Influenza viral RNA is a ligand for both human TLR7 and TLR8. (A) HEK/TLR8 cells (5 × 10⁴ cells) were stimulated with R-848 (3 μM), influenza virus RNA (X31, 0.2 nM) with or without lipofectamine transfection, or IL-1β (100 ng/mL). Supernatants were collected at 14 hours and IL-8 was measured by ELISA. (B) HEK/TLR7 cells were stimulated as in panel A. (C) HEK cells were also stimulated under these same conditions. Data shown are from one experiment. Two other experiments yielded similar results. Error bars represent the SD of triplicate samples. *P < .01 for influenza RNA compared with medium control by the 2-tailed paired t test.