CpG oligodeoxynucleotide induces bone marrow precursor cells into myeloid-derived suppressor cells

Dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) perform a number of functions in different immunological settings. In standard in vitro experiments, DCs are produced from mouse bone marrow (BM) cells in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4. Our previous study demonstrated that BM precursor cells could differentiate into MDSCs when co-cultured with poly (I:C). In the present study, BM precursor cells cultured in GM-CSF and IL-4 were treated with CpG oligodeoxynucleotide (CpG ODN). We observed that Gr1(+) CD11b(+) cells exhibiting MDSC functions accumulated in the co-culture system. A similar phenomenon was also observed in Listeria monocytogenes-infected mice. In conclusion, we demonstrated that prolonged CpG ODN stimulation could inhibit the development of DCs and induce the differentiation of BM precursor cells into MDSCs.