Objective      To demonstrate the mobilization of endothelial progenitor cells (EPCs) after acute ischemic stroke (AIS) and investigate its possible mechanism.       Methods      A total of 71 patients with AIS were examined at days 1

7

14 and 21 after stroke onset. Forty-two healthy controls were also examined. Circulating EPCs were defined by the surface markers CD133/KDR and analyzed

by flow cytometry. Serum stromal cell-derived factor-1 (SDF-1) concentrations were determined by enzyme-linked immunosorbent assay.       Results      Baseline EPCs level was significantly lower in patients with AIS than in control subjects (0.022±0.013 vs 0.051±0.020

P

0.01). Blood pressure

triglyceride

low-density lipoprotein (LDL) and fasting blood sugar were negatively correlated with EPCs levels (

P

0.01). Systolic blood pressure and LDL remained independent predictors of baseline EPCs levels. The number of circulating EPCs increased on day 7 after AIS

reached peak level on day 14 and started to decrease on day 21. The concentration of SDF-1 had similar changes. The increment of EPCs (absolute difference between the number of EPCs on day 14 and admission) was correlated with the infarct volume (r=0.708;

P

0.01) and SDF-1 concentration on day 14 (r=0.774

P

0.01).       Conclusions      Baseline EPCs level in patients with AIS may reflect the cumulative vascular endothelial damage

while increase of circulating EPCs results from the mobilization of EPCs in response to stroke stress. The mechanism may be associated with up-regulation of SDF-1 expression.