The largest multimers are referred to as ULvWF multimers and appear to bind with higher affinity to the platelets, inducing aggregation under conditions of increased fluid shear stress.
In normal plasma, a vWF-CP has been identified that cleaves the ULvWF multimers between tyrosine 842 and methionine 843 within the monomeric vWF subunits, producing a series of smaller multimers (Figure 1).
Alternatively, the disappearance of the ULvWF multimers could be checked by immunoblotting of fragments separated on a SDS-agarose gel.
Treatment with plasmapheresis improves survival dramatically (90% survival) in acute TTP presumably by removing ULvWF multimers and replacing vWF-CP.
Deficiency of ADAMTS-13 results in failure of cleavage of ULvWF
ADAMTS-13 digests ULVWF multimers as they are synthesized and secreted by endothelial cells.
ABBREVATIONS: ADAMTS = a disintegrin-like and metalloprotease domain with thrombospondin type motifs; HUS = hemolytic-uremic syndrome; LD = lactate dehydrogenase; MAHA = microangiopathic hemolytic anemia; PT = prothrombin times; PTT = partial thromboplastin times; TMA = thrombotic microangiopathy; TT = thrombin times; TTP = thrombotic thrombocytopenic purpura; ULVWF = ultralarge VWF; VTEC = verotoxin-producing Ecoli; VWF = Von Willebrand factor; VWF-cp = VWF-cleaving protease.
ABBREVATIONS: APC = activated protein C; AT = antithrombin; C4bBP = Cob binding protein; DIC = disseminated intravascular coagulation; EC = endothelial cells; EPCR = endothelial cell protein C receptor; GAG = glycosaminoglycans; PAF = platelet activating factor; PAI-1 = plasminogen activator inhibitor-1; PARs = protease activated receptor; PC = protein C; PDGF = platelet derived growth factor; TAFI = thrombin activated fibrinolysis inhibitor; TFPI = tissue factor pathway inhibitor; TM = thrombomodulin; TNF = tumor necrosis factor; ULVWF
= ultra-large multimers of von Willebrand factor.
The development of TTP seems to be directly related to the plasma accumulation of unusually large von Willebrand factor (ULVWF) multimers.
The detection of ULVWF multimers in patient samples after complete remission has predicted relapse accurately in 90% of the patients tested, this may prove to be useful in the long-term management of TTP.
The toxins enter the bloodstream and attach to renal glomerular capillary endothelial cells, which become damaged and swollen and release ULVWF multimers.