INDUCTION OF ENDOTOXIN TOLERANCE DEPLETES NUCLEAR FACTOR-KAPPA-B AND SUPPRESSES ITS ACTIVATION IN RAT ALVEOLAR MACROPHAGES

To investigate the mechanism of endotoxin tolerance in macrophages, a rat alveolar macrophage cell line (NR8383) was rendered endotoxin tole rant by treatment with endotoxin at 40 ng/mL for 48 h, This treatment induced a state of tolerance such that subsequent exposure to high-dos e endotoxin (5 mu g/mL) resulted in decreased production of macrophage inflammatory protein-2, tumor necrosis factor alpha, and nitric oxide compared to endotoxin-sensitive cells, Suppressed mediator production by endotoxin-tolerant cells was associated with impaired activation o f nuclear factor-kappa B (NF-kappa B) in response to treatment with 5 mu g/mL of endotoxin, This impairment of NF-kappa B activation was fou nd to be associated with depletion of latent NF-kappa B (both RelA and p50) in the cytoplasm of endotoxin-tolerant cells, These data suggest that a mechanism of endotoxin tolerance is depletion of RelA/p50, whi ch could limit the amount of NF-kappa B available for activation by su bsequent stimuli and thereby inhibit transcription of NF-kappa B-depen dent genes, Limiting NF-kappa B-dependent inflammatory gene transcript ion by inducing endotoxin tolerance is a potential therapeutic strateg y for diseases where excessive production of inflammatory mediators le ads to tissue injury.