FIG. 5.

Flow cytometric analysis of PE and PS exposure and EHEC binding to HEp-2. Cells were preincubated for various times (0 to 20 h) with 12.5 ng of VT1 per ml in serum-free media. (A to D) Cells treated both with annexin V-FITC (to detect PS) and anti-PE (visualized with phycoerythrin-GAR conjugate) to compare PS (abscissa) and PE (ordinate) exposure with VT1 incubation time. (A) No VT1; (B) VT1, 1 h; (C) VT1, 3 h; (D) VT1, 20 h. (E to H) Cells pretreated with VT1 or medium, infected with 10⁸ CL56, and stained with annexin V-FITC and a bacterium-specific antiserum to compare PS exposure (abscissa) with bacterial binding (ordinate). (E) Control (no VT1, no CL56); (F) VT1, 20 h (no CL56); (G) CL56 (no VT); (H) VT1 (20 h), CL56. Quadrant numbers refer to percentage of cells simultaneously stained with both fluorophores with intensities as indicated on the axes.