Identification of an erythroblast-binding motif in the second scavenger receptor domain of CD163. (A) Generated 13-mer peptides corresponding to sequences from each of the 9 extracellular scavenger domains of human CD163 (called p1-p9, respectively) and of the second domain of rat/mouse CD163 (called p2-rm). (B) Binding of K562 cells or freshly isolated rat erythroblasts to CD163 peptides. Peptides were used at 40 μg/mL coating concentrations, and cell binding was quantified by staining with the DNA-binding dye SYTO-13 followed by measurement of the fluorescence. Data shown are the means ± SD from at least 5 independent experiments. (C-D) Concentration dependence of K562 (C) and rat erythroblast (D) adhesion to the human (p2) or rodent (p2-rm) CD163-binding motif. Data shown are from 1 representative experiment of 3. (E) Binding of human erythroblasts, generated in vitro from CD34⁺ HSCs from 2 separate donors, to CD163p2 peptide. CD163p7 peptide is used as a negative control. K562 cell binding is shown for comparison. The 2 cell populations had comparable numbers (> 80%) of erythroblastic cells, with a similar subset distribution.