All mice were bred at the animal facility of the Helmholtz Centre for Infection Research (HZI) and maintained under specific pathogen-free conditions. For experiments, female mice 8 to 12 weeks of age were used. All mice used in this study were on the C57BL/6 background. IFN-b 2/2 [60] mice were backcrossed onto C57BL/6 for more than 15 generations. Conditional deletion/reporter mice IFN-b floxb-luc were generated using C57BL/6 ES-cells (Bruce4). To replace the IFN-b CDS by luciferase in germ line (IFN-b Db-luc ), IFN-b floxb-luc mice were crossed with K14cre mice [61] . To receive tissue specific IFN-b deletion as well as reporter expression, IFN-b floxb-luc were crossed to CD19cre [62] , CD4cre [63] and LysMcre [44] mice respectively (kindly provided by Dr. Angela Schippers, HZI). CD11ccre mice [64] were kindly provided by Prof. Dr. Ulrich Kalinke, Twincore. Additionally IFN-b +/Db-luc mice were crossed with albino C57BL/6 (C57BL/6-Tyr,c-2J.) kindly provided by Thomas Blankenstein (MDC, Berlin) to improve in vivo imaging.