CpG DNA Switches on Th1 Immunity and Modulates Antigen-Presenting Cell Function

DNA containing CpG motifs, which are present in bacterial DNA but suppressed in mammalian DNA, can stimulate immune cells and modulate immune responses. A CpG motif consists of an unmethylated CpG dinucleotide flanked by two 5' purines and two 3' pyrimidines (Krieg et al. 1995). CpG motifs are similar to palindromic sequences identified earlier in bacille Calmette-Guerin DNA, which increase the cytolytic function of natural killer (NK) cells (Yamamoto et al. 1992), and immunostimulatory sequences, which increase the immunogenicity of DNA vaccines (Sato et al. 1996). Bacterial DNA or oligodeoxynucleotides (ODN) containing CpG motifs can stimulate B cells (Krieg et al. 1995; Sun et al. 1997), macrophages (Stacey et al. 1996; Sparwasser et al. 1997b), dendritic cells (Jakob et al. 1998; Sparwasser et al. 1998), and NK cells (Yamamoto et al. 1992; Ballas et al. 1996).