Summary
Platelet adhesion to collagen under flow conditions was studied in 18 patients with
lupus anticoagulant, seven of which showed a prolonged bleeding time in the presence
of a normal platelet count. The effect of patient plasma, IgG and purified anticardiolipin
antibodies on platelet adhesion was also examined. We found a significant reduction
of platelet adhesion in patients with lupus anticoagulant, which was more evident
in patients with prolonged bleeding time. This platelet adhesion defect could be attributed
to a plasma factor. In fact, patients' platelets regained normal adhesion when mixed
with normal plasma, whereas controls' platelets showed abnormal adhesion in the presence
of patient plasma. A causative role of antiphospholipid antibodies was demonstrated
in experiments using purified immunoglobulins and anticardiolipin antibodies.
