Analysis of platelet von Willebrand factor antigen.

Platelet lysates were obtained from suspensions of normal washed platelets by freeze-thawing or Triton X-100 lysis. The resultant platelet lysates contained 0.34 +/- 0.15 U/10(9) platelets (n = 8) of von Willebrand factor antigen (vWf:Ag) as determined by radioelectroimmunoassay using a monospecific antibody to vWf:Ag. The vWf:Ag level was higher in platelet lysates prepared from freshly drawn blood than from outdated platelet packs. Platelet lysates from patients with severe von Willebrand's disease type I (n = 2) did not contain detectable vWf:Ag. When normal platelet lysates were analyzed by radiocrossed immunoelectrophoresis in agarose using a monospecific polyclonal antibody to plasma vWf:Ag, two immunochemically identical precipitin peaks were seen. One of the platelet vWf:Ag peaks corresponded in its electrophoretic mobility to plasma vWf:Ag, while the other peak, i.e. platelet vWf:Ag-peak II, migrated to a more anodal position. The presence of the platelet vWf:Ag-peak II suggests structural differences between plasma and platelet vWf:Ag and illustrates previously unrecognized heterogeneity of platelet vWf:Ag.