tRNA from different bacterial species varies in their IFN-α–inducing potential. (A) Purified tRNA from different bacterial species were visualized on a 12% polyacrylamide gel (lane 1: B. subtilis; lane 2: P. aeruginosa; lane 3: T. thermophilus; lane 4: E. coli Nissle 1917; lane 5: L. lactis; lane 6: M. marburgensis). One representative gel is shown (n > 3). (B) Human PBMCs were stimulated with 2 µg/ml of purified tRNA from different bacterial species as indicated and IFN-α production is depicted as percentage of activity of the TLR7 agonist RNA40. Experimental data were obtained from PBMCs preparations of 3–10 different donors per strain. Statistical analysis was performed using the paired Student’s t test (***, P < 0.0001; *, P = 0.02).