RIGI and viral infectious disease: The innate immune system is a first-line host immune defense against viral infection, by sensing invading viruses with its pattern recognition receptors (PRRs) expressed either on the cell surface or inside the cytoplasm (e.g., toll-like receptors: TLRs, retinoic acid-inducible gene I: RIG-I and the NOD-like receptor family member NOD-, LRR- and pyrin domain-containing 3: NLRP3) [61,62] (Figure 3).