The mycotoxin ochratoxin A (OTA), an ubiquitous contaminant of food products endowed with a wide spectrum of toxicity, affects several functions of mononuclear leukocytes. Monocytes/macrophages play a major role in fibrin accumulation associated with immune-inflammatory processes through the production of tissue factor (TF) and plasminogen activator inhibitor 2 (PAI-2). We studied the effect of OTA on TF and PAI-2 production by human blood mononuclear cells (MNC). The cells were incubated for 3 or 18 h at 37 degrees C with non toxic OTA concentrations in the absence and in the presence of lipopolysaccharide (LPS) or other inflammatory agents. TF activity was measured by a one-stage clotting test. Antigen assays were performed by specific ELISAs in cell extracts or conditioned media and specific mRNAs were assessed by RT-PCR. OTA had no direct effect on TF and PAI-2 production by MNC. However, OTA caused a dose-dependent reduction in LPS-induced TF (activity, antigen and mRNA) and PAI-2 (antigen and mRNA) production with >85% inhibition at 1 mug/ml. Similar results were obtained when monocyte-enriched preparations were used instead of MNC. TF production was also impaired by OTA (1 mug/ml) when MNC were stimulated with phorbol myristate acetate (98% inhibition), IL-1beta (83%) or TNF-alpha (62%). The inhibition of TF and PAI-2 induction might represent a hitherto unrecognized mechanism whereby OTA exerts immunosuppressant activity.