FIG. 5.

LDH release by monocytes exposed to C. difficile toxin A. Purified preparations of monocytes were incubated in the absence of toxin A (×) or in presence of 100 ng of toxin A per ml (▪), 1,000 ng of toxin A per ml (▴), or 30 μg of toxin A per ml (♦) for 2, 5, or 24 h. LDH levels were measured in supernatant samples and cell lysates. Extracellular release of LDH (levels in supernatant samples) was expressed as a percentage of the total cellular LDH activity (supernatant activity plus intracellular activity). The data are the means from three experiments. Compared to the control, there was significantly greater release of LDH following exposure to 30 μg of toxin A per ml for 2 h (56.1% ± 7.6%; P = 0.02), for 5 h (68.8% ± 9.3%; P = 0.01), and for 24 h (73.5% ± 8.4%; P = 0.01) and following incubation with 1,000 ng of the toxin per ml for 5 h (68.2% ± 7.8%; P < 0.01) and for 24 h (68.8% ± 9.8%; P = 0.01).