To investigate if infection with L. monocytogenes on a single cell level is a prerequisite for IFNβ production we infected BMDMs and GMCSF-DCs in vitro either with L. monocytogenes stained with BacLightTM (data not shown) or with GFP expressing L. monocytogenes (Figure 4D). Here, IFNB1 is linked to infection.