IFN-GAMMA PRIMING OF MONOCYTES ENHANCES LPS-INDUCED TNF PRODUCTION BYAUGMENTING BOTH TRANSCRIPTION AND MESSENGER-RNA STABILITY

The induction of cytokine expression in monocytes/macrophages by bacte rial endotoxin or lipopolysaccharide is a critical, highly regulated h ost defence response. The augmentation of LPS responses by interferon gamma (IFN-gamma), referred to as priming, is weil established. Howeve r, the mechanism(s) by which priming occurs is poorly defined. Using t umour necrosis factor (TNF) induction as a model, experiments were des igned to analyse in detail the printing effect on the LPS response in human monocytes. Priming by IFN-gamma was primarily manifested at the level of TNF mRNA accumulation. IFN-gamma pre-treatment affected the m agnitude rather than the sensitivity of the LPS response. Priming occu rred after several hours of treatment, and the primed state was induce d by either IFN-gamma or GM-CSF, but not M-CSF. Primed monocytes trans cribed TNF mRNA at a higher rate than freshly isolated monocytes upon activation with LPS. The increased transcriptional rate correlated wit h a marked increase in nuclear factor-kappa B activity in these cells as determined by electrophoretic mobility shift assay using a consensu s NF-kappa B oligonucleotide. An additional significant finding was th at TNF mRNA induced in primed cells was much more stable than in unpri med cells (T1/2 increased 6-8-fold). Consistent with the increased mRN A stability, the duration of mRNA accumulation was longer following LP S stimulation in primed monocytes, in addition to being of greater mag nitude. Finally, primed and unprimed cells possessed a differential se nsitivity to the kinase inhibitor H-89. H-89 substantially suppressed LPS-induced TNF mRNA accumulation in unprimed cells, but had no effect on primed monocytes following LPS stimulation. These results demonstr ate that priming amplifies LPS-inducible TNF expression by increasing both transcription and mRNA stability. (C) 1995 Academic Press Limited .