The canonical nucleosides adenosine, uridine and cytidine can be modified by enzymes that install new chemical groups (shown in red). The RNA modifications can change base-pairing interactions, protein binding and secondary structures, which can prevent the modified RNAs from forming immunogenic structures, such as double-stranded RNAs (dsRNAs), and evading detection by immune sensors, including Toll-like receptors (TLRs), RIG-I and protein kinase R (PKR). ADAR, double-stranded RNA-specific adenosine deaminase.