To overcome the restrictions of in vivo imaging with black mice, the results were corroborated by ex vivo quantification of luciferase activity (Fig. 5B ). Using this assay, we could confirm that T-and Bcells did not contribute to luciferase activity in spleen and lymph nodes at both time points. In contrast, LysMcre specific IFN-b reporter mice contributed with similar levels of luciferase activity compared to IFN-b +/Db-luc mice. Hence, LysM-expressing cells almost exclusively produce IFN-b in both spleen and lymph nodes upon infection with L. monocytogenes. Confirming the role of LysM-expressing cells during Listeria monocytogenes infection