Binding of immunoglobulins purified from the plasma of 2 patients and a healthy control to different tPA forms immobilized on microplates. The binding of purified IgG to human tPA (top panel), rtPA (middle panel), and the catalytic domain of tPA (bottom panel) was evaluated in patient no. 1 (), patient no. 2 (▪), and a healthy control (▴). The horizontal axis indicates the concentrations of purified immunoglobulins. The results are expressed as absorbance (OD) at 492 nm (mean values ± SE of 3 experiments) and indicate that both patients have immunoglobulins directed against the different tPA forms; no significant binding was observed in the healthy control.