 The role of RNA interference in mammalian innate immunity is poorly understood, and relatively little data is available.However, the existence of viruses that encode genes able to suppress the RNAi response in mammalian cells may be evidence in favour of an RNAi-dependent mammalian immune response, although this hypothesis has been challenged as poorly substantiated.Evidence for the existence of a functional antiviral RNAi pathway in mammalian cells has been presented.