Extravascular and intravascular cells support different levels of thrombin generation and fibrin formation. Recalcified (10mM, final) normal, pooled PFP was added to confluent cell monolayers. (A) Thrombin generation was measured using calibrated automated thrombography; data (± SD) shown are averaged from at least 5 separate experiments. (A inset) HUVECs were incubated with TNFα (0-1nM) for 4 hours at 37°C. Factor Xa generation (± SD) was measured by incubating cells with factors VIIa and X in the presence of CaCl₂, and measuring factor Xa generation by chromogenic substrate in 2 separate experiments. (B) Fibrin polymerization was measured by turbidity at 405 nm; data (± SD) shown are from 1 experiment, representative of at least 7 independent experiments. Symbols for panels A and B are as follows: fibroblasts, (●); SMCs, (♦); HUVECs, (■); and HUVECs stimulated with TNFα for 4 hours, (▴).