Another unexpected observation in this study was the delay in infection of the spleens and livers of TLR4 −/− and MyD88 −/− mice 1-2 weeks post-inoculation. These results suggest that TLR4 and MyD88 play significant roles in mediating Brucella dissemination from the lungs to other tissues, which is consistent with a previous observation indicating a role for TLR4 in the uptake of smooth Brucella by macrophage (Pei et al., 2008) , and that translocation of bacteria across mucosal or intestinal barriers is mediated by TLR4 (Neal et al., 2006) . Evaluation of Brucella infection dynamics derived from different routes of entry during the first week post aerosol exposure may be expected to confirm these results and potentially suggest post-exposure treatments.