Mechanism for Recognition of CpG DNA

Bacterial deoxyribonucleic acid (DNA) containing cytosine phosphate guanine (CpG ) motifs, but not vertebrate DNA, activates innate immune cells. CpG motifs in vertebrate DNA are suppressed and usually methylated. In contrast, CpG motifs in bacterial DNA are observed at the expected frequency and unmethylated, which causes immune cell activation. CpG DNA activation of immune cells is reproducible in synthetic oligonucleotides containing CpG motifs. Treatment with CpG DNA induces a potent immune response dominated by Th1 cell-mediated cellular immunity, which prevents and cures several infectious and immune diseases in animal models. CpG DNA is therefore promising as a clinically useful agent for the treatment of several human diseases including cancer, allergy, and infectious diseases. The molecular mechanism of CpG DNA-induced cellular activation has been investigated intensively, and a signaling pathway is now being revealed. The critical components that recognize CpG DNA have recently been identified. In this chapter, we focus on the recent advances in the CpG DNA-induced activation of innate immune cells.