Cytokines, in particular TNF-alpha, appear to be necessary to develop the pathological process of Shiga toxin-producing Escherichia coli (STEC) infection. In this study, we investigated whether CV6209, a PAF antagonist, could modulate Shiga toxin (Stx)-induced TNF-alpha production in human monocytic cells. Cells were stimulated by Stx1 or Stx2 (5 ng/ml) with or without CV6209 addition (12-100 microg/ml) for various periods of time. CV6209 significantly suppressed Stx-induced TNF-alpha production in a dose- and time-dependent manner. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that CV6209 suppressed Stx-mediated TNF-alpha mRNA expression. Our results indicated that CV6209 had an important regulatory effect on Stx-induced TNF-alpha production and gene expression.