Recent studies suggest that interleukin-1 beta (IL-1 beta) stimulates interleukin-6 (IL-6) production in human intestinal epithelial cells, but the intracellular mechanisms of this response are not known. In other reports, the nuclear factor-kappa B (NF-kappa B) regulated IL-6 production in certain cell types. We tested the hypothesis that IL-6 production in the enterocyte is associated with activation of NF-kappa B. Caco-2 cells, a human intestinal epithelial cell line, were grown in tissue culture whereafter they were treated with IL-1 beta (0.5 ng/ml). Cells were preincubated with pyrrolidine dithiocarbamate (PDTC; 10-500 microM), tosyl-lys-chloromethylketone (TLCK; 10-500 microM), or genistein (25-75 microM), all of which are known inhibitors of NF-kappa B. IL-6 levels in the culture media were measured after 24 hr by enzyme-linked immunosorbent assay (ELISA) and IL-6 messenger RNA (mRNA) levels were determined after 4 hr by competitive reverse-transcriptase polymerase chain reaction (RT-PCR). NF-kappa B activity was determined by electrophoretic gel mobility shift assay (EMSA). PDTC, TLCK, and genistein each inhibited IL-1 beta-induced IL-6 production by the Caco-2 cells in a dose-dependent fashion. These responses were also associated with a decrease in IL-6 mRNA levels. There was no NF-kappa B activity in untreated cells, but the addition of IL-1 beta resulted in the activation of NF-kappa B as determined by EMSA. The results suggest that IL-1 beta-induced IL-6 production in the enterocyte is associated with activation of NF-kappa B. The inhibition of IL-6 production by the NF-kappa B inhibitors indicates that the IL-6 production is regulated by NF-kappa B, although further experiments are needed to test that hypothesis.