Structural characterization of urinary von Willebrand factor by using monoclonal antibodies

The presence of von Willebrand factor (vWF) related antigens has been previously described in urine. By gel filtration, three immunoreactive peaks have been demonstrated having Mr about 350 kDa, 60 kDa and 20 kDa. In this report, a structural characterization of the urinary fragments of vWF was studied by using monoclonal antibodies having known specificities towards the plasma sub-unit. The biggest urinary fragments contain the C-terminal portion and the central portion of the sub-unit. The other two urinary fragments come from the central part of the sub-unit. Antibodies to the N-terminus of the sub-unit do not react with any of the urinary fragments. These results led to a picture for degradation of vWF that is complex and may involve sequential degradation by several proteases. Patients with different types of vWD show qualitatively the same vWF degraded material in their urines, suggesting that whatever the mechanisms for degradation of vWF they are intact in these patients. Quantitatively, it seems that in patients receiving factor VIII-vWF concentrates there is an increased tendency to vWF excretion, which may be due to the presence of denatured material in the concentrates infused to these patients.