Previous studies have shown that, depending on the inducing virus, IFN-ab is produced ubiquitously or in a cell type specific manner [13, 14] . Here we stimulated different primary mouse cells, including bone marrow derived mDCs (BMDC), bone marrow derived macrophages (BMM), bone marrow derived pDCs and mouse embryonic fibroblasts (MEFs), with Ad2 (species C) or Ad3 (species B). Six hours later, the IFN-ab content of culture supernatants and the expression of the viral E1A gene in the cells were determined. BMDC and BMM, but not MEFs, produced IFN-ab (Fig. 1D ), although all cell types were successfully infected as shown by RT-PCR ( Fig. 1E and not shown). Very similar results were obtained when, instead of Ad2, Ad3 or the recombinant Ad5-GFP were used for infection of the three cell types (not shown). In addition, pDCs also produced IFN-ab in response to Ad infection in vitro (Fig. S3A) ; however, only at high multiplicities of infection. Finally, like MEFs, L-929 cells infected with Ad2 produced no IFNab either (Fig. S3B ). In agreement with previous studies [36, 37] , MEFs and L-929 cells produced IFN-ab following transfection with purified DNA (Fig. 1D and Fig. S10C ). In addition to mouse DCs and macrophages we also found that human monocyte-derived DCs produced IFN-ab upon infection with the adenoviral vector Ad5-GFP (Fig. S3C) . The present data confirm that Ads can trigger IFN-ab production in various immune cells in vitro [10, 45, 46] . However, it furthermore indicates that production does not proceed ubiquitously in all types of infected cells.