Localization of endogenously and ectopically expressed HA-TGN38 in Tfn-loaded or Rab 11-GFP–expressing cells. RBL-Syt IX⁺ cells (A-C) or RBL-Syt IX⁺ cells transiently transfected with either Rab 11-GFP (D-F) or HA-TGN38 (G-I) cDNAs were grown on glass coverslips for 48 hours, serum starved for 1 hour, and allowed to internalize Texas red-conjugated Tfn (50 μg/mL) for 30 minutes (A-C,G-I). Cells were subsequently labeled with monoclonal anti-TGN38 (A-F) or anti-HA (G-I) antibodies followed by FITC- or Cy3-conjugated donkey anti–mouse IgG. Bars represent 4 μm.