A single naturally occurring 2′-O-methylation converts a TLR7- and TLR8-activating RNA into a TLR8-specific ligand

Abstract

TLR7 and TLR8 recognize RNA from pathogens and lead to subsequent immune stimulation. Here we demonstrate that a single naturally occurring 2′-O-methylation within a synthetic 18s rRNA derived RNA sequence prevents IFN-α production, however secretion of proinflammatory cytokines such as IL-6 is not impaired. By analysing TLR-deficient plasmacytoid dendritic cells and performing HEK293 genetic complementation assays we could demonstrate that the single 2′-O-methylation containing RNA still activated TLR8 but not TLR7. Therefore this specific 2′-O-ribose methylation in rRNA converts a TLR7 / TLR8 ligand to an exclusively TLR8-specific ligand. Interestingly, other modifications at this position such as 2′-O-deoxy or 2′-fluoro had no strong modulating effect on TLR7 or TLR8 activation suggesting an important role of 2′-O-methylation for shaping differential TLR7 or TLR8 activation.