Recognition of nucleic acid and nucleic acid analogs by Toll-like receptors 7, 8 and 9

The mammalian immune system senses pathogens through pattern recognition receptors (PRR) and responds with activation. Toll-like receptors (TLRs) that are expressed on immune and non-immune cells play a critical role in this process. As part of the innate immune response, TLRs lead to cellular activation and cytokine production with subsequent initiation of an adaptive immune response. TLR7–9 recognize single-stranded RNA, nucleoside analogs and single-stranded CpG-DNA, respectively, and their activation initiates the immune response against viruses and bacteria. Furthermore, the stimulation of these TLRs may be exploited for adjuvant therapy, vaccination and anti-tumor responses. However, a role in the generation or perpetuation of autoimmune diseases such as systemic lupus erythematosus (SLE) has also been suggested.