Abstract
Molecular linkages between von Willebrand factor (VWF) and the alternative complement
pathway (AP) have recently been discovered. Endothelial cell (EC)-anchored ultra-large
(UL) VWF multimeric strings function as an activating surface for the AP. C3 (in active
C3b form) binds to the EC-anchored ULVWF strings, and promotes the assembly of C3bBb
(C3 convertase) and C3bBbC3b (C5 convertase). These linkages may help to explain enigmatic
clinical problems related to thrombotic microangiopathies, including some cases of
refractory thrombotic thrombocytopenic purpura (TTP), TTP associated with only mild–modest
deficiencies of ADAMTS-13, the provocation (or exacerbation) of acute episodes in
patients with the atypical hemolytic uremic syndrome, and thrombosis in paroxysmal
nocturnal hemoglobinuria. Recent experiments have also demonstrated that complement
factor H performs a dual role: participating in regulation of the AP by binding to
EC-anchored ULVWF strings; and functioning as a reductase to decrease the size of
soluble VWF multimers.
Keywords
VWF - alternative complement pathway - factor H - thrombotic microangiopathies