We evaluated the ability of eosinophil granule major basic protein (MBP) to stimulate interleukin (IL)-8 production by neutrophils. MBP over the concentration range of 0.1 to 10 microM stimulated the release of up to approximately 8 ng/ml IL-8. Incubation with 2 microM MBP showed that, after a 1 h lag, the level of IL-8 release increased with time for approximately 10 h. At the 2 microM concentration, eosinophil cationic protein, eosinophil-derived neurotoxin, and eosinophil peroxidase did not stimulate significant levels of IL-8 production. MBP stimulated 2-fold increases in IL-8 messenger RNA (mRNA) after 1 and 3 h of incubation, which were blocked by pretreatment with actinomycin D. However, stimulation with MBP did not produce an increase in the binding activity of nuclear factor (NF)-kappaB or activator protein-1. No NF-IL-6 binding activity was detected in the same nuclear extracts. In addition, stimulation with MBP prolonged the stability of IL-8 mRNA. MBP also induced transient increases in mRNA for macrophage inflammatory protein (MIP)-1alpha and MIP-1beta, but did not stimulate the release of either chemokine. These findings indicate that MBP is selective among the eosinophil granule proteins as a stimulus for neutrophil IL-8 release and, further, that stimulation of neutrophil IL-8 release by MBP involves both transcriptional and posttranscriptional regulation. We postulate that MBP-induced release of IL-8 by neutrophils may contribute to the pathophysiology of acute asthma and other inflammatory lung diseases.