Tumor necrosis factor is required for the priming of peritoneal macrophages by trehalose dimycolate

Trehalose dimycolate (TDM), a glycolipid present in the cell wall of Mycoba cterium spp., is a powerful immunostimulant. We have developed an original model of macrophage activation where TDM is injected in vivo to prime perit oneal macrophages. These primed macrophages do not express inducible NO syn thase (NOS II), however, they can be fully activated, i.e. induced to expre ss NOS II and to develop a NOS II-dependent antiproliferative activity, fol lowing in vitro exposure to low concentrations of LPS. In a previous paper, we have shown that TDM-priming of mouse peritoneal macrophages is mediated by the sequential production of IL-12 and IFN-gamma. In the present paper, we investigated the role of TNF in the priming of macrophages by TDM. By s emi-quantitative RT-PCR, we have shown that TDM injection induced transcrip tion of TNF-alpha in peritoneal cells. TNF-mRNA levels peaked 5 hours after TDM injection and remained elevated for at least 32 hours. TNF expression was absolutely necessary for macrophage priming, as injection of an anti-TN F monoclonal antibody, 4 h before and 20 hours after TDM injection, prevent ed LPS-dependent activation of macrophages in vitro. This result was confir med by the inability of TDM to prime macrophages from LT-alpha/TNF-alpha kn ockout (LT/TNFKO) mice, In addition, analysis of LT/TNFKO mice treated with TDM revealed that induction of the IL-12 transcript in their peritoneal ce lls and expression of a functional NADPH oxidase in macrophages are TNF-ind ependent events.