Infection and the kinetics of clearance of Brucella from the spleens of mice is notably different from that observed in the lung. Initially, the organism exhibits a delay in systemic distribution to the spleen that requires up to 4 weeks to achieve maximum burden. The delay in systemic spread of infection is evident in the spleen and less dramatically in the liver (see below), with bacterial burden in 9 of 13 spleens from TLR4 −/− and 10 of 13 from MyD88 −/− mice below the detection limit (10 cfu/spleen). This compares with a delay in only 1 of 17 TLR2 −/− mice and 5 of 20 C57BL/6 mice. The MyD88 −/− knockout appears to have a reduced ability to control the infection as evidenced by the significant difference in spleen colonization by week 4 (Figure 2 , panel W4). Once established infection proceeds similarly, although the MyD88 −/− and TLR4 −/− mice exhibit a delay in clearance relative to the TLR2 −/− and C57BL6 mice ( week, which is accompanied by a delay in clearance at later times. Again, the exaggerated decline observed between weeks 8 and 10 in TLR4 −/− mice may be an artifact of the reduced animals numbers.