MODULATION OF LIPOPOLYSACCHARIDE-INDUCED MACROPHAGE GENE-EXPRESSION BY RHODOBACTER-SPHAEROIDES LIPID-A AND SDZ-880.431

Rhodobacter sphaeroides lipid A (RsDPLA) and SDZ 880.431 (3-aza-lipid X4-phosphate) are prototypic lipopolysaccharide (LPS) antagonists. Her ein, we examined the ability of these structures to regulate murine ma crophage tumor necrosis factor (TNF) secretion and LPS-inducible gene expression (tumor necrosis factor alpha [TNF-alpha], interleukin-1beta [IL-1beta], IP-10, type 2 TNF receptor [TNFR-2], D3, and D8 genes). W e report that RsDPLA alone (> 1 mug/ml) induced low levels of TNF-alph a secretion and a selective pattern of gene expression in peritoneal e xudate macrophages; SDZ 880.431 alone was completely inactive. When LP S was present at a low concentration (1 ng/ml), RxDPLA and SDZ 880.431 blocked TNF secretion and gene induction in a concentration-dependent fashion. In general, gene induction was measurably reduced by 10 to 3 0 ng of RsDPLA per ml or 300 ng of SDZ 880.431 per ml, but inhibition could be uniformly overridden by increasing the concentration of LPS. Although induction of all six genes by LPS was suppressed by either in hibitor, effective inhibitor concentrations depended on the gene of in terest. Induction of TNFR-2 by LPS was relatively resistant to inhibit ion by RxDPLA, and induction of TNFR-2 and D3 was relatively resistant to inhibition by SDZ 880.431. When LPS was present at greater-than-or -equal-to 100 ng/ml, correspondingly high concentrations (greater-than -or-equal-to 20 mug/ml) of either inhibitor influenced gene expression in a bidirectional manner. Under these conditions, LPS-induced expres sion of IP-10, D3, and D8 was suppressed regardless of the LPS concent ration used (concentrations tested up to 50 mug/ml), while expression of TNF-alpha mRNA was enhanced about fourfold. In toto, RsDPIA and SDZ 880.431, when present at low concentrations, act in a manner consiste nt with competitive inhibition of LPS, while at higher concentrations, these structures inhibit certain LPS responses noncompetitively and s ynergize with LPS for other responses.