CpG DNA: recognition by and activation of monocytes.

Unmethylated CpG motifs present in bacterial DNA rapidly trigger an innate immune response characterized by the activation of Ig- and cytokine-secreting cells. Synthetic oligonucleotides (ODNs) containing CpG motifs mimic this activity, triggering monocytes to proliferate, secrete and/or differentiate. Analysis of hundreds of novel ODNs led to the identification of two structurally distinct classes of CpG motif that differentially activate human monocytes. ODNs of the "K"-type interact with Toll-like receptor 9 and induce monocytes to proliferate and secrete IL-6. In contrast, "D"-type ODNs trigger monocytes to differentiate into mature dendritic cells.