Shortly after administration, a rapid release of reticulocytes and nucleated DRAQ5^pos erythroid progenitors is stimulated by EPO (epoetin-alfa), but less so by CNTO 530. Mice (n = 3 per treatment group) were administered CNTO 530 (0.15 μg/mouse gram-weight), epoetin-alfa (EPO; 2 U/mouse gram-weight), or 0.9% saline (to account for background staining levels) via tail vein injections. At 2 hours, peripheral blood samples were analyzed for levels of TO^pos DRAQ5^neg reticulocytes (A) and for DRAQ5^posCD71^high progenitors (B). (Note baseline levels of CD71⁺ TO⁻ and CD71⁺ DRAQ5⁺ cells were 1.2% and 1.4%, respectively.)