FIG. 5.

The CD11c⁺MHC-II^low DC subpopulation is most active in phagocytosing serovar Typhimurium. DC were coincubated with Salmonella phoP^c bacteria expressing GFP at a bacterium-to-cell ratio of 15:1. After 2 h, extracellular bacteria were washed away. The DC were subsequently labeled with monoclonal antibodies, cells were fixed in 1% paraformaldehyde and flow cytometry was performed. The dot plot shows the MHC-II and CD11c expression on infected DC and the regions R1 and R2, which were used to analyze the uptake of Salmonella phoP^c bacteria by CD11c⁺ cells. Histograms of flow cytometry analysis of CD11c⁺MHC-II⁺ (R1 + R2), CD11c⁺MHC-II^low (R1), and CD11c⁺MHC-II^high (R2) cells are shown. The y axis represents the number of DC, and the x axis represents log fluorescence intensity. Infections were done in the absence (thick line) or presence (thin line) of CCD. The numbers shown represent the percentage of DC infected with bacteria in the absence of CCD (i.e., actively internalized bacteria). In this gate 0.5% of the cells was infected when CCD was present. Similar results were obtained in at least four independent experiments.