Interactions among bovine and human factor VIII, ristocetin, and DL-polylysine in the induction of guinea pig platelet aggregation.

Guinea pig and human platelets were aggregated by bovine factor VIII plus ristocetin a concentrations not allowing either substance alone to induce aggregation. Using combinations, it was shown that aggregation required bovine factor VIII and restocetin at levels where the sum of their concentrations exceeded a critical value. With guinea pig platelets, combinations of polylysine and bovine factor VIII or polylysine and human factor VIII did not show full aggregations. These results do not support the hypothesis that aggregation by mixtures of factor VIII and ristocetin arises solely from neutralization of negative charges on the platelet surface membrane.