophage to culminate the activation process for NOS mRNA synthesis and NO-mediated tumor cytotoxicity.