Stimulation of Type I interferon's by the L.inn::vgc strain A striking phenomenon for cytosolic resident microbes is the ability to induce expression of Type I interferons. In contrast to the wild type Lm, its isogenic mutant lacking listeriolysin remains trapped in vacuoles and does not induce Type I interferon's [17] . We have recently documented that the L.inn::vgc can successfully survive inside phagocytic cells, thereby egressing from the phagolysosome [18] . In order to confirm if cytosolic persistence of the recombinant L.inn::vgc strain is efficient enough to stimulate production of such cytokines, we examined the transcriptional responses of IFN-a2 and IFN-b1 in bone marrow-derived macrophages following infection with Lm, L.inn as well as the recombinant L.inn::vgc strain. L.inn::vgc and the wild type Lm showed significantly higher transcriptional induction of both IFN-a2 and IFN-b1 than wild type L.inn at 2 hours post-infection (Fig. 1B) . This effect was more pronounced at a later time point (8 hours) post-infection reflecting the efficient intracellular survival pattern of the L.inn::vgc strain.