Effect of soluble fibrinogen on adhesion of U937 cells to the fibrin gel. (A) Fibrin gels were formed in 96-well format strips by mixing 100 μL of 2 mg/mL fibrinogen in HBSS with 0.5 U/mL thrombin in the absence (•) or presence (○) of factor XIIIa (10 μg/mL). After polymerization for 2 hours at 37°C, thrombin was inactivated by adding PPACK (50 μM). The gels were incubated with different concentrations of fibrinogen for 15 minutes at 37°, solutions above the gels were aspirated, and the gels were incubated for another 2 hours at 37°C. Adhesion assays with U937 cells were performed as described in Figure 1. (B) Fibrin gels were polymerized with or without FXIIIa and incubated with aliquots of ¹²⁵I-fibrinogen (100 μg/mL, 2 ×10⁷ cpm/mL) as described in panel A. Unbound label was removed by washing; the gels were collected by winding on glass rods, dissolved in 1% SDS containing 10 mM DTT, and electrophoresed through 12% SDS–polyacrylamide gel electrophoresis. After coomassie blue staining (lanes 1-3), gels were subjected to autoradiography (lanes 4-5). Lanes 1 and 4, samples without, and lanes 2 and 5, with FXIIIa added. Lane 3, markers with molecular weights shown on the left. Positions of fibrin α-, β-, and γ-chains, as well as γ-γ dimer and cross-linked α/γ-polymers are shown on the right.