Cells have evolved numerous ways to detect viral infection and set off the immune system's alarms. Extracellularly, Toll-like receptors spot double-stranded viral RNA, while inside the cell retinoic acid-inducible gene I ( RIG-I ) and melanoma differentiation-associated gene 5 ( Mda-5 ) are responsible for detecting viral RNA. Ultimately, through a sequence of activating events - with the complete set of steps yet to be characterized - all roads lead to interferon production, but some viruses are able to evade the system by exploiting weak links.













