Polyanionic ligands block the internalization of ADAMTS13 by MDMs. (A) Preincubation with mannan (dotted line) resulted in reduced endocytosis of ADAMTS13-AF488. (B) Antibody clone 15.2 blocking the mannose receptor did not affect ADAMTS13 uptake. (C) MDMs were incubated with ADAMTS13-AF488 at 37°C for 1 hour. Cells were stained for ADAMTS13-AF488 (green), MR (Alexa Fluor 568; red), and nuclei (DAPI; blue). Scale bars are 10 μm. (D-E) MDMs were incubated with fucoidan, poly-I, or poly-C before addition of ADAMTS13-AF488. Cells were analyzed by flow cytometry. (D-E) Effect of poly-I, poly-C, and fucoidan on ADAMTS13 uptake (gray shaded area represents controls incubated in the absence of ADAMTS13). Cells incubated with ADAMTS13 are indicated by a solid black line; cells preincubated with the inhibitors are indicated by a dotted line. Data in bar graphs are representative of 3 independent experiments ± SD. ***P < .001 (Student t test). AB, antibody.