HBEC-EMV origin and receptor-mediated transcytosis (RMT) receptors. (A) Number of proteins in HBEC-EMVs that are in common with HBEC endocytic proteins and/or HBEC plasma membrane proteins. Most of the RMT receptors shown in Table 2 were in common with plasma + endocytic membranes. (B) Detection of FC5 in HBEC-EMVs from either control cells or cells treated with 5 μg/mL of FC5 for 24 h in serum-free conditions using Western blot analysis with polyclonal anti-VHH antibody (obtained from Biogen Idec, Cambridge, MA, USA). Equal volume amounts were loaded and the blot is a representative blot of n > 3. (C) Levels of FC5-specific peptide detected by MRM as described in Methods. The levels are relative to median “untreated” values. *** represents p < 0.001 for Mann–Whitney U-test with n = 3.