Figure 5.

TLR4-mediated uptake and fluid-phase endocytosis result in differential intracellular sorting of internalized endotoxin. Cascade blue 4 KDa dextran, a marker of fluid-phase endocytosis, was injected systemically 16 h before imaging (A, E). Four hours before imaging, Alexa 568-labeled endotoxin 3 mg/Kg was injected systemically (B, F). Arrowhead in B points to red endotoxin that does not co localize with blue dextran in a S1 segment of WT mouse. S2 of WT and all tubules of TLR4 KO showed purple color indicating colocalization of red endotoxin with blue dextran. TLR4-mediated uptake of endotoxin in S1 of WT (but not KO) mice is even more evident when TLR4 receptors are upregulated with preexposure to 0.25 mg/Kg unlabeled endotoxin (C, G). Panels D and H show the distribution of red and blue fluorescence in each pixel from panels C and G, respectively. A two-compartment model is evident in WT but not TLR4 KO mice.