Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA), a molecular pattern associated with viral infection. Polyinosine-polycytidylic acid (poly(I:C)), a synthetic analog of dsRNA, is the ligand of choice for TLR3. Poly(I:C) is composed of a strand of poly(I) annealed to a strand of poly(C). The size of the strands varies. InvivoGen is the only company to provide poly(I:C) with two different sizes:
• Poly(I:C) (HMW) with a high molecular weight has an average size of 1.5-8 kb.
• Poly(I:C) (LMW) with a low molecular weight has an average size of 0.2-1 kb
Fluorescently-labeled poly(I:C)-HMW is available. InvivoGen supplies polyadenylic–polyuridylic acid "poly(A:U)" a synthetic dsRNA that signals only through TLR3. HEK-Blue™ TLR3 Cells are used to validate the functionality of these ligands. Poly(I:C) VacciGrade™ (preclinical grade: sterile and endotoxin level