Interactions between bacterial CpG-DNA and TLR9 bridge innate and adaptive immunity.

The astounding adjuvanticity and Th1-polarizing immunobiology of bacterial CpG-DNA and mimicking CpG-oligonucleotides continue to mirror promising therapeutic potential. The past year has witnessed some particularly impressive progress in knowledge of its molecular mode of action. Accordingly, CpG-DNA acts as a "pathogen-associated" molecular pattern that is recognized by TLR9 expressed, in particular, by dendritic cells. Interactions between CpG-DNA and TLR9 rapidly activate antigen-presenting dendritic cells through the ancient Toll/IL-1-receptor signaling pathway to upregulate co-stimulatory molecules and to produce Th1-polarizing cytokines, such as interleukin-12 and interleukin-18. Thus, interactions between CpG-DNA and TLR9 effectively bridge innate and acquired immunity.