The three cell lines were labeled with PAM Ab/protein A-gold complexes on ice and allowed to internalize PAM Ab/protein A-gold complex for 10 or 20 min at 37°C. (A) Representative images are shown for PAM-1 cells; scale bar, 500 nm. (B) Quantification of gold particles in early endosomes (EE, yellow), outer (Ext, green) and internal (Int, red) membranes of MVBs and aggregated (Aggr, black) in MVBs or lysosomes (± SEM of two separate experiments).