IL-6 inhibited the cleavage of ULVWF strings under different conditions. (A) PRP treated with preformed IL-6–sIL-6R complexes inhibited the cleavage of ULVWF strings similarly to that of IL-6 alone. IL-6 also inhibited cleavage of ULVWF strings in whole blood. (B) Pretreatment of partially purified ADAMTS13 with IL-6 inhibited the cleavage of ULVWF strings under flow by approximately 50%. Figures are mean ± SEM, Student t test, n = 6, *P < .01 compared to untreated PRP or purified ADAMTS13.