Search

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.

Although tissues become exposed to both exogenous and endogenous cell-activating mediators during infection, there is little appreciation of the effects of subjecting cells to multiple mediators. We examined the hypothesis that the response of neutrophils to bacterial lipopolysaccharide (LPS) is significantly altered in the presence of the endogenous mediator tumor necrosis factor alpha (TNF). The data showed that human neutrophils pretreated with TNF for 10 to 30 min, displayed significantly enhanced superoxide production in response to LPS (from either Escherichia coli K-235 or E. coli 0127:B8), measured as lucigenin-dependent chemiluminescence (CL), seen as an increase in the initial peak rate as well as the total CL accumulated over the incubation period. TNF amplified the response to LPS at 1 to 100 U of TNF/10 6 neutrophils and was able to enhance the response to a wide range of concentrations of LPS (0.01 to 1,000 ng/ml). The TNF-induced increase in the LPS response was paralleled by an increase in LPS binding to the neutrophils, which could be abrogated by an anti-CD14 monoclonal antibody. The results demonstrate that TNF significantly increases the LPS-induced release of oxygen radicals in neutrophils through the upregulation of cell surface CD14.