FIG. 4.

Confocal microscopy analysis of the F-actin rearrangements induced by L. pneumophila Lp02 and HtpB-coated beads in CHO-htpB cells not expressing eHtpB. (A to E) Representative single-slice overlay images of untreated CHO-htpB control cells (A), cells infected for 1 h with GFP-expressing Lp02 (B) or GFP-expressing Lp02dotB (D), or cells incubated with green fluorescent HtpB (C)- or GroEL (E)-coated beads for 1 h. F-actin was labeled with phalloidin-Alexa Fluor 546 (red). Size bars, 10 μm. The arrow in panel A points at cytoplasmic stress fibers, and the arrow in panel B points at peripheral F-actin bundles. The altered actin phenotype was characterized by the loss of stress fibers and the accentuation of peripheral F-actin bundles (clearly seen in panels B and C). (F) Bar graph showing percentages (means + 1 SD, n = 3 independent experiments) of CHO-htpB cells associated with bacteria or beads that show the altered actin phenotype at 1 and 3 h after infection or bead addition. P values were calculated in relation to HtpB-coated beads. **, P < 0.01; and *, P < 0.05.