Figure 3. Prominent role of RIG-I in orchestrating immunity against viable and virulent intracellular Listeria.

Schematic representation of the different PRRs and amplification mechanisms that operate in detection of intracellular infection with viable and virulent Listeria monocytogenes. Active secretion of small size nucleic acids through SecA2 from cytosolic Listeria is detected by DNA-sensing Aim2 as well as RNA-sensing RIG-I. RIG-I signaling is unique since it leads to concomitant activation of type I IFN induction through MAVS and inflammasome activation through ASC. This ensures that independent of cell surface or endosomal PRR activation in case of bacterial escape by direct cell-to-cell infection, the levels of cytosolic PRRs are increased, and through NF-κB activation, the expression of the pro-forms of IL-1β and IL-18 is augmented. The combination of type I IFN induction and inflammasome activation is important for rapid generation of protective anti-bacterial immunity.