Exosome clearance and distribution in vivo. (A) C57BL/6 or CD169^−/− mice were anesthetized and then IV injected with 100 µg Exo-bio (purified by ultracentrifugation). Mice were tail bled at the indicated time points. MHC-II⁺ exosome concentration was analyzed by enzyme-linked immunosorbent assay from plasma samples; Exo-bio spiked plasma was used as a standard. Closed circles, C57BL/6 mice; open circles, CD169^−/− mice. (B) C57BL/6 or CD169^−/− mice were IV injected with 100 µg Exo-bio. Mice were killed at the indicated time points, and spleens were harvested. Exo-bio was detected with streptavidin-Alexa-594 and nuclei counterstained with DAPI. (B) Original magnification, ×100. Bar represents 500 µm. Results representative of (A,B) 6 mice (120 minutes) and (B) 3 to 6 mice (5 and 60 minutes).