Merged images of fluorescence photomicrographs from animals injected intravenously at P20 show Alexa 488 (green) labelled and large (0.2 μm) red fluorescent microsphere containing cells. A: 30 minutes following IV injection. B: 1 hr following injection. C: 1 week following injection. D: 2 weeks following injection. Calibration bar in 'D' = 50 μm for all images.