In vitro-generated viral double-stranded RNA in contrast to polyinosinic : Polycytidylic acid induces interferon-α in human plasmacytoid dendritic cells

Double-stranded RNA (dsRNA) arises in the cytoplasm during viral replication and was shown to participate in the interferon (IFN)-a induction process. Besides the intracellular recognition, released dsRNA from dying, infected cells can function as a pathogen-associated molecular pattern (PAMP) for the innate immune system. In the present study, in vitro-generated dsRNA fragments of genomic sequences of Newcastle disease virus were used to induce IFN-a release in human peripheral blood mononuclear cells (PBMC), in immature myeloid dendritic cells (mDC) and in immature plasmacytoid DC (pDC). The extracellular administration of dsRNA fragments but not the application of the corresponding single-stranded RNA (ssRNA) strands led to an IFN-a production in PBMC. The synthetic dsRNA analogue polyinosinic acid : polycytidylic acid [Poly(I : C)] could only stimulate IFN-a production in enriched mDC but not in pDC. In contrast, dsRNA fragments induced IFN-a only in pDC. Complexation of dsRNA fragments with transfection reagents increased the efficiency of IFN-a induction and commuted ssRNA molecules into IFN-a inducers. However, stimulation of in vitro-generated murine Toll-like receptor 7 (TLR7) knockout DC and human TLR-transfected HEK293 cells with dsRNA fragments gave no evidences for the involvement of pDC-specific TLR7 or TLR9 in the observed IFN-a induction.