Analysis of H-ferritin and holo-transferrin uptake by hematopoietic cell lines.

(A) Uptake of AF488-labeled human holo-transferrin (Tf), H-ferritin (HFt), and L-ferritin (LFt). Cells were incubated with AF488-labeled ferritins (11 nM) or Tf (62 nM) for 60 min and analyzed by flow cytometry. The MFI ratio was defined as the MFI of cells treated with fluorescence-labeled ligand divided by the MFI of untreated cells. Filled columns denote the results of competition experiments using a 20-fold excess of unlabeled cognate ligand. Graphs for NB4, Reh, and THP–1 cell lines are shown on a larger scale in the in the enclosed areas. Data represent the mean ± standard error of three independent experiments. (B) Relationship between HFt and holo-Tf uptake. Cell lines shown in (A) are shown as blue dots by their MFI ratios for HFt and holo-Tf uptake in a scatter plot (Spearman’s coefficient, ρ = 0.95; P < 0.0001). A red dot in this plot represents the position of human bone marrow erythroblasts shown in Fig 3B.