Aim To investigate the effect of a synthetic dsRNA analog polyriboinosinic polyribocytidylic acid(PolyI:C) on quantity and activity of endothelial progenitor cells from human umbilical cord blood in vitro. Methods Mononuclear cells were isolated from human cord blood by Ficoll density gradient centrifugation and then the cells were cultured in EBM-2 medium to differentiate into endothelial progenitor cells.Endothelial progenitor cells were identified by demonstrating the expression of characteristic cell surface marker CD34,CD133 and KDR by reverse transcriptase polymerase chain reaction.CCK-8 reagent kit was used to analyze the effect of PolyI:C on the proliferation of endothelial progenitor cells.Flow cytometry was used to detect the apoptosis caused by PolyI:C.Reverse transcriptase polymerase chain reaction was performed to detect firstly the expression of Toll-like receptors in endothelial progenitor cells,secondly the expression of Toll-like receptor 3 and inflammatory cytokines induced by PolyI:C. Results Under basal condition,except Toll-like receptor 9,Toll-like receptor 1-10 were expressed in endothelial progenitor cells with high expression levels of Toll-like receptor 1,Toll-like receptor 3,Toll-like receptor 4,Toll-like receptor 6 and low expression levels of Toll-like receptor 2,Toll-like receptor 5,Toll-like receptor 7,Toll-like receptor 8,Toll-like receptor 10.Expression of Toll-like receptor 3 mRNA was upregulated by PolyI:C and there was dose-effect relationship in experiment range.Compared with thecontrol group,PolyI:C groups(1 g/L and 10 g/L) significantly inhibited the proliferation of endothelial progenitor cells and the inhibition of PolyI:C(10 g/L) on endothelial progenitor cells proliferation was time-dependent.PolyI:C induced the apoptosis of endothelial progenitor cells in dose-dependent manner.PolyI:C also upregulated the mRNA expression of inflammatory cytokines such as interleukin-1β,interleukin-6,interleukin-8,tumor necrosis factor-α,interferon-β. Conclusion Poly I:C inhibits the proliferation of endothelial progenitor cells via induction of cell apoptosis,simultaneously up regulates the expression of inflammatory cytokines probably by activating Toll-like receptor 3.