Effect of TTP plasma on the ULVWF-cleaving activity of ADAMTS-13.

Washed platelets suspended in Tyrode buffer formed the stringlike structures on the stimulated endothelial surface (A), whereas the VWF-platelet strings were cleaved in the presence of purified ADAMTS-13 (B). ADAMTS-13 failed to cleave the VWF strings when it was mixed with plasma from acquired TTP containing anti–ADAMTS-13 antibody (E), but functioned normally when mixed with plasma from congenital TTP with deficient ADAMTS-13 activity (D). Panel E is the summary of multiple sample analyses, and results are expressed as means ± SEM, n = 3.