Effect of soluble fibrinogen on adhesion of U937 cells and neutrophils to fibrin under flow conditions. The fibrin gels containing the inner capillary were prepared in glass tubes as described in the “Materials and methods.” The fibrin gels were flushed with HBSS-BSA buffer with or without 2 mg/mL fibrinogen for 15 minutes at 37°C. Calcein-labeled U937 cells or neutrophils were resuspended at 10⁶/mL in HBSS-BSA containing or not 2 mg/mL fibrinogen and perfused through the fibrin tubes. U937 cells were perfused at a wall shear rate of 50 sec⁻¹ for 20 minutes and neutrophils at 100 sec⁻¹ for 3 minutes. (A) Adherent cells were viewed with a Leica DMIRB fluorescence microscope. Fg indicates fibrinogen. (B) Fluorescence of adherent cells flowed through the fibrin substrates in the absence (⊡) or presence (▪) of fibrinogen was determined using a CytoFluor plate reader. Results shown are the means ± SE of 2 separate experiments performed with quadruplicate measurements.