Moreover, about 80% of pDCs are supposed to exhibit recombination in CD4cre mice [37] . Nevertheless, these mice did not show any luciferase production, confirming our data from above. Thus, we conclude that pDCs do not contribute to the type I IFN production during Listeria monocytogenes infection. Only cells, in which the LysM-promoter is active, significantly contribute to the IFN-b signal in spleen at 24 and in lymph nodes at 48 hours p.i. (Fig. 5A ). Of note, the bioluminescence signal in such mice is lower than in the mice displayed in Fig. 1A . Obviously, the signal is quenched by the black skin and fur of the recombinant C57BL/6 mice.