TLR7 mediates tRNA-induced immunostimulation. (A) WT and TLR7-deficient FLT3L-induced DCs were stimulated with 1 µg/ml RNA40 and 2 µg/ml tRNA from A. lwoffii complexed to DOTAP. The TLR9 ligand CpG-ODN2216 (1 µM) served as positive control. (B) Mouse FLT3L-induced DCs (gray bars) or human PBMCs (black bars) were incubated with 1 µg/ml RNA40 or 2 µg/ml tRNA from A. lwoffii and increasing amounts of the TLR7 inhibitory oligodeoxynucleotide IRS661 (1, 0.2, and 0.04 µM). Cells were incubated for 20 h with subsequent IFN-α detection by ELISA. For all panels, one representative experiment of at least two independent experiments is shown (n = 2 ± SD).