RNA-sensing Pattern Recognition Receptors (Toll-like receptor 3, Toll-like receptor 7, Toll-like receptor 8, Retinoic acid-inducible gene I, and Melanoma differentiation-associated protein 5) (RNA PRRs)

This target group represents the primary innate immune sensors responsible for detecting viral and endogenous RNA species. It includes the endosomal Toll-like receptors (TLR3, TLR7, and TLR8) and the cytosolic RIG-I-like receptors (RIG-I and MDA5). TLR3 recognizes double-stranded RNA (dsRNA), while TLR7 and TLR8 detect single-stranded RNA (ssRNA). RIG-I and MDA5 are cytosolic RNA helicases that sense various RNA structures, such as 5-triphosphorylated RNA and long dsRNA, respectively. Activation of these pathways initiates a coordinated immune response characterized by the production of Type I interferons and pro-inflammatory cytokines, which are critical for antiviral defense and the priming of adaptive immunity. In therapeutic development, agonists of these receptors are utilized as vaccine adjuvants and as immunotherapies to stimulate the tumor microenvironment in oncology. Conversely, dysregulated activation of these sensors is a key driver in the pathogenesis of several autoimmune and autoinflammatory disorders.

Other names

TLR3 / TLR7 / TLR8 / RIG-I / MDA5Nucleic acid-sensing receptorsRNA sensorsToll-like receptor 3 (CD283)Toll-like receptor 7 (CD287)Toll-like receptor 8 (CD288)Retinoic acid-inducible gene I (RIG-I, DDX58)Melanoma differentiation-associated protein 5 (MDA5, IFIH1)RIG-I-like receptors (RLRs)

Activation of these receptors by RNA ligands triggers distinct signaling pathways (TRIF for TLR3; MyD88 for TLR7/8; MAVS for RIG-I/MDA5) that activate transcription factors such as IRF3, IRF7, and NF-kappaB. This leads to the robust production of Type I and Type III interferons and pro-inflammatory cytokines, which establish an antiviral state and enhance adaptive immune responses.