Evaluation of the effect of muscle exercise on the recruitment of human CD133⁺ cells. CD133⁺ stem cells were incubated with PkH2 green to allow detection by fluorescence microscopy with a perfusion technique that showed the vasculature in 3 dimensions. Intra-arterially injected CD133⁺ stem cells were rarely found in the vessels of dystrophic muscles before exercise (A, C). In contrast, after swimming exercise intra-arterially injected scid/mdx mice showed an increased number of adhered cells in the capillary network (B, D) and to large vessels (E). (E) Large vessels perfused with a rubber silicon fluid were detected in transillumination. (inset) Cells were not evident in other fluorescence acquisitions, confirming that positively registered cells in vessels were not artefacts. (F) Statistical evaluation by Student t test of the number of CD133⁺ cells adhered to the vessel and confirmed significant improvement in recruitment after exercise. ^*P < .05. Scale bars represent 100 μm (A-C), 200 μm (D), and 25 μm (E). In panels A-E, arrows indicate the labeled cells. Error bars in panel F indicate standard deviation.