Distribution of CD82 after 5 and 60 min of chase with anti-CD82 mAb analyzed by electron microscopy. HB2/CD82wt and HB2/CD82ΔC were incubated with anti-CD82 mAb (TS82b) for 1 h and then with protein A gold 10 nm for 40 min at 4 °C and subsequently chased for 5 or 60 min at 37 °C. Then the cells were fixed and processed according to the protocol described under “Experimental Procedures.” A, B, and G, after 5 min of chase, CD82wt and CD82ΔC were distributed to the plasma membrane and in the uncoated invaginations of PM. C (main panel and inset), after 5 min of chase, internalized CD82wt was found in the uncoated structures (arrow) but not coated vesicles (arrowheads). D, after 5 min of chase, CD82wt was observed in rosette-like endosomal structures. E, after 60 min of chase, internalized CD82wt was mainly distributed to the intracellular multivesicular compartments (arrows) and found occasionally at the PM. F, after 60 min of chase, gold-labeled CD82wt was also found on extracellular vesicles (arrows). H–J, CD82ΔC after 60 min chase was found on internal (H and J) and on extracellular (I) vesicles. K, quantification of the distribution of gold particles (average 1500) between various membranous compartments after 5 and 60 min of chase with anti-CD82 mAb in HB2/CD82wt and HB2/CD82ΔC cells. Scale bar, 200 nm.