Endocytosed BSA-gold accumulates in lgp110-positive electron-dense lysosomes. (a through c) Pearl cells were allowed to endocytose BSA-10 nm gold for 4 hours followed by a chase in conjugate-free medium for 20 hours. Gold accumulated in electron dense lysosomes which could be immunolabeled with antibodies to the lysosomal marker lgp110 (15 nm gold). Although most of the lysosomes were of normal appearance (a), some were filled with rolled-up membranous inclusions (b and c; arrowheads indicate the 15 nm gold-labeled lgp110). (d through f) Plastic sections of BSA-10 nm gold-containing lysosomes, showing the internal membranes. Scale bar = 200 nm.