Tumor-derived factor synergizes with IFN-gamma and LPS, IL-2 or TNF-alpha to promote macrophage synthesis of TNF-alpha and TNF receptors for autocrine induction of nitric oxide synthase and enhanced nitric oxide-mediated tumor cytotoxicity.

Evidence has previously been presented for an immunomodulatory role of a soluble activity, designated as tumor-derived recognition factor (TDRF), which was produced constitutively by P815 mastocytoma, L 1210 leukemia and other murine tumor targets. TDRF synergized with IFN-gamma and IL-2 to promote TNF-alpha and mRNA synthesis and release by murine macrophages for increased autocrine induction of nitric oxide (NO)-mediated tumor cytotoxicity. We have now further assessed the modulatory role of TDRF on TNF-alpha, TNF receptors (TNF-R) and NOS mRNA synthesis. Macrophages activated by INF-gamma priming and triggering by rTNF-alpha bacterial lipopolysaccharide (LPS) of IL-2 evoked greater NO generation in the presence than in the absence of L1210 targets. TDRF-containing culture fluid from L1210 targets was subsequently confirmed to synergize with IFN-gamma and rTNF-alpha, LPS or IL-2 triggering agents to promote increased TNF-alpha mRNA for autocrine induction of NOS mRNA synthesis with resultant augmentation of NO generation. IFN-gamma selectively upregulated TNF-R1 mRNA expression, whereas either IL-2 or LPS upregulated only TNF-R2 mRNA expression. TDRF combined with IFN-gamma to further upregulate TNF-R1 mRNA and with either IL-2 or LPS to further upregulate TNF-R2, mRNA expression. These findings indicate that TDRF activity synergizes with either IL-2 or LPS triggering agents for enhanced activation of IFN-gamma-primed macrophages by promotion of TNF-alpha and TNF-R mRNA synthesis for autocrine induction of NOS with resultant increased NO-mediated tumor cytotoxicity.