We had previously demonstrated that lung cancer cells, upon contact with macrophages, could be induced to secrete angiogenic factors to promote tumor angiogenesis. In this study, we focused on the paracrine and autocrine regulation of interleukin (IL)-8 expression in sensitized lung cancer cells after interacting with macrophages. We found that the IL-8 mRNA expression in lung cancer cells significantly increased after coculture with phorbol myristate acetate-treated THP-1 cells and human primary lung macrophages. Fresh lung cancer CL1-5 cells cocultured with macrophage-sensitized lung cancer cells still had a 35% of increase in IL-8 mRNA expression. The addition of anti-inflammatory agents pyrrolidine dithiocarbamate, pentoxifylline, aspirin, and dexamethasone could completely suppress the expression of IL-8 mRNA in fresh/sensitized lung cancer cell cocultures. Human recombinant tumor necrosis factor (TNF)-alpha and IL-1alpha could induce IL-8 expression in lung cancer cells in a dose-dependent manner. Neutralization with TNF-alpha and IL-1alpha antibodies in cocultures decreased the levels of IL-8 expression in sensitized lung cancer cells. Nuclear factor-kappaB transcriptional activity was also suppressed by the same antibodies, as confirmed by a reporter gene assay and the electrophoretic mobility shift assay. Our results highly suggest that both autocrine and paracrine regulation are involved in IL-8 expression of lung cancer cells cocultured with macrophage. Also, the regulations of IL-8 expression in lung cancer cells were through the nuclear factor-kappaB pathway and modulated by TNF-alpha and IL-1alpha.