The immunostimulatory activity of CpG oligonucleotides on microglial N9 cells is affected by a polyguanosine motif

Our data show that N9 cells express Toll-like receptor 9 (TLR9) and are activated by CpG-ODN, which leads to expression of interleukin-12p40 (IL12p40), tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS). A 3′-end polyG motif inhibits phosphothioate (PS) CpG-ODN immunostimulatory activity but enhances the immunostimulatory activity of phosphodiester (PE) CpG-ODN. Correspondingly, a 3′-end polyG motif improves the cellular uptake of PE CpG-ODN but does not change their cellular distribution pattern. Furthermore, PE CpG-ODN with a 3′-end polyG motif interact with a much higher number of cellular proteins than PE CpG-ODN. These data indicate that the 3′-end polyG motif could enhance the immunostimulatory activity of PE CpG-ODN in microglial N9 cells through increasing interaction with cellular proteins. Therefore PE CpG-ODN containing a 3′-end polyG motif resulting in increased immunostimulatory activity might be promising alternate analogues for studies in the central nervous system.