Abstract
Ristocetin-induced platelet aggregation was studied in normal subjects and in patients with von Willebrand's disease (vWd), thrombasthenia and essential athrombia. The aggregation ranged between 38.2 and 71.2% (mean ± sd, 55.0 ± 10.3) in 10 normal subjects, 47.6 and 64.4% in 4 patients with essential athrombia and 45.5% in one patient with thrombasthenia, whilst 10 patients with vWd showed very poor aggregation between 7.4 and 36.4% (mean ± sd, 20.6 ± 9.7).
The defective aggregation in vWd was corrected by addition of a small amount of normal platelet poor plasma (PPP), crude AHF concentrate or hemophilic PPP. A rabbit antibody to human AHF completely inhibited the aggregation in normal subjects, which was corrected by further addition of either normal PPP, highly purified AHF or hemophilic PPP.
Fresh plasma transfusion to a patient with vWd resulted in a rise of the AHF-like antigen reactive to a rabbit antibody only for the first 12 hrs., and in a delayed elevation of AHF-procoagulant activity in excess which lasted for 72 hrs. after the transfusion. The correction of Ristocetin-induced platelet aggregation was noted for the first 12 hrs. after the transfusion and correlated well with the amount of AHF-like antigen.
These results suggest that a plasma factor deficient in vWd and necessary for Ristocetin-induced platelet aggregation could be AHF-like antigen itself or at least some part of the molecule and that AHF molecule essential for procoagulant activity would not be responsible for the defective platelet function in vWd.
