Recent studies have shown the involvement of different TLRs including TLR 2, 3, 4, 7 and 9 in the innate recognition of different viruses [16, 17, 18, 57, 58, 59, 60, 61] . Signaling via TLR9 was shown to be responsible for the strong type I IFN response of pDCs to Ad in vitro [10, 45, 46 ]. Here we investigated the possible involvement of TLR9 in the induction of type I IFNs by measuring IFN-ab in Ad infected wt and TLR9 2/2 mice. Fig. 4A shows that TLR9 2/2 mice produced normal levels of IFN-ab. upon infection with Ad3. Comparable results were obtained with the recombinant Ad5-GFP (Fig. S7A) . Moreover, Unc93B mice, deficient in signalling by intracellular TLRs showed normal IFN-ab responses to Ad5-GFP (Fig. S7A ). We further checked the possible involvement of the TLR system using mice deficient for TLR2, TLR4 or for the TLR adaptor proteins TRIF and MyD88. Fig. 4A shows that the Ad3 induced IFN-ab levels in all strains of mice were as high as in the respective wt controls. Similarly, comparable IFN-ab responses were also found in TLR-, MyD88-or TRIFdeficient mice and in the corresponding wt animals after infection with UV-inactivated Ad3, AdR700 and Ad5-GFP (not shown). Furthermore, comparable IFN-ab responses were found in cultures of Ad-infected BMDCs from wt, MyD88-and TRIFdeficient mice (Fig. 4B ). The various TLR deficient mice showed impaired responses to the corresponding ligands in control experiments (Fig. S7B ). Collectively, our data show that the TLR system plays no major role in the systemic IFN-ab responses to Ads in mice.