RIGI and infection: Upregulation of both RIG-I and MDA-5 was also observed up to 24.5- and 9.4-fold, in addition to the increased expression of MyD88, an adaptor protein in TLR signaling pathway, in HepG2 cells, indicating that the induction of the viral RNA sensors is in general responsive to infection in human liver epithelial cells (Fig. 7B).