IL-6 bound sIL-6R and stimulated ULVWF release from HUVECs. Recombinant human IL-6 (100 ng/mL) was incubated with sIL-6R (80 ng/mL), and IL-6 binding to sIL-6R detected using a monoclonal IL-6 antibody. (A). sIL-6R bound to immobilized IL-6, but not BSA (mean ± SEM, Student t test, n = 3, *P < .001, as compared to plates coated with BSA). (B). HUVECs were treated with preformed IL-6–sIL-6R complexes for 30 minutes and perfused with washed platelets at 2.5 dyne/cm² shear stress. The platelet-decorated ULVWF strings formed on the complex-stimulated HUVECs, but the number of strings was significantly less than those of cells stimulated with histamine, IL-8, and TNF-α (mean ± SEM, Student t test, n = 3, **P < .01, compared to stimulation with histamine).