Effect of the patient’s IgG on the cross-linking of clots obtained in mixtures with purified fibrinogen. (A) Incubations were performed at 37°C for 2 hours in 0.5 mL mixtures containing 50 mmol/L Tris-HCl, pH 7.5, 100 mmol/L NaCl, 0.5 mg/mL human fibrinogen, 2.5 μg/mL rA₂, 20 U/mL Trasylol, either no IgG (lanes 1 and 2) or 2 mg/mL normal IgG (lanes 3 and 4) or patient IgG (purified on a ZetaChrom 60 disk from serum drawn on 7/31/91; lanes 5 and 6), either 2 mmol/L EDTA (lanes 1, 3, and 5) or 10 mmol/L CaCl₂(lanes 2, 4, and 6), and 12.5 U/mL bovine thrombin. Washed clots were analyzed by SDS-PAGE after reduction with DTT. (B) Incubations were performed at 37°C for 2 hours in 0.5 mL mixtures containing 50 mmol/L Tris-HCl, pH 7.5, 100 mmol/L NaCl, 0.5 mg/mL human fibrinogen, 20 U/mL Trasylol, 2 mmol/L EDTA, either no IgG (lanes 1 and 2) or 2 mg/mL normal IgG (lanes 3 and 4) or patient IgG (lanes 5 and 6), in the absence (lanes 1, 3, and 5) or presence (lanes 2, 4, and 6) of 5 μg/mL human factor XIII (A₂B₂), and 12.5 U/mL bovine thrombin. Clots were processed and analyzed as in (A).