FACS analysis of chemokine receptor expression on CD34⁺ cells using MoAbs or biotinylated ligands. BMMNC were costained with an FITC-conjugated MoAb to CD34 and MoAbs to CXCR4 (B), CCR5 (C), and CCR2 (D), followed by PE-conjugated antimouse IgG or streptavidin-PE as described. Alternatively, cells stained with PE-conjugated anti-CD34 MoAb were also costained with biotinylated MIP-1 (E) or MCP-1 (F), followed by avidin-FITC. The forward versus side-scatter characteristics of the gated population, R1, is shown (A). Negative gates were drawn according to the threshold seen with either the isotype-matched negative controls or in the case of the biotinylated ligands, after the addition of neutralizing antichemokine antibodies provided by the manufacturer (R&D Systems).