Inhibition of IgG binding to insolubilized rtPA by soluble tPA forms, prothrombin, β2-GPI, and plasminogen. Plasma from patients no. 1 and 2 was incubated for 1 hour with rtPA or the catalytic (cat) domain of tPA at concentrations of 0.500 mg/mL, 0.250 mg/mL, 0.125 mg/mL, 0 mg/mL, with prothrombin up to a concentration of 4.500 mg/mL, with β2-GPI up to a concentration of 9.000 mg/mL or plasminogen up to a concentration of 5.000 mg/mL, and then tested using the solid-phase immunoassay as described in “Patients, materials, and methods.” The results are expressed as the percentage binding recorded in the absence of added soluble proteins (buffer). When added to the patients' immunoglobulins, both rtPA and the catalytic domain of tPA inhibited the binding of anti-tPA antibodies to the rtPA immobilized on microplates, but prothrombin, β2-GPI, and plasminogen did not inhibit the binding.
