Thrombin and PAR-1–specific peptide increase OSM production, whereas PPACK, hirudin, and hirulog inhibit the effect of α-thrombin on OSM in human monocyte-derived macrophages. MDMs were incubated with α-thrombin (1 U/mL), FPRck-thrombin (0.2 μg/mL), PAR-1–specific peptide (10 μM), PAR-3–specific peptide (10 μM) or PAR-4–specific peptide (10 μM) for 24 hours or preincubated with PPACK (1 μM), hirudin (1 U/mL), or hirulog (1 μg/mL) for 1 hour before addition of α-thrombin (1 U/mL) for 24 hours. Conditioned media of such treated cells were collected and OSM antigen was determined as described in “Quantification of OSM.” Values are given in nanograms per milliliter and represent mean values ± SD of 3 independent determinations. Experiments were performed 2 times with MDMs obtained from 2 different donors with similar results. A representative experiment is shown. *P < .001.