Fig. 3. Giant endosomes do not correspond to lysosomes. To further demonstrate the nature of the giant endosomes in rab5(Q79L) expressing macrophages, cells were incubated with 16 nm BSA-gold for 30 minutes, followed or not by a 16 hours chase period. After an internalization of 30 minutes (A), BSA-gold particles were found in large endocytic organelles (e). As in the kinetic experiment with the fluid phase tracer, a longer chase period (16 hours) resulted in the transfer of the BSA-gold particles to smaller electron dense vesicles (l) (B), while large vacuoles now devoid of BSA-gold particles could be observed. Bars, 100 nm.