Macrophages are required for the protective effect of ADAMTS13. (A) Plasma VWF multimeric compositions from 4 groups of S/S mice at basal level and at different time points after VOE induction (1, 2, and 3 hours). Control + saline, S/S mice treated with saline and control liposomes; control + ADAMTS13, S/S mice treated with ADAMTS13 and control liposomes; clodronate + ADAMTS13, S/S mice treated with ADAMTS13 after clodronate-mediated macrophage depletion; and clodronate + saline, S/S mice treated with saline after clodronate-mediated macrophage depletion. Data represent at least 4 independent experiments. HMWM, IMWM, or LMWM represents high, intermediate, or low molecular weight VWF multimers, respectively (denoted by red lines). (B) The percentage of LMWM among total VWF at each time point was quantified based on densitometry. Data represent at least 4 independent experiments. (C) Plasma levels of lactate dehydrogenase (LDH) and aspartate transaminase (AST) at 3 hours after VOE induction in different groups of S/S mice treated as described in panel A. Each dot represents 1 mouse. Data represent mean ± standard deviation. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001, 1-way ANOVA. (D) Representative confocal microscopic images of liver cryosections from different groups of S/S mice. These sections were stained with primary antibodies to VWF, macrophages (F4/80), and erythrocytes (Ter119). DAPI cell nuclear staining. The top panel shows efficient depletion of F4/80-positive macrophages in clodronate-treated mice. Bottom panel highlights that ADAMTS13 reduced VWF-positive vaso-occlusion and colocalization (yellow) of VWF with sickle erythrocytes (Ter119), which was abolished by clodronate-mediated depletion of macrophages. Data represent at least 4 independent experiments. (E) Quantification of VWF-positive vaso-occlusions in (D). Data represent at least 4 independent experiments. Data represent mean ± standard deviation. ∗∗∗∗P < .0001, 1-way ANOVA.