Short-term endothelial progenitor cell colonies are composed of monocytes and do not acquire endothelial markers.

BACKGROUND

The aim of this study was to identify circulating endothelial progenitor cells (EPC) with colony-forming capacity and compare them with the monocytic-macrophage lineage.

METHODS

Forty-two healthy donors were analyzed. EPC were cultured with VEGF and b-FGF. Sequential studies were performed on days +7 (colonies) +21 and +35. Monocytic cells were cultured using the same conditions as EPC until day +21 or alternatively by adding IGF.

RESULTS

The number of EPC colonies was higher in BM than in mobilized or steady-state PB. Using EPC medium, monocytic cells formed cord-like structures but no colonies. However, colonies grew when IGF was added to the medium. By immunocytochemistry, colonies showed CD45, CD31 and lysozyme but no vWF. Colonies were CD4+, CD13+dim, CD14+, CD15++, CD16-/+dim, CD31+dim, CD33+dim, CD45+, CD105-/+dim, lysozyme+ and VE-cadherin+, and constantly negative for CD34, CD133 and KDR, when flow cytometry was used. The immunophenotype of pre-cultured and cultured monocytes was similar to that described for EPC.

DISCUSSION

Our results suggest that the so-called 'EPC' obtained at 7 days of culture belong to the monocyte-macrophage lineage, as they share immunophenotypic and molecular features.