Figure 3. The C. jejuni–Containing Vacuole Is Accessible to Endocytic Tracers in Macrophages but Not in Epithelial Cells.

(A) Cos-1 cells were infected with S. typhimurium invA (invasin) expressing the dsRed protein or C. jejuni, pulsed with the endocytic tracers dextran to label lysosomes, and phagosomes containing bacteria that colocalized with endocytic tracer were quantified. Results are the means and standard deviation of three independent experiments. For each experiment, at least 100 phagosomes were counted. Alternatively, infected cells were pulsed with the endocytic tracer BSA-gold and visualized by electron microscopy. Electron micrographs of phagosomes containing S. typhimurium invA (invasin) (B and C) or C. jejuni (D, E and F) are shown. C. jejuni–containing vacuoles (CCVs) that do not colocalize with BSA-gold (D and E) as well CCVs that colocalize with BSA-Gold and resemble lysosomes (F) are shown for comparison (see text). In addition, bone marrow–derived macrophages were infected with C. jejuni and pulsed with BSA-gold and visualized by electron microscopy. Electron micrographs of phagosomes containing C. jejuni are shown (G and H). Arrows indicate BSA-gold. Higher magnifications of the indicated insets are also shown to the right of each electron micrograph. Quantification of the colocalization of BSA-gold with bacterial vacuoles in the different cells are shown (I). Results are representative of two independent experiments in which at least 50 vacuoles were counted for colocalization with BSA-gold.