Table 1. RNA ligand structures that indicate non-self.

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Structure	Recognized structure description	Receptor or effector molecule	Virus
	dsRNA >300 bp	TLR3, MDA5, OAS1 and PKR	dsRNA viruses, (+)ssRNA viruses and dsDNA viruses, such as HSV-1
	dsRNA >30–60 bp	TLR3; OAS1 and PKR (via RIG-I)	dsRNA viruses, (+)ssRNA viruses and dsDNA viruses, such as HSV-1
	5′ppp or 5′pp plus blunt base-paired RNA ≥19 bp	RIG-I	dsRNA viruses, (+)ssRNA viruses, (−)ssRNA viruses and intracellular bacteria
	5′ppp plus structured ssRNA ≥47 nt	PKR	(−)ssRNA viruses
	5′cap plus unpaired ssRNA ≥5 nt	IFIT1	Viruses with incomplete 5′capping
	Long RNA with strong secondary structures	MDA5 and ADAR1	Unmodified endogenous and viral RNA
...UGUGUGUGU... ...UUUUUUUUUUU...	PolyU and GU-rich RNA	TLR7 and TLR8	Unmodified endogenous, viral and bacterial RNA
...CG... ...UA...	CpG dinucleotide- and UpA dinucleotide-rich RNA impairs viral replication	Unknown	Viral mRNA

5′pp, 5′-diphosphate; 5′ppp, 5′-triphosphate; ADAR1, adenosine deaminase acting on RNA 1; ds, double-stranded; HSV-1; herpes simplex virus 1, IFIT1, IFN-induced protein with tetratricopeptide repeats 1; OAS1, 2′-5′-oligoadenylate synthetase 1; MDA5, melanoma differentiation associated gene 5; PKR, protein kinase R; RIG-I, retinoic acid inducible gene I; ssRNA, single-stranded RNA; TLR, Toll-like receptor.