IL-6, but not IL-8 and TNF-α, inhibited cleavage of ULVWF strings by ADAMTS13 under flow. Normal PRP samples were pretreated with each of the 3 cytokines and perfused over histamine-stimulated HUVECs at 2.5 dyne/cm2 shear stress. The platelet-decorated ULVWF strings were mostly cleaved in the presence of PRP treated with IL-8 or TNF-α, but not in the presence of IL-6–pretreated PRP. The maximal inhibitory effect on ULVWF cleavage was observed at 100 ng/mL IL-6. As controls, there was no string formed with untreated PRP (100% cleavage), whereas the perfusion of washed platelets suspended in Tyrode buffer resulted in a significant number of strings (no cleavage). Figures were mean ± SEM, Student t test, n = 6, *P < .01 compared to IL-8– and TNF-α–treated PRP.
