Fig. 1.

In vitro transcribed ssRNA has a feature other than the 5′-triphosphate necessary for RIG-I activation. (A) Primary human monocytes were stimulated with ss- and dsRNAs that were chemically synthesized (5′-OH) or generated by IVT (5′-ppp). After 36 h, IFN-α was quantified in the supernatant by ELISA. (B) The same set of RNA ligands was assayed for their ability to induce ATPase activity in recombinant purified full-length RIG-I protein. Each condition was done in the presence and absence of ATP. (C) Untreated or CIAP-treated 5′-ppp-ssRNA (IVT) was tested for immunostimulatory capacity on monocytes as in A. RNA treatment with heat-inactivated (hi)CIAP was used as a control. (D) Fluorescence signal of the ATPase assay was measured after incubation of full-length RIG-I protein with RNA oligonucleotides from C.