Sequence: 5'-tccatgaCGttcctgatgct-3' (Class B ODN 1668: Bases are phosphorothioate.) Synthetic oligodeoxynucleotides (ODN) containing unmethylated deoxycytosine-deoxyguanosine (CpG) motif are equivalent to bacterial DNA in the immunostimulatory activity, which can induce innate immunity via Toll-like receptor 9 (TLR9) in mammals. There are three major classes of CpG ODNs, and each ODN class exhibits different stimulatory effects on immune cell activation. Class A ODNs are potent inducers of IFN-alpha that leads to the plasmacytoid dendritc cell (pDC) maturation. Class B ODNs are relatively weak inducers of type I IFNs but strong stimulators of human B cells and monocyte maturation. Class C ODNs combine elements of both Classes A and B ODNs, which can induce IFN-alpha in pDC and activation of B cells.