It is known, that the LysM promoter is active not only in monocyte/macrophages and neutrophils, but also in part of the CD11c + DCs, while no expression is observed in T and B cells [44] . Since it was recently shown that CD11b + CD11c int Ly6C + cells previously defined as Tip-DCs are the major IFN-b producers upon Listeria infection [29] , we wanted to know whether Tip-DCs belong to LysM-expressing monocyte /macrophage population and whether we could confirm the production of IFN-b by such cells. Therefore, we sorted CD11b + CD11c 2 macrophages, CD11c + CD11b 2 dendritic cells (DCs), CD11b + CD11c int Ly6C + Tip-DCs and B220 + CD11c 2 B cells as a negative control from IFN-b +/floxb-luc x LysMcre mice 24 hours after Listeria infection and tested for LysM, LysMcre as well as IFN-b expression by RT-PCR. A strong signal was observed for LysM in Tip-DCs and macrophages and, to a lesser extent, in dendritic cells (Fig. 8) . Cre recombinase was expressed in macrophages and in Tip-DCs, but not in DCs. IFN-b mRNA was highly pronounced in Tip-DCs and weakly in DCs. Faint bands were also detectible for IFN-a in these cells. In contrast, CD11b + CD11c 2 macrophages failed to produce any detectable amount of IFN-b or IFN-a. Taking together, our results indicate that cells defined as Tip-DCs are within LysM-expressing cells and are responsible for the major IFN-b production upon Listeria monocytogenes infection.