A Tumor Necrosis Factor Mimetic Peptide Activates a Murine Macrophage Cell Line To Inhibit Mycobacterial Growth in a Nitric Oxide-Dependent Fashion

The control of mycobacterial infections depends on the cytokine-mediated activation of mononuclear phagocytes to inhibit the growth of intracellular mycobacteria. Optimal activation requires the presence of T-cell-derived gamma interferon (IFN-γ) and other signals, including tumor necrosis factor (TNF). Recently, an 11-mer peptide based on amino acids 70 to 80 of the human TNF sequence, TNF((70-80)), was found to have TNF mimetic properties, which include the activation of human and mouse neutrophils to kill Plasmodia spp. Therefore, we investigated the capacity of TNF((70-80)) to activate the murine macrophage cell line RAW264.7 infected with the vaccine strain Mycobacterium bovis bacillus Calmette-Guérin (BCG). When RAW264.7 cells were pretreated with human TNF or TNF((70-80)) in the presence of IFN-γ, there was a dose-dependent reduction in the replication of BCG as measured by the uptake of (3)H-labeled uracil and a concomitant release of nitric oxide as measured by the nitrite in the culture supernatants. TNF- or TNF((70-80))-induced macrophage activation was dependent on IFN-γ and was inhibited by neutralizing monoclonal antibody to human TNF and by anti-IFN-γ antisera. Both nitrite release and BCG growth inhibition were abrogated by competitive inhibitors of l-arginine, which blocked the activation of inducible nitric oxide synthase. A soluble form of the Type 1 TNF receptor blocked the activation of BCG-infected macrophages by human TNF and TNF((70-80)), demonstrating that the effect of TNF((70-80)) is dependent on signaling through TNF receptor I. The mimetic effects of TNF((70-80)) on macrophage activation in vitro suggest that treatment with TNF((70-80)) may modulate mycobacterial infections in vivo.