FIG. 4.
Influence of the antitoxins on the cytotoxic activity of toxin B. (A) Prevention of the cytotoxic effect of toxin B by antitoxin. Toxin B was pretreated with antitoxins or PBS for 15 min on ice. HeLa cells were incubated with PBS (a), with toxin B plus PBS (b), with toxin B plus anti-toxin A (c), with toxin B plus anti-toxin B (d), with toxin B plus anti-C. difficile (e), or with toxin B plus anti-CDB1-546 (f) for 2 h. The concentration of toxin B was 0.37 nM (0.1 μg/ml) in the cell medium. Phase-contrast micrographs of fixed cells are shown. (B) Intracellular antitoxin protects the cells from toxin B. HeLa cells were microinjected with either microinjection buffer (a and b), anti-CDB1-546 (c), anti-toxin B (d), or anti-toxin A (e). After 1 h, toxin B (b to e) (0.1 μg/ml) or PBS (a) was added to the medium, and incubation was continued for 2 h. Fixed cells were observed by phase-contrast micrography.