Recent Advances in Toll-like Receptor 9 and Its Ligands

The mammalian immune system senses pathogens through pattern recognition receptors.Toll-like receptor 9(TLR9)is one of innate immune pattern recognition receptors,and its natural ligands are unmethylated CpG dinucleotides(CpG-DNA)in the genomes of bacteria and viruses.Investigations of TLR9 stimulation in animal experiments and human trials generally use synthetic CpG ODN that have a nuclease-resistant backbone for improved stability.The activation of TLR9 by its ligands induces a strong T-helper-1 dominant immune response and has a prosperous future in the treatment of allergies,infectious diseases,and cancers.