Circulating endothelial cells and angiogenic proteins in patients with systemic lupus erythematosus

The aim of our study was to assess absolute counts of different subpopulations of circulating endothelial cells (CEC) in patients with active and inactive systemic lupus erythematosus (SLE). We have also investigated a potential correlation of CEC numbers with serum levels of angiogenic proteins as well as with clinical and laboratory symptoms of the disease. For the first time in SLE, CEC were enumerated directly, by the 'single platform' method. Resting (rCEC), activated (aCEC) and progenitor (pCEC) endothelial cells were identified in patients with SLE and healthy volunteers using four-colour flow cytometry. Serum concentrations of angiogenic proteins (vascular endothelial growth factor, placental growth factor (PIGF), soluble vascular cell adhesion molecule and endoglin) were evaluated by ELISA. The SLE activity was scored according to the Systemic Lupus Activity Measure system. We found that total CEC number in patients with SLE was significantly higher (median 14.2/microL) than in the control group (median 3.3/microL) (P < 0.0001). Absolute counts of aCEC, rCEC and pCEC (medians 4.9/microL, 6.8/microL and 2.3/microL, respectively) were also higher in patients with SLE than in healthy persons (medians 0.9/microL, 1.6/microL and 0.1/microL, respectively), with P < 0.0001 for all comparisons. There was no correlation between CEC or their subpopulations and SLE activity. Strong positive correlations were found between CEC, rCEC and pCEC numbers and serum levels of PIGF. Moreover, aCEC, rCEC and pCEC counts were significantly higher in SLE patients with leukopenia. In conclusion, our results show that absolute CEC counts and angiogenic proteins levels are elevated in patients with SLE as compared with healthy controls. These data may suggest that angiogenic process is involved in the pathogenesis of this disease.