TNF-α production induced by a human-type PO-CpG ODN2006 was also increased by co-incubation
with DNase I-treated GpC ODN2006 or DNase I-treated ODN1720 in the cells (Supporting Information Fig. 2). To evaluate the involvement of TLR9 in the DNase I-treated DNA-mediated increase in cytokine production, similar experiments were carried out using splenic macrophages and the production of TNF-α (Fig. 1C) and IL-6 (Fig. 1D) was examined. The addition of LPS, a positive control, induced significant TNF-α production in splenic macrophages from both WT and TLR9 knockout (KO) mice, indicating the ability of these cells to produce cytokines. In the cells from WT mice, DNase I-treated DNA significantly increased the ODN1668-induced production of TNF-α and IL-6. find more However, no such increase was observed in splenic macrophages from TLR9 KO mice. Next, we evaluated the effect of DNase I-treated DNA on the TNF-α production induced by ligands other than ODN1668. The following ligands were selected and used: pCMV-Luc, a double-stranded circular DNA containing many CpG motifs; ODN2216, a CpG ODN with phosphorothioate (PS) bonds at the both ends; PS-1668, a PS-type CpG ODN having the same sequence as ODN1668; non-CpG lipoplex, a complex consisting of pCpG-ΔLuc and cationic liposomes, which was reported to be a ligand for cytosolic DNA
receptors 18, 19; polyI:C, a double-stranded RNA and a ligand for TLR3; LPS, a ligand for TLR4; and imiquimod, a ligand for TLR7 20, 21. Based on preliminary experiments, the concentration of each ligand was set at low levels to avoid saturation of TNF-α production in cells. Each ligand induced Saracatinib supplier significant TNF-α production in RAW264.7 cells at varying levels (Fig. 2, hatched bars). DNase I-treated ODN1720 significantly increased pCMV-Luc-induced TNF-α production, but it hardly affected TNF-α production induced by other ligands (Fig. 2, black bars). Dipeptidyl peptidase Again, ODN1720 showed no significant effects on the TNF-α production induced by any of these ligands (Fig. 2, gray bars). These results indicate that the DNase-I-treated DNA-mediated increase in cytokine production is specific to two TLR9 ligands, ODN1668
and pCMV-Luc. Additionally, we examined the effects of DNase I-treated DNA on TNF-α production induced by another 26-mer ODN containing three potent CpG motifs, 5′-TCGACGTTTTGACGTTTTGACGTTTT-3′. The addition of DNase I-treated ODN1720 also increased the TNF-α production induced by this CpG ODN (data not shown). Taken together, these results suggest that the effect of DNase I-treated ODN1720 on cytokine production is independent of the sequence and length of CpG DNA, and not restricted to single-stranded DNA. To examine which components of DNase I-treated DNA were responsible for the increase in the CpG motif-dependent TNF-α production, RAW264.7 cells were incubated with ODN1668 in the presence of nucleotides or nucleosides (Fig. 3A).