Unique expression of von Willebrand factor by type IIA von Willebrand's disease endothelial cells

Endothelial cells (EC) were cultured from the umbilical cord of a male neonate whose mother was previously diagnosed with type IIA von Willebrand's disease (vWd). The diagnosis of type IIA vWd in the proband was confirmed by low ristocetin activity and the absence of the highest molecular weight (MW) forms of von Willebrand factor (vWf) in his platelet poor plasma. The vWf of EC cultured from the neonate's umbilical cord differed from that of control EC and the cell line EA.hy926 in two respects. Firstly, the full range of molecular weight forms was present in the patient EC lysate and, secondly, vWf:Ag expression was approximately seven‐fold greater than that of control cells, Platelet lysates prepared from other affected members of the type IIA vWd family in the presence or absence of proteolytic inhibitors demonstrated a near normal vWf multimeric distribution. Resistance of these high MW forms to heat degradation was conferred by the presence of proteolytic inhibitors. Moreover, the full plasma vWf multimeric distribution could not be restored by the inclusion of EDTA, N‐ethylmaleimide and leupeptin in the anticoagulant during the rapid preparation of platelet poor plasma. These findings lend support to the heterogeneous nature of type IIA vWd and has possible implications in the understanding of the intracellular processes involved in the biosynthesis and storage of the vWf macromolecular complex as well as the pathogenesis of type IIA vWd.