Abstract： Background C-reactive protein (CRP) has been reported to damage the vascular wall by inducing endothelial dysfunction and inflammation,and it is also speculated to have a role in attenuating angiogenic functions of human endothelial progenitor cells (EPCs).Interleukin-8 (IL-8) is an important mediator of the paracrine mitogenic effect of EPCs,which has direct angiogenic effects on mature endothelial cells.We,herein,investigated the direct effect of CRP on IL-8 production and gene expression in cultured human EPCs.Methods EPCs were isolated from the peripheral venous blood of healthy male volunteers.Cells were cultured in EndoCultTM liquid medium in the absence and presence of CRP at clinically relevant concentrations (5 to 25 μg/ml) for different durations (3 to 48 hours).IL-8 protein and mRNA of cultured EPCs were evaluated using ELISA and real-time PCR.Results The results showed that CRP at a concentration of 10 pg/ml significantly reduced IL-8 secretion of cultured EPCs with a peak at 25 μg/ml,and also decreased mRNA expression in EPCs with a peak at 12 hours.In addition,preincubation of EPCs with SB203580,an inhibitor of p38 mitogen-activated protein kinase (MAPK) decreased CRP inhibition of IL-8 mRNA expression at 12 hours in EPCs.Conclusions Our study,for the first time,demonstrates that CRP directly inhibits EPCs IL-8 secretion,a key cytokine player of angiogenesis induced by EPCs.Inhibition occurred in part via an effect of CRP to active the p38 MAPK signal transduction pathway in EPC.The ability of CRP to inhibit EPCs IL-8 secretion may represent an important mechanism that further links inflammation to cardiovascular disease.