Absence of MFG-E8 on mature exosomes does not account for their increased efficiency. (A) Western blot analysis of 3 μg of exosomes purified from immature WT or MFG-E8–deficient (Mfg^–/–) BMDCs. (B) ³H-thymidine incorporation by Marilyn T cells cultured with mature BMDCs and HY-bearing immature WT (WT HY Exo) or MFG-E8–deficient exosomes (Mfg^–/– HY Exo). One representative experiment out of 4.