Plasminogen activation on LM-TK⁻ cells. LM-TK⁻ cells (filled bars) and their extracellular matrix (hatched bars) were incubated in the absence or presence of uPA (10 nmol/L), as well as in the absence or presence of suPAR (1 μg/mL) and MoAb-13H1 (25 μg/mL) against VN for 2 to 3 hours at 4°C as indicated. The unbound uPA was then washed away and the rate of plasmin formation was measured (V_max, mOD/min at 405 nm). Results are mean ± SEM of triplicate wells and similar results were obtained in three separate experiments.