Factor VIII Related Properties in Platelets of Patients with von Willebrand’s Disease (VWD)

In 10 normal subjects washed human platelets (Pl)contained FVIII related antigen(VIIIR:AG) as measured by immunoradiometric assay (iRMA)and electroimmunodif fusion (EID);and ristocetin co-factor (VIIIR:RCo)as assayed by a washed platelet method. The observed values were: AG(IRMA) 0.11-0.24u/mg Pl protein; VIIIR:AG (EID)0.11-0.30u/mg; VIIIR:RCo 0.06-0.21u/mg, In 10pts with seve re homozygous VWD, VIIIR:AG was unmeasurable in 7 and extremely low (1x10^-3-0.6x10^-3u/mg) in 3 u-sing the very sensitive IRMA; VIII RCo was always unmeasurable. In 12 pts with “classical” dominant VWD characterized by very low plasma levels of VIIIR:AG(0.03-0.09u/ml)and VIIIR:RCo(<0.03u/ml), FVIII related properties were normal in Pl and the mobility of PI VIIIR:AG on bidimensional immunolectrophoresis was not different from that of normal controls. In 7 pts showing a faster mo bility of plasma VIIIR:AG, the same abnormality was found in Pl.Pl VIIIR:AG level was within the normal range when assayed by EID whereas IRMA gave lower values both in plasma and in PI.PI VIII R:RCo was lower than in normal subjects and pts with “classical”VWD without electrophoretic variant. These findings show that severe VWD is the expression of a marked reduction of VIII synthesis fully expressed both in PI and in plasma. In “classical” VWD the plasma defects are not reflected in PI, which show normal levels of FVIII-related properties accompanied by normal electro, phoretic mobility of VTIIR:AG; this suggests a defective transfer from PI to plasma. Patients with abnormal mobility are the expression of a qualitative alteration of the FVIII molecole functionally defective both in Pl and in plasma.