Quantitative Assay of a Plasma Factor Deficient in von Willebrand's Disease that is Necessary for Platelet Aggregation. RELATIONSHIP TO FACTOR VIII PROCOAGULANT ACTIVITY AND ANTIGEN CONTENT

Abstract

A B S T R A C T In a previous paper, we showed that the abnormality of ristocetin-induced platelet aggregation in platelet-rich plasma in 10 patients with von Willebrand's disease could be corrected by a factor in normal plasma that was present in the same fractions as factor VIII procoagulant activity (antihemophilic factor, AHF, VIIIAHF) when prepared by chromatography on BioGel 5 M (Bio-Rad Laboratories, Richmond, Calif.). This observation suggests that patients with this disorder are deficient in a plasma factor, associated with the factor VIII molecule, that is necessary for normal platelet function. In the present paper, we describe, an assay for this factor, the von Willebrand factor (VIIIvwF), based on the observation that a log-log relationship exists between the amount of ristocetin-induced aggregation of washed, normal platelets and the concentration of normal plasma present in the test system. We assayed the activity of VIIIvwF as well as antihemophilic factor procoagulant activity (VIIIAHF) and factor VIII antigen (VIIIAGN)

Common VWF exon 28 polymorphisms in African Americans affecting the VWF activity assay by ristocetin cofactor

“…When added to plasma, ristocetin binds VWF, facilitating VWF-GPIb binding in vitro and enabling a quantitative assessment of VWF "activity" by measuring platelet aggregation or agglutination. 33,34 Ristocetin in the presence of plasma VWF significantly decreased platelet electrophoretic mobility, probably because of VWF-platelet interactions promoted by ristocetin. 35 It can also precipitate plasma proteins, including both VWF and fibrinogen.…”

Properties of human asialo-factor VIII. A ristocetin-independent platelet-aggregating agent.

“…Thromboxane B2 was measured in the supernate as described by Lewy et al (27). VIII:C, FVIII-related antigen (VIII:Ag), and VIII:Rcf were assayed by standard methods (26,(28)(29)(30)(31).…”

Studies of the human factor VIII/von Willebrand factor protein. III. Qualitative defects in von Willebrand's disease.

“…In severe von Willebrand's disease (vWD), the deficiency of procoagulant and vWF activity (as judged by the ristocetin assay) is associated with a marked deficiency or absence of the F.VIII/vWF protein (7)(8).…”

“…In vWD there is usually a good correlation between the procoagulant F. VIII, antigen levels, and the vWF activity as judged by ristocetininduced platelet aggregation (7). To account for these observations it has been suggested that there is a quantitative reduction of a normal protein in von Willebrand's disease while there is a normal amount of an abnormal protein in hemophilia A. Recently four different vWD families have been described in whom some individuals were found to have normal procoagulant F. VIII and antigen levels but defective vWF activity (9)(10)(11)(12).…”