Reconstituted high-density lipoprotein (rHDL), an artificial lipoprotein consisting of apolipoprotein A-I and phosphatidylcholine (1:150, molar ratios) dose-dependently reduces lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha (TNF) production in in vitro, ex-vivo, and in-vivo model systems. In an in-vitro whole blood assay, rHDL (1 mg/ml) added concomitantly with LPS increased cellular resistence to LPS stimulation approximately 1000-fold. Even with extremely high levels of LPS (10 micrograms/ml), rHDL > or = 0.5 mg/ml caused > 50% decrease in TNF production. Preincubation of rHDL with LPS was not required for activity. rHDL (> or = 1 mg/ml) reduced TNF production by 50% even when added to cultures 2 hr after their stimulation with LPS (10 micrograms/ml). In an ex-vivo study, rabbits were infused with rHDL at doses of 25, 50, and 75 mg/kg. Blood was drawn and stimulated with LPS ex vivo and bioactive TNF was assessed using the L929 cytotoxicity assay. Fifteen minutes after rHDL infusion, there was a significant difference in ex-vivo-induced TNF activity between groups (750 +/- 160, 170 +/- 40, 80 +/- 30, 60 +/- 30 pg TNF/ml, for the control, 25, 50, and 75 mg/kg rHDL dose groups, respectively; P < 0.0001). The duration of ex-vivo TNF inhibition was dependent on the dose of rHDL. Even at 2 hr, rHDL showed a pronounced TNF inhibition (control: 950 +/- 120 pg TNF/ml; 75 mg/kg: 140 +/- 60 pg TNF/ml). Further studies showed that a prophylactic infusion of rHDL diminished LPS-induced TNF production in a rabbit endotoxemia model.(ABSTRACT TRUNCATED AT 250 WORDS)