PBMC were cultured in (A–C) SFM, (D–F) SFM with 2.5 µg/ml SAP, or (G–I) PFM with 2.5% (v/v) human serum in the presence of the indicated concentrations of (A,D,G) trypsin, (B,E,H) tryptase, or (C,F,I) thrombin for 4 hours, after which media was removed and replaced with (A–C) SFM , (D–F) SFM with 2.5 µg/ml SAP, or (G–I) PFM with 2.5% (v/v) human serum. Cells were then allowed to differentiate over the remainder of the five-day assay, and fibrocytes were counted as in Figure 1. Serum-containing and SAP-containing media completely inhibited fibrocyte differentiation in the protease-free control. Values are mean ± SEM, n = 5. * indicates p < .05, ** p < .01 and *** p < .001 compared to the protease-free control (t-test).