In BMM rapid synthesis of IFN-b is entirely dependent on IRF3, but not on IRF7, whereas in bone marrow-derived myeloid DC IFN-b synthesis requires both IRF3 and IRF7 [27] . We investigated the role of IRF3 and IRF7 in the production of IFN-b by PEM. To this end we infected irf3 2/2 and irf7 2/2 macrophages with EGDe or the DpgdA strains. Inactivation of IRF3 totally abrogated IFN-b mRNA induction in response to both strains (Fig. 6 ). IFN-b induction in IRF7-deficient macrophages was also strongly affected highlighting the important role of both transcription factors in response to Listeria infection (Fig. 6 ). PEM thus resemble bone marrow-derived myeloid DC, not BMM, in relation to their IRF requirement for Listeria-mediated IFN-b synthesis.