Bacterial lipopolysaccharide (LPS) can induce hype-responsiveness to its own toxic effects, as reflected by the diminished production of tumor necrosis factor (TNF) and other inflammatory mediators by animals (and by purified macrophages) upon re-challenge with LPS. We have examined the regulation of TNF and inducible nitric oxide synthase (INOS) production in the murine macrophage cell line RAW 264.7. These cells accumulated TNF mRNA and secreted TNF protein in a dose-dependent fashion after exposure to either LPS or recombinant murine interferon-γ (rIFN-γ). Pre-exposure of RAW 264.7 cells to relatively high concentrations of LPS (10 ng/mL) resulted in diminished production of TNF in response to subsequent challenge with either LPS or rIFN-γ. In contrast, production of iNOS mRNA was either unaffected or augmented by pre-exposure of these cells to LPS. Our findings indicate that the hyporesponsive state of RAW 264.7 macrophages preincubated with LPS is not specific for LPS and that the production of TNF and nitric oxide (NO) by macrophages are differentially regulated.
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