FIG. 1.

Schematic representation of the positive IFN feedback loop. Latent IRF-3 is activated through TLR3 and TLR4 signaling by dsRNA and LPS, respectively, or by virus infection. The early IFN-β (and early IFN-α subtypes) induces the expression of ISGs, including IRF-7. IRF-7 is activated again by dsRNA or LPS signaling or by virus infection. In addition, ligands of TLR7 and TLR8, including single-stranded RNA (ssRNA), and TLR9, including CpG DNA, can activate IRF-7. α-prom., IFN-α promoter; β-prom., IFN-β promoter.