FIG. 6.

Phagosomes containing wild-type L. pneumophila but not avirulent L. pneumophila exclude Rab5c. Suspensions of wild-type (A) or avirulent (B and C) L. pneumophila were spun down onto monolayers of pTRE/rab5c-HeLa Tet-off cells at 4°C, incubated at 37°C for 15 min, and either fixed immediately (A and B) or washed, incubated in fresh culture medium for 6 h, and then fixed (C). Cells were processed for cryoimmunoelectron microscopy. Rab5c has been stained using 15-nm gold particles (arrowheads), and L. pneumophila LPS has been stained using 5-nm gold particles (arrows). Rab5c is absent from the wild-type L. pneumophila phagosome (A), despite the presence of Rab5c immunogold staining on vesicles adjacent to the phagosome. Rab5c is present on the avirulent L. pneumophila phagosome at 15 min (B) but is absent by 6 h (C). Magnifications, ×72,827 (A), ×38,235 (B), and ×50,664 (C).