Present and not reporting for duty: dsRNAi in mammalian cells.

Double-stranded RNA interference (dsRNAi) represents a primary means of anti-viral defense in plants, worms, and insects, yet appears mostly supplanted bythe protein-based interferon (IFN) response in vertebrates such as mammals. The degree to which dsRNAi is anti-viral in mammals has been contentious. Maillard etal () find that dsRNAi retains sequence-specific silencing in mammalian cells incapable of triggering an IFN response, suggesting that dsRNAi is inhibited by the action of interferon-stimulated genes. Importantly, they observe that while dsRNA can vaccinate against the incoming cognate virus though dsRNAi silencing, no dsRNAi is observed with viral infection alone, suggesting that this evolutionarily conserved anti-viral pathway is present but functionally elusive in the cell types studied thus far.