The production of epithelial neutrophil-activating protein-78 (ENA-78) by normal human monocytes was studied in comparison with IL-8 upon stimulation with various stimuli. LPS at 100 ng/ml was a strong inducer of ENA-78, yielding a delayed up-regulation of steady state mRNA peaking at 24 h and causing a long-lasting ENA-78 protein secretion starting 20 h after induction. As shown by specific ELISA and immunoprecipitation, ENA-78 secretion by monocytes was not down-regulated for up to 72 h. Thus, ENA-78 production becomes effective when IL-8 synthesis is shut off, since IL-8 mRNA peaks at 4 to 12 h and approaches background levels at about 16 h. Induction of steady state ENA-78 mRNA by proinflammatory cytokines IL-1beta (10 ng/ml) and TNF-alpha (100 ng/ml) was weaker than that by LPS and yielded a biphasic kinetic with a first maximum at 8 to 12 h and a second at 20 to 28 h. Steady state IL-8 mRNA induced by LPS, IL-1beta, or TNF-alpha was superinduced or unchanged in the presence of cycloheximide (10 microg/ml). In contrast, ENA-78 mRNA was completely abrogated, suggesting the involvement of a newly synthesized protein intermediate necessary for ENA-78 up-regulation. Dexamethasone treatment reduced ENA-78 mRNA and protein levels by 60% of the LPS control level. This inhibition was identical when dexamethasone was added 8 h after LPS induction. These results demonstrate significant differences in the production of monocyte-derived IL-8 and ENA-78 and thus may suggest different roles for the two chemokines in acute or chronic inflammation.