RIGI and infection: The host innate immune system is composed of many molecules that sense infection, including pattern recognition receptors and restriction factors (RFs), which recognize viral proteins and nucleic acids as foreign, thereby triggering these responses as a means of warning surrounding cells to “arm themselves.” These include Toll-like receptors, retinoic acid-inducible gene I (RIG-I)-like receptors and the dsRNA-activated protein kinase R (PKR), among others.