INDEPENDENT SIGNAL-TRANSDUCTION PATHWAYS FOR IL-1 AND TNF IN LPS-TOLERANT MACROPHAGES

Macrophages rendered ''tolerant'' by pretreatment with low-dose endoto xin (LPS(p)) release less TNF and more IL-1 in response to a second ac tivating endotoxin exposure (LPS(a)). We hypothesized that LPS(p) pret reatment alters signal transduction pathways for TNF and IL-1 independ ently. The effect of pretreatment with LPS(p) alone was compared to pr etreatment with LPS(p) plus defined second-messenger pathway agonists or antagonists. Murine peritoneal macrophages were pretreated in vitro for 4 hr with LPS(p) or PMA or LPS(p) plus protein kinase C inhibitor (PKCi) or 8-bromo-cAMP. Cells were then washed and cultured with medi um alone for 20 hr. Macrophages were also pretreated with LPS(p) plus indomethacin for the total 24-hr pretreatment interval, Cells were the n stimulated for 24 hr with LPS(a), after which supernatant TNF and IL -1 were measured by bioassay. In the absence of LPS(p), mediators were increased by LPS(a) in a dose-dependent manner. LPS(p) pretreatment i nhibited TNF and augmented IL-1 in response to LPS(a). Pretreatment wi th PMA partially reproduced LPS(p) pretreatment. Pretreatment with PKC i alone increased both TNF and IL-1 release by LPS(a). The combination of LPS(p) plus PKCi pretreatment further enhanced IL-1 release withou t affecting TNF inhibition. The addition of indomethacin had a similar effect. The combination of LPS(p) plus 8-bromo-cAMP blocked the augme ntation of IL-1 without changing TNF inhibition, Macrophage endotoxin tolerance following LPS(p) pretreatment alters LPS(a)-triggered TNF an d IL-1 release by independent signal transduction pathways. (C) 1995 A cademic Press, Inc.