Figure 3.

Picture gallery of late endosomes. (A) HepG2 cells pre-incubated for 3 h with BSA⁵ and immunogold-labeled for LAMP2 (15-nm gold particles). LE vacuoles contain multiple ILVs but can differ in size and shape. Note the recycling tubule emerging from the LE (arrow). The lysosome (L) has not been reached by BSA⁵. (B) MVB/MHC class II compartment of a dendritic cell immunogold-labeled for MHC class II (15-nm gold) and CD63 (10-nm gold). Note that the ILVs are heterogeneous in size. CD63 is rather associated with smaller vesicles, whereas MHC class II is present on the larger vesicles and also with the limiting membrane. (C) Typical example of an LE/MVB. Immunogold labeling for LAMP1 (10-nm gold) is mainly restricted to the limiting membrane. Note the different morphological features of the ILVs present in these distinct MVBs (A–C). (D) HepG2 cells pre-incubated for 3 h with BSA⁵. Fusion profile (arrow) of an LE positive for BSA⁵ with a lysosome devoid of BSA⁵. Techniques used: (A–C) Chemical fixation and ultrathin cryosectioning; (D) HPF, rehydration, ultrathin cryosectioning. Scale bar, 200 nm.