RSP2 on the surfaces of erythroid precursor cells. (A) Cocultured. erythroblasts/parasites stained with Giemsa at merozoite reinvasion, showing interaction with the surface of a HEL 92.1.7 cell. (arrows) Merozoites interacting with the erythroblast surface. (B) Double labeling (IFA) of an FCR3^CSA/HEL 92.1.7 coculture at the time of reinvasion, using an anti-MSPp19 mAb (red) and B4 (green). (arrows) RSP2 transferred to the sites of interaction between merozoites and the cell. (C-D) L-IFA with the B4 (red) and anti-GA mAbs (green) of HEL 92.1.7 erythroblasts. GA⁺ (C) and KMOE-2 GA^- (D) cells isolated from cocultures with FCR3 parasites. Arrows indicate GA⁺ erythrocytes. Nuclei are labeled with DAPI (blue). Independently acquired images were overlaid. (E) L-IFA with anti-RSP2 mAb B4 (red), anti–GA mAb (green), and anti-CD45 mAb (blue) of ex vivo myeloid cells. Flow cytometry quantification of RSP2 on HEL 92.1.7 and KMOE-2 erythroblasts, normalized according to GA expression (F-G). The percentage of RSP2-positive cells was determined by subtracting cells positive for the isotypic controls. We found that 26.51% of KMOE-2 GA-erythroblasts cocultured with FCR3^CSA were RSP2⁺ (A) compared with 28.10% of HEL 92.1.7 GA⁺ erythroblasts (B).