Effect of rhEPO on EPC function. (A) Tube formation index of cocultered EPCs. Supplementation of rhEPO significantly stimulated the formation of tubelike structures in a dose-dependent manner (*P < .05 versus baseline). (B) Representative photomicrographs of tube formation with 1.2 IU/mL rhEPO. Fluorescent-labeled EPCs (red) were coplated with HUVECs (transparent) to form tubular structures. Both cell types were stained with endothelial cell–specific UEA-1 (green fluorescence). Superimposed light and fluorescent images of identical fields reveal that EPCs made a substantial contribution to the cellular network. Original magnification, × 200.