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A 16-yr-old girl with severe von Willebrand disease complicated by the development of precipitating alloantibodies to von Willebrand factor (anti-VWF) had a life-threatening anaphylactoid reaction immediately after the infusion of a commercial plasma concentrate of factor VIII/von Willebrand factor. An early post-infusion activation of the complement system was demonstrated by the appearance of C3 split products and by the drop of serum CH50 activity, occurring in parallel with a post-infusion drop in the anti-VWF antibody levels. Immune complexes remained unchanged in the early post-infusion period and rose to a moderate extent only after 24 h. We conclude that biologically active products of the complement system contributed to the onset of this life-threatening reaction which occurred after concentrate infusion.

Among all patients with von Willebrand disease (vWD), alloantibodies to von Willebrand factor (vWF) have been described only in severe vWD (type III). The relationship between the development of alloantibodies and the nature of the genetic lesion in vWD is not known. In hemophilia B, large deletions within the factor IX gene appear to correlate with the occurrence of alloantibodies, whereas in hemophilia A no such correlation is apparent. We have studied 19 patients with severe recessive vWD (type III) and 19 with autosomal dominant vWD (type I) by Southern blotting with probes encompassing the full 9 kilobases (kb) of the vWF cDNA. Two apparently unrelated patients were shown to have large deletions within the vWF gene. Both patients had severe vWD (type III) and were the only patients among those studied that had inhibitory alloantibodies to vWF. The extent of deletion was similar in both patients, corresponding to at least the 3'-7.4 kb of the vWF cDNA. The deletion in each patient was estimated to exceed 110 kb. In addition, the localization of the vWF gene to chromosome 12 was confirmed, and a homologous sequence on chromosome 22 was identified.

We have reexplored the role of the carbohydrate moiety (CHO) on the von Willebrand Factor (vWF) structure and function by critically evaluating its different purification steps and modifications in CHO content by specific enzymes. Structural and functional assays have been evaluated separately in each laboratory (Milano and Lille) and jointly in Utrecht during several organized experiments. Under our conditions, the CHOVWFs obtained were characterized by less than 5% of sialic acid "(Neu)asevWF" and about 45% of D-Galactose "(Neu-Gal)ase-vWF" remaining, by increased electrophoretic mobility without any significant losses of the high molecular weight multimers and by their capacity to induce spontaneous aggregation in normal platelet rich plasma (PRP). Platelet adhesion to these different CHO-vWFs was tested in the flat chamber devised by Sakariassen in the presence of different subendothelial matrices and data expressed as the percentage of the surface covered by platelets. The blood reconstituted with different plasma samples showed the following percentual values of surface coverage (mean ± SD):- Normal plasma = 15 ± 3.8- Severe vWd plasma = 4 ± 1.9- SvWd pl + Native vWF = 14 ± 2.8- SvWd pl + (Neu) ase-vWF = 23 ± 3.5- SvWd pl + (Neu-Gal) ase-vWF = 19 ± 2.9This significantly increased adhesion to the subendothelium of the CHO-vWFs corresponded to the spontaneous aggregation present in normal PRP but it disappeared when the multimeric structure was damaged by in vitro proteolysis and/or by storage conditions (changes in temperature and freezing and thawing). From these results we may conclude that removal of terminal sugars enhances not only platelet-vWF interactions, but also platelet adhesion to the subendothelium.

We have previously shown that carbohydrate (CHO) protects von Willebrand factor (vWF) from proteolytic degradation. We have now shown that removal of CHO from the vWF subunit exposes additional cleavage sites in the amino terminal region and that cleavages in this region are associated with loss of large multimers. We examined and compared the extent of large multimer loss with sites of subunit cleavage of native and GHO-modified vWF after treatment with plasmin, chymotrypsin, and trypsin. Highly purified vWF was treated with neuraminidase and β-galactosidase in the presence of proteinase inhibitors to remove 90-95% of the sialic acid and 45-50% of the D-galactose without loss of large multimers or diminution of the ristocetin cofactor activity. The extent and approximate location of subunit cleavage was determined by immunoblotting and monoclonal antibody epitope mapping. Multimeric analysis revealed an increasingly greater loss of large multimers when native vWF was digested with plasmin, chymotrypsin, and trypsin, respectively. Large multimer loss was more extensive with each enzyme after CHO-modification of vWF. On subunit analysis, plasmin, chymotrypsin, and trypsin were shown to produce both amino and carboxy terminal fragments. The number, location, and relative quantities of carboxy terminal fragments produced by these enzymes were unchanged after CHO modification. However, digestion of the amino terminal region was considerably more extensive as judged by a marked decrease or absence of the larger fragments seen when native vWF was digested, and by the appearance of new smaller molecular weight species. Thus, enzymatic digestion of vWF after removal of carbohydrate produced new cleavages in the amino terminal region but did not alter the location or extent of carboxy terminal cleavages. Therefore, the greater loss of large multimers that occurs after CHO modification is likely to be the result of cleavages in the amino terminal region of the molecule. It appears that by protecting the vWF subunit against amino terminal cleavage, carbohydrate inhibits the loss of large multimers.

Summary Spontaneous platelet aggregation appeared in a patient with von Willebrand disease type IIB during the 37th week of pregnancy. This phenomenon was not associated with symptoms of thrombosis and the patient delivered by caesarian section with no complications. Her platelet-poor plasma (PPP) aggregated normal platelet-rich plasma (PRP) and washed platelets. Aggregation was inhibited by monoclonal antibodies with known specificity for the platelet receptors of von Willebrand factor (vWF), i.e. the glycoprotein Ib (GPIb) and the GPIIb/IIIa complex. A monoclonal antibody, which selectively inhibits the binding of vWF to the GPIIb/IIIa complex, did not block aggregation, suggesting that spontaneous aggregation is not dependent on the binding to GPIIb/IIIa of vWF from patient plasma. Aggregation induced by patient plasma could also be blocked either by two monoclonal antibodies raised against vWF or by a fragment derived from trypsin digestion of normal vWF which blocks the ristocetin-induced binding of normal vWF to platelets. These findings indicate that the spontaneous platelet aggregation in this patient results from the binding of her vWF to GPIb but is independent from the binding of her vWF to GPIIb/IIIa.