Synthetic oligodeoxynucleotides (ODN) containing unmethylated deoxycytosine-deoxyguanosine (CpG) motifs. These CpG motifs are present at a 20 fold greater frequency in bacterial DNA than mammalian DNA. CpG ODNs are recognized by Toll-like receptor 9 (TLR9). Two types of CpG ODNs have been identified based on their distinct activity on plasmacytoid dendritic cells (pDC), which is the key sensors of the CpG motifs. CpG Type A induces IFN-a production in pDC whereas Type B strongly activates B cells and weakly activates IFN-a stimulation. The CpG ODN sequence differs between human and mouse, however both negative controls contain GpC instead of CpG.
