FIG 6.

Cellular response to hybrid toxins. Vero-d2EGFP cells were processed for cytofluorometry after an 18-h incubation with 10-fold serial dilutions of cell extracts from a nonpathogenic (Stx⁻) BL21 E. coli strain that was transformed with expression vectors encoding wild-type Stx1a (A), wild-type Stx2a (B), the 211 hybrid toxin consisting of the A1 subunit from Stx2a with the A2 and B subunits from Stx1a (C), or the 122 hybrid toxin consisting of the A1 subunit from Stx1a with the A2 and B subunits from Stx2a (D). The dilutions represented by each colored trace are as follows: black, 1:100,000; orange, 1:10,000; light blue, 1:1,000; blue, 1:100. Untreated Vero-d2EGFP cells are represented by the green trace.