FIG. 1.

Fusion of Brucella-containing phagosomes with preformed lysosomes. Colloidal gold particles (20 nm) coated with mannosylated BSA were internalized in J774 macrophages for 15 min at 37°C and chased into lysosomes by an additional 60-min incubation. B. abortus (opsonized [squares] or not opsonized [circles]) was incubated with the macrophages (100 Brucella bacteria/macrophage) for 5 min at 37°C. Cells were then washed five times with BME to remove nonadherent bacteria. Macrophages were incubated at 37°C for different times, fixed, and processed for transmission electron microscopy. (A) The percentage of phagosomes containing gold particles was calculated by counting at least 100 phagosomes for each condition. (B) The percentage of digested Brucella was estimated by counting at least 150 intraphagosomal bacteria. The results are from one of three independent experiments performed.