Direct identification and quantification of host and viral miRNAs after influenza infection using the next generation ultra-high throughput DNA sequencer.

The subtype of avian influenza H5N1 virus is epizootic and panzootic, and can transmit zoonotically to humans. The fatality rate of H5N1 disease remains high at about 60%, but this rate may be over-estimated, as H5N1 viruses cause both severe and subclinical infection in humans, and these mild non-hospitalised H5N1 cases are not counted by the World Health Organization as confirmed cases.1 Cytokine dysregulation is one of the key contributory factors to H5N1 pathogenesis.2 The precise mechanisms by which the H5N1 virus elicits the differential host responses remain poorly understood. MicroRNAs (miRNAs) are 21-23 nt RNA molecules that can modulate gene expression and play an essential role in the regulation of many diverse biological processes, including viral infection. Macrophages are key host immune cells that respond to viral infection and are a major source of many cytokines. The present study used the new generation ultra-high throughput Solexa sequencer to determine hostand viral-derived miRNAs (if any) induced by the highly pathogenic H5N1 and low virulent H1N1 viruses in human macrophages at early time points. Together with the mRNA expression profile, the possible regulating pathways/ mechanisms were revealed by identifying miRNAs that may lead to influenza pathogenesis.