Subcellular localization of internalized hFcγRIa/IgG/OVAgold complexes. Cells expressing hFcγRIa WT/γY65F,Y76F or hFcγRIa ▵315/γY65F,Y76F were incubated with rabbit IgG anti-OVA, followed by 5-nm OVAgold (OVAg), were washed, and were allowed to internalize for 60 minutes at 37°C, before fixation and preparation for IEM. Ultrathin cryosections were immunolabeled with antibodies to TfR (A) or MHC class II (B) and 10-nm protein gold particles. (A) Electron micrograph of a hFcγRIa ▵315/γY65F,Y76F expressing cell, showing that OVAg is present in small vesicles and tubules (1) and in an early endosome (2). Several of the small vesicles (arrows) display colocalization with gold particles for TfR (10 nm). A lysosome (4) shows some clustered OVAg. G, Golgi complex. (B) OVAg in a hFcγRIa WT/γY65F,Y76F transfected cell is present in type 1 vesicles and tubules (1), an early endosome (2), and two multivesicular type 3 compartments (3), the latter containing abundant MHC class II labeling (10 nm). Bars represent 100 nm.