Phagocytosis of exosomes by DCs. (A) Capture of DC exosomes labeled with PKH67 by BMDCs. (B) Role of surface molecules in internalization of exosomes by DCs. BMDCs were mixed with PKH67-labeled exosomes in the presence of blocking mAbs, peptides, O-phospho-D-serine (D-serine), or O-phospho-L-serine (L-serine). After incubation (1 hour, 37°C), DCs were labeled with PE CD11c mAb and analyzed by flow cytometry. The percentage of exosome uptake was considered only for CD11c⁺ cells. Uptake of PKH67⁺ exosomes relative to control represents the percentage of DCs with exosomes compared to their controls considered as 100% phagocytosis. Data represent 5 independent experiments. *P ≤ .01, ** P ≤ .001. (C) PKH67-labeled exosomes were internalized predominantly by immature (CD86^–) BMDCs. (D) Splenic CD8α^– and CD8α⁺ DCs (B10) capture PKH67-labeled DC exosomes (BALB/c) in vitro based on the absence of BALB/c exosome markers (IA^d, FasL, and mTNF-α) on the surface of the acceptor DCs. Numbers indicate percentage of cells. Data are representative of 4 independent experiments.