Injecting sP-selectin-Fc, but not sP-selectin, increases the frequency of deep vein thrombi. WT mice were injected intraperitoneally every 24 hours for 3 days (time 0, 24 hours, or 48 hours) with saline, sP-selectin, sP-selectin Fc, or control-Fc. Twenty-two hours after the first injection, the inferior vena cava was ligated to induce thrombosis. After 72 hours (48 hours after ligation), the incidence, size, and weight of thrombi were measured. (A) Frequency of thrombus. For each experimental group, the number of mice forming thrombi relative to the total number of mice is shown. (B) Thrombus length. (C) Thrombus weight. (D-E) Plasma levels of sP-selectin or sP-selectin-Fc at the indicated time after injection. The data represent the mean ± SEM from 10 to 16 experiments in each group. *P < .05.