CD163 mediates endocytosis of ADAMTS13 by MDMs. MDMs were incubated for 20 minutes at 37°C with monoclonal antibodies directed against CD163; with EDHu-1, -2, -3, or -4; or with a combination of EDHu-1, -2, -3, and -4. ADAMTS13-AF488 was subsequently added to the cells, and endocytosis was analyzed by flow cytometry. (A) Macrophages incubated with EDHu-1 (dotted line) show reduction in the uptake of ADAMTS13-AF488 compared with ADAMTS13-AF488 (solid red line). Blue shaded area corresponds to nontreated cells. (B-D) Macrophages incubated with EDHu-2, -3, or -4 (dotted line) show no reduction in uptake of ADAMTS13-AF488 when compared with ADAMTS13-AF488 only (solid red line). Blue-shaded area corresponds to nontreated cells. (E) Macrophages incubated with a combination of EDHu-1, -2, -3, and -4 (dotted line) show reduction in uptake of ADAMTS13-AF488 when compared with ADAMTS13-AF488 (solid red line) or nontreated control cells (blue-shaded area). (F) Quantification of the data presented in panels A-E. Data are expressed as percentage of MFI with 100% corresponding to the mean fluorescence signal observed for ADAMTS13-AF488 uptake in the absence of antibodies. Data are representative of 3 independent experiments ± SD. (G) ADAMTS13-AF488 was added to MDMs for 1 hour at 37°C. MDMs were stained for ADAMTS13-AF488 (green), CD163 (Alexa Fluor 633; red), and nuclei (DAPI; blue). Scale bars are 10 μm. **P < .01 (Student t test). ns, not significant.