A TUMOR-NECROSIS-FACTOR MIMETIC PEPTIDE ACTIVATES A MURINE MACROPHAGECELL-LINE TO INHIBIT MYCOBACTERIAL GROWTH IN A NITRIC OXIDE-DEPENDENTFASHION

The control of mycobacterial infections depends on the cytokine-mediat ed activation of mononuclear phagocytes to inhibit the growth of intra cellular mycobacteria. Optimal activation requires the presence of T-c ell-derived gamma interferon (IFN-gamma) and other signals, including tumor necrosis factor (TNF). Recently, an 11-mer peptide based on amin o acids 70 to 80 of the human TNF sequence, TNF(70-80), was found to h ave TNF mimetic properties, which include the activation of human and mouse neutrophils to kill Plasmodia spp, Therefore, we investigated th e capacity of TNF(70-80) to activate the murine macrophage cell line R AW264.7 infected with the vaccine strain Mycobacterium bovis bacillus Calmette-Guerin (BCG), When RAW264.7 cells were pretreated with human TNF or TNF(70-80) in the presence of IFN-gamma, there was a dose-depen dent reduction in the replication of BCG as measured by the uptake of H-3-labeled uracil and a concomitant release of nitric oxide as measur ed by the nitrite in the culture supernatants. TNF- or TNF(70-80)-indu ced macrophage activation was dependent on IFN-gamma and was inhibited by neutralizing monoclonal antibody to human TNF and by anti-TFN-gamm a antisera, Both nitrite release and BCG growth inhibition were abroga ted by competitive inhibitors of L-arginine, which blocked the activat ion of inducible nitric oxide synthase. A soluble form of the Type 1 T NF receptor blocked the activation of BCG-infected macrophages by huma n TNF and TNF(70-80), demonstrating that the effect of TNF(70-80) is d ependent on signaling through TNF receptor I. The mimetic effects of T NF(70-80) on macrophage activation in vitro suggest that treatment wit h TNF(70-80) may modulate mycobacterial infections in vivo.