Demonstration of endosomes in CHRF-288 cells. (A) 10-minute internalization of BSA-gold. Tracer is found in characteristic tubulo vesicular structures that are enriched in CI-MPR (arrowheads). MVBs positive for CD63 are negative for CI-MPR and do not contain the endocytic tracer at these times. (B) Simultaneous demonstration of CI-MPR (arrowheads) and GPIIb-IIIa (small arrows) in an endosome containing tracer. (C) Overnight incubation with medium containing 20% normal plasma. Simultaneous demonstration of fibrinogen and GPIIb-IIIa in an endosome close to the plasma membrane. mvb, multivesicular body; e, endosome; pm, plasma membrane. Bars, 100 nm.