Stimulation of human polymorphonuclear leucocytes (PMN) with phagocytosable particles [yeast-IgG (Y-IgG)], lipopolysaccharide (LPS), tumour necrosis factor (TNF) or formyl-methionyl-leucyl-phenyl-alanine (FMLP) results in an increase of the interleukin-8 (IL-8) mRNA accumulation and a subsequent release of the protein. Here, we report that interferon-gamma (IFN-gamma) down-regulates the constitutive IL-8 mRNA levels expressed by resting PMN. As shown by Northern analysis, this down-modulation occurred rapidly, was not dependent on new protein synthesis, and was not caused by an increased rate of degradation of IL-8 mRNA. Preincubation of PMN with IFN-gamma significantly inhibited their ability to release IL-8 upon stimulation with TNF, LPS, FMLP and Y-IgG, but enhanced the respiratory burst capability in response to FMLP and TNF. TNF-, LPS- and FMLP-induced expression of IL-8 mRNA was also selectively inhibited by IFN-gamma. Taken together these findings suggest that IFN-gamma has important regulatory effects on acute inflammatory response because of its capacity to modulate negatively IL-8 gene expression and secretion by human PMN. Further observations revealed that, in human PMN, degradation of IL-8 mRNA is finely regulated, and that cycloheximide (CHX), an inhibitor of protein synthesis, super-induces the mRNA accumulation for IL-8 in a dose- and time-dependent manner.