Bacterial and synthetic DNA containing unmethylated 2'-deoxyribo(cytidine-phosphate-guanosine) (CpG) dinucleotides in specific sequence contexts activate the vertebrate innate immune system. A molecular pattern recognition receptor, Toll-like receptor 9 (TLR9), recognizes CpG DNA and initiates the signalling cascade, although a direct interaction between CpG DNA and TLR9 has not been demonstrat...