RBCs from a thalassemic patient (HbE/β-thalassemia, splenectomized) enriched from the population labeled with AV-FITC using magnetic beads coated with an FITC antibody (see the Materials and Methods section). (A, B) Typical cells labeled with AV-FITC in the native unfixed state and then analyzed by serial optical sections in confocal fluorescent microscopy. Panel A shows the equatorial section of a cell homogeneously labeled with AV-FITC. Panel B shows three equatorial sections of a cell heterogeneously labeled with AV-FITC. (C,D) RBCs initially labeled with AV-FITC in the unfixed state and then labeled with monoclonal anti–α-globin chain antibody, and secondary Texas-Red–labeled goat antimurine antibody. This double-labeled cell was then analyzed by fluorescent microscopy. The areas where Texas Red (red) and FITC (green) overlap are yellow.