Cytokine Priming Reduces Dependence on TNF-R2 for TNF-α-Mediated Induction of Macrophage Nitric Oxide Generation

In the presence of interferon-γ(IFN-γ), human tumor necrosis factor-α (Hu-TNF-α), which binds to murine TNF-α receptor type 1 (TNF-R1) but not to murine TNF-R2, was effective in inducing nitric oxide (NO) production in spleen-derived macrophages (M ø), albeit at concentrations 12.5-fold greater than those required by murine TNF-α (Mu-TNF-α), to achieve the same result. Addition of anti-TNF-Rl completely inhibited the Mu-TNF-α-mediated induction of NO, demonstrating that TNF-R1 is critical to the IFN-γ-dependent TNF-α-mediated induction of M ø effector function. However, treatment with anti-TNF-R2 resulted in a partial inhibition of M γ activation. Spleen-derived M ø were more dependent on TNF-R2 than RAW 264.7 or peritoneal M ø based on their responsiveness to Hu-TNF-α. Priming of spleen-derived M ø with either IFN-γ or granulocyte-macrophage colony-stimulating factor (GM-CSF) heightened the maximal responses to both TNF-α species and increased the overall effectiveness of Hu-TNF-α without increasing expression of either TNF-α receptor. The dependence of spleen-derived M ø on both TNF-α receptors for signaling the induction of effector function supports an active signaling role for TNF-R2 in its synergy with TNF-R1 rather than a passive ligand passing role.