CpG oligodeoxynucleotides induce IL-8 expression in CD34+ cells via mitogen-activated protein kinase-dependent and NF-κB-independent pathways

To elucidate the role of Toll-like receptor 9 (TLR9) activation along with the intracellular signaling pathways triggered by CpG DNA in CD34(+) cells, we investigated whether synthetic oligodeoxynucleotides (ODNs), containing unmethylated CpG motifs, could induce IL-8 expression in CD34(+) cells through mitogen-activated protein kinase (MAPK) or nuclear factor-kappa B (NF-kappa B) pathway. We demonstrated evidence for the first time that CD34(+) cells constitutively expressed TLR9. Exposure of the cells to CpG ODN resulted in a time- and dose-dependent increase of IL-8 expression, and activation of phosphorylated ERK1/2 and phosphorylated p38. In addition, CpG ODN stimulated AP-1, but not NF-kappa B, signals. Moreover, inhibitors of MAPK (U0126 and SB203580) significantly reduced the IL-8 production, while the inhibition of NF-kappa B (pyrrolidinedithiocarbamate and retrovirus containing dominant-negative I kappa B alpha plasmid) did not affect the IL-8 expression increased by CpG ODN. Moreover, co-stimulation with LPS and CpG synergistically up-regulates IL-8 in CD34(+) cells. These results suggest that CpG DNA, acting on TLR9, activates CD34(+) cells to express IL-8 through MAPK-dependent and NF-kappa B-independent pathways.