Induction of IL-1Ra expression by poly(I:C) and Sendai virus infection is dependent on TLR3 and IRF3 in vivo. WT, TLR3−/−, and IRF3−/− mice were treated intraperitoneally with poly(I:C; 10 mg/kg in sterile endotoxin-free physiological saline, a, b) or Sendai virus (100 HA units/mL, c, d) for 24 h. The level of serum IL-1Ra was measured by ELISA. Results are presented as individual mean values of each mouse (n = 8 per group). The lines indicate the mean value for each group. * p < 0.05 vs. the WT mice group treated with poly(I:C) or Sendai virus. SenV, Sendai virus; IL-1Ra, IL-1 receptor antagonist; TLR3, toll-like receptor 3; IRF3, interferon regulatory factor 3.