Gm18-modified tRNA acts as antagonist for TLR7-mediated IFN-α production upon tRNA or ssRNA stimulation and viral infection. (A) Mouse FLT3L-induced DCs were stimulated with 2 µg/ml tRNA from A. lwoffii and various concentrations of tRNA from E. coli Nissle or T. thermophilus (2, 1.5, 1, 0.5, 0.2, 0.1, 0.05, 0.025, and 0.0125 µg/ml). (B) Human PBMCs were stimulated with 1 µg/ml RNA40 and various concentrations of tRNA from T. thermophilus or A. lwoffii (2, 0.5, 0.125, and 0.0313 µg/ml). (C) Human PBMCs were infected with various MOI (10, 1, and 0.1) of influenza virus A/PR/8/34 (IAV) and 2 µg/ml purified tRNA from T. thermophilus. For each stimulation, tRNA was complexed to DOTAP and incubated for 20 h with subsequent IFN-α detection by ELISA. For A–C, representative experimental data from one out of four responsive PBMCs or two mouse cell preparations are shown (n = 2 ± SD).