Fig. 4. Mycobacterial lysate inhibits phagosome maturation and fusion with lysosomes. (A,B) PKH-labeled cells were exposed to latex beads in the presence of 100 µg/ml of BSA (control) or a soluble fraction derived from whole-cell lysates of either M. tuberculosis (Mtb) or M. smegmatis (M.smeg). Phagosomes were isolated at 1 hour (A) and 2 hours (B) post phagocytosis, permeabilized and incubated with antibodies to Rab7 and LAMP-1, respectively, and samples were analyzed by flow cytometry as described in Fig. 2. (C) F-DXT-loaded THP-1 cells were stained with PKH and allowed to ingest latex beads in the presence of BSA, or a soluble fraction derived from whole-cell lysates of either M. tuberculosis or M. smegmatis. Phagosomes were prepared at 2 hours post phagocytosis and analyzed by FACS as described in Fig. 3. Values represent the averages of two independent experiments.