LIPOPOLYSACCHARIDE-INDUCED INTERLEUKIN-8 GENE-EXPRESSION IN HUMAN GRANULOCYTES - TRANSCRIPTIONAL INHIBITION BY INTERFERON-GAMMA

We recently showed that lipopolysaccharide (LPS) is a potent inducer o f interleukin-8 (IL-8) expression in human polymorphonuclear leucocyte s (PMN), at the level of both mRNA and protein, and that interferon-ga mma (IFN gamma) inhibits IL-8 mRNA accumulation in stimulated PMN. To further define the molecular basis of the regulation of IL-8 gene expr ession in PMN, we investigated the effects of LPS and IFN gamma at bot h the transcriptional and post-transcriptional levels. As determined b y Northern blot analysis, new protein synthesis was not required for t he induction of IL-8 mRNA expression by LPS. Neither did the half-life of IL-8 mRNA in LPS-treated PMN differ from that observed in untreate d cells. However, nuclear run-on analysis revealed that LPS increased the transcription of the IL-8 and IL-1 beta genes and that, in LPS-act ivated cells, IFN gamma markedly inhibited the rate of IL-8 gene trans cription, but not that of IL-1 beta. IFN gamma did not affect IL-8 mRN A stability in LPS-treated PMN, indicating that the cytokine does not regulate LPS-induced IL-8 gene expression through post-transcriptional events. These results provide the first evidence that human granulocy tes can actively transcribe the IL-8 gene, and that transcriptional in hibition is the mechanism by which IFN gamma inhibits IL-8 gene expres sion in PMN.