Trafficking of Shigella lipopolysaccharide in polarized intestinal epithelial cells

Bacterial lipopolysaccharide (LPS) at the apical surface of polarized intes tinal epithelial cells was previously shown to be transported from the apic al to the basolateral pole of the epithelium (Beatty, W.L., and P.J. Sanson etti, 1997. Infect. Immun. 65:4395-4404). The present study was designed to elucidate the transcytotic pathway of LPS and to characterize the endocyti c compartments involved in this process. Confocal and electron microscopic analyses revealed that LPS internalized at the apical surface became rapidl y distributed within endosomal compartments accessible to basolaterally int ernalized transferrin. This compartment largely excluded fluid-phase marker s added at either pole. Access to the basolateral side of the epithelium su bsequent to trafficking to basolateral endosomes occurred via exocytosis in to the paracellular space beneath the intercellular tight junctions. LPS ap peared to exploit other endocytic routes with much of the internalized LPS recycled to the original apical membrane. In addition, analysis of LPS in a ssociation with markers of the endocytic network revealed that some LPS was sent to late endosomal and lysosomal compartments.