Objective    To investigate the isolation

culture

proliferation and differentiation of endothelial progenitor cells (EPCs) from rat circulating blood and to study of magnetic resonance imaging of nano-bioprobe that was constructed with endothelial progenitor cells and superparamagnetic iron oxide (SPIO).     Methods    The mononuclear cells (MNCs) were isolated from SD rat peripheral blood

and EPCs were selected by adherence method. Then the expressions of cell markers of EPCs were assessed by immunohistoche

mistry. EPCs were incubated with Fe

2

O

3

-arginine for 24 h

then intracellular iron was detected by Prussian blue stain and the cells underwent in vitro MR imaging with three sequences (T

1

WI

T

2

WI

T

2

*WI).     Results    Immunocytochemical stain showed that the adherent cells were positive for CD31

CD34

Flk21 and vWF 4 d after adherent culture. Iron-containing intracytoplasmatic vesicles could be observed clearly with Prussian blue staining

and the labeling rate of EPCs were nearly 100%. The signal intensity on MRI was significantly decreased in labeled EPCs compared with unlabeled cells.     Conclusion    EPCs can be obtained from mononuclear cells in rat peripheral blood and be differentiated into endothelial cells. EPCs can be labeled with Fe

2

O

3

-arginine to construct nano-bioprobe in vitro without significant changes in viability and proliferation. The labeled EPCs can be imaged with standard 1.5 T MR equipment.