A positive feedback-loop regulates transcriptional response to murine pandemic influenza infection

The biological basis for the increased severity of influenza A viruses during the 2009 influenza pandemic remains unclear. Intra-host evolution of quasispecies and strong inflammation were identified as important hallmarks of severe pandemic H1N1 influenza A virus 2009 (A(H1N1)pdm09) infection. HA-222D/G quasispecies of A(H1N1)pdm09 were shown to undergo fast evolution and to cause severe influenza in human and mice. Here, we analysed the whole genome transcriptional response of mice infected with the A/Jena/5258/09 (mpJena/5258) virus over a period of 12 days to gain insights into the pathogenesis of A(H1N1)pdm09 HA-222D/G quasispecies on a molecular level. Remarkably, the transcriptional response to severe mpJena/5258 showed biphasic expression profile for the majority of genes which was never shown before. The gene expression analysis shows first peak with 968 differentially expressed genes at day 2 post infection (p.i.), followed by a stagnant recovery phase with 359 differentially expressed genes at day 4 p.i., and a second peak with 1001 differentially expressed genes at day 7 p.i., finally followed by a recovery phase. Using a reverse engineering strategy, a regulatory network was inferred to identify key interactions leading to severe pathogenesis of mpJena/5258. Known regulatory interactions were extracted by Pathway Studio 9.0 and softly integrated during network inference. The results demonstrate a hyper-responsive action and a positive feedback loop of IFN gamma (Ifng), Stat1 and Tlr3 signalling during mpJena/5258 infection. In conclusion, mpJena/5258 infection is associated with biphasic gene expression profile and a positive feedback mechanism of Ifng which correlates with the evolution of HA-222D/G quasispecies and leads to overwhelming immune response. A significant correlation were found between the co-expression action of three genes (Ifng, Stat1 and Tlr3) with a phenomenological clinical symptom score. Total RNA obtained from isolated lung of each mice subjected to Influenza A virus infection (A/Jena/5258/09) pover a period of 12 days compared with control mice.