P. REUTHER¹, K. GÖPFERT², A. DUDEK², D. DORNFELD², M. SCHWEMMLE<sup>2

1</sup>Department of Biomedicine, Experimental Virology, University of Basel, 4009 Basel, Switzerland, ²Department of Virology, University of Freiburg, 79104 Freiburg, Germany

Reporter viruses represent valuable tools to study dynamics of a viral infection in cell culture and animal models. Furthermore, they facilitate screens for host factors or antiviral agents. We generated A/SC35M (H7N7) viruses encoding a Renilla luciferase, a secreted Gaussia luciferase, GFP-derivates (GFP, dsRed, Azurite) as well as a virus encoding a Cre-recombinase. These viruses grow to high titers and, importantly, do not loose the inserted gene while passaging.
To evaluate the suitability of the luciferase-encoding viruses for drug screenings, we treated infected MDCKII cells with different concentrations of the nucleosid inhibitor ribavirin. We could show that antiviral effects can be visualised by a luciferase assay already 3-6 hours post infection. We also tested these viruses for their suitability for screens for host factors. Knock down of the antiviral host protein MxA resulted in a significant increase of luciferase activity in human A549 cells upon infection with the reporter viruses.
The Cre/loxP system is a widely used method to specifically control the expression of target genes. To evaluate the applicability of the Cre-encoding virus as a tool for in vivo studies, we employed rosamT/mG reporter mice. Upon infection of these mice with a sublethal viral dose, we made use of the Cre-mediated switch from red to green fluorescence in order to localize and characterize cells that survived acute viral infection by fluorescent microscopy as well as flow cytometry. Surviving cells were present in different lung tissues and belonged to diverse lineages. Strikingly, we identified fort he first time a population of stem/progenitor cells, which survived viral infection.