SDF-1 stimulates capillary formation in vitro. (A-E) HUVECs were coated on polystyrene beads and embedded in a fibrin matrix; 12nM (B) or 120nM (C) SDF-1 added to the media stimulates both the length of the longest sprout per bead and sprout number per bead in a dose-dependent manner. A total of 1μM AMD3100 (D) alone has no effect on capillary outgrowth but reduces SDF-1–stimulated outgrowth to control levels (E). Quantification is shown in panels F and G. Original magnification × 40. Scale bar represents 100 μm. For quantification, 2.5× images were taken of the center of a 4-well plate. Sprout lengths and numbers were quantified from 10 beads from the upper left-hand quadrant of this image. Beads were not counted if their sprouts did not lie entirely within the image. If fewer than 10 beads were found in the upper left quadrant, beads were counted from the upper right quadrant and so on in a clockwise manner until 10 were quantified. For each experiment, 2 wells for each condition were quantified. Experiments were repeated 3 separate times, and representative data are shown. Error bars represent SEM. Statistical analysis was performed using the unpaired Student t test assuming equal variance for pairwise comparison of treatment groups: **P < .05, ***P < .005.