Summary
The ristocetin induced binding of vWF to GPIb, which is routinely tested in a platelet
agglutination assay, can be reproducibly studied in an ELISA where plasma vWF binds
to a captured rGPIbα-fragment (His1-Val289) in the presence of ristocetin. This binding
is specific since the vWF-GPIb interaction could (i) be blocked by inhibitory antiGPIb
or anti-(vWF A1 domain) monoclonal antibodies (mAbs) and (ii) be enhanced by an anti-vWF
mAb that also facilitates ristocetin induced platelet agglutination. Further studies
were undertaken to determine whether the test could be used to differentiate vWF from
patients with different types of von Willebrand’s disease. The median vWF:RiCof activity
in controls (n = 24) was 0.75 U/ml, in type 1 vWD patients (n = 17) 0.28 U/ml, in
type 2A (n = 18) 0.055 U/ml, in type 2B (n = 4) 0.094 U/ml and in type 3 (n = 3) <0.0005
U/ml. Moreover, the values correlated well with those obtained from the vWF:RiCof-agglutination
assay (r = 0.873). The vWF:RiCof-ELISA has several advantages: the use of a recombinant
fragment instead of donor platelets results in a more reproducible test with a low
inter-and intra-assay variability (<14% CV), the test can further be readily automated
and for a single determination, only minimal amounts of patient plasma are required
(8 µl).
Keywords
Recombinant GpIbα fragment - vWF:RiCof - von Willebrand’s disease - diagnosis