Figure 6.

Typical sizes of vesicles formed during endocytosis. The reported size ranges of vesicles formed by the three most common endocytosis pathways are shown, along with typical tracers used in endocytosis studies, albumin for caveolae-mediated pathway, transferrin for clathrin-mediated pathway, and 70 kDa dextran for macropinocytosis. Further studies are needed to compare the sizes of each of these vesicles directly for the same cell type and with the same tracers. While intracellular vesicles exhibit reported size limitations, there are reported cases of caveolae expanding to carry 100 nm nanoparticles. Since all of the tracers are well below the typical sizes of endocytosis vesicles, meaning that each vesicle type can physically accommodate each tracer type, there is a factor of specificity for endocytosis uptake of nanoparticles (and tracers) that is beyond physical size.