ODN 2216 sequence: 5’-ggGGGACGA:TCGTCgggggg-3’ (20 mer), Specificity: human TLR9 agonist, Working concentration: 1-5 µM, Solubility: 5 mg/ml in water. CpG oligonucleotides (ODNs) are synthetic ODNs that contain unmethylated CpG dinucleotides in particular sequence contexts (CpG motifs). These CpG motifs are present at a 20-fold greater frequency in bacterial DNA compared to mammalian DNA. CpG ODNs activate Toll-like receptor 9 (TLR9), leading to strong immunostimulatory effects. ODN 2216 is a Class-A CpG ODN that preferentially binds to human TLR9. Class A CpG ODNs are characterized by a phosphodiester central CpG-containing palindromic motif and a phosphorothioate 3’ poly-G string. They induce high IFN-α production in plasmacytoid dendritic cells (pDC) but are weak stimulators of TLR9-dependent NF-κB signaling.