FIG 4.

Dose-dependent association of Stx1a and Stx2 with the cell surface. Vero cells were processed for cytofluorometry after a 30-min 4°C incubation with the fluorophore-labeled B subunits of Stx1a or Stx2a. (A and B) Cells were incubated without toxin (black line) or in the presence of various quantities of either the Stx1a B subunit (A) or Stx2a B subunit (B) at 0.2 μg (magenta line), 0.5 μg (yellow line), 1.0 μg (blue line), or 2.0 μg (red line), all in a 500-μl volume. (C) The signals recorded for 2 μg of either the Stx1a B subunit (red line) or Stx2a B subunit (blue line) were overlaid on the same plot. (D) The signals recorded for 0.2 μg of the Stx1a B subunit (red line) and 0.5 μg of the Stx2a B subunit (blue line) were overlaid on the same plot. One of three representative experiments is shown for the aggregate data.