Induction of the IFN-b gene was independent of the TLR adapter Mal/TIRAP, but, unexpectedly required the TLR3/4 adapter TRIF. Francisella tularensis has recently been shown to signal through TLR2 from the phagosome in a Mal/TIRAP independent manner [32] , and it was shown that Mal/TIRAP is dispensable in TLR2 signaling at high concentrations of ligands [33] . Thus our study reinforces the view that TLR2 can act independently from Mal/TIRAP. In addition our report suggests a synergy between a TLR2 pathway and TRIF, an adapter previously known to trigger the synthesis of pro-inflammatory cytokines and type I IFNs upon engagement of TLR3 and TLR4. TLR3 is known to bind viral dsRNA to induce secretion of type I IFN and lead to control of viral infections [3, 34, 35] . To our knowledge Chlamydia muridarum is the only bacterium reported to induce a TLR3-dependent IFN-b response specifically in murine oviduct epithelial cells [36] . We tested whether the dual requirement for TLR2 and TRIF resulted from a functional or physical interaction between TLR2 and TLR3. In fact, IFN-b production was reduced in TLR3-deficient macrophages, but significantly less so than in trif2/2 PEM. Therefore, there is no evidence for a putative TLR2/TLR3 interaction. Another possibility to incorporate TRIF into the pathway stimulated in PEM by Listeria would be a cooperation of TLR2 and TLR4. This was ruled out by showing that Listeria-infected tlr4 2/2 PEM produced a similar amount of IFN-b as their wild-type counterparts. TRIF could possibly orchestrate an additional pathway. Along these lines, TRIF has recently been shown to be required for IFN-b synthesis by dendritic cells upon activation of the cytosolic receptor complex DDX1/DDX21/DDX36 by viral RNA [19] .