Both cellular PCA and elevated fibrinogen promote fibrin formation. (A-F) Recalcified (16mM, final) human NPP spiked with fibrinogen or HBS was added to confluent cell monolayers. Fibrin polymerization was measured by turbidity at 405 nm. (A-C) Polymerization curves representative of 4 independent experiments with human NPP and unstimulated HSVECs (A), SMCs (B), and TNF-α-HSVECs (C). Insets expand the x-axis (time) for each panel. Symbols are as follows: 3 mg/mL (○), 4.5 mg/mL (●), 6 mg/mL (■), and 7.5 mg/mL (♦) fibrinogen, final. (D-F) The onset, final turbidity, and fibrin formation rate (mean ± SD) of all 4 experiments with human NPP, respectively. *P < .05 vs 3 mg/mL fibrinogen on HSVECs. #P < .05 vs 3 mg/mL within each cell type. (G) Recalcified murine PPP was spiked with human fibrinogen or HBS, diluted 1:3 in HBS, and clotting was initiated with TF addition (Innovin 1:30 000 final) and monitored by turbidity at 405 nm. Symbols are as follows: 2.4 mg/mL (○), 4.4 mg/mL (▴), or 6.4 mg/mL (▾) fibrinogen, final. Polymerization curves are from a single experiment representative of 4 independent experiments.