Effect of fibrinogen immobilization conditions on the “adhesion peak.” (A) Position of the peak depends on fibrinogen immobilization time. The wells of microtiter plates were coated with fibrinogen at 2 and 5 μg/mL for various times (0.5-4 hours) at 37°C and coated afterward, and the adhesion of U937 cells was determined as described in “Materials and methods.” (B) Immobilization of fibrinogen in agents that prevent complex formation eliminates an “adhesion peak.” Microtiter plates were coated with different concentrations of fibrinogen (0-10 μg/mL) in PBS (•), in PBS containing 6 M guanidine hydrochloride (▾) or 0.015% SDS (○) for 3 hours at 37°C. The wells were coated afterward with PVP, and the adhesion of U937 cells was assessed. The data shown are the means ± SE of 2 separate experiments performed with quadruplicate measurements.