FIG. 10.

The phenotype of M. tuberculosis phagosomes and avirulent L. pneumophila phagosomes but not wild-type L. pneumophila phagosomes is altered by expression of the constitutively active Rab5c Q79L mutant. Suspensions of wild-type L. pneumophila (A), avirulent L. pneumophila (B), or M. tuberculosis and latex beads (D) were added to monolayers of HeLa cells expressing Rab5c Q79L and centrifuged at 1,160 × g for 20 min at 4°C, incubated at 37°C for either 30 min (L. pneumophila [A and B]) or 2 h (M. tuberculosis [D]), fixed, and processed for cryoimmunoelectron microscopy. Rab5c was stained with 15-nm immunogold particles (large arrowheads), LAMP-1 was stained with 10-nm immunogold particles (small arrowheads), and L. pneumophila LPS (A and B) or mycobacterial LAM (C and D) was stained with 5-nm immunogold particles (arrows). (A) Wild-type L. pneumophila resides in a morphologically tight phagosome that lacks immunogold staining for Rab5c and LAMP-1, which are present on an adjacent large vacuole (∗). (B) A large vacuole contains numerous avirulent L. pneumophila and stains positive for both Rab5c and LAMP-1. (C and D) M. tuberculosis resides in large vacuoles that stain positively for Rab5c and for LAMP-1. M. tuberculosis often shares the large vacuole with latex beads (D). Nu, nucleus. Magnifications, ×37,310 (A), ×37,310 (B), ×37,310 (C), and ×42,770 (D).